Pekka Jalovaara

Comparison of three-point bending test and peripheral quantitative computed tomography analysis in the evaluation of the strength of mouse femur and tibia.

We compared the mechanical and densitometric testing methods in evaluating the mechanical strength of mouse cortical bones. The femora and tibiae of 10 male mice (weight 32.8 +/- 4.0 g) were utilized. Volumetric cortical bone mineral density (vCtBMD), cross-sectional cortical area at midshaft (CSA), cross-sectional moment of inertia (CSMI), and strength strain index (SSI) were measured by peripheral quantitative computed tomography (pQCT). The precision of pQCT expressed as a coefficient of variation (CV) was 1.1%, 2.7%, and 6.4% for vCtBMD, CSA, and CSMI, respectively. The mechanical properties were measured by a three-point bending test. The method error measured from paired bones was 7.3%-10.1% for breaking bending force, 15.0%-15.2% for stiffness, 2.0%-2.4% for vCtBMD, 5.2%-6.4% for CSA, 13.5%-17.6% for CSMI, and 8.9%-18.1% for SSI. CSMI and CSA were found to be the best explanatory variables for the breaking force of femur and tibia, respectively, while CSA and CSMI were the best predictors for the elastic modulus of femur and tibia, respectively. CSA had a higher correlation with mechanical parameters than vCtBMD. On the basis of this study, the mechanical tests and the pQCT measurements are relevant in biomechanical studies on mouse bones and justify the use of the murine model. High-resolution pQCT gives better precision than the three-point bending test in studies of mouse bones.

Combination of bone mineral density and upper femur geometry improves the prediction of hip fracture

Bone mineral density (BMD) measured by dual-energy X-ray absorptiometry (DXA) is the main determinant of the clinical evaluation of hip fracture risk. However, it has been shown that BMD is not the only predictive factor for hip fracture, but that bone geometry is also important. We studied whether the combination of bone geometry and BMD could further improve the determination of hip fracture risk and fracture type. Seventy-four postmenopausal females (mean age 74 years) with a non-pathologic cervical or trochanteric hip fracture without previous hip fracture or hip surgery constituted the study group. Forty-nine had a cervical fracture (mean age 73 years) and 25 had a trochanteric fracture (mean age 76 years). The control group consisted of 40 age-matched females (mean age 74 years). The geometrical parameters were defined from plain anteroposterior radiographs, and the potential sources of inaccuracy were eliminated as far as possible by using a standardized patient position and calibrated dimension measurements with digital image analysis. BMD was measured at the femoral neck (FEBMD), Ward’s triangle (WABMD), and the trochanter (TRBMD). Stepwise linear regression analysis showed that the best predictor of hip fracture was the combination of medial calcar femoral cortex width (CFC), TRBMD, neck/shaft angle (NSA), and WABMD (r=0.72, r2=0.52, P<0.001). The area under the receiver operating characteristic curve (ROC) for this model was 0.93, while the area under ROC for TRBMD alone was 0.81. At a specificity of 80%, sensitivity improved from 52.5% to 92.5% with this combination compared with TRBMD alone. The combined predictors of cervical and trochanteric fracture differed, being NSA, CFC, TRBMD, and WABMD for cervical and TRBMD and femoral shaft cortical thickness for trochanteric fracture. In addition, we found a statistically significant correlation between FEBMD and femoral shaft and femoral neck cortex width (r=0.40, P<0.01 and r=0.30, P<0.01, respectively). The results confirm that the combination of BMD and radiological measures of upper femur geometry improve the assessment of the risk of hip fracture and fracture type compared to BMD alone, and that bone geometry plays an important role in the evaluation of bone strength.

