Original Article

Precision in Medial pivot total knee arthroplasty: A retrospective study on mechanical axis alignment and functional outcomes with CT-guided patient-specific instrumentation

¹ AOA Accredited Fellow, Mulgrave Private Hospital, 48 Blanton Dr, Mulgrave, VIC 3170, Australia
² Ozorthopaedics, Centre for Adult Joint Arthroplasty, 1356 High Street, Malvern, VIC 3144, Australia

^* Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 19 August 2025
Accepted: 6 May 2026

Abstract

Background: Total Knee Arthroplasty (TKA) is the standard treatment for end-stage osteoarthritis, with optimal outcomes dependent on precise mechanical alignment and accurate implant positioning. Patient-specific instrumentation (PSI), facilitated by preoperative CT imaging, has emerged as a technique to enhance surgical precision; however, the relationship between alignment and functional outcomes remains less clear. Objective: To evaluate the effectiveness of medial pivot CT-guided PSI TKA in achieving mechanical axis alignment and its correlation with functional outcomes over a 12-month period. Methods: This retrospective study analysed 389 primary medial pivot TKA procedures performed by a single surgeon between January 2015 and December 2024 using CT-guided PSI. Functional outcomes were assessed using the Oxford Knee Score (OKS) and Lysholm Knee Score (LKS) preoperatively and at three, six, and twelve months postoperatively. Mechanical alignment was evaluated using the Hip-Knee-Ankle (HKA) angle pre- and postoperatively. Descriptive statistics and paired t-tests were applied, with significance set at p < 0.05. Results: The cohort included 389 patients, 62.7% female, with a mean age of 69.6 years and mean BMI of 31.4 kg/m². PSI significantly improved mechanical alignment, with mean HKA increasing from 172.2° preoperatively to 179.5° postoperatively. Functional outcomes also improved, with mean OKS increasing from 18.5 to 38.6 and mean LKS from 52.4 to 85.5. Patients classified as alignment outliers with severe preoperative deformities showed no significant improvement in alignment but demonstrated substantial functional gains. Conclusion: CT-guided PSI improves mechanical alignment and functional outcomes in medial pivot TKA, particularly in mild to moderate deformities. The weak correlation between alignment and functional recovery suggests other factors, including soft tissue balance, prosthesis factors and rehabilitation, to be critical in total knee arthroplasty. Further studies with larger cohorts, longer follow-up, and comparative groups are required.