Adolescents are predisposed to osteochondral (OC) injuries in the knee. The medial facet of the patella, the femoral trochlea, and the lateral femoral condyle are the most common sites of injury. Most of these injuries are classically traumatic but noncontact injuries. Surgery is warranted in most cases of OC fracture. Depending on size, condition, and location of the lesion, options include OC fragment reduction and internal fixation or excision and cartilage resurfacing. Understanding of how to diagnose and treat OC fractures will help optimize outcomes.
Acute traumatic and sports-related osteochondral (OC) injuries occur in a variety of settings in the pediatric knee. The pediatric population is more susceptible to OC fractures because the calcified cartilage layer is incompletely formed, which results in a weakened interface between the articular cartilage and subchondral bone. OC fractures occur in the patella or trochlea of children after a noncontact flexion-rotation injury to the knee, which results in an acute patellar dislocation. Such injuries can also occur in the femoral condyles after a patellar dislocation or either a contact or noncontact injury to the knee, causing a shearing force on the condyles. Acute OC fractures should be addressed surgically in cases where the OC fragment is large and the donor site is in a weight-bearing area.
OC injuries can lead to progressive chondral damage and early-onset arthritis. There is a small window of time in which surgical repair of the loose OC fragment is optimal. Over time, the loose OC fragment swells and chondral degeneration occurs. In addition, the loose fragment can damage other chondral surfaces in the knee. Early surgical repair of a large intact OC fragment has the potential to restore anatomy and preserve the native chondral surface. When the fragment is deemed unsalvageable, the loose body is removed and the donor site is treated with cartilage resurfacing techniques, such as microfracture, OC plugs, and autologous chondrocyte implantation (ACI). These techniques generate repair tissue with inferior histologic and long-term wear characteristics compared with the native chondral surface.
Background and mechanism of OC fracture during patellar dislocation
Acute lateral patellar dislocations are the most common cause of OC fractures in the pediatric knee. A noncontact flexion-rotation injury to the knee causes the patella to dislocate laterally and shear across the lateral femoral condyle (LFC). Impaction of the medial border of the patella to the LFC/trochlea during patellar relocation results in the fracture. OC fractures occur in 25% to 75% of acute patellar dislocations in the pediatric and adolescent population. These injuries most often involve the medial facet of the patella and are missed on standard radiographs in up to 36% of cases. Two studies emphasized how common OC injuries can be after acute patellar dislocations. Using radiography and arthroscopy, Stanitski and Paletta assessed articular lesions in 48 pediatric patients (24 male and 24 female; mean age 14 years) with acute, initial, noncontact patellar dislocations. Of 48 patients, they identified arthroscopically 32 patients with OC fractures and 2 patients with chondral injuries as well as 28 patients with OC loose bodies. Only 32% of the arthroscopically visualized OC/chondral lesions were noted on preoperative radiographs. Nomura and colleagues arthroscopically evaluated the knees of 39 pediatric patients with initial lateral patellar dislocation. Knees of 37 of their 39 patients (95%) had a chondral injury, including 28 patients with OC fractures, which were most commonly noted at the medial patellar facet.
OC fractures of the weight-bearing femoral condyles can present in isolation or in the setting of a traumatic patellar dislocation. This fracture is rare and occurs almost exclusively in the LFC. Two studies reported a rate of 8% and 20% for OC fractures of the associated weight-bearing LFC with patellar dislocations. Both studies were small in number, and the study by Nomura and colleagues included patients up to the age of 40 years with 72% of patients aged 12 to 19 years. OC fractures of the medial femoral condyle (MFC) are rare and are only described as case reports in the literature. Review of these articles shows that more of these injuries are in the non–weight-bearing portion of the MFC. Bowers and Huffman reported an MFC fracture after a forced hyperextension injury in a 25-year-old woman. Occult subcortical and/or depression fractures of the femoral condyles have also been described. These injuries can occur in isolation or in combination with a ligamentous injury.
