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The purpose of this study was to use an analytical approach to determine the forces in the glenohumeral ligaments during joint motion. Predictions from the analytical approach were validated by comparing them to experimental data. Using a geometric model, the lengths of the four glenohumeral ligaments were determined during anterior-posterior loading simulations and forward flexion-extension. The corresponding force in each structure was subsequently calculated based on length data via load-elongation curves obtained experimentally. During the anterior loading simulation at 0 deg of abduction, the superior glenohumeral ligament carried up to 71 N at the maximally translated position. At 90 deg of abduction, the anterior band of the inferior glenohumeral ligament had the highest force of 45 N during anterior loading. These results correlated well with those found in previous experimental studies. We believe that this validated analytical approach can be used to predict the forces in the glenohumeral ligaments during more complex joint motion as well as assist surgeons during shoulder repair procedures.

Superior labral anterior-to-posterior (SLAP) lesions can cause shoulder pain partly by causing glenohumeral instability. The purpose of this study was to examine the effect of a simulated type II SLAP lesion and subsequent repair on glenohumeral translation of the vented shoulder. In eight cadaver joints, a robotic/UFS testing system was used to measure joint translation by applying an anterior, posterior, or inferior load of 50 N to each shoulder. The "apprehension tests" for anterior and posterior instability were simulated by applying an anterior load of 50 N with an external rotation torque of 3 Nm or a posterior load of 50 N with an internal rotation torque of 3 Nm. Each loading condition was applied at 30 degrees and 60 degrees of glenohumeral abduction with a constant joint compressive load (44 N) to the intact, simulated SLAP lesion, and repaired shoulder. Repair of the type II SLAP was then performed by placing a Suretac through the labrum both anterior and posterior to the biceps anchor and testing was repeated. ANOVA was used to compare translation of the intact joint, the joint after the type II SLAP lesion had been simulated, and after repair. At 30 degrees of abduction, anterior translation of the intact vented shoulder joint from anterior loading was 18.7+/-8.5 mm and increased to 26.2+/-6.5 mm after simulation of the type II SLAP lesion ( por =0.05). The arthroscopic repair did not restore anterior translation (23.9+/-8.6 mm) to the same degree as the intact joint ( por =0.05). At 60 degrees of abduction, anterior translation of 16.6+/-9.6mm in the intact joint was not significantly increased at 19.4+/-10.1 after simulation of the type II SLAP lesion ( p=0.0527). AP loading also resulted in inferior translation. At 30 degrees of abduction it was 3.8+/-4.0 mm in the intact joint and increased to 8.5+/-5.4 mm after the type II SLAP lesion ( por =0.05. After repair the inferior translation decreased significantly to 6.7+/-5.3 mm ( por =0.05). Although inferior translations were less at 60 degrees of abduction, results were similar to those at 30 degrees after repair. There were no significant increases in translation after SI/AP combined external rotation torque or posterior-anterior combined internal rotation torque loading. In this study the repair of a type II SLAP lesion only partially restored translations to the same degree as an intact vented shoulder joint. Therefore, improved repair techniques or an anteroinferior capsulolabral procedure in addition to the type II SLAP lesion repair might be needed to restore normal joint function.

Ligament, tendon, and fascia are soft tissues composed primarily of collagen fibers. In ligaments and tendons these fibers are organized into roughly parallel bundles to transmit tensile forces between two bones (ligament) or between muscle and bone (tendon). In tendons the bundles are nearly all oriented along the long axis, whereas in ligaments, typically shorter than tendons, the bundles are also generally organized except for bends and twists at insertion sites to bone, e.g. the anterior cruciate ligament in the knee [1]. Fascia, on the other hand, is a sheet of fibrous tissue which encloses muscle. In the leg, fascia lata encompasses the entire thigh musculature and becomes thicker as it progresses distally [2].

A general continuum model for the nonlinear viscoelastic behavior of soft biological tissues was formulated. This single integral finite strain (SIFS) model describes finite deformation of a nonlinearly viscoelastic material within the context of a three-dimensional model. The specific form describing uniaxial extension was obtained, and the idea of conversion from one material to another (at a microscopic level) was then introduced to model the nonlinear behavior of ligaments and tendons. Conversion allowed different constitutive equations to be used for describing a single ligament or tendon at different strain levels. The model was applied to data from uniaxial extension of younger and older human patellar tendons and canine medial collateral ligaments. Model parameters were determined from curve-fitting stress-strain and stress-relaxation data and used to predict the time-dependent stress generated by cyclic extensions.

