The knee is the body part most commonly injured as a consequence of collisions, falls, and overuse occurring from childhood sports. The number of sports-related injuries is increasing because of active participation of children in competitive sports. Children differ from adults in many areas, such as increased rate and ability of healing, higher strength of ligaments compared with growth plates, and continued growth. Growth around the knee can be affected if the growth plates are involved in injuries. This article discusses fractures, anterior and posterior cruciate ligament injuries, and meniscal and patellar conditions.
The knee is the body part most commonly injured as a consequence of collisions, falls, and overuse occurring from childhood sports . The knee is also the site most prone to chronic and permanent disability . The number of sports-related injuries is increasing because of active participation of children in competitive sports. Sports-related injuries account for one fourth of all injuries in children . Approximately 30 million children are involved in organized sports, and up to a third of these children sustain an injury that requires medical attention . Certain sports have increased potential for knee injuries, such as soccer, football, basketball, cycling, and Alpine sports .
Children differ from adults in many areas, such as increased rate and ability of healing, higher strength of ligaments compared with growth plates, and continued growth. Growth around the knee can be affected if the growth plates are involved in injuries. The distal femoral physis is the most active growth plate in the body and contributes approximately 1 cm of growth per year, which provides 70% of the growth of the femur and 37% of the growth of the lower limb. The proximal tibial physis contributes approximately 0.7 cm of growth per year and contributes 55% of the growth of the tibia and 25% of the growth of the lower limb . Injuries to these active growth plates may result in significant limb length discrepancies or angular deformities.
Children often have inadequately developed motor skills and coordination. They may have intrinsic factors that predispose to injury, such as inadequate strength, flexibility, and endurance for their chosen sport. They also may have abnormal morphology or biomechanics. Extrinsic factors, such as poor training techniques and conditioning, poor supervision and coaching, lack of or improper use of safety equipment, excessive loading of the knee, and physical or psychologic stress, also contribute to injury.
History
The history initially should be directed toward the type of sport played, the equipment or footwear being worn, the playing surface, any history of direct trauma, and any history of previous injury. The magnitude and direction of force involved in the injury also should be assessed. Patients should be asked whether there was a pop or snap at the time of injury, whether there was a fall, and if it was possible to get up unassisted. They should be questioned about whether they were able to continue playing and for how long. Also questioned is the presence of swelling and the rapidity with which it occurred, which may differentiate a cruciate ligament injury, dislocation, or fracture from a meniscal injury or ligament sprain. Patients are asked whether there was any displacement of the patella and whether it reduced spontaneously. The onset of pain, and type, severity, and radiation of pain should be determined, as should any aggravating or relieving factors. Any history of crepitus, locking, or giving way of the knee after the injury is elicited, as is the medical treatment received and its effectiveness.
Physical examination
The neurovascular status of the lower limbs should be documented, followed by inspection of the leg at rest. It is assessed for the presence of intra-articular effusion, extra-articular swelling, ecchymosis, deformity, or quadriceps wasting. The coronal alignment of the knees and leg lengths should be determined. Children are asked where their pain is located, and palpation of that area is reserved for last so as not to upset children unnecessarily. Palpation should include the joint lines, physes of the distal femur and proximal tibia, femoral condyles, tibial plateau, pes anserinus, medial and lateral collateral ligaments (LCLs), proximal end of the fibula, tibial tuberosity, patella tendon, superior and inferior poles of the patella, patellar retinaculum, and quadriceps. Passive translation of the patella medially and laterally and apprehension testing should be performed.
Passive and active range of motion of the knee and patellar tracking are assessed, followed by stress testing of the anterior and posterior cruciate ligaments and medial and lateral collateral ligaments and provocative testing of the menisci. The presence of crepitus is noted if present. It is important to remember that ligaments are stronger than the bones or physes in children and that an apparent ligamentous instability may actually may be a physeal injury or fracture. It is also helpful to compare the stability of ligaments with those of the normal knee to avoid confusion in ligamentously lax individuals.
Range of motion of the hip should be assessed with minimal motion of the knee to avoid confusing the hip examination. Hip disorders such as slipped capital femoral epiphysis and Legg-Calvé-Perthes disease may refer pain to the knee. Ligamentous hypermobility also should be assessed. Gait examination should be performed if possible; however, the presence of acute injury and pain usually results in an antalgic gait, provided that the patient is able to walk unaided.
