Conversion of hemi into reverse shoulder arthroplasty: implant design limitations

Conversion of Hemiarthroplasty to Reverse Shoulder Arthroplasty with Humeral Stem Retention

The purpose of this study is to evaluate the mid-term clinical results of an ongoing case series on conversion reverse shoulder arthroplasty (RSA) with a modular prosthesis system. We included 17 elderly patients revised for failed hemiarthroplasty after proximal humeral fracture, of which 13 were converted using a modular reverse shoulder prosthesis. Four could not be converted due to overstuffing. For the conversion RSA, we determined the Constant score, American Shoulder and Elbow Surgeons Shoulder Score, visual analogue scale for pain and satisfaction, and range of motion preoperatively, at one year, and at the last follow-up. All measured clinical outcomes improved significantly at both follow-up time points (p < 0.05). The mean duration of surgery was 118.4 min (range: 80.0 to 140.0 min). We observed complications in three patients; these included one late infection and two aseptic stem loosenings. Modular shoulder arthroplasty is a suitable procedure for conversion RSA in elderly patients. All measured postoperative clinical outcomes improved significantly, the complication rate was acceptable, and no prosthesis-related complications occurred. Conversion RSA, although not feasible in every case, is a viable treatment option in the elderly, which can provide successful mid-term results.

Software simulations of changing offsets and thus soft tissue tension when revising anatomic to reverse total shoulder arthroplasty in convertible platform systems

BACKGROUND

Revision shoulder arthroplasty may involve the need to remove a well-fixed humeral stem. To avoid this, convertible platform systems have been introduced. The biomechanics of reverse total shoulder arthroplasty (rTSA) differs from anatomic shoulder arthroplasty (aTSA). The different humeral osteotomy and soft tissue tension may jeopardize the optimal results of the converted rTSA. The aim was to evaluate the radiographic parameters of soft tissue distraction when converting an aTSA to rTSA in a platform system and assess the capability of conversion without "over-stuffing" the shoulder in the "best-case scenario".

METHODS

Radiographic analysis of soft tissue distraction parameters: difference in acromio-humeral distance, difference in lateral humeral offset and difference in latero-inferior displacement were evaluated in aTSA and in the converted rTSA in six different implants. Image analysing software was used on 10 non-deformed osteoarthritic shoulder X-rays to simulate conversion.

RESULTS

The greatest increase in arm length was found for Tornier Ascend Flex (26.8 ± 3.6 mm) while the smallest increase was observed with Lima SMR (19.3 ± 4 mm). The humerus remained most lateralized with the Zimmer Anatomical/Inverse ( - 1.4 ± 2.9 mm) while Lima SMR ( - 15.8 ± 2.7 mm) was more medialized. The greatest increase in latero-inferior distance was found in the onlay systems. A group analysis of onlay rTSA showed an increase of 46% in arm length (p < 0.0001), 83% larger humeral offset (p < 0.0001) and 144% increase in latero-inferior distraction (p < 0.0001) when compared to inlay rTSA.

CONCLUSION

The conversion of aTSA to rTSA using a convertible platform system may lead to significant increase in radiographic parameters corresponding to soft tissue tension. This may alter the biomechanics, restrict the convertibility or jeopardize the optimal clinical outcome of rTSA even in the best-case scenario.

Functional Outcomes of Modular Conversion of Hemiarthroplasty or Total to Reverse Total Shoulder Arthroplasty

BACKGROUND

The advent of modular shoulder arthroplasty systems has allowed the conversion of hemiarthroplasty or total shoulder arthroplasty to reverse total shoulder arthroplasty (RTSA) without removing a well-fixed stem.

QUESTIONS/PURPOSES

To determine the feasibility, functional outcome, and complication profile of RTSA modular conversion.

METHODS

A prospective shoulder arthroplasty registry was queried for consecutive patients scheduled for a modular conversion from January 1, 2007, to April 1, 2015. Eligible patients had medical charts and operative records reviewed for preoperative diagnosis, age, medical comorbidities, preoperative American Shoulder and Elbow Society (ASES) score, preoperative Visual Analogue Scale (VAS) pain and instability scores, and intraoperative findings. Each patient was then contacted by telephone or mail to complete up-to-date ASES and VAS questionnaires.

RESULTS

Seventeen patients underwent a modular conversion. Nine patients were scheduled for modular conversion but underwent humeral revision due to excessive soft tissue tension (65.3% modular conversion rate). Average follow-up was 37.4 months (range 10.0-67.6 months). Pain scores improved from 5.3 (range 0.4 to 8.0) to 2.4 (range 0 to 9.3) (p < 0.01), instability VAS from 5.2 (range 0 to 10) to 1.1 (range 0 to 6.8) (p < 0.01), and ASES scores improved from 35.2 (range 20.7 to 61.3) to 65.6 (range 11.8 to 92) (p < 0.01).

CONCLUSIONS

Modular conversion of an anatomic to a RTSA is feasible in a majority of patients. Despite the complexity of the procedure, modular conversion of hemiarthroplasty or TSA to RTSA can significantly improve functional outcomes with a low rate of complications.

Conversion of total shoulder arthroplasty to reverse shoulder arthroplasty made possible by custom humeral adapter

Reverse shoulder arthroplasty (RSA) is increasingly being used to revise anatomical total shoulder arthroplasty cases. This procedure's high complication rate has been reduced by the availability of modular shoulder systems, which allows the humeral component to be preserved during the conversion. This case report describes the revision of an anatomical shoulder implant inserted in 1998. Polyethylene wear and the resulting metal-on-metal contact had caused metallosis. Since the existing humeral implant was not compatible with standard conversion products, the manufacturer provided a custom humeral adapter that allowed the humeral stem to be preserved. This approach greatly simplified the surgical procedure and resulted in good anatomical and clinical outcomes after 9 months of follow-up.