Influence of the upper femur and pelvic geometry on the risk and type of hip fractures

The geometry of the upper femur has been reported to associate with the hip fracture risk in postmenopausal women. However, these associations seem to be partly conflicting, probably because of differences in measurement setup. Here, we compared the upper femur and pelvic geometries of 70 hip fracture patients (46 cervical and 24 trochanteric fractures) and 40 age‐adjusted controls based on plain anteroposterior radiographs, eliminating the possible sources of inaccuracy as far as possible by using a standardized patient position and calibrated dimension measurements by digital image analysis. The femoral neck/shaft angle (NSA) was larger in the fracture patients compared with the controls (p < 0.001). The fracture group had thinner cortices in the upper femur than the controls (p < 0.001). The femoral shaft diameter (FSD; p < 0.001), trochanter width (TW; p < 0.01), and the pelvic dimensions, that is, the smallest outer pelvic diameter (SOPD; p < 0.01) and the largest inner pelvic diameter (LIPD; p < 0.05) were smaller in the fracture group. Comparing the fracture types, we found NSA larger in the cervical hip fracture patients than in the patients with a trochanteric fracture (p < 0.01). The femoral neck/shaft cortex ratio was lower and the FSD was smaller in the cervical hip fracture group (p < 0.05). Acetabular width (AW) was greater and the SOPD was wider in the cervical fracture patients (p < 0.01). We concluded that the upper femur and pelvic dimensions as defined from calibrated and position‐standardized plain radiographs are useful in the evaluation of hip fracture risk and fracture type.

Quality of life after primary hemiarthroplasty for femoral neck fracture: 6-year follow-up of 185 patients

Totally, 185 patients with a mean age of 80 years treated by Austin-Moore cementless hemiarthroplasty for an acute femoral neck fracture were compared with age- and sex-matched nonfracture controls. There were 22 early complications, notably 7 percent dislocation and 4 percent deep infection. Later on, two acetabular protrusions and four loosenings of the prosthesis requiring admission were recorded. Mortality after the fracture was 12 percent above the control level at 3 months, 19 percent at 12 months, and 21 percent at 18 months. The 5-year mortality was about 60 percent in both patients and controls. The average loss of life in the fracture group compared with the control group was 425 days. After a mean follow-up period of 6 years, 24 of the 65 patients still alive and the 49 of the 60 controls were living in their own homes; and 28 of the patients were institutionalized in a hospital unit for chronic care. Half of the patients and most of the controls were able to move about independently. We concluded that Austin-Moore hemiarthroplasty is associated with serious complications that prevent social rehabilitation and function to reach acceptable levels.

Femoral neck strength of mouse in two loading configurations: method evaluation and fracture characteristics

We evaluated the mechanical strength of murine femoral neck in two loading configurations. The mechanical strength of the left femora of 25 male mice (weight 39 +/- 4 g) were measured in an axial configuration simulating one-legged stance in a human, and the right femora were tested in a configuration simulating a fall to the lateral side, on the trochanter. The reproducibility of the mechanical testing was 1.6% in the axial configuration and 3.7% in the fall configuration. The femoral neck was slightly stronger in the fall configuration. Typically, a load in the fall direction associated with a basicervical fracture, while axial loading resulted in both mid- and basicervical fractures. The linear bivariate correlation coefficient between the mechanical strengths in the two loading configurations was 0.83. Total bone mineral content (BMC), cortical bone mineral content (CtBMC), volumetric cortical bone mineral density (vCtBMD), and cross-sectional cortical area (CSA), measured at the femoral neck by peripheral quantitative computed tomography (pQCT), had a significant relationship with the femoral neck strength in the axial configuration. The coefficient of variation of the pQCT measurements was 9.1, 5.5, 2.3 and 5.5% for BMC, CtBMC, vCtBMD and CSA, respectively. We conclude that the precision of pQCT is moderate in evaluating the femoral neck of the mouse, and vCtBMD is the most reproducible parameter. The mechanical strength of the murine femoral neck can be measured with high precision by the two mechanical testing configurations presented here.

Long-term effects of clodronate on growing rat bone.

