Popliteus Tendinitis

Popliteus Tendinitis arises secondary to other biomechanical changes in the knee or lower extremity or secondary to repetitive stress. The popliteus muscle is often injured in conjunction with other knee injuries.

Popliteus inflammation manifests itself similarly to IT band friction syndrome except that individuals suffering from popliteus tendinitis describe pain in the proximal portion of the tendon, immediately posterior to the LCL. As with IT band friction syndrome, patients who excessively pronate during gait are predisposed to this condition, which worsens when running downhill.

Popliteus tendinitis is common in runners who used canted surfaces, which produce oblique lateral rotary stresses to the knee, or who run downhill frequently.

See Also: Popliteus Muscle

Popliteus Anatomy & Function

The popliteus originates from the lateral femoral condyle near the LCL. The muscle has several attachments, including:

1. the lateral aspect of the lateral femoral condyle,
2. the posteriormedial aspect of the head of the fibula
3. the posterior horn of the lateral meniscus.
4. The larger base of this triangular muscle inserts obliquely into the posterosuperior part of the tibia above the soleal line.

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The muscle has several important functions including:

1. the reinforcement of the posterior third of the lateral capsular ligament
2. the unlocking of the knee during flexion from terminal knee extension. It performs this task by internally rotating the tibia on the femur (a good example of an arcuvial muscle),
3. preventing impingement of the posterior horn of the lateral meniscus by drawing it posteriorly,
4. with the PCL, preventing a posterior glide of the tibia.

See Also: IT Band Friction Syndrome

Since knee joint injury frequently involves some component of transverse-plane rotation and the popliteus muscle has been described as an important, primary, dynamic, transverse-plane, rotatory knee joint stabilizer, an understanding of its function in relation to other posterolateral knee joint structures is important.

Attached to the popliteus tendon is the popliteofibular ligament, which forms a strong attachment between the popliteal tendon and the fibula. This ligament adds to posterolateral stability.

A medial portion of the popliteus penetrates the joint, becoming intracapsular with the lateral meniscus. This part of the popliteus tendon is pain sensitive, and an injury here can often mimic a meniscal injury on the lateral aspect of the joint line. Differentiation between these two lesions can be elucidated with the reproduction of pain with resisted flexion in an extended and externally rotated position of the tibia if the popliteus is involved.

Because the popliteus helps retract the lateral meniscus during knee flexion, inhibition or dysfunction of this muscle may alter the biomechanics of the lateral meniscus, possibly resulting in an increased load on the cartilage.

See Also: Knee Muscles Anatomy

Popliteus Tendinitis Symptoms

The patient presents with insidious pain in the popliteal fossa radiating along the length of the popliteus tendon posterior to the LCL.

The Popliteus Tendinitis typically manifests as point tenderness in the lateral aspect of the knee corresponding to the popliteus insertion site, which is exacerbated with eccentric loading.

In chronic conditions, swelling may be noted along the lateral joint line.

Palpation of the popliteus tendon is easiest when the foot of the involved leg is placed on the uninvolved knee in the figure- 4 position, a position that may produce pain in and of itself.

Imaging

MRI can be used to rule out rupture of the popliteus tendon. Thickening of the tendon may be identified on MR images.

Differential Diagnosis

Differential Diagnosis of Popliteus Tendinitis include:

1. Biceps femoris tendinopathy,
2. IT band friction syndrome,
3. gastrocnemius tear (lateral head),
4. lateral meniscus tear,
5. LCL sprain,
6. PCL sprain,
7. posterolateral corner instability.

Popliteus Tendinitis Treatment

As with other tendinous conditions, Popliteus Tendinitis Treatments include:

1. correction of abnormal biomechanics,
2. the use of nonsteroidal anti-inflammatory agents,
3. the use of local modalities to decrease inflammation.
4. Improving strength and endurance of the proximal hip musculature is often necessary.

References

1. Nyland J, Lachman N, Kocabey Y, Brosky J, Altun R, Caborn D. Anatomy, function, and rehabilitation of the popliteus musculotendinous complex. J Orthop Sports Phys Ther. 2005 Mar;35(3):165-79. doi: 10.2519/jospt.2005.35.3.165. PMID: 15839310.
2. Harner, CD, et al: The effects of a popliteus muscle load on in situ forces in the posterior cruciate ligament and on knee kinematics: a human cadaveric study. Am J Sports Med, 26:669, 1998.
3. Chuncharunee, A, Chanthong, P, and Lucksanasombool, P: The patterns of attachments of the popliteus muscle: form and function. Med Hypotheses, 78:221, 2012.
4. Quinlan, JF, et al: Isolated popliteus rupture at the musculo-tendinous junction. J Knee Surg, 24:137, 2011.
5. Schinhan, M, et al: Electromyographic study of the popliteus muscle in the dynamic stabilization of the posterolateral corner structures of the knee. Am J Sports Med, 39:173, 2011.
6. Weresh, MJ, et al: Popliteus function in ACL-deficient patients. Scand J Med Sci Sports, 7:14, 1997.