Elizabeth Hofheinz, M.P.H., M.Ed.
New work looking at anatomic total shoulder arthroplasty (aTSA) has advanced the field by offering a chance to identify—early—patients at risk for stress shielding.
A team of researchers from Scripps Research in California, noting that in aTSA, an increasing diaphyseal filling ratio has been correlated with stress shielding in cases involving traditional stem lengths, decided to go beyond conventional X-rays.
Their study, “Three-dimensional Volumetric Filling Ratio Predicts Stress Shielding in Short-stem Anatomic Total Shoulder Arthroplasty,” was published in the Journal of the American Academy of Orthopaedic Surgeons.
Co-author Haluk Celik, M.D. told OSN, “This research displays that filling of the bone by an implant may cause focal osteoporosis which is known as stress shielding in the literature. Despite previous studies having reported using conventional X-rays, our study brings a new perspective to look at that using 3 dimensional CT scans.”
The team looked at 44 patients who underwent short-stem aTSAs, had preoperative CT scans, and at least three-year followup. Patients were divided into Groups A (stress shielding) and B (no stress shielding). The researchers measured the standard implant filling ratios using plain radiographs. Using MIMICS software, they calculated the 3-D shape of the metaphyseal and diaphyseal regions of the humeral cancellous bone.
“We virtually implanted the humeral stems into the humerus as same as the corresponding surgery and we checked the stress shielding on the follow-up imaging,” said Celik, M.D. to OSN.
“Stress shielding with bone loss was identified by comparing the first postoperative radiographs with the final or most recent follow-up radio- graphs at a minimum of 3 years,” wrote the authors. “The stems were divided into 10 zones in both AP and Ax views…humeral stem alignment changes, stem subsidence, and stem loosening were recorded on final radiographs.”
Using 3-D volumetric filling ratio (VFR), the patients in Group A had statistically higher filling ratios than Group B; no important differences were found between the two groups when using standard techniques. The researchers determined that the 3-D VFR method had an area under and receiver operator characteristic curve of 92%, indicating it as a good predictor of stress shielding.
“I hope that this information will be used in clinical practice and new implant designs will be produced using our methodology,” said Dr. Celik.
The researchers are from the Shiley Center for Orthopaedic Research and Education (SCORE) at Scripps Clinic and the Division of Sports Medicine Department of Orthopaedic Surgery, Scripps Clinic, La Jolla, California.