Treatment of neuropathic unstable knee osteoarthritis by a condylar, rotating-hinge prosthesis with cementless pentagonal stem: a case series

INTRODUCTION AND IMPORTANCE: Total knee arthroplasty (TKA) in the neuropathic unstable knee (NUK) setting is classically a challenging orthopedic problem due to intraoperative technical difficulties and a higher frequency of periprosthetic complications. More recently, satisfactory results have been reported using improved constraints, stems and revision-type TKA components. The study aims to present long-term results of a small case series with NUK osteoarthritis reconstructed by a condylar, semi-constrained prosthesis with a polygonal, hydroxyapatite-coated (HA-coated) press-fit stem. CASE PRESENTATION: From 2009 through 2010, three knees in three patients with advanced NUK arthropathy underwent TKAs in our institution using the PENTA® prosthesis. The average age at surgery was 44 years (32–58). The patients were followed up for a mean period of 124 months (120–128). The etiology of NUK was determined to be poliomyelitis sequela in 2 cases and spinal cord injury in one case. Functional outcomes were assessed with Knee Society (KS) Knee and Function Scores, and radiological outcomes were evaluated with ISOLS radiographic implant scores. Patients were monitored for complications clinically and radiologically. CLINICAL DISCUSSION: KS knee scores improved from a mean of 12,3 (0–37) preoperatively to 71,3 (65–77) and KS function scores improved from a mean of 1,7 (0–5) preoperatively to 68,3 (55–80) at the latest follow-up. Radiological outcomes were excellent according to ISOLS scores, and no complications were observed. CONCLUSION: Although this is a small case series, the significant improvement in functional scores, excellent radiological outcome, and implant survival at the end of a long follow-up period warrants TKA with a semi-constrained hinged implant in the setting of NUK. PENTA® prosthesis offers a good choice of implant with its hydroxyapatite-coated, press-fit, pentagonal stem and precisely designed rotating hinge.