A Comparison Of Glenohumeral Joint Kinematics And Functional Outcomes In Adults With Rotator Cuff Tear

Margaret E. French1, Alyssa J. Schnorenberg1,2, Briana N. Magruder1, Justin M. Riebe1, Ryan R. Inawat3, Dana H. Washburn1, Dara J. Mickschl3, Steven I. Grindel3, Brooke A. Slavens1

1University of Wisconsin-Milwaukee; 2Marquette University; 3Medical College of Wisconsin


Approximately one quarter of U.S. adults will have a rotator cuff (RC) tear in their lifetime, and about 300,000 RC repair surgeries are performed annually [1]. The supraspinatus is the most commonly torn rotator cuff muscle requiring surgical repair [2]. RC tears can impede physical function, such as one's ability to perform activities of daily living (ADLs), and maintain functional independence [3,4]. The American Occupational Therapy Association defines ADLs as the tasks of taking care of one’s own body [5]. The goal of surgical repair is to decrease pain, increase range of motion (ROM), and allow return to the workforce [6]. Although patients may be able to perform ADLs independently before surgery, they may be using altered kinematics due to injury and pain. While studies have compared post-operative thoracohumeral (humerus relative to thorax) joint kinematics of various populations, there is no known research assessing upper extremity (UE) joint kinematics of ADLs pre- and post-operatively, which may provide insight on the rehabilitation process. [7,8]. The purpose of this study is to compare glenohumeral (GH) joint kinematics of three ADLs and shoulder function before and after supraspinatus repair surgery. It is hypothesized that GH joint kinematics and functional shoulder outcomes will be significantly different following rotator cuff surgery.



Six (6) adult subjects (63.5 ± 7.1 years) with a full-thickness, supraspinatus RC tear participated in this study (Table 1). Subjects who had a previous shoulder surgery, currently have systemic inflammatory arthritis, or shoulder pathology in both shoulders were excluded. This study was approved by the University of Wisconsin-Milwaukee (UWM) Institutional Review Board; written informed consent was obtained from each participant.

Table 1. Subject and supraspinatus tear characteristics (mean ± 1 standard deviation)
Subject Gender Surgical Arm Dominant Arm Tear Thickness Tear Size (cm) Age (years) Pre session to Surgery (days) Surgery to Post session (days)
1 F R R Full 1.25 59 34 78
2 M L R Full 1.50 75 2 85
3 F L R Full 1.00 55 19 71
4 M R R Full 1.00 66 4 79
5 F R R/L Full 2.50 66 9 76
6 M R R Full 4.00 60 5 80
Average ± SD 1.9 ± 1.2 63.5 ± 7.1 12.2 ± 12.2 78.2 ± 4.6

Data collection

This is a photo of a female subject wearing the marker set in the center of our testing room. The subject is holding a purple, plastic comb in her right hand. Her surgical arm is performing the motion of combing with the comb at the top of her head. Her other arm rests at her side.
Figure 1. Participant (top) performing the combing task on surgical side with the upper extremity marker set [12] with the corresponding Vicon image (bottom).
Each subject completed two sessions; 0-12 weeks before surgery and 9-12 weeks after surgery with an average of 78 days post-surgery. The validated Simple Shoulder Test (SST) [9] and the University of California-Los Angeles (UCLA) shoulder test were administered to assess perceived shoulder function. A higher score indicates better shoulder function for both assessments. The SST is a 12-item assessment with yes/no responses with a maximum score of 12. The UCLA, also a self-reported outcome, has a maximum possible score of 35; a score less than 27 indicates fair/poor shoulder function, while a score greater than 27 indicates good shoulder function [10,11]. A 15- camera Vicon T-series motion analysis system (Oxford Metric Group, Oxford, UK) tracked 27 reflective markers on the upper extremities (UE) during three ADL tasks: combing the hair, reaching to the back pocket, and reaching across the body (Figure 1). Each subject started with their arm resting at their side, performed the ADL, and ended with their arm back at their side. Subjects were instructed to perform all tasks to the best of their ability.

Data processing

All data was processed using Vicon Nexus Software to label marker trajectories, fill gaps, and filter the data (Figure 1). A custom inverse dynamics model [12] was used to calculate the three-dimensional (3-D) upper extremity joint kinematics. The 3-D GH joint angles were calculated as the motions of the humerus relative to the scapula. Peak angles and ranges of motion (ROM) were determined for each trial, and the group means and standard deviations were computed for each task. The Wilcoxon signed-ranks test, a nonparametric statistical procedure, compared pre-operative to post-operative sessions (p < 0.05) via IBM SPSS Statistics (IBM, Armonk, NY).


