Calipered kinematic alignment restored the arithmetic hip–knee–ankle angle, achieved high satisfaction and improved clinical outcomes

Abstract Purpose The purpose of this study was to determine whether unrestricted calipered kinematic alignment (KA), coupled with a medial‐stabilised (MS) implant system, can reproduce the patient's constitutional alignment as per the arithmetic hip–knee‐ankle (aHKA) and improve clinical outcomes. Methods One‐hundred and ninety‐three patients received total knee arthroplasty by the senior author. To determine whether the constitutional alignment was achieved, the postoperative hip–knee–ankle (HKA) alignment was compared against the aHKA. Range of motion (ROM) was determined preoperative and postoperatively at 6 months and 2 years by measuring the active flexion and extension. Patient‐Reported Outcomes Measures (PROMs) including Oxford Knee Score (OKS), Knee Injury and Osteoarthritis Outcome Score (KOOS), Forgotten Joint Score (FJS) and Visual Analogue Scale for Satisfaction were also completed. The Sports and Recreation component of KOOS was used to assess the patient's ability to return to sports and daily activities. Results There was a strong correlation between postoperative HKA and aHKA ( r = 0.7, p < 0.05). There was a significant improvement in both extension and flexion seen from as early as 6 months postoperatively, with a mean flexion of 123° ± 11° and extension of 1° ± 3° at 2 years. PROMs had significant improvements with a mean score of 42.8 ± 6.0 for the OKS and all KOOS subscales consisting of Symptoms (88.0 ± 11.7), Pain (91.4 ± 11.6), Activities of Daily Living (91.1 ± 12.4), Sports (76.8 ± 22.1) and Quality of Life (83.0 ± 19.1). The FJS had significant improvements from 6 months to 2 years of 19.9 ( p < 0.05), with a mean score of 69.2 ± 26.6 at 2 years. Ninety‐three percent (180 patients) were classified as ‘satisfied’ at the 2‐year timepoint. The KOOS Sports component was completed by 64% (124 patients), whereby the mean age was younger than the noncompliant patients (67.7 ± 9.4 vs. 71.7 ± 8.2 years). Conclusion Unrestricted calipered KA can result in an alignment that closely resembles the patient's constitutional alignment, as per the aHKA. This resulted in improved knee ROM and patient satisfaction, as well as assisting younger patients to return to sports and daily activities. Level of Evidence Level IV.