The rectus femoris muscle has a high proportion of type II fibres (65%), which means it has high strength and the ability to generate power that in turn makes the rectus femoris highly susceptible to injury. A kicking injury mostly involves the thigh of the kicking leg and is frequently diagnosed as a rectus femoris muscle strain, often injured during eccentric loading. Studies have found that a vast majority of rectus femoris injuries (94%) involved the proximal tendons, which means the quadricep muscle and tendon closer to the where it attaches to the front of the hip.

A rectus femoris injury typically presents with sharp pain in the front of, or anterior thigh, often worsening with activities that require muscular power such as running, jumping, or squatting. Symptoms may include swelling and bruising around the injury site, along with tenderness when palpating the muscle. There will be provocation of pain with muscle contraction and muscle lengthening. Weakness in knee extension or hip flexion is common, as the rectus femoris is responsible for both actions. In more severe cases, an audible pop or feeling of tearing may occur at the time of injury.

A thorough clinical examination and patient history can diagnose a rectus femoris injury. The mechanism of injury is important in diagnosing as rectus femoris injuries will occur in activities where there are eccentric contractions of the rectus femoris muscle. The onset of pain, activity level and previous injuries should also be taken into account. A physical examination including observation of swelling, bruising and deformity, palpation of the rectus femoris and tendon insertion at the hip and knee, and range of motion testing of hip flexion and knee extension can help confirm a rectus femoris injury. In addition, strength testing of the quadriceps muscles and special tests such as straight leg raise and Thomas test can be used to indicate injury to the rectus femoris muscle.

If deemed necessary, imaging can be used to show the severity of the injury and grade the level of injury to guide rehabilitation. An ultrasound may show tears, hematomas and swelling of the rectus femoris and is the most-cost effective imaging technique. An MRI is the gold standard for muscle strain assessment and can show muscle tears, hematomas and edema, as well as distinctly visualise mild strains to complete ruptures.

A rectus femoris injury can be graded into the following categories:

• Grade 1: mild strain with small tears where mild discomfort is present.
• Grade 2: partial tear of the muscle with noticeable pain and functional limitations as well as bruising, swelling and weakness.
• Grade 3: complete rupture or avulsion of the muscle or tendon resulting in severe pain, swelling, hematoma and complete loss of function of the rectus femoris muscle.

Evidence-based physiotherapy treatment for a rectus femoris injury focuses on a combination of strategies to reduce pain, promote healing, and restore function. A systematic, progressive rehabilitation approach has proven to be most effective.

Initial phase (acute injury): In the first 48-72 hours post-injury, the primary goal is to reduce inflammation and control pain. This can be achieved through protect, elevate, avoiding anti-inflammatories compression and education (PEACE) and loading, optimism, vascularisation and exercise (LOVE). 

Subacute phase (recovery): After the acute phase, the focus shifts to restoring range of motion and strength. Gentle mobility and range-of-motion exercises are implemented and it is encouraged that slight pain is elicited. Isometric strengthening of the quadriceps and surrounding muscles and appropriate isotonic exercises can be incorporated.

Rehabilitation phase (strengthening and return to activity): Once pain is controlled and range of motion is restored, strengthening exercises with progressive load are key. Open-chain and closed-chain exercises, such as leg extensions, squats and lunges, are effective for building strength and improving function. Eccentric exercises targeting the rectus femoris have shown superior results in tendon healing and reducing the risk of re-injury.

Throughout recovery, functional progression and sport-specific drills are incorporated gradually, ensuring a safe return to activity without compromising the healing process.