Variability of glenohumeral positioning and bone-to-tendon marker length measurements in repaired rotator cuffs from longitudinal computed tomographic (CT) imaging

Abstract Background To address the need for more objective and quantitative measures of tendon healing in research studies, we intend to use computed tomography (CT) imaging with implanted radiopaque markers on the repaired tendon to measure tendon retraction following rotator cuff repair. In our small prior study, retraction at 1 year follow-up averaged 16.1± 5.3mm and exceeded 10.0mm in 12 of 13 patients, and thus tendon retraction appears to be a common clinical phenomenon. This study’s objectives were to assess, using five longitudinal CT scans obtained over one year following rotator cuff repair, the variability in glenohumeral positioning due to pragmatic variations in achieving perfect arm repositioning, and to estimate the associated measurement variability in bone-to-tendon marker length measurements. Methods Forty-eight patients underwent rotator cuff repair with intra-operative placement of radiopaque tendon markers at the repair site. All patients had a CT scan with their arms at the side on the day of surgery and at 3, 12, 26, and 52 weeks postoperatively. Glenohumeral position (defined by the orientation and distance of the humerus with respect to the scapula) and bone-to-tendon marker lengths were measured from each scan. Within-patient variation in glenohumeral position measurements was described by their pooled within-patient standard deviations (SD), and variation in bone-to-tendon marker lengths by their standard errors of measurement (SEM) and 95% confidence level minimally detectable distances (MDD95) and changes (MDC95). Results The mean glenohumeral orientation from the five longitudinal CT scans averaged across the 48 patients was 12.6° abduction, 0.4° flexion and -0.1° internal rotation. Within-patient SDs [95% confidence intervals] of glenohumeral orientation were 3.0° [2.7°–3.4°] in extension/flexion, 5.2° [4.6°–5.8°] in abduction/adduction and 8.2° [7.3°–9.2°] in internal/external rotation. The SDs of glenohumeral distances were less than 1mm in any direction. The estimated SEMs of bone-to-tendon lengths were consistent with a common value of 2.4mm for any of the tendon markers placed across the repair, with MDD95 of 4.7mm and MDC95 of 6.7mm. Conclusion Apparent tendon retraction of 5mm or more, when measured as the distance from a tendon marker’s day of surgery location to its new location on a volumetrically registered longitudinal CT scan, may be considered above the usual range of measurement variation. Tendon retraction measured using implanted radiopaque tendon markers offers an objective and sufficiently reliable means for quantifying the commonly expected changes in structural healing following rotator cuff repair.