Rectus Femoris Myofascial Pain Syndrome

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Rectus Femoris Myofascial Pain Syndrome

Rectus femoris myofascial pain syndrome is a common source of referred pain to the anterior knee and thigh. Myofascial pain syndrome of the rectus femoris muscle is frequently overlooked because its trigger point is commonly located near the hip and well away from the site of pain.

The rectus femoris muscle is usually described in conjunction with the vastus lateralis, vastus medialis, and vastus intermedius muscles, collectively known as the quadriceps femoris muscles. The rectus femoris is unique within this group of muscles, given that it crosses two joints and is capable of both knee extension and hip flexion, while the other three muscles are only involved in knee extension. The rectus femoris muscle originates from the pelvis by two tendons, one attached to the anterior inferior iliac spine and the other to a groove above the acetabular rim and fibrous capsule of the hip joint. It inserts via the patellar tendon to the patella and continues to the tibial tuberosity.

Please note: Trigger points may be located anywhere within muscles and their fascia. Therefore, the entire muscle should be examined thoroughly, particularly because trigger points are often located well away from the site of pain. However, based on clinical experience, the trigger point in the rectus femoris muscle is most commonly found in the upper thigh just distal to the anterior inferior iliac spine (as depicted by the black cross in the image below).

Myofascial pain is prevalent and is a frequent cause of visits to primary care physicians and pain clinics. Different studies have demonstrated that myofascial trigger points are associated with several pain conditions including headache and pain in the neck, low back, and upper and lower extremities.

Myofascial Trigger Points – A myofascial trigger point is a contraction knot found within a band of a muscle or in the muscle’s fascia. This contraction knot is considered to be responsible for nodularity which can be detected by palpation. Previous publications have suggested that trigger points are found in specific locations within a muscle. However, more recent publications suggest that they can be found anywhere within a muscle. Therefore, the entire muscle should be thoroughly examined in order to locate them.

Diagnostic Criteria for Myofascial Trigger Points – A 2019 international consensus concluded that moderate to excellent reliability for the presence of myofascial trigger points is based on the combination of a taut band, tender spot, local twitch response, and referred pain. The consensus was that at least two of the above criteria are required for a myofascial trigger point diagnosis.

Taut Band and Tender Spot – Myofascial trigger points typically involve an exquisitely tender spot found within a taut band of the muscle or in the muscle’s fascia.

Local Twitch Response – A local twitch response is defined as a quick visible or palpable contraction of the muscle fibers when pressure is applied within a taut band of a trigger point.

Active and Latent Trigger Points – Myofascial trigger points can be classified as active or latent. An active trigger point is one that reproduces or intensifies the patient’s familiar (referred) pain when it is compressed. A latent trigger point is one that does not reproduce the patient’s familiar pain when it is compressed.

Referred Pain – A key feature of an active trigger point is the presence of referred pain which is a manifestation of central sensitization. This central sensitization results in a spread of perceived pain to distant and larger areas of the body than just the local tenderness found at the taut band.

Research suggests that the combination of acidic pH and pro-inflammatory mediators at the active trigger point contributes to the segmental spread of nociceptive input into the dorsal horn of the spinal cord. The dorsal horn neuron, in turn, sensitizes the central nervous system by transmitting nociceptive impulses superiorly to activate the somatosensory cortex, where pain information is perceived and interpreted. This is believed to cause hyperalgesia and referred pain.

