Implant design may influence knee flexor activation patterns during stair ascent and descent

This study examined the effects of surgical alignment techniques and implant design on sagittal plane moments and neuromuscular control during stair navigation in total knee arthroplasty (TKA) patients. We hypothesized that alignment techniques would affect joint biomechanics and neuromuscular control, while implant design would not influence lower limb biomechanics.

A total of 52 TKA patients were analyzed one year postoperatively, categorized by alignment technique (mechanical alignment (MA) or kinematic alignment (KA)) and implant design (cruciate-retaining fixed bearing (CRFB), medial congruent (MC), and medial stabilized (MS)). Each participant performed five trials of overground walking, then stair ascent and descent at their preferred speed. Sagittal plane lower limb joint moments were calculated using a six-degree-of-freedom model in Visual 3D. Surface electromyography signals were analyzed over the entire gait cycle to assess muscle activation patterns.

The KA alignment group demonstrated greater knee extension moments and a knee-dominant strategy compared with the ankle-dominant strategy in the MA group. Implant design did not affect extension moments, but significantly impacted neuromuscular control. Implants with greater medial anteroposterior (AP) constraint showed lower biceps femoris (BF) activation, while designs with greater AP movement required higher BF activation.

Surgical-alignment techniques, particularly KA, significantly impacted joint biomechanics, promoting a knee-dominant strategy during stair negotiation. Implant design influenced neuromuscular control, with less stable designs requiring higher hamstring activation for stabilization. Those results highlighted the importance of considering both alignment technique and implant design in post-TKA rehabilitation.