Primary Monoblock Inset Reverse Shoulder Arthroplasty Resulted in Decreased Pain and Improved Function
Authors: Levy Jonathan C. , Berglund Derek , Vakharia Rushabh , DeVito Paul , Tahal Dimitri S. , Mijc Dragomir , Ameri Bijan 
Published: May 2019

Abstract

Background
The first-generation, lateral-center-of-rotation reverse shoulder arthroplasty (RSA) modular design has demonstrated durable early-, mid-, and long-term outcomes. The second-generation monoblock implant shares a similar design but eliminates the modular junction and facilitates inset placement within the metaphysis to avoid humeral-sided junctional failures and facilitate metaphyseal press-fit. However, no paper has specifically examined the radiographic findings and improvements in pain and function after the use of this next generation design.

Questions/purposes
(1) After second-generation, lateral-center-of-rotation monoblock RSA, what are the improvements in shoulder scores, general health scores, and ROM at a minimum of 2 years of followup? (2) Are the differences in shoulder scores, health scores, and ROM associated with fixation (cemented versus cementless components)? (3) How frequently do complications occur (defined as humeral loosening, dislocation, baseplate failure, scapular notching, acromial fractures, and revision surgery) after inset monoblock RSA?

Methods
We retrospectively studied patients undergoing primary RSA between 2010 and 2015 with preoperative data and a minimum of 2 years of clinical followup. Of the 329 primary RSA performed during this period, 125 were excluded based on the use of a different generation humeral stem of the same design, three based on need for a nickel-free implant, and 39 due to a lack of preoperative shoulder scores. Of the remaining 162 patients, 137 patients (85%) met the inclusion criteria with a mean age of 74 years (range, 46–90 years). The predominant indications were osteoarthritis with a massive rotator cuff tear (74%) and fracture sequelae (16%). During the study, humeral implants were typically inserted using an uncemented press-fit technique (85%), with only 21 patients requiring a cemented humeral stem. The mean clinical and radiographic followup period was 37 months (range, 24–82 months). Patient-reported outcome measures (PROMs) including the Simple Shoulder Test, American Shoulder and Elbow Surgeons Total, VAS for pain, SF-12, Single Assessment Numeric Evaluation, and measured active motion (forward elevation and external and internal rotation) were recorded at pre- and postoperative intervals. Postoperative radiographs were evaluated for baseplate failure, glenoid and humeral loosening, scapular notching, and acromion fractures. Complications were recorded in the longitudinally maintained institutional repository.

Results
At the most recent followup examination, there were improvements in measured motion, general health outcomes, and all PROMs. There were no differences between the cemented and press-fit techniques. Complications observed included 17 of 137 patients (12%) with scapular notching, six postoperative acromion fractures (4%), and two revision procedures (1%). No patients experienced gross humeral loosening or baseplate failure.

Conclusions
Primary RSA using a second-generation monoblock inset humeral component resulted in improvements in pain and functional outcomes as well as low rates of acromion fractures, humeral radiolucency, and complications. Future studies are needed to provide a more definitive analysis on the use of an uncemented technique for humeral stem fixation and the effect of an inset stem on postoperative acromion fractures.

Level of Evidence
Level IV, therapeutic study.