As the most medial of the three muscles that make up the hamstring, the semimembranosus muscle is subjected to an amazing degree of stresses, especially at its distal insertion on the posterior medial condyle of the tibia (Fig. 138.1). When this musculotendinous insertion becomes inflamed, it presents clinically as a constellation of symptoms consisting of localized tenderness over the posterior aspect of the medial knee joint with severe pain being elicited on palpation of the attachment of the semimembranosus muscle at the posterior medial condyle of the tibia. This clinical presentation is known as semimembranosus insertion syndrome. Semimembranosus insertion syndrome most commonly occurs after starting an overaggressive exercise program or following direct blunt trauma to the posterior knee from kicks or tackles during football or rugby.

The semimembranosus bursa that lies between the medial head of the gastrocnemius muscle, the medial femoral epicondyle, and the semimembranosus tendon can become concurrently inflamed further exacerbating the patient’s pain and functional disability.

Patients suffering from semimembranosus insertion syndrome will present with point tenderness over the attachment of the semimembranosus muscle at the posterior medial condyle of the tibia. The tenderness may extend to the posteromedial knee. If the symptoms progress, the patient will exhibit a positive twist test for semimembranosus insertion syndrome (Fig. 138.2). The twist test is performed by placing the knee in 20 degrees of flexion and passively rotating the flexed knee. The test is positive if the pain is reproduced. Activity makes the pain worse, with rest and heat providing some relief. The pain is constant and characterized as aching. Sleep disturbance is common with awakening when the patient rolls over onto the affected knee. Some patients complain of a grating, catching, or popping sensation with range of motion of the joint, and crepitus may be appreciated on physical examination. Bursitis, meniscal tears, tendinopathy, osteoarthritis, synovitis, avulsion fractures, and impingement syndromes may coexist with semimembranosus insertion syndrome and may contribute to the patient’s pain symptomatology and confuse the clinical diagnosis (see Fig. 138.1).

Plain radiographs are indicated in all patients who present with semimembranosus insertion pain as not only semimembranosus insertion pathology, as well as other regional pathology including tibial plateau abnormalities may be perceived as semimembranosus insertion pain by the patient. Based on the patient’s clinical presentation, additional testing may be indicated, including complete blood cell count, sedimentation rate, and antinuclear antibody testing. MRI or ultrasound of the semimembranosus tendinous insertion is indicated if the diagnosis is in question or if avascular necrosis, bursitis, or meniscal tear is suspected (Figs. 138.3 and 138.4).

The semimembranosus muscle is the most medial of the three muscles that make up the hamstrings. It finds its origin from the ischial tuberosity and inserts into a groove on the medial surface of the medial condyle of the tibia (Figs. 138.5 and 138.6). The semimembranosus muscle flexes and medially rotates the leg at the knee as well as extending the thigh at the hip joint. A fibrous extension of the muscle called the oblique popliteal ligament extends upward and laterally to provide support to the posterior knee joint. This ligament, as well as the tendinous insertion of the semimembranosus muscle, is prone to the development of inflammation from overuse, misuse, or trauma. The semimembranosus muscle is innervated by the tibial portion of the sciatic nerve. The common peroneal nerve is in proximity to the insertion of the semimembranosus muscle, with the tibial nerve lying more medial. The popliteal artery and vein also lie in the middle of the joint. The semimembranosus bursa, which lies between the medial head of the gastrocnemius muscle, the medial femoral epicondyle, and the semimembranosus tendon, also serves as a source of medioposterior knee pain.

The benefits, risks, and alternative treatments are explained to the patient and informed consent is obtained. The patient is then placed in the supine position with the lower extremity externally rotated (Fig. 138.7). The skin overlying the medioposterior knee is then prepped with antiseptic solution. A sterile syringe containing 4.0 mL of 0.25% preservative-free bupivacaine and 40 mg of methylprednisolone is attached to a 1½-inch, 22-gauge needle using strict aseptic technique. A high-frequency linear ultrasound transducer is placed over the medial semimembranosus insertion joint in the oblique longitudinal plane with the superior portion of the ultrasound transducer turned about 20 degrees toward the patella (Fig. 138.8). A survey scan is taken, which demonstrates the characteristic appearance of the medial joint space with the hyperechoic medial margins of the femur and the tibia with the thick hyperechoic filaments of the medial collateral ligament overlying the triangular-shaped medial meniscus (Fig. 138.9). The medial meniscus is visualized as a triangular-shaped hyperechoic structure resting between the bony medial margins of the femur and tibia (Fig. 138.10). Just inferior to the joint space is the hypoechoic rounded tendon of the semimembranosus muscle at its tibial insertion. The tendon can be seen to lie within the medial contour of the tibia (Fig. 138.11). After the semimembranosus tendon is identified, the needle is placed through the skin ˜1 cm above the middle of the longitudinally placed transducer and is then advanced using an out-of-plane approach with the needle trajectory adjusted under real-time ultrasound guidance until the needle tip lies in proximity to the tendon as it lies within the contour of the medial tibia (Fig. 138.12). When the tip of needle is thought to be within proximity to the semimembranosus insertion, a small amount of local
anesthetic and steroid is injected under real-time ultrasound guidance to confirm that the needle tip is outside the substance of the tendon. There should be minimal resistance to injection. After proper needle tip placement is confirmed, the remainder of the contents of the syringe are slowly injected. If synechiae, loculations, or calcifications are present, the needle may have to be repositioned to ensure that the entire intra-articular space is treated. The needle is then removed, and a sterile pressure dressing and ice pack are placed at the injection site.