Cranial translation of the humeral head on radiographs in rotator cuff tear patients: the modified active abduction view

Errors in Measuring Glenohumeral Arthrokinematics With 2-Dimensional Fluoroscopy

Two-dimensional fluoroscopic imaging allows measurement of small magnitude humeral head translations that are prone to errors due to optical distortion, out-of-plane imaging, repeated manual identification of landmarks, and magnification. This article presents results from in vivo and in vitro fluoroscopy-based experiments that measure the errors and variability in estimating the humeral head translated position in true scapular plane and axillary views. The errors were expressed as bias and accuracy. The variability with repeated digitization was calculated using the intraclass correlation coefficient (ICC) and the standard error of measurement. Optical distortion caused underestimation of linear distances. The accuracy was 0.11 and 0.43 mm for in vitro and in vivo experiments, respectively, for optical distortion. The intrarater reliability was excellent for both views (ICC = .94 and .93), and interrater reliability was excellent (ICC = .95) for true scapular view but moderate (ICC = .74) for axillary views. The standard error of measurement ranged from 0.27 to 0.58 mm. The accuracy for the humeral head position in 10° out of true scapular plane images ranged from 0.80 to 0.87 mm. The current study quantifies the magnitude of error. The results suggest that suitable measures could be incorporated to minimize errors and variability for the measurement of glenohumeral parameters.

Reliability and discriminative accuracy of 5 measures for craniocaudal humeral position: an assessment on conventional radiographs

Hypothesis

This study aimed to examine the reliability and diagnostic discriminative accuracy of 5 different methods that quantity the craniocaudal humeral position with respect to the scapula on conventional radiographs.

Methods

In this retrospective, cross-sectional diagnostic study, 2 observers randomly assessed the conventional anteroposterior shoulder radiographs of 280 subjects with rotator cuff imaging for the (1) acromiohumeral (AH) interval, (2) upward migration index (UMI), (3) glenohumeral center-to-center measurement (GHCC), (4) glenohumeral arc measurement (GHa), and (5) scapular spine–humeral head center method (SHC). Reliability was assessed by means of relative consistency (intraclass correlation coefficient) and absolute consistency. Discriminative accuracy for detecting a rotator cuff tear was calculated.

Results

Relative consistency (intraclass correlation coefficient) for the AH interval, UMI, GHCC, GHa, and SHC was 0.961, 0.913, 0.806, 0.924, and 0.726, respectively. The AH interval had the highest absolute consistency with a random residual measurement error of 0.58 mm compared with 1.0-3.2 mm for the other measurements. The discriminative accuracy of the AH interval did not significantly differ from that of the UMI (−0.010; 95% confidence interval [CI], −0.042 to 0.022; P = .545) but was significantly better than that of the GHCC (0.112; 95% CI, 0.043-0.181; P = .001), GHa (0.074; 95% CI, 0.009-0.139; P = .027), and SHC (0.178; 95% CI, 0.100-0.256; P < .001).

Conclusion

Assessment of the craniocaudal humeral position is performed with good to excellent intraobserver and interobserver reliability. The discriminative accuracy for detecting a rotator cuff tear on a single radiograph was highest for the AH interval and UMI. We recommend using the AH interval or UMI as an indirect measure of the presence of a rotator cuff tear on conventional radiographs.

Three-dimensional shoulder motion after teres major or latissimus dorsi tendon transfer for posterosuperior rotator cuff tears

BACKGROUND

Teres major (TM) transfer and latissimus dorsi (LD) transfer are essential treatment options in patients with posterosuperior rotator cuff (RC) tears. The purpose of this study was to quantify shoulder kinematics before and after TM transfer and LD transfer in posterosuperior RC tear patients.

METHODS

In this prospective cohort study, we quantitatively measured shoulder movements using an electromagnetic tracking device (Flock of Birds) preoperatively and 1 year after either TM (n = 13) or LD (n = 9) tendon transfer. Additional outcome measures included the Constant score (CS), patient-reported pain, and quantitative range of motion. Scapular kinematics were evaluated during arm abduction.

RESULTS

By use of a quantitative assessment, forward flexion (from 87° to 106°, P = .007), abduction (from 86° to 106°, P = .010), and external rotation in abduction (from 52° to 70°, P = .019) improved. Both transfers reduced pain (from 50 to 10 mm, P < .001), and the CS improved (from 37 to 62 points, P < .001). No significant differences in postoperative improvement in pain and function were found between TM and LD tendon transfers. The TM transfer group showed increased scapular lateral rotation compared with the LD transfer group (13°; 95% confidence interval [CI], 4.8° to 21.7°; P = .003). We were unable to detect differences between TM transfer and LD transfer in the change in protraction (3.2°; 95% CI, -6.3° to 12.8°; P = .489) and posterior tilt (3.5°; 95% CI, -3.5° to 10.5°; P = .313).

