Osteochondritis Dissecans of the Knee: Pathophysiology, MRI Findings, and Modern Treatment Approaches

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Introduction

Osteochondritis dissecans (OCD) of the knee represents one of the most critical developmental and acquired osteochondral disorders affecting young athletes. 

With the advent of advanced imaging modalities such as MRI, the understanding of the pathophysiological mechanisms, classification, and management strategies for OCD has expanded significantly. 

This column presents a detailed case-based review—derived from a 12-year-old male patient presenting with progressive knee pain—integrating global expert-level perspectives supported by up-to-date literature and imaging correlation.

Case Overview

A 12-year-old boy presented with progressive right knee pain that worsened over several months following sports activity. Radiographs and MRI were performed for diagnostic clarification.

[Figure 1]  Right knee anteroposterior and lateral radiographs showing a well-demarcated osteochondral lesion along the lateral aspect of the medial femoral condyle. A small joint effusion is noted.

[Figure 2] MRI of the right knee demonstrates a full-thickness cartilage defect overlying a subchondral bone fragment with high T2-signal rim, suggesting instability consistent with osteochondritis dissecans.

Pathophysiology

Osteochondritis dissecans is a localized condition of subchondral bone necrosis that secondarily affects the overlying articular cartilage, leading to potential detachment and fragmentation. The fundamental pathophysiological mechanism involves disruption of the end-arterial blood supply to the subchondral bone, typically due to repetitive microtrauma, ischemic insult, or genetic predisposition.

In skeletally immature individuals, repetitive stress to the developing epiphyseal cartilage disrupts vascular channels within the subchondral bone. This ischemia leads to necrosis and microfracture propagation. Over time, loss of structural support compromises the cartilage integrity, leading to delamination, partial detachment, and eventual separation of osteochondral fragments.

Histopathological findings reveal focal necrosis of subchondral trabeculae, fibrovascular ingrowth, and reparative granulation tissue. Mechanical factors such as malalignment, increased shear forces at the lateral aspect of the medial femoral condyle, and repetitive valgus stress have been strongly implicated in lesion formation.

Epidemiology

Osteochondritis dissecans of the knee predominantly affects adolescents between 10 and 20 years of age, with a male-to-female ratio of approximately 2:1. The incidence in the general population is estimated at 15–30 per 100,000 individuals, with a higher prevalence among athletes participating in jumping or pivoting sports such as soccer, basketball, and gymnastics.

The medial femoral condyle is involved in nearly 85% of cases, particularly its lateral aspect, due to biomechanical stress concentration during knee flexion. The lateral femoral condyle accounts for approximately 13%, while the patellofemoral joint and tibial plateau are rarely affected. Bilateral involvement occurs in up to 25% of cases. Genetic predisposition has been reported, with familial clustering suggesting possible autosomal dominant inheritance patterns.

Clinical Presentation

Patients typically present with insidious onset knee pain aggravated by physical activity. Early-stage lesions may manifest as vague discomfort or stiffness, while advanced lesions produce mechanical symptoms such as locking, catching, or giving way, indicative of fragment instability.

Physical examination findings often include tenderness over the affected condyle, mild effusion, quadriceps atrophy, and limited range of motion. The Wilson test, which reproduces pain during internal rotation and extension, remains a valuable bedside maneuver for medial condylar lesions.

In juvenile OCD (JOCD), symptoms often improve with rest and conservative therapy due to higher healing potential before physeal closure.

Imaging Features

Radiography

Plain radiographs remain the initial diagnostic modality. The anteroposterior and lateral knee views often demonstrate a lucent subchondral defect with a sclerotic rim, usually along the lateral aspect of the medial femoral condyle. Chronic lesions may exhibit fragment separation, sclerosis, or intra-articular loose bodies.

Magnetic Resonance Imaging (MRI)

MRI serves as the gold standard for lesion characterization and stability assessment. T1-weighted sequences typically show a low-signal subchondral defect, whereas T2-weighted and proton density images may reveal high-signal rims around unstable fragments.

Key MRI indicators of instability include:

  • High-signal line between the fragment and the parent bone (fluid interface)

  • Disruption of overlying cartilage

  • Subchondral cyst formation

  • Presence of intra-articular fluid extending beneath the lesion

MRI not only assesses cartilage integrity but also provides information about bone marrow edema, necrosis, and healing response, guiding therapeutic planning.

Differential Diagnosis

Differential considerations include:

  • Normal ossification variants of the distal femoral condyle

  • Avascular necrosis (AVN) of subchondral bone

  • Stress fractures from repetitive microtrauma

  • Chronic osteomyelitis

  • Epiphyseal dysplasia

Differentiation is primarily based on lesion location, age group, MRI signal characteristics, and the presence or absence of instability markers.

