Total shoulder arthroplasty - is 'new' or 'modularity' necessarily 'improved'?

Does an increase in modularity improve the outcomes of total shoulder replacement? Comparison across design generations.

These authors reviewed  75 second generation modular total shoulders for primary osteoarthritis that were followed for a minimum of 2 years (mean 7.4 years) or until reoperation.

The results were compared with first generation monoblock TSAs and third generation TSAs which offered multiple humeral head shape options to more precisely replicate patient anatomy. All components were  manufactured by Smith-Nephew (Memphis, TN, USA).

Survivorship among the 3 groups was similar at 5 years but was estimated to be higher in the 1st generation group at 7 years. Survivorship for the second generation implants was estimated to be 89.0 % at 10 years. More glenoids were radiographically at risk in the 2nd and 3rd generation groups than in the 1st; however, this did not reach significance.

Seven shoulders experienced clinically apparent postoperative subluxation of the glenohumeral joint with visible translation of the humeral head during active range of motion (anterior 2, posterior 3, superior 2). One patient developed a seroma that required no additional treatment. One patient suffered an intraop non-displaced fracture of an osteopenic greater tuberosity treated with bone grafting. One patient required removal of cement anterior to the glenoid after extrusion during placement of the glenoid component. Seven shoulders required reoperation. Four shoulders underwent revision arthroplasty for glenoid loosening an average of 6.1 years post-operatively (range 4 to 143 months). Two of these shoulders were converted to reverse total shoulder arthroplasties, and two were converted to hemiarthroplasty. Two shoulders underwent rotator cuff repairs in the setting of instability, with one undergoing concurrent humeral stem revision. One shoulder underwent open reduction internal fixation for a periprosthetic fracture.

Comment: This paper points out that (1) newer is not necessarily better and (2) the modularity of prosthesis is not necessarily the major determinant of the outcome. The case of a second generation prosthesis  from the paper demonstrates this point (shown below). This prosthesis was placed in an excessively superior position because of incarceration of the stem in the diaphysis - trying to seat the prosthesis in a more distal position would have risked intraoperative fracture. The head being high seems to have resulted in glenoid component loosening. This situation, however, is not a result of the system being modular or its generation, but rather the technique with which it was inserted.

We're sure the authors are striving to find out why the newer versions of this prosthesis system seem to be yielding inferior results. The answer may lie among the 4 Ps: there may be differences in the patients, the problems (type of pathology and pathoanatomy), the details of the procedures or the providers doing the surgery.

In our practice the major advantage of modularity is the ability to adjust the head thickness and to use eccentricity to improve stability.

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Results of Cemented Total Shoulder Replacement with a Minimum Follow-up of Ten Years JBJS

Results of Cemented Total Shoulder Replacement with a Minimum Follow-up of Ten Years JBJS

While most journals require a minimum of two years of followup for reconstructive procedures, patients are interested in knowing longer term outcomes as well. This study is a Level IV followup of 39 out of 60 arthroplasties performed between June 1995 and October 2000 at a minimum of 10 years after a 'third generation' Tornier total shoulder arthroplasty with keeled flat-back glenoid components.  Glenoid anatomy was characterized by standardized anteroposterior and axillary radiographs of the shoulders obtained preoperatively and postoperatively. The morphology of the glenoid was recorded according to the classification described by Walch. The glenoid was type A2 in eleven cases, type B1 in sixteen, type B2 in ten, and type C in two. Loosening was defined as a radiolucent line score of over 12 (out of a maximum of 18), tilting over 5 degrees or subsidence. The authors observed that some shoulders showed loosening only on the AP view, some only on the axillary and some on both. Over a third of the glenoid components were radiographically loose at the time of followup. The mean radiolucent line score for the B2 and C glenoids was significantly greater than that for the A2 and B1 glenoids.

Superior migration of the humeral component was observed in over two thirds of the cases. None of the glenoid components required revision and the Constant scores showed significant improvement.

The high radiographic loosening rates observed in this study for keeled components are consistent with two previous long term result reports, here and here.

So again, glenoid component fixation, especially when the glenoid is biconcave or retroverted, remains a challenge. While shoulders with loose glenoids may remain functional, this loosening remains a concern that has not been resolved by later generation prostheses.

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Use the "Topics" box to the right to find other posts of interest to you.

You may be interested in some of our most visited web pages including:shoulder arthritis, total shoulder, ream and run, reverse total shoulder, CTA arthroplasty, and rotator cuff surgery.

See the countries from which our readers come on this post.