Murine patellar tendon transplantation requires transosseous cerclage augmentation - Development of a transplantation model for investigation of systemic and local drivers to healing

Background: Tendon injuries are common musculoskeletal injuries that heal with scar tissue formation, often achieving reduced biomechanical and functional properties. The murine patellar tendon is a research tool that holds potential for investigating tendon healing and can be useful for exploring therapeutic strategies. Since healing is a complex process that results from the collaboration between the systemic and local tissue environment, a murine tendon transplantation model that can be applied to transgenic mice and genetic mutants would allow isolation of systemic versus local tendon factors in driving effective tendon healing. Preliminary studies have shown that transplantation with simple tendon sutures results in a proximalization of the patellar bone due to the involuntary quadriceps muscle force leading to tearing of the graft and failure of the knee extensor mechanism. To avoid this elongation of the graft, two cerclage techniques for murine patellar tendon transplantation were introduced and validated. Methods: Three developed surgical techniques (no-cerclage-augmentation (NCA)), transfascial suture cerclage with encirclement of the patellar tendon (TFSC), and dual-cerclage-augmentation with a transosseous bone-to-bone cerclage through the patella bone and an additional musculotendinous cerclage (DCA)) were compared at 4 and 8 weeks macroscopically in regards to graft continuity, cerclage integrity, gap formation, and radiologically by measuring the patello-tibial distance and using a patella bone position grading system. Results: The NCA group showed complete failure at 5-7 days after surgery. The TFSC has led to 69% functional failure of the cerclage. In contrast, the DCA with a has led to 78% success with improvement in patellar bone position and a similar patello-tibial distance to the naïve contralateral murine knees over the time period of 8 weeks. Conclusions: This study shows that a bone-to-bone cerclage is necessary to maintain a desired graft length in murine patellar tendon models. This surgery technique can serve for future graft trans- and implantations in the murine patellar tendon.