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Trial Reduction of Shoulder Arthroplasty:

- Discussion:
    - its essential to restore anatomic length of humerus to provide proper amount of tension in deltoid so that patient will maintain the ability to forward flex;
           - in the case of a hemiarthroplasty performed for 4 part frx, length will always have to be regained;
                  - insert a small broach into the medullary canal and have an assistant apply a small traction force;
                  - then bring the trial prosthesis so that it is reduced w/ in the glenoid;
                  - measure the differential, and note that the definative prosthesis will have to be proud by this same distance, which can often be achieved by using the next larger sized prosthesis;
    - oversizing of the prosthetic humeral head may significantly reduce laxity of the joint and ROM;
    - measure lateral offset: distance from base of coracoid process to lateral-most point of greater tuberosity and compare this to the ititial offset measurement;
    - there should be no impingement against the acromion;
    - need to assess rotator cuff tension laterally and posteriorly; 

    - ensure optimal ROM:
           - 75° of internal rotation with the arm positioned in 90° of abduction;
           - 45° of external rotation with the subscapularis approximated to the proximal humeral osteotomy site;
           - ensure that there is no impingement of medial edge of transected humeral neck and the tip of glenoid (as the shoulder is maximally adducted);
    - ensure optimal stability:
           - traction should displace prosthetic head in glenoid about 50% inferiorly, and w/ no traction, surgeon passes a finger between acromion and humeral head;
           - inferior stability is tested by downward traction on the arm in neutral rotation; 
           - posterior stability:
                  - posterior stability is tested w/ the posterior drawer test and with flexion of the internally rotated arm; 
                  - posterior drawer testing shows 40-60% posterior translation of the humeral head relative to the center of the glenoid
           - anterior stability is assessed w/ an anterior drawer and by external rotation with the arm adducted and abducted;
           - if there is instability, re-assess instability w/ a larger humeral head;
           - if anterior or posterior instability is present and this does not improve with increase in humeral head size, then anteversion/
                   retroversion will have to be changed (which often requires cementing the humeral component in position); 
    - reference:
           - The effect of articular conformity and the size of the humeral head component on laxity and motion after glenohumeral arthroplasty. A study in cadavera.
    - pre-cementing considerations:  (see cementing considerations for THR)
           - if the tuberosities have been quarterd off the humerus, then consider placing sutures thru drill holes on either side of the bicipital tuberosity to help allow for more secure fixation at the time of wound closure;
                  - these sutures should be placed prior to cementing;
                  - generally 2 holes are maded anteromedially, 2 holes anteriorly, and 2 holes are made anterolaterally in the proximal humerus;
                  - generally 2 holes are made in each tuberosity fragment