Physical examination
The neurovascular status of the lower limbs should be documented, followed by inspection of the leg at rest. It is assessed for the presence of intra-articular effusion, extra-articular swelling, ecchymosis, deformity, or quadriceps wasting. The coronal alignment of the knees and leg lengths should be determined. Children are asked where their pain is located, and palpation of that area is reserved for last so as not to upset children unnecessarily. Palpation should include the joint lines, physes of the distal femur and proximal tibia, femoral condyles, tibial plateau, pes anserinus, medial and lateral collateral ligaments (LCLs), proximal end of the fibula, tibial tuberosity, patella tendon, superior and inferior poles of the patella, patellar retinaculum, and quadriceps. Passive translation of the patella medially and laterally and apprehension testing should be performed.
Passive and active range of motion of the knee and patellar tracking are assessed, followed by stress testing of the anterior and posterior cruciate ligaments and medial and lateral collateral ligaments and provocative testing of the menisci. The presence of crepitus is noted if present. It is important to remember that ligaments are stronger than the bones or physes in children and that an apparent ligamentous instability may actually may be a physeal injury or fracture. It is also helpful to compare the stability of ligaments with those of the normal knee to avoid confusion in ligamentously lax individuals.
Range of motion of the hip should be assessed with minimal motion of the knee to avoid confusing the hip examination. Hip disorders such as slipped capital femoral epiphysis and Legg-Calvé-Perthes disease may refer pain to the knee. Ligamentous hypermobility also should be assessed. Gait examination should be performed if possible; however, the presence of acute injury and pain usually results in an antalgic gait, provided that the patient is able to walk unaided.
Investigations
Anteroposterior and lateral radiographs are routinely obtained. The Merchant or skyline views to visualize the patellofemoral articulation and the anteroposterior notch view to visualize the posterior aspect of the femoral condyles may be helpful. Oblique radiographs may help to reveal subtle fractures. MRI or CT is useful in further evaluation of bones and soft tissue, which is especially true when the injury is not apparent on plain radiographs and there is a preceding traumatic event, effusion, or swelling together with a refusal to weight bear on the leg .
The use of radiographs may be decreased by 31% with the use of the Ottawa Knee Rules, which have a sensitivity of 100% and specificity of 43% for detecting a fracture . Although MRI of the knee has been shown to have a sensitivity of 92% to 100% and a specificity of 87% to 100% , Kocabey and colleagues have shown that there was no difference between MRI and a well-trained orthopedic surgeon in terms of ability to diagnose intra-articular soft tissue knee injuries.
Fractures
Distal femoral physeal fractures
These fractures are relatively uncommon, accounting for 7% of physeal injuries of the lower extremities . The distal femoral physis has a complex shape with four depressions, into which four matching processes of the distal femoral metaphysis fit. This shape provides increased resistance to shear but also results in an increased risk of focal damage to the physis if injury occurs because of the decreased odds of a “clean” cleavage plane across the physis . Juvenile injuries occur mostly after a high-velocity trauma, such as a motor vehicle accident (44% of injuries), whereas adolescent injuries occur mainly in relatively low-energy activities, such as sports (25% of injuries) . Hyperextension is the most common mechanism of injury. Individuals who play sports that involve jumping, such as high jump, hurdles, and basketball, have a higher incidence of this injury .
The commonly used classification for physeal injuries is that of Salter and Harris ( Fig. 1 ) . In type I fractures, there is separation through the physis with no metaphyseal or epiphyseal involvement. Type II fractures are the most common physeal injuries in this area and form 54% of all injuries . The fracture line traverses the physis before exiting obliquely through the metaphysis. The metaphyseal fragment (Thurston-Holland fragment) is often opposite the direction of force, and the physis attached to it is least susceptible to growth arrest because the physis is not disrupted. Type III fractures consist of a fracture through the physis that exits through the epiphysis into the joint ( Fig. 2 A–D). Type IV fractures consist of a fracture line that crosses the metaphysis, physis, and epiphysis into the joint. Type V fractures are crush injuries to the physeal cartilage. They are rare and difficult to diagnose initially, often presenting 6 to 12 months later with limb shortening or angular deformity. Comparison radiographs of the normal contralateral physis may distinguish narrowing of the injured physis.
