The Effect of Knee Height Asymmetry on Gait Biomechanics.

BACKGROUND: Though the primary goal for limb length discrepancy (LLD) management is to equalize the leg lengths, symmetry between corresponding long bones is usually not achieved, leading to knee height asymmetry (KHA). To date, there is minimal information on what effect KHA has on gait biomechanics and joint loading. Thus, the purpose of this study is to determine the impact of KHA on gait biomechanics. METHODS: Seventeen subjects with KHA after limb equalizing surgery and 10 healthy controls were enrolled. Subjects participated in 3D gait analysis collected using self-selected speed. Lower extremity kinematics, kinetics, work generated/absorbed, and total work were calculated. Standing lower limb x-rays and scanograms were used to measure LLD and calculate the tibia-to-femur (TF) ratio for each limb. Two sample t tests were used to compare differences in standing LLD, TF ratio, and work between groups. Bivariate correlation using Pearson correlation coefficients was conducted between TF ratio and total mechanical work, as well as between knee height asymmetry indices and total work asymmetry (α=0.05). RESULTS: Among participants, there were no differences between LLD; however, there were differences between TF ratio and knee height asymmetry. We found a nonsignificant relationship between TF ratio and total mechanical work for individual lower extremities. Therefore, the length of individual bones (TF ratio) relative to each other within the individual lower extremity was not associated with the amount of work produced. However, when a difference exists between sides (asymmetry, ie, TF ratio asymmetry), there were associated differences in work (work asymmetry) produced between sides (r=0.54, P =0.003). In other words, greater knee height asymmetry between limbs resulted in more asymmetrical mechanical work during walking. CONCLUSIONS: These findings may have implications for the management of LLD. Asymmetrical total mechanical work could lead to atypical joint loading during gait. Surgeons may want to consider prioritizing achieving knee height symmetry as a postoperative goal when correcting limb length discrepancy. LEVEL OF EVIDENCE: Level III, Case Control Study.

Level and Downhill Walking to Assess Implant Functionality in Bicruciate- and Posterior Cruciate-Retaining Total Knee Arthroplasty.

BACKGROUND: The goal of this study is to set up a functional motion analysis test to examine effects of the anterior cruciate ligament in total knee arthroplasty (TKA) patients by comparing knee kinematics, kinetics, and muscle activation patterns during level and downhill walking for patients with posterior cruciate-retaining (PCR) and bicruciate-retaining (BiCR) TKAs. METHODS: Motion and electromyography (EMG) data were collected for 12 subjects (4/8 male/female, 64 ± 11 years, 31.3 ± 7.3 body mass index, 6/6 right/left) with BiCR TKAs and 15 subjects (6/9 male/female, 67 ± 7 years, 30.5 ± 5.1 body mass index, 4/11 right/left) with PCR TKAs during level and downhill walking using the point cluster marker set and surface electrodes placed on the vastus medialis obliquus, rectus femoris, biceps femoris, and semitendinosus muscles. RESULTS: Level walking exhibited no significant differences in knee kinematics, kinetics, or EMG patterns. During downhill walking, BiCR subjects had significantly lower peak muscle activity in the vastus medialis obliquus and rectus femoris (P = .045 and .018, respectively), a trending higher peak knee flexion moment (2.0 ± 0.6% BW*HT vs 1.5 ± 0.6% BW*HT, P = .076), and significantly more knee flexion at heel strike (5.1° ± 4.7° vs 1.8° ± 2.8°, P = .044) compared with PCR subjects. CONCLUSION: Anterior cruciate ligament retention led to altered muscle recruitment during downhill walking in BiCR subjects compared with PCR subjects; thus, BiCR TKAs may offer some neuromuscular benefits for stabilizing the knee joint. In conclusion, level and downhill walking knee kinematics and kinetics combined with corresponding quadriceps and hamstrings EMG signals begin to build an overall picture of implant functionality.

Are Instrumented Knee Forces Representative of a Larger Population of Cruciate-Retaining Total Knee Arthroplasties?

BACKGROUND: It is not known if the loads and motions reported for instrumented knees are generalizable to a larger population of total knee arthroplasty (TKA) patients. The purpose of this study is to (1) report axial implant force data for chair and stair activities for a population of cruciate-retaining TKA patients and (2) compare the population forces to those measured with instrumented TKAs. METHODS: Twenty-three subjects with a cruciate-retaining TKA underwent motion analysis during stair ascending, stair descending, chair sitting, and chair rising activities after informed consent in this institutional review board approved study. Axial TKA forces were calculated using a previously validated computational model. Differences between the mean and variability of population instrumented TKA peak forces and force impulses were tested using t tests and Levene test. RESULTS: Peak axial forces were 3.06, 2.74, 2.65, and 2.60 kN for stair ascent, stair descent, chair rising, and chair sitting, respectively. Force impulses were 123.3, 123.4, 153.5, and 154.0 kN*% activity cycle for stair ascent, stair descent, chair sitting, and chair rising, respectively. Population TKA and instrumented TKA peak forces were different for stair ascent (P = .03) and stair descent (P = .03) in the second half of the activity cycles. The variability of the peak forces and impulses were not different (P = .106 to P = .99). CONCLUSION: The forces and motions presented in this study represent cruciate-retaining TKA patients and could be used for displacement-driven knee wear testing. The forces are similar to those in the literature from instrumented prostheses of an ultracongruent cruciate-sacrificing TKA.