Theodore J. Ganley, Gilbert Chan, and Aaron B. Heath
DEFINITION
Osteochondritis dissecans (OCD) is a relatively common cause of knee pain and dysfunction in children, adolescents, and young adults.
OCD is an acquired potentially reversible idiopathic lesion of subchondral bone resulting in delamination and sequestration with or without articular involvement and instability.
ANATOMY
Initially, softening of the subchondral bone and overlying articular cartilage is noted with an intact articular surface; this can progress to early articular cartilage separation and later osteochondral separation.
PATHOGENESIS
Although the exact pathogenesis of OCD is unknown, several factors have been historically implicated, including repetitive trauma, ischemia, inflammation, accessory centers of ossification, and genetic factors.
Overall it is likely that chronic repetitive microtrauma potentially leads to microfractures causing focal subchondral ischemia or alteration of growth. Some patients are believed to have a genetic, biochemical, or behavioral predisposition toward this condition.
The name “osteochondritis dissecans” implies that this condition has an inflammatory etiology, but further study has not supported inflammation as a primary cause of OCD.
Although abnormalities in ossification do not account for most cases of OCD as proposed by Ribbing in 1955,16 some incidentally found lateral femoral condyle lesions in younger children that resolve spontaneously may represent ossification variants.
Based on their anatomic and histologic findings, Green and Banks8 proposed that ischemia was implicated in OCD, although further studies have failed to find a relative ischemic watershed of the lateral aspect of the medial femoral condyle, suggesting that this is not the primary causative factor.
Petrie14 found OCD in 1 of 86 first-degree relatives, although Mubarak and Carroll12 reported 12 instances of family members with OCD over the course of four generations. While some familial tendencies exist, it is widely believed that the most common form of OCD is not familial.
In 1933, Fairbanks6 suggested that OCD might be due to a “violent rotation inwards of the tibia, driving the tibial spine against the inner condyle.” Although isolated acute trauma and anterior tibial spine impingement may not be the etiology of lesions in the most common location of the posterolateral aspect of the medial femoral condyle, the frequent occurrence of OCD in patients who are involved in sports with repetitive impact supports a repetitive microtrauma etiology.
NATURAL HISTORY
Crawfurd and associates5 followed 21 patients with undetached lesions left in situ with an average follow-up of 7.5 years.
Healing was noted in the medial femoral condyle in 3 of 10 patients; healing elsewhere was noted in 10 of 11 patients.5
PATIENT HISTORY AND PHYSICAL FINDINGS
Physical examination findings are often subtle.
Children and adolescents with stable OCD lesions may walk with a slight antalgic gait.
In late presentations in which an osteochondral flap or loose body is present, classic biomechanical symptoms including locking, catching, buckling, and giving way may occur.
With careful palpation through varying amounts of knee flexion, a point of maximal tenderness often can be located over the anterior medial aspect of the knee. The tender area corresponds to the lesion, usually on the lateral aspect of the distal medial femoral condyle.
With stable lesions, knee effusion, crepitus, and extreme pain through a normal range of motion are rarely observed.
The Wilson sign may be helpful but is often not present. The Wilson test is performed by starting with the knee flexed to 90 degrees. The tibia is then internally rotated as the knee is extended from 90 degrees toward full extension.
In a positive Wilson test, pain is elicited over the anterior aspect of the medial femoral condyle. This pain has been described as resulting from contact of the medial tibial eminence with the OCD lesion.
The mechanical symptoms are more pronounced in the unusual circumstance in which the child or adolescent presents with an unstable lesion. An antalgic gait is common, and there is usually a knee effusion, possibly associated with crepitus, as the knee is taken through a range of motion.
In stable and unstable presentations, both knees should be examined to determine whether the condition is bilateral. Ipsilateral quadriceps atrophy may also be noted if the patient has been having pain for more than an extended period of time.
IMAGING AND OTHER DIAGNOSTIC STUDIES
Imaging protocols have received close attention in the literature as a result of the varied success of nonoperative treatment. The goals of imaging are to characterize the lesion, determine the prognosis of nonoperative management, and monitor the healing of the lesion.
Imaging workup begins with plain radiographs, including anteroposterior (AP), lateral, and tunnel views (FIG 1A–C).
