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Tuesday, June 6, 2023

Comparison of 3-dimensional Shoulder Complex Kinematics in Individuals with and without Shoulder Pain

Brent Brookbush

Brent Brookbush


Research Review: Altered Scapular Kinematics in Individuals with Shoulder Pain

By Jinny McGivern DPT, PT, Certified Yoga Instructor

Edited by Brent Brookbush DPT, PT, MS, PES, CES, CSCS, ACSM H/FS

Original Citation: Lawrence, R. L., Braman, J. P., Laprade, R. F., & Ludewig, P. M. (2014). Comparison of 3-dimensional shoulder complex kinematics in individuals with and without shoulder pain, part 1: sternoclavicular, acromioclavicular, and scapulothoracic joints. journal of orthopaedic & sports physical therapy, 44(9), 636-A8. ABSTRACT

Note the four joints that make up the shoulder complex . This article will discuss motion at the Sternoclavicular (SC), Acromioclavicular (AC) and Scapulothoracic (ST) joints.

Image courtesy of http://www.eorthopod.com/online-courses/online-courses/shoulder-dislocations/topic/224

Why is this relevant?: Shoulder pain is one of the most commonly reported musculoskeletal complaints, and the etiology is a commonly debated topic. Altered joint mechanics and impaired scapulohumeral rhythm are often observed in individuals reporting shoulder pain. The researchers of this study performed a kinematic analysis of individuals with and without shoulder pain using bone affixed markers to provide precise information on the nature of these altered mechanics. Knowledge of altered mechanics gives the human movement professional a foundation for designing both assessments and interventions for clients/patients.

Study Summary

Study Design Cross sectional laboratory study - Descriptive Study
Level of Evidence Level VI - Evidence from a single descriptive or qualitative study
Subject Demographics
  • Age:
    • 10 individuals in Symptomatic Group (SG) = 35.7 +/- 13.4 yrs
    • 11 individuals in Asymptomatic Group (AG) 29.3 +/- 6.8 yrs

  • Gender:
    • Symptomatic Group (SG) = 7 male/3 female
    • Asyptomatic Group (AG) = 5 male/6 female

  • Characteristics: Individuals with & without shoulder pain.  Details described below.
  • Inclusion Criteria:
    • SG criteria included 18-60 yrs of age; anterolateral shoulder pain of a minimum 1 week in duration; pain with shoulder active range of motion (AROM); pain with resisted shoulder internal rotation (IR) and/or external rotation (ER); visibly impaired scapulo-humeral rhythm during shoulder elevation & lowering; min 2 positive impingement tests (Hawkins-Kennedy, Neer, Jobe)
    • AG criteria included 18-60 yrs of age; pain free shoulder ROM

  • Exclusion Criteria:
    • SG criteria included 25% or greater reduction in shoulder IR or ER compared to opposite side; history of trauma coinciding with onset of pain; symptom reproduction with cervical spine screen; (+) drop arm or apprehension test; history of shoulder surgery, labral tear or rotator cuff (RC) tear; history of fracture of scapula, clavicle or humerus; diagnosis of joint disease (RA or OA)
    • AG criteria included history of shoulder pain; history of fracture of scapula, clavicle or humerus; history of subluxation of any joint in shoulder complex; any asymmetrical loss of shoulder ROM; pain provocation during above listed impingement tests; visibly impaired scapulo-humeral rhythm during shoulder elevation & lowering

Outcome MeasuresAngular Positions for the SC, AC and ST joints during the following movements:
  • Shoulder Flexion (at 30, 60, 90 & 120 degrees during elevation & lowering)
  • Shoulder Abduction (at 30, 60, 90 & 120 degrees during elevation & lowering)
  • Shoulder Abduction in Scapular Plane (Scaption) (at 30, 60, 90 & 110 degrees* during raising & lowering)

*Not all participants in symptomatic group (SG) could achieve 120 degrees Abduction.

  •  No differences were found between groups at SC, AC or ST joints in the relaxed standing position.

