Larry S. Matthews

The mechanical properties of human tibial trabecular bone as a function of metaphyseal location

Experimental determination of the elastic modulus and ultimate strength of human tibial trabecular bone as a function of metaphyseal location is presented. A 1 cm cubic matrix with planes parallel to the subchondral plate was defined on five fresh frozen cadaver tibias. Approximately 400, 7 mm X 10 mm cylindrical bone plugs were cut from the locations defined by the matrix and tested in uniaxial compressive stress at a strain rate of 0.1%S-1. Results of the study indicate that the trabecular bone properties vary as much as two orders of magnitude from one location to another. As might be predicted from Wolffs law, and noted by previous investigators, concentrations of strength arise from the medial and lateral metaphyseal cortices toward the major medial and lateral contact regions. These results may be valuable for improved analytical modeling and optimal prosthetic design.

Trabecular bone remodeling: An experimental model

An experimental model, capable of inducing controlled stress fields to the distal femoral metaphyses of large dogs, is presented. This model utilized an implantable hydraulic device incorporating five loading cylinders and platens in direct contact with an exposed plane of trabecular bone. A microprocessor controls the loading characteristics, and finite element models were created to calculate the induced stress and strain fields. The trabecular remodeling response is measured using serial in vivo computed tomography, in vitro microcomputed tomography, and histologic analysis. The results of the experiment indicate that significant remodeling can be induced by the activated implant. An increase in trabecular orientation toward the loaded platens was observed, and a statistically significant decrease in connectivity was documented. The greatest effect was associated with a change in the loading rate. A fast rise time (70 ms) loading waveform induced significant bone ingrowth at the implant interface when compared to a slow rise time waveform (700 ms), and demonstrated high correlations with the calculated stress fields as remodeling approached an equilibrium state.

Load bearing characteristics of the patello-femoral joint

This study of normal patello-femoral biomechanics defines some functional specifications which may be useful in future total knee prosthesis design. Serial lateral X-rays of 15 fresh knees and their patellar mechanisms at several flexion angles provided definition of the direction of the resolved patello-femoral forces. Assuming that the patella acts as a frictionless pulley, the magnitude of the patello-femoral forces during several activities was calculated using data from Morrison (1970) and Smidt (1973). It ranged between 421 and 3420 newtons for the various activities and for isometric exercise. A methylene blue contact print technique was used to measure the bearing areas. These data indicate that between 13 and 38 per cent of the patellar surface bears joint loadings. Patello-femoral contact stresses were calculated to range from 1.28 to 12.6 N/mm2. A 696 new-ton man climbing stairs would, for example, generate a patello-femoral force of 1754 newtons and would experience patello-femoral contact str...

The effect on supination-pronation of angular malalignment of fractures of both bones of the forearm.

UNLABELLED Ten fresh human upper-extremity cadaver specimens were tested for the effect of residual angulation from simulated fractures of both bones of the forearm on the potential for range of rotation of the forearm and for limitations of pronation and supination specifically. Ten and 20-degree angulations for the radius and ulna, such as might be encountered in all reasonable clinical situations, were tested. Little significant loss of forearm rotation resulted from angulations of 10 degrees in any direction. With 20 degrees of angulation, there was statistically significant and functionally important loss of forearm rotation. CLINICAL RELEVANCE A residual angulation of 10 degrees in mid-shaft fractures of the radius, ulna, or both bones of the forearm will not limit forearm rotation anatomically. Loss in the range of rotation can be expected with residual angeles of 20 degrees or more.

Fractures of the patella

Patellar fractures usually occur from distraction and three-point bending of the patella as well as from direct blows. Surgical treatment is necessary for fractures that are displaced more than 2 mm and may include open reduction and internal fixation, partial patellectomy, or rarely, total patellectomy. We have presented a new technique for the stabilization of a simple transverse fracture that has provided superior results in laboratory tests. Postoperative complications can be minimized by good attention to wound care, accurate fracture reduction, secure fracture fixation and an early range of motion. Despite the surgeons best efforts, however, post-traumatic osteoarthrosis can develop and may require additional treatment.

