Osteochondritis Dissecans of the Knee
Thomas W. Wang, MD; William D. Knopp, MD; Charles A. Bush-Joseph, MD; Bernard R. Bach, Jr, MD
American Medical Society for Sports Medicine
THE PHYSICIAN AND SPORTSMEDICINE - VOL 26 - NO. 8 - AUGUST 98
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In Brief: Osteochondritis dissecans (OCD) should be considered in young, active patients who have generalized or anterior knee pain. A careful physical exam includes a Wilson test, thigh girth measurements, diagnostic tunnel view radiographs, and other imaging studies as needed for grading and prognosis. Two case reports demonstrate the signs and symptoms of OCD. Treatment by primary care physicians with sports medicine training may be conservative if lesions are medial and in situ and if patients are not skeletally mature; otherwise, referral is advised. Prompt surgical treatment is generally successful.
Many athletic activities place considerable repetitive stress on the legs. The knee is vulnerable to both repetitive stresses leading to overuse injuries and to acute injuries. As a result, many active patients have generalized or anterior knee pain. Without definitive abnormalities on physical examination, a course of conservative management is frequently recommended.
In young, active patients whose knee pain continues, however, osteochondritis dissecans (OCD) should be considered. OCD is a painful condition in which a section of articular cartilage and its underlying bone slowly separates from the surrounding bone.
The following case reports demonstrate the importance of a physical exam that includes thigh girth measurements and appropriate imaging studies in the young, active patient with knee pain. Accurate diagnosis can then lead to targeted treatment.
Case 1. A 16-year-old boy who participated in high school football, baseball, and wrestling had right anterior knee pain of 1 year's duration. His pain increased 4 weeks into football season. Although he denied specific injury, his pain worsened with contact drills. In varsity baseball and wrestling, he had had only minor discomfort, and training room examinations had found no abnormalities.
Physical examination revealed a right thigh girth difference of 1.5 cm relative to the left and a 1+ effusion of the right knee. There was no peripatellar pain. A click, noted on resisted knee flexion with the tibia internally rotated, did not occur with the tibia externally rotated.
Plain radiographs, including a tunnel view (figure 1a), revealed OCD of the medial femoral condyle in this skeletally mature patient's knee. Sclerotic changes at the base of the lesion suggested a chronic finding. Arthroscopic examination revealed an unstable OCD fragment, which was stabilized with cannulated screws (figure 1b).
The postoperative course and rehabilitation were uneventful. Following screw removal and rehabilitation, the patient returned to competitive varsity sports without symptoms. Radiographs obtained 2 years postoperatively revealed complete healing with no degenerative changes (figure 1c).
Case 2. A 15-year-old male football player and wrestler had an acute onset of pain and swelling of the right knee. As he attempted to block an opposing football player, his knee twisted to a valgus position with an audible "pop." He described no direct contact to the knee. The patient also described a 2-year history of aching discomfort in the same knee. Previous examinations by his primary care physician had revealed no abnormalities.
Initial on-field examination showed diffuse tenderness without obvious swelling, deformity, or ligamentous instability. A repeat examination within 24 hours revealed a thigh girth difference of 2.5 cm relative to the left with a 2+ effusion of the knee. No peripatellar tenderness was noted. Range of motion was limited by pain and swelling to 10° to 90° of flexion.
Despite a mechanism of injury consistent with ligament disruption, his Lachman's test was equivocal, and posterior cruciate and collateral ligament testing was normal.
Plain radiographs revealed only minimal blunting of the posterolateral femoral condyle, which was compatible with irregular ossification (figure 2a). Magnetic resonance imaging (MRI) showed sclerosis and irregularity of the posterolateral femoral condyle with loose body formation (figure 2b). Arthroscopic evaluation revealed a 3-cm x 3-cm defect of the posterolateral femoral condyle with an OCD fragment in the suprapatellar pouch (figure 2c).
