Original Research

Use of an Anti-Gravity Treadmill for Early Postoperative Rehabilitation After Total Knee Replacement: A Pilot Study to Determine Safety and Feasibility

Am J Orthop. 2016 May;45(4):E167-E173

The objective was to determine the safety, feasibility, and effects of anti-gravity gait training on functional outcomes (Knee Injury and Osteoarthritis Outcome Score [KOOS], the Timed Up and Go test [TUG], Numerical Rating Scale [NRS] for pain) with the AlterG^® Anti-Gravity Treadmill^® device for total knee arthroplasty (TKA) rehabilitation. Subjects (N = 30) were randomized to land-based vs anti-gravity gait training over 4 weeks of physical therapy after TKA. Adverse events, complications, and therapist satisfaction were recorded. All patients completed rehabilitation protocols without adverse events. KOOS, TUG, and NRS scores improved in both groups with no significant differences between groups. For the AlterG group, Sports/Recreation and Quality of Life subscales of the KOOS had the most improvement. At the end of physical therapy, TUG and NRS pain scores improved from 14 seconds to 8 seconds and from 2.8 to 1.1, respectively. Subjectively, therapists reported 100% satisfaction with the AlterG. This initial pilot study demonstrated that the AlterG Anti-Gravity Treadmill device was safe and feasible. While functional outcomes improved over time with use of the anti-gravity gait training, further studies are needed to define the role of this device as an alternative or adjunct to established rehabilitation protocols.

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References

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Patients undergoing total knee arthroplasty (TKA) may benefit from focused postoperative rehabilitation. Although there is limited research comparing different rehabilitation protocols after TKA,¹ any type of rehabilitation often helps to optimize range of motion (ROM), strength, balance, and ambulation.² Early mobilization and rehabilitation after TKA reduces pain, fear, anxiety, and risk of postoperative venous thromboembolic disease.³ Earlier discharge to home or community settings deceases time for inpatient rehabilitation, patient and family education, and gait training, which places a greater emphasis on outpatient rehabilitation.⁴

Although rapid rehabilitation protocols have gained wide acceptance, concern remains that a higher intensity intervention initiated immediately after hospital discharge could lead to an increased incidence of pain and swelling, and to poorer ROM and functional outcomes.⁵ Progressive weight-bearing activities, such as walking, are routinely recommended during rehabilitation to facilitate return to normal function. Not all patients are capable of full weight-bearing activity in the early postoperative period and assistive devices (ADs), such as walkers, crutches, and canes, are routinely employed. An opportunity to enhance early TKA rehabilitation exists with devices that allow functional gait training while modifying weight-bearing forces across the joint. Assistive devices, hydrotherapy (walking in water),^6,7 and lower body positive-pressure chambers⁸ can reduce the forces at the knee during weight-bearing exercise.

Lower body positive-pressure devices have been extensively studied in physiological response of healthy humans;^9-12 in disease states such as cerebral palsy¹³ and obesity;¹⁴ and in other postoperative orthopedic conditions, such as anterior cruciate ligament reconstruction, meniscectomy,⁸microfracture,¹⁵ TKA,¹⁶ and Achilles tendon repair.¹⁷ These studies demonstrate that a lower body positive-pressure treadmill is associated with minimal cardiovascular effect while producing a significant decrease in ground reaction forces without altering gait kinematics.

We postulated that an anti-gravity treadmill may be safe and effective for gait training during rehabilitation following TKA. The primary objective was to determine the safety and feasibility of using the AlterG^® Anti-Gravity Treadmill^® device for postoperative gait training during rehabilitation following TKA. The secondary objective was to determine the effects of gait training (land-based vs anti-gravity) during postoperative rehabilitation on subjective patient outcomes assessed by Knee Injury and Osteoarthritis Outcome Score (KOOS), mobility assessed by the Timed Up and Go test (TUG), and pain assessed by a Numerical Rating Scale (NRS) to conduct a power analysis to determine sample sizes for efficacy studies based on these preliminary findings.

MethodsParticipants/Patient Enrollment and Study Overview

After signing an Institutional Review Board-approved consent, 30 patients were enrolled, and TKA surgeries were performed by 1 of 5 surgeons at 1 hospital. To be enrolled in the study, subjects must have (1) had a unilateral primary TKA, (2) been discharged from the hospital to home (not to a skilled nursing facility), (3) had only 3 to 4 home physical therapy (PT) sessions, (4) agreed to further outpatient PT at a single site, and (5) agreed to complete patient questionnaires. Exclusion criteria included (1) inability to meet inclusion criteria, (2) gross musculoskeletal deformity, (3) uncontrolled chronic or systemic disease, and (4) inability to follow instructions because of mental impairment, substance abuse, or addiction. Home PT was conducted for 3 to 4 sessions after surgery, and outpatient PT was continued at the study site per protocol for 4 weeks; subjects were asked to return for follow-up 3 months postoperatively. Patients were randomized on the first day of their outpatient PT to either a land-based (control) or an anti-gravity-based group using the AlterG Anti-Gravity Treadmill (AlterG group) gait training during outpatient PT sessions. Patients attended outpatient PT 2 days per week for 4 weeks for a total of 8 sessions. Therapy sessions lasted 45 to 60 minutes and included manual therapy, gait training, and therapeutic exercises/activities. The KOOS^18,19 and TUG²⁰ scores were evaluated at baseline (ie, first therapy session), end of physical therapy (EOPT) (ie, at final therapy session), and end of study (EOS) (ie, 3 months postoperatively). The NRS for pain was evaluated at baseline and at EOPT. Physical therapists were questioned for satisfaction with the anti-gravity rehabilitation protocol at EOPT.

Physical Therapy Protocols

All patients were treated consistently by 1 of 5 physical therapists at 1 outpatient setting; physical therapists averaged 11 years of experience in treating orthopedic conditions. Care was delivered in accordance with professional standards and the therapist’s assessment of medical necessity. Considerations included, but were not limited to, overall general health, any medical comorbidity, support system, and an ongoing assessment of ROM, strength, pain, and functional status. Each PT session started with a 5- to 10-minute warm-up on a standard cycle ergometer and was followed by manual therapy, gait training (land-based vs anti-gravity), therapeutic exercises/activities, and treatment modalities.