The location of the biceps femoris muscle is on the lateral side of the posterior thigh. It joins the semimembranosus and semitendinosus muscles, both of which are on the medial aspect of the posterior thigh, to become the hamstring complex. The biceps femoris muscle is the strongest of the hamstring complex and is responsible for flexion, external rotation and posterolateral stability of the knee.
The biceps femoris muscle has a long and a short head. In some normal variants, the short head of the biceps femoris may be absent. The long head of the biceps femoris muscle originates from the medial aspect of the ischial tuberosity and the inferior aspect of the sacrotuberous ligament. The short head of the biceps femoris muscle arises from the lateral lip of the linea aspera of the femur, proximal two-thirds of the supracondylar line, and the lateral intermuscular septum. These two heads of the biceps femoris form the biceps femoris tendon and then insert on the fibular head, the crural fascia, and the proximal tibia.
The two heads of the biceps femoris muscle receive innervation by different components of the sciatic nerve. The long head receives innervation from the tibial component of the sciatic nerve, whereas the short head receives innervation from the peroneal component of the sciatic nerve. This unique innervation pattern of the biceps femoris muscle may result in incoordination of both heads and vulnerability to a sports injury.
Injury to the biceps femoris muscle has an association with decreased flexion force and rotational stability of the knee. Brunet (1987) observed that the flexion force had a 75% decrease if the biceps femoris tendon gets transferred to the fibular collateral ligament. By transferring either a part or the entire biceps femoris tendon to the fibular collateral ligament, it is anticipated to resist the anterolateral rotatory instability of the knee, which usually arises from the anterior cruciate ligament insufficiency and injury to the lateral capsule of the knee. On the other hand, Frazer (1988) showed that the biceps femoris muscle had increased activity in the knees with torn anterior cruciate ligaments. The electromyographic activity of the biceps femoris tendon also increased during quadriceps setting and straight leg raising exercises.
Rupture of the biceps femoris tendon can be treated conservatively or surgically, depending on the severity of the tendon retraction. Most of the patients recover well and are able to return to high-level sports activities if they receive a timely diagnosis and appropriate treatment.
The biceps femoris tendon rupture usually develops following knee hyperextension with concomitant hip flexion. The most common sport associated with biceps femoris tendon injury is football (soccer). Some case series reported that the injury developed while playing hockey, jogging, and water skiing.
Complete rupture of the biceps femoris is rare, and only a few case reports mention it. However, the biceps femoris tendon is the most frequently injured part of the hamstring complex since it is the most powerful leg flexor and a crucial dynamic stabilizer of the knee.
The biceps femoris muscle becomes active in the in the late mid- or terminal swing phase of the gait cycle. The muscle contracts eccentrically to control the angular acceleration of the knee during its extension. The tendon is more vulnerable to injury during eccentric contraction than concentric contraction. Aging and muscle fatigue also render the muscle more susceptible to suffer injury.
The patients suffering from the biceps femoris tendon rupture may complain of sharp pain at the back of the knee following hyperextension of the affected knee. They may feel a pop on the affected knee during knee extension. Most of the victims had an injury while performing activities such as soccer, running, or water skiing. The injury usually renders the patient unable to walk.
The clinician may palpate a gap next to the ruptured biceps tendon. Sometimes, the examiner can also palpate a subcutaneous hematoma. Tenderness over the posterolateral aspect of the affected knee is common. The flexion force of the affected knee may decrease in severe cases.
Imaging modality can assist in defining the extent and severity of the biceps femoris tendon injury. Plain films can be used to check the presence of avulsion injury, in which an avulsed bony fragment may be apparent.
However, in adults, the avulsed osseous fragment is not easily seen. In contrast, due to incomplete ossification, a detached bony chip is easier to find on adolescents.
Magnetic resonance imaging can be used to assess the degree of the tendon retraction and integrity of the surrounding bony structure. Ultrasonography offers the advantage of zero radiation and is relatively inexpensive. Besides, sonography allows a dynamic assessment, which can be employed to assess the reciprocal movement the biceps femoris tendon against the surrounding soft tissues (Figure 1). Color or power Doppler ultrasound can be used to assess intra-tendinous/muscular hypervascularity, which is indicative of neovascularization or inflammation of the injured tendon. Comparison with the contralateral side may be valuable for diagnosis.
Isolated rupture of the biceps femoris tendon typically receives non-operative therapy. Cohen (2007) indicated that in the patients with biceps femoris tendon rupture with tendon retraction less than 2cm, most athletes can return to high-intensity sport (e.g., professional football) approximately six weeks after injury. The ruptured tendon gradually heals, allowing the affected knee return to full strength. The non-operative treatment includes rest, ice, non-steroid anti-inflammatory drugs, gentle stretching and therapeutic exercise for 4 to 6 weeks.
An acute biceps femoris tendon rupture may be associated with the injury of the semitendinosus and semimembranosus muscles. If there is a significant tendon retraction (> 5 cm), a surgical repair is usually needed.
Surgical repair of the ruptured biceps femoris tendon includes transverse incision over the gluteal crease, exposing the ruptured tendon, protection of the sciatic nerve, mobilization of the ruptured tendon and then reattaching it to the ischial tuberosity.
Most cases recover well after a non-operative treatment or a timely repair. But no specific guidelines address when should be treated surgically. Several case studies suggest that a complete biceps femoris tendon rupture should undergo surgical treatment.
The differential diagnosis includes:
Clinicians should be mindful that not all posterior thigh pain derives from the biceps femoris tendon injury. Besides, the biceps femoris tendon injury often occurs with an injury of the entire hamstring complex.
The prognosis of the biceps femoris tendon injury is good if the injury receives prompt and appropriate diagnosis and treatment. Most athletes return to professional sports after treatment.
The education should be given to the public as more and more people participate in high-intensity exercises. The health-care providers should offer the best practice according to evidence-based medicine.
An interprofessional approach for biceps femoris tendon rupture is recommended. Biceps femoris tendon rupture is relatively common among young athletes and the physically-active population. Many patients visit the emergency department or the primary care provider once they have an injury. Hence, these professionals need to know about the diagnosis and management about the disorder. The key to prevent these injuries is education about the importance of warmup and stretching before exercise. For most patients, the prognosis is good. The non-operative treatment usually provides optimal symptom relief and functional recovery. The indication for surgical intervention remains uncertain.