Higher satisfaction after total knee arthroplasty using restricted inverse kinematic alignment compared to adjusted mechanical alignment

Abstract

Purpose: Various alignment philosophies for total knee arthroplasty (TKA) have been described, all striving to achieve excellent long-term implant survival and good functional outcomes. In recent years, in search of higher functionality and patient satisfaction, a shift towards more tailored and patient-specific alignment is seen. The purpose of this study was to describe a restricted 'inverse kinematic alignment' (iKA) technique, and to compare clinical outcomes of patients that underwent robotic-assisted TKA performed by restricted iKA vs. adjusted mechanical alignment (aMA).

Methods: The authors reviewed the records of a consecutive series of patients that received robotic-assisted TKA with restricted iKA (n = 40) and with aMA (n = 40). Oxford Knee Score (OKS) and satisfaction on a visual analogue scale (VAS) were collected at a follow-up of 12 months. Clinical outcomes were assessed according to patient acceptable symptom state (PASS) thresholds, and uni- and multivariable linear regression analyses were performed to determine associations of OKS and satisfaction with six variables (age, sex, body mass index (BMI), preoperative hip-knee-ankle (HKA) angle, preoperative OKS, alignment technique).

Results: The restricted iKA and aMA techniques yielded comparable outcome scores (p = 0.069), with OKS, respectively, 44.6 ± 3.5 and 42.2 ± 6.3. VAS Satisfaction was better (p = 0.012) with restricted iKA (9.2 ± 0.8) compared to aMA (8.5 ± 1.3). The number of patients that achieved OKS and satisfaction PASS thresholds was significantly higher (p = 0.049 and p = 0.003, respectively) using restricted iKA (98% and 80%) compared to aMA (85% and 48%). Knees with preoperative varus deformity, achieved significantly (p = 0.025) better OKS using restricted iKA (45.4 ± 2.0) compared to aMA (41.4 ± 6.8). Multivariable analyses confirmed better OKS (β = 3.1; p = 0.007) and satisfaction (β = 0.73; p = 0.005) with restricted iKA.

Conclusions: The results of this study suggest that restricted iKA and aMA grant comparable clinical outcomes at 12-month follow-up, though a greater proportion of knees operated by restricted iKA achieved the PASS thresholds for OKS and satisfaction. Notably. in knees with preoperative varus deformity, restricted iKA yielded significantly better OKS and satisfaction than aMA.

Level of evidence: Level III, comparative study.

Keywords: Arthroplasty; Inverse kinematic alignment; Knee replacement; Patient satisfaction; Patient-reported outcomes; Patient-specific alignment; Robotic surgical procedures.

Fig. 1

Study flowchart

Fig. 2

Illustration of the iKA and aMA philosophy in a common knee, with an MPTA of 87°. * iKA technique: Tibial resection: tibial resection parallel to tibial joint line TJL, medial tibial resection (MTR) = lateral tibial resection (LTR). Hip–knee–ankle (HKA) angle: restored to pre-arthritic HKA angle by tensioning soft-tissue envelope in extension and performing distal femoral resection. Extension gap laxity: 1–2 mm opening. Flexion gap: femoral rotation governed by soft-tissue tension in flexion with patella-in-place; 1–2 mm medial and 1–3 mm lateral residual laxity.*aMA technique: Tibial resection: 90° with the mechanical tibial axis mTA. HKA angle: restored to pre-arthritic HKA angle by soft-tissue envelope in extension and performing distal femoral resection, but within a HKA angle safe zone of 177–183. Extension gap laxity: 1–2 mm opening. Flexion gap: femoral rotation governed by soft-tissue tension in flexion with patella-in-place; 1–2 mm residual laxity medial and lateral. Abbreviations: mTA mechanical tibial axis; mFA mechanical femoral axis

Fig. 3

Postoperative radiographs of 76 years, male patient who received a left TKA by iKA. The patient suffered invalidating knee pain caused by tricompartmental osteoarthritis and progressive varus deformity with obliteration of the medial joint space (grade 4). a Postoperative standing full-leg X-ray (EOS) showing a restored HKA angle of 174,5° and bilateral symmetrical joint line obliquity, parallel to the floor. b Postoperative weight-bearing X-ray of the knee detailing a restored MPTA of 86° incombination with an mLDFA of 91,5°