Electromyographic analysis of rowing stroke biomechanics.

Electromyography was used to study muscle activity in the upper and lower extremities and torso during the rowing stroke. Five experienced male rowers were tested while rowing on a Concept II ergometer. In order to fully evaluate the rowing stroke, six phases were utilized to identify the transition points where individual muscles become more active due to body angle or nature of the motion. The results indicate that the strength of an individual muscle is most likely not as important to the rowing stroke as the combined activity of two or more groups of muscles. Thus, in addition to strength, it is of great value to the oarsman to develop technical skill to coordinate his upper and lower body reactions.

Tissue response to porous-coated implants lacking initial bone apposition.

Although initial bone apposition of a porous-surfaced implant is desirable, it is not always achieved surgically. A model to study the effect of a gap on the quantity and quality of bone growth in both the cancellous and cortical regions has been developed. Implants were surgically placed in the intramedullary canals of adult dogs producing uniform gap spaces 0.0-2.0 mm wide. Histologic and microradiographic evaluations were conducted after 3, 6, and 12 weeks in situ. The results demonstrate that the initial apposition of a porous implant to the surrounding bone surface is not necessary for fixation by bone ingrowth. New bone will grow up to and within the porous structure of an implant even when there is a gap as large as 2.0 mm. However, the rate and degree of maturity and mineralization is enhanced when the gap width is 0.5 mm or less. The amount of bone activity in the cortical region was greater than in the cancellous region at 3 and 6 weeks after operation. After 12 weeks in situ bone growth in gap spaces and into the porous coating was approximately equal.

Fatigue failure of the femoral component of a unicompartmental knee.

A unicompartmental knee implant was retrieved after 11 years in situ. The cast stainless steel femoral component had fractured approximately 1 cm from the anterior tip. The implant and clinical tolerance were analyzed to ascertain the factors associated with the mechanical failure. Increased tensile stresses owing to poor surgical placement and wear on the weight-bearing surface of the component, together with the quality of implant material, influenced the mechanical failure. Examination of the fracture surface revealed fatigue to be the mode of failure. Microscopic analysis of sections through the specimens showed a high inclusion content and inhomogeneous grain size, typical of the cast stainless steel from which the femoral component was fabricated.

Clinical performance of endoprosthetic and total hip replacement systems.

A retrospective study of endoprosthetic replacements and total hip prostheses was undertaken to determine factors that have the greatest effect on the success or failure of femoral hip components. A total of 227 endoprostheses were inserted within the years 1970-1985. Of these, 67 components (29.5 percent) required removal for various reasons. For an endoprosthesis, the most significant factor in determining the chances of success appeared to be the initial insertion diagnosis. Patients who received an endoprosthesis for an ailment which affected only the femoral side of the joint (such as traumatic fracture) had a much lower rate of failure than those patients with disease etiologies that could affect the acetabulum (such as osteoarthritis). The opposite was found for total hip prostheses. Of the 641 total hip devices inserted, 148 (23.0 percent) required removal. The highest rate of failure among these total hip components was for those devices inserted for trauma and the lowest rate of failure was for those inserted for osteoarthritis. Age at the time of insertion also proved to be of importance when estimating a hip component's chance of survival. For both endoprosthetic replacements and total hip arthroplasties, patients younger than 50 years of age at insertion experienced a failure rate almost twice that of those patients more than 50 years of age at insertion.

Metallurgical analysis of five failed cast cobalt-chromium-molybdenum alloy hip prostheses.

The clinical and metallurigical characteristics of five cast cobalt-chromium-molybdenum alloy femoral hip prostheses which failed in vivo were evaluated. The devices included: two of the Howmedica Muller-Charnley design, two of the Howmedica Charnley design, and one of the Zimmer Aufranc-Turner design. Fractographic analyses demonstrated that the five devices had failed by fatigue which originated on the lateral aspect. Failure occurred after an average in vivo time of 80.4 months (approximately 6.7 years). Only two of the devices had Rockwell hardness values that were within the ASTM specifications for the alloy. Upon metallurgical examination, moderate to severe levels of gas porosity, interdendritic shrinkage, and nonmetallic inclusions were found in all of the devices. As expected, extremely large grain sizes also were observed in the devices examined. These results indicate that the metallurgical flaws and defects associated with the cast cobalt-chromium-molybdenum alloys used in these devices may preclude successful longterm performance and warrant manufacturer's attention.

The mechanical properties of immature osteopetrotic bone.

The elastic properties of the longer bones of the fore and hind limbs of an osteopetrotic Angus calf were measured using an ultrasonic technique. The same bones of a second Angus calf with unaffected bone tissue were also studied. The osteopetrotic bones were found to exhibit statistically significant lower values of density and mineral content than did the unaffected bones (P = .0054 and P = .0492, respectively). This result is contrary to what has been reported in the literature. The variations of the elastic properties and the density around the circumference of both the immature osteopetrotic femur and the unaffected femur were found to be similar to those previously measured on normal adult bovine femora.