Muscle force and movement variability before and after total knee arthroplasty: A review

Table 2 Summary of the literature addressing gait variability in older adults and those with osteoarthritis before and after total knee arthroplasty

Study	Population	Purpose/hypothesis	Variables assessed	Significant findings
Older adults with native, non-arthritic knees
Brach et al[62], 2012	n = 552 (Older adults; Mean age = 79.4 yr)	1. Determine the magnitude of STV that discriminates individuals who currently have mobility disability. Determine the magnitude of STV that predicts a new onset of mobility disability at 1 yr	Gait Variability: Stance time variability Self-reported walking disability	1. Values of STV may be useful in recognizing mobility disability and future disability 2. Recommend using 0.034 s as the cutoff
Brach et al[63], 2010	n = 241 (Older adults; Mean age = 80.3 yr)	1. To estimate clinically meaningful change in gait variability over time. Greater gait variability is a predictor of future falls and mobility disability	Gait Variability: Step width, Stance time, Swing time, Step length	Preliminary criteria for meaningful change are 0.01 s for stance time and swing time variability, and 0.25 cm for step length variability
Brach et al[61], 2008	n = 558 (Older adults; Mean age = 79.4 yr)	1. CNS impairments will affect motor control and be manifested as increased stance time and step length variability. Sensory impairments would affect balance and manifest as increased step width variability	Gait Variability: Step width, Stance time, Step length, Strength Measures: Grip strength, Repeated chair stands	CNS impairments affected stance time variability especially in slow walkers, while sensory impairments affected step width variability in fast walkers
Brach et al[64], 2007	n = 379 (Older adults; Mean age = 79 yr)	To determine if gait variability adds to the prediction of incident mobility disability independent of gait speed	Gait speed, Step length, Stance time, STV	1. After adjusting for gait speed and other comorbidities, only stance time variability remained an important indicator of disability 2. STV of 0.01 s was associated with a 13% higher incidence of mobility disability
Brach et al[65], 2005	n = 503 (Older adults; Mean age = 79 yr)	To examine the linear and nonlinear associations between gait variability and fall history in older persons and to examine the influence of gait speed	CV of step width, CV of step length, CV of step time, CV of stance time, Gait speed, Fall history	1. Step width variability had the highest correlation with fall history, which only existed in subjects that walked > 1.0 m/s 2. Step length, stance time, and step time variability were not associated with fall history
Callisaya et al[66], 2011	n = 411 [Older adults; Mean age = 72.6 yr (lost to follow-up); 71.2 yr (no falls); 72.3 yr (single fall); 73.9 yr (multiple falls)]	To investigate the associates of gait and gait variability measures with incident fall risk	Gait Variability: Step length, Step width, DSP, Gait speed, Cadence, Step time	Associations with multiple falls were present for gait speed, cadence and step time variability
Maki et al[67], 1997	n = 75 (Older adults; Mean age = 82 yr)	To determine whether specific gait measures can predict the likelihood of experiencing future falls or whether they are more likely to be indicative of adaptations associated with pre-existing fear of falling	Gait Variability: Stride length, Stride width, Stride period, Double-support, Stride velocity	1. Stride-to-stride variability in gait is a predictor of falling 2. Wider stride does not increase stability but does predict an increased likelihood of experiencing falls
Older adults with osteoarthritic knees
Lewek et al[10], 2006	n = 15 (Older adults with OA; Mean age = 48.7 yr); n = 15 (Controls; Mean age = 48.4 yr)	Quantify the variability of knee motion in patients with medial knee OA	Joint kinematics and kinetics, Knee motion variability, Knee joint laxity, Co-contraction index	Patients with medial knee OA displayed altered kinematics and kinetics
Kiss et al[68], 2011	n = 90 (Older adults with moderate or severe OA; Mean age = 68.9 yr) n = 20 (Controls; Mean age = 70.7 yr)	To clarify how the variability of gait parameters is influenced by the severity of knee OA	Gait variability: Stride length, Stride width, Speed, Cadence, Duration of double-support, Duration of support	1. Variability of gait associated with knee OA is gender-dependent 2. Severity of OA affects step length, duration of support and cadence
Older adults following total knee arthroplasty
Kiss et al[69], 2012	n = 45 (Older adults with TKA; Median age = 68.3 yr) n = 21 (Controls; Median age = 76 yr)	To evaluate the influence of different surgical techniques on gait variability and stability	Gait Variability: Stride length, Stride width, Speed, Cadence, Duration of double-support, Duration of support	1. Type of surgical technique influences gait variability and stability 2. Differences in the variability of angular parameters predict gait instability and increased risk of falling after TKA
Fallah-Yakhdani et al[11], 2010	n = 16 (Older adults with TKA; Mean age = 62.3 yr) n = 12 (Healthy, older adults; Mean age = 62.0 yr)	To evaluate treadmill walking at various speeds in OA patients pre- and post-TKA, to assess dynamic stability and variability of sagittal knee movements	Knee motion variability as measured by the angular velocity of sagittal knee movements; Walking speed; and Variability of knee movements	After TKA, knee motion variability decreased and was related to a reduction of fall risk. Stability control was also improved after surgery
Fallah-Yakhdani et al[70], 2012	n = 14 (Older adults with TKA; Mean age = 62.3 yr) n = 12 (Healthy, older adults; Mean age = 62.0 yr) n = 15 (Healthy, young adults; Mean age = 22.9 yr)	To identify the determinant of co-contractions during gait in patients with knee OA before and 1 year after TKA	Gait speed at seven different speeds (0.6-5.4 km/h) EMG activity Variability of angular velocity of sagittal knee movements over the first 30 strides at each speed	1. Variability of sagittal plane knee movements (measured in deg/s) increased with speed; 2. Pre-operatively, the patients’ affected and unaffected legs were less variable than those of the young controls and the affected leg was less variable than the healthy peers 3. Post-operatively, variability in the knee OA group was further decreased to a level significantly below both control groups

CV: Coefficient of variation; OA: Osteoarthritis; TKA: Total knee arthroplasty; STV: Stance time variability; CNS: Central nervous system.