Hip Flexor Strain

Anatomy

The hip flexor muscles are the iliopsoas, rectus femoris, gracilis, and sartorius. These muscles connect the pelvis to the femur and help aid in flexion of the femur forward, bringing the leg up toward the body. These muscles, along with the rest of the quadriceps muscles, which act to extend the knee, are the largest and most powerful muscles in the body. They are responsible for producing large concentric, isometric, and eccentric forces, resulting in powerful movements of the leg.

Causes

Acute injury and overuse injury are the two main causes of hip flexor strain. Acute injury typically involves a forceful eccentric contraction (contraction while the muscle lengthens) of the iliopsoas muscle. The athlete may experience one specific instance when he or she may feel the hip flexor pull. This may be associated with specific activities including sprinting, cutting, or kicking. Tight muscles and poor flexibility will contribute to a hip flexor injury. When muscles are tight, there is an increased amount of tension on the tissues. When this increased tension is compounded by an explosive movement, injury can occur (Figure 1). Soccer players are at high risk for this injury due to the powerful kicks associated with crossing passes, corner kicks, and shots on the goal. Other activities that may predispose to hip flexor strain include dancing, ballet, resistance training (weight lifting), rowing, running (particularly uphill), track-and-field events, and gymnastics.

Overuse injury may occur in activities involving repeated hip flexion or external rotation of the thigh. Injury can also be the result of overuse (repetitive kicking or long-distance running) and associated microtraumas. Microtrauma can occur in the form of a tiny, imperceptible tear. These tiny tears accumulate over time and eventually result in a strain and pain. The onset of this type of hip flexor strain is less acute and is progressive over time. Hip flexor strains of this type are often associated with a recent increase in activity.

Symptoms

The most common symptom of a hip flexor strain is pain. It occurs along the front of the hip and may radiate down the front of the thigh. Pain increases with movement, especially when attempting to lift the knee toward the chest. Running, jumping, and even walking can be painful, and sports performance may be limited. There may be a small [Page 657]amount of swelling, but this is not very common. Muscle spasm and bruising may also occur, depending on how severe the injury is. There is often weakness noted with activities associated with hip flexion. The injured athlete may notice a limp or pain with normal daily activities.

Figure 1 Hip Flexor Strain

Note: A powerful contraction of the iliopsoas muscle, usually when the leg is fully extended or trapped in place, can result in acute injury at the site where the tendon inserts into the femur.

Diagnosis

Often, the history of a hip flexor strain is very straightforward, with either an acute injury or a history of overuse preceding the onset of symptoms. With any adult who has acute hip pain, there are “red flags” that may indicate a more serious medical condition as the source of the pain. Fever, malaise, night sweats, weight loss, night pain, a history of cancer, or a history of an immune system deficiency should prompt consideration of conditions such as tumor, infection, or inflammatory arthritis, as opposed to a simple muscular injury.

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