Growth factors have been shown to stimulate fibroblast division and thus may influence ligament healing. We analyzed the effects of individual growth factors on the proliferation of fibroblasts from the medial collateral and anterior cruciate ligaments of the rabbit in vitro in order to identify growth factors that might enhance proliferation of fibroblasts and to compare the responses of the fibroblasts from the two ligaments to these growth factors. Through measurement of the uptake of [3H]-thymidine into DNA, fibroblasts from these ligaments that had been treated with epidermal growth factor and basic fibroblast growth factor were found to proliferate nearly eight times more than control fibroblasts. Additionally, the fibroblasts of both ligaments proliferated at similar rates when exposed to platelet-derived growth factor-AA, platelet-derived growth factor-BB, basic fibroblast growth factor, insulin-like growth factor-1, and interleukin-1-alpha. However, epidermal growth factor and transforming growth factor-beta caused the fibroblasts from the medial collateral ligament to proliferate at a rate 1.3-1.4 times greater than that of fibroblasts from the anterior cruciate ligament. The reverse was true with acidic fibroblast growth factor, which stimulated the fibroblasts from the anterior cruciate ligament to proliferate at a rate 1.3-1.6 times greater than that of fibroblasts from the medial collateral ligament. This study demonstrated that growth factors can stimulate cell division in ligaments and may be effective in enhancing ligament healing but that these differences were not great enough to explain fully the clinical differences observed between healing of the medial collateral and anterior cruciate ligaments.

This study presents morphometric analyses of collagen subfascicle area fraction and collagen fibril diameter distributions for the anterior cruciate (ACL) and medial collateral (MCL) knee ligaments from transmission electron micrographs of ligament cross sections of five mature, female New Zealand White rabbits. Statistically significant differences in subfascicular area fractions were found between the ACL and MCL (0.89 +/- 0.02, 0.97 +/- 0.01, respectively; p less than 0.001). Mean fibril diameters for the ACL and MCL were also significantly different (0.059 +/- 0.005, 0.085 +/- 0.011 microns, respectively; p less than 0.025). Fibril eccentricity (a measure of parallel alignment of collagen fibrils within the ligaments, defined as the ratio of minor to major axes of elliptical fibril outlines) was 0.89 +/- 0.03 and 0.85 +/- 0.08, respectively, for the ACL and MCL; these data were not significantly different (p greater than 0.1). The relative amount of variation in the pooled fibril diameter data due to variation between animals, ligaments, locations within ligaments, and among fibrils at individual locations are reported. The variation of fibril diameter distributions between the ACL and MCL was substantially greater than the variation between different locations within each ligament cross section as well as between different animals. The structural differences reported may help explain known differences in the biomechanical properties of the ACL and MCL.

The response to a compressive load of a repaired cartilage surface, consisting of full-thickness repair tissue adjacent to normal cartilage, was predicted by the u-p finite element method and compared to that of a normal cartilage surface under the same loading conditions. By individually varying the aggregate modulus, permeability and Poisson's ratio for the repair tissue, analyses were performed to assess the contributions of each to the changes in mechanical behaviour. In comparing the repaired to normal surfaces, the presence of a softer repair tissue resulted in increased axial and decreased radial deformations at any given time point, while a repaired surface with an increased permeability compressed more easily due to the increased fluid flow and caused equilibrium to occur sooner. For smaller Poisson's ratio, the axial deformation was not different from normal if the aggregate modulus was the same as normal; however, the radial expansion was reduced as the repair tissue experienced a larger volume change. These results indicate that the presence of repair tissue in a joint surface can have a strong influence on the mechanical behaviour of the surface.

The ligaments of the knee serve to guide normal joint motion and provide stability. They are composed of densely packed collagen fibers, running parallel to the axis of loading. When unloaded, the tissue has a characteristic crimp pattern. As the ligament is stretched, more collagen fibers are recruited to bear load and the collagen crimp pattern disappears (Viidik and Lewin 1966). This gradual recruitment of ligament fibers results in a nonlinear constitutive relation for the ligament as a whole. During normal activity levels, the ligaments maintain normal knee joint kinematics with relatively small loads. When the knee is subjected to large externally applied forces such as those that occur in sporting activities, excessive joint motion is restricted by the increasing stiffness of the ligament.

