by Tyler Tice, PT, DPT, MS, ATC
Over 700,000 total knee arthroplasty (TKA) surgeries are performed each year in the US with this number expected to increase to over 3 million by 2030. A TKA is typically performed to reduce knee pain as well as self-reported physical function ability. However, even when considered full recovered 12 months after surgery, patients’ physical function when formally measured by performance-based measures and quadriceps strength are rarely improved compared to pre-surgery function. As shown in previous research, post-op protocols that include strengthening and functional exercises that are progressed based on clinical milestones promotes better outcomes compared to protocols that lack these interventions. However, there is no current research that compares patients who completed a progressive strengthening post-op protocol to healthy age-matched peers, which makes it difficult to determine whether these protocols are effective in fully restoring physical function. As younger, more active populations begin to undergo TKA surgeries, it’ll be imperative to know whether these progressive strengthening interventions are effective in restoring the level of physical function required to return to physically demanding occupations and recreational activities.
This study investigated at 205 participants who underwent a unilateral primary TKA for knee osteoarthritis (OA). Additionally, 88 participants were recruited to serve as the healthy age-matched control group. Exclusion criteria for both groups can be found in the original article. Participants who underwent a TKA were randomized into one of three groups: progressive strengthening rehabilitation, progressive strengthening rehabilitation plus neuromuscular electrical stimulation for the quadriceps, or standard of care. All participants received inpatient rehabilitation in the hospital, followed by home and outpatient PT. Participants in the progressive strengthening rehabilitation groups completed at least 12 outpatient PT visits at the University of Delaware Physical Therapy clinic. Treatment focused on addressing the physical impairments after TKA as well as progressive strengthening exercises that targeted muscle groups in the lower extremity. Participants in the standard of care group attended other physical therapy clinics in the community and completed an average of 23 outpatient PT sessions with no set guidelines for clinicians to follow. Treatment primarily consisted of range of motion (ROM) exercises, stationary cycling, and various straight-leg exercises.
The Knee Outcome Survey – Activity of Daily Living (KOS-ADL), active knee ROM, maximal voluntary isometric contraction (MVIC) of the quadriceps, the Timed Up and Go (TUG), stair climbing time (SCT), and 6-minute walk (6MW) test were measured 12 months following surgery as well as in the control group to compare between groups.
There was a significant between-group effect for all clinical variables.
A higher proportion of participants in the progressive strengthening group achieved the lower bound cut-off for knee extension ROM, quadriceps strength, and SCT compared to the standard of care group.
Participants in the progressive strengthening group were 2-4 times more likely to achieve performance above the lower bound of the of the confidence interval of the control group for knee extension angle, performance on SCT, and quadriceps strength.
The percentage of participants in the progressive strengthening group that achieved the lower bound cutoff in at least one of the seven variables analyzed was greater compared to the standard of care group (67% vs. 47.5%).
Similar to previous research, participants who underwent a TKA demonstrated worse self-reported scores, greater physical impairments, and lower performance-based outcomes compared to the control group. However, a greater proportion of patients in the progressive strengthening protocol achieved what could be considered normal clinical and functional scores when evaluating the outcomes individually. This suggests that patients who follow a progressive strengthening protocol post-TKA may improve their likelihood of achieving normal age-matched outcomes. Also, a greater proportion of participants in the progressive strengthening group achieved the lower bound cut-off for quadriceps strength, knee extension angle, and SCT, suggesting progressive exercises may be more effective in optimizing outcomes after TKA.
It’s important to note that all participants still had substantial impairments 12 months after surgery compared to the control group. Failing to restore function by 12 months after surgery may overall impact the patient’s ability to achieve normal function as progress measured by outcome measures typically plateaus around 12 months post-surgery. There are many factors that may contribute to this such as pre-operative function, lack of consensus between providers regarding rehabilitation protocol and surgical procedure. Regardless, this highlights the importance of including the inherent limitations of the surgical procedure and post-op rehabilitation at restoring normal function for patients with end-stage OA when educating patients.
Take Home Messages:
TKA is a surgery that is becoming increasingly more common as time goes on and research has consistently showed that after surgery, it is difficult for patients to achieve pre-surgery function that can be comparable to age-matched peers without knee pathology. As more active patients begin to undergo this surgery, it’ll be important that they are able to achieve pre-surgery function to enable them to participate in recreational activity or more physically demanding occupations. While this study showed that overall, all participants demonstrated worse functional outcomes compared to the control group, participants in the progressive strengthening group demonstrated better functional outcomes compared to the standard of care group. This suggests that the inclusion of these exercises may be beneficial to the functional recovery of TKA patients. There are still many other factors that may be contributing to why TKA patients have difficulty recovering to their pre-surgery function, which emphasizes the role of patient education in the recovery process to set realistic expectations for these patients while also enabling them to recover to their greatest ability.
Pozzi, F., White, D. K., Snyder-Mackler, L., & Zeni, J. A. (2020). Restoring physical function after knee replacement: a cross sectional comparison of progressive strengthening vs standard physical therapy. Physiotherapy theory and practice, 36(1), 122–133. https://doi.org/10.1080/09593985.2018.1479475