Lower limb biomechanics after total knee arthroplasty
Abstract
Knee osteoarthritis is a painful and disabling disease that is prevalent among elder adults. Total knee arthroplasty (TKA) can effectively alleviate knee arthritic pain and improve patient quality of life. Unfortunately, there are evidences showing that (1) patients after TKA still exhibit function limitations in ascending/descending stairs; (2) ankle, knee and hip biomechanics are not restored to normal after TKA; (3) about 20% patients are not satisfied with their current TKA. The objective of this study is to investigate ankle, knee and hip joint biomechanics of TKA patients during activities of daily living (i.e. level walking, stair ascent/descent, sit-to-stand and pivoting), and how three different factors affect their joint mechanics. The first factor is the existence and progression of contralateral knee osteoarthritis (CKOA). After unilateral TKA, a high percentage of patients have CKOA. The existence of CKOA has been associated high knee adduction moment on the contralateral knee and at least 35% incidence of future contralateral knee replacement in 10 years. However, few studies have examined the effect of CKOA progression on the mechanics of other joints. Thirteen moderate and 13 severe CKOA patients were tested during level walking (LW), stair ascent (SA), stair descent (SD), and sit-to-stand (S2S). The severity of CKOA were classified by clinical decision of contralateral knee replacement and radiographical scoring. As we expected, the results supported that both contralateral ankle and hip biomechanics were altered. Contralateral ankle reduced dorsiflexion and moment/power, while contralateral hip increased hip internal rotation, hip moment and contribution to dynamic support of the body. The progression of CKOA also impacted task performance (reduced speed and increased time) and decreased loading on contralateral leg. Unexpectedly, operated knee axial rotation at heel strike during level walking and knee moment of pulling up body at stair ascent was increased, and hip of the operated side increased abduction angle and moment during stair ascent/descent. These findings suggested that the progression of CKOA not only changes biomechanics of the affected knee but also impacts the operated knee and hip joints on both sides.The second factor is the replacement of both knees. Bilateral TKA (BTKA) replaces both knees so it is hypothesized that they would have different biomechanical outcomes and asymmetry from unilateral TKA (UTKA). The biomechanics of ten staged BTKA patients and thirteen UTKA patients during level walking, stair ascent/descent and sit-to-stand were compared. BTKA was associated symmetrical biomechanics, despite that the latest TKA side had a lower peak hip adduction moment during level walking and stair ascent than the first TKA side. UTKA was associated asymmetrical biomechanics. Knee flexion angle and ankle dorsiflexion angle, hip extension moment/power, knee flexion moment and power, and ankle power were lower on the operated side than on the non-operated side. The operated side also reduced knee contribution but increased hip contribution to total support moment during sit-to-stand. Compared to UTKA operated side, BTKA had higher flexion moment and total support moment at weight acceptance of stair ascent, knee power generation at sit-to-stand. BTKA patients also had less extended hip and more anteriorly tilted pelvic during level walking and standing than UTKA patients. The third factor is the bearing mobility in TKA. Mobile-bearing TKA may promote natural knee rotation and reduce rotation torque at proximal tibia. Twenty MB knees and 17 FB knees were tested during LW, SA, SD, step turn (outside turn) and spin turn (inside turn). Knee rotation angle and knee rotation moment were compared. The results showed that bearing mobility did not significantly change transverse plane biomechanics of the operated knee.In summary, this dissertation provided biomechanical targets for physical therapists to improve outcomes for different subgroups of TKA patients and evidences for the transverse plane comparison between MB and FB TKA.