Original article
Contact forces in the subacromial space: Effects of scapular orientation

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The purpose of this study was to examine the effects of scapular orientation on clearance in the subacromial space. Eight glenohumeral joints from fresh-frozen human cadavers were secured to an Instron mechanical testing machine via a custom-made translation table. Forces were applied to simulate rotator cuff and deltoid contraction. Superior translation of the glenohumeral joint was simulated, and the distance before the development of significant subacromial contact force was measured. Specimens were tested at varying orientations of scapular posterior tilting, upward rotation, and external rotation. Results demonstrated no significant effect of posterior tilting and external rotation. Subacromial clearance was found to decrease with an increase in upward rotation, which is contrary to what was expected. These results suggest that changes in upward rotation observed in patients with impingement syndrome may serve to open the subacromial space. Future work needs to focus on confirming these results and determining contact location.

Section snippets

Materials and methods

Eight human glenohumeral joints (mean age, 76 years) were harvested from fresh cadavers and dissected to the level of the rotator cuff. Specimens were stored frozen and thawed just before experimentation. On the humerus, all soft tissue between the rotator cuff and distal condyles was removed. On the scapula, the inferomedial portions of the infraspinatus, teres minor, and subscapularis were resected. The glenohumeral capsule was vented, thus eliminating any effects of intraarticular pressure.

Results

As expected, during the initial translation period of most trials, the force data before and after removal of the acromion were very similar. It was only after larger displacements were achieved that these 2 curves diverged (Figure 4, A). Once the difference between these 2 curves was calculated, it was relatively straightforward to determine the displacement at 20 N (Figure 4, B). This displacement value was defined as the subacromial clearance. The reliability of this clearance measurement

Discussion

Impingement syndrome is one of the most commonly diagnosed shoulder conditions. It is characterized by a mechanical compression of the soft tissues in the subacromial space with symptoms that typically include shoulder pain, stiffness, tenderness, and weakness. Although the etiology of rotator cuff disease is still not completely understood, many researchers and clinicians believe that there is an association between subacromial contact and the development of rotator cuff disease. On the basis

References (36)

  • T.W. Rudy et al.

    A combined robotic/universal force sensor approach to determine in situ forces of knee ligaments

    J Biomech

    (1996)
  • J.J.P. Warner et al.

    Superoinferior translation in the intact and vented glenohumeral joint

    J Shoulder Elbow Surg

    (1993)
  • J. Brossmann et al.

    Shoulder impingement syndromeinfluence of shoulder position on rotator cuff impingement—an anatomic study

    AJR Am J Roentgenol

    (1996)
  • W.C. Burns et al.

    Anatomic relationships in the shoulder impingement syndrome

    Clin Orthop

    (1993)
  • R.B. Cohen et al.

    Impingement syndrome and rotator cuff disease as repetitive motion disorders

    Clin Orthop

    (1998)
  • S.G. Doody et al.

    Shoulder movements during abduction in the scapular plane

    Arch Phys Med Rehabil

    (1970)
  • E.L. Flatow et al.

    Excursion of the rotator cuff under the acromion. Patterns of subacromial contact

    Am J Sports Med

    (1994)
  • F.H. Fu et al.

    Shoulder impingement syndromea critical review

    Clin Orthop

    (1991)
  • Cited by (0)

    This work was supported by a grant from the Whitaker Foundation.

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