The tunnel view is particularly valuable since the typical OCD lesion is located on the flexion surface of the lateral aspect of the medial femoral condyle.
FIG 1 • AP (A) and lateral (B) radiographs of the knee demonstrating osteochondritis dissecans lesion. C. Tunnel view of the knee is particularly useful in lesions over the flexion surface of the medial femoral condyle. D,E. T1-weighted MR images of the knee demonstrating extent of osteochondritis dissecans lesion.
A Merchant view should be included to best reveal any OCD lesions of the patella or trochlea.
Plain radiographs usually characterize and localize the lesion and rule out other bony pathology of the knee region.
MRI is most useful for determining the size of the lesion and the status of the cartilage and subchondral bone (FIG 1D,E).
The extent of bony edema, the presence of a high-signal zone beneath the fragment, and the presence of other loose bodies are also important findings on initial MRI.
While less commonly used, technetium bone scans have been employed to provide information about the biologic capacity of an OCD lesion to heal.
DIFFERENTIAL DIAGNOSIS
Irregular ossification
Acute osteochondral fractures
Meniscal injuries
NONOPERATIVE MANAGEMENT
An initial course of nonoperative management is the treatment of choice for skeletally immature children with small intact lesions.
Controversy exists regarding the ideal nonoperative management for these patients. Clinicians who adhere to treating the subchondral bone as the primary source of pathology favor a period of immobilization. Those whose focus is on the articular cartilage as a source of pathology tend to favor maintaining mobilization.
The options for immobilization include casting, bracing, and standard knee immobilization.
We recommend a three-phase approach to the nonoperative management of OCD lesions.
Phase I
Weeks 1 to 6
Knee immobilization in a hinged brace. The patient may walk with the hinged brace locked in extension. The brace may be unlocked to work on range of motion for 5 minutes 5 times per day.
Phase II
Weeks 6 to 12
If the patient is pain-free and radiographs show signs of healing after 6 weeks, he or she is allowed to begin weight bearing without immobilization and to begin a physical therapy protocol to improve knee range of motion and quadriceps and hamstring strength.
Phase III
This phase is instituted if the patient continues to remain pain-free and shows radiographic evidence of healing.
This phase begins typically 3 months after treatment. Running, jumping, and cutting sports are permitted under close observation.
High-impact activities and activities that might involve shear stress to the knee should be restricted until the child has been pain-free for several months and the radiographs show a healed lesion.
The goal of nonoperative intervention is to promote healing in the subchondral bone and potentially prevent chondral collapse, subsequent fracture, and crater formation.
SURGICAL MANAGEMENT
It is widely accepted that operative treatment should be considered for patients with unstable or detached lesions, and in patients whose lesions have not resolved with an appropriate period of nonoperative management, especially in those approaching skeletal maturity.
Operative treatment is recommended if one or more of the following conditions are met: persistently symptomatic juvenile lesions, the presence of symptomatic loose bodies, predicted physeal closure within 1 year, or fragment detachment.
The goals of operative treatment are to promote healing of subchondral bone, to maintain joint congruity, to fix rigidly unstable fragments, and to replace osteochondral defects with cells that can replace and grow cartilage.
Optimal surgical treatment provides a stable construct of subchondral bone, calcified tidemark, and repair cartilage with viability and biomechanical properties equivalent to or similar to native hyaline cartilage.
Preoperative Planning
Careful preoperative evaluation and preparation are always imperative to the success of treatment.
All imaging studies obtained before surgery should be reviewed. If the avulsed fragment has a relatively large osseous component, then plain radiographs will usually demonstrate the lesion. However, radiographs do not demonstrate the actual size of the cartilaginous component. To demonstrate the cartilaginous component, MRI may be required to determine the extent of the lesion. Any other lesion noted on imaging studies should likewise be addressed.
A thorough physical examination should be performed under anesthesia.
Positioning
For arthroscopic procedures, the position largely depends on the surgeon's preference. A variety of positions can be used.
The leg can be placed in a leg holder on the operating table with the knee joint past the end of the operating table, thus allowing the knee to flex 90 degrees and the lower leg to hang freely.
The leg can be placed supine on the operating table, with the hip flexed and the knee flexed 90 degrees. The knee can be flexed and the lower leg can in this case hang freely over the side of the operating table.
