This video discusses the case presentation of an 18-year-old man with unstable osteochondritis dissecans. Most osteochondritis dissecans involve the lateral aspect of the medial femoral condyle and can be managed arthroscopically or via an anterior arthrotomy. This video demonstrates a unique case of osteochondritis dissecans that involved the posterior aspect of the lateral femoral condyle. The unusual location required a posterior approach to the knee joint to achieve adequate exposure and correct orientation of fixation.

The patient reported a 1-year history of knee pain, intermittent locking, and recurrent effusions that precluded participation in sports-related activity. The video demonstrates pertinent physical examination findings, including a visual pop on the anterolateral aspect of the knee as the knee is brought through the flexion/extension arc. Radiographs demonstrated a clear osteochondral fragment laterally with sclerotic borders. MRI revealed two unstable osteochondral fragments in the posterolateral femoral condyle, with fluid interposed between the fragment and underlying bone. Given the physical examination and imaging findings, which indicated symptomatic instability of the osteochondral fragment, surgical fixation was indicated.

The video demonstrates arthroscopic evaluation of the knee via an anterolateral portal. A view of the lateral compartment shows two large, posterior osteochondral fragments that are clearly detached from the surrounding cartilage. Because of the inability to access the posterior fragments via an anterior approach, the lesion was accessed via a posterior approach to the knee joint. The senior author performed the approach with the assistance of an orthopaedic oncologist who frequently performs the approach. The incision for the posterior approach is shown, and dissection proceeded in the following order: dissection down to the popliteal fossa, with elevation of skin flaps and incision through the popliteal fascia; identification and protection of the neurovascular structures; elevation of the lateral gastrocnemius tendon off the distal femur; and a T-shaped capsulotomy through the posterolateral femoral condyle. The video then demonstrates preparation of the osteochondral fragments by booking open the fragment and burring down the opposing surfaces to stimulate bleeding. Provisional fixation of the fragment was achieved with the use of Kirschner wires. Definitive fixation of the fragments was achieved with the use of two 3.0-mm and four 3.5-mm bioabsorbable screws. The stability of the fragment is then demonstrated through manual palpation and knee range of motion.

The final portion of the procedure shows repair of the lateral gastrocnemius tendon with a 4.5-mm biocorkscrew suture anchor. One end of each of the two nonabsorbable, braided sutures from the anchor were passed through the tendon in a Mason-Allen fashion, with the sutures exiting on the posterior aspect of the tendon. The second limb of each suture also was brought through the tendon so that tension on the simple limb could serve as a pulley to pull the tendon back to its attachment site. The sutures were then tied. The video ends by comparing the patient's preoperative and postoperative radiographs. The postoperative radiographs demonstrate a well-aligned femoral condyle, with no fragment visualized and no areas of sclerotic bone.

Given the rarity of osteochondritis dissecans in this location, a case series on the fixation of these lesions via a posterior approach is not available. In the literature, osteochondritis dissecans lesions of the knee managed via internal fixation are associated with good results, with a high union rate and good to excellent outcomes. In addition, outcome studies on patients who underwent posterior approaches to the knee joint report high rates of success, with very low complication rates despite complicated anatomy. The orthopaedic oncologist who frequently performs the approach has experienced similar success, with very few complications.