Reverse shoulder arthroplasty

Development of the reverse polarity prosthesis

Themistocles Gluck most likely developed a shoulder arthroplasty in the 1800s but did not publish an operation in humans.¹ The first shoulder arthroplasty is attributed to Jules Emile Péan in 1893² who implanted a platinum and rubber replacement in a shoulder resected for tuberculosis. The early pioneers of modern shoulder arthroplasty including Neer initially employed a humeral hemiarthroplasty. Results were good in terms of pain relief, but Neer identified his results were poorer in terms of strength and range of motion in those with irreparable rotator cuff tears.³ Failure of the absent cuff to centre the humeral head on the glenoid resulted in defunctioning of the prime movers and greater implant stresses.⁴ Superior humeral head migration in these patients was noted by Marmor who proposed adding a glenoid component in a conventional anatomic design to improve constraint and stability.⁵ Neer’s solution for failure due to instability was to design his Mark I large-head reverse prosthesis, believing that this would preclude the need for a functioning rotator cuff. His design evolutions struggled to maintain a balance of stability and range of motion; the Mark III prosthesis allowed axial rotation of the humeral stem but a high failure rate led to abandonment. Other groups developed reverse polarity shoulders in the 1970s and 1980s, including the Leeds shoulder group,⁶ Kessel shoulder group,⁷ Bayley-Walker⁸ and the Liverpool shoulder group. These early attempts with either conventional anatomic or reverse designs led to high failure rates and poor functional results with loosening of the glenoid component seen due to high implant stresses.

Paul Grammont developed a concept in reverse polarity prostheses which varied from previous designs by focusing on four features:

1. The prosthesis must be inherently stable;

2. The weightbearing surface must be convex and the supported part concave;

3. The centre of rotation must be at or within the glenoid neck; and

4. The centre of rotation must be distalised and medialised.⁹

The movement of the centre of rotation both increases the lever arm of the deltoid and facilitates its function (Fig. 2), with the added advantage of reducing the shearing forces at the glenosphere-bone interface that were responsible for premature failure. While his original system has undergone changes in design, the original principles adopted by Grammont largely underpin all of the present day models of RSA.