Glenohumeral joint kinematics

This is a series of three graphs. Each graph shows one ADL task range of motion. Graph a is GH joint combing, graph b is GH joint crossbody, and graph c is GH joint reach to back pocket. All graphs have degrees along the y axis and three planes of motion along the x axis. These planes of motions are adduction/abduction, flexion/extension, and internal/external rotation, respectively. There are two bar graphs per motion. The first bar is pre-operative and the second bar is post-operative. For example, there is a pre bar and post bar for adduction/abduction. Two of the three graphs have asterisks above or below the bar graphs, indicating a significant difference from pre to post surgery. One asterisk means a significant difference in average maximum angle, two asterisks indicates a difference in the minimum angle, and three indicates differences in range of motion. The first graph, a, is the glenohumeral joint combing task. This graph has two asterisks over adduction/abduction bars. It also has three asterisks over internal/external rotation. The second graph, b, has two, single asterisks over adduction/abduction and internal rotation. There are no asterisks on the third graph indicating now significant differences in the reach to back pocket task.
Figure 2. Mean glenohumeral joint pre-operative (black) vs. post-operative (gray) average peak angles during ADL tasks in each plane with ± 1 standard deviation bars. One asterisk (*) indicates significant difference (p-value < 0.05) in average maximum angle, two asterisks (**) indicates significant difference in average minimum angle, and three asterisks (***) indicates significant difference in average ROM. (a) Combing task. (b) Reach to back pocket task. (c) Cross-body task.
There was a statistically significant decrease in GH joint external rotation range of motion pre-operatively (79.4° ± 22.8°) to post-operatively (43.6° ± 15.4°) (p= 0.028) during the combing task (Figure 2a). This is due to the significant decrease in maximum external rotation angle from 89.6° ± 27.6° pre-operatively to 58.9° ± 16.3° post-operatively (p = 0.028)(Figure 2a). The average minimum abduction angle was significantly different pre (13.0°± 5.4°) to post 6.2°± 3.5°, p= 0.028) to complete the combing task. For the crossbody task (Figure 2b), the average maximum abduction angle was decreased significantly from pre (37.2°± 13.4°) to post (25.2°± 11.8°, p=0.028), while the average maximum external rotation angle increased significantly pre-operatively (41.5°± 29.3°) to post-operatively (50.1°± 26.7°, p=0.028). There were no significant differences in kinematics during the reach to the back pocket ADL task (Figure 2c).

Shoulder functional outcomes

While there was no significant difference between the group average SST scores pre (5.8 ± 2.6) to post (4.8 ± 3.2, p=0.343). Although there were no significant differences in the SST scores within the group, subject 2’s score did increase to 9 post- operatively (Figure 3). Although there was no significant difference between the group average UCLA scores pre (16.3 ± 4.6) to post (20.7 ± 5.7, p=0.144), there was substantial individual variability. Three subjects’ scores increased (subjects 2, 4 and 5), two stayed the same (subjects 1 and 3) and 1 decreased (subject 6) (Figure 3). Additionally, for the UCLA question regarding satisfaction with the affected limb, five subjects reported an increase post- operatively. Active forward flexion on the UCLA scores averaged 129.2° at 9-12 weeks post-operatively.


This is two bar graphs. Graph a is the Simple Shoulder Test (SST) and graph b is the UCLA Shoulder test. Both graphs have the scores on the y axis and the subject number on the x axis. Each graph also has two bars per subject number. The first bar is pre-operative score and the second is post-operative score. No significant differences were found in either shoulder test score, so no asterisks are present.
Figure 3. Individual subjects’ pre-operative (black) and post-operative (gray) scores of the SST and UCLA functional shoulder assessments.
To our knowledge, this is the first work that compares biomechanics of the shoulder and shoulder function outcomes pre- and post-supraspinatus repair. We successfully characterized glenohumeral joint motion and functional performance in six patients.

We examined ADLs to evaluate functional performance. We found a significant difference in GH joint external rotation ROM and a decreased maximum abduction angle during the combing task. When combing the hair, less external rotation, while abducted, increases the subacromial space, thereby reducing the risk of shoulder impingement. Although we found differences in external rotation ROM, a recent study found differences in internal rotation during the combing task [7]. Patients may still retain independence with functional tasks pre and post-operatively even if they do not achieve what is considered full shoulder ROM. A study conducted on healthy females found the minimum angles required to perform the combing hair task were 73 degrees of GH scaption, 38 degrees of GH external rotation, and 112 degrees of elbow flexion [13]. Although obtaining full motion is a reasonable goal by therapists for shoulder treatment, less ROM may be sufficient to perform functional tasks and still be independent. Significant differences were found in the average maximum abduction angle (decrease) and maximum external rotation angle (increase) for the combing task. Subjects’ ROM was the same, but they may be reallocating ROM amongst different planes to still complete the task. After surgery, the mechanics of the joint may change during the recovery process when structures have been restored to their original function.

We found no significant differences in the SST score at 9-12 weeks, which is similar to other findings of subjects not improving at this point in time [14,15]. Healthy subjects scored within the range of 9 to 12, so subject 2’s post- operative score of 9 indicates they reached healthy shoulder function range [16]. Although it depends on the physician and clinic, most current rehabilitation protocols suggest patients have full active ROM by post-operative week 12. Mean UCLA item scores of active forward flexion (129.2°) demonstrates patients are close to recovering almost full range of motion of the allowed 180 degrees (71.8%). Pre-operative knowledge could help therapists identify a change in intervention or rehabilitation protocols to benefit those who are not progressing as well as other patients. Other factors to consider in future analyses are age, duration of symptoms, tear size, and pre-post window time.


We were able to successfully compare GH joint kinematics during three ADLs and shoulder assessments before and after a RC repair surgery. Although patients may be able to perform ADLs independently before surgery, they may be using altered kinematics and compensation strategies due to injury and pain. A comparison of the pre-operative

Figure 3. Individual subjects’ pre-operative (black) and post-operative (gray) scores of the SST and UCLA functional shoulder assessments.

to post-operative performance may influence appropriate rehabilitation after surgery. Research is underway to investigate shoulder motion, pain, and function in a larger population with additional ADLs. Ultimately this work may aid occupational therapists in ADL interventions to improve rehabilitation outcomes and increase independence.



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This study was supported under grants from the University of Wisconsin-Milwaukee College of Health Sciences and the Medical College of Wisconsin Department of Orthopaedic Surgery. We would like to thank Andrew Barnett for assisting with subject recruitment.