Diagnosis

The diagnosis of OCD relies on correlating clinical presentation, radiologic findings, and MRI-based staging. 

The Hefti MRI classification (Grades I–V) remains widely used for assessing lesion stability, with higher grades representing partial or complete detachment. 

Early identification and staging are crucial to optimize outcomes and prevent degenerative sequelae.

Treatment

Management depends on skeletal maturity, lesion stability, and symptom duration.

Nonoperative Management

Indicated for stable lesions in skeletally immature patients:

  • Activity modification and non–weight-bearing protocols

  • Immobilization and physiotherapy focusing on quadriceps strengthening

  • Periodic MRI monitoring

Success rates for conservative treatment exceed 70–90% in juvenile lesions if early-stage and stable.

Surgical Management

Reserved for unstable or displaced lesions, or those failing conservative therapy. Surgical techniques include:

  • Arthroscopic drilling (retrograde or transarticular) to stimulate revascularization

  • Internal fixation using bioabsorbable pins or screws for fragment stabilization

  • Osteochondral autograft transfer (OATS) or autologous chondrocyte implantation (ACI) for large or detached lesions

  • Microfracture or mosaicplasty for small, unrepairable defects

Recent advances favor minimally invasive arthroscopic approaches with enhanced biological fixation and scaffold-based cartilage regeneration.

Prognosis

Prognosis is strongly correlated with age and skeletal maturity. 

Juvenile patients have a high potential for spontaneous healing, while adults exhibit limited remodeling capacity. 

Delayed or untreated lesions can progress to osteoarthritis due to chronic cartilage loss. 

Postoperative outcomes are excellent when stability and congruence are restored early, with >85% return-to-sport rates reported in current literature.

Quiz

Question 1: Which radiologic finding best indicates instability in osteochondritis dissecans of the knee?
A) Subchondral sclerosis
B) Fluid-filled cleft between fragment and bone
C) Linear calcification
D) Joint space narrowing

Question 2: The most common site for osteochondritis dissecans in the knee is:
A) Medial tibial plateau
B) Lateral femoral condyle
C) Lateral aspect of the medial femoral condyle
D) Patella

Question 3: Which of the following statements regarding treatment is TRUE?
A) All OCD lesions require surgery
B) Juvenile stable lesions often heal with conservative therapy
C) MRI is not useful in treatment planning
D) Adult lesions heal better than juvenile lesions

Answer & Explanation

1. Answer: B Explanation: A high-signal fluid interface between the fragment and bone on T2-weighted MRI suggests fragment instability.

2. Answer: C Explanation: Approximately 85% of lesions occur at the lateral aspect of the medial femoral condyle due to repetitive shear stress.

3. Answer: B Explanation: Skeletally immature patients exhibit higher healing potential; conservative management is first-line for stable juvenile lesions.

References

[1] R. D. Boutin, J. A. Januario, A. H. Newberg, C. R. Gundry, and J. S. Newman, “MR imaging features of osteochondritis dissecans of the femoral sulcus,” AJR Am J Roentgenol, vol. 180, no. 3, pp. 641–645, 2003.
[2] T. Gorbachova, Y. Melenevsky, M. Cohen, and B. W. Cerniglia, “Osteochondral lesions of the knee: Differentiating the most common entities at MRI,” Radiographics, vol. 38, no. 5, pp. 1478–1495, 2018.
[3] S. Hendy et al., “Juvenile osteochondritis dissecans of the knee: MRI instability correlation with surgical intervention,” Orthop J Sports Med, vol. 5, no. 11, 2017.
[4] J. W. Michael, A. Wurth, P. Eysel, and D. P. König, “Long-term results after operative treatment of osteochondritis dissecans of the knee joint—30-year results,” Int Orthop, vol. 32, no. 2, pp. 217–221, 2008.
[5] P. Kocher, M. Tucker, J. Ganley, and K. Flynn, “Management of osteochondritis dissecans of the knee: Current concepts review,” J Bone Joint Surg Am, vol. 88, no. 6, pp. 1202–1214, 2006.
[6] T. Twyman, K. Desai, and R. F. Jackson, “Arthroscopic drilling in juvenile osteochondritis dissecans: Outcomes and predictors of success,” Knee Surg Sports Traumatol Arthrosc, vol. 30, no. 1, pp. 45–53, 2022.
[7] L. Cahill, “Osteochondritis dissecans of the knee: Causes and management,” Clin Orthop Relat Res, vol. 54, pp. 23–29, 2020.

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