Miniarthrotomy of the sheep knee joint for the experimental production and subsequent treatment of osteochondral defects of the femoral condyle

An experimental study concerning the production of focal chondral and osteochondral defect of the weight-bearing surface of the ovine femoral condyle and their subsequent treatment was initially attempted through a traditional medial or lateral parapatellar arthrotomy. Arthroscopic access was ruled out because continuous intraarticular irrigation would have prevented the desired adhesion of the substances under investigation to the defect. Clinical observations 10-15 days after surgery on the first 12 operated subjects showed a high percentage of sheep (>60%) still lame due to evident changes in the surgical site, mainly patellar luxation and wound dehiscence with infection, especially in those with lateral arthrotomy. Although these complications may have been related to poor postoperative care of the animals, and facilitated by the gregarious behavior of sheep which makes it difficult to care for a single animal in a flock, an attempt was made to find a surgical modality that could overcome this. In the next 33 animals, therefore, the goal was to reach the joint cavity via a route that, in addition to being much smaller in length, spared as much of the ligamentous structures as possible, especially the patello-femoral ligaments. The femoral condyle site for the experiment was identified by careful transcutaneous digital palpation of the knee with the sheep in dorsal recumbency and applying gentle flexion-extension movements to the joint held in maximum flexion. Maximum knee flexion and consequent distal sliding of the patella exposes the high-load surface of the condyle to palpation. A 1-cm long full-thickness proximal-distal miniarthrotomy was then performed just above the site, close to the patellar tendon, with a no. 11 blade. A first self-retaining Gelpi retractor was applied proximal-distal on the opening, and a second retractor was positioned orthogonally to the first. Due to the elasticity of the tissues and the action of the Gelpi retractors, a condyle surface area of approximately 1 cm2 was exposed. After marking with a 6 mm diameter punch, the planned 2 mm deep, sharp-edged cylindrical osteochondral defect on the high-load bearing surface of the condyle was then produced with a cylindrical-tipped burr and finished with curettes. The osteochondral defect was then filled with the substances under investigation, such as embryonic stem cells, fibrin glue, platelet-rich plasma, conditioned autologous plasma, and nanoceria, without encountering any difficulty in performing the experiment attributable to the limited exposure of the condyle. The miniarthrotomy was closed with two layers of suture. By day 1 after surgery, none of the subjects who underwent miniarthrotomy showed lameness or alteration at the surgical site, which made it possible to continue with the subsequent phases of the study. This miniarthrotomy is probably similar to that used by Hangody (1998) in his performance of the mosaicplasty procedure for the treatment of osteochondral lesions <15 mm in the human knee (1). In our opinion, with this technique it is possible to reach the chondral surface of either the designated condyle (medial or lateral) or, after knee extension, the femoral trochlea in its trochlear groove. Although the exposure of the condylar surface is small, with careful targeting of the surgical site, miniarthrotomy may be a viable alternative to arthrotomy and arthroscopy in certain cases.