Knee injuries in children and adolescents are common. , There has been a significant increase in sport participation among young athletes in recent years, and overuse and traumatic injuries about the knee in young patients often prompt medial evaluation. , Many injuries mirror those seen in the adult population; however, there are some unique considerations in the treatment of children and adolescents with knee injuries. Children can have distinct pathological conditions, often related to their growth and development. In addition, surgical outcomes in kids have often been described as different from their adult counterparts. In this chapter we highlight some of the most common knee injuries that children and adolescents sustain and discuss the unique aspects of treatment of these injuries in this population.
Skeletal immaturity introduces a challenge to the management of paediatric knee injuries. The growth plates, or physes, around the knee are among the fastest growing in the body and as such are subject to metabolic or mechanical insult that can lead to growth disturbances or angular deformities. Injury to the physis can occur from injury alone but can also be iatrogenic, and surgical treatment of skeletally immature patients requires careful attention to physeal status to minimise the chance of iatrogenic injury. Normal physeal ossification and closure occurs after puberty in adolescents. Girls generally grow 2 years after the onset of menses, typically until age 14.5, and boys have slightly delayed maturation and grow until age 16.5. Historically, assessment of the level of physiological maturity was done with the Tanner staging system, which assesses the presence or absence of secondary sex characteristics. More recent literature, however, has suggested that Tanner staging is not reliably reproducible among orthopaedic surgeons, with significant variations in inter- and intrarater reliability. Thus the most predictable assessment of skeletal maturity is with a bone age posteroanterior (PA) radiograph of the left hand. Bone age can be determined by comparing this radiograph to a series of maturation standards, as depicted in the Greulich and Pyle Atlas. In 2013 a short hand bone age assessment was developed and validated, and this system offers easy and ready use in an office setting ( Fig. 36.1 ).
In addition to physeal development and maturation, injury to the physis should be considered and ruled out with any traumatic injury to the knee in young patients. Because of the lack of mineralisation of this area in the growing child, the physis serves as a weak point in the system, surrounded by stronger bone, ligaments and the joint capsule. Salter-Harris fractures can occur through the physis, and the hypertrophic zone of the physis is the most often affected because this zone particularly lacks collagen and calcification. Although paediatric patients can certainly sustain injuries to ligaments and other intraarticular structures, ruling out a physeal fracture is an important step in the management of knee injuries in young patients.
Paediatric Knee Assessment
A comprehensive knee physical examination has been described in a previous chapter, and this should be referenced, because a thorough physical examination of the lower extremity should be performed in children presenting with knee pain. Assessing swelling, areas of tenderness, range of motion, strength, ligamentous stability and provocative manoeuvres as described are key to honing in on a proper diagnosis. Given the propensity for physeal fractures in children, careful attention should be paid to palpating for bony tenderness about the distal femur or proximal tibia. In addition, we recommend examining the hip for any child or adolescent presenting with knee pain because a slipped capital femoral epiphysis (SCFE) can often present with knee pain as the chief complaint. Pain with range of motion or axial loading of the hip and obligate external rotation of the hip with flexion should prompt further radiographic evaluation of the hips with anteroposterior (AP) pelvis and frog-leg lateral radiographs of the hips.
The presence of a knee effusion is abnormal in a child or adolescent, and intraarticular pathology conditions should be suspected if an effusion is noted. The most common cause of a knee effusion in a child is acute hemarthrosis as a result of trauma. However, infectious, rheumatological, haematological and oncological processes can also cause knee effusions in a child and should be considered and ruled out. High rates of patellar dislocations, anterior cruciate ligament (ACL) tears, and meniscal injuries were reported in paediatric and adolescent patients (10 and 18 years) undergoing knee MRI for traumatic knee effusions. These conditions may require surgical intervention, and an accurate diagnosis is critical. A high index of suspicion and more advanced workup should be considered in young patients with knee effusions.
Infectious causes of pain and swelling should also be significantly considered in the differential diagnosis of children with knee pain. Lack of trauma or the presence of only minor trauma in the setting of increasing pain, swelling/effusion, painful or limited range of motion or limping may suggest underlying osteomyelitis or septic arthritis. Hematogenous bacterial seeding of bones and joints is more common in children than in adults. Systemic symptoms such as fever, chills, or malaise often accompany pain complaints in the setting of infection; however, in the very early, or alternatively very chronic, stages, these findings may not be present. Treating physicians should have a low threshold to order testing for inflammatory markers, including complete blood cell count (CBC), erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) if an infectious pathological condition is suspected based on history and examination.
Ligamentous laxity is also more common in paediatric patients compared with adults, and this may have implications for treatment of certain pathological conditions of the knee, including patellar dislocations and ACL tears. Generalised laxity or hypermobility can be assessed using the Beighton Hypermobility Score ( Fig. 36.2 ) , which measures flexibility at the thumbs, small fingers, elbows, knees and flexion of the trunk. A score higher than 6 suggests hypermobility, and this may inform future prognosis or surgical decision making. Young age and female sex have been associated with hyperlaxity, and teenage girls can be a particularly at-risk population.
Physical examination of the child or adolescent can be challenging for a number of reasons. Young age can make cooperation and compliance with examination difficult, particularly in the setting of pain or discomfort. There can be significant anxiety in young patients about moving the injured extremity, and this can limit the provider’s ability to adequately and confidently evaluate the knee. Examination under anaesthesia may be the most reliable way to obtain an unbiased examination in a young patient, and this should be considered as an important step in surgical management.
As described in previous chapters, knee imaging is a critical component of diagnosis. In children, plain radiographs of the knee can be very helpful in identifying fractures, avulsions, physeal abnormalities or osteochondral injuries about the knee. For many paediatric knee injuries, radiographs alone can inform the proper treatment course, and this is the case for many fractures. Complex or intraarticular fractures can be further defined and understood with computed tomography (CT) scans; however, minimising radiation in children, when possible, is preferable.
Skeletal maturity is most accurately assessed with a PA bone age radiograph of the left hand. Other valuable radiographic studies include standing long-leg alignment films, which can help assess for genu varum or genu valgum. This can be particularly helpful in skeletally immature patients with ACL tears to assess and document preoperative alignment or assess alignment in patients with patellar instability or osteochondritis dissecans lesions of the lateral or medial femoral condyles. In patients with open physes, there is an opportunity to use guided growth procedures as an adjunct to surgical procedures about the knee to correct malalignment without requiring osteotomies.
