A new preclinical sheep model of medial meniscus anterior root repair: Part 2-Surgical strategy, technical considerations, pearls and pitfalls.

purposeTo address a gap in translational research by developing a preclinical sheep model of medial meniscus anterior root (MAR) repair in vivo and to compare probabilities of potential pitfalls and difficulties with humans.

methodsPreoperative planning and surgical procedures applied to patients were adapted to adult sheep. Eight healthy, skeletally mature, female Merino ewes between 2 and 4 years of age underwent a mini-open medial parapatellar approach to both stifle joints without luxating the patella. Next, the MAR was transected in 16 knees (8 sheep) resulting in a subtype 2A tear according to the LaPrade classification, followed by a transtibial pull-out repair through a 3.2 mm diameter bone tunnel with a reinforced Mason-Allen suture and non-absorbable suture material. Animals were followed until 21 days after surgery.

resultsThe surgery time per knee ranged between 30 and 50 min (mean, 40.0 ± 7.8 min). The surgical technique was safe without intra- or post-operative complications. Solid repair is most likely if the following surgical principles are respected: (1) Selection of the MAR and the open technique allow for elegant tunnel positioning and less post-operative loading stress due to the normal extension deficit of sheep; (2) careful preparation of the MAR is mandatory; (3) considering the oval shape of the MAR attachment (MARA) results in anatomic tunnel placement; (4) robust suture placement and configuration avoids suture cut out. The probabilities of potential pitfalls and difficulties differ from the human situation.

conclusionA clinically adapted MAR repair model in adult sheep was developed following its complete transection close to the MARA, followed by an open transtibial pull-out repair. The surgical technique was safe without intra- or short-term post-operative complications. This model may be suitable to study the biomechanics and pathophysiology of meniscal root injuries and their repair. LEVEL OF EVIDENCE: Level IV.