Load transfer after cemented total shoulder arthroplasty.

Glenoid loosening is the primary reason for failure after a total shoulder arthroplasty (TSA), but the failure mechanism is not yet known. This study determined how the load transfer and stress distribution are affected by the introduction of a glenoid implant. We developed a finite-element model of a scapula with and without a virtually implanted modern glenoid prosthesis design. Two load magnitudes were considered: normal and high. Loading locations were simulated at the center and at 4 eccentric positions on the glenoid. A metal-backed implant was also simulated to understand the effect of fixation stiffness. In the intact glenoid, for both center and eccentric loading, the majority of stress was distributed in the cancellous bone, whereas after a reconstruction, stresses in that region were lower. Metal-backed implants further decreased the joint load carried by the bone. Stresses in the cement layer increased during eccentric and high-magnitude loading. This study provided a basic understanding of the load-sharing phenomenon after a TSA that could explain glenoid loosening failure. Our results suggest that with reconstruction of the glenoid with a contemporary implant, the load transfer pattern is significantly altered, with eccentric and high-magnitude loads increasing stresses in the cement indicating potential for failure. The use of a metal-backed implant reduces the load carried by the bone, which may be detrimental to long-term TSA survival.

Patel RJ ，Wright TM ，Gao Y 《-》

Effects of osteoarthritis on load transfer after cemented total shoulder arthroplasty.

Total shoulder arthroplasty is commonly performed to treat glenohumeral osteoarthritis (OA); however, little is understood of the mechanics of the reconstructed OA shoulder. We sought to establish the effects of OA-induced changes in bone density and retroversion angle on load transfer and stress distribution in the bone-implant system of the scapula. We developed finite element models of reconstructed healthy and OA scapulas with a virtually implanted glenoid prosthesis design. For the OA scapula, models with uncorrected and corrected retroversion were created. Loads were applied at the center or posteriorly on the glenoid surface. Our results suggest that with reconstruction of the corrected glenoid with a contemporary implant, cement stresses increase and the load transfer pattern changes with eccentric loads. The load transfer and local stresses in the bone-implant system in the retroverted glenoid are less sensitive to changes in loading location. Furthermore, the load transfer in the OA glenoid is less sensitive to the effect of peg proximity to the cortical shell than in the healthy glenoid. We provided evidence of how load sharing is altered among healthy, corrected OA, and retroverted OA glenoids. We demonstrated that correction of retroversion in OA glenoids may actually increase the risk for stress shielding and cement failure compared with retroverted glenoids, and OA patients can accommodate shorter pegs because of the higher glenoid bone stiffness in the OA glenoid.

Patel RJ ，Gulotta L ，Wright TM ，Gao Y ... -  《-》

Three-dimensional finite element analysis of glenoid replacement prostheses: a comparison of keeled and pegged anchorage systems.

Lacroix D ，Murphy LA ，Prendergast PJ 《JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME》

Finite element analysis of the mechanical behavior of a scapula implanted with a glenoid prosthesis.

Couteau B ，Mansat P ，Estivalèzes E ，Darmana R ，Mansat M ，Egan J ... -  《CLINICAL BIOMECHANICS》

Evaluation of the glenoid implant survival using a biomechanical finite element analysis: influence of the implant design, bone properties, and loading location.

Mansat P ，Briot J ，Mansat M ，Swider P ... -  《-》