Magnetic resonance imaging (MRI) is the gold standard for diagnosing most intraarticular injuries of the knee, such as ligament tears, patellar dislocations, chondral or meniscal injuries and occult injuries, or better defining osteochondral injuries and evaluating osteochondritis dissecans lesions. Traumatic knee effusions in children and adolescents are associated with higher rates of ACL tears, meniscal injuries and patellar dislocations, and MRI should be strongly considered in young patients with knee effusions in the absence of plain radiograph abnormalities.
Anterior Cruciate Ligament Ruptures
Unique Concerns in the Paediatric Population
ACL tears and reconstructions in children and adolescents significantly increased over the past 20 years. , Once thought to be a rare injury among skeletally immature patients, paediatric ACL tears are becoming routine in sports medicine offices across the United States. Appropriate management of ACL tears in children and adolescents depends on an accurate assessment of the level of skeletal maturity to help inform treatment options. Multiple studies have shown increased risk of secondary chondral or meniscal injuries with delayed treatment of ACL tears in young patients, and surgical stabilisation of the knee with ACL reconstruction should be strongly considered in paediatric patients with unstable ACL tears unless there are significant medical, psychological, or social deterrents or barriers for surgery.
Decision making for young athletes with ACL tears can be challenging. Preoperative alignment and skeletal maturity need to be taken into account because iatrogenic physeal injury can occur with surgical intervention in skeletally immature patients. Some animal studies show disruption of even a small percentage of the cross-sectional area of the physis (4% of the tibial physis, 7% of the femoral physis) can cause growth disturbances. , Physeal-respecting and physeal-sparing surgical techniques have been described as options for younger patients. These include transphyseal reconstructions, partial transphyseal reconstructions, all-epiphyseal reconstructions and combined physeal-sparing intraarticular/extraarticular reconstructions using iliotibial band autograft. These techniques are described in detail in the next section. Multiple treatment algorithms have been proposed for surgical treatments based on age and level of maturity. Fig. 36.3 was published by DeFrancesco et al. in 2018 and is a helpful, graphic representation that summarises the surgical options available, based on the level of maturity.
In addition to deciding on the appropriate surgical procedure, attention must also be directed towards choosing an appropriate graft for the reconstruction. Use of allograft in young patients has consistently shown higher failure rates in young patients and should be avoided if possible. , Common soft tissue autografts used for paediatric ACL surgery include the hamstring and quadriceps tendons and iliotibial band. Bone–patellar tendon–bone grafts are also commonly used in adolescents approaching skeletal maturity and in those already skeletally mature; however, it is prudent to avoid this graft in skeletally immature patients with significant growth remaining because of the risk of the bony plugs crossing the physis and leading to the creation of a bony bar that can result in growth disturbance.
Surgical Treatment Options
Surgical treatment of ACL tears is becoming the standard of care in young patients and has yielded excellent surgical results, , minimising the risk of further chondral injury resulting from the risk secondary instability exposures. Multiple surgical techniques can be employed, depending on the age and maturity of the patient, with preoperative decision making in this age group being a crucial step. Surgical priorities include avoiding iatrogenic injury to the physes, which can be mitigated by physeal-sparing or physeal-respecting techniques, using soft tissue autografts and employing fixation constructs that do not cross the physis. Fig. 36.4 summarises the types of reconstructions that can be performed in skeletally immature patients.
Physeal-Sparing Iliotibial Band Reconstruction
Initially described by Kocher, Garg, and Micheli, , physeal-sparing iliotibial band reconstruction can be effectively used in skeletally immature patients with significant growth remaining. The initial series of patients were Tanner stages 1 and 2. No tunnels are drilled with this technique and there is all-suture fixation, which minimizes iatrogenic risk to the physis. The iliotibial band (ITB) is harvested proximally, leaving it attached to Gerdy’s tubercle. The ITB is then wrapped around the lateral femoral condyle in the over-the-top position, passed through the femoral notch, underneath the intermeniscal ligament and is secured to the proximal tibial periosteum distal to the tibial physis ( Fig. 36.4A ). The graft is secured proximally to the lateral femoral condyle periosteum and the intermuscular septum using heavy suture in a position of 90 degrees of knee flexion and neutral rotation of the foot to avoid overconstraint of the knee. Distally, full-thickness periosteal flaps are developed and the graft is folded into the periosteum and secured with nonabsorbable suture in a position of full extension or slight knee flexion, depending on surgeon preference for tibial sided fixation.
This technique has demonstrated favourable results with low revision rates in paediatric patients and no reported cases of growth disturbance. , , In the initial series of 44 patients with an average age of 10.3 years, Kocher et al. reported a 4.5% revision rate, with high International Knee Documentation Committee (IKDC) and Lysholm knee scores. A follow-up study included 237 patients (240 knees) with a mean age of 11.2 and a mean follow-up of over 2 years. Graft rupture occurred in 6.6% of knees, and patients continued to report high Pedi-IKDC, Lysholm and Tegner scores. Two surveys of surgeons in the Pediatric Research in Sports Medicine (PRISM) Society showed that this technique is being used with regular frequency across the country for skeletally immature patients with ACL tears. ,
Biomechanically, multiple studies have found that the ITB reconstruction has demonstrated superior results, despite being a nonanatomical reconstruction. This technique has been reported to better restore anteroposterior and rotational stability to the knee compared with other physeal-sparing reconstructions. , In addition, no implants or tunnels are used in this procedure, and thus more options are available to the surgeon if a revision surgery is required. Kocher et al. noted that thigh asymmetry from ITB harvest was the most commonly observed complication in their patient cohort, but only 1.6% of patients reported symptoms related to this.
The physeal-sparing ITB technique is the authors’ preferred method of ACL reconstruction in a skeletally immature patient with significant growth remaining (boys with bone age younger than 13, girls with bone age younger than 12). There is a low revision rate, favourable biomechanical profiles and patient outcomes and no cases of reported growth disturbance, and it optimises options for revision surgery if needed.
All-epiphyseal ACL reconstructions have also been endorsed for skeletally immature patients with significant growth remaining. These techniques involve tunnels or sockets that remain entirely within the epiphyses of the distal femur and proximal tibia to minimise injury to the physes ( Fig. 36.4B ). The original technique was described by Anderson; however, since then, multiple modifications have developed. Various graft types (typically hamstring or quadriceps tendon) and fixation options have been described with this all-epiphyseal technique, including suspensory fixation, interference screw within the epiphyses and distal post fixation below the level of the physis.