SC joint

  • The SC joint demonstrated progressive elevation, posterior rotation & retraction in both groups in varying amounts during elevation.
  • SG demonstrated 5.2 degrees less SC elevation at 30 degrees of scaption during arm elevation
  • SG demonstrated less SC posterior rotation as compared to AG at all joint angles during all types of elevation. (5.2 degrees less during Abduction; 5.9 degrees less during flexion; 5.5 degrees less during scaption)
  • There were no significant differences between groups in SC retraction at any point in range or plane of motion.

AC joint

  • The AC joint demonstrated progressive IR, upward rotation & posterior tilting in both groups in varying amounts during elevation.
  • No significant differences between the groups at any point in the range or plane of motion were observed at the AC joint.
  • There was a trend toward reduced posterior tilt in the SG during scaption, however further analysis did not reveal significant differences between groups.

ST joint

  • The ST joint demonstrated progressive upward rotation, posterior tipping & IR in both groups in varying amounts during elevation.
  • The SG demonstrated reduced scapular upward rotation at 30 & 60 degrees abduction (6.5 degrees less at 60 degrees during elevation; 6.3 degrees less at 30 degrees during lowering.
  • The SG demonstrated reduced scapular upward rotation at 30 & 60 degrees of scaption elevation (6.8 degrees less at 30 degrees; 3.1 degrees less at 60 degrees).
  • There was a trend toward reduced posterior tilt in the SG during flexion, however further analysis did not reveal significant differences.
  • No significant differences between the groups at any point in the range or plane of motion were observed for IR.
Conclusions This research supports the importance of examining movement quality throughout the range of motion.  Abnormal mechanics early in the range may contribute to the pain experienced by individuals with shoulder impingement further into the ROM of shoulder elevation.
Conclusions of the Researchers Individuals with and without shoulder pain demonstrate differences in shoulder complex kinematics. Primary differences observed were reduced posterior rotation at SC joint throughout range during elevation and reduced upward rotation at the ST joint during lower positions in the ROM of elevation.

Note the relationship between the scapula and the humerus in producing shoulder active range of motion.

Image Courtesy of http://charlieweingroff.com/online-courses/online-courses/2011/10/couple-of-qs/scapulohumeral-rhythm/

Review & Commentary:

Lawrence et al., the authors of this study, report that there is conflicting evidence about the changes in scapulothoaracic movement in individuals who complain of shoulder pain. In an attempt to provide clarity on this subject, the authors made two choices which greatly strengthened the methodology of this study. First, they clearly defined their population. Lawrence et al. observed individuals with multiple indicators of "impingement." Impingement is a broad term used to describe a wide variety of pathoanatomical and pathomechanical processes resulting in shoulder pain and limited range of motion (ROM). The authors used very specific inclusion criteria (listed above) to define their population, thereby allowing readers to place their findings in a clear context. Second, the authors utilized sensors attached directly to bone via pins (following recommended protocols for placement) in order to provide the most accurate and direct measure of movement at the SC, AC and ST joints. Often in research, motion sensors are attached to soft tissue on the surface of the body. This leads room for potential error when observing joint motion. Soft tissue may have its own dysfunction and restrictions influencing its capacity for motion, thereby resulting in movement that differs from what is occurring between the bones at the joint (arthrokinematics). Lawrence et al. explain that another method of analyzing movement at the SC and AC joints has been via estimation using biomechanical models, rather than direct measurements. Direct measurement of movement of the clavicle and scapula, without the assumptions inherent in models, allows for very accurate analysis of movement at these joints.

While specificity in subject selection is a strength of this research, it is also a limitation. These findings may not be applicable to individuals with impairments that differ greatly from the inclusion criteria of this sample. It is important to note that the individuals in the SG reported a mean of 10 years (+/- 7.9 yrs) of intermittent shoulder pain. Based on their scores on the "Disabilities of the Arm Shoulder and Hand questionnaire (DASH)," these subjects were minimally limited in daily and work activities (approximately 20% disabled). They were significantly more limited in recreation and sport activities (approximately 50% disabled). It is possible that movement patterns observed in individuals with a more acute onset of pain or with greater functional limitations might demonstrate differences from what has been reported in this research. On average the individuals in the SG were older than the AG, although the difference was not found to be statistically significant. There was a small sample size limiting the power of statistical significance.

