Human Studies

The purpose of this randomized controlled trial is to determine whether the quantity of opioid pills prescribed at discharge is associated with the number of opioid pills consumed or unused by patients after primary hip and knee arthroplasty within 30 days after discharge.

Up to 30% of patients experience persistent pain and functional limitations following total knee replacement (TKR). Rapid symptom relief in the early postoperative period may be linked to longer-term outcome improvements. We sought to identify early improvement trajectories and to identify risk factors for suboptimal outcomes.

Cross-sectional studies confirm, as expected, a positive association between jaw injury and painful temporomandibular disorders (TMDs), but prospective evaluations are lacking. We prospectively assessed incident jaw injury, injury type, and development of TMD in adults ages 18-44 years.Data were collected from 3,258 individuals from communities surrounding four U.S. academic institutes between 2006 and 2008. At enrollment, participants reported no TMD history and no facial injuries in the previous 6 months. Quarterly follow-up questionnaires assessed incident jaw injury, which was classified as intrinsic (attributed to yawning or prolonged mouth opening) or extrinsic (attributed to other causes). Examiners classified incident TMD during a median follow-up period of 2.8 years (range 0.2-5.2 years). Cox regression models used jaw injury as a time-dependent covariate to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for the association with incident TMD.Among 1,729 participants with complete data, 175 developed TMD. Eighty percent of injuries were intrinsic. TMD annual incidence was nearly twice as high in those experiencing jaw injury (5.37%) compared to those who did not (3.44%). In the Cox model that accounted for timing of injury, the corresponding HR was 3.94 (95%CI=2.82-5.50) after adjusting for study site, age, race, and gender. Hazard ratios did not differ (p=0.91) for extrinsic injuries (HR=4.03, 95%CI=2.00-8.12) and intrinsic injuries (HR=3.85, 95%CI=2.70-5.49).Jaw injury was strongly associated with incident TMD. If surveillance and intervention following jaw injury is to be effective in preventing TMD, they should focus on both intrinsic and extrinsic injuries.

Osteoarthritis (OA) is the most common cause of pain in people aged >45 years, and the knee is the most commonly affected joint. There is a growing interest in understanding the biological factors that influence pain among older adults, but few studies have examined the relationship between β-endorphin and experimental pain sensitivity in older adults with knee OA pain. The purpose of this study was to investigate the relationship between resting plasma levels of β-endorphin and experimental pain sensitivity. This study was a secondary analysis of data for 40 adults with knee OA pain in whom quantitative sensory testing was used to measure experimental sensitivity to heat- and mechanically induced pain. The mean age of the sample was 60 years ( SD = 9 years), and approximately half were female (53%). Regression analyses indicated that β-endorphin level was negatively related to pressure pain threshold (β = -17.18, p = .02) and positively related to punctate mechanical pain (β = 17.13, p = .04), after controlling for age, gender, and OA severity. We did not find a significant relationship between β-endorphin and heat pain tolerance. The results suggest that higher circulating levels of β-endorphin at rest are associated with increased sensitivity to mechanical pain in older adults with knee OA. These findings add to the literature regarding biological factors associated with pain sensitivity in older adults with chronic pain. Additional studies are needed to identify mediators of the relationship between β-endorphin and pain sensitivity in OA and other musculoskeletal pain conditions.

Chronic eye pain, which has previously been assumed to be due to ocular surface abnormalities (i.e., "dry eye disease"), has recently garnered attention as a potential indicator of neuropathic ocular pain in some patients. The purpose of this study was to evaluate the psychometric properties of a modified version of the Neuropathic Pain Symptom Inventory in individuals with eye pain (NPSI-Eye). Enrolled participants (n = 397) completed the NPSI-Eye, general pain severity questionnaires, dry eye symptom report, and psychological health indices. Participants also underwent mechanical pain sensitivity testing of the cornea, tear film assessment, and evaluation of the efficacy of anesthetic eye drops to relieve pain. Short-term test-retest reliability of the NPSI-Eye was excellent (intraclass correlation coefficient = 0.98, p < 0.001). Correlations between the NPSI-Eye and indicators of general eye pain were ≥ 0.65 (p < 0.001), while correlations between the NPSI-Eye and dry eye symptom severity and psychological health indices were lower (rho= 0.56, 0.32, 0.37; all p < 0.001). Individuals who reported little or no decrease in pain after anesthetic eye drops (hypothesized to indicate eye pain with at least partial central involvement) had significantly higher NPSI-Eye scores than participants whose eye pain was completely relieved by anesthetic (p < 0.05). Overall, our results support preliminary validation of the NPSI-Eye, yielding similar metrics to those reported in Bouhassira et al.'s original NPSI publication (2004). However, additional evaluation and refinement of some questions may be desirable, including the potential elimination of items that were not highly endorsed.