DISCUSSION
This was the first study to assess the predictive value of functional performance and ROM measures on acute and long-term outcomes after TKA. Acute measures of knee ROM were not related to long-term ROM outcomes, whereas preoperative measures of ROM were. Both preoperative and acute measures of functional performance were predictive of long-term functional performance. However, preoperative functional performance was a stronger predictor of long-term functional performance than acute functional performance.
Factors affecting ROM after TKA have been examined in several studies. Preoperative ROM has been the strongest predictor of postoperative ROM, with contributory factors of age, sex, obesity, a history of knee surgery, presence of an extensor lag, diagnosis, intraoperative ROM, use of a posterior capsule release, and postoperative tibiofemoral angle.10,25–27 In the current study, preoperative ROM was also found to be a significant predictor of long-term ROM. However, acute ROM, measured at a time when discharge planning had begun, was not related to long-term ROM outcomes. This suggests that ROM measurements on postoperative day 2 are not indicative of how a patient will do long-term. Ideally, limited preoperative ROM should be used to identify individuals who will require more intensive, supervised rehabilitation to minimize poor ROM outcomes or subsequent need for manipulation.
The poor correlation of acute ROM measures with long-term ROM measures could be contributed to several potential variables. For example, high levels of pain immediately after surgery may cause patients to be tentative about challenging their limit of mobility. Therefore, differences in pain tolerance, anesthesia type, and postoperative dosing of pain medication may have led to increased ROM variability at this time point and a lack of relationship to long-term ROM. Time since surgery may also play a role. The measurements on postoperative day 2 in this study were not related to long-term outcomes. However, in Australian studies28,29 in which hospital stays are longer, inpatient ROM measurements of extension performed at discharge on postoperative days 6–8 were related to long-term extension ROM; the same relationship was not observed for flexion.
Functional performance after TKA is known to be related to preoperative functional performance, comorbid conditions, age, sex, quadriceps strength in the involved and uninvolved limbs, and postoperative rehabilitation.5–9,24,30–32 In this study, both preoperative and acute performance on the TUG were predictive of long-term functional performance on the 6MW test. However, after adjusting for the effects of age, sex, and preoperative functional performance, acute TUG performance was no longer predictive of long-term functional performance. This suggests that preoperative functional performance is a better measure for determining prognosis when both preoperative and acute postoperative outcomes are available. However, because clinicians do not always have access to preoperative functional data, acute TUG performance can be used to guide discharge planning in the acute setting and predict long-term functional performance.
The primary limitation of this study was that the inclusion criteria for the two pooled clinical trials were fairly strict. Thus, the results cannot be generalized to the population of all individuals who undergo TKA. Comorbidities are known to influence ROM and functional performance, and patients with significant comorbidities were excluded from both clinical trials. An additional limitation was that the rehabilitation intervention used in this study may not be representative of practice patterns in other regions of the United States, which may have affected long-term outcomes.
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CONCLUSIONS
For discharge planning in the acute setting, preoperative ROM and functional performance should ideally be used to identify patients who may require close monitoring or intensive rehabilitation. If preoperative measures are not available, acute postoperative performance on the TUG test can be useful for establishing a prognosis. However, acute postoperative ROM measurements have very limited prognostic utility.
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Acknowledgments
Disclosures:
Supported by the National Institutes of Health (NIH) (K23 AG029978, R03 AR054538, T32 AG00279, UL1 RR025780) and the Foundation for Physical Therapy Promotion of Doctoral Studies II Scholarship. The authors certify that no party having a direct interest in the results of the research supporting this article has or will confer a benefit on the authors or on any organization with which they are associated, and, if applicable, the authors certify that all financial and material support for this research (e.g., NIH or NHS grants) and work are clearly identified in the title page of this article.