Impact of exercise on bone health and contraindication of oral contraceptive use in young women.

PURPOSE: The effect of quantified resistance and high impact exercise training on bone mass as modified by age and oral contraceptive (OCont) use in young women was studied. METHODS: Women were categorized by age (18-23 vs 24-31 yr) and OCont use, and were then randomized into either three sessions of resistance exercise plus 60 min.wk-1 of jumping rope or a control group for 24 months. Total body, spine, femoral neck, greater trochanter, Ward's area, and radial bone mineral density (BMD) and/or content (BMC), biochemical markers of bone turnover, dietary intake of calcium, lean body mass, maximal oxygen uptake, and strength were determined at baseline and every 6 months. RESULTS: Total body (TB) BMC percent change from baseline was higher in exercisers compared with nonexercisers at 6 and 24 months. OCont users had lower bone turnover at baseline and a decrease in TBBMC from baseline compared with non-OCont users at 24 months. Spine BMC and BMD decreased in the exercise and OCont group at 6 months and remained significantly below nonexercisers who used oral contraceptives at 2 yr. Femoral neck BMD also decreased in the exercise and oral contraceptive group at 6 months. CONCLUSIONS: Exercise prevented a decline in TBBMC seen in the nonexercisers. On the other hand, exercise in oral contraceptive users prevented the increase observed in the spine of the nonexercise plus OCont group.

In vitro comparison of the use of two large-animal, centrally threaded, positive-profile transfixation pin designs in the equine third metacarpal bone.

OBJECTIVE: To compare the in vitro holding power and associated microstructural damage of 2 large-animal centrally threaded positive-profile transfixation pins in the diaphysis of the equine third metacarpal bone. SAMPLE POPULATION: 25 pairs of adult equine cadaver metacarpal bones. PROCEDURE: Centrally threaded positive-profile transfixation pins of 2 different designs (ie, self-drilling, self-tapping [SDST] vs nonself-drilling, nonself-tapping [NDNT] transfixation pins) were inserted into the middiaphysis of adult equine metacarpal bones. Temperature of the hardware was measured during each step of insertion with a surface thermocouple. Bone and cortical width, transfixation pin placement, and cortical damage were assessed radiographically. Resistance to axial extraction before and after cyclic loading was measured using a material testing system. Microstructural damage caused by transfixation pin insertion was evaluated by scanning electron microscopy. RESULTS: The temperature following pin insertion was significantly higher for SDST transfixation pins. Periosteal surface cortical fractures were found in 50% of the bones with SDST transfixation pins and in none with NDNT transfixation pins. The NDNT transfixation pins were significantly more resistant to axial extraction than SDST transfixation pins. Grossly and microscopically, NDNT transfixation pins created less damage to the bone and a more consistent thread pattern. CONCLUSIONS AND CLINICAL RELEVANCE: In vitro analysis revealed that insertion of NDNT transfixation pins cause less macroscopic and microscopic damage to the bone than SDST transfixation pins. The NDNT transfixation pins have a greater pull out strength, reflecting better initial bone transfixation pin stability.

In vitro comparison of metaphyseal and diaphyseal placement of centrally threaded, positive-profile transfixation pins in the equine third metacarpal bone.

OBJECTIVE: To evaluate in vitro holding power and associated microstructural and thermal damage from placement of positive-profile transfixation pins in the diaphysis and metaphysis of the equine third metacarpal bone. SAMPLE POPULATION: Third metacarpal bones from 30 pairs of adult equine cadavers. PROCEDURE: Centrally threaded positive-profile transfixation pins were placed in the diaphysis of 1 metacarpal bone and the metaphysis of the opposite metacarpal bone of 15 pairs of bones. Tensile force at failure for axial extraction was measured with a materials testing system. An additional 15 pairs of metacarpal bones were tested similarly following cyclic loading. Microstructural damage was evaluated via scanning electron microscopy in another 6 pairs of metacarpal bones, 2 pairs in each of the following 3 groups: metacarpal bones with tapped holes and without transfixation pin placement, metacarpal bones following transfixation pin placement, and metacarpal bones following transfixation pin placement and cyclic loading. Temperature of the hardware was measured with a surface thermocouple in 12 additional metacarpal bones warmed to 38 C. RESULTS: The diaphysis provided significantly greater resistance to axial extraction than the metaphysis. There were no significant temperature differences between diaphyseal and metaphyseal placement. Microstructural damage was limited to occasional microfractures seen only in cortical bone of diaphyseal and metaphyseal locations. Microfractures originated during drilling and tapping but did not worsen following transfixation pin placement or cyclic loading. CONCLUSIONS AND CLINICAL RELEVANCE: Centrally threaded, positive-profile transfixation pins have greater resistance to axial extraction in the diaphysis than in the metaphysis of equine third metacarpal bone in vitro. This information may be used to create more stable external skeletal fixation in horses with fractures.

In vivo observations of hydraulic stiffening in the canine femoral head.

The role that intertrabecular contents and their boundary conditions have on the dynamic mechanical response of canine femoral heads was investigated in vivo. Femoral heads from paired intact hind limbs of canine specimens were subjected to a sinusoidal strain excitation at physiologic frequencies, in the cranio-caudal direction. The fluid boundary conditions for the contralateral limbs were changed by predrilling through the lateral femoral cortex and into the femoral neck. The drilling procedure did not invade the head itself. This femoral head fluid boundary alteration reduced the stiffness by 19 percent for testing at 1 Hz. The results of this study demonstrate that fluid stiffening occurs in vivo as previously observed ex vivo.

