Primary Fixation of Single Stitch All-Inside and Inside-Out Meniscal Devices for Repairing Vertical Longitudinal Meniscal Tears: A Human Microscopic Imaging and Biomechanical Study

BACKGROUND: Optimized surgical fixation and meniscal stabilization during rehabilitation increase healing success. However, the latest generation of all-inside devices has not yet been biomechanically compared with inside-out suture tape (IO-ST) repair.

HYPOTHESIS: (1) The contact area of a suture anchor (SA) would compensate for a meniscal defect better than polyether ether ketone anchors (PA); (2) adjustable tensioning for all-inside meniscal repair fixation would result in higher initial load than IO-ST repair; and (3) stiffer constructs would decrease secondary displacement.

STUDY DESIGN: Controlled laboratory study.

METHODS: This study investigates human menisci (N = 39) via microscopic imaging and a biomechanical testing protocol. For the imaging protocol, needles of an all-inside SA or PA device and an IO-ST device were inserted after staining to measure the iatrogenic defect created by the needle insertion (n = 20) and the length, width, and meniscus contact area of deployed all-inside anchors (n = 6). For biomechanical testing, menisci with longitudinal bucket handle tears were prepared, and single stitches were repaired (each n = 9). After suture tensioning (50 N) and fixation, initial load, initial stiffness, and relief displacement were measured. Constructs underwent cyclic loading between 2 and 20 N, with 10,000 cycles (0.75 Hz), and stiffness and displacement were measured. Ultimate stiffness and load-to-failure were analyzed at 3.15 mm/sec.

RESULTS: All-inside needles created greater iatrogenic meniscal defects ( P < .001) than IO-ST repair. While PAs were longer ( P < .001), SAs were wider with a greater meniscal contact area (both P < .001). IO-ST repair resulted in the lowest initial load ( P < .001) and relief displacement ( P < .001), whereas SA repair resulted in a higher initial load ( P < .007) and stiffness ( P < .023) than PA repair. The overall stiffer SA fixation ( P < 001) significantly reduced cyclic displacement compared with other repairs ( P < .044). The PA group failed due to an anchor fracture at a significantly lower load (84.3 ± 10.7 N; P < .001) than the IO-ST (136.4 ± 10.5 N) and the SA repair (122.1 ± 17.5 N), with a suture-based failure mode. The ultimate stiffness of SA constructs was higher ( P < .045) than that of other repairs.

CONCLUSION: While all-inside devices showed improved primary stability, the IO-ST construct demonstrated the highest load-to-failure. In a human cadaveric model, meniscal repair with a more compact and conforming SA was stiffer and reduced cyclic displacement compared with PA and IO-ST repair.

CLINICAL RELEVANCE: All-inside SA repair improved primary stability. Future clinical series will define the overall significance of healing rates.