Risk Factors – Many different activities and medical conditions may place individuals at greater risk for developing myofascial pain syndrome. These include:

• Joint hypermobility or ligamentous laxity (i.e., when the ligaments are unable to provide joint stability, muscles remain in constant contraction to stabilize the joint. This is believed to cause the formation of trigger points within muscles)
• Musculoskeletal injuries
• Unaccustomed or intense exercise
• Muscle overload or repetitive physical activity
• Prolonged incorrect posture (e.g., poor ergonomics or habitual postures)
• Cold drafts or an intense cooling of muscles (e.g., sleeping in front of an air conditioner or under a ceiling fan)
• Lack of sleep or poor sleep
• Leg length inequality or other biomechanical disturbances
• Psychological stress, anxiety, and depression
• Fatigue

• Pain that is felt at the anterior knee around the patella
• Pain that may also be felt in the anterior distal thigh and deep within the knee joint
• Pain that may wake the patient at night (often described as a deep ache)
• Weakness in the knee that may be present when descending stairs
• Pain that may be relieved by stretching the rectus femoris muscle (by combining hip extension with knee flexion)

• Palpation reveals the presence of one or more trigger points within the rectus femoris muscle, identified by at least two of the following: taut band, tender spot, local twitch response, and/or referred pain.
• Trigger points are most commonly located near the muscle insertion at the anterior inferior iliac spine. They are occasionally found in the distal portion of the muscle within approximately 10 cm of the superior aspect of the patella.
• Pressure applied to the trigger points causes the reproduction of the patient’s anterior knee and distal thigh pain.

Imaging is not usually required in cases of myofascial pain syndrome, except to help rule out other conditions.

The following are examples of “red flags” for patients presenting with knee pain:

• History of a significant injury
• Severe pain
• Unrelenting pain
• Nocturnal pain
• Unexplained weight loss
• Fever
• Deformity
• Large joint swelling
• Significant loss of range of motion
• Significant neurological impairment
• Severe tenderness on palpation or severe pain with any examination procedure

If any “red flags” are identified during history taking and clinical examination, referral for urgent medical evaluation and further investigation is warranted.

Trigger Point Pressure Release Technique

When performing the Trigger Point Pressure Release Technique:

Step 1: Begin by applying gentle pressure on the trigger point and gradually increase this pressure until the patient reports some initial local pain (you will feel an increase in tissue resistance). Maintain this pressure without increasing it until the patient reports that the pain has eased (you will feel a concurrent easing of tissue resistance).

Step 2: Once the pain has eased, gradually apply deeper pressure on the trigger point until the patient once again reports the return of local pain (you will once again feel an increase in tissue resistance). Maintain this pressure until the patient reports that the pain has eased.

Step 3: Once the pain has eased again, gradually apply an even deeper pressure on the trigger point until the patient reports the return of local pain (you will feel an increase in tissue resistance). Maintain this pressure until the patient reports that the pain has eased.

The Relationship Between Chilled Muscles and Myofascial Pain Syndrome

Prolonged exposure of the muscles to a cold draft (e.g., sleeping in front of an air conditioner or under a ceiling fan and leaving hair wet after a shower) is considered a risk factor for the development of myofascial pain syndrome. Patients are usually unaware that chilled muscles can be the cause of the development of their pain. Therefore, it is essential that practitioners ask the patient if they have had any exposure to a cold draft prior to the development of their complaint.

Differential Diagnosis for Anterior Knee Pain

In addition to rectus femoris myofascial pain syndrome, the differential diagnosis of anterior knee pain in adults should include other conditions such as:

• Vastus medialis myofascial pain syndrome (see below)
• Patellar tendinopathy
• Patellofemoral pain (also known as patellofemoral pain syndrome and Runner’s Knee)
• Suprapatellar, prepatellar, or infrapatellar bursitis
• Quadriceps strain
• Tibiofemoral joint dysfunction
• Internal knee derangement
• Osteoarthritis
• Knee inflammatory joint disease
• Lumbar radiculopathy or femoral neuropathy

Vastus Medialis Myofascial Pain Syndrome Causing Anterior Knee Pain

The trigger point in the vastus medialis muscle refers pain to the medial aspect of the anterior knee. The trigger point may be located anywhere within the muscle and its fascia. Therefore, the entire muscle should be examined thoroughly. However, based on our clinical experience, the common location for the trigger point in the vastus medialis muscle is above the knee (as presented in the image below).