Effect of Outpatient Rehabilitation on Functional Mobility After Single Total Knee Arthroplasty: A Randomized Clinical Trial

“Numerous studies have shown that rehabilitation is associated with improved post-TKA [total knee arthroplasty] outcomes, whether comparing rehabilitation received at different settings or examining different physical therapy (PT) protocols. This typically requires active patient engagement by incorporating weight bearing exercise, active range of motion, and gait training. However, patients’ fear of falling and postsurgical pain accompanying weight bearing and range of motion exercises often limit patient’s ability to fully participate in PT and thus prolong a patient’s recovery.

[..] This randomized clinical trial used a Food and Drug Administration–cleared treadmill using patented National Aeronautics and Space Administration technology to unload a proportion of body weight during therapy without any harness or straps. The treadmill provides precise partial weight bearing that can be adjusted as patients progress over time.

[..] The study compared post-TKA rehabilitation outcomes among 3 newly developed PT protocols and a traditional protocol that uses a recumbent bike serving as a control arm among patients with a unilateral TKA in outpatient settings. The 3 new interventions included (1) a body weight–adjustable treadmill, (2) a patterned electrical neuromuscular stimulation (PENS) device, and (3) both together.

[..] Eligible individuals for the study were those who (1) underwent an elective unilateral TKA and initiated outpatient PT within 24 days after TKA; (2) were aged 40 years or older; and (3) weighed less than 300 lb (to convert to kilograms, multiply by 0.45), owing to the body weight–adjustable treadmill weight limitation.

Participants were excluded if they (1) underwent any lower extremity joint replacement procedure less than 1 year prior to the current TKA; (2) were in litigation related to injury or disease associated with their current TKA; (3) had a recent medical history of neurologic disorders, rheumatoid arthritis, or gout; (4) were under active cancer treatment with history of malignant neoplasm in lower extremities or had recent evidence of signs or symptoms of cancer, chemotherapy, or radiation; (5) were unable to proceed or continue the planned outpatient program because of complications, such as wound infection, related to the TKA procedure or required manipulation under anesthesia due to knee stiffness after TKA; and (6) had received more than 2 weeks of other postacute services prior to outpatient PT.

[..] Each rehabilitation treatment session over the course of 8 to 12 weeks (2-3 times per week) consisted of 3 phases: an exercise and conditioning phase (15-20 minutes), a hands-on therapy and treatment phase (30-40 minutes), and a final pain management and edema control phase (15 minutes). The study’s control intervention and the 3 new interventions were used in the exercise and conditioning phase.

The exercise and conditioning phase seeks to increase blood flow and pliability of the tissue surrounding the surgical joint to the following hands-on therapy phase. Patients in the control group used a standard recumbent bike.

Intervention group 1 used a body weight–adjustable treadmill during the exercise phase to unload partial body weight when walking on the treadmill. Physical therapists identified the threshold body weight unloading that minimized pain and allowed patients to move freely while on the treadmill. Over time, physical therapists decreased body weight support as tolerated. Physical therapists also determined the appropriate walking speed allowing patients to maintain a proper gait pattern while on the treadmill.

Intervention group 2 used PENS on the leg that underwent TKA while using a recumbent bike during the exercise phase. A PENS unit supports early restoration of agonist/antagonist muscular timing patterns to encourage neuromuscular re-education following a TKA.

Intervention group 3 used both the body weight–adjustable treadmill and PENS during the initial phase. The combination simultaneously unloaded a proportion of patient’s body weight and facilitated the proper muscle recruitment pattern during ambulation.

The hands-on and treatment phase addressed strengthening, neuromuscular re-education, and manual therapy. Designed by physical therapists, this phase was tailored to individual patient needs and functional goals. It was typically a 1-on-1 format working directly with a physical therapist.

The final phase provided transition from exertion to rest after an intensive therapy session. Physical therapists sought to minimize secondary injury and loss of progress through pain and inflammation management prior to finishing the treatment session.

[..] The study’s primary outcome measures were the Activity Measure for Post-acute Care (AM-PAC) basic mobility score and the 6-minute walk test. Both were measured at initial evaluation, monthly, and at discharge from outpatient PT. The AM-PAC is a patient-reported instrument to measure functional levels in 3 domains: basic mobility, daily activity, and applied cognition. For purpose of the study, only the basic mobility domain was measured. This study used the AM-PAC paper short form designed for outpatient settings. The short form consists of 18 questions and produces a raw score (range, 18-72) transformed into a score ranging from 29.41 to 80.30 based on item degree of difficulty. Higher transformed scores denote higher functional mobility (ie, limited indoor mobility, ≤51.9; enhanced indoor mobility, 52-65.9; and outdoor mobility, 66-84).