Damage to articular cartilage frequently occur following trauma and pathology (Curtiss 1969; Mankin and Brandt 1984). The limited ability of cartilage to heal has presented a continuous challenge in the treatment of damaged articular surfaces (Haggart 1940; Furukawa et al. 1980; Mankin and Brandt 1984). Many procedures have been explored and implemented to remedy this problem (Coletti et al. 1972; Charnley and Cupic 1973; Coventry et al. 1974; Aston and Bentley 1986; Meyers 1989), and the popular one by far is artificial joint replacement (McKee and Farrar 1966). The long-term survival problems associated with artificial joint replacement (Miller et al. 1978), however, have contraindicated this procedure as an ideal treatment for cartilage resurfacing. Alternatives have thus been sought, and in recent years efforts have been focused on biological arthroplasty. The basic approach in biological arthroplasty is to repair the cartilage defect with an implantable biological graft containing a chondrogenic cell source which will promote growth of a new cartilaginous tissue and eventual functional healing of the defect. The joint surface regenerated this way may potentially last for longer periods of time than the artificial implants.

In the last decade a number of chemically fixed, soft tissue based bioprostheses have become commercially available. Chemical fixation of these materials changes a number of their physical and chemical properties. Quantitation of these effects has been difficult because of: anisotropy of the biopolymers, variable composition of the materials, and sample size and configuration limitations. Collagen tape, made from reconstituted collagen, has been chosen as a model material because it alleviates many of the aforementioned problems. Its constituent fibers are homogeneous and unidirectional. The cross-sectional area is constant. Thus, the resultant uniaxial tensile stress-strain relationship is reproducible to allow for systematic parametric studies. Results are presented for the change in tensile properties of the collagen tape as a function of exposure time to glutaraldehyde fixative. These properties are described by the equation: sigma = A (eB epsilon-1) The tensile properties of fresh and fixed pericardial tissue were also tested and corroborative results were found.

This investigation presents a new approach in the measurement of the mechanical properties of the ligament substance from tensile testing of a bone-ligament-bone complex. Such basic information should be one of the necessary prerequisites in the evaluation of ligament repair as well as reconstruction by autogenous tissue grafts or artificial ligament implants. The use of a video system permits the determination of tensile strains of the mid-medial collateral ligaments from the canine, swine, and rabbit without mechanically interfering with the ligament deformation during testing. This methodology further eliminates the difficulties of measuring the initial length of the entire medial collateral ligament, as its insertions to bones are ambiguous and cover a large area. It was found that the strain of the ligament substance is consistently and considerably less than specific deformation of the bone-ligament-bone complex. These data suggest that the ligament-bone structure stretches nonuniformly with the highest deformation occurring near or at the ligament insertion sites to bone. Other interesting findings include the variation of tensile strains along the ligament substance for all animal species studied.

Enucleated human eyes, 1–3 days post mortem, were sectioned equatorially and the anterior or posterior segment of the corneoscleral shell was clamped on a metal chamber for pressurization. A flying spot scanner system was used to measure horizontal surface deformations while the pressure in the chamber was changed stepwise. Lateral deformations in directions 90° and 45° to the original horizontal direction were also measured to establish surface isotropy of the material when the eye specimens were pressurized in their natural geometries. The finite element numerical method was then used to construct a mathematical model of the posterior segment of the eye mounted on the metal chamber. This model uses trilinear stress-strain relationships which were adjusted until the predicted surface deformations agreed with the experimental results. Using a similar procedure on the anterior segment, a trilinear stress-strain relation was obtained for the corneal stroma. The trilinear relations were then converted to exponential form by a least square method. The finite element, axisymmetric mathematical model can assign these nonlinear material properties for different portions of the eye and specific variations in geometry such as central corneal or equatorial scleral thinning. Such geometric complexity and material heterogeneity and nonlinearity could not be modeled conveniently by previous mathematical models of the corneoscleral shell. The model will be useful in the analysis of stress and strain in portions of the eye, pressure-volume relations and tonometry.

The nonlinear mechanical properties of the cornea, sclera, and optic disk determined previously are incorporated in a finite element mathematical model of a human corneo-scleral shell. This mathematical model is then used to calculate a nonlinear intraocular pressure-volume relation and the forces and volumes in applanation tonometry. These results are compared with experimental results obtained by other investigators. Friedenwald's coefficients of ocular rigidity were also calculated using the model and were found to decrease with increased intraocular pressure.