Evaluation of muscle size and fatty infiltration with MRI nine to eleven years following hamstring harvest for ACL reconstruction

Quantitative and qualitative MR-imaging assessment of vastus medialis muscle volume loss in asymptomatic patients after anterior cruciate ligament reconstruction

BACKGROUND

To quantitatively and qualitatively assess vastus medialis muscle atrophy in asymptomatic patients with anterior cruciate ligament reconstruction, using the nonoperated leg as control.

METHODS

Prospective Institutional Review Board approved study with written informed patient consent. Thirty-three asymptomatic patients (men, 21; women,12) with ACL-reconstruction underwent MR imaging of both legs (axial T1-weighted spin-echo and 3D spoiled dual gradient-echo sequences). Muscle volume and average fat-signal fraction (FSF) of the vastus medialis muscles were measured. Additionally, Goutallier classification was used to classify fatty muscle degeneration. Significant side differences were evaluated using the Wilcoxon test and, between volumes and FSF, using student t-tests with P-value < 0.05 and < 0.025, respectively.

RESULTS

The muscle volume was significantly smaller in the operated (mean ± SD, 430.6 ± 119.6 cm(3) ; range, 197.3 to 641.7 cm(3) ) than in the nonoperated leg (479.5 ± 124.8 cm(3) ; 261.4 to 658.9 cm(3) ) (P < 0.001). Corresponding FSF was 6.3 ± 1.5% (3.9 to 9.2%) and 5.8 ± 0.9% (4.0 to 7.4%), respectively, with a nonsignificant (P > 0.025) difference. The relative muscle-volume and FSF differences were -10.1 ± 8.6% (7.1 to -30.1%) and 10.9 ± 29.4% (39.7 to 40.1%). The qualitative assessment revealed no significant differences (P > 0.1).

CONCLUSION

A significant muscle volume loss of the vastus medialis muscle does exist in asymptomatic patients with ACL-reconstruction, but without fatty degeneration.

Medial hamstring muscle activation patterns are affected 1-6 years after ACL reconstruction using hamstring autograft

PURPOSE

Although changes in hamstring muscle morphology after anterior cruciate ligament reconstruction (ACLR) using a semitendinosus autograft hamstrings-gracilis (HG) of the ipsilateral limb are recognized, alterations in muscle activation patterns have not been extensively studied. The purpose of this controlled laboratory trial was therefore to monitor muscle activation levels of the medial (MH) and lateral (LH) hamstring muscles in athletes who had undergone ACLR using a HG autograft and to contrast these to activation levels demonstrated by healthy controls.

METHODS

Surface electromyography (EMG) was sampled from bilateral hamstring muscles of 18 athletes 1-6 years after ACLR and 18 matched controls (CTRL) during the performance of two dissimilar exercises, both involving eccentric knee flexor activity. Peak normalized muscle activation levels were identified for MH and LH of both limbs during the performance of the Nordic Hamstring (NH) exercise and TRX) hamstring curl (TRX) exercise.

RESULTS

A statistically significant limb by exercise interaction was found for peak activation levels of LH, due to significant interlimb differences in activation during the performance of the TRX exercise compared to more symmetrical activation during the NH (p < 0.001). A three-way interaction was found for peak activation levels of MH, due to group differences in peak muscle activation between limbs and exercise type (p = 0.025). Whereas CTRL group participants consistently favoured one limb over the other during the performance of both exercises, ACLR participants demonstrated dissimilar peak MH activation patterns between limbs during the performance of the NH exercise compared to the TRX.

CONCLUSIONS

In light of these results and considering the surgical procedure, patients who undergo ACLR using a HG autograft from the ipsilateral limb may benefit from post-operative rehabilitation that involves muscle activation and strengthening specifically targeting the MH component.

Semitendinosus muscle fatty infiltration following tendon harvest in rabbits

The hamstring tendon autograft is one of the most commonly used graft choices in Anterior cruciate ligament (ACL) reconstruction. There are conflicting results regarding postoperative hamstring strength deficits in patients who have had a hamstring graft. The semitendinosus tendon has been shown to regenerate after harvesting for ACL autograft, suggesting that the muscle has the potential to regain normal function. However, no studies have been performed to define the microstructural changes that occur in the semitendinosus muscle after tendon resection. In this study, we hypothesized that fatty infiltration of the semitendinosus muscle after tendon harvest in New Zealand White rabbits increases postoperatively and remains constant or increases during the first year of repair. The semitendinosus tendon was unilaterally detached and harvested from 15 rabbits. Five rabbits were sacrificed at 3-, 6-, and 12-month intervals, and the semitendinosus muscle-tendon units were analyzed. The contralateral unoperated limb served as the control. The gross tendon and muscle dimensions and histologic percentage of fatty infiltration were measured. We found no significant difference in fatty infiltration at any time point between the control muscle and test specimens and that there was no progression of fatty infiltration over time. If these results hold true in humans, natural repair of the hamstring muscle following tendon harvest during ACL autograft reconstruction is not inhibited by fatty infiltration.