Keywords
biceps femoris - tear - isolated
Introduction
The biceps femoris forms an integral part of the posterior compartment of the thigh
and plays a pivotal role in knee flexion.[1] Distally the biceps femoris tendon forms part of the posterolateral corner structures
of the knee.[1] Injury to these structures is usually associated with rotational trauma. It is rare
to have an isolated distal biceps femoris tendon disruption as this injury is often
associated with other posterolateral corner structure injuries and intra-articular
pathology such as ACL tears.[2]
We present two cases of isolated complete biceps femoris tendon disruption proximal
to the fibular head insertion together with a review of the current literature.
Background
The biceps femoris tendon is an essential component of the posterolateral corner acting
as a dynamic stabilizer, while the lateral collateral ligament, along with the popliteus
tendon and popliteofibular ligament act as static stabilizers.[3] Altogether, they prevent varus and external rotation forces and posterior tibial
translation.[3]
The biceps femoris muscle is the strongest of the hamstring complex. It is composed
of a long and a short head. 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, while 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.[4] Because the short and long heads of the biceps femoris muscle are innervated by
the peroneal and tibial components of the sciatic nerve, respectively, this may result
in an increased risk of sports injury as a result of uncoordinated muscle contractions.
Distally, the biceps femoris tendon inserts predominantly onto the head of the fibula
and has two tendinous insertions. A direct arm that attaches to the posterolateral
edge of the fibular head and a reflected arm blends into the iliotibial tract. Also,
crossing lateral to the lateral collateral ligament is the anterior arm[1] ([Fig. 1]). The biceps femoris is the strongest hamstring involved in knee flexion and also
contributing to external rotation. It plays an important role in varus angulation,
controlling tibial internal rotation. In collaboration with the medial hamstrings,
it also prevents excessive tibiofemoral anterior translation.[6]
Fig. 1 Schematic showing the posterolateral corner structures POP FIB, popliteofibular ligament;
LCL, lateral collateral ligament; Lateral Gastroc, lateral gastrocnemius.
We present two cases of isolated biceps femoris tendon injury immediately proximal
to the fibular attachment.
Case 1
A 60-year-old gentleman presented with acute onset knee pain following an attempt
at kicking a football. He reported a snapping sound followed by sudden onset swelling.
On examination, there was tenderness to palpation over the fibular head and associated
overlying bruising and swelling. As a general rule, the clinical examination should
include assessment of ligamentous stability to anterior and posterior drawer tests
as distal biceps injury rarely occurs in isolation. As the peroneal nerve is closely
related to the distal biceps, femoris a neurological examination should be performed
to exclude associated injury.[7]
An MRI was performed a week after the injury that demonstrated a full-thickness tear
of the biceps femoris just proximal to the fibular insertion with moderate soft tissue
edema and a small hematoma. A short distal stump of the biceps femoris tendon was
attached to the fibula head ([Fig. 2]). There was no bony avulsion of the fibular head. The rest of the posterolateral
corner was intact. The peroneal nerve was also preserved.
Fig. 2 Coronal (A) and axial (B) proton density fat-saturated images of the knee, demonstrating peritendinous edema
around the distal biceps femoris tendon with tear and some retraction of the tendon
proximally (image A, white arrow). A short distal stump of the biceps femoris tendon remains attached
to the fibula head (image B, white arrow).
Case 2
A 23-year-old gentleman presented to the clinic after a sudden knee flexion with external
rotation during a football game. On examination, the patient demonstrated tenderness
on palpation of the fibular head. This was exacerbated on resisted prone knee flexion,
particularly nearing a full extension.
An MRI performed within days after the injury demonstrated hematoma and edema in the
lateral aspect of the knee with a near full-thickness tear of the distal biceps femoris
tendon proximal to its insertion. A small distal tendon stump was noted. The lateral
collateral ligament and remaining posterolateral stabilizing structures and peroneal
nerve were also intact ([Figs. 3] and [4]).
Fig. 3 Axial (A) and coronal (B) proton density fat-saturated images of the knee, demonstrating hematoma and edema
in the lateral aspect of the knee. Intra-tendinous high signal intensity in keeping
with hemorrhage and edema in the torn biceps femoris tendon (white arrow: image A) and intact lateral collateral ligament (arrow: image B).
