Osteochondritis Dissecans is an acquired joint defect which involves the subchondral bone and the overlying articular cartilage. The cause of osteochondritis dissecans is not fully understood. Osteochondritis dissecans can often be a progressive pathologic process: evolving to joint deformity and occasionally bone and cartilage fragmentation to intra-articular cartilage instability. When osteochondritis dissecans affects the ankle it typically occurs on the inner or medial portion of the ankle (talus). The bone lesions on the lateral or outside portion of the talus are most often related to trauma. Most cases of osteochondritis dissecans of the talus occur around the time of skeletal maturity (10-14 years of age for girls and 12-16 years of age for boys). There is an increasing prevalence of this condition in athletic teenage girls. Relative to osteochondritis dissecans of the knee, the ankle lesions tend to be smaller, more difficult to diagnose and less likely to heal despite treatment efforts. The osteochondritis dissecans lesion is an area of the bone within a joint that has deterioration and softening and subsequent overlying cartilage damage. This can result in detachment of the softened bone and cartilage leaving a crater in the bone that is exposed to the joint surface and a loose fragment within the joint.
Although the exact cause of osteochondritis dissecans is unknown, there are several factors such as high demand impact sports, underlying disease conditions, local bone blood flow and genetic factors. Most cases of osteochondritis dissecans do not run in families. Increased incidence of osteochondritis dissecans in the ankle is seen in developing bone and joints that are subject to large amounts of physical activity. This includes the year around sports and significant impact activity such as running, gymnastics, soccer and basketball as well as training at a high level of intensity, that is, everyday with minimal rest between activities. Chronic repetitive micro trauma may lead to stress within the subchondral bone which results in bone necrosis, softening, desiccation and separation.
Osteochondritis dissecans of the ankle tends to have a low level of chronic persistent pain, a variable amount of swelling which is often intermittent and not severe. A history of locking, catching or ankle sprains on multiple occasions is common. There is often a history of multiple ankle problems that do not have a clear cause or diagnosis. Physical findings are relatively minimal with pain to palpation over the anterior aspect of the ankle. Rarely are there any limitations of joint range of motion. Routine x-rays of the ankle can easily miss a small osteochondritis dissecans lesion, so it often goes undiagnosed for a long period of time. Oblique and plantar flexion radiographs of the right ankle generally will improve the visualization of the osteochondral lesions often because they are in the posterior aspect of the talus. Even the smallest osteochondritis dissecans lesion will appear on a MRI of the ankle and talus region. MRI is the single best study for both the diagnosis and prognosis of the osteochondritis dissecans lesion of the talus. Occasionally other studies may be helpful such as a computed tomography (CT scan) to further define the anatomy of the lesion and occasionally a bone scan is helpful to judge the ability of the lesion to heal and help manage a treatment protocol.
The goal of non-operative treatment is to promote healing in the subchondral bone and prevent chondral collapse, subsequent fracture and significant crater formation. The treatment options depend on the skeletal maturity of the patient, size and stability of the lesion as well as the location of the lesion within the bone. Non-surgical treatment is the treatment of choice for small skeletal lesions in skeletally immature patients with no signs of instability on a MRI. Initial treatment has traditionally been non-operative. Symptoms often resolving after a period of non weight bearing and activity modifications but rarely does the lesion resolve radiographically. Non operative treatment usually requires the patient to be nonweightbearing for a minimum of 6 weeks with activity restrictions and the use of a cast and/or brace. These are typically monitored by interval radiographs and occasional use repeat MRIs. Lesions that are symptomatically resolved but not radiographically resolved need persistent follow up even if the child has returned to full physical activity. It is not uncommon for lesions that are unresolved radiographically to have reoccurrence of symptoms when activities resume or within 6-12 months of initial treatment. Other non-operative measures have been proposed such as electrical bone stimulators. To date there is no clear data regarding the benefits of these adjunct therapies. If non-operative treatments have failed to control symptoms after a period of 3-9 months other forms of more invasive treatment may be necessary.
The goals of operative treatment are the same as the goals for non-operative management. Some more advancement lesions need to be managed surgically. Operative treatment is the treatment of choice for patients with unstable or detached lesions or failed non-operative management and for patients that are at or past skeletal maturity. Surgical attempts to improve the healing of the osteochondritis dissecans lesion to the native bone, stabilize loose fragments or to replace defective tissue with either an autograft or allograft transfer osteochondral tissue. Operative treatment also provides the benefit of a more dynamic assessment of the lesion and the severity of lesion instability and assessment of injury to the overlying cartilage. The treatment for stable lesions with intact articular cartilage often involves drilling the subchondral bone with the intention of stimulating vascular ingrowth and subchondral bone healing. If the lesion is unstable or hinged, fixation is often indicated in an attempt to heal the lesion back to native bone. Occasionally bone grafting is indicated in unstable lesions that do not have significant joint congruity to allow restoration of articular congruency and enhance the healing potential. Fixation of these lesions can be performed using metal screws, wires, or bioabsorbable nails. Associated complications can include pin migration, adjacent cartilage damage, hardware failure, failure of healing and the need for repeat surgery. If the fixation of the lesion is not possible and the lesion needs to be debrided there are several salvage techniques for full thickness defects including marrow stimulation techniques (ie micro fracture), autogulous chondrocyte implantation, osteochondral autograft transplantation and osteochondral allograft transplantation. These techniques however have limited clinical outcome data in the adolescent and children. These techniques would also be applied to defects that are larger than 5mm2 . Most of these operative treatments are performed as an arthroscopic outpatient procedure. Often patients need to undergo a period of non-weight bearing with either cast or brace immobilization to promote healing for approximately 1-2 months after surgery.
Options for Procedures
Options for procedures are determined by the size and location of the lesion and also several patient characteristics.
Debridement of the lesion is an operative procedure which removes the dead (necrotic) to promote healing stimulation of the lesion and underlying bone. Drilling is also an arthroscopic procedure to promote stimulation of the underlying bone.
A fragment of the lesion is sometimes loose and either removal or repair such as fixation with a screw is necessary.
Osteochondral allograft or autograft which is performed on large lesions is a procedure which is either done with using another piece of bone to fill in the lesion. Fresh osteochondral allograft is a procedure which is done on very large lesions. This procedure requires the fresh graft to be obtained by a donor and once graft is obtained needs to be done on “urgent” basis; usually within 10 days while the graft is still “fresh”.
Our understanding of Osteochondritis dissecans of the talus is continually evolving, but there is general acceptance that these lesions are similar to those found in other joints, including the knee. Therefore, the treatment algorithms are also similar. When initially assessing a child with evidence of this pathologic process, one should first consider the skeletal maturity. With that in consideration, embarking on a period of non-surgical management is ideal, but the results in the literature suggest that you should be prepared to proceed with surgical intervention if this treatment fails.
Surgical intervention itself is not always successful, but with the appropriate intra-operative algorithm and a conservative post-operative plan, many children can avoid a second surgery. As mentioned above, there are many back-up plans that can be undertaken given each child’s individual needs. With proper diligence most patients can be treated to full resolution of symptoms and radiographic appearance. It does behoove the treating physician to remain persistent in the treatment plan and for the child and parents to remain patient with the often slow healing process.
[box type=”note”]Roger M. Lyon, MD. Children’s Hospital of Wisconsin. Medical College of Wisconsin[/box]