Undisplaced fractures are treated with immobilization in an above-knee cast or hip spica for 4 to 6 weeks. Serial weekly radiographs for 3 weeks help to exclude secondary displacement. Gentle closed reduction is attempted for displaced type I and II fractures because excessive manipulation can damage the growth plate. The common rule is 90% traction and 10% manipulation. Fractures with greater displacement, especially hyperextension injuries, are associated with an increased risk of displacement, thus percutaneous fixation is recommended . Large thigh girths make cast immobilization more difficult and may indicate fixation to maintain reduction . Open reduction may be necessary if closed reduction is unsuccessful ( Fig. 3 A, B).
Types I and II fractures can be fixed with one or two smooth pins from the epiphysis to the metaphysis. These pins are bent and left under the skin, with removal after fracture healing. If the Thurston-Holland fragment is large enough, type II fractures can be fixed with percutaneous screws across the fragment and into the metaphyseal area. Types III and IV fractures are fixed with intra-epiphyseal screws and usually require open reduction to anatomically reduce to joint line. Failure to achieve anatomic reduction may result in the formation of an osseous bar, which can result in limb length discrepancy and angular deformity .
These injuries are frequently complicated by limb length discrepancy, angular deformity, stiffness of the knee, or neurovascular compromise. Riseborough and colleagues found that younger children aged 2 to 11 with displaced fractures more than half the diameter of the femoral shaft were more likely to have subsequent growth problems. Angular deformity occurs in 24% of patients and limb length discrepancy in 32% . Detection of these injuries requires at least 6 to 12 months of follow-up. Physeal injuries have even been noted in nonphyseal fractures of the lower limb, causing angular deformity that was noted on average 22 months after the injury . MRI is used to determine if physeal osseous bars are present. Resection is indicated if less than 50% of the physis is involved and there are more than 2 years of growth remaining ( Fig. 4 ) . Angular deformity is corrected by completion epiphysiodesis or osteotomy. Limb length discrepancy of less than 5 cm can be treated with contralateral epiphysiodesis, whereas discrepancy of more than 5 cm can be treated with limb lengthening or contralateral shortening procedures.
Neurovascular injuries are rare and occur in 2% of fractures . Hyperextension injuries result in anterior displacement of the femoral physis and may injure the closely attached popliteal artery, whereas varus angulation may injure the peroneal nerve. Vascular injuries require immediate reduction and fixation of the fracture and on-table angiogram and vascular repair as necessary.
Proximal tibial physeal fractures
These fractures are rare and account for 3% of physeal injuries of the lower extremities . Their incidence is half that of distal femoral physeal injuries, which is theorized to be caused by the collateral ligament and tendon insertions being located mainly in the metaphysis rather than the epiphysis, as compared with the distal femoral physis . The mechanism of injury is usually a hyperextension force that results in an apex posterior angulation of the metaphysis. This force can injure the popliteal artery, which is tethered by the anterior tibial artery, as it perforates the interosseous membrane. The fracture subsequently can reduce to an innocuous position on radiographs , so care must be taken to assess the neurovascular status of the limb.
The most common fractures are Salter-Harris type II (43%), followed by type III (22%), type IV (17%), type I (15%), and type V (2%) . Most type I and II fractures can be treated with closed reduction and immobilization ( Fig. 5 A–C). Types III and IV fractures can be treated with closed reduction and percutaneous pinning or screw fixation. Open reduction is indicated if anatomic reduction cannot be achieved, and for type II fractures this is rarely caused by pes anserinus interpositioned in the fracture site .
The most common complications are angular deformity (28%) and limb length discrepancy (19%), which mainly occur after open lawnmower injuries that damage the perichondral ring of the proximal tibial physis . Vascular injury occurs in 5% to 7% of cases and necessitates immediate reduction and fixation of the fracture and angiography and revascularization as appropriate. More uncommonly, anterior compartment syndrome, peroneal nerve palsy, and ligamentous and meniscal injuries can occur.
