PATIENTS ADOPT A CAUTIOUS GAIT PATTERN WHILE DESCENDING A RAMP ONE YEAR AFTER TOTAL KNEE ARTHROPLASTY

Poor knee function after surgery is on of the main factors of patient dissatisfaction after total knee arthroplasty (TKA). Descending tasks are more demanding on the knee joint than level walking, and patients report discomfort performing these tasks. The purpose of this study was to investigate how implant design can influence knee biomechanics during a ramp descent gait task. This study included 28 patients (female=12/male=16, age=63.6±6.9, BMI=29.9±7.4kg/m2) with end stage knee osteoarthritis who underwent TKA with either cruciate-sacrificed medial congruent (MC) or posterior stabilized (PS) implants. Patients underwent motion analysis which measured knee biomechanics as they descended a nine-degree instrumented ramp before and 12 months after TKA, and results were compared with 14 healthy controls (CTRL: female=6/male=8, age=64.4±5.6, BMI=24.9±2.1kg/m2) of similar age. Knee joint angles, moments, and powers were compared at each interval of the movement cycle using statistical parametric mapping with walking speed used as a covariate (ANCOVA SPM). Pre-operatively, three different gait patterns were observed in the patient groups. These gait patterns were classified by different knee flexion/extension moment patterns at the start and end of single limb support phase within the gait cycle. However, post-operatively all TKA patients adopted the same movement pattern, which was characterized by a knee extension moment throughout single limb support. Additionally, patients walked with limited knee power generation and primarily absorbed power through the knee joint. These differences existed in all TKA patients, regardless of implant type, or how they walked pre-operatively. Although both MC and PS groups walked with the same gait pattern, the MC group achieved greater knee flexion angle throughout most of the gait cycle (0–52% and 64–100% gait cycle) and had a larger knee power absorption at the start of single limb support (10–17% gait cycle). Controls walked with one of two gait patterns, either a knee extension moment (CTRLExt) or with a knee flexion followed by knee extension moment (CTRLFlexExt) throughout stance phase. When compared to the CTRLExt, both MC and PS groups achieved similar knee joint moments and powers throughout stance phase. However, compared to the CTRL-FlexExt group, both MC and PS groups loaded their knee joint differently throughout stance phase. All TKA patients in this study adopted a cautious gait pattern which stiffened their knee and absorbed energy as their body moved into single-limb support. Patients after TKA lack joint stability, and their muscles around the knee worked primarily to dissipate the mechanical energy from descending the ramp rather than generate power. In contrast, half the controls were able to dissipate and generate power at the knee joint during the ramp descent task, indicating a more stable movement pattern. Future studies should evaluate muscle activity during the ramp descent task to understand how the muscles are activating to provide stability in the PS and MC groups. In conclusion, after one year of surgery, all TKA patients descended a ramp with a cautious gait pattern, regardless of which implant they received or how they walked pre-operatively.