Proximal tibial osteotomy. Factors that influence the duration of satisfactory function

Survival analysis studies of 40 patients treated with high tibial osteotomy for arthritis with angular deformity were performed to determine the dominant factors that adversely affected long-term knee function. Obesity, advanced age, and postoperative overcorrection or undercorrection resulted in short durations of successful function. On the average, the probabilities for continued useful function of the knee at tested intervals were: one year, 86%; three years, 64%; five years, 50%; and nine years, 28%.

The joint-contact area of the ankle. The contribution of the posterior malleolus.

Eight ankles from fresh cadavera were tested under simulated clinical conditions to determine the effect of increasing the size of the posterior malleolar fracture on the contact area of the ankle joint and on the distribution of joint pressure. The surface area of contact decreased with increased size of the posterior malleolar fragment. However, the documented changes were smaller than expected on the basis of the findings of Ramsey and Hamilton; they reported a 42 per cent reduction in contact area with only a one-millimeter lateral shift of the talus, which clinically would be associated with a similar one-millimeter shift of the distal tibial fragment. In addition, clinical experience has shown a high rate of post-traumatic degenerative arthritis associated with an inadequately reduced one-half-size posterior fragment. There were considerable changes in the load-distribution patterns, with increased confluence and concentration of loads as the size of the fragment was increased. In plantar flexion, many specimens had three separate areas of contact between the tibia and the talus. With increased size of the posterior fragment, the three areas of contact always joined to become one. Similarly, for all positions of the ankle, increased size of the posterior fragment caused decreases in the contact area. The maximum loss of contact area was 35 per cent for specimens with one-half-size fractures that were tested in the neutral position.

Viscoelastic properties of cat tendon: Effects of time after death and preservation by freezing

Abstract In this study postmortem changes in the character of the stress-strain limit cycle were analyzed for cat extensor communis and extensor lateralis tendons maintained in a stream of Ringers solution and loaded with a short series of symmetrical triangular-wave stress cycles. The mechanical behavior of these tendons was compared with that of similar tendons which had been preserved by freezing. It was found that the overall stiffness (average apparent elastic modulus) of these tendons did not change significantly in the first 3 hrs after death and that the shape characteristics of the stress-strain curves changed little under these conditions. Tendons preserved by freezing displayed stress-strain limit cyclessimilar to those for fresh material. The average moduli for frozen tendons were lower than those from fresh tendons to a degree which was statistically significant.

A biomechanical model of the lumbosacral joint during lifting activities

A biomechanical model of the lumbosacral region was constructed for the purpose of systematically studying the combined stresses and strains on the local ligaments, muscles and disc tissue during sagittal plane two-handed lifting. The model was validated in two ways. The first validation was a comparison of experimental study results with model predictions. In general predictions compared very reasonably with observed values of several authors with the exception of strain predictions on the articular ligaments. Second, a sensitivity analysis was performed over a wide range of lifting tasks. The predicted stress/strain values followed anticipated patterns and were of reasonable magnitudes. On the basis of the results of the sensitivity analysis it was concluded that typical lifting tasks can lead to excessive disc compressive forces, muscle moment generation requirements, and possibly lumbodorsal fascia strains. Conversely, annulus rupture of a healthy disc due to overstrain appears very unlikely.

ANALYSIS OF CUMULATIVE STRAIN IN TENDONS AND TENDON SHEATHS

Twenty-five fresh frozen flexor digitorum profundus tendons stratified by sex were subjected to uniaxial step stress and cyclic loads in twelve intact human cadaver hands. By attaching specially designed clip strain gage transducers on tendons just proximal and distal to an undisrupted carpal tunnel, the interactions of the tendons, tendon sheath and retinacula were measured. The elastic and viscous response of the tendon composites to step stresses were found to fit fractional power functions of stress and time respectively. A significant and quantifiable decrease in strain from the proximal to the distal tendon segment was found to be a function of wrist deviation. The results indicate that an accumulation of strain does occur in tendinous tissues during physiologic loading.