Popliteus Muscle

Original Editors - Hardik Bhatt as part of the Vrije Universiteit Brussel Evidence-based Practice Project

Top Contributors - Hardik Bhatt, Saumya Srivastava, Kim Jackson, Mariam Hashem, Rachael Lowe, Admin, Oyemi Sillo, Joao Costa, Yvonne Yap, Lucinda hampton and Shreya Pavaskar

Description

Popliteus

The Popliteus is a small, thin, flat, triangular shaped muscle of the lower leg. It is a deep muscle of the knee joint which forms the floor of the popliteus fossa. It also forms the lateral musculature of the knee joint, along with the iliotibial band.It is the only muscle in the posterior compartment of the lower leg (which also includes tibialis posterior, flexor digitorum longus, and flexor hallucis longus) which is mono-articular and does not influence the ankle joint.

It is one of the main posterolateral stabilisers of the knee joint, causing rotation of the knee medially and laterally, thereby being involved in both the closed chain phase and open chain phase of the gait cycle.

Origin

The muscle fibres originate from the lateral condyle of the femur and the posterior horn of the lateral meniscus, via strong tendon called the popliteus tendon. Cadaveric dissections have also shown fibres originating from the styloid portion of the fibular head, which then run obliquely blending with the main muscular structure.

From there it runs inferiorly and mediolaterally towards the Tibia. It courses diagonally across the posterior upper tibia and a portion of the joint capsule, to lie as the deepest muscle of the posterior knee region. It's tendon pierces the joint capsule but does not enter the synovium and is crossed by the arcuate ligament, the lateral collateral ligament and the tendon of biceps femoris ( these 3 structures, along with the popliteus and other structures form the posterolateral corner (PCL) of the knee).

The popliteus bursa, which is usually an extension of the synovial membrane, separates it from the lateral femoral condyle. Although the popliteus muscle has extra articular areas, it is a capsular structure separating the lateral meniscus of the knee from the lateral collateral ligament. An additional head of popliteus may arise from the sesamoid bone in the lateral head of the gastrocnemius muscle. Rarely an additional inconstant muscle called the popliteus minor is seen which arises from the femur on the inner side of the plantaris muscle and inserts into the posterior ligament of the knee-joint.

Insertion

It is inserted on the tibia just proximal to the soleal line but below the tibial condyles.

Nerve

The popliteus muscle is supplied by the tibial nerve, from spinal nerve roots L5 through S1, with approx 2 to 3 parallel tibial nerve branches. The entry point of the nerve is the lateral distal margin of the muscle, which is found inferior to the fibular head, and then splits into anterior, medial, and lateral distributions throughout the muscle.

Artery

The popliteus muscle is supplied by 2 arteries -

• the medial inferior genicular branch of the popliteal artery
• the muscular branch of the posterior tibial artery.

Function

The popliteus muscle assists in knee flexion and its function is decided according to position of the lower extremity, i.e. weight bearing or non weight bearing, as it is a primary internal rotator of the tibia in a non weight bearing position.

1. In open chain kinematics, it rotates tibia medially
2. In close chain kinematics, it laterally rotates femur in the initial phase of knee flexion.
3. With extension during weight bearing, 'locking' of the knee occurs. In this state, the femur medially rotates on the tibia, allowing for full extension without muscular expenditure. To 'unlock' the knee, the popliteus muscle needs to contract, causing flexion and lateral rotation of the femur on the tibia, thereby giving the muscle the term - 'key' to the locked knee.
4. During knee flexion the popliteus muscle retracts the lateral meniscus posteriorly to avoid being entrapped between the femur and tibia.
5. In knee stability - as the popliteus tendon is frequently found to be connected to the lateral capsule, this gives the muscle a possible role in postero-lateral stability of the knee. Krudwig et al consider the Popliteus as an important structure resisting excessive external tibial rotation and maintaining the neutral tibial rotation, even if all other postero-lateral ligaments were severed.

Clinical relevance

It is commonly involved in the posterolateral (PCL) corner injuries of the knee, which occur secondary to -

1. varus force applied to a flexed knee.
2. direct blow to the knee (from medial to lateral).
3. varus/hyperextension ( both from contact and non contact injuries)
4. dislocation of knee.

What ever the mechanism of injury to the PCL corner (from the above), urgent evaluation of the patient's neurovascular status of the limb is performed

Further to trauma, poor movement patterns and posture can often weigh heavily on the popliteus muscle leaving it prone too weakness and injury. Iatrogenic injury to this muscle is common, which can lead to poor functional prognosis and hence becomes vital to be addressed esp following knee reconstruction surgery. Anatomical smaller knees also need extra attention as the risk of popliteal injury is increased.

Any injury to the knee will likely involve the popliteus muscle.

If the hamstrings towards the outer thigh are stronger than the inner hamstrings, the popliteus muscle will be weaker. Excessive pronation or collapse of the inner foot when walking or running will stress the popliteus in the opposite direction.

Different EMG studied showed that popliteus muscle activity increases with knee extension and downhill walking so it is playing role to control hyperextension of knee. The referred pain pattern in case of trigger point of popliteus muscle is back of knee.

More about popliteus muscle pathology on physiopedia Popliteus strain,Popliteus Tendinitis

Assessment

Due to deep location isolated injury to popliteus muscle is rare but it may be associated with other knee injuries such as ACL injury, meniscus injuries.

There are general symptoms of muscle injury like swelling, tenderness, oedema, bleeding, patient keeps leg (tibia) in lateral rotation during knee flexion..

Following should be checked to rule out popliteus muscle injury.

1. Tenderness;-.As many neurovascular structure lie over it only terminal portions of popliteus muscle can be palpated.Tenderness over proximal popliteus tendon checked in prone lying position while tenderness over posterolateral knee may be sign of biceps femoris tendon strain and lateral meniscus injury.
2. Garrick test In high sitting position where hip and knee both flexed to 90 degrees resisted external rotation of lower leg is checked. Pain during manoeuvre considered as positive test
3. Shoe removal manoeuvrePatient tries to remove contralateral shoe by internally rotating affected leg to reach heel of another leg. Pain during manoeuvre indicates injury to popliteus muscle.

As said earlier isolated injury to popliteus muscle is rare ,nn isolated acute rupture of the popliteus tendon was found in 2 of 2412 knee MRI studies. 

The popliteus muscle along with PCL (posterior cruciate ligament ) of knee stabilises femur over fixed tibia in stance phase specially when extra stability is needed like running downhill.So running downhill specially on banked surface and hyperpronation leads to popliteus muscle injury like tenosynivitis, tendinopathy, ruptute, strain.

Treatment

The treatment for popliteus muscle pathology same as per any soft tissue injury and muscle injury or tendinopathy. RICE Therapy OR PRICE Therapy (protection, rest, elevation, compression, elevation, and other anti-inflammatory drugs are given.

Physiotherapy treatment is on the line with other soft tissues and muscle injuries, mobility exercises, strengthening exercises, eccentric training and many more rehab protocols depending upon pathology, associated injuries and patients condition.

Related Pages

Popliteus Strain

Popliteus Tendinopathy