Osteochondritis Dissecans

                             Dr. KS Dhillon

Introduction

Osteochondritis dissecans (OCD) was first described in 1888 by the German surgeon Franz König (1). Osteochondritis dissecans is also known as an osteochondral lesion. It is not a fully understood process, though it is believed to be multi-factorial in etiology. OCD is an idiopathic condition that can develop from childhood through adult life. The majority of patients present in their teenage years. The severity of these lesions can range from being asymptomatic to mild pain or in advanced cases having symptoms of joint instability and locking. The lesions can progress from stable to fragmentation of the overlying cartilage with the formation of a loose body in the joint space. Eventual early onset osteoarthritic changes of the joint can occur at any level of severity if not diagnosed and adequately treated. Therefore, early recognition and treatment are important to achieve good long-term outcomes.

Etiology

The etiology of osteochondritis dissecans has yet to be fully elucidated. It is believed to be multi-factorial. Postulated etiologies include spontaneous avascular necrosis, genetic predisposition, inflammation, and repetitive microtrauma. Originally it was believed to be related to osseous inflammation, hence the term osteochondritis. Multiple studies have failed to prove inflammation as the underlying cause. Spontaneous osteonecrosis is believed to occur during the maturation of the overlying cartilage during adolescence. At this time, the vascular supply to the subchondral bone moves from a juvenile perichondrial supply to mature supply from the medullary cavity. It is believed that during this transition period, the epiphyseal bone is predisposed to avascular necrosis. A higher prevalence of OCD in young athletes also suggests an etiology of repetitive microtrauma.  These theories have been studied with varying success in coming to a conclusion about the cause of this disease. The most commonly accepted etiology is that of repetitive microtrauma, with or without an inciting event. (2,3).

Epidemiology

The incidence of osteochondritis dissecans is approximately 15 to 29 per 100,000 patients (4). The majority of patients are 10 to 20 years of age although it can occur from childhood through adult life (5). Males are affected twice as often as females (5). There is a higher incidence in young athletes. The knee, particularly the lateral aspect of the medial femoral condyle, is the most affected joint. The elbow (capitellum) and ankle (talus) are also affected to a lesser degree (2,6).

Pathophysiology

Osteochondritis dissecans is an idiopathic focal joint disorder affecting the subchondral bone regardless of the etiology. Fragmentation of a small focus of subchondral bone creates a defect between the osteochondral lesion and the parent bone. This leads to decreased vascularization and osteonecrosis of the fragment. Fragments that are held in place by intact overlying articular cartilage are stable. Progression of the defect to involve the overlying cartilage is possible. This will lead to instability of the fragment. If lesions become unstable, they may displace from the parent site and become a loose body within the joint. In a large percentage of these affected patients, early-onset osteoarthritis occurs due to the altered articular surface caused by the osteochondral lesion.

History and Physical

Discovery and presentation of osteochondral lesions are variable. Patients can be asymptomatic. The lesion may be incidentally detected at imaging. This is true in patients who have been asymptomatic or those who never presented for evaluation but had remote chronic mild pain that resolved without treatment. Other patients present when they have chronic mild pain of the affected joint, with or without an acute injury. Typically these patients present several months to a year after the onset of symptoms. When there is a loose fragment, symptoms are generally more severe, with marked joint pain, swelling, locking, and joint instability (2,3).

Examination shows that these patients may have joint tenderness with painful or decreased range of motion of the involved joint, and swelling or effusion. Other injuries, such as ligamentous injuries and fracture has to be excluded (3).

Evaluation

Imaging plays a key role in the evaluation and treatment of these patients. Routine radiographs of the affected joint are obtained. Radiographs will show an ovoid lucency in the subchondral bone with adjacent sclerotic bone. Occasionally the bony fragment can be seen within the subchondral defect or, if displaced, elsewhere within the joint. Radiographs cannot determine the osseous fragment's stability and underestimate the lesion size. An MRI is usually used to confirm the diagnosis when an abnormality is detected on radiographs. It helps to differentiate a developmental ossification variation from OCD and aids in treatment planning, and helps to determine if the lesion is likely to be stable at the time of arthroscopy.  An MRI is highly sensitive and specific in the evaluation of fragment stability. Therefore, it is recommended for patients in whom stability is a clinical concern.

According to De Smet, the following four signs on MRI are associated with OCD lesion instability (7): 

• A discrete round focus of hyperintense signal deep to the OCD lesion measuring 5 mm or more

• Line of hyperintense signal equal to the fluid at the fragment bone interface measuring 5 mm or more in length

• Focal defect in the overlying cartilage measuring 5 mm or more

• Hyperintense signal equal to the fluid that traverses the articular cartilage and the subchondral bone which extends to the lesion.  

To evaluate for stability these same findings can be applied to any joint with an OCD lesion. These criteria have high specificity and sensitivity in the determination of OCD lesion stability.  MRI arthrography can be useful in difficult cases. Although CT arthrography is not as sensitive, it can be used in the patient when MRI is contraindicated.

MRI is also useful in monitoring treatment of the patients if conservative or surgical treatment is chosen.  The recommended time interval to perform an MRI to evaluate healing depends on the institutional protocol and surgeon. MRI findings that suggest healing following conservative management include: 

• Decrease or resolution in the surrounding bone marrow edema pattern

• A decrease in lesion size

• Decrease or the resolution of the hyperintense T2 signal rim or cyst-like foci

• Ingrowth of bone within the bed of the OCD lesion with osseous bridging.

