Popliteal (Baker’s) Cysts in the Setting of Primary Knee Arthroplasty

Abstract

Background:

Popliteal (Baker’s) Cysts are rare complications of knee arthroplasty. Enlargement, irritation, or rupture of the cyst can lead to significant pain, tightness, and tenderness. The literature regarding popliteal cysts occurring following knee arthroplasty is limited and does not report prevalence, natural history, and treatment of popliteal cyst in the setting of knee arthroplasty.

Methods:

Following Institutional Review Board approval, 2,025 primary total and partial knee arthroplasties by four surgeons at one institution from 2011-2016 were reviewed for occurrence of popliteal cysts. Twelve cases occurring after arthroplasty were identified, including four unicompartmental knee arthroplasties and eight total knee arthroplasties. Demographic data were evaluated and symptoms, time of onset following arthroplasty, attempted treatment strategies, and success or failure of attempted treatments or interventions were recorded.

Results:

The mean age of patients that presented with a popliteal cyst was 63.6 years old (range = 45 – 78 years). There were 5 males and 7 females. The mean BMI was 26.32 (range = 19.0 – 35.0). In 2,205 primary knee arthroplasties performed from 2011-2016 (including 175 partial and 1850 total), the prevalence of popliteal cysts following surgery was 0.6% (n=12). All popliteal cysts were discovered between six weeks and two years following surgery, with the majority occurring during the first year. Twenty-five percent (3/12) of patients presented with minimal symptoms. These were managed expectantly. Seventy-five percent (9/12) were symptomatic. One patient had only a diagnostic ultrasound, two patients underwent ultrasound-guided aspiration and steroid injection, three underwent simple aspiration. Two underwent surgical excision. One cyst ruptured. All cases went on to symptomatic resolution.

There was no association with diabetes, smoking, or body mass index. A disproportionately high number (25% or 4/12) occurred in partial knee arthroplasty.

Conclusion:

While popliteal cysts following primary total knee arthroplasty are rare, they can become a persistent and even disabling problem for arthroplasty patients. Given the lack of formalized recommendations in the existing literature, we propose a treatment algorithm that has been successful in our clinic, including observation initially, ultrasound-guided injection/aspiration if symptomatic, and surgical excision as a last resort.

Level of Evidence:

Level IV

Keywords:

total knee arthroplasty, baker’s cyst, popliteal cyst

Introduction

Popliteal (Baker’s) cysts represent an enlargement of the popliteal bursa or an outpouching of the synovial tissue, most commonly through the posterior wall of the knee joint capsule¹. They are typically secondary to joint injury or degenerative or auto-inflammatory disease and may result from the overproduction of synovial fluid. In the native knee, popliteal cysts often develop due to underlying knee pathology including osteoarthritis, rheumatoid arthritis, and meniscal tears².

Popliteal cysts, when asymptomatic, are usually found incidentally. However, they have the potential to become symptomatic, appearing as palpable swellings in the posterior knee that may mimic other pathologies. While there exists a substantial body of literature concerning popliteal cysts in the native knee, discussion of popliteal cysts following knee arthroplasty is limited to a few case reports^3-10. Though popliteal cysts are an infrequently reported complication of a knee arthroplasty, it is evident that patients develop popliteal cysts at an appreciable rate following knee arthroplasty. Popliteal cysts that occur following knee arthroplasty should not be confused with preexistent popliteal cysts that fail to resolve following knee arthroplasty, which remain symptomatic in 31% of patients and resolve only 15% of the time¹¹. Among other causes of knee pain in the setting of knee arthroplasty, rupture or enlargement of a popliteal cyst can lead to acute calf pain and tightness, tenderness, or erythema¹⁰. Rarely, peripheral nerve symptoms can occur as a result of tibial nerve compression¹². Several treatment methods for popliteal cysts in the setting of knee arthroplasty are described, including percutaneous aspiration and/ or injection, arthroplasty revision, as well as a two-stage operation including arthroplasty revision followed by complete resection of the cyst.

The etiology, incidence, natural history, and role for treatment of popliteal cysts following knee arthroplasty remain unclear. The purpose of this study is to elucidate the natural history popliteal cysts in the setting of knee arthroplasty and propose a treatment algorithm based upon clinical outcomes.

