Relation of Sensitization and Conditioned Pain Modulation to Post-Knee Replacement Pain

Tuhina Neogi¹, Na Wang², Cora E. Lewis³, Michael C. Nevitt⁴ and Laura Frey-Law⁵, ¹Clinical Epidemiology Research and Training Unit, Boston University School of Medicine, Boston, MA, ²Boston University School of Medicine, Boston, MA, ³University of Alabama Birmingham, Birmingham, AL, ⁴Epidemiology and Biostatistics, University of California, San Francisco, San Francisco, CA, ⁵University of Iowa, Iowa City, IA

Meeting: 2018 ACR/ARHP Annual Meeting

Keywords: Joint arthroplasty and pain

Session Information

Date: Monday, October 22, 2018

Title: 4M103 ACR Abstract: Pain Mechanisms–Basic & Clinical Science (1917–1922)

Session Type: ACR Concurrent Abstract Session

Session Time: 4:30PM-6:00PM

Background/Purpose: Alterations in pain processing, such as pain sensitization and inadequate conditioned pain modulation (CPM), may contribute to the observed pain persistence post-knee replacement (KR) in 20-30% of patients, but studies to date have been conflicting. Further, many studies have been small and comprised only subjects who experienced post-KR pain improvement. It is therefore not known if altered pain processing is present in those with persistent post-KR pain. We undertook a comprehensive evaluation of pain sensitization and CPM in relation to post-KR pain.

Methods: The Multicenter Osteoarthritis (MOST) Study is a NIH-funded longitudinal cohort of persons with or at high risk of knee OA. We evaluated subjects prior to KR and 12-18 months post-KR with a standardized somatosensory evaluation of mechanical pressure pain thresholds (PPT) at the wrist and patellae, temporal summation (TS) at the wrist, and WOMAC pain questionnaires. CPM was assessed post-KR. PPT was assessed with an algometer (1cm²tip, 0.5 Kg/sec) as the point at which pressure first changed to slight pain; 3 trials at each anatomic site were averaged. Lower PPT indicates more pain sensitivity, reflecting peripheral sensitization at a site of disease and central sensitization at a site without disease. Temporal summation, indicating central sensitization, was defined by increased pain during repeated mechanical stimulation (1 Hz x 30-sec) with a 60g monofilament. CPM was assessed using the forearm ischemia test. Inadequate CPM was defined as a ratio of <1, indicating lack of increase in post-conditioning stimulus PPT. We evaluated the relation of pre- and post-KR PPT and TS, and of post-KR CPM to post-KR WOMAC pain and to a minimal clinically important difference (MCID) in WOMAC pain, adjusting for potential confounders.

Results: There were 171 subjects in our study who were seen before and after their KR (mean age 69, 62% female, mean BMI 31). Pre-KR PPT and pre-KR TS were not associated with post-KR WOMAC pain (Table). Post-KR TS and inadequate CPM were significantly associated with a worse WOMAC pain score post-KR, and nonsignficantly with lower likelihood of achieving the MCID.

Conclusion: Pre-KR PPT and TS were not associated with post-KR pain levels or pain improvement. Thus, while PPT and TS are associated with pain severity overall in knee OA subjects, they do not adequately predict pain response to KR. Post-KR presence of TS and inadequate CPM were associated with worse pain post-KR, suggesting a role for central altered pain processing in pain persistence post-KR, and provide support for pain phenotyping to guide mechanism-based treatment approaches.

	Post-KR WOMAC Pain		Minimal Clinically Important Difference (MCID) in Post-KR WOMAC Pain **
	Mean difference in WOMAC Pain* (95% CI)	P-value	OR (95% CI)	P-value
Pre-KR Measures:
Pre-KR TS	0.11 (-0.31, 0.54)	0.6	0.93 (0.70, 1.24)	0.6
Pre-KR PPT at wrist	-0.19 (-0.59, 0.20)	0.3	1.11 (0.84, 1.47)	0.5
Pre-KR PPT at patella	-0.07 (-0.32, 0.19)	0.6	1.02 (0.84, 1.23)	0.9
Post-KR Measures:
Post-KR TS	0.82 (0.19, 1.45)	0.01	0.73 (0.44, 1.21)	0.2
Post-KR PPT wrist	-0.21 (-0.63, 0.21)	0.3	0.99 (0.75, 1.31)	0.9
Post-KR PPT patella	-0.15 (-0.45, 0.15)	0.3	1.02 (0.82, 1.26)	0.9
Inadequate CPM (<1)	1.47 (0.26, 2.68)	0.02	0.78 (0.56, 3.00)	0.6
Mean differences refers to an increase (positive value, indicating worsened pain) or decrease (negative value indicating pain improvement) in WOMAC pain post-KR relative to pre-KR value per unit increase in continuous variables (TS, PPT) or for those with vs. without that feature for dichotomous variables (inadequate CPM) *Defined as an improvement of at least 5.6/20 (Escobar, et al. 2007) Analyses were adjusted for age, sex, BMI, depressive symptoms, pain catastrophizing, clinic site, time of clinic assessments relative to KR date

Disclosure: T. Neogi, None; N. Wang, None; C. E. Lewis, None; M. C. Nevitt, None; L. Frey-Law, None.

To cite this abstract in AMA style:

Neogi T, Wang N, Lewis CE, Nevitt MC, Frey-Law L. Relation of Sensitization and Conditioned Pain Modulation to Post-Knee Replacement Pain [abstract]. Arthritis Rheumatol. 2018; 70 (suppl 9). https://acrabstracts.org/abstract/relation-of-sensitization-and-conditioned-pain-modulation-to-post-knee-replacement-pain/. Accessed .

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