Eric L. Radin

Response of joints to impact loading, III: relationship between trabecular microfractures and cartilage degeneration

Abstract The knee joints of adult rabbits were subjected to daily one hour intervals of impulsive loading equivalent to their body weight at 60 cpm. They developed changes in their knee joints consistent with those of degenerative joint disease. The cartilage destruction was preceded by stiffening of the underlying subchondral bone. Numerous healing trabecular microfractures were associated with this increased stiffening. Similar microfractures have been observed in human specimens. The implications of these findings to bone remodelling and osteoarthritis are discussed.

The response of joints to impact loading. II. In vivo behavior of subchondral bone.

The knee joints of live guinea pigs, subjected to repeated longitudinal impaction, developed obvious cartilage degeneration over a 3 week period. In vitro tests had previously shown that articular cartilage is particularly susceptible to injury from impact loading and that subchondral bone acts as a cushion to protect the overlying cartilage from damage during such loading. Associated with, and slightly preceding the earliest cartilage changes, as judged histochemically, was a stiffening of the underlying subchondral bone. The bone stiffness measurements returned to within the normal range as the cartilage degeneration progressed.

Fractures of the Radial Head: A Review Of Eighty-eight Cases And Analysis Of The Indications For Excision Of The Radial Head And Non-operative Treatment

The controversy surrounding the treatment of radial-head fractures is based, we feel, on the failure to separate undisplaced, displaced, comminuted, complicated, and pediatric fractures. Considering only isolated injuries in adults and each type of fracture separately, we have personally re-examined eighty-eight patients treated at the Massachusetts General Hospital from 1950 to 1962. Our major findings were: (1) early motion may displace otherwise undisplaced fractures; (2) if more than one-third of the radial head is displaced, limitation of motion will probably result; (3) the range of motion depends on the anatomical result; (4) inferior radio-ulnar subluxation does occur, but is of so little significance that it can be ignored as an argument against excision of the radial head when this procedure is indicated. We would treat undisplaced fractures involving less than one-third of the radial head with active motion as soon as the patient is comfortable. We have had no experience in treating undisplaced fractures involving more than one-third of the radial head by immobilizing the elbow until displacement by active motion is no longer possible, but such a procedure might improve the results. Displaced fractures involving less than two-thirds of the radial head should, we think, be treated by early active motion, started when the patient is comfortable. Displaced fractures involving more than two-thirds of the radial head should be treated by early total excision, as should all comminutcd fractures.

Buckling studies of single human trabeculae

The nonideal inelastic buckling behavior of single trabeculae from the subchondral region of the human medial tibial plateau was investigated. Wet specimens exhibited ductile buckling, whereas dry specimens buckled in a brittle manner. Extrapolation to ideal slenderness ratios showed Youngs modulus to be 1·65 × 106 psi in the wet state and 2·05 × 106 psi in the dry state, reasonably similar to cortical bone.

Elastic and viscoelastic properties of trabecular bone: Dependence on structure

Abstract For small amplitude mechanical excitation at frequencies from 100 to 3000 Hz, the response of trabecular bone has no appreciable viscous component. Both fresh wet bone and defatted bone exhibit the same behavior, indicating that the fluid in the intertrabecular spaces has no effect on the dynamic mechanical behavior. Relative stiffness measurements on human trabecular bone correlate well with both trabecular contiguity and volume fraction bone. The correlation with contiguity indicates that plate-bending deformation is important in explaining the mechanical behavior of trabecular bone.

Role of hyaluronic acid in joint lubrication.