Materials and Methods

Following Institutional Review Board approval, 2,025 primary total and partial knee arthroplasties by four surgeons at one institution from 2011-2016 were reviewed for occurrence of popliteal cysts. Twelve cases occurring after arthroplasty were identified, including four unicompartmental knee arthroplasties and eight total knee arthroplasties. An additional seven cases were identified that presented prior to knee arthroplasty. Demographic data, including age, gender, body mass index (BMI), laterality, smoking status, and presence or absence of diabetes were noted. Clinical notes were reviewed to determine the symptomatology of popliteal cysts, time of onset following arthroplasty, attempted treatment strategies, and success or failure of attempted treatments or interventions. Prevalence was estimated by dividing new presentations by the total number of knee arthroplasties performed over the study period.

Results

The mean age of patients that presented with a popliteal cyst was 63.6 years old (range = 45 – 78 years). There were 5 males and 7 females. The mean BMI was 26.32 (range = 19.0 – 35.0). In 2,205 primary knee arthroplasties performed from 2011-2016 (including 175 partial and 1850 total), the prevalence of popliteal cysts following surgery was 0.6% (n=12). All popliteal cysts were discovered between six weeks and two years following surgery, with the majority occurring during the first year. Twenty-five percent (3/12) of patients presented with minimal symptoms or had popliteal cysts that were incidentally noted on exam. These either resolved with expectant management including physical therapy or remained asymptomatic without further intervention. Seventy-five percent (9/12) of patients with a popliteal cyst presented with significant swelling and pain in the posterior popliteal fossa. One patient had only a diagnostic ultrasound, two patients underwent ultrasound-guided aspiration and steroid injection, and three underwent simple aspiration. One patient was noted to have pigmented villonodular synovitis in addition to a popliteal cyst and underwent cyst excision, and another patient had an arthroscopic synovectomy. An additional patient became symptomatic when a popliteal cyst ruptured, and received a steroid injection. All cases went on to symptomatic resolution.

There was no association with diabetes, smoking, or body mass index. A disproportionately high number (25% or 4/12) occurred in partial knee arthroplasty. An additional seven Baker’s cysts were detected pre-operatively, all of which resolved or remained asymptomatic following primary knee arthroplasty.

Discussion

Popliteal cysts are an infrequently reported complication of primary knee arthroplasty. In our series, they occur rarely in 0.6% of knee arthroplasties and generally become symptomatic and evident during the first post-operative year. Several treatment strategies for symptomatic popliteal cysts in the native knee have previously been proposed. Conservative management is often the first strategy attempted, followed by aspiration and/or injection, with or without ultrasound^13,14. Surgical treatment options include correction of the intra articular knee pathology¹⁵, closure of the communication between the cyst and the articular cavity to eliminate flow of synovial fluid¹⁶, expansion of the communication between the cyst and cavity to eliminate unidirectional flow of synovial fluid^2,16-19. and removal of the cyst wall^20,21. Existing literature discussing treatment of popliteal cysts that result following a total knee arthroplasties is limited to case reports. In two studies, dissecting popliteal cysts were reported as the presenting symptom of a malfunctioning total knee arthroplasty. In this series, the cysts resolved with revision of the TKA and did not require further treatment^6,10.

In our series, several different treatment strategies were employed. All were eventually successful in alleviating symptoms caused by popliteal cysts. In cases that did not resolve with expectant management or observation, ultrasound-guided aspiration and/or injection provides similar results to its performance in the native knee^13,14. Based on our experience, we propose a treatment algorithm that has been successfully utilized in our clinic for partial and total knee arthroplasty patients. For initial management of a symptomatic popliteal cysts we recommend observation and expectant management. If observation fails or if the cysts remain persistently symptomatic, ultrasound-guided aspiration and steroid injection is a safe and viable treatment strategy. Lastly, surgical excision of the Bakers cyst is a treatment option that is effective, but that should be used as a last resort due to the invasive nature of the procedure.

This study has several limitations. It is possible that this study underreports the prevalence among our study population. Current procedural terminology codes were used to locate charts with popliteal cysts. Additionally, it is possible that not all asymptomatic popliteal cysts were detected on exam. The investigation is limited by its small number of patients treated. Finally, it is possible that some of our reported popliteal cysts were simply never noticed pre-operatively and did not in fact occur initially in the post-operative knee.

While popliteal cysts following a primary total knee arthroplasty are rare, they should be recognized as a potential cause of pain and dysfunction with an expected rate of occurrence, and should be treated in a systematic way to provide symptomatic relief.