Friday, January 20, 2017

Managing intraoperative posterior instability encountered during total shoulder arthroplasty

Plication of the posterior capsule for intraoperative posterior instability during anatomic total shoulder arthroplasty

These authors have found that "restoration of soft tissue balance for intraoperative posterior instability during anatomic total shoulder arthroplasty (TSA) is particularly difficult". In their experience when excessive intraoperative posterior subluxation is noted at the time of TSA, a number of changes may be trialed to achieve adequate soft tissue balance. Provided component version and bone loss management have been optimized, they find that trial heads of increasing thickness may be used to tension the posterior capsule and cuff while still allowing subscapularis repair. However, in some shoulders, they find that intraoperative posterior subluxation continues. In these circumstances, they consider posterior capsular plication (PCP).

The purpose of their study was to report the outcomes, complications, and reoperations of 38 primary TSAs in which a posterior capsular plication (PCP) was performed to correct excessive intraoperative posterior subluxation. 

Their approach was to proceed with a standard prosthetic glenoid arthroplasty performed through a deltopectoral approach.  After implantation of the glenoid component, the humeral head trial  was placed and stability evaluated. When posterior subluxation  of >40% to 50%, the head size thickness and diameter were  increased in an attempt to tension the posterior soft tissues while  still allowing subscapularis closure. In all shoulders included in this report, posterior subluxation persisted and a PCP was added.  A bone hook was used to retract the humerus laterally to create  a working space for the PCP procedure. Then, multiple nonabsorbable sutures were placed lateral to medial to shorten the posterior capsule. All the sutures were first placed and then the bone hook was removed to allow adequate tightening of the sutures as they are tied.

They found that PCP resulted in restoration of soft tissue balance in 27 shoulders (71%). The remaining 11 shoulders had evidence of posterior subluxation, including posterior dislocation in 2 shoulders. Revision surgery was performed in 3 shoulders (7.9%), all for instability. However, there was a high rate of radiographic glenoid component loosening (12 shoulders, 32%). Overall results were excellent in 24 (63.2%), satisfactory in 10 (26.3%), and unsatisfactory in 4 (10.5%) shoulders. Recurrence of posterior subluxation was associated with worse motion and strength as well as with a higher rate of glenoid component loosening. The type of glenoid wear did not affect, with the numbers available, the radiographic or clinical/functional outcomes in this study.

Comment: We agree with the authors that intraoperative decentering of the trial humeral head component needs to be identified and managed at surgery. Because the surgical exposure and osteophyte resection can alter the soft tissue balance, preoperative clinical and radiographic evaluation may not correspond to what is observed at surgery. 

In the past we tried posterior capsular plication and found that the tightening had a tendency to fail, either because the sutures pulled through the attenuated posterior soft tissue or because the posterior capsule stretched out with time. As a result our current approach for the management of intraoperative posterior decentering employes anteriorly eccentric humeral heads without or with rotator interval plication. Shoulders treated with this approach have not appeared to have problems with recurrent posterior instability, suggesting that this may be a more robust approach than PCP.

A prior blog post on this topic is reproduced here:
Management of intraoperative posterior decentering in shoulder arthroplasty using anteriorly eccentric humeral head components 

This article reports the use of anteriorly-eccentric humeral head components to manage posterior instability recognized at shoulder arthroplasty when standard trial components are in place. Radiographic centering was characterized before surgery and at follow-up on standardized axillary radiographs with the arm held in a position of functional elevation. Preoperative posterior humeral head decentering did not correlate with preoperative glenoid version.

In 33 shoulder arthroplasties with 2-year outcomes the preoperative radiographic humeral decentering was reduced from 10.4% ± 7.9% to 0.9% ± 2.3% postoperatively (P < .001). SST scores improved from 4.8 ± 2.3 to 10.0 ± 2.3 (P < .001).  Glenoid retroversion was 19.8° ± 8.9° preoperatively and 15.5° ± 7.5° postoperatively. Rotator interval plication was performed in 16 cases as an adjunctive stabilizing procedure. No cases of postoperative instability were identified.

Posterior instability after a shoulder arthroplasty can result in pain, functional loss and rocking horse loosening or rim wear of a glenoid component.

While posterior decentering can be identified before surgery by the 'truth' view (an axillary taken with the arm in a functional position of elevation in the plane of the scapula) as shown below

often this preoperative posterior instability will respond to soft tissue balancing and use of standard humeral components. In other cases, the posterior instability persists at surgery, being manifest by a posterior 'drop back' when the arm is elevated. 

Not infrequently a shoulder without apparent posterior instability before surgery becomes posteriorly unstable at surgery after osteophyte resection and soft tissue releases. 

In cases where posterior instability is identified at surgery when trial components are in place, centering of the humeral head can usually be established through the use of an anteriorly eccentric humeral head without or with a rotator interval plication.

resulting in a stabilized head without needing to change glenoid version. Below is the postoperative view of the case shown in the earlier x-ray in which these methods were used.

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