Clinical Results after Design Modification of Lospa Total Knee Arthroplasty System: Comparison between Posterior-Stabilized (PS) and PS Plus Types

Abstract

Background: Lospa posterior-stabilized (PS) Plus type is a modified version of Lospa PS, in which the polyethylene insert shape is modified to reinforce stability and prevent patella-post impingement compared to Lospa PS. However, studies comparing the clinical and radiographic results of the two designs have not been reported yet. This study aimed to compare the clinical results of total knee arthroplasty (TKA) using the existing PS type and the modified Lospa PS Plus type.

Methods: A retrospective study was performed on 558 knees of 342 patients who underwent TKA using the Lospa PS or PS Plus types and were followed up for at least 2 years. Cases were divided into two groups according to the implant used: 212 cases in the PS group and 346 cases in the PS Plus group. For clinical outcome assessment, knee range of motion (ROM), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score, and Knee Society Score (KSS) were recorded before surgery and at the 2-year follow-up. Radiographic outcomes were evaluated according to the American Knee Society method. The incidence of postoperative complications and survival rates were compared between the two groups.

Results: Both groups showed significant clinical improvement after surgery. The average KSS significantly improved from 53.4 points in the PS group and 52.3 points in the PS Plus group preoperatively to 91.3 points and 93.2 points after surgery, respectively (p < 0.001). The average WOMAC score improved from 50.4 points in the PS group and 52.3 points in the PS Plus group before surgery to 15.6 points and 14.8 points after surgery, respectively (p < 0.001). There was no significant difference between the two groups in ROM, the alignment of the lower limbs, and the implant position after surgery. The complication rates were also similar between the groups (p = 0.167).

Conclusions: The Lospa PS Plus model is a modified design that improves the post structure from the previous PS type. Compared to the PS type, the PS Plus type showed similar statistical results at 2-year follow-up and good clinical results. The short-term average survival rate was over 98%, showing promising results.

Keywords: Knee; Posterior-stabilized; Total knee arthroplasty.

Fig. 1. Comparison of Lospa posterior-stabilized (PS; A) and PS Plus (B) types. The pictures are reproduced by courtesy of the manufacturer.

Fig. 2. Modified polyethylene design may help to avoid impingement of the patellar component with anterior post fillet during high-flexion of the knee joint. PS: posterior-stabilized. The pictures are reproduced by courtesy of the manufacturer.

Fig. 3. The bottom chamfer cutting may allow easier insertion of the polyethylene insert so excessive anterior dislocation of the tibia is not required. The pictures are reproduced by courtesy of the manufacturer.

Fig. 4. Radiographs showing the measurement of prosthesis alignment angles according to the Knee Society total knee arthroplasty roentgenographic evaluation system. α: femoral valgus angle, β: tibial valgus angle, γ: femoral flexion angle, δ: tibial flexion angle.

Fig. 5. Kaplan-Meier curves illustrating prosthetic survival, with reoperation for any reason as the end point, after Lospa posterior-stabilized (PS) and PS Plus total knee arthroplasty.