Comparative responsiveness of four elbow scoring instruments in patients with rheumatoid arthritis.

OBJECTIVE: This prospective study investigated the comparative responsiveness to change of 4 different elbow scoring instruments: 2 Hospital for Special Surgery elbow assessment scales, the Mayo Clinic Elbow Performance Index, and the Elbow Functional Assessment (EFA) Scale. METHODS: A group of patients with rheumatoid arthritis (RA) (median age 60 yrs) undergoing either elbow arthroplasty (22 elbows) or synovectomy with radial head excision (3 elbows) were evaluated both before and after surgery (median 7 mo postoperatively). Changes in the scores obtained using the scales under study were calculated and analyzed. The patient's opinion of global perceived effect of the intervention was used as an external criterion to classify them as "improved" or "non-changed." Responsiveness was evaluated with 3 different statistical approaches: using paired t statistics (pre and postsurgery scores), effect size statistics (standardized response mean, effect size, and responsiveness ratios), and receiver operator characteristic curves. Minimal clinically important difference was estimated using patient satisfaction as the external criterion. RESULTS: Each of the elbow rating measures under study proved to be responsive to change when evaluating patients with RA undergoing elbow arthroplasty or synovectomy. The EFA scale had the highest power to detect a clinically meaningful difference and had the best discriminative ability to distinguish improved from no-change patients, as shown by all responsiveness statistics applied. CONCLUSION: Using the EFA scale requires smaller sample sizes to achieve a fixed level of statistical power than the other scales we studied.

Determining the optimal flexion-extension axis of the elbow in vivo - a study of interobserver and intraobserver reliability.

In the current study the interobserver and intraobserver reliability of a recently developed method to obtain the position and orientation vectors of the flexion-extension axis of the elbow in vivo is determined. The method uses the Flock of Birds six degrees-of-freedom electromagnetic tracking device. Ten subjects performed three trials comprising five flexion and extension cycles. The movements of the forearm with respect to the upper arm were recorded. Observer A measured two trials and observer B measured one trial. Optimal instantaneous helical axes were calculated in a humeral coordinate system for each trial. Intraclass correlation coefficients and 99% confidence intervals were computed to compare the three measurements. Zero was in the range of all the narrow confidence intervals, which is strong indication for resemblance. Interobserver intraclass correlation coefficients values for orientation vectors were good to excellent and intraobserver values were fair to good. The intraclass correlation coefficients values for position vectors were lower, probably due to the lack of variance between subjects. It is concluded that the method is reliable and can be used in certain clinical settings.

Clinical reliability and validity of elbow functional assessment in rheumatoid arthritis.

OBJECTIVES: (1) To investigate the measurement characteristics of the Hospital for Special Surgery (HSS) and Mayo Clinic elbow assessment instruments, utilizing methodological criteria including feasibility, reliability, validity, and discriminative ability; and (2) to develop an efficient and disease-specific rating system for elbow function assessment (EFA) in adult patients with RA, using a combination of self-reported subjective items and objective measures, and comparing its characteristics with the HSS and Mayo Clinic scales. METHODS: (1) Selection of elbow-specific items. (2) Investigation of reliability and validity of all separate items, as well as the total HSS and Mayo Clinic scores, in 42 patients with RA (mean age 60 yrs). Direct observation of functional elbow performance was defined as the gold standard against which criterion validity was compared. (3) Reaching agreement within a team of professionals on the different scale dimensions and the assigned weight. (4) Item reduction by eliminating unreliable, inaccurate, unfeasible, and ambiguous items. Finally, the EFA scale was constructed by selecting the most reliable and accurate items. RESULTS: The EFA scale showed a superior or equal degree of reliability as reflected in intraclass correlation coefficients of more than 0.88, and also superior validity, compared with the HSS and Mayo Clinic measures. CONCLUSION: Although the elbow scoring systems currently available provide a reliable measure, they seem restricted in evaluating elbow-specific functional ability. The EFA scale was found to be most suitable to measure elbow functional ability in RA, and was also shown to be highly reliable and practical in clinical practice.

Determination of the optimal elbow axis for evaluation of placement of prostheses.

OBJECTIVE: To present a method to determine the position and orientation of the mean optimal flexion axis of the elbow in vivo to be used in clinical research. DESIGN: Registering the movements of the forearm with respect to the upper arm during five cycles of flexion and extension of the elbow using a 6 degrees-of-freedom electromagnetic tracking device. BACKGROUND: Loosening of elbow endoprostheses could be caused by not placing the prostheses in a biomechanically optimal way. To evaluate the placement of endoprostheses with regard to loosening, a method to determine the elbow axis is needed. METHODS: The movements of the right forearm with respect to the upper arm during flexion and extension were registered with a 6 degrees-of-freedom electromagnetic tracking device. A mean optimal instantaneous helical axis of 10 elbows was calculated in a coordinate system related to the humerus. RESULTS: The average position of the flexion/extension axis was 0.81 cm (SD 0.66 cm) cranially and 1.86 cm (SD 0.72 cm) ventrally of the epicondylus lateralis. The average angle with the frontal plane was 15.3 degrees (SD 2 degrees). CONCLUSIONS: A useful estimation of the position and orientation of a mean optimal flexion axis can be obtained in vivo.