Thursday, March 9, 2017

Instability after shoulder arthroplasty - an issue of surgical technique

The main cause of instability after unconstrained shoulder prosthesis is soft tissue deficiency

These authors reviewed 532 patients having shoulder arthroplasties and found 27 who experienced instability after surgery, for an overall incidence of 5.07%

They found 10 isolated subscapularis tears, 6 massive rotator cuff tears, 8 component malpositions, 2 component dissociations or loosening, and 1 humeral shortening. Half of the instability cases had type B or C glenoid or an anterior glenoid defect. Dislocations occurred early (within the first 6 months) in 20 patients and later in 7.

The authors provided data on each patient:

AGBL, anterior glenoid bone loss;  hemi, hemiprosthesis; LAD, locked anterior dislocation;  OA, (primary) osteoarthritis;  PL, post-Latarjet; PTOA, post-traumatic osteoarthritis; RCT, rotator cuff tear; SScp, subscapularis; PE, polyethylene; TSACG, total shoulder arthroplasty cemented glenoid component; TSAMB, total shoulder arthroplasty metal-backed component.

Comment: This paper is interesting for several reasons: 
(1) one in twenty arthroplasties were complicated by instability
(2) ten of the cases of instability were associated with subscapularis failure - indicating the need for great care in the subscapularis repair and protection until the repair heals
(3) six of the cases were associated with massive cuff tears - most of which occurred at or after two years, suggesting the need to inform patients of this risk and advising them to avoid heavy use of the reconstructed shoulder
(4) nine of the cases were associated with prosthesis malposition - indicating the importance of surgical technique
(5) two of the cases were associated with glenoid component loosening or dissociation - again suggesting the importance of prosthesis selection and surgical technique.

These are educational points: most of the factors associated with instability appear to be addressable by better surgical technique and careful rehabilitation after surgery.