Sunday, October 12, 2014

Conversion of anatomic arthroplasty to reverse total shoulder: what is the place for modular stems?

Conversion of Stemmed Hemi- or Total to Reverse Total Shoulder Arthroplasty: Advantages of a Modular Stem Design

These authors point out that revision of a well-fixed humeral stem has the potential risk of loss of humeral bone stock, nerve injury, periprosthetic fracture, and malunion or nonunion of a humeral osteotomy with later humeral component loosening.

They conducted a retrospective study of 48 hemiarthroplasties and eight total shoulder arthroplasties that were converted to a reverse total shoulder arthroplasty system. 19 of the stems were modular and 37 were non-modular. The incremental cost of a modular stem design over a standard implant are not stated.

The commonest reasons for conversion to a reverse shoulder arthroplasty was rotator cuff lesion with instability/loss of function (29), aseptic stem loosening (8), stem malposition with functional deficit (8), failure of glenoid component (6), and glenoid erosion (5). 

In 13 cases (all with modular stems) the surgeon elected to retain the humeral stem and in 43 (6 with modular stems and 37 without modular seems) the surgeon elected to change the stem because of stem loosening in 10 cases, stem malposition in 8, and difficulty in conversion of a non modular stem to a reverse in 25. In 12 cases a longitudinal humeral osteotomy was required for stem removal.

Blood loss, surgical time, the rate of complications (principally fractures) and revision rate were greater in the cases where the surgeon chose to perform a full stem exchange. 

Comment: It is of interest that most of the anatomic hemiarthroplasties and total shoulder arthroplasties in this series that were revised to reverse total shoulders were for diagnoses (proximal humeral fractures, post traumatic arthritis and cuff tear arthropathy) that today may well be treated with primary reverse total shoulders rather than an anatomic arthroplasty with a modular stem.

While the authors conclude that "..modularity of a shoulder arthroplasty system has proven and substantial advantages if conversion to reverse total shoulder arthroplasty becomes necessary and might be considered as prerequisite for stemmed shoulder arthroplasty systems", it is unclear for which patients they recommend the modular stem.  It would be important to know whether the number of cases of primary arthroplasty with modular stems that need revision and which can be successfully revised without stem removal offsets the incremental cost of the general use of modular stem designs.

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