Wearable robot helps with post-TKA rehab

Using a wearable robot such as the hybrid assistive limb (HAL) after total knee arthroplasty (TKA) facilitates postsurgical training, leading to improvements in mobility of the knee and hip joints, according to a recent study. The wearable device likewise assists in the rehabilitation of walking ability, particularly of step length.

During postsurgical rehabilitation 5 weeks after TKA, nine patients (10 knees) received the HAL device, while another nine patients (nine knees) were designated as controls. Analysis of joint angles of the walking cycle revealed no significant between-group difference at all phases and sites. However, large effect sizes of HAL were detected at the maximum hip extension (d, 0.87), knee swing phase (d, 0.94), and knee varus (d, 0.87). [Geriatr Orthop Surg Rehabil 2021;doi:10.1177/21514593211049075]

Similarly, average joint moments were all statistically comparable between the HAL and control groups, though a large effect size was reported for hip flexion (d, 0.86).

Notably, t-test with Welch’s correction showed that patients wearing the HAL device had a longer mean step length than controls (0.63±0.0 vs 0.46±0.09 m), corresponding to a large and statistically significant effect size (t, 5.06; p=0.001; d, 2.74).

Despite significant differences in terms of joint angles and moments, “HAL training contributed not only to improving the mobility of the knee joint but also to increasing the mobility of the hip joint,” the researchers said.

“Furthermore … the hip joint extension in the late stance phase was increased to prepare for the forward swing of the lower limbs, and the flexion angle of the knee joint was increased in the swing phase to promote the body forward,” they added.

These were indeed reflected in generalized linear mixed model (GLMM) analysis, which revealed that the HAL device significantly increased hip extension by around 70 percent (odds ratio [OR], 1.741; p=0.033) and knee flexion during the swing phase by 50 percent (OR, 1.501; p=0.021) compared with controls.

Such improvement in knee joint flexion during the swing phase correlated with a significant progress in step length, according to GLMM analysis (t, 2.153; p=0.047). Knee varus thrust in the early stance phase also significantly affected step length (t, –2.323; p=0.034).

“In contrast, we found no statistically significant difference in the exertion moment of the lower limb joint between the HAL and control groups,” the researchers said, adding that such a null finding suggested that after TKA, “it takes a lot of time to improve muscle strength, and it is considered important to follow the long-term course in the future.”

“In addition, future studies need some standardized functional ambulation outcomes and pain scores and not just joint mechanics and stride length as a measure of ambulation outcome,” they said.