Distal biceps femoris tendon

Last revised by Yahya Baba on 16 Oct 2021

The distal biceps femoris tendon is a complex musculotendinous unit that connects the long and short head of the biceps femoris muscle to the fibular head, the superolateral portion of the lateral tibial condyle and the lateral and anterior fascia of the lower leg.

Both heads of the distal biceps femoris musculotendinous unit are composed of two tendinous components the direct and anterior arms originating from the short head and long head biceps femoris muscle bellies which are partially intertwined or coalescent 1-3. The average length of the long head and short head biceps femoris tendons from the myotendinous junction to the fibular head has been quoted approximately 9 cm and 5 cm with 20% of the population showing significantly shorter variants 4.

Besides the distal biceps femoris tendon features several fascial components including 1-3:

  • connections to the iliotibial tract from both heads
  • capsular arm originating from the short head
  • fascial attachments to the lateral and anterior aponeuroses

The function of the distal biceps femoris tendon unit is the transmission of force generated by the biceps femoris muscle to the lower leg, in addition, it acts as a dynamic stabilizer of the knee and restraint to combined anterolateral-anteromedial rotatory instability 1.

Tendinous attachments or footprints of the distal biceps femoris tendon include 1-3:

  • posterolateral fibular head: consisting of fibers from both the long head and the short head (direct arms) 2
  • anterolateral fibular head: consisting predominantly of distal long head tendon fibers (anterior arm)
  • anteromedial fibular head: consisting predominantly of fibers from the short head (direct arm)
  • lateral tibial condyle insertion: posterior to Gerdy tubercle and distal to the insertion of the anterolateral ligament, variable fiber composition from both heads (anterior arm)

The distal biceps femoris tendon is literally split by the distal portion of the lateral collateral ligament of the knee which inserts at the lateral border of the fibular head surrounded by the distal biceps femoris tendon footprints 1,2. The anterior arm of the long head crosses the fibular collateral ligament laterally separated from it by a small biceps femoris bursa 1.

The anterior arm of the distal biceps femoris tendon inserting onto the lateral tibial condyle is superficial and in close relationship to the superior bundle of the anterior tibiofibular ligament and might blend with it 1,2.

There is a close relationship between the fibular insertion of the distal biceps femoris tendon and the common peroneal nerve 4.

There are variations in the length of the distal biceps femoris tendons of both short and long heads with shorter distances between the myotendinous units and the fibular head in up to 20% of the population, thus creating an intermuscular tunnel between the more distal and posterior extension of the short head biceps femoris muscle and the lateral gastrocnemius muscle. This tunnel is considered a potential entrapment site and a risk factor for common peroneal nerve entrapment 4,5.

The direct and anterior arm of the distal biceps femoris tendon can be distinguished in about 70% of cases 3, However, several slips can appear as one unit on MRI and merge with the distal lateral collateral ligament.

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