Overall, more than half of patients (55.2%; 16/29) discontinued their AD during the 4-week PT period, with the remaining discontinuing prior to EOPT (24.1%; 7/29) or after EOPT (20.7%; 6/29). No statistically significant differences were found between the control and AlterG groups regarding discontinuance of AD.
Among those randomized to the AlterG group, all patients performed within the protocol established for the device for body-weight setting, treadmill speed, and duration of walking. The average body-weight treadmill setting increased by ~30% over the treatment period, from 55% at baseline to 84% at EOPT. The average speed increased by ~70%, from 1.6 mph at baseline to 2.7 mph at EOPT. The mean duration of AlterG use increased by ~75%, from 7.2 minutes at baseline to 12.7 minutes at EOPT. All physical therapists (100%) reported satisfaction with the AlterG for use in early postoperative rehabilitation and reported that patients’ treatment progressed positively.
While functional outcomes (KOOS, TUG, or NRS) did not vary with the type of gait training (P > .2 for land-based vs anti-gravity), functional outcomes improved over time (all P < .01 from baseline to EOPT and all P < .01 from baseline to EOS).
The KOOS scores improved from baseline to EOPT and from baseline to EOS (ie, 3-month follow-up visit) for both treatment groups (Figure 3). More patients completed the sports/recreation portion of the KOOS scores at EOPT and EOS compared to baseline. Forty-three percent and 25% of patients did not complete KOOS sports/recreation questions at EOPT and EOS, respectively, compared to 50% at baseline. This suggests that patients were improving to a level where sports/recreation scores were more applicable than directly after TKA surgery. The TUG scores had the greatest improvement from baseline to EOPT, with a decrease in time of 5 seconds and 7 seconds for the control and AlterG groups, respectively, and slight improvement from EOPT to EOS, with a decrease in time of 1 second and 2 seconds for the control and AlterG groups, respectively (Table 2). By the EOS, the values for the TUG tests for both treatment groups were within normal (<10 seconds) range.20 The NRS scores improved from baseline to EOPT with a score of 1 ± 1 in both control and AlterG groups.
Using these preliminary efficacy results, a post-hoc power analysis (α = .05 and 1β = 80%) was performed with the ADL domain of KOOS as the primary endpoint. Based on a standard deviation of 20 points and an effect size of 5 points, the sample size was estimated to be N = 250 per treatment group.
Discussion
We conducted a pilot study to assess, primarily, the feasibility and safety, and, secondarily, the efficacy, of a lower body positive-pressure treadmill for rehabilitation of patients after TKA. This small study showed that use of the AlterG Anti-Gravity Treadmill was not only safe and feasible during postoperative TKA rehabilitation, but also was well tolerated by patients and was rated highly satisfactory by physical therapists. Patients who used AlterG during gait training improved functionally (in terms of KOOS, TUG, and NRS) after 8 treatment sessions compared to baseline. However, there were no statistical differences between groups (control vs AlterG). Thus, these results suggest that an anti-gravity device for gait training may be a useful adjunct for postoperative TKA rehabilitation, but further studies are needed to determine the efficacy of anti-gravity compared to traditional land-based gait training.
The study of rehabilitation protocols during postoperative PT involved consideration of a number of issues. First, differences in functional outcomes compared to traditional rehabilitation could not be detected in this study because of the small number of patients, but the patients treated with anti-gravity gait training showed improvement in functional outcomes over time and did not report any added complications. Given that the primary outcome of this study was safety and feasibility, these added efficacy results are supplemental and useful in helping to plan studies. Second, the functional outcomes used to measure the efficacy of the anti-gravity treadmill may not be sensitive enough to detect differences between rehabilitation protocols. Use of a treadmill to measure speed improvement, endurance, and tolerance in both groups could be valuable in future studies. More studies may need to refine characteristics that are important to postoperative rehabilitation success, and quantitative and subjective measures that must be defined.
The results reported here using an anti-gravity treadmill for postoperative TKA rehabilitation support the safety and feasibility that has been reported in other orthopedic rehabilitation settings. Anti-gravity treadmills, which have been used to study patients after meniscectomy or anterior cruciate ligament reconstruction8 and Achilles repair,17 have demonstrated predictable decreases in ground reaction forces with increasing positive-pressure unweighting, reductions in pain with ambulation, and allowance of earlier institution of walking and jogging during rehabilitation.17