CONCLUSION

Tendon transfer surgery resulted in an overall improvement in CS, pain relief, and quantitative range of motion in the treatment of an irreparable posterosuperior RC tear. Scapular lateral rotation gradually increased after TM transfer, reminiscent of RC function, whereas such an increase was not observed after LD transfer.

Molecular signatures of age-associated chronic degeneration of shoulder muscles

Chronic muscle diseases are highly prevalent in the elderly causing severe mobility limitations, pain and frailty. The intrinsic molecular mechanisms are poorly understood due to multifactorial causes, slow progression with age and variations between individuals. Understanding the underlying molecular mechanisms could lead to new treatment options which are currently limited. Shoulder complaints are highly common in the elderly, and therefore, muscles of the shoulder's rotator cuff could be considered as a model for chronic age-associated muscle degeneration. Diseased shoulder muscles were characterized by muscle atrophy and fatty infiltration compared with unaffected shoulder muscles. We confirmed fatty infiltration using histochemical analysis. Additionally, fibrosis and loss of contractile myosin expression were found in diseased muscles. Most cellular features, including proliferation rate, apoptosis and cell senescence, remained unchanged and genome-wide molecular signatures were predominantly similar between diseased and intact muscles. However, we found down-regulation of a small subset of muscle function genes, and up-regulation of extracellular region genes. Myogenesis was defected in muscle cell culture from diseased muscles but was restored by elevating MyoD levels. We suggest that impaired muscle functionality in a specific environment of thickened extra-cellular matrix is crucial for the development of chronic age-associated muscle degeneration.

Evaluation of supraspinatus strengthening exercises based on fiber bundle architectural changes

Supraspinatus strengthening is an integral part of rehabilitation programs. However, there is disparity regarding the best exercise. Thus, we investigated the effects of supraspinatus strengthening exercises on muscle fiber bundle architecture using real-time ultrasound. Participants were randomized into full-can (FC; n = 12), empty-can (EC; n = 11,) and prone horizontal abduction (PHA; n = 11) groups and performed three sessions/week for 8 weeks. Each session involved four sets of exercise for weeks 1-4 and six sets for weeks 5-8 with eight repetitions/set. Images of supraspinatus were captured in 0° (relaxed) and 60° (contracted) glenohumeral abduction. Fiber bundle length (FBL), pennation angle, and muscle thickness were measured at beginning, mid, and end of training. Maximum isometric abduction strength was measured in full-can, empty-can, and prone horizontal abduction positions using a hand-held dynamometer. FBL decreased after 4 weeks in FC [relaxed: Δ = -0.54 cm, P = 0.001, d = 0.92; contracted: Δ = -0.27 cm, P = 0.008, d = 0.27] and EC [relaxed: Δ = -0.59 cm, P = 0.008, d = 0.86; contracted: Δ = -0.36 cm, P = 0.013, d = 0.59], but not in PHA [relaxed: Δ = -0.11, P = 0.121, d = 0.31; contracted: Δ = -0.06 cm, P = 0.486, d = 0.13]. Strength increased significantly from week 4-8 only in PHA (Δ = +0.96 kg, P = 0.004, d = 0.47) when tested in prone horizontal abduction position. Maintenance of FBL with increased strength indicates prone horizontal abduction may be a better exercise to strengthen supraspinatus.

Glenohumeral translations during range-of-motion movements, activities of daily living, and sports activities in healthy participants

BACKGROUND

Glenohumeral translations have been mainly investigated during static poses while shoulder rehabilitation exercises, activities of daily living, and sports activities are dynamic. Our objective was to assess glenohumeral translations during shoulder rehabilitation exercises, activities of daily living, and sports activities to provide a preliminary analysis of glenohumeral arthrokinematics in a broad range of dynamic tasks.

METHODS

Glenohumeral translations were computed from trajectories of markers fitted to intracortical pins inserted into the scapula and the humerus. Two participants (P1 and P2) performed full range-of-motion movements including maximum arm elevations and internal-external rotations rehabilitation exercises, six activities of daily living, and five sports activities.

FINDINGS

During range-of-motion movements, maximum upward translation was 7.5mm (P1) and 4.7mm (P2). Upward translation during elevations was smaller with the arm internally (3.6mm (P1) and 2.9mm (P2)) than neutrally (4.2mm (P1) and 3.7mm (P2)) and externally rotated (4.3mm (P1) and 4.3mm (P2)). For activities of daily living and sports activities, only anterior translation during reach axilla for P1 and upward translation during ball throwing for P2 were larger than the translation measured during range-of-motion movements (108% and 114%, respectively).

