In Search of Long-term TSA Success

Grant recipient seeks lasting results for all patients
Long-term success after total shoulder arthroplasty (TSA) remains elusive for patients with advanced glenohumeral arthritis or severe bone loss. The main culprit is loosening of glenoid implants, which accounts for a 7 percent revision rate within 15 years after primary surgery. In recent years, multiple device manufacturers have introduced augmented glenoid implants to address the problems and the need for revision TSAs. These implants feature variances in thickness designed to reduce loading and shear stresses and improve implant stability.

With support from a 2015 Orthopaedic Research and Education Foundation (OREF)/American Shoulder and Elbow Surgeons (ASES)/Rockwood Clinical Research Grant in Shoulder Care, Vani J. Sabesan, MD, is leading an investigation to further understand the performance of augmented glenoid implants and how better results might be achieved.


Vani J. Sabesan, MD

Shoulder arthroplasty with augmented glenoid implants is a novel and technically challenging procedure. As a result, there is little clinical evidence comparing outcomes and performance of augmented implants to conventional devices.

“We don’t yet know what the long-term outcomes are for these new implant designs,” Dr. Sabesan said. “We know they are a solution, but we’d like to know what we can expect 5 to 10 years from now.”

Dr. Sabesan conducted a prior study that used biomechanical testing to correlate loosening of standard glenoid implants with reduced component stability. Could a more advanced research approach lead to reliable guidance for shoulder surgeons considering augmented implants for treating patients with advanced glenohumeral deterioration?


Vani J. Sabesan, MD, is leading an investigation to further understand the performance of augmented glenoid implants and how better results might be achieved. Pictured are components of a joint reaction force shown in a glenoid lateralized design (A/P, anterior-posterior; S/I, superior-inferior).
Courtesy of Vani J. Sabesan, MD

Taking the next step with FEA
Finite element analysis (FEA) is a type of computer modeling used to solve complex structural mechanical problems. It is commonly relied on in high-stakes industries such as aviation. For example, FEA is used at airports to simulate the landings of thousands of aircraft. The data generated are used to develop flight path control strategies that synchronize landings and allow sufficient spatial and temporal clearances so that people, cargo, and equipment come and go safely.

For medical researchers, FEA offers several advantages over more familiar methods of predicting surgical outcomes, such as cadaver and clinical studies that follow patients over a 5- or 10-year period. A comprehensive set of FEA scenarios can be run quickly and are particularly helpful in answering questions that involve many interrelated variables.

“Hopefully computer models can predict outcomes quicker than current methods of study, and we won’t have to wait 10 years to see failures. For now, we’ll still need to follow implants over time to ensure the computer models are valid; but, if they are, we’ll be able to investigate outcomes more rapidly and with less cost even before implantation,” Dr. Sabesan explained.

Specific to evaluating shoulder components, FEA yields detailed data on loading behavior and on localized stresses and strains. Combined FEA kinematic modeling also makes it possible to examine force distribution, soft-tissue tensioning, and muscle forces, all of which contribute to device performance and longevity.

In the driver’s seat
As with Dr. Sabesan’s previous study of conventional glenoid implants, the research team performed the investigation using the shoulder portion of a finite element male human body model originally developed by an international consortium of automakers and automotive suppliers for crash simulations. The shoulder portion of the model includes major shoulder bones, rotator cuff muscles, ligaments, and muscles.

“We’ve taken this particular FEA, which had already been validated with cadaver work, and used it to model two different commercially available augmented glenoids,” Dr. Sabesan said. “We’re putting the models through loads and the normal range of motion of a shoulder to learn how each type of implant performs.”

Dr. Sabesan’s team made several refinements to the model for clinical rigor. For example, they adjusted the scapula and humeral head structures to measure variations <1 mm. This allows for greater precision in determining stress and strain measurements and muscle forces and range of motion to advance clinical applicability.

Focal points
The study is based on the hypothesis that augmented glenoid implants represent a better treatment choice for patients with moderate to severe glenoid retroversion. Specifically, it seeks to determine the following:

  • optimal glenohumeral conformity based on a set of stress and strain profiles
  • the relative advantages of augmented over standard glenoid components
  • relative performance of two different augmented glenoid component designs, both options for severe glenoid bone loss in TSA
  • clinically relevant assessment of functional range of motion combined with complex FEA modeling to evaluate augmented glenoid implant performance

In the short term, Dr. Sabesan hopes results of the study will lead to the development of clinical guidelines for the use of augmented glenoid implants.

Longer term, the study may offer insights for component design and more complex modeling. More broadly, her goal is to help reduce TSA revision rates and alleviate patients’ distress and their time away from work and other activities.

Dr. Sabesan currently is compiling her results for publication, including significant findings comparing the different wedged and step augment designs. She hopes the data gathered during this study will help her obtain National Institutes of Health funding for further research.

Orthopaedic collaboration twice over
The study might not have happened at all were it not for the AAOS/OREF/Orthopaedic Research Society Clinician Scholar Career Development Program (CSCDP). Dr. Sabesan’s first proposal for an OREF grant to fund this study was declined. When she was accepted to participate in the 2012 CSCDP, she brought along her rejected proposal for a formal critique.

“I received positive feedback and encouragement. I took the grant reviewers’ feedback as well as the experience of the CSCDP into account, revised the grant, resubmitted it, and we got funded,” Dr. Sabesan said.

Sustaining research for better care
As a scientist, research is a pathway to answers; as a clinician, the goal is helping patients. “You’re answering a question. You’re also giving a patient a key, an expectation of what their surgery might produce over time. All of this requires resources,” Dr. Sabesan said.

Asked if she had a message for nonresearch colleagues, Dr. Sabesan said, “Every procedure we do today is built on a history of learning. If we want to keep advancing the field and we want to keep making sure we give patients the best options possible, it’s critical to have research.”

Funding for the OREF/ASES/Rockwood grant was made possible by the Dr. and Mrs. Charles Rockwood Family Endowment Fund.

Sharon Johnson is a contributing writer for OREF. She can be reached at communications@oref.org.
© Orthopaedic Research and Education Foundation (OREF).