The adductor magnus “mini-hamstring”: MRI appearance and potential pitfalls

Objective: To examine the anatomic MRI characteristics of the adductor magnus mini hamstring (AMMH) and explore its involvement in cases of hamstring avulsion. Materials and methods: An IRB-approved retrospective review of patients undergoing “hamstring protocol” MRI between March 2009 and June 2014 was performed. Two musculoskeletal radiologists recorded multiple AMMH anatomic characteristics and involvement in cases of hamstring avulsion. Results: Seventy-six AMMHs were analyzed in 66 patients [35 females and 31 males, mean age 49.3 ± 15.2 years (range 17–81)]. Eleven percent of AMMHs were poorly visualized, 51 % visualized, and 37 % well visualized. Seven percent demonstrated round, 73 % ovoid, and 21 % flat/lenticular tendon morphologies. Most (88 %) demonstrated typical origins. Average cross-sectional area (CSA) was 22.4 ± 10.6 mm² (range 6–56), diameter was 7.2 ± 2.5 mm (range 2.9–15), medial distance from the semimembranosus tendon was 7.5 ± 2.5 mm (range 3–14), and tendon length was 6.8 ± 3.3 cm (range 1.2–14.1). There was no gender difference in AMMH anatomic measurements or correlation between age and CSA or diameter. Of 17 complete hamstring avulsion cases, the AMMH was intact in 13, partially torn in 3, and completely torn in 1. Conclusion: The AMMH is a constant finding with variable anatomic characteristics. It is visualized or well visualized by MRI in 88 % of cases and is a sizable tendon located in close proximity to the semimembranosus tendon. Because it is uncommonly completely torn (6 %) in cases of complete hamstring avulsion, radiologists should be aware of its presence and appearance to avoid diagnostic confusion.