Hamstring graft for ACL reconstruction achieves semitendinosus and gracilis tendon regeneration, but with functional deficits with deep knee flexion

Image: CC

Key study points:

1.     Semitendinosus and gracilis tendons are able to achieve regeneration and regain near normal points of insertion and cross sectional areas.
2.     Patient’s show significant improvement in functional strength and internal rotation.
3.     Strength deficits remain in deep knee flexion.

Primer:  Hamstring grafts for ACL reconstruction have become increasingly popular due to the benefits versus bone patellar-tendon-bone graft. Hamstring grafts are generally favored due to their ease of harvesting, and ability to avoidance cosmetic defects. There is also a decrease in anterior knee pain and extension loss, and decreased risk of further patellar injuries seen with hamstring grafts. The surgery requires grafts from the semitendinosus and gracilis tendons. However, there is a lack of data in the literature about the graft fixation time and ability of the hamstring muscles to return to prior of level function. Hamstring grafts can lead to functional and strength deficits affecting patient outcomes, particularly in the young, athletic population. Furthermore, there are varying rates of tendon regeneration rates. This study attempts to measure those traits in terms of regeneration potential, point of insertion, and strength in flexion and rotation.

Background Reading:

1. Endoligamentous revascularization of an anterior cruciate ligament graft. (Clin Orthop Relat Res)

2. Intratunnel versus extratunnel fixation of hamstring autograft for anterior cruciate ligament reconstruction. (Arthroscopy) 

This [case series] study: involved nineteen patients age 17 to 40 years, 9 women and 10 men, who underwent ACL reconstruction surgery with ipsilateral semitendinosus and gracilis (ST/G) autografts. MRI imaging was utilized to evaluate tendon regeneration, cross sectional area and diameters a minimum of  years post-operatively (range 6-11 years). Functional and strength measurements (Lysholm score, Tegner activity, Single-legged hop, and isokinetic testing for knee flexion and internal rotation) were measured for comparison.

Significant improvements were seen in all functional outcomes through Lysholm score (P<.02) and Tegner activity level (P<0.001). Patients were able to regain single leg hop function of the contralateral side 95% of the time on average. Deficits were seen at deep knee flexion angles (90 degrees), where flexion torques were lower compared to the contralateral side. Internal rotation strength reported at 60degrees/sec and 180 degres/sec had no significant weakness and patients were able to return to strengths similar to contralateral leg.Tendon regeneration was confirmed with tendon insertion point being similar compared to the contralateral side (3.5cm vs 4.2cm).

In sum: This study showed that with Hamstring grafts for ACL reconstruction (ST/G) near normal function and strength can be restored in patients. Given the study results, concerns of tendon regeneration and insertion in the hamstring were alleviated and it demonstrated that these grafts are unlikely to significantly change the biomechanics of the knee. The ST/G are the main movers of knee flexion and internal rotation. The study displayed a regain to normal knee internal rotation strength. On the other hand, knee flexion strength displayed significant weakness, particularly in deep flexion at 90 degrees. This should be considered in athletic individuals or patient’s who require movements in deep flexion positions.

The authors did not measure actual muscle volume and EMG activity of the ST/G, which would have been a better measurement of functional strength and nerve conduction. Moreover, it would be interesting to see the study performed sooner after surgery, as most patient’s requiring deep knee flexion would likely return to their activities within 2 years rather than the 6 year follow-up period.

Click to read the study in AM J Sports Medicine

By [RZ] and [AH]

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