Finger joint force minimization in pianists using optimization techniques.

A numerical optimization procedure was used to determine finger positions that minimize and maximize finger tendon and joint force objective functions during piano play. A biomechanical finger model for sagittal plane motion, based on finger anatomy, was used to investigate finger tendon tensions and joint reaction forces for finger positions used in playing the piano. For commonly used piano key strike positions, flexor and intrinsic muscle tendon tensions ranged from 0.7 to 3.2 times the fingertip key strike force, while resultant inter-joint compressive forces ranged from 2 to 7 times the magnitude of the fingertip force. In general, use of a curved finger position, with a large metacarpophalangeal joint flexion angle and a small proximal interphalangeal joint flexion angle, reduces flexor tendon tension and resultant finger joint force.

Stiffening of the femoral head due to inter-trabecular fluid and intraosseous pressure.

The mechanical properties of cancellous bone, as measured from bone plug samples have been widely documented. However, few tests have been attempted to explore the effects the intertrabecular contents may have on the load bearing capabilities. In this study, canine femoral heads were subjected to dynamic compressive strain cycles. The femoral heads were tested intact, as well as with disrupted boundary conditions of the continuous, intraosseous fluid space. A significant reduction in mechanical stiffness was observed when the fluid compartment boundary was disrupted by drilling a hole part way into the femoral neck. A finite element model of a typical femoral head showed that the stiffness change was not due to removal of material from the neck, hydraulic effects notwithstanding. Refilling the hole in the neck with saline solution and sealing the boundary restored the stiffness to the intact baseline level. However, an increase in the fluid pressure did not cause a statistically significant increase in the stiffness of the femoral head.

The effect of intertrabecular fluid on femoral head mechanics.

The effect of intraosseous fluid on the mechanical characteristics of bone is unclear. To determine the potential effects of alteration in the fluid boundary conditions of the femoral head, a decompression procedure was performed. The stiffness of femoral heads from normal adult mongrel dogs was measured after the heads were subjected to a physiologic mechanical load. When the fluid boundary conditions were altered by drilling the femoral neck, femoral head stiffness was reduced by more than 30% (p = 0.045). Refilling of the femoral specimen with saline restored the stiffness to the baseline value. These observations demonstrate that in vitro changes of fluid boundary conditions can alter the mechanical integrity of the femoral head. Alteration in osseous fluid boundary conditions in vivo could affect joint integrity and be of pathogenetic significance in joint disease.

Component wear of total knee prostheses using Ti-6A1-4V, titanium nitride coated Ti-6A1-4V, and cobalt-chromium-molybdenum femoral components.

A knee simulator was used to study the wear of carbon fiber reinforced UHMWPE (Poly Two) (Poly Two is a registered trademark of Zimmer, USA) tibial and patellar components against Ti-6A1-4V, titanium nitride (TiN)-coated Ti-6A1-4V, and cobalt-chromium-molybdenum femoral components. The prostheses tested were regular sized Miller-Galante total knees mounted on 316L stainless steel fixtures using bone cement. An environmental chamber surrounded the knee and maintained bovine serum lubricant at 37 degrees C. The specimens were tested using consecutive blocks of 464 level walking steps, 8 ascending stairs and 8 descending stairs for a total of 100,000 steps. The wear mechanisms found on the tibial components were scratching, carbon-fiber associated damage, surface deformation, pitting, minor abrasion, and delamination. Three forms of carbon fiber associated damage were identified; fibers pulled from the surface, broken fibers, and UHMWPE removed from the surface fibers. The SEM evaluation revealed a pit forming mechanism. No correlation was found between femoral component material and tibial surface damage. Visual examination of the femoral components revealed no signs of wear or scratching on the cobalt-chromium-molybdenum or TiN-coated Ti-6A1-4V components. There were, however, many light surface scratches on the uncoated Ti-6A1-4V components, which were also observed in a supplementary test of an uncoated Ti-6A1-4V component tested with a conventional polyethylene tibial component.

Degenerative arthritis of the knee secondary to fracture malunion.

Degenerative arthritis of the knee is a complication of femoral or tibial fractures potentially avoidable by the correction of various degrees of malalignment. To better clarify the malalignment problem, the records of 14 patients (15 limbs), with degenerative arthritis of the knee and a history of tibial or femoral fracture were retrospectively reviewed. The average follow-up was 31.7 years. Static biomechanical frontal plane analyses were evaluated. The calculated increased force on either the medial or lateral tibial plateau, due to the malunion, was strongly associated with presence of a varus or valgus deformity at the knee (p less than 0.0005). A normal tibial plateau force for the malaligned condition multiplied by the time since fracture correlated directly with the amount of subsequent varus or valgus deformity at the knee (p less than 0.01). Lower limb fracture alignment should be restored to as near normal as possible to reduce the likelihood of gonarthrosis.

Preliminary study of the in vivo motion in the canine shoulder.

An instrumented spatial linkage was used to measure the total motion in a canine shoulder as the dog was engaged in a variety of activities, including walking on a level carousel track, as well as over a hurdle, up and down a step, and up and down a ramp placed on the same track. For each activity, the motion data were analyzed, using 2 procedures. First, the linkage data and the joint contour data were combined by computer, and the motion was represented by a series of sequential computer drawings showing the scapular and humeral articular surfaces in their proper relative positions for selected increments of time during the various activities described. As an alternate but approximate method for describing the relative humeral-scapular motion, rotations about 3 mutually perpendicular axes through the average center of the shoulder joint were determined.