For evaluating the long-term effects of the bisphosphonate compound clodronate on the rat skeleton, 100 female rats were given subcutaneous injections of clodronate at doses of 0 (vehicle), 4 (low), or 12 (high) mg/kg per week, or 50 mg/kg every fourth week (cyclical). The treatment was started at 3 months of age and was continued for 6 months. The mechanical strength of bones was studied by torsion of the tibia, three-point bending of the femur, axial compression of the femoral neck, and compression of a lumbar vertebra. Quantitative histomorphometric variables were determined from distal femur and lumbar vertebra, and variables reflecting bone metabolism were measured in serum and urine. Bone mass, indicated by ash weight of the tibia, was increased with the low and high clodronate doses compared with the vehicle. The maximum load in vertebra compression was increased with the low dose of clodronate compared with the vehicle, whereas changes in other variables concerning bone strength were not significant. In bone histomorphometry, clodronate treatment induced more pronounced changes in cancellous bone volume in distal femur than in lumbar vertebra, the differences not being statistically significant between the groups at either site, however. The longitudinal growth rate of the femur, measured by double-fluorochrome labeling for 1 week at the end of the treatment period, was significantly decreased in the high-dose clodronate group compared with the other groups. Serum values for calcium, tartrate-resistant acid phosphatase, and alkaline phosphatase did not differ between the groups. However, serum osteocalcin was significantly lower in the high-dose group compared with the vehicle group. Urinary calcium, hydroxyproline, and hydroxylysylpyridinoline were decreased at all the clodronate doses administered. In conclusion, the beneficial effects of long-term clodronate treatment on bone mass and strength were observed at the lowest dose used. A high dose of clodronate decreased bone growth rate, which was, however, not reflected in the mechanical quality of bone.

Treatment of hip fracture in Finland and Sweden Prospective comparison of 788 cases in three hospitals

A prospective population-based study of hip fracture treatment was performed during 1989 in the regional hospitals of Oulu (Finland) and Sundsvall and Lund (Sweden). For cervical fractures hemiarthroplasty was preferred in Oulu and osteosynthesis in Sundsvall and Lund. For trochanteric fractures screw-plate was preferred in Oulu and Lund and Ender-nailing in Sundsvall. A shorter mean time at the orthopedic department in Oulu (13 days) was compensated by a lower (14 percent) fraction of patients directly discharged to own home. A somewhat longer mean orthopedic hospitalization time in Sundsvall (19 days) and Lund (17 days) was combined with a higher discharge to own home (49 percent and 35 percent). Prospective multicenter comparisons of treatment combinations (both operation and rehabilitation) permit identification of programs that are optimal for both patient and society.

Native bovine bone morphogenetic protein improves the potential of biocoral to heal segmental canine ulnar defects.