All-epiphyseal reconstructions have also shown high scores in patient-reported outcomes regarding knee function and return to sport rates. , , , , Revision rates in these studies have ranged from 4% to 15%.
All-epiphyseal reconstructions can be technically challenging, particularly in very young patients who may have narrow epiphyses and in whom it should be performed with intraoperative fluoroscopy or CT scan to minimise the chance of iatrogenic injury to open physes. , Cases of growth disturbance and leg overgrowth have been reported in association with this technique in the literature, some of which were subclinical, but others required corrective surgery. , ,
Although this technique is a more anatomical reconstruction of the ACL in paediatric patients, biomechanical testing suggests it does not restore knee stability to the same extent as the ITB reconstruction. ,
Partial Transphyseal and Transphyseal Reconstructions
Partial or conventional transphyseal reconstructions have been advocated by many as appropriate for the treatment of paediatric patients with ACL tears. The authors recommend considering these techniques in older adolescents with less than 2 years of growth remaining (boys 13 to 16, girls 12 to 14) because they involve violating the physis. In a typical partial transphyseal reconstruction ( Fig. 36.4C ), the femoral graft and fixation is intraepiphyseal, and a tibial tunnel is drilled through the physis, with fixation preferably kept away from the physis. With a conventional transphyseal technique ( Fig. 36.4D ), tunnels are drilled through both the femoral and tibial physes. The chance of iatrogenic growth plate injury can potentially be mitigated by using smaller, more vertically positioned tunnels to avoid oblique or large tunnels, which can affect more cross-sectional area of the physis, using soft tissue grafts and maintaining fixation away from the physis.
Many studies have reported good clinical outcomes with transphyseal reconstructions, and no cases of growth disturbance or angular deformity. In fact, a recent French survey found increased popularity with transphyseal techniques, even in prepubertal children. However, it is very important to minimise injury to the physes around the knee. MRI studies have shown damage to physes with transphyseal drilling. , One recent study of partial transphyseal reconstructions showed a high rate of growth disturbance (16.7%) among patients; however, most of these did not require surgical correction.
Cordasco et al. found that adolescents with transphyseal soft tissue reconstructions had higher failure rates and lower return to sport rates compared with younger patients with all-epiphyseal reconstructions and older adolescents with patellar tendon autograft. In addition, there is some evidence that augmenting small hamstring grafts with allograft for transphyseal reconstructions may lead to increased failure rates. ,
Postoperative Concerns – Reinjury and Revision Surgery
Young, active patients continue to be the most at-risk population for ACL graft failure and contralateral ACL tear. This is concerning for young patients with high activity demands, many of whom have aspirations for high-level sports participation at the college or elite levels. Paterno et al. found a 30% rate of secondary ACL injury (20.5% contralateral, 9% ipsilateral) among adolescents who underwent ACL reconstruction. Complications and revision rate do not seem to significantly differ when all-epiphyseal patients were compared with transphyseal adolescents. In addition, younger skeletally immature patients were found to have similar reoperation and early revision rates compared with more skeletally mature adolescents. There is still much debate over timing of return to sports, and more high level studies are needed to identify predictive parameters for safe return to sport.
In terms of revision surgery for paediatric patients, outcomes have mirrored adult studies showing lower patient reported outcomes and return to sport rates. Christino et al. reported a 20% revision graft reinjury rate and contralateral ACL injury rate in adolescents undergoing revision, and 55% of patients returned to sport at the same level. Ouillette et al. found similar revision graft failures (21%), but only a 27% rate of return to sport after revision. In addition, allograft revisions had higher failures rate than autograft revisions in their study (27% versus 11%), but this result was not statistically significant.
ACL tears in skeletally immature patients are common injuries. Careful attention should be directed towards surgical decision making and avoiding iatrogenic growth disturbance with injury to the physes around the knee. Physeal-sparing and transphyseal reconstructions can safely be performed in young patients, based on the level of skeletal maturity, with good expected outcomes. Young patients continue to be the most at risk for subsequent ACL injury, and exploring ways to decrease this risk should be the focus of continued research.
The medial and lateral menisci are important fibrocartilaginous structures that function as shock absorbers, protecting against axial and sheer forces, reduce joint contact forces and also act as secondary stabilisers of the knee. Meniscal injuries in paediatric patients are common, either in isolation or in combination with additional intraarticular injuries such as ligament injuries or tibial eminence fractures. Discoid meniscal pathological conditions are also common in the paediatric age group, and this topic will be discussed separately from nondiscoid meniscal injuries.
Meniscal anatomy has been detailed in a prior chapter; however, there are some developmental phenomena that are important to consider in young patients. The meniscus is fully vascularised at birth, and progressively this vascularisation recedes towards the periphery with growth and ageing. At 9 months the inner one-third of the meniscus has become avascular (white-white zone), and the vascular supply continues to regress to become exclusively concentrated in the peripheral one-third of the meniscus by age 10 (red-red zone). , This vascular anatomy persists until adulthood and has implications for healing of the meniscus after injury. The increased vascularisation of the menisci during development may allow better healing with meniscal repair attempts.
Nondiscoid and discoid meniscal tears may both present with joint line pain, effusion and mechanical symptoms. Acute meniscal tears are often the result of trauma or a twisting injury to the knee. In cases of discoid meniscal tear, painless popping or attritional tearing can occur and history may not be as consistent with an acute mechanism. Physical examination in young patients has been shown to be reliable for diagnosing meniscal tears, with good sensitivity and specificity. In addition to assessing for effusion, joint-line tenderness and provocative meniscal tests, careful attention should also be paid to assessment of the ACL with Lachman testing because a significant percentage of meniscal tears also have anterior cruciate injury.
Although MRI is still generally recognised as the diagnostic imaging test of choice for meniscal tears, there are diagnostic limitations in young patients. The changing vascularity within the developing meniscus can show signal changes on MRI that can be interpreted mistakenly as tears. In addition, one MRI study in skeletally immature patients showed that diagnostic accuracy was equivalent for MRI and clinical examination when agreement with arthroscopic findings was compared. This same study found that MRI for younger patients (<12 years) had lower sensitivity and specificity compared with older patients. Another study looked at the sensitivity and specificity of MRI in detecting meniscal injuries in young patients undergoing ACL reconstruction. They found that a significant percentage of patients (24.3%) had meniscal tears identified at the time of arthroscopy that were not identified on the initial MRI (primarily vertical tears of the posterior horn lateral meniscus). These studies highlight the importance of a careful physical examination in diagnosing meniscal pathological changes in young patients, as well as the importance of a thorough diagnostic arthroscopy.
