Structural properties of the intact proximal hamstring origin and evaluation of varying avulsion repair techniques: an in vitro biomechanical analysis

Abstract

Background: Although surgical repair has been reported to provide improved outcomes compared with nonoperative treatment in the management of complete proximal hamstring origin avulsions, no intact or avulsion repair biomechanical data exist to support various repair strategies or guide postoperative rehabilitation.

Purpose: To compare failure load among 4 proximal hamstring tendon conditions: (1) intact, (2) repair with 2 small anchors (2S), (3) repair with 2 large anchors (2L), and (4) repair with 5 small anchors (5S).

Study design: Controlled laboratory study.

Methods: Twenty-four human cadaveric hemipelvises were randomly allocated to 1 of the 4 testing groups. Intact and repaired specimens were subjected to cyclic loading at 1 Hz between 25 N and a progressively increasing maximum load that was incremented by 200 N every 50 cycles, beginning at 200 N and increasing to 1600 N. Displacement, maximum load, stiffness, number of cycles to failure, and mode of failure during cyclic loading were recorded and analyzed.

Results: The intact proximal hamstring tendons failed at the highest cyclic force of all tested groups, yet no significant differences existed between the intact (1405 ± 157 N) and 5S repair (1164 ± 294 N) conditions. Both the 2S and the 2L repair groups failed at a level significantly lower than the intact hamstring (474 ± 145 N [P < .001] and 543 ± 245 N [P < .001], respectively). The maximum load attained by the 5S repairs was significantly greater than the loads attained by the 2S (P = .005) and 2L (P = .013) repairs.

Conclusion: Repairs using 5 small anchors were similar to the intact tendon and were significantly stronger than repairs using only 2 large or 2 small anchors in the repair of complete avulsions of the proximal hamstring tendons. Additionally, no significant differences in strength were observed when only anchor size differed.

Clinical relevance: This finding supports the clinical investigation of postoperative range of motion rehabilitation protocols that permit full flexion and extension of the hip and knee when a 5-anchor repair construct is used.

Keywords: hamstring avulsion; hamstring repair; proximal hamstring rehabilitation; proximal hamstring structural properties.