Direct and indirect costs to employers of patients with systemic lupus erythematosus with and without nephritis.

OBJECTIVES: To estimate the medical- and productivity-related cost burden of systemic lupus erythematosus (SLE) and SLE with nephritis in an employee population. METHODS: Using administrative data, annual costs were calculated for SLE patients, a subset with nephritis, and a matched control group of patients without SLE. These costs were compared with the cost of other chronic conditions. RESULTS: Mean annual medical expenditures and short term disability costs for SLE patients were $12,238 and $1184 greater (2005 dollars), respectively, than those of controls. Mean medical expenditures for SLE/nephritis patients were $46,862 greater than for controls. When compared with other chronic health conditions faced by employees, SLE/nephritis was the most costly condition. CONCLUSIONS: SLE, particularly with nephritis, is associated with substantial costs. Therapies that can better manage SLE may provide opportunities for savings to employers.

A multi-subject evaluation of uncertainty in anatomical landmark location on shoulder kinematic description.

An accurate assessment of shoulder kinematics is useful for understanding healthy normal and pathological mechanics. Small variability in identifying and locating anatomical landmarks (ALs) has potential to affect reported shoulder kinematics. The objectives of this study were to quantify the effect of landmark location variability on scapular and humeral kinematic descriptions for multiple subjects using probabilistic analysis methods, and to evaluate the consistency in results across multiple subjects. Data from 11 healthy subjects performing humeral elevation in the scapular plane were used to calculate Euler angles describing humeral and scapular kinematics. Probabilistic analyses were performed for each subject to simulate uncertainty in the locations of 13 upper-extremity ALs. For standard deviations of 4 mm in landmark location, the analysis predicted Euler angle envelopes between the 1 and 99 percentile bounds of up to 16.6 degrees . While absolute kinematics varied with the subject, the average 1-99% kinematic ranges for the motion were consistent across subjects and sensitivity factors showed no statistically significant differences between subjects. The description of humeral kinematics was most sensitive to the location of landmarks on the thorax, while landmarks on the scapula had the greatest effect on the description of scapular elevation. The findings of this study can provide a better understanding of kinematic variability, which can aid in making accurate clinical diagnoses and refining kinematic measurement techniques.

Evaluation of three methods for determining EMG-muscle force parameter estimates for the shoulder muscles.

BACKGROUND: Accurate prediction of in vivo muscle forces is essential for relevant analyses of musculoskeletal biomechanics. The purpose of this study was to evaluate three methods for predicting muscle forces of the shoulder by comparing calculated muscle parameters, which relate electromyographic activity to muscle forces. METHODS: Thirteen subjects performed sub-maximal, isometric contractions consisting of six actions about the shoulder and two actions about the elbow. Electromyography from 12 shoulder muscles and internal shoulder moments were used to determine muscle parameters using traditional multiple linear regression, principal-components regression, and a sequential muscle parameter determination process using principal-components regression. Muscle parameters were evaluated based on their sign (positive or negative), standard deviations, and error between the measured and predicted internal shoulder moments. FINDINGS: It was found that no method was superior with respect to all evaluation criteria. The sequential principal-components regression method most frequently produced muscle parameters that could be used to estimate muscle forces, multiple regression best predicted the measured internal shoulder moments, and the results of principal-components regression fell between those of sequential principal-components regression and multiple regression. INTERPRETATION: The selection of a muscle parameter estimation method should be based on the importance of the evaluation criteria. Sequential principal-components regression should be used if a greater number of physiologically accurate muscle forces are desired, while multiple regression should be used for a more accurate prediction of measured internal shoulder moments. However, all methods produced muscle parameters which can be used to predict in vivo muscle forces of the shoulder.

Shoulder kinematics in patients with full-thickness rotator cuff tears after a subacromial injection.

The purpose of this study was to test the hypothesis that scapulohumeral rhythm (SHR) is altered in patients with full-thickness rotator cuff tears due to pain. Fifteen subjects (mean age, 60.2 +/- 8.9 years; mean height, 1.72 +/- 0.10 m; mean weight, 85.43 +/- 18.32 kg) performed humeral elevation in the 3 planes before and after a lidocaine injection. Pain was assessed by use of a visual analog scale, and data were collected with an electromagnetic tracking system. Three-dimensional scapular kinematics (scapulothoracic motion) and glenohumeral elevation were assessed. A linear regression model was used to calculate SHR (ratio of scapulothoracic motion to glenohumeral elevation) for equal phases of elevation (I, II, and III) and lowering (IV, V, and VI). Pain was significantly reduced (P

Comparison of model-predicted and measured moment arms for the rotator cuff muscles.

BACKGROUND: The ability of mathematical models of the shoulder to accurately replicate physiological muscle moment arms is unknown. The purpose of this study was to compare model-predicted and experimentally measured moment arms for the rotator cuff muscles during arm elevation. METHODS: Moment arms obtained from six mathematical models and seven experimental studies were compared for the supraspinatus, infraspinatus, teres minor, and subscapularis for elevation in the scapular plane. RESULTS: All of the included models generated moment arms that generally fell within the range of experimentally measured data. INTERPRETATION: The quantitative agreement between model-predicted and experimentally measured moment arms supports the use of the included models for biomechanical shoulder analyses.

