1. From a systematic review of 18 publications, 79% of semitendinosus tendons and 72% of gracilis tendons harvested for ACL repair were regenerated after at least 1 year of follow-up.
Evidence Rating Level: 2 (Good)
Study Rundown: Hamstring tendons, specifically the semitendinosus and gracilis tendons, have been increasingly harvested for primary anterior cruciate ligament (ACL) repairs. Hamstring tendon grafts have been more frequently employed than conventional bone-patellar tendon-bone autografts, owing to comparatively reduced post-operative donor site morbidity. The extent of the regeneration of the donor-site hamstring tendon and the consequences of a lack of regeneration have been points of contention and not systematically studied. Thus, authors in this study sought to characterize regeneration rates of hamstring tendons harvested for ACL repair, time course for regeneration, and the clinical consequence and predictive factors for non-regenerating tendons.
Through a systematic review of 18 studies, researchers found regeneration rates of 79% and 72% over 1 year after harvest for semitendinosus and gracilis tendons respectively, with regeneration predominantly occurring within 1 month and 1 year after ACL reconstruction. There was conflicting evidence regarding the clinical effect of hamstring tendon regeneration, with some studies reporting no statistical difference in hamstring strength between regenerated and non-regenerated tendons while others noted strength deficits in non-regenerated tendons. No predictive factors for regeneration were reported in any study. The characterization of overall hamstring tendon regeneration rates and its relative time course are significant for clinical practice in both the selection of graft site and post-operative care and rehabilitation methods. This review is limited by a lack of homogeneity among included studies. Studies differed markedly in their means of assessing regeneration, using diverse criteria, time points, imaging modalities, and often reporting regeneration dichotomously which is inconsistent with the continuous, progressive process of tendon regeneration. Additionally, patient populations and characteristics varied between studies as did study design.
In-Depth [systematic review]: Eighteen studies, published between 1999 and 2014, fulfilled the eligibility criteria. Studies must have included at least 10 patients evaluating a surgical procedure in which a hamstring tendon graft was harvested with tendon regeneration noted post-operatively. Studies employed MRI (12/18), 3D-computed tomography (2/18), biopsy (3/18) and ultrasound (3/18) to asses regeneration. Rates of regeneration varied across studies, from 50-100% for semitendinosus tendons and 46-100% for gracilis tendons. After pooling data, the regeneration rate of hamstring tendons at one year post-op was 91% (177/195) for semitendinosus and 100% (22/22) for gracilis tendons. At over 1 year of follow-up, the pooled average regeneration rate was 79% (142/179) for semitendinosus and 72% (74/103) for gracilis. Analysis by sex and demographic data did not reveal any determinants for tendon regeneration. A single study evaluating the time period of immobilization after ACL repair also found no significant difference in rates between a short immobilization (3 days post-op) and long immobilization (10 to 14 days).
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