Murine patellar tendon transplantation requires transosseous cerclage augmentation — development of a transplantation model for investigation of systemic and local drivers of 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.

Force Comparison of Commercially Available Transfascial Suture Passers

Background. Transfascial suture passers (TSPs) are a commonly used surgical tool available in a wide array of tip configurations. We assessed the insertion force of various TSPs in an ex vivo porcine model. Methods. Uniform sections of porcine abdominal wall were secured to a 3D-printed platform. Nine TSPs were passed through the abdominal wall both without and with prolene suture under the following scenarios: abdominal wall only and abdominal wall plus underlay ePTFE or composite ePTFE/polypropylene mesh. Insertion forces were recorded in Newton (N). Results. When passed without suture through the abdominal wall, smaller diameter TSPs required less insertional force (1.50 ± 0.17 N vs 9.68 ± 1.50 N [ P = 0.00072]). Through composite mesh, the solid tipped TSPs required less force than hollow tipped ones (3.87 ± 0.25 N vs 7.88 ± 0.20 N [ P = 0.00026]). Overall, smaller diameter TSPs required less force than the larger TSPs when passed through ePTFE empty (Gore 2.95 ± 0.83 N vs Carter-Thomason 16.07 ± 2.10 N [ P = .0005]) or with suture (Gore 8.37 ± 2.59 N vs Carter-Thomason 19.12 ± 1.10 N [ P = .003]). Conclusions. Diameter plays the greatest role in the force required for TSP penetration. However, when passed through underlay mesh or while holding suture, distal tip shape, the mechanism of suture holding, and shaft diameter all contribute to the forces necessary for penetration. These factors should be considered when choosing a TSP for intraoperative use.