Hyaluronic acid is the macromolecule which endows synovial fluid with its viscoelastic properties and it is often assumed these properties are important for the lubrication of the tissue surfaces in diarthrodial joints (Barnett, Davies, and MacConaill, 1961). The relationships, if any, that exist between the chemical and physical properties ofsynovial fluid and its lubricating ability, however, have not been determined. Recent in vitro studies concerned with the types of molecules present in synovial fluid which are responsible for the lubrication of the joint tissues have indicated that hyaluronic acid is a good lubricant for the synovial membrane (Radin, Paul, Swann, and Schottstaedt, 1971), but showed that this constituent was not essential for the lubrication of the articular cartilage (Radin, Swann, and Weisser, 1970). After the fractionation of synovial fluid by sedimentation equilibrium centrifugation in a cesium chloride density gradient, it was shown that the articular cartilage lubricating moiety was present in the protein fraction. More recent experiments have confirmed these data and shown that the lubricating moiety is complex and contains peptide and glycopeptide constituents (Swann and Radin, 1972). It thus appears from these in vitro studies that the different types of macromolecular constituents in synovial fluid can function independently in the lubrication of the different types of tissues in the joint. However, these constituents in vivo are intimately associated and the articular lubricating moiety interacts with hyaluronic acid and is retained as a component of the ultrafiltrate residue after the ultrafiltration of the synovial fluid (Swann and Radin, 1972). For this reason it is important to find out if hyaluronic acid has any effect on the lubricating ability of the protein fraction in an articular cartilage system. A well known fact is that the concentration and intrinsic viscosity of hyaluronic acid are both lower in synovial fluid from patients with rheumatoid arthritis (Balazs, Watson, Duff, and Roseman, 1967), but it is not clear whether these changes modify the lubricating properties of the fluid. A characteristic feature of rheumatoid disease is morning stiffness, and a suggestion was made recently that this is caused by a failure in periarticular soft tissue lubrication (Radin and others, 1971). It is also important, therefore, to determine whether the changes in the structure of hyaluronic acid and the composition of synovial fluid in patients with rheumatoid arthritis alters its ability to lubricate synovial tissue. The present experiments were performed in an attempt to answer some of these questions.

Peak dynamic force in human gait

Abstract Studies were made of the forces generated at heel stroke in human gait using both force plates having a high resonant frequencies (capable of picking up high frequency components in the contact force) as well as a force transducer inserted into the heel of the shoe of the subjects. The output traces were analyzed for the existence of high frequency impulsive loads during a normal walking cycle. The effect of the complicance of the foot and floor was studied with the force transducers. The results showed that during normal human gait the lower limb is subjected to a high frequency impulsive load at heel strike. The severity of this impulse varied with the individual, the velocity and angle with which the limb aproached the ground and the compliance of the two materials coming in contact at heel strike. The magnitude of this peak force varied from 0.5 to 1.25 times body weight and its frequency components from 10 to 75 Hz.

Intercondylar T Fractures of the Humerus in the Adult: A Comparison Of Operative And Non-operative Treatment In Twenty-nine Cases

The treatment of intercondylar fractures in adults should be determined on the basis of the amount of rotatory deformity and comminution. Severely comminuted fractures do not lend themselves to open reduction and are best treated with skeletal traction and gentle closed manipulation when necessary. In the minimally displaced fractures, good results can be obtained by immobilization in a plaster cast. The findings in this small series suggest that fractures with significant rotatory deformity but without gross comminution are more likely to have a good result when skeletal traction is used rather than open reduction and internal fixation. Open reduction and adequate internal fixation are not easy and would seem to offer little chance of a good outcome. We feel that open reduction is very rarely indicated.

Trabecular architecture of the human patella

Abstract The internal architecture of the human patella was studied by quantitative stereological analysis of microradiographs made from sagittal and horizontal sections. The predominant structural (trabecular) element was found to be oriented sheets of hard tissue connected laterally by rods of the same material. The sheets change orientation in a correlated and systematic manner which appears to be in response to the biomechanical demands made on the patella. The predominant variable in the determination of density (and, presumably, other physical properties) was the intertrabecular spacing rather than trabecular thickness. It was found that the sheet-and-rod model could be used to calculate all of the structural parameters in a consistent manner.

A comparative study of total hip replacement prostheses

Abstract A comparative laboratory study has been made of three widely used types of total hip replacement prostheses. With the aid of hip joint simulators and a specially designed wear measuring gauge the friction and wear characteristics of the prostheses have been measured during 1000 hr laboratory tests. Scanning Electron Microscope studies have shown the wear mechanisms operating in the different types of prostheses during the simulator tests. Similar studies of prostheses removed from patients have shown the validity of drawing conclusions about the clinical performance of the prostheses from the laboratory test results.