[..] A total of 505 patients who underwent TKA were screened for eligibility, among whom 45 did not meet the inclusion criteria and 74 declined to participate. The remaining 386 eligible patients agreed to participate. [..] Data from 23 patients were excluded from the analysis owing to insufficient data and withdrawal from the study. Consequently, data from 363 patients, including 92 patients in the control group, 91 patients in intervention group 1, 90 patients in intervention group 2, and 90 patients in intervention group 3, were included in the final analysis.

[..] Overall, patients did not differ across groups: the mean (SD) age was 63.4 (7.9) years old, 222 (61.2%) were women, 244 (67.2%) were White, 183 (50.4%) had at least a bachelor’s degree, and 361 (99.4%) were living at home. Most patients were overweight (108 patients [29.8%]) or obese (200 patients [55.1%]). Most had private insurance (220 patients [60.6%]) or Medicare (117 patients [32.3%]).

[..] Many patients received some form of post-TKA rehabilitation, mostly through home health, prior to their outpatient PT. The median (interquartile range) durations between patients’ TKA and initial outpatient evaluation were 20 (10-22) days in the control group, 18 (9-21) days in intervention group 1, 20 (14-21) days in intervention group 2, and 19 (7-21) days in intervention group 3. Each group had a similar level of functional mobility as measured by AM-PAC scores and by the 6-minute walk test at baseline.

[..] Outpatient treatment courses lasted approximately 60 days, including approximately 14 to 15 visits across 4 groups. On discharge, most patients were able to bear their full weight without an assistive device (330 patients [90.9%]). More than half of study patients still used pain medications (204 patients [56.2%]), mainly over-the-counter medications as needed. Almost all lived at home on discharge from outpatient rehabilitation (362 patients [99.7%]).

[..] Across groups, mean (SD) AM-PAC scores on discharge were similar (control: 61.3 [5.3]; intervention group 1: 61.3 [5.4]; intervention group 2: 61.1 [6.1]; intervention group 3: 61.2 [6.4]; P = .99). From baseline to discharge from outpatient rehabilitation, patients’ AM-PAC scores improved across groups (mean [SD] change: control, 9.0 [8.4]; intervention group 1, 10.0 [7.3]; intervention group 2, 9.3 [6.4]; intervention group 3: 9.4 [7.2]; P = .80).

[..] From baseline to discharge from outpatient therapy, patients were able to walk at least an additional 144.2 m across groups (mean [SD] change: control group, 155.6 [95.9] m; intervention group 1, 144.2 [112.9] m; intervention group 2, 159.1 [125.2] m; intervention group 3, 168.4 [116.7] m; P = .55).

[..] This randomized clinical trial found no statistically significant differences in mobility outcomes among the control group and all 3 intervention groups as measured by AM-PAC scores. Patients achieved a similar functional level at discharge and progressed from baseline to discharge more than 2-fold (ie, ≥9.0 points) the suggested minimally detectable clinical change of 4 points. More than 92% of study patients were able to either move around indoors (AM-PAC score, 52-65.9) or outdoors (AM-PAC score, 66-83.9) on discharge, a substantial improvement from almost half of patients with limited mobility indoors (AM-PAC score, 34-51.9) at baseline. We also found no statistically significant differences in patient performance on the 6-minute walk test. Patients were able to walk at least an additional 144.2 m, more than 2-fold the minimal detectable change of 61.3 m suggested by Kennedy et al.

[..] It may be possible that the lack of significant differences among the control and intervention groups is, in part, mediated by the prolonged period prior to the initiation of outpatient PT (ie, 15-16 days after TKA). The optimal window, if any, to incorporate either the body weight–adjustable treadmill or a PENS unit to address key barriers (fear of falling and post-TKA pain) may have subsided by the time some study patients started outpatient therapy.

[..] This study’s findings of no clinically or statistically significant differences across 4 arms suggest that an important next step is to identify the most cost-effective protocol that will provide the best functional outcomes for this increasing population.”

Full article, Hsieh CJ, DeJong G, Vita M et al. JAMA Network Open 2020.9.17