Approach
Standard arthroscopic parapatellar portals are initially used (FIG 2A).
Accessory portals may be created higher or lower to the standard parapatellar portals if the lesion is excessively large or in an atypical location.
Transarticular drilling can be used for intact lesions, but it is particularly valuable when the lesion is detached, partially detached, or unstable (FIG 2B).
Epiphyseal drilling is reserved for cases with intact lesions (FIG 2C).
FIG 2 • A. Standard arthroscopic portals are used for arthroscopic drilling techniques. Accessory portals can be used for visualizing or treating lesions at the patellotrochlear interval. B,C. Arthroscopic drilling of an osteochondritis dissecans lesion by way of the transarticular and epiphyseal approaches, respectively.
TECHNIQUES
ARTHROSCOPIC DRILLING OF INTACT OCD LESIONS
The knee is exsanguinated and the tourniquet applied.
An anterolateral portal is made for visualization and an anteromedial portal is made for instrumentation.
A complete arthroscopic inspection of the knee is performed. Any other pathologies in the knee are recorded and treated accordingly.
Transarticular Drilling
The lesion is identified (TECH FIG 1A).
A 0.62-inch Kirschner wire is positioned perpendicular to the lesion (TECH FIG 1B). The portal used depends on the location of the defect.
The key is to keep the Kirschner wire as perpendicular as possible. Additional portals as well as varying the degree of knee flexion and extension may be used as needed to achieve adequate position.
The drilling is performed under arthroscopic visualization.
Appropriate depth of penetration is confirmed by the efflux of blood or fat from the drilled holes (TECH FIG 1C,D).
The drilling should be performed through the calcified tidemark in immature patients, taking care not to penetrate the physis.
TECH FIG 1 • A. The knee is inspected and the lesion is identified. The solid arrow shows the intact cartilage side and the open arrow shows the osteochondritis dissecans side. B. A Kirschner wire is shown superimposed over a T1-weighted MRI. The arrow shows the direction of drilling. The smooth 0.62-inch Kirschner wire should be kept as perpendicular to the lesion as possible to prevent undermining the defect. C,D. The appearance of fat or blood demonstrates that subchondral bone has been penetrated.
Epiphyseal Drilling
Once complete inspection has been performed, a 0.62-inch Kirschner wire is directed toward the lesion in a proximal-to-distal direction with fluoroscopic guidance and a guide (TECH FIG 2) to help maintain an appropriate angle.
The starting point of the Kirschner wire is immediately distal to the physis to avoid any damage.
The Kirschner wire is slowly advanced through the subchondral bone, taking care not to penetrate the articular cartilage.
The Kirschner wire is kept as perpendicular to the lesion as possible.
The position and depth of the Kirschner wires are confirmed using fluoroscopy.
Kirschner wires are inserted through the lesion several millimeters apart as needed.
Final inspection of the knee is performed and the Kirschner wires and instrumentation are removed.
Closure of the knee is performed and sterile dressing is applied before placing the knee in a knee immobilizer.
TECH FIG 2 • Appropriate guides can be used for antegrade arthroscopic drilling.
ARTHROSCOPIC DRILLING OF HINGED OCD LESIONS
The entire lesion is assessed and the bed is prepared. A débridement is performed until all granulation tissue and sclerotic bone beneath the flap is removed and subchondral bone is reached.
In deep lesions, autograft or allograft cancellous bone grafting may be required to ensure that the hinged portion of the lesion is not recessed relative to the remaining unaffected cartilage within the knee.
The lesion is reduced into its bed and fixed with a variety of implants, such as cannulated screws and Herbert screws. The fixation devices may be made of metal or bioabsorbable materials. The implant used depends on the surgeon's preference.
We prefer to use small bioabsorbable double-ended threaded compression screws for hinged lesions in which there is appropriate subchondral support (TECH FIG 3).
Once the lesion is secured, drilling may be performed to augment healing.
TECH FIG 3 • Small bioabsorbable double-ended threaded compression screws are used for hinged lesions in which there is appropriate subchondral support.
ARTHROSCOPIC DRILLING OF UNSTABLE OCD LESIONS
The knee joint is inspected and loose fragments are removed from the knee joint as necessary (TECH FIG 4A–C).