Tibial tuberosity fractures
These fractures are Salter-Harris type III avulsion fractures of the proximal tibial physis and account for 14% to 15% of proximal tibial fractures . Watson-Jones believed they were caused by either a violent contraction of the quadriceps muscle or sudden passive flexion of the knee against a contracted quadriceps muscle. Böhler described them as being the result of “jumps with a bad landing.” Ninety percent are sports related, and they occur at an average age of 15 . They should be differentiated from Osgood-Schlatter’s disease, which is a stress reaction of the anterior ossicle of the tuberosity with no involvement of the physis. The presence of acute symptoms for a tibial tuberosity fracture should help distinguish it from Osgood-Schlatter’s disease. Ogden and colleagues suggested that Osgood-Schlatter’s disease predisposed to acute avulsion of the tibial tuberosity and found this association in 56% of his patients. Other authors have noted it in only 10% of patients, however .
Ogden and colleagues modified the classification by Watson-Jones to place more emphasis on intra-articular extension of the fracture and comminution of the tuberosity. Type I fractures involve a small avulsed fragment of the tuberosity, which is displaced upward. Type IA fractures are incompletely separated from the metaphysis, whereas type IB fractures are completely separated. Type II fractures involve the entire tibial tuberosity without extension of the fracture line into the proximal tibial epiphysis. Type IIA fractures are not comminuted, whereas IIB fractures are comminuted. Type III fractures extend proximally into the anterior tibial epiphysis and involve the articular surface. Type IIIA fractures are not comminuted, whereas IIIB fractures are comminuted.
Patients with type I fractures are usually able to actively extend their knee except against resistance, whereas patients with type II and III fractures are usually unable to extend the knee. Patella alta may be present depending on the amount of displacement of the tuberosity. Lateral radiographs in slight internal rotation afford the best view of the fracture. Undisplaced type I fractures are treated with a cast in extension for 6 weeks. Small type I avulsed fragments are treated by attaching tendon-holding sutures in the patella tendon and anchoring them to a screw in the proximal tibia. Larger fragments are fixed directly to the metaphysis with screws for older adolescents or K-wires and periosteal sutures for children, followed by casting at 30° for 4 to 6 weeks ( Fig. 6 A–D). Intra-articular fractures require inspection of the joint surface for anatomic reduction and to visualize any associated meniscal tears, detachment, or interfragmentary entrapment . Progressive rehabilitation of the quadriceps continues until normal strength is achieved with full range of motion of the knee. Sports activities are allowed 3 to 5 months after the injury .
Complications are rare. Genu recurvatum may develop in the rare tuberosity fracture before the age of 11 ( Fig. 7 ) . Damage to the anterior tibial recurrent artery in the region of the tibial tuberosity has been reported to cause compartment syndrome , and patients should be monitored closely for this condition postoperatively.
Tibial eminence fractures
The anterior tibial eminence, or spine, is the site of insertion for the anterior cruciate ligament (ACL). Before ossification of the proximal physis is complete, the insertion consists of a chondroepiphysis, which is weaker than the ACL. Traumatic forces, which in a mature individual would cause an ACL tear, usually result in a tibial eminence fracture in a child. These injuries account for 2% of knee injuries in children and typically occur between the ages of 8 and 14. They are commonly associated with falls from bicycles that result in forceful hyperextension of the knee or a direct blow on the distal end of the femur with the knee flexed . Decreased intercondylar notch width has been associated with decreased ACL size and increased risk of ACL rupture .
Meyers and McKeever classified these fractures according to the amount of displacement and the fracture pattern. Type I fractures are minimally displaced ( Fig. 8 ). Type II fractures have a posterior hinge with an elevated anterior portion. Type III fractures are completely displaced fragments and may be rotated. Zaricznyj has added a type IV, which are comminuted fractures of the tibial eminence.
Radiographs often underestimate the size of the largely cartilaginous fragment, and MRI may be useful for further assessment . Types I and II fractures, which can be reduced by closed means, are treated with cast immobilization in 10° of flexion for 6 weeks, followed by rehabilitation. Failure of closed reduction is usually caused by interposed medial or lateral meniscus or the intermeniscal ligament. Irreducible types II and III fractures require open or arthroscopic reduction and fixation. Fixation may consist of K-wire, suture, or screw fixation, either transphyseal or intraepiphyseal. Transphyseal wires or screws require operative removal after fracture union.
Complications include arthrofibrosis, residual laxity and instability, extension loss, extension block from malunion, nonunion, and prominence or irritation of fixation devices . Residual anterior laxity has been reported in up to 64% of patients at 4 years follow-up, regardless of treatment method . Wiley and colleagues did not report any long-term functional instability, whereas Grönkvist and colleagues found functional instability in 38% of their patients and noted that children younger than age 10 were much less likely to have functional instability.
