A 17-year-old sports student suffering from stress-related pain in the knee joint presented in our outpatient clinic. The pain has been present for about 1 year, mainly during sports activities, but also when walking stairs. Currently, the student is completing his high school diploma and is planning to become a junior basketball player in the first league.
The clinical examination revealed a straight leg axis without malalignment and regular soft tissues. The range of motion was 0/0/130  for extension/flexion, and the medial collateral ligament (MCL) and the lateral collateral ligament (LCL) were stable in full extension and in 30  of flexion. The anterior and posterior drawer tests were negative as was the Lachman test. Furthermore, the meniscus signs were negative and without tenderness over the joint space. Peripheral circulation, motor function, and sensibility were intact.
Magnetic resonance imaging (MRI) revealed subchondral cystic changes at the lateral trochlea with a size of 23 x 18 mm. The cartilage layer appeared intact. Computed tomography (CT) scans showed multiple subchondral cysts (Figure 1). The long leg standing radiograph demonstrated almost straight legs with a valgus of 0.8 . The diagnosis was osteochondrosis dissecans (OCD) stage II-III according to Bruns.
With the cartilage layer still intact, an arthroscopy of the left knee joint with cartilage staging and retrograde drilling was performed. The lesion demonstrated to be stable in the probe examination during arthroscopy. This treatment initially led to an improvement in the symptoms. However, when the patient resumed his basketball training after 12 weeks, thereby increasing the weight-bearing, the same complaints as those preoperatively reappeared.
MRI six months after initial retrograde drilling revealed persistent subchondral cysts and increased detachment of the cartilage layer (OCD stage III). Given the persistent pain and the increasing cartilage detachment, all therapeutic options were discussed in detail with the patient and his parents. Because of the defect morphology and size, a two-stage procedure with initial bone augmentation with autologous bone grafting and cartilage cell harvesting with two-stage matrix-associated autologous chondrocyte transplantation (MACT) would be the preferred therapy. However, this was refused by the patient due to the two-stage procedure, which would have led to a prolonged exercise pause. Therefore, a one-stage procedure with autologous bone augmentation from the tibial head and autologous chondrocyte transplantation using minced cartilage (AutoCart, Fa. Arthrex) was carried out instead.
Surgery started with arthroscopy, which revealed an unstable osteochondral defect of 20 x 15 mm. The unstable cartilage remnants were reprocessed with the minced cartilage instrumentation. The underlying avital cancellous bone with cystic changes was completely debrided with a curette and a sharp spoon. An anterolateral miniarthrotomy with a skin incision of 3 cm was performed to insert the cancellous bone, which was harvested from the anterolateral tibial head. Then, the prepared minced cartilage was applicated, and fixation was secured using platelet-rich plasma and fibrin. In this way, the osteochondral defect was completely filled (Figure 2). It was of importance not to overfill the defect, thereby creating a prominent surface. The stratum synoviale of the joint capsule was closed using PDS suture, and the stratum fibrosum was closed using vicryl. Then, the skin incision was closed.
The rehabilitation protocol consisted of partial weight-bearing for 8 weeks postoperatively, followed by muscle strengthening and coordination training. The patient was back to basketball four months postoperatively and was pain free demonstrating full range of motion at the last follow-up examinations six and twelve months postoperatively.