Description
Normal knee kinematic is not reproduced following total knee arthroplasty (TKA). The kinematic alignment (KA) has been proposed to improve patients’ satisfaction, guarantee better knee proprioception and, ultimately, closer-to-normal kinematics. The hypothesis of this gait analysis study was that the intra-operative reproduction of a slight medio-lateral gap asymmetry improved the postoperative knee kinematic respect to the traditional inter-compartmental gap symmetry.
Two matched (age, sex, BMI) groups of patients underwent medial pivot TKA because of isolated knee disease: A) Group A (25 patients) underwent “unrestricted” KA (uKA) according to Howell; B) Group B (25 patients) underwent robot-assisted “restricted” (rKA) with an alignment goal (Hip-Knee-Ankle axis-HKA) ±5° respect to mechanical axis. Intra-operatively, in Group B, the flexion gap at 90° was first set at an average of 2.5 mm (min.0.5mm-max.3.2mm) tighter in the medial compartment respect to the lateral; in the same way, the extension gap was then set at an average of 1.8 mm (min.0.3mm-max.2.7mm) tighter in the medial compartment respect to the lateral. All patients, including a non-arthritic cohort (Group C: 5 controls) underwent gait analysis evaluation using an instrumented treadmill (WalkerView–WV) equipped with an instrumented belt enriched with 8 load cells, a 48’’LCD screen providing continuous virtual reality/biofeedback, a 3D camera for motion picture and a 15” touchscreen. The WV software evaluated multiple spatiotemporal and kinematic parameters, including: 1) Contact time (sec); 2) Knee ROM during gait cycle; 3) Step length percentage respect to total gait (%) and pure step length (cm). Statistical analyses included t-Test and ANOVA in SPSS.
At final FU, significant differences were noted during gait between the two TKA groups (uKA-rKA) and the controls. 1) Contact time: both TKA groups showed superior mean contact time on the surgical knee (uKA 1s; rKA 0.97s) respect to the controls (0.72s) (p=0.002) while no differences were found between them (p=0.11). 2) Knee ROM during gait cycle: TKA groups showed a lower maximum ROM in the surgical knee (mean uKA 36º; mean rKA 49º) respect to the controls (mean 57º) (p<.05) but a statistical difference was found between them (p=0.003). 3) Step length: both TKA groups showed a higher step length percentage respect to the total gait and a shorter step length on the surgical-side (uKA: mean 8.28% and mean step-length 35.5cm; rKA: mean 8.38% and mean step-length 34.6cm) respect to the controls (mean 3.38%; mean step length 71.4cm) (p<.05) while no statistical differences were found between them.
To the authors knowledge, this is the first study showing the kinematic advantages of a slightly asymmetric gap balancing during TKA. The combination of a medial pivot implant design and a surgical technique aiming to obtain a tighter medial compartment represents a promising approach to improve patients’ satisfaction after TKA.
