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

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.