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Research Profiles

Farmer,KevinW.,MD_intheOR1_recd053014

Getting Reverse Shoulder Arthroplasties Just Right

Kevin W. Farmer, MD 2011 Young Investigator Grant

Research Summary

Research topic: Investigating the protocols orthopaedic surgeons should use to objectively determine the optimal soft-tissue tension in reverse shoulder arthroplasty.

Research results: Objective protocols that can be applied to determine optimal soft-tissue tension in reverse shoulder arthroplasty.

Patient care application of results: Reverse shoulder Arthroplasty with fewer complications and better results.

Simplified patient care application: Better results for reverse total shoulder replacement patients. 

Getting Reverse Shoulder Arthroplasties Just Right 
OREF grant recipient aims to set new tensioning protocols
Sharon Johnson

Reverse total shoulder arthroplasty (RTSA) was developed to bring back functionality for patients with cuff-deficient arthritic shoulders. Although the first reverse implant designs emerged in the early 1970s, it took 30-some years of perseverance on the part of forward-looking clinicians and researchers before the FDA released RTSA for use in specific clinical situations in 2004.
 
Subsequent advances in technique and technology have brought greater precision to the procedure. Still, there is currently no objective standard for determining optimum soft-tissue tension across the glenosphere-humeral socket, which contributes to a stable and safe RTSA. With support from the Orthopaedic Research and Education Foundation (OREF), Kevin W. Farmer, MD, hopes to change that.

Dr. Farmer, assistant professor in the department of orthopaedic surgery, sports medicine division at the University of Florida, Gainesville, Fla., said receiving a 2011 OREF Young Investigator Grant was pivotal to going forward with his research. "The OREF grant was the piece that allowed my research to happen, he said."

Objectivity, efficiency and fewer complications
In current RTSA practice, Dr. Farmer explained, soft-tissue tension is gauged through trial and retrial. This not only relies on subjective judgement but also adds time to the procedure. Given the growing popularity of RTSA, a study that aims to develop objective methods to determine optimal soft-tissue tension will benefit a growing number of patients and orthopaedists, including general orthopaedic surgeons who perform the procedure less frequently than surgeons who specialize in shoulder care. 

Introducing greater objectivity and efficiency to RTSA will potentially decrease complications, too, Dr. Farmer said. He hopes his OREF-supported research will help reduce both the incidence of dislocation, associated with too little soft-tissue tension, and acromial fracture and decreased motion, associated with too much.

From the lab to the OR
Phase one of the study was undertaken in the lab where researchers replaced three cadaveric shoulders with then-available instrumented implants that had been developed for total hip arthroplasty. 

Postprocedure, the researchers subjected the joints to range-of-motion testing and documented real-time force vector measurements. This phase ensured proper functioning of the instrumented implant, confirmed design specifications for custom instrumented glenosphere implants for use with participating patients, and delineated proper procedures for intra-operative testing. 

"We found significant force changes throughout the range of motion that were principally different than what we had anticipated," Dr. Farmer said. "The force in the deltoid changed significantly based on the position of the arm."

In phase two, Dr. Farmer and colleague Dr. Tom Wright performed an RTSA for 20 patients (men and women older than age 50) who consented to using a custom, sensor-instrumented glenosphere implant as a trial prosthesis. After the custom trial implant was in place, they subjected the shoulder to the same range-of-motion testing as was undertaken with cadaveric specimens while the implant recorded force vector measurements for analysis. 

Then, they used a hand-held tensiometer to record the same range-of-motion measurements as the instrumented glenosphere implant. Repeat testing with the hand-held instrument facilitated data confirmation, and gave the team an opportunity to assess the use of alternate (and less costly) technology. 
As of this writing, the team is in process of evaluating study findings, including any information that may help to inform future care of participating patients. 

A pebble in the pond
Dr. Farmer said he finds great satisfaction in answering open questions through research. Still greater satisfaction comes, he said, from applying new knowledge in clinical practice, and in sharing new insights with upcoming orthopaedic surgeons. 

"I have already begun helping design an arthroscopic surgical skills curriculum utilizing our onsite surgical skills and cadavaer labs. I may also help design a formal shoulder/elbow/sports education series. I look forward to continuing my involvement in research and the education of future generations of orthopaedic surgeons throughout my career."

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