Forensic analysis of retrieved score knees: A failure of fixation?

Abstract

Background: The SCORE total knee arthroplasty (Amplitude, France) has a deep trochlear groove designed to reduce polyethylene wear, risk of loosening, and patellofemoral complications. In 2014, the AOANJRR reported a higher revision rate when implanted cementless compared to cemented. The aim of the study was to forensically examine retrieved SCORE TKA’s and determine failure modes. Methods: Retrieval analysis was performed at the Centre of Implant Technology and Retrieval Analysis (Royal Perth Hospital). 27 SCORE primary total knee implants from 26 patients requiring revision were forensically analysed for failure mode. Macroscopic examination and quantitative assessment of tissue ingrowth was combined with clinical record findings and radiographic analysis. Statistical analysis was performed. Results: On average the patients were relatively young (mean age 65.5 years) and obese (mean BMI=32.5) with almost equal numbers of male and females and a mean short time of service (2.4 years). The majority of the implants were cementless and without patella resurfacing. Secondary analysis of patient demographics found no difference in age, BMI, gender and activity levels between the patients with loose femoral components and the population as a whole. Radiological analysis revealed an overall satisfactory alignment using the Knee Society TKA Roentgenographic Evaluation and Scoring System. Although six uncemented femoral components (22%) were found grossly loose at time of revision, only one was identified pre-operatively from plain x-rays. Macroscopic analysis confirmed coating delamination and deposition of fine metallic debris on tissue attached to components. Polyethylene inserts had a degree of wear greater than expected with embedded metal debris. Histomorphometric analysis revealed poor bony ingrowth on both uncemented femoral and tibial components. Conclusions: Retrieval analysis revealed a higher than expected rate of cementless femoral loosening in SCORE TKAs. Clinically, surgeons should be aware of patients with this implant presenting with pain that femoral loosening cannot be excluded as a diagnosis by imaging.