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Implications for practice and research
Younger patients with higher preoperative pain and depression are more likely to have higher pain on postoperative day 2 following total knee arthroplasty.
Cutaneous pain sensitivity correlates with postoperative knee movement pain but not rest pain, which suggests different underlying pain mechanisms.
Future research should investigate whether presurgical intervention on pain and psychological factors can improve postoperative pain and long-term outcomes following total knee arthroplasty (TKA).
TKA is generally regarded as a highly successful procedure to improve pain and function in patients with advanced degenerative joint disease. Perioperative pain management remains a major concern for patients contemplating TKA and residual pain has been associated with dissatisfaction and poor outcome. This study aims to identify which preoperative characteristics are predictive of knee pain immediately following TKA using a comprehensive set of physiological and psychological variables.
This investigation was a prospective cohort study of 215 patients undergoing TKA at two institutions. Prior to surgery, participants were assessed for both pain at rest and pain with movement of their surgical knee, were given a series of quantitative sensory tests (heat, pressure and mechanical stimulation), and were evaluated for anxiety, depression and pain catastrophising. Pain intensity at rest and with movement was measured again on postoperative day 2 prior to physical therapy. Knee range of motion and analgesic medication requirements were also documented. Logistic regression analysis was performed to identify predictors of postoperative knee pain at rest versus pain with movement.
High preoperative pain was the strongest predictor of both rest and movement pain following TKA. Positive screening for depression also predicted both rest and movement pain. Interestingly, younger age was predictive of rest pain only, whereas cutaneous pain sensitivity to force and heat stimuli was predictive of movement pain only. This finding raises the possibility that the underlying pain mechanisms are different. Anxiety and pain catastrophising were associated with postoperative pain in the univariate analysis but were not statistically significant in the regression analysis.
This study provides a relevant and novel analysis of pain in the immediate postoperative period following TKA and should be of interest to clinicians caring for patients as well as those seeking to understand variability in patient experience. The primary conclusion of this study confirms previous reports regarding the importance of preoperative pain and psychological factors in the outcome of TKA. Unique to this study, however, is the inclusion of physiological measures of cutaneous pain. Distinguishing between movement pain and resting pain is also a novel approach.
Identifying the importance of preoperative psychological and physiological factors on immediate postoperative pain provides clinicians with potentially modifiable variables to improve outcomes and patient satisfaction. Although identifying and managing at-risk patients with depression and preoperative pain prior to TKA would seem to be a logical way to optimise outcomes, the efficacy of specific interventions and treatment methods remains to be determined. For example, prescribing opioids in an attempt to improve preoperative pain control has in fact been associated with poorer outcomes following TKA.1 Future investigations will be needed to determine whether devised interventions to treat depression, reduce pain or diminish cutaneous sensitivity will have the intended postoperative result.
The generalisability of this study is limited by the fairly small and homogeneous sample size of predominantly white and educated patients. The study was limited to immediate postoperative pain, and while the severity of early postoperative knee pain has been associated with persistent pain and poor outcome following TKA at mid-term follow-up,2 the relationship between predictors and outcomes may vary with time. It remains to be seen whether or not the predictors of early pain, along with the distinction between rest versus movement pain, continue to be important variables in the long term. The current findings should be examined in the context of functional outcomes, patient satisfaction and the ultimate ‘success’ of the procedure. Finally, the practicality and clinical role of cutaneous sensory testing requires critical assessment prior to implementation.
Despite these limitations, this study is a valuable and timely contribution to our understanding of early outcomes following TKA. This study identifies patients at-risk for immediate postoperative pain, raises important questions regarding the preoperative management of pain and mental health, provides support for counselling patients and managing expectations and may help introduce factors that can be targeted with interventions designed to improve outcomes.
Competing interests None.
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