Abstract
Objectives:
After failed conservative treatment of proximal hamstring tendon injuries, significant retraction occurs leading to the use of allografts for augmented repairs. Prior studies comparing proximal hamstring reconstruction using distal hamstring grafts and fascia lata grafts, demonstrated superiority of the distal hamstring grafts. Although the study indicates that distal hamstring grafts are superior to fascia lata grafts, Achilles tendon grafts are still commonly used for surgical repair for chronic proximal hamstring reconstruction. This study compares the biomechanical failure load, stiffness, and number of cycles until failure of proximal hamstring reconstruction techniques using a semitendinosus tendon allograft and an Achilles tendon allograft. We hypothesized that the semitendinosus tendon allograft will yield higher failure load and stiffness than the Achilles tendon graft.
Methods:
Eight pairs of human cadaveric hemi-pelvises with no evidence of prior injury or abnormality were dissected to the proximal hamstring origin. The ischial tuberosity was potted and mounted to a dynamic tensile testing system secured to the base, while the musculotendinous portion of the hamstrings were fixed using a custom clamp to the end effector between 6cm and 11cm distal to the ischial enthesis. All specimens underwent a 1Hz cyclic loading protocol with loads cycling from 25N to a maximum load that increments by 75 N every 50 cycles. To calculate native stiffness, post the cyclic loading step, the tendon was pulled at 1mm/s for 20mm, and applied load was returned to 25N. Each pair of specimens were randomly assigned to receive the reconstruction with an Achilles tendon allograft or with a semitendinosus allograft. After surgical repair, the specimens underwent 17 biomechanical testing consisting of a preconditioning phase followed by a pull to failure to assess 18 failure loads, elongation at failure, stiffness, and mode of failure.
Results:
Graphical display of the results can be found in Figure 1. The Achilles tendon allograft group had a significantly lower failure load than the semitendinosus group (213 ± 48 N vs. 366 ± 85 N; p=0.005). There was no difference in elongation at failure between the Achilles and semitendinosus groups (21.0 ± 10.2 mm vs. 25.0 ± 10.4 mm; 22 p=0.457). Native stiffness was not significantly different between the Achilles and the semitendinosus groups (49.8 ± 12.6 N/mm vs. 51.4 ± 10.8 N/mm; p=0.995). Reconstruction stiffness was not significantly different from native stiffness of the Achilles group (45.2 ± 13.7 N/mm vs. 49.8 ± 12.6 N/mm; p=0.881). Reconstruction stiffness was not significantly different from native stiffness of the semitendinosus group (51.7 ± 12.4 N/mm vs. 51.4 ± 10.8 N/mm; p=1.00). The Achilles group exhibited a significantly higher percent difference of native stiffness as compared to the semitendinosus group (34.4 ± 14.1 % vs. 13.1 ± 6.4 %; p=0.003).
Conclusions:
This study revealed that the proximal hamstring reconstruction using a semitendinosus tendon allograft had significantly higher failure load and smaller percent difference of the native in stiffness compared to the reconstruction using an Achilles tendon allograft. There was no significant difference in elongation at failure between the two groups, native stiffness between the two groups, and the reconstruction stiffness of the Achilles and the semitendinosus group. These results indicate that it is more clinically appropriate to perform the proximal hamstring reconstruction using a distal hamstring allograft than an Achilles tendon allograft.