Electromyographic analysis of physical examination tests for type II superior labrum anterior-posterior lesions.

Physical examination tests that place tension on the long head of the biceps may best reproduce symptoms in patients with type II superior labrum anterior-posterior (SLAP) lesions. The objective of this study is to compare the normalized electromyographic signal of the long head of the biceps for SLAP lesion physical examination tests. The active compression test, anterior-superior SLAP test, biceps load test II, biceps tension test, and pain provocation test were performed on 13 subjects while biceps electromyographic data were recorded. The active compression test and biceps tension test had significantly higher electromyographic signals than the other tests. We found no significant differences when comparing forearm supination and pronation within individual tests. Because the active compression and biceps tension tests maximize muscle activation on the long head of the biceps, they may be the best physical examination tests by which to identify type II SLAP lesions.

Shoulder muscle activity increases with wrist splint use during a simulated upper-extremity work task.

OBJECTIVE: The purpose of this study was to test the hypothesis that wearing a wrist splint while performing a common light manufacturing task (moving an object from a bin) increases shoulder muscle activity. METHODS: Electromyography (EMG) signals were evaluated from the anterior, middle, and posterior deltoid, trapezius, supraspinatus, and infraspinatus of 14 volunteers while they moved an object from a bin. Two test conditions were measured: with and without a wrist splint. The height of the bin was also varied. RESULTS: Wearing a wrist splint increased maximum EMG for all six muscles and average levels for the deltoid (anterior, middle, posterior) and trapezius. As bin height increased, maximum muscle activity increased in the deltoid (anterior, middle, and posterior) and trapezius, and the average increased in the deltoid (middle and posterior) and trapezius. CONCLUSIONS: Workplace factors can modify the activation of a patient's shoulder muscles when he or she is wearing a wrist splint. An ergonomic job analysis should be conducted for patients who are returning to work wearing wrist splints.

The effect of wearing a wrist splint on shoulder kinematics during object manipulation.

OBJECTIVES: To test the hypotheses that (1) wearing a flexible wrist splint while taking an object from a box increases known postural risk factors for shoulder disorders and (2) that the height of the front of the box modulates the effect on shoulder kinematics of wearing a wrist splint. DESIGN: A controlled laboratory experiment with 2 factors (splint wearing, box height). SETTING: Human performance laboratory. PARTICIPANTS: Ten consecutive healthy volunteers (5 men, 5 women; age range, 19-32 y). INTERVENTIONS: Experimental manipulation of wrist immobilization and box height. MAIN OUTCOME MEASURES: Humeral plane of elevation, humeral elevation, and humeral axial rotation. RESULTS: Wearing a wrist splint increased the maximum humeral elevation angle (P<.001), and the height of the barrier also increased the maximum humeral elevation angle (P<.001). The average difference in maximum humeral elevation between the splint and the no splint conditions was 6.8 degrees . CONCLUSIONS: Wearing a wrist splint while performing a job that requires removing objects from a box can increase risk factors for shoulder disorders. Workplace analysis should be performed to avoid secondary injuries before a patient wearing a wrist splint returns to work.

Effect of rotator cuff pathology on shoulder rhythm.

The purpose of this study was to test the hypothesis that shoulder rhythm is affected by rotator cuff pathology during arm elevation. We divided 42 subjects into 3 groups: those with full-thickness rotator cuff tears (RCTs) (n = 14), those with tendinopathy (n = 13), and control subjects (n = 15). Shoulder kinematics was recorded while subjects performed elevation in the sagittal and scapular planes. Euler angles were computed for scapular and humeral elevation. Data were divided into 3 equal phases. Lines were fit and the slope determined for each phase. Significant differences in slopes ( P < .05) were found between experimental groups for both motions. The RCT group had higher slopes in the initial and middle phases for sagittal elevation and in the middle phase for scapular abduction. The scapula was elevated more in the RCT group in the initial two thirds of movement. This motion may change the length of remaining muscles so that they operate on a more effective part of their length-tension curve.

Changes in the long head of the biceps tendon in rotator cuff tear shoulders.

BACKGROUND: Morphologic changes in the long head of the biceps tendon have been described in association with rotator cuff disease, yet mechanical significance of these changes remains unclear. METHODS: An experiment was designed to test the hypotheses that the cross-sectional area and material properties of the long head of the biceps tendon are different in shoulders with full thickness rotator cuff tears and shoulders with intact rotator cuff tendons. Seven pairs of cadaver shoulders were tested. In each pair one shoulder had a full thickness rotator cuff tear and the other did not. Thus, a matched design was used. Cross sectional areas were measured. Tendon material properties were measured using an optical strain system. FINDINGS: We were unable to detect a statistically significant difference in the long head of the biceps area or material properties between tendons in shoulders with and without rotator cuff tears. An a priori power analysis was conducted indicating the sample size was sufficient to detect a difference of 70 MPa in the elastic modulus measurement. INTERPRETATION: Our data indicate there is no difference in the long head of the biceps cross sectional area or material properties. Therefore, the long head of the biceps tendon appears to retain its material properties in the presence of a rotator cuff tear. The clinical significance of this finding is that the long head of the biceps can be retained in the presence of a rotator cuff tear without concern that mechanical properties have substantially deteriorated.