The bed of the lesion is inspected and a débridement is performed to remove any granulation tissue and sclerotic bone (TECH FIG 4D–F).
In reducible lesions, the fragment is prepared as necessary by trimming the edges and securing the lesion into its bed. A variety of implants may be used to secure the lesion based on the surgeon's preference.
The joint is inspected before final closure.
The arthroscopic instrumentation is removed and the arthroscopic portals are closed.
The knee is placed in a hinged knee brace.
TECH FIG 4 • A. The lesion is identified. B,C. Any loose bodies within the joint that cannot be reduced appropriately are removed. D,E. Débridement of the lesion is performed until subchondral bone is reached, after which arthroscopic drilling is performed using a 0.62-inch Kirschner wire. Drill holes are added appropriately. F. The appearance of blood or fat marks the endpoint of drilling.
POSTOPERATIVE CARE
For patients with intact lesions.
We use a hinged knee brace in extension or slight flexion for 4 to 6 weeks.
Patients are permitted partial (1st week) then complete weight bearing with brace locked in extension.
This allows compression to stimulate healing while highimpact running and jumping activities are eliminated.
After the hinged brace is removed, patients are sent to physical therapy, where range-of-motion and strengthening exercises are performed.
Patients are restricted from running and jumping during weeks 6 through 12.
After 3 months repeat imaging (AP, lateral, notch, and tunnel views) is obtained.
Healing is typically noted in intact lesions. Occasionally the lesion is not completely healed and another 2 to 3 months of activity restriction are maintained until complete healing.
For patients with full-thickness lesions:
Continuous passive motion (CPM) has been used to enhance the healing of the articular surface in the postoperative period for patients with full-thickness lesions. We prefer 6 weeks of CPM use.
CPM was shown to promote articular cartilage healing for moderately small lesions in rabbits (less than 3 mm in diameter). Similar effects were found in humans with predominantly 1- to 2-cm lesions by Rodrigo and colleagues;17 they reported that CPM for 6 hours per day for 8 weeks produced an improved clinical result.
Regardless of the treatment selected, the patient should have a rehabilitation program that combines protection of the compromised articular surface and underlying subchondral bone with maintenance of strength and range of motion.
Straight-leg raising and isometric exercises can be performed in the postoperative or immobilization period. In general, the straight-leg raising exercises are performed without resistance initially and advanced by adding 2 to 3 pounds per week, or as tolerated, until 10% of the patient's body weight is reached.
A 6- to 8-week home or formal physical therapy program is instituted, incorporating range of motion, stretching, progressive strengthening, and functional or sport-specific training.
Closed-kinetic-chain exercises are initiated on the sixth week. During this time, the patients are kept out of running and jumping sports but are permitted to perform low-impact activities such as walking, submaximal biking, swimming, and activities of daily living.
All high-impact activities are limited until 6 months after surgery for those patients treated for full-thickness lesions.
If patients return to activity before the cartilage has become firm, they will typically complain of pain with maneuvers such as squatting or jumping.
OUTCOMES
Nonsurgical treatment is often regarded as the treatment of choice for small stable lesions in skeletally immature patients. Typically a period of 3 to 6 months of nonoperative treatment is instituted, with numerous authors reporting a success rate of 50% to 94%.2–4,6–10
Skeletally immature patients with wide open physes and no signs of instability on MRI are more likely to respond to nonoperative measures.16
Bradley and Dandy2 reviewed 11 knees in 10 children treated with arthroscopic drilling and found evidence of healing in 9 of 11 knees after 12 months.
Aglietti and coworkers1 reviewed 14 children (16 knees) treated with transarticular drilling after 1 year of conservative management and found all cases progressed to healing after treatment.
Kocher and associates10 reviewed 30 knees in 23 patients treated with arthroscopic transarticular drilling after 6 months of conservative therapy. All patients who failed to respond to nonoperative measures were noted to have healed after drilling.
COMPLICATIONS
Potential failure to heal, especially in older adolescents treated nonsurgically. The prognosis for OCD lesions is worse in those patients who have reached skeletal maturity. Patients who have been treated nonsurgically and have not shown progressive healing and those patients with large lesions that are approaching skeletal maturity are therefore treated surgically to promote healing.
REFERENCES
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