Addition of the Sartorius Tendon Improves Biomechanics of a Four-Strand Hamstring Anterior Cruciate Ligament Autograft

PURPOSE The purpose of this study was to quantify and compare the biomechanical properties and change in graft size when adding the sartorius tendon as a fifth strand to a four-strand ST-G hamstring autograft. Additionally, the sartorius tendon was tested individually to quantify its independent biomechanical properties. METHODS Four-strand and five-strand hamstring tendon grafts were harvested from matched cadaveric knees (mean age, 81.6 ± 9.8). These matched grafts were biomechanically tested using a MTS servohydraulic test system at a rate of testing representative of physiologic tears. The mean diameter, cross-sectional area, and ultimate load to failure were quantified and compared with a one-sided, paired Student's t-test. A p < 0.05 was considered statistically significant. RESULTS The mean diameter of the five-strand graft was significantly larger than the four-strand graft (9.30 ± 0.84 mm vs. 8.10 ± 0.42 mm, p = 0.002). The average ultimate load to failure of the five-strand graft was 65.3% higher than the four-strand graft (2984.05 ± 1085.11 N vs. 1805.03 ± 557.69 N, p = 0.009) and added 14.8% to the diameter of the four strand ST-G autograft. CONCLUSIONS The addition of the sartorius tendon to a four-strand hamstring autograft significantly increased ultimate load to failure by 65%, graft cross-sectional area by 32%, and graft diameter by 15% compared to a traditional four-strand ST-G autograft. This information can be helpful to surgeons who wish to improve the strength of a four-strand ST-G autograft and for undersized grafts as an alternative to allograft supplementation. CLINICAL RELEVANCE The addition of the sartorius to the four-strand ST-G hamstring autograft significantly increases the ultimate load to failure and overall graft diameter, which can be particularly helpful in undersized autografts as an alternative to allograft supplementation.