Mini arthrotomy was performed and the fragment was fixed with cannulated screws (figure 2d). Arthroscopic screw removal 8 weeks later revealed complete healing of the fragment. The patient was placed in an aggressive rehabilitation program that encouraged full range of motion and closed-chain exercises. He returned to competitive wrestling within 4 months. A 1-year follow-up examination revealed no abnormalities.
Characteristics and Causes
OCD is most commonly seen in 13- to 21-year-olds (1), and the most commonly affected site is the medial femoral condyle (2). Both of the young athletes in the above case reports had the low-grade pain typical of OCD. Patients may have swelling, locking, and crepitus.
No specific cause of OCD was evident with either of the patients; however, in case 2, acute trauma may have caused the patient's lesion to become a loose body. Many causes for OCD in general have been suggested, including trauma, repetitive impact with the tibial spine, skeletal abnormalities from endocrine dysfunction, and abnormal ossification of the epiphyseal cartilage (3,4). Currently, the cause is believed to be multifactorial with an end result of avascular necrosis of subchondral bone and changes in the overlying articular cartilage (5,6).
Physical findings. Physical exam findings are often inconclusive. The most consistent finding, present in both of our patients, is thigh atrophy (3).
Signs and symptoms vary with the degree of separation of a lesion from the femoral condyle. Patients with in situ lesions typically have pain proportional to activity and minimal physical findings. Once the fragment separates, it may produce mechanical signs such as catching, locking, or giving way, as well as pain and effusion.
Lesions of the medial condyle tend to be anterior and usually do not involve the tibiofemoral articular surface. Therefore, they are less likely to cause degenerative changes (7).
Lesions of the lateral femoral condyle tend to be large and occur more posteriorly, directly on the tibiofemoral weight-bearing surface. This defect may produce a painful "clunk" each time the knee is flexed or extended. With lesions of the lateral femoral condyle, degenerative changes commonly occur over time (7).
Meniscal tests are frequently positive with lateral or medial lesions, and the Wilson test (figure 3) can detect an early medial lesion (8). Frequently, the patient subconsciously reduces pressure on the affected side by walking with the foot laterally rotated. This may cause the thigh atrophy commonly found in OCD.
Often, OCD may go undiagnosed until an acute injury occurs. In adolescents with diffuse knee pain, therefore, OCD should be considered in the differential diagnosis even in the absence of mechanical symptoms.
Imaging studies. Patients whose objective findings include joint swelling, diminished thigh girth, or a positive Wilson test warrant radiographic study. Frequently, the x-ray finding of OCD is an incidental one in a clinically asymptomatic joint.
The series should include anteroposterior, lateral, Merchant's, and tunnel views (3). If OCD is present, lesions are best observed on a tunnel view (figure 4) (6,7), in which a well-delineated lesion is usually seen in the subchondral bone in various stages of separation.
More than 75% of OCD patients have lesions on the lateral side of the medial femoral condyle. Another 5% to 10% have extended lesions that border on the major weight-bearing area. The remaining 10% to 15% have them on the lateral femoral condyle and patella. Less than 10% of patients have lesions bilaterally (9,10).
Any uncertainty with regard to the lesions warrants further evaluation. Bone scans assist in diagnosis as well as prognosis; a positive but imprecise relationship exists between radionucleotide uptake and healing potential (11,12). MRI is especially useful in differentiating stage 2 from stage 3 lesions (table 1) (10,13). Evidence of synovial fluid (increased signal intensity) between the lesion and subchondral bone indicates that the fragment is unstable and will require surgical treatment (14).
Several outcomes are possible with OCD. Lesions may remain in situ and eventually heal, or they may become partially or completely dislodged, forming a loose body within the joint. Conservative management is frequently successful in skeletally immature patients; however, skeletally mature patients or those with evidence of a loose body generally require surgical management.
Patient age greater than 20 years often indicates a poor prognosis. These patients tend toward fragment instability and loose body formation and should be referred (15).
