An Avulsion of the Semitendinosus and Biceps Femoris Conjoined Tendons

Strains of the hamstrings (HS) at their proximal attachment to the ischial tuberosity (i.e., a traumatic enthesitis) is the most frequent injury to occur during high-impact sports. However, a complete rupture of the HS usually occurs distally at its musculotendinous junction. After an on-the-job twisting, falling injury, a 64-yr-old male presented 6 mos later with both a right sciatic radiculopathy and an ipsilateral antalgic hip gait. Limited internal rotation of the hip was associated with a weak iliopsoas muscle and increased pain limiting straight-leg raising. Magnetic resonance imaging demonstrated moderate spinal stenosis at L4–5, a normal hip, and a complete evulsion of the semitendinosus and biceps femoris conjoined tendons (Fig. 1). Thermotherapy, intermittent split-table pelvic traction, and a left-handed cane progressively resolved the abnormal gait and pain complaints.FIGURE 1: An avulsion of conjoined tendon of the right semitendinosus and biceps femoris tendon (arrow) with associated edema.Together, the semitendinosis and biceps femoris attach to the ischial tuberosity as a conjoined tendon medial to the origin of the semimembranosus tendon and the sciatic nerve, which, in turn, lies 1.0 cm lateral to the ischial tuberosity.1 The HS play a major role in both hip extension and knee flexion. Acute injury occurs during simultaneous hip flexion and knee extension, with the HS forcibly in extreme eccentric contraction. The HS are two-joint muscles crossing both the hip and knee. Functionally, they have the capacity to reverse their attachments at both their proximal origin and distal insertion (i.e., the fixed and moving attachments, respectively) as the muscles underload cycles from a concentric/shortening to an eccentric/elongating contraction. In this process, the muscles’ elastic modulus may not be “fast enough” to absorb the shock of recoil. Instead, these undamped forces may be transmitted proximally, disrupting the attachment to the ischial tuberosity. This occurs more often in aging muscle “stiffened” by progressive degradation of its viscoelastic properties and/or at a younger age, with insufficient preexercise stretching. Although strains at the musculotendinous junction usually heal conservatively, those at the tendinous insertion can remain disabling, and they may eventually require surgery.2