Influence of Age on Mechanical Properties of Healing Fractures and Intact Bones in Rats

Mechanical properties of fractured and intact femora have been studied in young and adult, male rats. A standardized, closed, mid-diaphyseal fracture was produced in the left femur, the right femur serving as control. The fracture was left to heal without immobilization. At various intervals, both fractured and intact femora were loaded in torsion until failure.

The fractured femora regained the mechanical properties of the contralateral, intact bones after about 4 weeks in young and after about 12 weeks in adult rats. For intact bones, both the ultimate torsional moment (strength) and the torsional stiffness increased with age of the animals, whereas the ultimate torsional angle remained unchanged. For bone as a material, however, the ultimate torsional stress (strength) and the modulus of rigidity (stiffness) increased with age only in young rats, being almost constant in the adult animals.

The various biomechanical parameters of the healing fractures did not reach those of the contralateral, intact bones simultaneously. The torsional moment required to twist a healing femoral fracture 20 degrees (0.35 radians), a deformation close to what an intact femur can resist, proved to be a functional and simple measure of the degree of fracture repair in rats.     

Calcitonin Producing Tumour: Effects on Fracture Repair and Normal Bone in Rats

The mechanical properties and the collagen metabolism of healing fractures and intact bones have been studied in rats with a transplanted, calcitonin (CT) secreting, medullary thyroid carcinoma (MCT). Sham operated animals served as controls. the MCT was transplanted beneath the kidney capsule. Seven months later, when the rats with MCT had increased circulating levels of CT, a standardized femoral fracture was produced in all the animals.

The serum levels of CT were 3-40 times higher in tumour bearing rats than in controls in the period following the fracture. the fracture strength of rats with MCT was reduced by about 60 per cent compared to controls at 16 weeks after the fracture. the strength of intact femora (ultimate torsional moment) seemed to be progressively impaired by increasing levels of circulating CT. Also the strength of bone as a material (ultimate torsional stress) was reduced in the rats with MCT. the collagen synthesis was reduced in MCT rats, but the amounts of collagen in fractured or intact bones were not changed compared to controls.

We conclude that chronic hypercalcitoninaemia due to MCT seems to have a negative influence both on fracture healing and on bone metabolism.     

Mechanical Property Distributions in the Cancellous Bone of the Human Proximal Femur

Proximal femurs obtained at routine autopsy were sectioned into large numbers of 5 mm cubic specimens, in order to obtain detailed quantitative information about the spatial and directional variations of the material properties of the cancellous bone. Low strain rate compression tests were performed, evaluating the apparent elastic modulus and yield strength, in three perpendicular testing directions, for each cube. A computer contouring program was used to assemble the experimental data into smoothed distribution plots across sections of interest.

The results revealed stiffness and strength elevations/reductions which clearly correspond to roentgenographic features. Especially prominent stiffness elevations (160 to 400 percent above the overall cancellous bone average) were found in the regions traversed by the primary trabeculation system, although the modulus of the bone samples was substantially reduced when measured in directions other than those of habitual weight-bearing. Similar but less pronounced effects were observed for the arcuate trabeculation system. Conversely, Wards triangle and the intertrochanteric regions exhibited significant (as much as 40 to 90 percent below average) stiffness and strength reductions.

There was close qualitative agreement between the stiffness and yield strength distributions for all sections examined. This phenomenon was found to be a corollary of the remarkably linear proportionality between the modulus and yield strength values for individual compression tests.     

Tibia Vara (Osteochondrosis Deformans Tibiae or Blount's Disease): Treatment and Follow-up Examination

The collagen metabolism of callus tissue from closed, non-immobilized rat femoral fractures was studied in vitro after in vivo treatment with indomethacin 2 mg/kg/day for 6, 9 and 12 days after fracture. Total hydroxyproline synthesis and incorporation of hydroxyproline into collagen were found to be significantly increased after indomethacin treatment, whereas no significant difference was found regarding collagen resorption. The results Surggest that the recently demonstrated inhibition of fracture healing by indomethacin is not brought about by an inhibition of collagen synthesis.     

Calcitonin Producing Tumour: Effects on Fracture Repair and Normal Bone in Rats

The mechanical properties and the collagen metabolism of healing fractures and intact bones have been studied in rats with a transplanted, calcitonin (CT) secreting, medullary thyroid carcinoma (MCT). Sham operated animals served as controls. the MCT was transplanted beneath the kidney capsule. Seven months later, when the rats with MCT had increased circulating levels of CT, a standardized femoral fracture was produced in all the animals.

The serum levels of CT were 3-40 times higher in tumour bearing rats than in controls in the period following the fracture. the fracture strength of rats with MCT was reduced by about 60 per cent compared to controls at 16 weeks after the fracture. the strength of intact femora (ultimate torsional moment) seemed to be progressively impaired by increasing levels of circulating CT. Also the strength of bone as a material (ultimate torsional stress) was reduced in the rats with MCT. the collagen synthesis was reduced in MCT rats, but the amounts of collagen in fractured or intact bones were not changed compared to controls.

We conclude that chronic hypercalcitoninaemia due to MCT seems to have a negative influence both on fracture healing and on bone metabolism.     

Mechanical Properties of Fractured and Intact Rat Femora Evaluated by Bending, Torsional and Tensile Tests

Mechanical properties of healing fractures and growing, intact bones were studied in male rats aged 8 weeks at the beginning of the study period. A standardized, closed fracture was produced in the middle of the left femur. The fracture was not immobilized. At various intervals after the fracture, the healing fractured femora and the contralateral, intact femora were subjected to bending, torsional and tensile tests.

The fractured femora regained the strength and the ultimate deformation of the contralateral, intact femora after about 8 weeks when tested in bending, and after about 13 weeks when tested in torsion. In the first phases of fracture repair, the healing fractures could resist more torsional than bending load, whereas the opposite was found for solidly consolidated fractures and intact bones.