Most meniscal tears in children and adolescents are appropriate for surgical intervention, unless a patient is truly asymptomatic, which is rare in young people with high activity levels. The risk of further propagation of tears if left untreated is a concern. In addition, most meniscal tears are peripheral longitudinal tears in children and are thus amenable to repair, with good healing potential, and there is an opportunity to preserve this meniscal tissue over time with repair. Tear patterns in young patients can be similar to those seen in the adult population, ranging from vertical/longitudinal tears to flap tears, radial tears, bucket handle tears, horizontal tears, complex tears and root tears. Degenerative tear patterns are uncommon in paediatrics, and these may be more amenable to partial meniscectomy compared with repair.
Surgical techniques for meniscal repair and partial meniscectomy are nearly identical to adult techniques. For meniscal repair, all-inside, inside-out and outside-in suture constructs are commonly employed depending on the tear pattern. Given the increased vascularity, particularly in younger patients, meniscal repair for meniscal preservation should be attempted if possible. In small patients it is important to be mindful of anatomy, with closer position of neurovascular structures as they relate to the joint capsule. This should be especially considered with all-inside repairs because many of the available devices have predetermined penetration depths.
Meniscal repair in young patients has become more common and has demonstrated favourable outcomes in the literature. Studies have shown high healing rates in this population after meniscal repair. , A meta-analysis of adolescent patients with isolated meniscus tears suggested an increase in meniscal repairs compared with meniscectomies in recent years, possibly related to reports during this period of poor long-term outcomes after meniscectomy. Two 2019 systematic reviews concluded that meniscal repair in adolescent patients overall has low failure rates and favourable patient-reported outcomes and preserves meniscal tissue. ,
A study of 970 first-time meniscal procedures in patients, with an average age of 13.2 and average follow up of 20 months, found that 9% of patients required subsequent meniscal surgery, and this was three times more likely in the meniscal repair group. Another study of 280 patients (average age 15.5) with bucket handle meniscus tears found that 65% of these were treated with meniscal repair, and this was more common in younger patients and with tears of the lateral meniscus. Ninety-two percent of patients were pain free at final follow-up, but reoperation was more common in those who had an initial meniscal repair compared with meniscectomy (32% versus 8%, P = .001) and less common in those that had initial concomitant ACL reconstruction ( P = .07). Tagliero et al. looked at long-term outcomes of meniscal repair in young patients (average age 16) in the setting of ACL reconstruction, with average follow-up of more than 15 years. The long-term survival of meniscal repair was 72%, with 28% requiring revision meniscal surgery, and patients reported favourable outcomes at final follow-up. Although these studies show higher numbers of subsequent procedures in meniscal repair cohorts, large percentages of patients are not requiring additional procedures after meniscal repair, and the benefit of potentially preserving meniscal tissue over time with repair should be heavily weighted.
A discoid meniscus is an anatomical variant of the formation of meniscal tissue and is thought to be present in 3% to 5% of the general population, with a slightly higher incidence in Asian populations. , Discoid meniscal tissue is thickened and enlarged, with abnormal collagen organisation and peripheral attachments that can predispose the meniscus to tearing. Discoid menisci can be bilateral (up to 20% to 25%) and are far more common in the lateral compartment of the knee; however, medial discoid pathological conditions have also been described.
Although discoid pathological conditions can be asymptomatic, symptom development during childhood and adolescence is common and this can be the result of discoid meniscal tearing, meniscal instability, or a combination of the two. Pain, swelling, limited knee extension, popping, clicking, clunking and catching are commonly reported symptoms. A painless lateral popping or clunking of the knee with flexion can be seen particularly in young children. Discoid meniscal tearing can certainly result from traumatic mechanisms; however, a history of significant trauma may not be present in patients with this condition because tearing of this abnormal meniscal tissue can be attritional over time. Notable knee symptoms without a history of significant trauma should elicit suspicion for possible discoid pathological condition.
Imaging should start with radiographs to rule out bony pathological condition or loose bodies that can also produce mechanical symptoms. Although most radiographs will be normal in the case of a discoid lateral meniscus, subtle findings of squaring of the femoral condyle, cupping of the tibial plateau and widening of the joint space can be observed from the mass effect of an abnormally large and thickened meniscus. Lateral femoral condyle osteochondritis dissecans (OCD) has also been reported in association with discoid lateral menisci. MRI is the best modality to evaluate meniscal integrity and shape; however, one study has shown decreased sensitivity of MRI compared with physical examination in young children. Characteristic findings on MRI are sagittal images showing continuity of the meniscus between the anterior and posterior horns on three or more sequential 5-mm slices.
Watanabe classified discoid menisci into three basic types based on arthroscopic evaluation: Type 1, complete; type 2, incomplete; and type 3, Wrisberg variant. Complete discoid menisci cover the entirety of the tibial plateau in the affected compartment, whereas incomplete discoids cover less than 80% of the tibial plateau but more surface area than the normal-appearing meniscus. Both these variants are described as stable, with intact meniscotibial attachments. The Wrisberg variant is an unstable variant that lacks posterior meniscotibial attachments, and the ligament of Wrisberg serves as the only posterior attachment to the meniscus on the lateral side. Meniscal instability can be a significant contributor to symptoms with this condition. This classification is helpful in more accurately describing the range of morphology that exists with discoid menisci because size, shape and instability patterns can vary.
Nonoperative management can be employed for asymptomatic or minimally symptomatic discoid menisci in patients with full range of motion and no pain. A discoid meniscus may also be incidentally encountered during routine arthroscopy for other indications, and treatment for this is generally not indicated unless there is evidence of tearing or instability at the time of arthroscopy.
Surgical intervention is appropriate for symptomatic discoid menisci that demonstrate obvious tears on MRI or cause pain, limited range of motion or mechanical symptoms. Stable complete or incomplete discoids can be treated with partial meniscectomy of the central meniscal tearing and saucerization of the meniscus to a more normal meniscal shape with a stable rim of meniscal tissue. Resecting enough abnormal central meniscal tissue is important to minimise the chance of retearing; however, care should also be taken to preserve meniscal tissue in young patients, and total and subtotal meniscectomy should be avoided if at all possible. , , Meniscal repair is indicated for discoid tears that extend to involve the periphery of the meniscus as well as those that demonstrate instability, such as Wrisberg variants or hypermobile discoid menisci. Combinations of inside-out, outside-in and all-inside techniques, as previously described, can be employed for successful meniscal repair.
