Bone Cysts and Osteolysis in Ankle Replacement

Background: Total ankle replacements (TARs) have higher rates of osteolysis than hip or knee replacements. It is unclear whether this is a pathologic immunologic process in response to wear debris, or expansion of pre-existing osteoarthritic bone cysts. We aimed to determine the incidence of bone cysts in patients with end-stage ankle arthritis prior to surgery and review the literature on bone cysts and osteolysis in relation to TAR. Methods: This is a descriptive/prevalence study in which all patients with end-stage ankle arthritis underwent plain radiographic imaging and computed tomographic (CT) scans prior to TAR surgery. Their imaging was assessed for the presence of cysts, measured on sagittal, axial, and coronal slices of the CT scan at the widest diameter. All cysts that would be removed as a result of the bone resection for the implant were excluded using digital analysis software. We assessed 120 consecutive patients with mean age of 63.4 years. Results: Seventeen patients (14%) did not have any bone cysts based on CT images. Ten patients (8%) had cysts that would have been completely removed by surgery, leaving 93 patients for analysis (78%). In 60% of these cases, the cysts were not seen on the plain radiographs. In 39 patients (33%), the cysts were greater than 5 mm in size. The medial (36%) and lateral malleoli (33%) were the most common location for the cysts (mean diameter 4.6±2.0 and 4.2±2.3 mm, respectively). Conclusion: Bone cysts outside of the resection margins for a TAR were present in 78% of patients with ankle arthritis prior to undergoing surgery. In 30% of cases, cysts were greater than 5 mm in size. In 60% of cases, the cysts were not seen on plain radiographs. Preoperative 3-dimensional imaging can provide a foundation to observe and quantify cyst presence, expansion, and time of onset in the postoperative setting. Level of Evidence: Level IIc, diagnostic/prevalence study.