Similar to OC injuries in the trochlea, the postulated mechanism for weight-bearing condylar fractures in association with a patellar dislocation is when the relocating patella directly impacts the femoral condyle, producing fracture. The difference is thought to be the degree of knee flexion present during injury. Knee flexion at 90° or more at the time of dislocation and/or relocation are thought to be present for this injury pattern. In isolation, a valgus-shearing mechanism coupled with a twist between the femoral condyle and the tibial plateau is thought to occur. This latter mechanism has also been proposed to explain the weight-bearing OC condyle fracture even in association with patellar dislocations, given the highly constrained nature of the patella when the knee is highly flexed. These injuries are typically noncontact. This mechanism is applicable mainly to LFC fractures. MFC fractures are so rare that no clear mechanism has been described. Generalized joint hypermobility may be a risk factor for the occurrence of this injury.
Clinical presentation and diagnosis
An acute patellar dislocation with an associated OC injury can occur after both traumatic contact and noncontact twisting injuries to the knee. Patients often present with a large knee effusion, tenderness over the medial retinaculum/medial patellofemoral ligament, and lateral patellar subluxation. The effusion, if aspirated, reveals a lipohemarthrosis resulting from the OC fracture. Range of motion may or may not be significantly disturbed depending on the location of the loose OC fragment. Often, the fragment can end up in the suprapatellar pouch or in one of the gutters. Significant crepitus of the area may be appreciated on range of motion. Patients often are unable to bear weight. The examiner should assess for ligament integrity and an intact extensor mechanism.
Lateral, sunrise, and Merchant-view radiographs of the knee may be helpful in identifying loose bodies and assessing pertinent anatomic factors, such as patella alta and trochlear dysplasia ( Fig. 1 ). In patients with a large hemarthrosis and a traumatic mechanism, the clinician should have a strong suspicion for OC injury. Initial radiographs can be misleading. Often they are negative or show only a small fleck of bone. Nonstandard oblique views may be needed to appreciate the OC fragment. If radiographs do not reveal any loose bodies, further imaging may be indicated. Magnetic resonance imaging (MRI) is typically the study of choice for high-resolution scanning and evaluation of OC lesions. Improved MR protocols using intravenous gadolinium and appropriate orthogonal tilting on a 1.5-T magnet have increased MRI sensitivity and specificity to 90% to 95% for localizing and characterizing OC injuries ( Fig. 2 ). MRI may underestimate the true size of the defect because the partially attached chondral fragments have an irregular shape that may not correspond to the plane of the image. Computed tomography (CT) may also be used to better visualize the donor site and loose fragment as well as plan the operative management ( Fig. 3 ). Arthroscopy remains the gold standard for the accurate identification and characterization of OC injuries.
Clinical presentation and diagnosis
An acute patellar dislocation with an associated OC injury can occur after both traumatic contact and noncontact twisting injuries to the knee. Patients often present with a large knee effusion, tenderness over the medial retinaculum/medial patellofemoral ligament, and lateral patellar subluxation. The effusion, if aspirated, reveals a lipohemarthrosis resulting from the OC fracture. Range of motion may or may not be significantly disturbed depending on the location of the loose OC fragment. Often, the fragment can end up in the suprapatellar pouch or in one of the gutters. Significant crepitus of the area may be appreciated on range of motion. Patients often are unable to bear weight. The examiner should assess for ligament integrity and an intact extensor mechanism.
Lateral, sunrise, and Merchant-view radiographs of the knee may be helpful in identifying loose bodies and assessing pertinent anatomic factors, such as patella alta and trochlear dysplasia ( Fig. 1 ). In patients with a large hemarthrosis and a traumatic mechanism, the clinician should have a strong suspicion for OC injury. Initial radiographs can be misleading. Often they are negative or show only a small fleck of bone. Nonstandard oblique views may be needed to appreciate the OC fragment. If radiographs do not reveal any loose bodies, further imaging may be indicated. Magnetic resonance imaging (MRI) is typically the study of choice for high-resolution scanning and evaluation of OC lesions. Improved MR protocols using intravenous gadolinium and appropriate orthogonal tilting on a 1.5-T magnet have increased MRI sensitivity and specificity to 90% to 95% for localizing and characterizing OC injuries ( Fig. 2 ). MRI may underestimate the true size of the defect because the partially attached chondral fragments have an irregular shape that may not correspond to the plane of the image. Computed tomography (CT) may also be used to better visualize the donor site and loose fragment as well as plan the operative management ( Fig. 3 ). Arthroscopy remains the gold standard for the accurate identification and characterization of OC injuries.