Optimal treatment for best outcomes in patients with discoid menisci is still in evolution. Historically, complete meniscectomy was a treatment of choice with good early clinical outcomes reported in young patients. , There are considerable concerns about suboptimal long-term function and progression to osteoarthritis with complete meniscectomy or meniscal insufficiency, however. With increased arthroscopic technological advances, meniscal preservation, when possible, has been adopted by most in the treatment of discoid meniscus tears. ,
In a series of 30 paediatric knees, Good et al. showed that 77% of patients with symptomatic discoids had tearing of the meniscus at the time of arthroscopy and 77% also had signs of meniscal instability. In their study, 93% of knees were able to be successfully treated with meniscus-preserving procedures, including saucerization and meniscal repair, with good short-term outcomes. Carter et al. also reported short-term follow-up on 57 paediatric knees undergoing arthroscopic meniscal saucerization or repair for discoid menisci and reported no difference in complication rates or outcomes between repair and partial meniscectomy patients. A 10-year follow-up study of discoid paediatric patients showed 94% had good to excellent clinical results after surgical intervention. Significantly more degenerative changes were seen in the subgroup of patients who had subtotal meniscectomy, compared with partial meniscectomy or meniscal repair, supporting the argument for meniscal preservation.
Revision surgery is common after discoid meniscal intervention. One study cited a 15% revision rate in discoid patients younger than 20 years old with average follow-up of 40 months. A smaller study of 21 patients showed a 36.8% reoperation rate with an average follow up of 11 years. In young patients with significant meniscal insufficiency or who underwent complete meniscectomy, meniscal allograft transplantation can be an option; , however, more studies are needed to determine the efficacy of this for long-term joint preservation.
Decision Making – Unique Concerns in the Paediatric Population
Patellar instability in paediatric patients represents a spectrum of pathological conditions ranging from acute traumatic dislocations to chronic recurrent dislocations and congenital dislocations. The management of patellar instability in skeletally immature patients can be especially challenging because limited potential surgical options exist compared with their adult counterparts as a result of concerns about iatrogenic physeal injury that can contribute to deformity. Specifically, tibial tubercle osteotomies should not be performed in young patients with open tubercle apophyses because of risk of creating a recurvatum deformity; however, this procedure can be an important aspect of treatment of patellar instability in skeletally mature adolescents. In paediatric patients the patella starts to ossify between the ages of 3 and 5 years, and the tibial tubercle apophysis does not fuse until age 13 to 15 for girls and 15 to 19 for boys.
The peak incidence of patellar dislocation has been found to be in the adolescent years, with most being the result of trauma during athletic activity. , , An incidence of 0.6 per 1000 children has also been reported for first-time patellar dislocation in children ages 9 to 14 years old. Ligamentous laxity, coronal or rotational malalignment, trochlear dysplasia and positive family history are risk factors for patellar instability. Signs and symptoms often involve the patient feeling a ‘pop’ with associated pain and effusion; thus patellar dislocation should be high on the differential of any child or adolescent presenting with a knee effusion. Osteochondral fractures of the patella or lateral femoral condyle that may require fixation are common after patellar dislocation , and are best evaluated with radiographs and/or MRI scan of the affected knee. Assessing the tibial tubercle–trochlear groove (TT-TG) distance on MRI or CT scan has become a standard approach for determining whether distal realignment procedures may be indicated, particularly in patients with trochlear dysplasia. The patellar tendon lateral to the lateral trochlear ridge (PT-LTR) distance is a newer measurement that has been described in young patients and has been shown to a reliable predictor of patellar instability, with similar sensitivity to the TT-TG but greater specificity. In addition, MRI or CT scans to assess femoral or tibial version can also be useful adjuncts to the standard work-up because significant rotational malalignment may benefit from derotational osteotomies, particularly in congenital cases.
A prospective MRI study looked at anatomical patellofemoral risk factors between skeletally immature children with and without patellar dislocation. This study showed children with first-time patellar dislocations had significantly more trochlear dysplasia, patella alta, lateral patellar tilt and TT-TG distance compared with children without patellar dislocation, and trochlear dysplasia was the strongest risk factor associated with patellar dislocation. These same anatomical factors have also been implicated in recurrent patellar dislocation.
Recurrent instability in young patients has been associated with trochlear dysplasia and skeletal immaturity, with recurrence rates up to 70% after first-time dislocation. Two randomised controlled trials investigated recurrent dislocation rates in children after acute medial repair compared with nonoperative management. Palmu et al. found that acute operative repair did not improve long-term patient outcomes compared with conservative treatment, and there were high rates of recurrent instability in both groups. Askenberger et al. found acute operative repair of medial patellofemoral ligament (MPFL) injury had a lower redislocation rate compared with nonoperative management (22% versus 43%) at 2-year follow-up; however, patient-reported outcomes did not differ significantly between groups, and most patients in each group were satisfied with their knee function. In light of these results and the absence of a significant intraarticular pathological condition that would require surgical intervention, the mainstay of treatment for children and adolescents continues to be nonoperative management.
In patellar dislocation, skeletally immature children more commonly injure the MPFL at the patellar attachment site. Additionally, the insertion of the MPFL in the paediatric knee has been found to be variable. A 2018 cadaver study (specimens 2 to 11 years old) showed the mean midpoint of the MPFL origin was located just distal to the physis. Younger patients (<7 years) were found to have more distal and posterior attachments, whereas older patients (>7 years) had more proximal and anterior attachments and were more likely to have an MPFL origin above the level of the physis. Patella and trochlear morphology also change concurrently with age, with deepening of the trochlear sulcus as age increases in childhood. Anatomical variations and physeal status in young patients should be heavily considered in surgical decision making, and intraoperative use of fluoroscopy is essential to avoid physeal injury.
Nonsurgical Treatment Options
Nonsurgical treatment is the mainstay of treatment for uncomplicated, first-time patellar dislocations in children and adolescents. Surgical treatment has not been associated with improved outcomes. Nonoperative treatments, including bracing, physical therapy focusing on vastus medialis oblique (VMO) strengthening and activity restriction can be helpful in alleviating symptoms and strengthening the patellofemoral mechanism to provide dynamic stability. In patients without significant anatomical risk factors for recurrence, nonoperative treatment may be a reasonable approach after a subsequent instability episode as well. Given that anatomical risk factors are common in those who sustain patellar dislocation, however, a high number of patients are likely to go on to develop recurrent instability, , and families should be appropriately counselled about this possibility.