Patellar fractures
Patellar fractures make up less than 5% of all knee injuries and are uncommon because of the large ratio of cartilage to bone, increased mobility, and tissue resilience . These fractures result from direct trauma or avulsion forces across the patella. Most fractures are caused by motor vehicle accidents, and only 17% are related to sports . Direct trauma in older adolescents usually results in a transverse fracture of the patella. Sleeve fractures occur when an extensive sleeve of cartilage is avulsed off the main body of the patella along with a bony fragment from the distal pole ( Fig. 9 ) . These fractures can be missed on radiographs because of the radiolucent sleeve of cartilage and small bony fragments.
The knee is swollen, usually with an extension lag, palpable gap in the extensor mechanism, and patella alta. Minimally displaced fractures, which allow active extension, can be treated with a long leg cast for 4 to 6 weeks. Displaced fractures or disruption of the extensor mechanism requires open reduction and internal fixation with the tension band technique, a circumferential wire loop, or interfragmentary screws. The patella retinaculum is repaired at the same time ( Fig. 10 ).
Outcomes are generally good. Results are poor with more displaced and comminuted fractures . Inadequate reduction or fixation can result in patella alta, extensor lag, and quadriceps muscle atrophy .
Patellar dislocation
The incidence of acute patellar dislocation in children between ages 9 and 15 has been reported as 1 in 1000 per year . The typical mechanism is an indirect twisting injury, with the femur internally rotating over a planted foot and valgus knee. This is a similar mechanism of injury for ACL tears, which should be excluded during the assessment of this injury. Other mechanisms include a direct trauma to the lateral aspect of the knee or medial edge of the patella. Predisposing factors include patella alta, abnormal patellar morphology, lateral patellar displacement, trochlear dysplasia, increased Q angle, genu valgum, vastus medialis hypoplasia, ligament hyperlaxity, external tibia torsion, subtalar joint pronation, and increased femoral anteversion . The Q angle is defined as the angle formed at the center of the patella by the line of pull of the quadriceps tendon and that of the patellar tendon. This angle is normally 15° or less, and a larger angle would indicate an increased tendency for lateral subluxation of the patella.
The patella is typically dislocated laterally, and spontaneous reduction usually occurs with the knee in extension. Occasionally, the patient presents with a painful flexed knee and persistent dislocation. Immediate reduction is performed with the patient being as relaxed as possible and bringing the knee to full extension, with gentle medializing pressure on the dislocated patella if necessary. Examination reveals medial retinacular tenderness and a positive apprehension test. Palpation of the patella and femoral articular surfaces may reveal tenderness over chondral or osteochondral injuries.
Treatment of first-time patellar dislocations is by immobilization of the knee in extension for 3 weeks. A lateral compression pad also can be added . Quadriceps isometrics, straight leg raises, and single plane motion exercises begin early. Relative indications for early surgical treatment include the presence of an osteochondral fracture, substantial disruption of the medial patellar stabilizers, laterally subluxated patella with normal patellar alignment in the contralateral knee, recurrent dislocation, and lack of improvement with appropriate rehabilitation . Rorabeck and Bobechko described three patterns of fracture for osteochondral fractures associated with patellar dislocations: inferomedial fracture of the patella, fracture of the lateral femoral condyle, and a combination of the two ( Fig. 11 ). They estimated that it occurred in 5% of patellar dislocations, but Nietosvaara and colleagues reported an incidence of 39%, whereas Stanitski and colleagues reported a 71% incidence of articular injury on arthroscopy. MRI is more effective than plain radiographs at visualizing fragments, which are largely cartilaginous, and helps to visualize injuries to the medial patellar stabilizers and articular surfaces ( Fig. 12 A–C) . The presence of an osteochondral fracture is an indication for surgery, which may range from arthroscopic excision of small fragments from non–weight-bearing surfaces to fixation of larger fragments from weight-bearing surfaces using Herbert screws or biodegradable pins. If fixation is used, weight bearing should be avoided until radiographic healing occurs. Chondral injuries can be treated with débridement, microfracture, or drilling for smaller defects. Larger defects may require the use of resurfacing techniques, such as osteochondral autograft or autologous chondrocyte implantation.
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