Humeroscapular Positions and Motion.
Last updated Wednesday, January 26, 2005
Figure 5 - Coracohumeral ligament Figure 6 - Humeral head and glenoid in contact Figure 7 - Proximal humeral shaft contacting the acromion Figure 8 - Humeral head is forced posteriorly Figure 9 - Shoulder flexion Factors limiting humeroscapular motion
A number of different anatomic factors limit normal humeroscapular
motion, including capsuloligamentous check reins, abutment of the cuff
and capsular insertions against the margin of the glenoid, and
humeroscapular bony contact.Capsule and ligaments Tension in the glenohumeral capsule and ligaments limits rotation of
the humeral head. Tension in the inferior capsule, for example,
restricts elevation. Tension in the anterior and posterior portions of
the capsule restricts external and internal rotation, respectively.
In eight cadaver shoulders, we investigated the kinematic effects of
the rotator interval capsule/coracohumeral ligament, a particularly
important aspect of the glenohumeral capsular complex, which lies
between the coracoid process, the bicipital groove, the subscapularis
tendon, and the supraspinatus tendon.
We found that this area of the capsule limited humeroscapular
elevation in the plus 90 degree and minus 90 degree scapular planes,
but not in the zero degree scapular plane. Tightness of this
specialized portion of the capsule also restricted adduction and
external rotation, but not internal rotation of the humerus. Insertional abutment against glenoid At the extremes of humeroscapular rotation the margins of the articular
surfaces of the humeral head and glenoid come into contact. The humeral
attachments of the capsule and rotator cuff border the articular
surface of the humeral head. The labrum borders the articular surface
of the glenoid. When these two groups of structures come into contact,
motion is limited unless the cuff insertions slide past the labrum and
into the joint.Bony contact Bony factors can limit the range of humeroscapular motion. In
abduction, the proximal humeral shaft can contact the acromion. In
cross-body movement the humerus can contact the coracoid. In internal
rotation the lesser tuberosity can contact the glenoid.Soft tissue causes of limited humeroscapular motion Shoulder stiffness resulting from abnormalities of the glenohumeral
joint surface is discussed in a later section. Here we consider
stiffness in the presence of normal glenohumeral joint surfaces, that
is, stiffness resulting from problems of the humeroscapular soft
tissues. Two variations of soft tissue restriction of humeroscapular
motion are recognized. The term frozen shoulder refers to an idiopathic
limitation of humeroscapular motion from contracture and loss of
compliance of the glenohumeral joint capsule. By contrast, in a
post-traumatic or post-surgical stiff shoulder, adhesions, scarring,
and capsular contracture result from previous injuries or surgery to
the soft tissues around the glenohumeral joint and non-articular
humeroscapular motion interface.
Contracture of the glenohumeral capsule may be generalized or
localized. Localized capsular contractures produce predictable
limitations of shoulder motion:
- Posterior-inferior tightness limits anterior elevation, internal rotation of the elevated arm, and cross body adduction.
- Posterior-superior tightness limits reach up the back.
- Anterior-superior tightness limits external rotation at the side.
- Anterior-inferior tightness limits external rotation of the elevated arm.
Capsular tightness not only limits motion but causes obligate
translation. When rotational torque is applied to the humerus in a
direction that tightens one aspect of the capsule, the head of the
humerus may be forced in the opposite direction. Therefore, we would
expect that when the capsule is tight anteriorly and an external
rotation torque is applied, the humeral head is forced posteriorly.
This phenomenon may relate anterior capsular tightness and posterior
humeral subluxation to the posterior glenoid wear seen commonly in
glenohumeral osteoarthritis. It is also consistent with the posterior
glenohumeral subluxation and posterior glenoid erosion in shoulders
with excessively tight anterior capsular repairs--a condition we refer
to as capsulorrhaphy arthropathy.
Similarly, tightness of the posterior capsule may produce obligate anterior-superior translation with shoulder flexion.
In a series of experiments using cadaver shoulders, we found that
humeral elevation in the plus 90 degree scapular plane with a torque of
three Newton-meters produced anterior translation of 5 mm and superior
translation of 0.5 mm. When the posterior capsule was shortened
surgically, the anterior translation on forward elevation increased to
over 7 mm and the superior translation to over 2 mm. These translations
are sufficient to press the humeral head and cuff against the
coracoacromial arch, producing "subacromial impingement." These data
suggest that "impingement signs" (either in maximal flexion or in
abduction internal rotation) are likely to be positive in the presence
of a tight posterior capsule.
The phenomenon of obligate translation suggests that caution should
be exercised in applying large rotational torques to shoulders with
tight capsules because of the risk of forcing obligate translation and
increasing joint contact pressures. Disclaimer
This resource has been provided by the University of Washington Department of Orthopaedics and Sports Medicine as general information only. This information may not apply to a specific patient. Additional information may be found at http://www.orthop.washington.edu or by contacting the UW Department of Orthopaedics and Sports Medicine.
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