Medial Hamstrings Used as Autograft for ACL Reconstruction Show an Abnormal Neuromuscular Pattern at the Time of Return to Sport

Abstract

Background:

Anterior cruciate ligament reconstruction (ACLR) is the preferred treatment for ACL rupture. Medial hamstring (HS) tendons are the most common autografts. An abnormal mediolateral HS muscle activation pattern after ACLR with an HS autograft could influence return to sport (RTS).

Purpose:

To evaluate patients who underwent ACLR with concurrent isokinetic tests and surface electromyography (sEMG) of the medial versus lateral HS compared with a group of healthy controls to identify potential abnormal patterns at RTS.

Study Design:

Comparative study; Level of evidence, 3.

Methods:

The mean medial versus lateral HS sEMG amplitude and timing were measured during isokinetic tests at 60, 180, and 300 deg/sec in 92 participants: 46 patients who underwent primary HS-grafted ACLRs (ACLR group) and 46 healthy controls matched for age (18-45 years), sex, and level of physical activity (Tegner, 4-9) (control group). After the 8th postoperative month, the ACLR group were evaluated with an isokinetic test combined with sEMG of the medial and lateral HS. The control group were tested with the same procedure. sEMG data were included only if the minimum criteria for RTS were met according to the published literature (HS/quadriceps ratio ≥60% and quadriceps and HS interlimb peak torque difference at 60, 180, and 300 deg/sec ≤10%).

Results:

There was no difference in isokinetic peak torque normalized to body mass between ACLRs and controls at any tested angular velocity. The mean sEMG amplitude for both the medial and lateral HS showed no between-group difference at 60, 180, and 300 deg/sec. No intergroup differences emerged for the mediolateral HS ratio during all tests. Instead, the mean sEMG time-to-peak for the medial HS was consistently faster in the ACLR group (P = .02 at 60 deg/sec; P = .01 at 180 deg/sec; P = .04 at 300 deg/sec), with no intergroup difference for the lateral HS at 60, 180, 300 deg/sec.

Conclusion:

The grafted medial HS showed consistently faster sEMG time-to-peak in the ACLR group than in the control group at all tested velocities. No differences emerged on sEMG amplitude for the medial HS and on both sEMG amplitude and timing for the lateral HS. Those who underwent HS-grafted ACLR showed a higher neuromuscular demand on the grafted medial HS at RTS. This altered overall HS muscle coordination could affect lower limb biomechanics during active movements, potentially increasing the risk of ACL reinjury.