Management and surgical technique
Nonoperative management is often successfully used for acute patellar dislocations without the presence of a loose body. Occult subcortical OC fractures with an intact cartilage surface can usually be treated nonoperatively with protected weight bearing and restricted range of motion. Rarely a large subcortical depression fracture may warrant surgery. Arthroscopically assisted antegrade elevation with restoration of the normal joint surface curvature has been reported.
Surgery is indicated in most cases of displaced OC fractures. Historically, OC fractures have been treated with excision and early range of motion. Fixation of loose OC fragments was first described in the 1970s. At present, fixation of weight-bearing condylar lesions is preferred unless the lesion is small or the OC fragment is damaged. If the loose OC fragment has minimal subchondral bone or a damaged chondral surface, or if the donor site is located in a non–weight-bearing area, loose body removal and donor site resurfacing are indicated. If the OC fragment is excised, options such as microfracture, OC autograft plugs, OC allografts, and ACI exist. Indications and techniques are described in the literature. OC fractures with intact cartilage and sufficient subchondral bone that occur in the weight-bearing regions should be treated with reduction and fixation. Several methods of fixation have been described in the literature.
Reduction and repair of OC fractures
The Authors’ Preferred Technique
Initial arthroscopic assessment followed by appropriate exposure and rigid fixation is the preferred technique. For patients with a loose OC fracture after an acute patellar dislocation, both injuries must be addressed. A standard knee arthroscopy is performed and the hemarthrosis is lavaged. The OC fragment is often discovered in the suprapatellar pouch. An accessory superolateral or superomedial portal can facilitate the removal of loose body, which should be done carefully to avoid damaging the chondral surface of the fragment. The loose body is then inspected to establish whether the fragment has sufficient subchondral bone attached and to examine the status of the overlying cartilage. The donor site is next evaluated to determine if it is in a weight-bearing articular area. For trochlear lesions, the knee should be flexed to find out if the donor site is located under the patella during normal motion.
For patellar and trochlear lesions, a mini-arthrotomy is usually required to best access the donor site for reduction and fixation. Lesions on the medial aspect of the patella in the setting of a patellar dislocation can often be accessed through the same incision used for an open medial retinacular repair that often accompanies this procedure. Lesions on the lateral trochlea or lateral aspect of the patella may be accessed by a mini-lateral arthrotomy. A lateral retinacular release may facilitate patellar eversion and surgical exposure for lateral patellar lesions. An arthroscopic approach may be possible for lateral trochlear lesions. In these cases, an accessory superolateral portal is created directly over the area of repair to facilitate perpendicular access to the lesion.
Femoral condyle OC fractures are often best accessed with a mini-arthrotomy. The corresponding arthroscopic portal is extended in a longitudinal manner to access the lesion. If the lesion is far posterior, the knee can be hyperflexed for exposure. For arthroscopic repair, a perpendicular path to the lesion must be established using an accessory portal, and the synovium should be cleared from the path. If multiple implants are thought to be necessary to achieve stable fixation, a mini-arthrotomy allows greater degrees of freedom for the fixation instruments and implants.
The donor site is first prepared by carefully removing the nonviable tissue from the donor base by using small curets. Excessive debridement is avoided to minimize the loss of bone and subsequent fragment depression. The chondral surface is then debrided to stable edges, and the subchondral bone is perforated to promote bleeding. If significant loss of subchondral bone exists, autologous bone graft may be packed into the donor site before reduction and fixation. The fragment is reduced and provisionally stabilized with 1 or 2 Kirschner wires. Depending on the length of time from injury, the fragment may need to be trimmed to facilitate reduction because of chondral swelling.
Definitive fixation is then performed ( Fig. 4 ). The choice of implant depends on the preference and comfort level of the surgeon as well as the availability of implants. Fixation can be achieved with a variety of devices, including smooth or threaded pins, headless or low-profile compression screws (countersunk below the articular surface), bioabsorbable implants, and absorbable sutures. Partially threaded cannulated screws provide the most compression; however, they leave an indentation on the articular surface and, if not countersunk, may scuff the tibial surface, requiring later removal. Headless screws can be buried below the articular cartilage surface and provide compression, but may back out over time and require removal. Bioabsorbable implants are useful for smaller lesions with scant subchondral bone, but are more costly and provide less interfragmentary compression in comparison with metallic devices. Because of the lack of comparative studies or long-term follow-up studies in the pediatric population, no one implant can be recommended over another.
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