1
Background
Osteochondritis dissecans (OCD) of the knee is a focal abnormality that affects the subchondral bone. It can cause knee instability by a detachment of bone and cartilage fragments resulting in a progression to osteoarthritis.
The incidence of this condition is estimated at 9.5/100,000 [ ]. The diagnosis may be made in adult athletes and children between the ages of 12 and 19 years [ ]. Epidemiological data indicate a mean age at diagnosis of 16.5 years [ ]. OCD has never been diagnosed in children younger than 6 years old. The risk of developing this nontraumatic knee condition is 3.8 times higher in boys than in girls [ ].
It has been reported that the terms “open physes” and “closed physes” should be preferred over the terms “juvenile” and “adult” osteochondritis [ ]. Despite advances in understanding this condition, many questions remain unanswered, particularly regarding the pathophysiology, indications for magnetic resonance imaging (MRI), signs of instability, and treatment methods.
Both recreational and professional athletes may be affected by OCD. The most common site for this injury is the medial femoral condyle. The lateral femoral condyle and patella are affected less often and the tibial plateau is very rarely involved [ ].
Microtraumatic origin is by far the most supported pathophysiologic mechanism [ ].
Several risk factors were reported in the literature. In young baseball players, who frequently perform a squatted position, a study showed that the OCD lesions were located more posteriorly on the femoral condyle [ ]. Some authors pointed out the close relationships between the development of OCD and the femoral posterior cruciate ligament insertion [ , ]. A study has reported that a distal location of the insertion of the posterior cruciate ligament may amplify repetitive traction stress and result in the development of OCD [ ].
This microtrauma-induced mechanism may result in uneven growth in young athletes with the production of irregular subchondral bone. Patients with lateral condyle OCD often have a discoid meniscus responsible for repetitive abnormal stress [ ].
OCD can heal spontaneously or worsen over time. In patients with open physes, younger age is associated with a higher chance of healing with conservative management [ ].
If the lesion fails to heal, the patient experiences intermittent pain which may last for years until the fragment becomes unstable. This event is a turning point in the course of OCD, after which osteoarthritis will develop inevitably.
Younger athletes should be monitored until the radiographs are completely normal, since progression of the lesion may resume after years of latency.
Age is a key prognostic factor and OCD lesions diagnosed in adulthood are latent lesions [ ]. Outcomes are better in patients with open physes [ ]. Another major determinant is the surface area of the lesion since better outcomes were seen in patients with smaller surface lesions [ ]. MRI visibility of a lesion measuring 1.3 mm or more in diameter predicts poor outcome [ ].
2
Synonyms
Chondromalacia of the patella.
Articular cartilage disorder.
Unspecified internal knee derangement.
Chondromalacia of medial or lateral compartments of the knee.
Knee chondral injuries.
3
Clinical Study
3.1
Symptoms
Patients with OCD typically present with pain and swelling of variable amounts.
Pain is generally vague, poorly localized in the knee region, and exacerbated by exercise and stair climbing. Patients may present with an antalgic gait, especially in external rotation, and may report a history of multiple knee effusions [ ].
Maximal tenderness is elicited over the anteromedial aspect of the knee during flexion motion. This corresponds to the most common site of OCD lesions on the lateral aspect of the distal medial femoral condyle [ ].
As the lesion progresses, mechanical symptoms such as catching, locking, and giving way appear and increase in frequency and intensity, usually indicating the presence of an unstable fragment [ ].
The presence of an atrophy of the quadriceps muscles of the athlete usually indicates the chronicity of symptoms [ ] ( Fig. 9.1 ).
The functional impact of OCD is usually moderate compared to other overuse knee injuries [ ].
3.2
Physical Examination
A thorough physical examination must be performed as the pain may be related to a concomitant injury.
Femorotibial alignment in the sagittal plane should be assessed as medial condyle OCD is associated with varus and lateral condyle OCD with valgus of the knee [ ].
Palpation of the femoral condyle at various degrees of knee flexion may trigger the patient’s usual pain.
3.2.1
The Wilson test
This test consists in bending the knee at 90° then passively moving it to 30° of flexion while rotating the foot medially [ ].
If the usual pain occurs during the test and resolves when the foot is rotated laterally, the test is positive. The Wilson test detects only medial condyle lesions and has only a positive predictive value. This test is a helpful diagnostic and follow-up tool.
A joint effusion [ ] or a sudden increase in pain intensity while performing this test suggests an unstable lesion.
4
Differential Diagnosis
4.1
Meniscal Tear
A history of knee trauma is frequently found and meniscal tests are positive.
4.2
ACL Tear
The patient reports a feeling of instability and ligamentous tests are commonly positive on examination.
4.3
Osteoarthritis
Knee swelling, tenderness of the joint line, and limitation of knee ROM are suggestive of osteoarthritis. Standard knee radiographs allow diagnosis confirmation.
4.4
Plica Syndrome
The main symptom of plica syndrome is knee pain localized at the anterior aspect of the knee that is worsened when using the stairs, squatting, or bending and a catching or locking sensation can be felt when extending the knee.
5
Imaging
5.1
Standard X-rays
Conventional radiography is the first step of the imaging study. An anteroposterior view, a lateral view, and a view with the knee flexed at 60° should be obtained. A sunrise view is required if an OCD lesion of the patella or femoral trochlea is suspected [ ]. As OCD is bilateral in about 15% of cases, radiographs of the asymptomatic knee should be taken ( Fig. 9.2 ).
A classification for OCD based on radiographic findings was described in 1988 [ ] and modified in 2005 to increase accuracy [ ]. The stages are focal lucency, attached fragment, and detached fragment. The stage is defined based on the bone trabecula abnormalities, without taking into consideration the condition of the overlying cartilage and viability of the fragment ( Fig. 9.3 ).
