Interobserver reproducibility of the assessment of severity of complaints, grip strength, and pressure pain threshold in patients with lateral epicondylitis

Objective: To evaluate the interobserver reproducibility of the assessment of severity of complaints, grip strength, and pressure pain threshold in patients with lateral epicondylitis in primary care.Design: Two physiotherapists assessed independently, and in randomized order, the severity of complaints scored on an 11-point numeric rating scale, pain-free grip strength, maximum grip strength, and pressure pain threshold.Setting: Primary care center in the Netherlands.Participants: Fifty patients were assessed by both physiotherapists.Interventions: Not applicable.Main Outcome Measures: Intraclass correlation coefficients (ICCs) and 95% confidence intervals (CIs) were calculated to assess interobserver reliability. The Bland and Altman method was used to assess interobserver agreement, which included calculation of the mean difference between the observers (d), the 95% CI for d, the standard deviation of the differences, and the 95% limits of agreement. Finally, the smallest detectable difference (SDD) was calculated.Results: The ICC for the severity of complaints was .90. The ICCs for the pain-free grip strength and maximum grip strength were .97 and .98, respectively. The pressure pain threshold showed a lower reliability (ICC=.77). The interobserver agreement for all outcome measures was good, but systematic differences in assessment between the physiotherapists were found for the maximum grip strength and pressure pain threshold. For pressure pain threshold, the SDD was clearly larger than the predefined acceptable difference of 10% of the total range of measurement.Conclusions: The interobserver reliability of severity of complaints and grip strength was excellent, whereas the pressure pain threshold showed unsatisfactory reliability. Grip strength and overall assessment of the severity of complaints are useful and reliable measures for the assessment of lateral epicondylitis. Pain-free grip strength, in particular, is relatively easy to perform and has been shown to be associated with other measures of functional disability in patients with lateral epicondylitis. We, therefore, recommend the use of pain-free grip strength in both research and clinical practice.