Surgical Treatment Options
Surgical intervention for patellar instability in children is indicated in cases of recurrent instability and in primary cases where significant osteochondral injury has occurred, requiring treatment of the fracture fragment or loose body to prevent mechanical symptoms or further cartilage damage. Careful attention should be paid to the level of skeletal maturity of the patient, and surgical options in children are often limited because of this. As mentioned previously, tibial tubercle osteotomy should be considered only in skeletally mature adolescents because iatrogenic injury to the tubercle apophysis can cause recurvatum deformity. Soft tissue distal realignment procedures can be considered, if needed, in skeletally immature patients, and options for these and other surgical techniques for young patients with patellar instability are described in the subsequent sections.
In patients with significant lower extremity malalignment, physeal tethering with guided growth techniques can be employed to correct alignment in skeletally immature children. Genu valgum has been associated with abnormal patellofemoral mechanics and is a contributing factor to patellar instability. In children with patellar instability, improving the mechanical axis can improve symptoms of patellar instability, and this can be done without disrupting growth of the limb or requiring osteotomy. Guided growth is indicated in children with significant valgus alignment, patellar instability and significant growth remaining. Common approaches to hemiepiphysiodesis include applying either a tension band plate that bridges the medial physis or a single transphyseal screw across the medial physis. These devices tether growth on the medial side of the knee, while allowing for continued lateral growth and correction of the deformity. Once adequate correction has been obtained, hardware should be removed to prevent significant overcorrection. Distal femoral guided growth is often sufficient to correct deformity, especially when the deformity manifests mostly as a lower lateral distal femoral angle; however, in cases of significant deformity, correction at both the distal femur and proximal tibia may be required.
Guided growth techniques have been found to be safe and simple surgical options for young patients with reproducible correction of deformities. In children with patellar instability, guided growth has been shown to be successful at improving instability symptoms. One study showed 69% of paediatric patients had complete symptom resolution and an additional 31% had significant reduction in symptoms after guided growth, with no additional procedures required for patellar instability. Another study looked at combining guided growth with a transphyseal medial distal femoral screw and simultaneous MPFL reconstruction and reported adequate deformity correction with no apparent compromise to the stability of the patella. Guided growth is a reasonable surgical option in skeletally immature patients, and correction of valgus can potentially mitigate a contributing factor to recurrent patellar instability for these patients in the future.
Congenital and Obligate/Fixed Dislocations
Congenital patellar dislocations and those that have fixed dislocations can be challenging problems in children, and these often present at young ages. Congenital dislocations are often associated with syndromic conditions such as Marfan’s syndrome, Ehlers-Danlos syndrome, Down’s syndrome, cerebral palsy and nail-patella syndrome. With irreducible dislocations, extensive lateral release or lengthening is often required to appropriately medialise the patella into the groove, and both proximal and distal soft tissue realignment may need to be performed to provide adequate stability and prevent recurrent subluxation or dislocation. Bony procedures should be avoided in very young patients. Soft tissue realignment procedures been successful in syndromic children and habitual dislocators. There is also some evidence to support the idea that trochlear remodelling may occur in young patients, with deepening of the groove in response to a centred patella. Early intervention to fixed or congenital patellar dislocations may thus be beneficial; however, more studies are needed in this specific patient population. Patellectomy can be an option in low-demand patients with refractory or recurrent cases of patellar instability who have failed prior surgical stabilisation procedures; however, indications for this should be reserved for extreme cases with low functional demands.
Lateral Release or Lengthening
Lateral retinacular release or lengthening can be an important component of proximal realignment as contracted lateral patellar attachments predispose to a laterally directed pull on the patella. Lateral release should not be performed in isolation because it does not improve patellar stability alone and there have been reported concerns of creating iatrogenic medial instability. In cases of obligate or fixed patellar dislocation, lateral release or lengthening is often an especially critical step in realignment procedures.
Medial Retinacular Plication/Reefing/Repair
Medial retinacular repair has been described as an option for young patients with patellar instability. This can be performed either as an adjunct to guided growth or distal realignment procedures or in the acute setting with a concomitant intraarticular pathological condition that needs to be addressed, particularly if the MPFL is avulsed from either the patellar or femoral side.
Medial plication or MPFL repair has demonstrated mixed results in the literature. Although isolated MPFL repair for recurrent patellar dislocation was successful in 72% of patients, a high number of patients (28%) sustained a recurrent lateral patellar dislocation and more than half of these patients required a subsequent operation for further patellar stabilisation. One study randomly allocated 80 primary dislocation patients undergoing delayed arthroscopy to either MPFL repair or conservative management groups and found that MPFL repair did not reduce the redislocation rate or result in improved outcomes. A 2018 randomised study of children with first-time dislocations showed a statistically lower redislocation rate among repair patients compared with a conservatively treated group (22% versus 43%); however, outcomes were worse and limb symmetry index was lower in the repair patients. Pedowitz et al. found a 62.5% recurrent patellar instability rate among MPFL repairs in paediatric patients. This was compared with a redislocation rate of 60% in patients who had no medial repair at the time of arthroscopic treatment of osteochondral loose bodies associated with patellar dislocation. Medial imbrication/repair techniques can be successful for some patients; however, more stable reconstructions should be considered in patients with high risk for redislocation.
Medial Patellofemoral Ligament Reconstruction
MPFL reconstruction has become a treatment of choice in skeletally immature patients. This reconstruction can be performed with autograft or allograft tissue and, with image guidance, can safely avoid iatrogenic injury to the distal femoral physis. Although there is variability in MPFL anatomy, paediatric cadaver studies have shown the MPFL to originate distal to the medial femoral physis in most cases; thus a femoral tunnel can be drilled within the epiphysis at the Schottle point for femoral sided fixation. Nguyen et al. described safe drilling techniques for the paediatric femoral tunnel based on cadaveric analysis. When drilling into the epiphysis, aiming 15 to 20 degrees distally and anteriorly minimises damage to the nearby physis and penetrating the notch or articular cartilage. Growth disturbance after MPFL reconstruction has not yet been reported in the literature.
Spang et al. described a double limb graft construct in adolescent patients, reconstructing the MPFL and the medial quadriceps tendon–femoral ligament (MQTFL), that may more thoroughly restore native anatomy and minimise the risk of patellar fracture with a double-limbed MPFL graft. Good clinical outcomes and low revision rates have been reported.
