Semimembranosus Insertion Syndrome – The Clinical Syndrome
Semimembranosus insertion syndrome is a constellation of symptoms including a localized tenderness over the posterior aspect of the medial knee joint, with severe pain elicited on palpation of the attachment of the semimembranosus muscle at the posterior medial condyle of the tibia. Semimembranosus insertion syndrome occurs most commonly after overuse or misuse of the knee, often after overaggressive exercise regimens.
Direct trauma to the posterior knee by kicks or tackles during football also may result in the development of semimembranosus insertion syndrome. Coexistent inflammation of the semimembranosus bursa that lies between the medial head of the gastrocnemius muscle, the medial femoral epicondyle, and the semimembranosus tendon may exacerbate the pain of semimembranosus insertion syndrome. Rarely, muscle abnormalities may contribute to the patient’s pain symptomatology.
The semimembranosus muscle has its origin from the ischial tuberosity and inserts into a groove on the medial surface of the medial condyle of the tibia. The semimembranosus muscle flexes and medially rotates the leg at the knee and extends 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 and the tendinous insertion of the muscle are prone to 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 lie in the middle of the joint. Also serving as a source of pain in the posterior knee is the semimembranosus bursa, which lies between the medial head of the gastrocnemius muscle, the medial femoral epicondyle, and the semimembranosus tendon.
What are the Symptoms of Semimembranosus Insertion Syndrome
On physical examination, the patient exhibits point tenderness over the attachment of the semimembranosus muscle at the posterior medial condyle of the tibia. The patient may feel tenderness over the posterior knee and exhibits a positive twist test for semimembranosus insertion syndrome. 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. Internal derangement of the knee also may be present and should be searched for on examination of the knee.
How is Semimembranosus Insertion Syndrome diagnosed?
Plain radiographs are indicated in all patients with pain thought to be emanating from semimembranosus insertion syndrome to rule out occult bony pathology, including tibial plateau fractures and tumor. Based on the patient’s clinical presentation, additional tests may be indicated, including complete blood count, prostate-specific antigen, sedimentation rate, and antinuclear antibody testing.
Magnetic resonance imaging (MRI) and ultrasound imaging of the knee is indicated if internal derangement, occult mass, or tumor is suspected as well as to confirm the diagnosis of semimembranosus insertion syndrome.
Radionucleotide bone scanning may be useful to rule out stress fractures not seen on plain radiographs. Injection of the semimembranosus insertions with local anesthetic and steroid may serve as a diagnostic and therapeutic maneuver. Ultrasound guidance may help improve the accuracy of needle placement and decrease the incidence of needle-induced complications.
Differential Diagnosis
Internal derangement of the knee and a ruptured Baker cyst may mimic the clinical presentation of semimembranosus insertion syndrome. If trauma has occurred, the possibility of occult tibial plateau fracture, especially in patients with osteopenia or osteoporosis, should be considered, and radionucleotide bone scanning should be obtained. Villonodular synovitis and hemarthrosis of the knee may produce knee pain that can mimic the clinical presentation of semimembranosus insertion syndrome. Entrapment neuropathy or stretch injury or both to the tibial branch of the sciatic nerve and common peroneal nerve, plexopathy, and radiculopathy should be considered if there is the physical finding of neurological deficit in patients thought to have semimembranosus insertion syndrome because all of these clinical entities may coexist.
Treatment
Initial treatment of the pain and functional disability associated with semimembranosus insertion syndrome should include a combination of nonsteroidal antiinflammatory drugs (NSAIDs) or cyclooxygenase-2 (COX-2) inhibitors and physical therapy. Local application of heat and cold may be beneficial. For patients who do not respond to these treatment modalities, the injection of the semimembranosus insertion with a local anesthetic and steroid may be a reasonable next step.
Complications and Pitfalls
If trauma is present, the possibility of occult fracture always should be considered, as should the possibility of occult malignancy of the distal femur or proximal tibia and fibula. Trauma to the tendons of the knee from injection of the tendinous insertion is a possibility. Tendons that are highly inflamed or previously damaged are subject to rupture if they are directly injected. This complication can be greatly decreased if the clinician uses gentle technique and stops injecting immediately if significant resistance to injection is encountered. Approximately 25% of patients report a transient increase in pain after this injection technique, and patients should be warned of this possibility.
Clinical Pearls
The proper use of exercise equipment can greatly reduce the incidence of semimembranosus insertion syndrome. Injection of the semimembranosus tendon insertion is extremely effective in the treatment of pain secondary to the previously mentioned causes of knee pain. Gentle injection technique decreases the incidence of traumatic rupture of the tendons as a result of injection. Coexistent bursitis and arthritis also may contribute to knee pain and may require additional treatment with a more localized injection of a local anesthetic and depot steroid. The use of physical modalities, including local heat and gentle range-of-motion exercises, should be introduced several days after the patient undergoes this injection technique for knee pain. Vigorous exercises should be avoided because they would exacerbate the symptoms. Simple analgesics and NSAIDs may be used concurrently with this injection technique.
