A Validated, Specimen-Specific Finite Element Model of the Supraspinatus Tendon Mechanical Environment.

Rotator cuff tears are a significant clinical problem previously investigated by unvalidated computational models that either use simplified geometry or isotropic elastic material properties to represent the tendon. The objective of this study was to develop an experimentally validated, finite element model of supraspinatus tendon using specimen-specific geometry and inhomogeneous material properties to predict strains in intact supraspinatus tendon at multiple abduction angles. Three-dimensional tendon surface strains were determined at 60 deg, 70 deg, and 90 deg of glenohumeral abduction for articular and bursal surfaces of supraspinatus tendon during cyclic loading (5-200 N, 50 cycles, 20 mm/min) to serve as validation data for computational model predictions.

Non-uniform strain distribution in anterolateral capsule of knee: Implications for surgical repair.

The existence of a ligamentous structure within the anterolateral capsule, which can be injured in combination with the anterior cruciate ligament, has been debated. Therefore, the purpose of this study was to determine the magnitude and direction of the strain in the anterolateral capsule in response to external loads applied to the knee. The anterolateral capsule was hypothesized to not function like a traditional ligament.

Exercise therapy for treatment of supraspinatus tears does not alter glenohumeral kinematics during internal/external rotation with the arm at the side.

Purpose: Rotator cuff tears are a significant clinical problem, with exercise therapy being a common treatment option for patients. Failure rates of exercise therapy may be due to the failure to improve glenohumeral kinematics. Tears involving the supraspinatus may result in altered glenohumeral kinematics and joint instability for internal/external rotation with the arm at the side because not all muscles used to stabilize the glenohumeral joint are functioning normally.

Biomechanical evaluation of knee endpoint during anterior tibial loading: Implication for physical exams.

Background: Physical exams that apply anterior tibial loads are typically used to evaluate knees with anterior cruciate ligament (ACL) injuries. The amount of anterior tibial translation that occurs during these exams can be difficult to assess due to a "soft" endpoint. Therefore, the objective of this study is to determine the biomechanical characteristics of the endpoint for the intact and ACL deficient knee using quantitative criteria.

Use of Robotic Manipulators to Study Diarthrodial Joint Function.

Diarthrodial joint function is mediated by a complex interaction between bones, ligaments, capsules, articular cartilage, and muscles. To gain a better understanding of injury mechanisms and to improve surgical procedures, an improved understanding of the structure and function of diarthrodial joints needs to be obtained. Thus, robotic testing systems have been developed to measure the resulting kinematics of diarthrodial joints as well as the in situ forces in ligaments and their replacement grafts in response to external loading conditions.

Basic biomechanic principles of knee instability.

Motion at the knee joint is a complex mechanical phenomenon. Stability is provided by a combination of static and dynamic structures that work in concert to prevent excessive movement or instability that is inherent in various knee injuries. The anterior cruciate ligament (ACL) is a main stabilizer of the knee, providing both translational and rotatory constraint.

Tensile properties of a split quadriceps graft for ACL reconstruction.

Purpose: Anatomic double-bundle ACL reconstruction can be performed using different grafts, such as quadriceps tendon. Grafts can be split in either coronal or sagittal planes to approximate the two bundles of the native ACL, but it is unknown whether a difference exists in the graft tensile properties depending on splitting plane. The purpose of this study was to evaluate the tensile properties of split human quadriceps tendon-bone grafts.

Collagen fiber alignment and maximum principal strain in the glenohumeral capsule predict location of failure during uniaxial extension.

The glenohumeral joint is frequently dislocated resulting in injury to the glenohumeral capsule. Repair techniques that focus on restoring the capsule after dislocation to re-establish its stabilizing function could benefit from predictions of the location of failure in this continuous sheet of tissue with a random collagen fiber alignment in the unloaded state. Therefore, the objective of this study was to determine the collagen fiber alignment and maximum principal strain in all regions of the capsule during uniaxial extension to failure and to determine whether these parameters could predict the location of tissue failure.

Capsule function following anterior dislocation: implications for diagnosis of shoulder instability.

During shoulder dislocation, the glenohumeral capsule undergoes non-recoverable strain, leading to joint instability. Clinicians use physical exams to diagnose injury and direct repair procedures; however, they are subjective and do not provide quantitative information. Our objectives were to: (1) determine the relationship between capsule function following anterior dislocation and non-recoverable strain; and (2) identify joint positions at which physical exams can be used to detect non-recoverable strain in specific capsule regions.