Nelitz et al. described an additional MPFL reconstruction technique in young patients that uses a pedicled slip of superficial quadriceps tendon autograft left attached to the patella distally and secured to the femur in anatomical position distal to the physis, without the use of hardware. Of 25 skeletally immature patients who underwent this technique (average age 12.8 years, average follow-up 2.6 years), there were no cases of reported instability recurrence, and the authors suggest this procedure is a safe and effective alternative to traditional MPFL reconstruction techniques.
Successful outcomes with high rates of return to sport and patient satisfaction ratings have been reported in adolescents and young adults after MPFL reconstruction. , In adolescent patients, indices of patella alta were found to significantly improve to normal values after MPFL reconstruction, suggesting this procedure may help improve patellar mechanics and anatomy. A meta-analysis of slightly older patients (average age 23) showed that double-limb grafts were associated with lower failure rates but no significant differences have been found between the use of autograft or allograft tissue. Both allograft and autograft tissue are commonly being used in the paediatric population for MPFL reconstruction. One study in paediatric patients showed successful results with low recurrence rates using allograft gracilis tendon for MPFL reconstruction, and more other studies have demonstrated continued success with allograft tissue.
Major complications after MPFL reconstruction in young patients include recurrent instability, loss of knee motion, arthrofibrosis, deep infection and patellar fractures. A series of 179 knees with an average age of 14.9 years demonstrated an overall complication rate of 16.2%. Female sex and bilateral MPFL reconstruction were risk factors for complications, and a significant number of complications (47%) were thought to have been preventable and caused by technical problems. Despite the risk of complications, based on the literature MPFL reconstruction in young patients has been generally successful at restoring stability and allowing return to function. A recent systematic review and meta-analysis of paediatric patellar instability patients reported an 86% return to activity rate, with a weighted average rate of instability recurrence after MPFL reconstruction of 3% ± 20% (range 0 to 45%, depending on the study). This analysis served to highlight the need for more high-level studies and systematic evaluation of paediatric patients with patellar instability.
Distal patellar realignment procedures may also be required in young patients to adequately balance patellofemoral anatomy. In skeletally mature adolescents, with a closed tibial tubercle and proximal tibial physes, tibial tubercle osteotomy is an effective technique for distal realignment and can be employed with similar indications for the management of adults with patellar instability. However, tibial tubercle osteotomies should not be performed in skeletally immature patients because of the risk of causing a recurvatum deformity from physeal disruption. Soft tissue distal realignment procedures have been described for use in young patients with open physes as alternatives to tubercle osteotomy, and although more studies are needed to determine the optimal physeal sparing technique, many of the following options have been employed with some success. Similar to adults, these procedures are often combined with the proximal soft tissue realignment procedures described in the previous section.
The Roux-Goldthwait procedure involves changing the vector of the patellar tendon. The patellar tendon is split and the lateral half of the patellar tendon is detached distally. The lateral half is then passed underneath the medial portion of the tendon that remains intact with its insertion on the tubercle and is secured to the proximal tibial periosteum between the tubercle and the pes anserine. A study of 30 paediatric knees reported improved clinical results using this technique in combination with a lateral retinacular release. Although few studies have examined the long-term outcomes of patients undergoing a Roux-Goldthwait procedure, a systematic review showed overall favourable results in the treatment of patellar instability, even in young patients.
Multiple techniques have been described using the semitendinosus tendon to provide a more distal and medial pull on the patella to improve alignment. The originally described Galeazzi semitendinosus tenodesis involves harvesting the semitendinosus tendon proximally, while leaving it attached on the tibia distally and sewing the harvested tendon to the inferomedial aspect of the patella and/or medial retinaculum to reconstruct the medial patellotibial ligament. This technique has been subsequently modified to include securing the tendon to the patella via bone tunnels. , One study in paediatric patients found a high rate of recurrent patellar instability after this procedure (82%), questioning its value as a distal realignment option.
Nietosvaara further modified this technique by taking this semitendinosus tenodesis technique and adding an MPFL component. The semitendinosus tendon insertion was left intact on the tibia and the harvested proximal end was brought through a vertical tunnel in the medial aspect of the patella from inferior to superior and then secured to the femoral insertion of the MPFL. More studies are needed to assess the efficacy of this technique, but limited early results and the principle of combining this distal tenodesis procedure with a proximal medial patellar restraint may be promising.
Medial Patellar Tendon Transfers
Reconstructing the medial patellotibial ligament with a medial portion of the patellar tendon has been described by Hinckel et al. In this procedure the medial third of the patellar tendon is split and detached from its insertion. This portion is then transferred medially, about 2 cm from the patellar tendon insertion, maintaining an approximately 20-degree angle with the rest of the patellar tendon. In children they prefer anchor fixation within the epiphysis of the proximal tibia, just above the level of the tibial physis. The authors who endorse this technique report that it may be especially important in skeletally immature patients to reconstruct these secondary stabilising ligaments when osteotomies cannot be performed. At this time, outcomes in paediatric patients are limited and more research is needed to determine the efficacy of this technique. Oliva et al. described a similar technique combining a medial third patellar tendon transfer, lateral release and VMO advancement and followed a series of 25 skeletally immature patients to skeletal maturity with an average follow-up of 3.8 years. They reported one recurrent dislocation after a traumatic mechanism, as well as favourable and improved patient-reported outcomes after this procedure. Further research on patient outcomes and recurrence rates is still clearly needed among paediatric patients undergoing distal and proximal patellar realignment surgery.
Osteochondral Fractures and Chondral Injuries
Chondral and osteochondral injuries can occur in isolation in young patients but are also especially common after patellar dislocation, most often involving the medial patellar facet or lateral femoral condyle. Symptoms of chondral or osteochondral fractures include pain, significant knee effusion, difficulty weightbearing and mechanical symptoms such as locking or catching. Osteochondral injuries are common in children presenting with acute hemarthrosis of the knee, and because of the purely cartilaginous nature of many of these fragments, the diagnosis is often missed on plain radiographs. , High numbers of osteochondral fractures have been associated with patellar dislocation. , , Suspicion for articular injury should be suspected with patellar dislocation or significant traumatic knee effusion, and MRI is the most sensitive test to diagnose osteochondral injuries. Acute traumatic chondral or osteochondral fractures also need to be distinguished from OCD of the knee, which is a more chronic disease of the subchondral bone that can lead to fragmentation and loose bodies. OCD is an important pathological condition in young patients, and management of this condition has been described elsewhere in this text.
