Mechanics of Glenohumeral Arthroplasty.
Last updated Thursday, January 27, 2005
|
Figure 25 - Humeral cut made in excessive retroversion Figure 26 - Overstuffing the joint places the cuff under tension when the arm is adducted or rotated Strength
The strength of the shoulder after shoulder arthroplasty is dependent
on reestablishing the integrity, strength and coordination of the
muscles controlling the glenohumeral and scapulothoracic articulations.Stuffing and strength The amount of stuffing of the joint sets the resting length of the cuff
muscles and to a lesser extent that of the deltoid. If the components
are too small, the cuff will be slack at rest and thus place the
muscles at the low end of the ideal length-tension relationship. If the
joint is overstuffed, the cuff muscles may be at the high end of their
length-tension curve. The distance between the effective cuff insertion
and the humeral head center establishes the moment arm for the cuff.The deltoid The deltoid is the most important motor of the shoulder arthroplasty.
The integrity of its origin, insertion, and nerve supply must be
maintained. This is most easily accomplished by gently approaching the
joint through the deltopectoral interval and by identifying and
protecting the axillary nerve both anterior-medially as it crosses the
subscapularis and inferior capsule and laterally as it exits the
quadrangular space and winds around the tuberosities on the deep
surface of the deltoid. Rehabilitation of the deltoid is critical to
the active motion following arthroplasty.The rotator cuff The rotator cuff mechanism is in jeopardy in shoulder arthroplasty
for several reasons. The suprascapular nerve, which supplies the
supraspinatus and infraspinatus, is at risk during surgical releases as
it courses medial to the coracoid and then down the back of the glenoid
1 cm medial to the glenoid lip. The cuff tendons are at risk during
surgery because the humeral cut must come close to their insertion to
the tuberosities superiorly and posteriorly. A humeral cut made in
excessive retroversion is likely to detach the cuff posteriorly, and a
cut made too low on the humerus is likely to detach the cuff
superiorly. Overstuffing the joint places the cuff under tension when
the arm is adducted or rotated. Most shoulder arthroplasties are
performed for older individuals in whom the quality of the cuff tissue
may be compromised not only from age-related changes, but also from
disuse enforced by chronic glenohumeral roughness. Shoulder
arthroplasty may quickly restore motion and smoothness to the joint,
placing new and substantial demands on the disused cuff tissue. Thus
the rehabilitation program and the patient's activities after
arthroplasty must gradually increment the loads on the cuff, allowing
the tissue the opportunity to toughen over time.
If a cuff defect exists at the time of the arthroplasty, a cuff
repair to bone should be carried out, if the quantity and quality of
the cuff tissue are sufficient to allow a durable repair under
physiologic tension with the arm at the side. If the tuberosities are
nonunited or if a tuberosity osteotomy is performed, secure fixation is
required to restore cuff function. Under these circumstances the
rehabilitation after arthroplasty is changed dramatically to allow for
secure healing of the cuff mechanism to the humerus.
How useful was this page or article?
|
|