BICEPS FEMORIS

BICEPS FEMORIS. The biceps femoris is a fusiform muscle that contains 2 heads, long and short. The long head of the biceps femoris muscle originates from the ischial tuberosity and is part of the common hamstring origin. It is innervated by the tibial division of the sciatic nerve. The short head of the biceps femoris muscle originates just medial to the linea aspera of the distal femur, and is innervated by the peroneal division of the sciatic nerve. Both heads flex the leg at the knee joint and laterally rotate the leg when it is flexed.7 The long head of the biceps has 5 major insertions at the knee. It divides into 2 tendinous components called the direct and anterior arms, and 3 fascial components called the reflected arm and, anterior and lateral, aponeurotic expansions. The most important of these structures are the direct and anterior arms, and the lateral aponeurotic expansion. The direct arm inserts onto the lateral aspect to the fibular styloid. 

The anterior arm courses lateral to the fibular collateral ligament (FCL) and inserts onto the lateral tibial plateau.6 A small biceps femoris bursa separates this arm from the FCL.8 The lateral aponeurotic expansion connects the long and short heads of the biceps femoris to the posterolateral aspect of the FCL.5,6 The short head of the biceps femoris muscle divides into 6 components. These components consist of direct,
capsular, and anterior tendinous arms, along with 3 nontendinous insertions. The 3 nontendinous attachments
insertions include a muscular insertion onto the long head of the biceps femoris tendon, a lateral aponeurotic expansion attaching both the short and long heads to the postero-medial aspect of the FCL, and a third insertion, just lateral to the capsular arm, forming a confluence with the capsulo-osseous layer of the iliotibial
tract. This confluence with the capsulo-osseous layer forms an intimate attachment between the fascia of the
iliotibial band and the biceps femoris5,6 (Fig. 2).

The most important insertions of the short head of the biceps femoris are the 3 tendinous arms. They are most easily identified at the level of the fibular head. The direct arm is the least important of the 3 and attaches to the posterolateral aspect of the fibular styloid. 

FIGURE 2. Retraction of the superficial layers of the iliotibial tract reveals the capsulo-osseous layer (COITT), short head of the biceps tendon (SHB), short head of biceps-capsuloosseous layer confluens (CON), long head of biceps tendon
(LHB), fibular collateral ligament (FCL), lateral capsular incision (Cap Inc), and iliotibial tract insertion (I). Reprinted with
permission.16

The capsular arm extends from the main tendon of the short head of the biceps to the posterolateral aspect of the capsule, and inserts just lateral to the tip of the fibular styloid. It provides a stout attachment between the posterolateral capsule, lateral gastrocnemius tendon, and capsulo-osseous layer of the iliotibial band. The most distal edge of the capsular arm is the fabellofibular ligament.5,6 The anterior arm passes medial to the FCL and inserts with the meniscotibial portion of the midthird lateral capsular ligament onto the proximal-lateral tibia. In association with ACL injuries, the anterior arm of the short head of the biceps, along with the meniscotibial component of the midthird lateral capsular ligament, is frequently found to be avulsed off the anterolateral aspect of the tibia. This may occur with a small bony avulsion called a Segond fracture4 (Fig. 3). The peroneal nerve lies deep and posterior to the biceps femoris tendon, and should be the first structure identified during dissection of the PLC. It is located approximately 1.5 to 2 cm distal to the fibular styloid as it travels along the lateral aspect of the fibular head.7