For intact bones, the ultimate bending and torsional moments increased with increase in age and weight of the animals, whereas the ultimate angular deformation remained constant. The ultimate bending and torsional stresses (bone material strength) increased to reach a plateau when the rats were about 14 weeks old. No significant differences were observed between the bending, torsional and tensile test methods. For the evaluation of fracture repair, each test has its particular application.     

A protocol for angiographic embolization in exsanguinating pelvic trauma: A report on 31 patients

Background?The indication for acquiring angiographic embolization in the initial treatment of severe pelvic fractures is controversial. We describe the characteristics and outcome of 31 patients with traumatic pelvic bleeding who underwent percutaneous angiography with embolization according to a standardized protocol.

Patients and methods?During an 8.5-year period, 1,260 patients were treated for pelvic trauma. We performed a prospective registration of the 46 patients who underwent angiography, and report the 31 patients who had signs of significant arterial injury on angiography, necessitating embolization.

Results?The rate of significant arterial injury after pelvic trauma was 2.5%. All patients had been subjected to high-energy injuries and all were severely injured as measured by the Injury Severity Score: 41 (17–66). Pelvic arterial injury was observed with all types of pelvic trauma, including isolated acetabular (4/31) and sacral fractures (3/31). The internal iliac artery or its branches was injured in 28 of 31 patients. Survival rate after embolization was 84%, and correlated inversely with increasing patient age. None of the patients died of bleeding.

Interpretation?Our findings show that significant pelvic arterial injuries occur in a minority of patients after pelvic trauma, and predominantly affect patients with multiple high-energy injuries regardless of fracture type. The effect of angiographic embolization was good.     

Primary hemiarthroplasty in old patients with displaced femoral neck fracture

103 patients with displaced femoral neck fractures (Garden 3–4) treated with primary hemiarthroplasty in the Department of Orthopedics, Malmö University Hospital, Sweden 1998–1999 were followed in a prospective, consecutive study for 1 year. Inclusion criteria were age of at least 80 years, signs of mental changes and/or residence in an institution. The control group consisted of 69 patients with internal fixation (Hansson hook pins).

The arthroplasty group required more blood transfusions, a longer operation and had more superficial infections. No differences were detected as regards other complications, length of hospital stay, in-hospital mortality or ability to return home. The 1-year mortality rates were similar in the arthroplasty (29/103) and control groups (28/69). Within 1 year, we found a lower failure rate in the arthroplasty group (6/103) than in the control group (18/69). In the arthroplasty group, 2/103 had dislocations. Of the surviving arthroplasty patients at 12 months, 31/74 could walk as well as before the fracture and 55/74 had no pain.

We recommend primary hemiarthroplasty for demented and/or institutionalized patients over 80 years with displaced femoral neck fractures.     

Mechanotransduction and functional response of the skeleton to physical stress: The mechanisms and mechanics of bone adaptation

The skeleton's primary mechanical function is to provide rigid levers for muscles to act against as they hold the body upright in defiance of gravity. Many bones are exposed to thousands of repetitive loads each day. During growth and development, the skeleton optimizes its architecture by subtle adaptations to these mechanical loads. The mechanisms for adaptation involve a multistep process of cellular mechanotransduction including: mechanocoupling— conversion of mechanical forces into local mechanical signals, such as fluid shear stresses, that initiate a response by bone cells; biochemical coupling— transduction of a mechanical signal to a biochemical response involving pathways within the cell membrane and cytoskeleton; cell-to-cell signaling from the sensor cells (probably osteocytes and bone lining cells) to effector cells (osteoblasts or osteoclasts) using prostaglandins and nitric oxide as signaling molecules; and effector response— either bone formation or resorption to cause appropriate architectural changes. These architectural changes tend to adjust and improve the bone structure to its prevailing mechanical environment. Structural changes can be predicted, to some extent, by mathematical formulas derived from three fundamental rules: (1) bone adaptation is driven by dynamic, rather than static, loading; (2) extending the loading duration has a diminishing effect on further bone adaptation; (3) bone cells accommodate to a mechanical loading environment, making them less responsive to routine or customary loading signals. Received for publication on Dec. 25, 1997; accepted on Feb. 24, 1998     

Effects of Repetitive Loading on Bone Mass and Geometry in Young Male Tennis Players: A Quantitative Study Using MRI

Pre‐ and early puberty seem to be the most opportune times for exercise to improve bone strength in girls, but few studies have addressed this issue in boys. This study investigated the site‐, surface‐, and maturity‐specific exercise‐induced changes in bone mass and geometry in young boys. The osteogenic effects of loading were analyzed by comparing the playing and nonplaying humeri of 43 male pre‐, peri‐, and postpubertal competitive tennis players 10–19 yr of age. Total bone area, medullary area, and cortical area were determined at the mid (40–50%) and distal humerus (60–70%) of both arms using MRI. Humeral bone mass (BMC) was derived from a whole body DXA scan. In prepubertal boys, BMC was 17% greater in the playing compared with nonplaying arm (p < 0.001), which was accompanied by a 12–21% greater cortical area, because of greater periosteal expansion than medullary expansion at the midhumerus and periosteal expansion associated with medullary contraction at the distal humerus. Compared with prepuberty, the side‐to‐side differences in BMC (27%) and cortical area (20–33%) were greater in peripuberty (p < 0.01). No differences were found between peri‐ and postpuberty despite longer playing history in the postpubertal players. The osteogenic response to loading was greater in peri‐ compared with prepubertal boys, which is in contrast with our previous findings in girls and may be caused by differences in training history. This suggests that the window of opportunity to improve bone mass and size through exercise may be longer in boys than in girls.