August 22, 2021
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Popliteus Tendinopathy: A Poorly Understood Cause of Knee Pain

Popliteus Tendinopathy, sometimes referred to as popliteal tendonitis or tenosynovitis, is a rare and poorly described cause of knee pain. It was first described by Barnes in 1995[1]Barnes CL, Scott RD. Popliteus tendon dysfunction following total knee arthroplasty. J Arthroplasty. 1995 Aug;10(4):543-5..

Image1. Politeus tendon anatomy[2]https://www.sportsinjurybulletin.com/popliteus-assessment-and-rehabilitation/.

Case Vignette

You are evaluating a 49 year old male in your clinic who recently underwent a total knee arthroplasty out of state. He has pain in his postoperative knee in the posterolateral space. Garrick test is positive and you suspect popliteal tendinopathy. Which of the following correctly describes the Garrick Test?

A) Patient seated, hip and knee flexed to 90°, active external rotation

B) Patient seated, hip and knee flexed to 45°, active Internal rotation

C) Patient standing, hip and knee flexed to 90°, active external rotation

D) Patient seated, hip and knee flexed to 90°, active Internal rotation

Introduction

The popliteus muscle ‘unlocks’ the knee joint and stabilizes the knee. In an open chain, popliteus serves to internally rotate the tibia concentrically on the femur, and in closed chain, acts eccentrically during external rotation of the femur on the tibia. It originates on the lateral condyle of the femur, with some fibers extending into the lateral meniscus and inserts on the posteromedial surface of the tibia.
Image 2. Total knee replacement (left) and postoperative ultrasound (right). This longitudinal view shows an echogenic osteophyte (red arrow) impinging on the popliteus tendon (white arrow). The prosthesis is seen deep to this (yellow arrow)[3]Geannette, Christian, et al. “Ultrasound diagnosis of osteophytic impingement of the popliteus tendon after total knee replacement.” Journal of Ultrasound in Medicine 37.9 (2018): … Continue reading.

Pathophysiology

The pathophysiology is poorly understood and the disease is often unrecognized due to its relatively deep location and close proximity to adjacent structures[4]Garrick J, Webb D. Sports Injuries: Diagnosis and Management. Philadelphia, PA: WB Saunders Co; 1990.. It has been associated with the following moderate or greater knee trauma, minor twisting injuries, tendon instability, impingement against osteophytes, impingement following total knee arthroplasty[5]Barnes CL, Scott RD. Popliteus tendon dysfunction following total knee arthroplasty. J Arthroplasty 1995; 10:543–545., calcific tendinopathy[6]Tibrewal SB. Acute calcific tendinitis of the popliteus tendon: an unusual site and clinical syndrome. Ann R Coll Surg Engl 2002; 84:338–341., and overuse injury in runners[7]Cooper DE. Snapping popliteus tendon syndrome: a cause of mechanical knee popping in athletes. Am J Sports Med 1999; 27:671–674.. Among runners, hills and banked surfaces appear to be a risk factor. In pediatrics, injuries tend to involve avulsion fractures of the popliteus tendon from the femur.

Presentation

Because of the widely varied and poorly understood etiologies, patients may report acute or chronic presentations with or without trauma. The pain is typically posterolateral and worse with running, walking and stairs. Popping may be reported during flexion and extension. There may be tenderness at the lateral epicondyle of the femur wrapping around posteriorly into the muscle. The ‘Garrick test’ is a provocative test which can be used to help with diagnosis. The test is performed with the patient seated, hip and knee are both flexed to 90°. The patient actively externally rotates the lower leg and this is resisted by the examiner. A positive test is pain during the maneuver in the location of the popliteus muscle or tendon.

Diagnosis and Management

Evaluation should begin with standard radiographs, which are typically normal. MRI is likely the imaging modality with the highest diagnostic yield, although this is not definitively established in the literature. Potential findings include focal tendon enlargement, increased intratendinous or myotendinous signal, complete tendon rupture or avulsion from the femur. The role of US and CT are not clearly established.

Image 3. Long axis view of popliteus tendon corticosteroid injection with needle in plane[8]Smith, Jay, et al. “Sonographically guided popliteus tendon sheath injection: techniques and accuracy.” Journal of Ultrasound in Medicine 29.5 (2010): 775-782.

There are no clear, evidence based guidelines for management. Most cases can be managed nonoperatively, although it will depend on the underlying etiology. In addition to relative rest, elevation and ice therapy; physicians can recommend compression sleeve, physical therapy and NSAIDS. There are case reports of ultrasound guided corticosteroid injections. Surgery is indicated in recalcitrant cases, recurrent instability and posterolateral corner injuries. There are no clear rehabilitation or return to play guidelines.

Case Conclusion

Answer A. The ‘Garrick test’ is used to help identify the popliteus muscle as the cause of knee pain and is associated with total knee arthroplasty. It’s also very difficult to identify clinically. The test is performed by having the patient in a seated position with the hip and knee flexed to 90 degrees. The examiner then grasps the lower leg and asks the patient to externally rotate it against resistance. A positive test is pain during the maneuver in the posterolateral corner of the knee or along the distribution of the tendon.

Garrick J, Webb D. Sports Injuries: Diagnosis and Management. Philadelphia, PA: WB Saunders Co; 1990.

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