Prompt surgical treatment of the skeletally mature patient or one with a loose body will likely lead to a successful outcome. Early stabilization and/or fixation of the OCD fragment can prevent the development of degenerative joint disease, depending on the stage and location of the lesion.
Location of lesion. Because the prognosis differs for medial vs lateral lesions, the treatment approach also differs.
Medial. Treatment of medial femoral condyle lesions depends on the stage of the lesion and age of the patient. In general, these lesions in children may be followed nonoperatively by the primary care physician unless there is evidence of a loose body or mechanical symptoms. Adults have higher morbidity, and conservative therapy is usually less successful (5).
Lateral. In general, any lesion of the lateral femoral condyle should be referred to an orthopedic surgeon. These lesions are usually larger and affect weight-bearing surfaces, lead to degenerative joint disease, and often require surgical treatment.
Stage of lesion. OCD lesions can be seen as progressing through four stages. Intervention at any stage may arrest the process (table 1) (10,13).
Stage 1. For stage 1 (evolving in situ) lesions, activity should be modified to the point of minimal or nonexistent pain. Repeat x-rays and examinations, depending on size and evolution of the lesion, are recommended at 3- to 6-month intervals. Any sudden increase in pain or swelling should prompt immediate reevaluation. Surgery is generally not required.(14 )
Stage 2. Restriction of activity, use of crutches, and 2 to 4 weeks of cast immobilization are often required for patients who have stage 2 (separating or chronically symptomatic) lesions. Arthroscopy should be considered if symptoms or radiologic signs progress. Percutaneous drilling to promote revascularization of the fragment is frequently successful (14,16).
Stage 3. Arthroscopy is generally necessary with stage 3 lesions (loose osteochondral body in situ). Fixation with cannulated screws is the ideal treatment method when the osteochondral fragment is still in its bed (1,17). Protected weight bearing is used for 6 to 12 weeks, and pivoting is prohibited until the patient is pain free with straight-ahead ambulation. Rehabilitation focuses on overcoming quadriceps wasting (14).
Stage 4. At arthroscopy, the typical approach for stage 4 (displaced) lesions, the loose body is retrieved and removed. The fragment is incongruous and rarely serves as a suitable graft for reimplantation at the site of defect. Usually, the best option is to curette the base, perhaps with associated drilling, followed by 3 months of significantly protected weight bearing and restricted activity. Numerous salvage techniques, including osteochondral allograft, osteochondral autografts, and autologous cartilage transplantation, are currently being evaluated.
Referral and Prognosis
In general, in situ lesions that produce no mechanical symptoms may be followed nonoperatively in children. A lesion of the lateral femoral condyle should prompt referral, and any lesion in an adult should be referred to an orthopedic surgeon. With prompt surgical treatment, the outcome for the skeletally mature or those with a loose body is generally successful.
This is the first in a series of articles from the American Medical Society for Sports Medicine (AMSSM), which is a forum for primary care sports medicine physicians. Dr Wang is on the clinical faculty of MacNeal Family Practice and is director of the sports medicine fellowship at MacNeal hospital, both in Berwyn, Illinois. Dr Knopp is in private practice in Minnetonka, Minnesota. Dr Bush-Joseph is an assistant professor and Dr Bach is a professor and director of the sportsmedicine section, both in the department of orthopedic surgery at Rush-Presbyterian-St Luke's Medical Center in Chicago. Dr Harmon is a primary care sports medicine physician at the University of Washington in Seattle, a clinical instructor in the department of family practice at the University of Washington Medical School, a member of the AMSSM, and holder of a certificate of added qualifications in primary care sports medicine. Drs Harmon and Bach are members of the editorial board of The Physician and Sportsmedicine. Address correspondence to Thomas W. Wang, MD, MacNeal Family Practice, 3231 S Euclid Ave, Berwyn, IL 60402.
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