Fig. 4 Sagittal proton density fat-saturated, demonstrating normal anterior cruciate ligament.
Both our patients were treated conservatively with relatively good function. The functional
result following conservative treatment is reported in the literature as having a
better outcome than cases treated surgically.[8] Predisposing factors for isolated ruptures of the distal biceps femoris include
pre-existing tendinopathy.[9] In the cases we presented, there were no predisposing factors.
Discussion
Injuries to the distal biceps femoris tendon do not tend to occur in isolation. It
often occurs in conjunction with injury to the posterolateral corner components. Isolated
distal biceps femoris injuries are therefore rare and only a few cases are reported
in the literature.[1]
The biceps femoris is therefore often injured in conjunction with other posterolateral
corner structures. The main posterolateral corner structures include the lateral collateral
ligament, popliteus tendon complex, iliotibial band, fabellofibular ligament, and
the middle third of the lateral capsule and lateral meniscus.[5]
[6]
One of the main posterolateral corner structures, the lateral collateral ligament
protects the knee against excessive varus forces. It extends from the lateral femoral
epicondyle attaching to the anterior border of the fibular head.[6]
The popliteus tendon inserts onto the fibular head, anterior and distal to the lateral
collateral insertion. It is however a dynamic stabilizer, externally rotating the
knee during hyperflexion.
The iliotibial band also contributes to knee stability in varus and extension.[6] The lateral structures are stretched to their full potential during the stance phase
of the gait cycle during which the varus angulation of the limb reaches a maximum
during full extension of the knee.
The knee has 4 quadrants - anterolateral, anteromedial, posteromedial and posterolateral.
The most commonly injured quadrant is the anterolateral quadrant involving the anterior
fibers of the iliotibial band. The mechanism of action is usually a varus force with
internal rotation of the tibia. The posterolateral quadrant structures, namely the
lateral collateral ligament, biceps femoris, and popliteus tendon are usually involved
in varus and external rotation or sudden hyperextension.[8]
The main function of the posterolateral corner structures is to provide lateral stability
and protect the knee against excessive varus forces and external tibial rotation ([Table 1]). The following table illustrates the main components of the posterolateral corner
and their contribution to stability.
Table 1
Function of different components of posterolateral corner
|
Structure
|
Action
|
Function
|
|
Biceps femoris
|
External rotation and flexion
|
Dynamic stabilizer
|
|
Lateral collateral ligament
|
Prevents excessive varus force
|
Static stabilizer
|
|
Popliteus
|
Externally rotating the knee during hyperflexion
|
Dynamic stabilizer
|
After a review of the literature and the presentation of our cases, we propose that
to produce an isolated tear of the biceps femoris tendon, the mechanism of injury
would have to be a lack of varus force and would therefore involve eccentric contraction
of the biceps muscle during hyperextension. What makes the biceps femoris unique when
compared with the other posterolateral corner structures is that its long head spans
across two major joints, the hip joint and the knee joint. The action of forcible
hip flexion and simultaneous knee hyperextension has been shown to place a high strain
on the distal biceps femoris rendering it at high risk of injury. A review of the
literature by Knapik et al suggests that the distal biceps is more susceptible to
eccentric loading than the tendinous insertion in the fibular head.[9]
A review of the literature by Kusma et al[10] shows that the most common mechanism of injury leading to isolated biceps femoris
is extension and hyperextension. This motion was present in both our cases as both
involved the patient's kicking, therefore flexion followed by sudden extension/hyperextension.
However, resisted flexion may also result in increased tension load on the tendon
and may be caused by running or kicking backward.[9] The lack of varus loading in our cases suggests that the absence of this is paramount
in protecting the lateral collateral ligament complex in particular.
Conclusion
In summary, we propose that to tear solely the distal biceps femoris tendon, the forces
should be lacking a varus component and would therefore involve eccentric contraction
of the biceps muscle during hyperextension. Dedicated biomechanical studies would
be needed to confirm the proposed mechanism of injury.