INTERPRETATION

While previous electromyography-based studies recommended external rotation during arm elevation to minimize upward translation, measures of glenohumeral translations suggest that internal rotation may be better. Similar amplitude of translation during ROM movement and sports activities suggests that large excursions of the humeral head may be caused not only by fast movements, but also by large amplitude movements.

The minimal detectable change of the Constant score in impingement, full-thickness tears, and massive rotator cuff tears

HYPOTHESIS

The purpose of this study was to determine the minimal detectable change (MDC) for the Constant score in patients with impingement, a supraspinatus tear, or a massive rotator cuff (RC) tear as observed changes smaller than the MDC might be the result of measurement error.

METHODS

The Constant score was recorded in a total of 180 patients, including 34 patients with impingement, 105 with supraspinatus tears, and 41 with massive RC tears. We assessed the MDC in the 3 subgroups and total group using the samples standard deviation (SD), internal consistency (Cronbach α), and standard error of the measurement. Floor and ceiling effects were also reported.

RESULTS

The absolute mean Constant score was 72 (SD, 11.2) in the impingement group, 44 (SD, 14.7) in the supraspinatus tear group, and 46 (SD, 18.9) in the massive RC tear group. There were no floor and ceiling effects for the absolute Constant score. In the total group, the internal consistency was 0.8 and the standard error of the measurement was 8. The MDC was 23 points on the Constant score in the total group and 17, 18, and 23 points on the Constant score for impingement, RC tears, and massive RC tears, respectively.

CONCLUSION

This study demonstrates that the MDCs of the Constant score are different in patients with impingement, supraspinatus tears, and massive RC tears. Studies reporting the Constant score should be interpreted by use of the population-specific MDC and minimal clinical important change.

Multivariate analyses of rotator cuff pathologies in shoulder disability

Background

Disability of the shoulder joint is often caused by a tear in the rotator cuff (RC) muscles. Four RC muscles coordinate shoulder movement and stability, among them the supraspinatus and infraspinatus muscle which are predominantly torn. The contribution of each RC muscle to tear pathology is not fully understood. We hypothesized that muscle atrophy and fatty infiltration, features of RC muscle degeneration, are predictive of superior humeral head translation and shoulder functional disability.

Methods

Shoulder features, including RC muscle surface area and fatty infiltration, superior humeral translation and RC tear size were obtained from a consecutive series of Magnetic Resonance Imaging with arthrography (MRA). We investigated patients with superior (supraspinatus, n = 39) and posterosuperior (supraspinatus and infraspinatus, n = 30) RC tears, and patients with an intact RC (n = 52) as controls. The individual or combinatorial contribution of RC measures to superior humeral translation, as a sign of RC dysfunction, was investigated with univariate or multivariate models, respectively.

Results

Using the univariate model the infraspinatus surface area and fatty infiltration in both the supraspinatus and infraspinatus had a significant contribution to RC dysfunction. With the multivariate model, however, the infraspinatus surface area only affected superior humeral translation (p<0.001) and discriminated between superior and posterosuperior tears. In contrast neither tear size nor fatty infiltration of the supraspinatus or infraspinatus contributed to superior humeral translation.

Conclusion

Our study reveals that infraspinatus atrophy has the strongest contribution to RC tear pathologies. This suggests a pivotal role for the infraspinatus in preventing shoulder disability.

Shoulder biomechanics and the success of translational research

In 2009, the International Shoulder Group (ISG) had the opportunity to propose to the readers of Medical and Biological Engineering and Computing a Special Issue on shoulder biomechanics. At that time, we pointed out that the field was evolving to include more applied research. After 4 years, we can confirm that impression: 10 out of 12 papers included in this second Special Issue deal with clinical related questions, through theoretical and experimental methodologies. This demonstrates that the translational research at the base of ISG foundation in 1989 is effective. We think that the papers of this issue will have an impact on clinics in general and on the treatment of work-related injuries and diseases in particular. Based on the statistics of the Italian Workers' Compensation Authority (INAIL), injuries at the shoulder are first in terms of average duration of "temporary total disability to work". Moreover, occupational diseases at the shoulder in the industrial and services sector represented 16 % of all occupational diseases in 2012, i.e., 46 % of those related to the upper limb. These data stress the need for specific interventions, with the contribution of both researchers and policy makers. Starting from the papers included here, we would encourage additional efforts on: (1) quantitative analysis of shoulder loading during tasks associated with musculoskeletal injuries, and ways to reduce that loading, (2) simple and effective tools to improve the diagnosis and outcome assessment of motion-related shoulder diseases, and (3) the development of rehabilitation treatments focused on occupational tasks, taking advantage of state-of-the-art biofeedback technologies, and exploiting the power of biomechanical models for muscle force prediction.