After surgery, an MRI allows for noninvasive evaluation of the repair of the articular surface and the bone cartilage interface (7).

Treatment

The patient’s age, presentation time, severity of symptoms, and lesion stability will dictate treatment. Several systems to classify the lesions have been developed. The important feature is the degree of overlying cartilage involvement and mobility of the lesion fragment. In stable lesions, conservative management is the treatment of choice. Immobilization is carried out and protected weight-bearing is done for a length of time, depending on which joint is affected. When conservative treatment fails in patients with stable lesions they may be treated with drilling techniques (retroarticular or transarticular drilling). These drilling procedures have shown healing rates and symptom improvement in 92% to 100% of the patients. Transarticular drilling has slightly higher success rates. When lesions are displaced or unstable, surgical intervention is necessary. The drilling is typically performed arthroscopically. The knee lesions most often require surgery. Fifty-eight percent of procedures for OCD lesions are performed on the knee. There are various modalities and techniques that exist, such as debridement, fixation, microfracture, and cartilage grafting/transplantation. In situ fixation of lesions can be done using various types of bioabsorbable implants, metallic screws, or osteochondral plugs. Metallic screw fixation shows high successful healing rates of 84% to 100%. The disadvantage of using metallic screws is that there is a need for a second procedure to remove the screws. Bioabsorbable implants do not require a second procedure for removal. They show successful healing rates of around 90%. These implants however show higher rates of complications. Osteochondral autograft or allograft plugs can also be used. The clinical outcomes are “good to excellent” in 72% of patients receiving allograft plugs. The overall aim of surgery is to promote cartilage reformation and/or repair of the articular surface to prevent early-onset osteoarthritis (8).

Differential Diagnosis

Meniscus injury

Osteoarthritis

Prognosis

Stable osteochondral lesions have a better outcome as compared to unstable lesions. Spontaneous healing typically occurs when stable lesions are treated with conservative treatment alone. There is no single uniform grading scale for lesions treated surgically. Unstable lesions and those that fail conservative management undergo surgical treatment which has a success rate of 30% to 100% depending on the technique utilized (8). However, a large majority of patients treated surgically will still develop early-onset osteoarthritis. Patients presenting during adolescence tend to have a better outcome than adult patients.

Complications

Chronic pain

Arthritis

Nonunion

Conclusion

The diagnosis and management of osteochondritis dissecans is carried out by an interprofessional team that consists of a radiologist, orthopaedic surgeon, physical therapist, and primary caregiver. The treatment is dictated by the patient’s age, time of presentation, the severity of symptoms, and stability of the lesion. There are several systems that have been developed to classify the lesions. The important feature is the degree of overlying cartilage involvement and mobility of the lesion. In stable lesions, conservative management is preferred with immobilization and protected weight-bearing for a length of time, that depends on which joint is involved. When conservative treatment fails the patient can be treated with drilling techniques (retroarticular or transarticular drilling). These procedures have shown healing rates and symptom improvement ranging from 92% to 100%. Transarticular drilling has slightly higher success rates. When lesions are unstable or displaced, surgical intervention is necessary. The outcomes of stable lesions are better than unstable lesions (9,10). 

References

1. Kessler JI, Jacobs JC, Cannamela PC, Shea KG, Weiss JM. Childhood Obesity is Associated With Osteochondritis Dissecans of the Knee, Ankle, and Elbow in Children and Adolescents. J Pediatr Orthop. 2018 May/Jun;38(5):e296-e299.

2. Edmonds EW, Polousky J. A review of knowledge in osteochondritis dissecans: 123 years of minimal evolution from König to the ROCK study group. Clin Orthop Relat Res. 2013 Apr;471(4):1118-26. 

3. Zanon G, DI Vico G, Marullo M. Osteochondritis dissecans of the talus. Joints. 2014 Jul-Sep;2(3):115-23.

4. Andriolo L, Candrian C, Papio T, Cavicchioli A, Perdisa F, Filardo G. Osteochondritis Dissecans of the Knee - Conservative Treatment Strategies: A Systematic Review. Cartilage. 2019 Jul;10(3):267-277. 

5. Michael JW, Wurth A, Eysel P, König DP. Long-term results after operative treatment of osteochondritis dissecans of the knee joint-30 year results. Int Orthop. 2008 Apr;32(2):217-21. 

6. Kubota M, Ishijima M, Ikeda H, Takazawa Y, Saita Y, Kaneko H, Kurosawa H, Kaneko K. Mid and long term outcomes after fixation of osteochondritis dissecans. J Orthop. 2018 Jun;15(2):536-539.

7. Zbojniewicz AM, Laor T. Imaging of osteochondritis dissecans. Clin Sports Med. 2014 Apr;33(2):221-50.

8. Bauer KL, Polousky JD. Management of Osteochondritis Dissecans Lesions of the Knee, Elbow and Ankle. Clin Sports Med. 2017 Jul;36(3):469-487.

9. Cheng C, Milewski MD, Nepple JJ, Reuman HS, Nissen CW. Predictive Role of Symptom Duration Before the Initial Clinical Presentation of Adolescents With Capitellar Osteochondritis Dissecans on Preoperative and Postoperative Measures: A Systematic Review. Orthop J Sports Med. 2019 Feb;7(2):2325967118825059. 

10. Yamagami N, Yamamoto S, Aoki A, Ito S, Uchio Y. Outcomes of surgical treatment for osteochondritis dissecans of the elbow: evaluation by lesion location. J Shoulder Elbow Surg. 2018 Dec;27(12):2262-2270.