How to ream a biconcave glenoid and when to use an eccentric humeral head in total shoulder replacement

Biconcave glenoids are usually associated with slight or significant subluxation of the humeral head with an associated wear of the posterior aspect of the glenoid. The glenoid is dysplastic is this cases and the wear is usually seen at the posterior superior aspect of the glenoid. The following case of shoulder osteoarthritis with a biconcave glenoid was approached with reaming of the glenoid without correction of the deformity and with placement of an eccentric head with the eccentricity anteriorly to compensate for the posterior subluxation of the humeral head. Preoperative and postoperative xrays are shown below.

CLICK ON IMAGE FOR LARGER VERSION. Axillary view demonstrates the biconcave glenoid

CLICK ON IMAGE FOR LARGER VERSION. Grashey view demonstrates the glenohumeral arthritis 

Postoperative images below demonstrate the eccentric humeral head used for this case to avoid drop back of the humeral head during forward elevation of the shoulder. If there is still drop back after the placement of the trial eccentric head then rotator cuff interval closure is necessary.

CLICK ON IMAGE FOR LARGER VERSION. Axillary view demonstrates the eccentric humeral head

CLICK ON IMAGE FOR LARGER VERSION. Grashey view shows the position of the implants

There are two ways to ream a biconcave arthritic glenoid. One way requires no correction of the deformity and less bone removal and the other requires correction of the deformity and more bone removal. Generally, the reaming should not be done beyond the subchondral plate and preservation of bone stock at the glenoid is critical in the stability and longevity of the glenoid component. The more bone is removed the less cortical bone is left at the implant - glenoid bone interface to support the all polyethelene glenoid component. Implanted glenoids on cancellous bone run the risk of loosening in the short term. The drawings below demonstrate the two different methods of reaming a biconcave glenoid in total shoulder arthroplasty.

REAMING WITHOUT correction of the deformity. (A) a biconcave glenoid is depicted. (B) First with the use of a curette the biconcavity is eliminated and the biconcave glenoid is converted to a concave glenoid (C) the reaming is performed and minimal bone is removed until the reamer "sits" on the glenoid.

REAMING WITH correction of the deformity. (A) a biconcave glenoid is depicted (B) The reamer is levered more anteriorly to correct the deformity and convert the biconcave glenoid to a concave glenoid (C) the reaming is performed and MORE bone is removed compared to the previous example until the reamer "sits" on the glenoid

Comparing the two methods it is obvious that without correction of the deformity (A) there is no significant bone removal. With correction of the deformity (B) there is MORE bone removed compared to method (A).

(A) No correction of the deformity does not correct the posterior  subluxation of the humeral head (B) Correction of the glenoid deformity does correct to a certain degree the posterior subluxation of the humeral head. Notice the distance of the plane of the scapula relative to the center of the humeral head

(A) Placement of an eccentric head can compensate for the posteriorly subluxated humeral head (B) In cases where the glenoid deformity is corrected a concentric humeral head may or may not provide stability and correct posterior subluxation of the humeral head.