Biomedical subjects

Gerard A Ateshian

Publications and source records attributed to Gerard A Ateshian.

40 records · Page 3Linked to original sources

PubMedDate not supplied

Biomechanical evaluation of a novel glenoid design in total shoulder arthroplasty.

The amount of articular curvature mismatch providing optimal performance in total shoulder arthroplasty (TSA) is unknown. The objectives of this study were to quantify glenohumeral joint mechanics before and after TSA and to compare the performance of 3 glenoid components: (1) nonconforming, (2) conforming, and (3) a novel design featuring a conforming center extending into a nonconforming periphery. Six fresh-frozen cadaveric shoulders (mean age, 43 years) were mechanically tested on a custom apparatus by use of simulated muscle forces and a coordinate-measuring machine to determine joint kinematics. B-spline models of the natural and prosthetic articular surfaces were generated, and joint contact was computed by use of a proximity criterion. During both centered ( P = .02) and eccentric ( P = .05) loading protocols, glenoid contact migrated posteriorly in conforming implants. No statistical differences in kinematics and contact were found among the nonconforming design, the new design, and the natural joint. Therefore, adding a central region of conformity does not compromise the ability of nonconforming TSA components to reduce rim loading.

Adult↗

PubMedDate not supplied

Computer simulations of patellofemoral joint surgery. Patient-specific models for tuberosity transfer.

BACKGROUND: Variable clinical outcomes of tibial tuberosity transfer surgery have been reported. HYPOTHESES: The biomechanical outcome of surgery is patient-specific; no single procedure produces superior results for all patients. Use of patient-specific computer models can optimize choice of procedure. STUDY DESIGN: Computer simulation study using clinical data. METHODS: We used patient-specific multibody models of the patellofemoral joints of 20 patients with a diagnosis of patellar subluxation and osteoarthritis. Four tibial tuberosity transfer procedures (two anterior and two anteromedial) were simulated for each patient and compared with their preoperative model. RESULTS: When results for all patients were averaged, all simulated operations produced a statistically significant decrease in surface-wide mean contact stress, although no significant difference was found among them. CONCLUSIONS: The simulated surgical outcomes were patient-specific: no single procedure was consistently superior at decreasing peak or mean stress and each procedure produced a potentially detrimental outcome, an increase in either mean stress or peak stress, in at least one patient. CLINICAL RELEVANCE: Computer simulation may serve as a valuable tool for tailoring procedures to specific patients.

Biomechanical Phenomena↗

PubMedDate not supplied

Codominance of the individual posterior cruciate ligament bundles. An analysis of bundle lengths and orientation.

BACKGROUND: It is unclear how each bundle of the posterior cruciate ligament contributes to posterior knee stability. HYPOTHESIS: Changes in bundle orientation and length occur such that neither bundle dominates in restraining posterior tibial motion throughout knee flexion and extension. STUDY DESIGN: Controlled laboratory study. METHODS: Six fresh-frozen cadaveric knees were studied in a joint-testing rig with individual quadriceps and hamstring muscle loading. Kinematic data for the tibia and femur were obtained at knee flexion angles from 0 degrees to 120 degrees. The joint was then disarticulated, and the insertions of the two bundles on the tibia and femur were digitized. RESULTS: Length of the anterolateral bundle increased with increasing knee flexion angle from 10 degrees to 120 degrees. Length of the posteromedial bundle decreased with increasing knee flexion angle from 0 degrees to 45 degrees and increased slightly from 60 degrees to 120 degrees. Length of the anteromedial bundle was significantly less than that of the posteromedial at 0 degrees, 10 degrees, and 20 degrees of knee flexion. The anterolateral bundle was significantly more horizontal at flexion angles of 0 degrees, 10 degrees, 20 degrees, 30 degrees, and 45 degrees (P < 0.05). The posteromedial bundle was more horizontal at 120 degrees. CONCLUSIONS: Changes in orientation take place such that neither bundle dominates in restraining posterior tibial motion throughout knee flexion and extension. CLINICAL RELEVANCE: Double-bundle reconstructions achieve more physiologic knee function.

Aged↗

PubMedDate not supplied

Dynamic deformational loading results in selective application of mechanical stimulation in a layered, tissue-engineered cartilage construct.

The application of dynamic physiologic loading to a bilayered chondrocyte-seeded agarose construct with a 2% (wt/vol) top layer and 3% (wt/vol) bottom layer was hypothesized to (1) improve overall construct properties and (2) result in a tissue that mimics the mechanical inhomogeneity of native cartilage. Dynamic loading over the 28 day culture period was found to significantly increase bulk mechanical and biochemical properties versus free-swelling culture. The initial depth-distribution of the compressive Young's modulus (EY) reflected the intrinsic properties of the gel in each layer and a similar trend to the native tissue, with a softer 2% gel layer and a much stiffer 3% gel layer. After 28 days in culture, free-swelling conditions maintained this general trend while loaded constructs possessed a reverse profile, with significant increases in EY observed only in the 2% gel. Histological analysis revealed preferential matrix formation in the 2% agarose layer, with matrix localized more pericellularly in the 3% agarose layer. Finite element modeling revealed that, prior to significant matrix elaboration, the 2% layer experiences increased mechanical stimuli (fluid flow and compressive strain) during loading that may enhance chondrocyte stimulation and nutrient transport in that layer, consistent with experimental observations. From these results, we conclude that due to the limitations in 3% agarose, the use of this type of bilayered construct to construct depth-dependent inhomogeneity similar to the native tissue is not likely to be successful under long-term culture conditions. Our study underscores the importance of other physical properties of the scaffold that may have a greater influence on interconnected tissue formation than intrinsic scaffold stiffness.

Animals↗