Abstract We studied the effect of a composite implant consisting of coral and native bovine bone morphogene-tic protein (BMP) on the healing of 2 cm segmental defects in the canine ulna. Plain coral and cortical autograft bone implants were used as controls. The fixation was temporary for 9 weeks with an intramedullary Kirschner wire (6 ulnas with a composite implant of coral and BMP, 6 with plain coral and 6 with an autograft) or a plate and screws (3 ulnas with a composite implant and 3 with plain coral). X-rays were taken at 3, 6, 9, 12, 16, 26 and 36 weeks, and mechanical torsion tests were performed at the end of the study. The score for bone formation and bone union evaluated from radiographs was significantly higher in the composite implant group than in the plain coral group at 16 weeks, but the score was even higher with autografts. BMP accelerated the resorption of the coral implant. The mechanical strength of the composite implants was higher than that of the bones with a plain coral implant (P<0.05), while the mechanical strength of the coral implants, even with BMP, was significantly lower than the strength of autografts (P<0.01). In conclusion, BMP enhanced the capacity of a coral implant to heal a segmental ulnar defect by increasing bone formation, but the effect of this combination was not as good as that of a cortico-cancellous autograft.Résumé Nous avons étudié l’effet d’un implant composite, fait de corail imprégné de protéine de la morphogenèse osseuse (BMP) bovine, sur la consolidation d’une perte de substance de 2 cm de l’os ulnaire canin. Des implants comprennent du corail simple ou des autogreffes d’os cortical étaient employées comme contrôles. Une fixation temporaire intramedullaire de 9 semaines était réalisée, soit avec des broches de Kirschner (6 os ulnaires avec un implant composite, 6 avec du corail simple, et 6 avec une autogreffe), soit avec une plaque-à-vis (3 avec un implant composite et 3 avec du corail simple). Des radiographies étaient prises 3, 6, 9, 12, 16, 26 et 36 semaines aprés la mise en place des implants, et des tests mécaniques de torsion étaient réalisées en fin d’étude. Aprés 16 semaines, les taux de formation et d’union osseuses étaient significativement plus élevés avec les implants composites qu’avec les implants de corail simple, mais des taux encore plus élevés étaient observés dans les essais avec les autogreffes. La BMP a accéleré la résorption de l’implant de corail. La résistance mécanique des os avec un implant composite était plus forte que celle des os ayant un implant de corail simple (P<0.05), alors que la résistance mécanique des os traités par une autogreffe était plus forte (P<0.01) que celle des os ayant un implant de corail, avec ou sans BMP. En conclusion, la BMP améliore le pouvoir de consolidation des implants de corail qui reste cependant inférieur à celui observé avec les autogreffes.

Femoral Neck Is a Sensitive Indicator of Bone Loss in Immobilized Hind Limb of Mouse

The present study was carried out to evaluate a unilateral hind limb immobilization model in the mouse. The right legs of male mice (age 10–12 weeks) were immobilized for 3 weeks against the abdomen by an elastic bandage. Body weight decreased significantly during the immobilization. Peripheral quantitative computed tomography (pQCT) analysis showed that the cross‐sectional cortical area (CSA), the bone mineral content (BMC), and the bone mineral density (BMD) of the tibial diaphysis were lower in both legs of the immobilized animals than in age‐matched controls, but the difference was mainly due to weight reduction. At the tibial metaphysis, CSA, BMC, and BMD were reduced in both legs of the immobilized animals, even after weight adjustment. At the femoral neck, CSA, BMC, and BMD were significantly lower in both legs of the immobilized animals, and the difference between the hind legs of the immobilized animals was also highly significant. The findings of the pQCT study were in good agreement with the changes in mechanical strength. The tibia was a more sensitive indicator of diaphyseal bone weakening than the femur when measuring the bending breaking force of the diaphysis. The femoral neck showed significantly decreased strength, and the difference between the immobilized leg and the contralateral leg was most clearly seen in lateral loading. We conclude that 3 weeks of hind limb immobilization weakened the tibia and femur significantly compared with their contralateral counterparts. The reduction was more significantly seen in the mechanical bending strength than in the pQCT evaluation, and the femoral neck was the most sensitive indicator of bone weakening.

Bone loss from the proximal femur after arthroplasty with an isoelastic femoral stem:BMD measurements in 25 patients after 9 years

To quantify the bone loss from the proximal femur after total hip arthroplasty with an isoelastic femoral stem, the bone mineral densities (BMD) around 25 such stems were measured after an 8.5 (7.5-9.5)-year follow-up. The contralateral, healthy side was used as a control. The BMD on the prosthesis side was lower by a mean of 14 percent than on the control side. The difference was greatest in the calcar area and smallest in the cortex medially of the prosthesis stem. The decreases in BMD around the metaphyseal and diaphyseal areas of the stem were smaller than those reported for stiff stems. The marked bone loss in the calcar region is possibly due to stress bypass-i.e., the axial load is transmitted directly into the metaphyseal area of the femoral shaft, causing an increase in its stiffness and in the jamming of the prosthesis stem.