A systematic review was published in the American Journal of Sports Medicine last month which tackled those questions (2). The review pooled the data of 18 published studies and aimed to summarize whether the hamstring tendons do regenerate, the time course of regeneration, the loss of function of tendons that do not regenerate, and factors that may influence the process of regeneration.
The hamstring tendons in most cases do regenerate. Across the studies, the rate of regeneration varied between 50% to 100% for the semitendinosus tendon, and 46% to 100% for gracilis. The pooled, mean rate of regeneration after 1 year post ACL reconstruction was 79% for semitendinosus and 72% for gracilis.
Five studies included in the review assessed the rate of regeneration. Two of these studies reported no evidence of regeneration in the first 2-4 weeks, however the majority had regenerated at 6-9 months. Four of the studies found full regeneration after 1 year.
The review also looked at whether a patient’s sex, age, height, weight, or duration of immobilisation had an influence on regeneration of tendons. No significant differences were found.
Probably the most important point of discussion is whether or not regeneration of the tendons influences strength and function. Unfortunately there was conflicting findings across the studies. One study (3) reported that people without regenerated tendons had 4 times greater hamstring weakness compared with patients with both tendons regenerated. However other studies found no differences at all. Rehabilitation methods were not discussed in the review – something that may have a bearing on clinical outcome in each study.
For me, I can now safely assure my patients who undergone an ACL reconstruction with a hamstring graft that they have a 7/10 chance of their tendons regenerating. However from the results of this systematic review, there is no certainty that having tendons that regenerate have any positive or negative influence on a patient’s clinical outcome.
If you treat ACL injuries, or are currently undertaking a rehabilitation program following an ACL injury or reconstruction, you may be interested in our criteria-driven ACL Rehabilitation Protocol written by two leading sports physiotherapists. The Melbourne ACL Rehabilitation Guide has 6 phases, and there’s a list of goals and outcome measures that need to be satisfied at the end of each phase to move onto the next one. Click here to learn more.
1. Ahlden M, Samuelsson K, Sernert N, Forssblad M, Karlsson J, Kartus J. The Swedish National Anterior Cruciate Ligament Register: a report on baseline variables and outcomes of surgery for almost 18,000 patients. Am J Sports Med. 2012;40(10):2230-2235.
2. Mathijs A.M. Suijkerbuijk, Max Reijman, Susanne J.M. Lodewijks, Jorien Punt and Duncan E. Meuffels. Hamstring Tendon Regeneration After Harvesting: A Systematic Review. Am J Sports Med 2015;43(10):2591-2598
3. Choi JY, Ha JK, Kim YW, Shim JC, Yang SJ, Kim JG. Relationships among tendon regeneration on MRI, flexor strength, and functional performance after anterior cruciate ligament reconstruction with hamstring autograft. Am J Sports Med. 2012;40(1):152-162.
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