A 20 year-old female complained for knee pain and burning sensation of her left leg of a few weeks duration. The clinical examination was normal. An MRI examination of her left knee was requested for possible internal derangement of joint.
There is a fusiform mass-like structure located between the lateral head of gastrocnemius muscle and the vessels of the popliteal fossa (fig.1, 2, 3). Rostrally it has a thin attachment to the posterior cortex of the femur. The signal intensity of this structure follows that of muscle on all pulse sequences. Caudally it is fused with the lateral head of gastrocnemius muscle. The popliteal vessels are not compressed, coursing through the lateral head of gastrocnemius and this structure. The findings are suggestive of an accessory split of the lateral head of the gastrocnemius muscle.
There is a small amount of intraarticular fluid (fig.1a, 3) and a small amount of soft tissue oedema in front of the patella (fig.1b, 1c).
There are numerous accessory muscles in the human body. Most of them are asymptomatic and are discovered incidentally during imaging or surgery [1]. In some cases the discovery of these variations in musculature may explain patient’s symptoms and aid in diagnosis and treatment [1]. At the knee region there are variations of skeletal musculature that may provoke anomalous course of the popliteal vessels and may be responsible for symptoms of popliteal artery entrapment syndrome [2][fig.4]. An accessory muscle should be carefully evaluated, during imaging, as it may compress the neurovascular structures of the popliteal fossa and produce symptoms [3]. MR angiography will reveal the vascular compression [4]. The combination of plain MRI and MR angiography is needed to avoid unsuccessful and mainly unnecessary angioplasty procedures [4].
In our case the young woman had knee pain and intermittent claudication of the ipsilateral leg after physical activity. Symptoms subsided with rest and leg elevation. The MRI disclosed an accessory split of the lateral head of gastrocnemius muscle but the popliteal vessels were not compressed. The patient's symptoms could not be attributed to these findings, so conservative treatment and follow-up of the patient were suggested.
Accessory split of lateral head of gastrocnemius muscle.
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This is a 20-year-old female patient presenting with left knee pain and a burning sensation in the lower leg. MRI examination shows an additional muscle slip in the lateral head of the gastrocnemius (LG) at the posterior aspect of the left knee, running parallel to the main muscle belly. According to the images, there is no apparent vascular or nerve compression, and the popliteal vessels demonstrate normal course and signal. The other internal structures of the knee joint (meniscus, ligaments, bone) appear essentially normal in signal, with no evidence of tears, fractures, or soft tissue swelling.
Based on the patient’s age, symptoms, and MRI features, the most likely diagnosis is an accessory lateral gastrocnemius muscle belly, with no current evidence of popliteal artery or other neurovascular compression. Considering that the patient’s symptoms are mild and without hallmark signs of arterial entrapment or ischemia, conservative treatment and follow-up observation are recommended.
1. Conservative Treatment: Advise the patient to reduce or avoid high-intensity activities that may trigger pain or burning sensations. During acute pain episodes, local ice application or heat therapy can be used to alleviate symptoms. If pain is significant, short-term use of nonsteroidal anti-inflammatory drugs (NSAIDs) may be considered for pain relief and inflammation control.
2. Physical Therapy: Includes local massage, muscle stretching, and strength training to reduce local soft tissue tension and improve lower limb strength and stability. Physical therapy should be carried out under professional guidance to avoid excessive stretching or improper movements that may lead to secondary injury.
3. Rehabilitation/Exercise Prescription (Example Based on the FITT-VP Principle):
4. Follow-Up and Observation: Periodic check-ups are recommended. If pain worsens or if numbness or signs of impaired blood supply in the lower limb occur—symptoms suggestive of popliteal artery entrapment—further examination and consultation with vascular surgery or a musculoskeletal specialist may be necessary to assess possible surgical intervention.
Disclaimer: This report is a reference analysis based on the provided examination and clinical information. It cannot replace in-person consultation or professional medical advice. If the condition worsens or new symptoms appear, please seek medical attention promptly.
Accessory split of lateral head of gastrocnemius muscle.
