Abstract
Background
More and more patients with end-stage knee OA are treated with total knee replacements (TKR). A modern TKR (Persona PS system, Zimmer Inc.) was designed with the hope to improve fit by providing additional sizing options on the femur and tibia. To date, there is very little information regarding the knee strength and knee mechanics during gait after the TKR. Furthermore, as a great percentage of knee OA patients have OA limited in one knee compartment and in the patellofemoral joint, a bi-compartmental knee replacement (BKR) (iDUO system, ConforMIS Inc.) was designed to treat OA at these affected areas. The BKR re-creates the individual's knee shape while correcting for any deformity. In addition, the BKR procedure results in less bone loss and retains the cruciate ligaments. To date, the influence of the BKR on knee strength and knee mechanics remains unknown. The purpose of the study was to evaluate knee strength and mechanics during level walking after the TKR and BKR surgeries.
Methods
Twelve healthy control participants (age=57±6 yr.; mass=82±11 kg; height=175±11 cm), eight patients (age=63±10 yr.; mass=87±20 kg; height=166±8 cm) with ten BKR systems (post-op time = 17±9 mo.), and nine patients (age=65±9 yr.; mass=90±35 kg; Height=169±12 cm) with twelve TKR systems (post-op time = 14±5 mo.) participated in the study. In a laboratory setting, maximal isometric knee strength was evaluated. Motion capture and 3D kinematic and kinetic analyses were conducted for level walking. One way ANOVA was used to determine differences among the BKR, TKR, and the healthy control knees.
Findings
The TKR knee extensor strength was 34% and 20% less than that of the control limb (p<0.05) and the BKR limb (p=0.07), respectively. The TKR limb had less knee extensor moment during walking than both the control limb (40% less) and the BKR limb (24% less) (p<0.05). The TKR knee displayed smaller internal rotation at stance than that of the control knee (60% less) and the BKR knee (50% less) (p<0.05). Both the control and BKR groups walked at a faster pace (24% and 17% faster, respectively) than the TKR group (p<0.05). No differences were found for peak knee abduction and abduction moment among the TKR, BKR, and control limbs during walking (p0.05).
Interpretations
BKR patients saw their knee extensor strength returned to a normal level and were able to produce the same level of knee extensor moment of the healthy control limbs during walking. The TKR patients still experienced knee strength deficit after one year post-surgery. Both the TKR and BKR groups exhibited similar frontal plane mechanics when compared to the control limbs during walking. However, BKR patients were able to walk significantly faster than their TKR counterparts, at speeds similar to the control subjects. Patients with OA limited in the medial/lateral compartment and the patellofemoral joint may consider the BKR procedure for better knee strength recovery and functional outcomes.
Acknowledgement
Funding source: ConforMIS Inc.