It has been proposed that adolescents may be at increased risk for osteochondral injury. One bovine biomechanical study showed that the osteochondral junction was more likely to fail in adolescent pigs compared with more immature or mature specimens. Fracture toughness was found to be decreased in this age group and this was thought to be due to maturational changes that occur as this area transitions to its mature state and a tougher layer of calcified cartilage develops.
There is great variability when it comes to acute osteochondral and chondral injuries, related to fragment size, location, mechanism of injury and other associated injuries. Treatment of these injuries is thus often determined on a case by case basis, taking all these factors into account.
Nonoperative management can be appropriate for some osteochondral and chondral injuries. Nondisplaced osteochondral fractures can undergo bone to bone healing, and observation with serial radiographs can monitor appropriate healing progression. These fractures may be particularly amenable to nonoperative treatment with an intact cartilaginous surface. For displaced fragments, very small fragments (<5 mm) may synovialize and not contribute to mechanical symptoms or additional intraarticular wear, especially when these fragments are entirely cartilaginous with no bone attached. As fragments increase in size, however, surgical intervention should be considered because intraarticular loose bodies can be symptomatic and lead to further chondral wear and early-onset arthritis.
Surgical management for displaced osteochondral fractures or chondral injuries should be considered in most cases in paediatric patients. Options include fragment excision (with or without microfracture or cartilage restoration procedures) to reduction and fixation of the fragment back to its donor site. Surgical excision can be considered for smaller fragments that do not involve the major weightbearing areas of the knee. In addition, purely cartilaginous loose bodies have historically often been removed because of concerns about the ability to heal to the underlying bone, given the avascular nature of cartilage. Fragments that are significantly damaged, where the cartilage surface is compromised or the fragment is comminuted, may also not be amenable to surgical fixation and excision is preferred.
Depending on the size and location of the fracture fragment, fixation can be accomplished either through open or arthroscopic means, and both bioabsorbable and metal fixation devices exist. With good subchondral bone attached, as in the case of osteochondral fractures, these fragments have excellent healing capacity. Large osteochondral fracture fragments should be fixed, if possible, to preserve articular integrity and congruency of the joint.
Despite the theoretical and historic dogma that cartilage cannot be adequately repaired to bone, fixation of chondral-only fragments in young patients has been gaining some attention and has demonstrated promising outcomes. An early case report of a large lateral femoral condyle chondral injury was fixed in an 11-year-old boy with bioabsorbable pins. Second-look arthroscopy demonstrated healing, and complete healing of the cartilage to the subchondral bone was confirmed with core biopsy. Additional case reports have showed similar success with fixation of chondral-only lesions. In one of the larger series, 10 paediatric patients had chondral-only fragment repairs with bioabsorbable implants or suture in the acute setting at a median of 1.3 weeks from injury. Nine out of these 10 patients did not require subsequent fragment removal, and postoperative MRI findings were largely favourable. An additional multicentre retrospective review found successful healing outcomes in most patients with chondral fragment repair and favourable return to sport rates. In young patients with displaced cartilage sheer injuries, consideration should be given to acute repair because adequate healing can occur in this patient population and may mitigate downstream sequelae of full-thickness cartilage loss at a young age.
Patellar instability is often encountered in the paediatric population. Sequelae of patellar dislocation such as recurrent instability, osteochondral fractures and chondral sheer injuries have operative indications. Multiple surgical options exist for proximal and distal patellar realignment in skeletally immature patients, as well as fixation versus excision of loose body fragments. More high-level studies are needed to better define the effectiveness of varied surgical techniques and patient outcomes after patellar stabilisation in young patients.
Tibial Eminence Fractures
Tibial eminence fractures are common fractures in the paediatric and adolescent knee, and appropriate assessment and management of these injuries is important for any surgeon taking care of young, active patients. Nondisplaced fractures can often be managed conservatively, with cast immobilisation. Displaced fractures, however, often require surgical fixation, and taking care to avoid injury to growing physes and to not span a physis with rigid fixation constructs are important paediatric principles.
Epidemiology and Pathophysiology
Tibial eminence fractures are avulsion fractures of the ACL insertion on the tibia. These are common intraarticular injuries in young patients, with a predilection for the later childhood and early adolescent years. , Historically, tibial eminence fractures were considered to be the paediatric equivalent of an ACL tear; however, newer research has shown the two to be distinct diagnoses in young people. The thought is that an incompletely ossified tibial eminence can be weaker than the ACL midsubstance and is thus at risk for subchondral bone failure in skeletally immature patients with slower loading conditions. , Kocher et al. found that skeletally immature patients with larger intercondylar notches tended to suffer tibial eminence fractures, as opposed to those with narrow notches, where ACL midsubstance injury was more common. The most common mechanisms for this type of injury include sport-related injuries, bicycle accidents, motor vehicle accidents and falls. , In addition to bony injury, the ACL itself can undergo stress and stretch, and residual ACL laxity can result after treatment of these injuries.
Similar to other intraarticular injuries, patients often present with pain, knee effusion, decreased range of motion and difficulty with weightbearing in the acute setting. They may have an inability to achieve full knee extension because of a displaced bony block caused by the fracture. Laxity with Lachman testing and a positive pivot shift examination are also expected; however, ligament examination can sometimes be difficult in young patients with a painful knee. Most tibial eminence fractures can be adequately visualised on plain radiographs, including AP, lateral and notch views; however, findings may be subtle if only a small ossified portion of the chondroepiphyseal fragment is avulsed. A CT scan can help better define the size and characteristics of the bony fragment. MRI is often the best diagnostic test to evaluate displacement of the fragment, while also assessing for additional intraarticular injury, which is common with tibial eminence fractures.
The most common classification system for tibial eminence fractures is the Myers and McKeever classification, which was subsequently modified by Zaricznyj. , Pictorial representation of this classification system can be seen in Fig. 36.5 . Type 1 fractures are minimally displaced. Type 2 fractures are hinged fragments, where the anterior portion of the fragment is displaced superiorly but continuity remains in the posterior portion. Type 3 fractures are completely displaced avulsion fragments with no continuity with the proximal tibial epiphysis. Type 4 fractures, as added by Zaricznyj, are displaced, comminuted fractures of the tibial eminence. More recent fracture classifications based on MRI findings have also been described, which take into account fracture displacement as well soft tissue entrapment.