The researchers acknowledge that there is tremendous variability in pain free shoulder motion. We cannot assume that all subjects in the AG demonstrated optimal mechanics. It is possible for an individual to have joint dysfunction and not have pain. It may be beneficial for future researchers to recruit asymptomatic individuals who are also further screened for truly "optimal" shoulder complex mechanics (including active ROM, neuromuscular control/scapulohumeral rhythm, passive joint play, normal end feel at the end of passive ROM, cervico-thoracic mobility, etc).

It may be tempting to draw conclusions that abnormal mechanics of the shoulder result in pain. However, as previous research reviews have reported in incidences of low back pain, it is also possible that the abnormal mechanics may result from pain. The design of this research does not allow us the identify causation, only association. A prospective study is needed to further examine the temporal relationship between abnormal mechanics and shoulder pain.

Why is this study important?

This provides highly accurate information on the movement of the SC, AC and ST joints  relative to shoulder impingement syndrome. This information may be used to support techniques with the goal of improving arthrokinematics of the AC, SC and ST joints as we expand upon an evidence-based model of practice.

How does it affect practice?

This knowledge has implications for both manual therapy and exercise based interventions. For the manual therapist, it provides a checklist of structures in the shoulder girdle that must be addressed with release and mobilization techniques such as the SC joint, the ST joint, pectoralis minor, levator scapula, rhomboids , trapezius, serratus anterior, coracobrachialis and possibly the biceps brachii and long head of the triceps. Because of the significant limitations in clavicular posterior rotation demonstrated by this study, pectoralis major and the pectoral fascia may be considered and potentially mobilized along the full length of the clavicle, as well as, activation of the upper trapezius. Restrictions at any point along its length can limit posterior rotation at the SC joint . This research appears to indicate that the AC joint may trend toward developing hypermobilities. With respect to bony articulations, ST joint movement occurs as a sum of movement at the SC and AC joints (although these are far from the only structures determining scapular movement). This research indicates that the SC became limited in motion in the SG. These limitations resulted in alterations in ST joint movement below 90 degrees of humerus abduction. Above this point, scapula movement in the SG group appeared to "catch up" and demonstrate more similar mechanics to the individuals in the AG. It is possible that the AC joint compensated for a lack of movement at the SC joint. While this is useful information to have, it is still essential to consider each patient individually and treat restrictions as we find them (which may or may not include the AC joint).

With respect to exercise selection, self administered release techniques as well as stretching would be applicable for the muscles discussed above. This research indicates how important it is to monitor scapula motion throughout the range of motion and to look out for poor neuromuscular control early in the range of motion. Rehabilitation guidelines typically stress normalization of scapular mechanics below 90 degrees of glenohumeral abduction before progressing to overhead motion, a strategy that is support by this research. Suggestions of specific exercises are discussed below in the following section.

How does it relate to Brookbush Institute Content?

This research supports the predictive model of Upper Body Dysfunction (UBD)  as described by the Brookbush Institute. The dysfunctional arthrokinematics demonstrated by the SG group in this study (lack of scapular upward rotation, reduced clavicular elevation and reduced posterior tipping) are not surprising based on the muscle imbalances often found in those with UBD. The scapular downward rotators & anterior tippers are often found to be short and overactive, whereas the upward rotators & posterior tippers are found to be long and under-active. Below is a sequence of videos that describe techniques utilized by the Brookbush Institute to correct these imbalances. For more detailed information on UBD, click here.

Levator Scapulae SA Static Release

Levator Scapulae SA Active Release

Pectoralis Minor SA Static Release

Levator Scapula SA Static Stretch

Levator Scapulae Active Stretch

Pectoralis Major and Minor SA Static Stretch

Pectoralis Major and Minor SA Active Stretch

Trapezius Isolated Activation

Serratus Anterior Isolated Activation

Serratus Anterior Activation Progressions

© 2014 Brent Brookbush

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