By Robert C. Schenck, Jr., MD
Much like the treatment of any defect in the articular surface, surgical management of osteochondritis dissecans (OCD) lesions has tremendous challenges to create a stable, hyaline surface. OCD (from the Latin "to separate") is commonly seen in the knee, ankle, and elbow, but has been described in virtually every anatomic site. The pathophysiology is different depending upon location (contrast talar OCD vs knee) and age of presentation. Furthermore, the literature is replete with many differing types of articular injuries categorized under OCD and can be confusing when studying the topic. The focus of this discussion will be on OCD of the knee and the treatment options currently available.
OCD of the knee has varying presentations but can be categorized as either juvenile (open physes) or adult onset (closed physes). Trauma in conjunction with an underlying developmental abnormality of the epiphysis is considered to be the most common mechanism for juvenile OCD. Classically, juvenile OCD presents in the lateral aspect of the medial femoral condyle (85%). Radiographic evaluation of the painful knee in the adolescent (in addition to a careful clinical examination of the hip and spine) involves a tunnel view of the knee whereby the medial and lateral edges of the condyles can be viewed more clearly than in a standard AP radiograph. By using magnetic resonance imaging the presence of OCD separation and loose bodies can be further evaluated. Adult onset OCD presents with similar radiographic findings but has much less healing potential than in a patient with open physes.1,2
With the presence of open growth plates, the initial management of the stable juvenile OCD lesion involves immobilization and protected weight bearing.2 Due to the relative vascularity and repair potential of the child/adolescent, potential for healing with such management is good. The use of arthroscopy and drilling of OCD lesions in those youngsters failing conservative treatment has been shown to be successful.3 Kocher and associates reported on 23 patients with a stable OCD lesion of the knee treated with transarticular drilling to heal both clinically and radiographically on average at 4.4 months. They questioned the technique of retrograde drilling, noting the difficulty in accuracy of pin placement. In addition, they also questioned the length of conservative treatment prior to proceeding with surgery, but reaffirmed the long held adage of the younger the patient, the better the healing noted.
In contrast, the unstable OCD lesion requires a more aggressive approach, either arthroscopic or open. There are long-term clinical data that patients do poorly with simple removal of the OCD fragment.1,2 Most authors recommend that the clinician should make every effort to repair the unstable OCD lesion with one of a variety of fixation techniques described. The early use of internal fixation devices prompted the development of biodegradable screws and pins to create a stable construct, with compression of the unstable OCD lesion to promote optimal healing. For this reason, screw fixation may be considered optimal over simple pin fixation. The use of differing pitched headless screws allows for internal fixation of the fragment without the need for hardware removal.
An interesting recent advance is the use of osteochondral plug transfer to internally fix an unstable OCD lesion. In 2 separate reports, Berlet and Yoshizumi report on their techniques for fixation and grafting of an OCD lesion about the knee.4,5 Such a technique (COR®, Mitek Worldwide, Westwood, Mass) using smaller diameter plugs can function to both stabilize the lesion as well as graft across the lesion into healthy bone. Careful attention to surgical technique is required to insure reduction of the OCD lesion as well as avoiding breakage of the osteochondral plug while performing the transfer. Crossing a large OCD lesion can be problematic, especially in the presence of a sclerotic base. Although osteochondral plug transfer doesn’t necessarily provide compression of the unstable OCD lesion, in essence the placement of a biologic "bony" pin has tremendous advantages over metal or biodegradable fixation devices as it functions to both fix and bone graft the unstable fragment.
Lastly, the clinician should give consideration to fixation of the free-floating, large OCD fragment as the chondrocytes on the fragment remain viable, bathed in synovial fluid. Such fragments, when large and involving the weight-bearing surface, should be given an attempt at internal fixation. The fragment frequently has slight overgrowth and may require some trimming, but then is reducible and can be internally fixed with good potential for healing. Predrilling the bed to allow for vascular ingrowth in combination with bone grafting, compression fixation, and/or osteochondral plugs can provide an excellent salvage for an otherwise challenging orthopaedic problem.
This leads to the difficult problem of the large empty articular defect due to a chronic OCD lesion. Such clinical scenarios have historically functioned poorly with chronic pain, instability, and degenerative change. These lesions require consideration of transplantation of osteochondral allografts or autografts vs. consideration for autologous chondrocyte implantation. Treatment options must take into consideration the common finding of a large bony defect that in most instances must be simultaneously addressed. Allograft osteoarticular substitution has the advantage of a 1-stage procedure treating both the bony and articular defects. Disadvantages include the risk of disease transmission, availability of transplantation tissues, and the long-term viability and incorporation of bone and hyaline surfaces. Osteochondral plug transfer is a consideration, but has size and donor site limitations, and is best reserved for smaller lesions between 2 and 4 cm2 in size. Cell transplantation technologies have gained tremendous popularity due to the availability and the autologous nature of the tissue source. The need to perform a 2-stage procedure (both for bone grafting of the defect site, and simultaneous harvest of hyaline tissue for chondrocyte replication) and cost are relative disadvantages for this technique. Regardless of the treatment option, patient education with hyaline repair is critical for any successful result.
In summary, OCD of the knee requires thoughtful treatment with options dependent upon age and presentation. Failure of initial conservative treatment in those patients presenting with open physes and a stable OCD lesion requires drilling techniques. Aggressive treatment to save the OCD fragment is advocated with the knowledge of poor clinical results with simple excision of the involved osteoarticular segment. Future treatment is still dependent upon early recognition of an OCD lesion to allow for appropriate treatment. The presence of an empty articular defect requires articular grafting. Depending upon lesion size, this involves allo- or autograft osteochondral transplantation vs. bone grafting and chondrocyte implantation. OCD of the knee is a complex orthopaedic problem and requires a careful approach for successful treatment.
Dr. Schenck, Deputy Chairman, Department of Orthopaedics, University of Texas Health Science Center, San Antonio, TX, is Associate Editor of Sports Medicine Reports.
References
1. Schenck RC, Goodnight JM. J Bone Joint Surg Am. 1996;78(3):439-456.
2. Cahill B. J Am Acad Orthop Surg. 1995;3:237-247.
3. Kocher MS, et al. Am J Sports Med. 2001;29(5): 562-566.
4. Berlet GC, et al. Arthroscopy. 1999;15:312-316.
5. Yoshizumi Y, et al. Am J Sports Med. 2002;30(3): 441-445.
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