Pseudotumor following total hip arthroplasty: experience of a tertiary referral center and proposal of the new “PCS” classification system

Introduction: This study summarizes outcomes in treating pseudotumors of the hip at a tertiary referral center and introduces a classification system to aid treatment decisions and enhance communication among providers. Materials and methods: We collected data from 39 patients who underwent surgery for hip pseudotumor, analyzing implant failures based on patient history, revision reasons, bearing surface type, mass location and size, bone loss, revision type, and whether it was single- or two-stage. We introduce the PCS classification: 'P' for Pseudotumor (with 's' for symptomatic, 'e/I' for intra/extrapelvic location, and 'm' for high Chromium/Cobalt levels), 'C' for implant status, and 'S' for bone loss extent. In 37 patients, we evaluated Cohen's kappa coefficient to evaluate interobserver reliability. Results: Twenty (51.2%) patients were female, with a mean age of 71 years (range 36-89; σ 12.11); the mean follow-up duration was 54.43 months (range 12.2-128.3). The average size of the pseudotumor was 13.10 cm (range 3.3-37.2; σ 7.11) with 61.5% exhibiting extra-pelvic localization only. Bearing surfaces were MoM in 27 patients (69.2%). Single-stage revision surgery was performed in 87.1% of patients. There were 7 (17.9%) implant failures. No significant differences in failure rates were observed based on considered parameters. The agreement following Cohen's coefficient for the combined PCS classification was k = 0.43. Moderate to almost perfect agreement was obtained for parameter P and S, with k = 0.48 for parameter C. Conclusion: No correlation was found between failures and analyzed characteristics. Our classification assesses clinical scenarios and stratifies surgical complexity for indication purposes. While interobserver agreement varies with parameter C, it is consistent with parameters P and S.