Our aim was to determine the precision of the measurements of bone mineral density (BMD) by dual-energy x-ray absorptiometry in the proximal femur before and after implantation of an uncemented implant, with particular regard to the significance of retro- and prospective studies. We examined 60 patients to determine the difference in preoperative BMD between osteoarthritic and healthy hips. The results showed a preoperative BMD of the affected hip which was lower by a mean of 4% and by a maximum of 9% compared with the opposite side. In addition, measurements were made in the operated hip before and at ten days after operation to determine the effect of the implantation of an uncemented custom-made femoral stem. The mean increase in the BMD was 8% and the maximum was 24%. Previous retrospective studies have reported a marked loss of BMD on the operated side. The precision of double measurements using a special foot jig showed a modified coefficient of variation of 0.6% for the non-operated side in 15 patients and of 0.6% for the operated femur in 20 patients. The effect of rotation on the precision of the measurements after implantation of an uncemented femoral stem was determined in ten explanted femora and for the operated side in ten patients at 10° rotation and in 20 patients at 30° rotation. Rotation within 30° influenced the precision in studies in vivo and in vitro by a mean of 3% and in single cases in up to 60%. Precise prediction of the degree of loss of BMD is thus only possible in prospective cross-sectional measurements, since the effect of the difference in preoperative BMD, as well as the apparent increase in BMD after implantation of an uncemented stem, is not known from retrospective studies. The DEXA method is a reliable procedure for determining periprosthetic BMD when positioning and rotation are strictly controlled

We aimed to evaluate the precision and longitudinal sensitivity of measurement of bone mineral density (BMD) in the pelvis and to determine the effect of bone cement on the measurement of BMD in femoral regions of interest (ROI) after total hip arthroplasty (THA). A series of 29 patients had duplicate dual-energy x-ray absorptiometry (DXA) scans of the hip within 13 months of THA. Pelvic analyses using 3- and 4-ROI models gave a coefficient of variation (CV) of 2.5% to 3.6% and of 2.5% to 4.8%, respectively. Repeat scans in 17 subjects one year later showed a significant change in BMD in three regions using the 4-ROI model, compared with change in only one region with the 3-ROI model (p < 0.05). Manual exclusion of cement from femoral ROIs increased the net CV from 1.6% to 3.6% (p = 0.001), and decreased the measured BMD by 20% (t = 12.1, p < 0.001). Studies of two cement phantoms in vitro showed a small downward drift in bone cement BMD giving a measurement error of less than 0.03 g/cm. 2. /year associated with inclusion of cement in femoral ROIs. Changes in pelvic periprosthetic BMD are best detected using a 4-ROI model. Analysis of femoral ROI is more precise without exclusion of cement although an awareness of its effect on the measurement of the BMD is needed

We used dual-energy x-ray absorptiometry (DEXA) to evaluate the extent of periprosthetic bone remodelling around a prosthesis for distal femoral reconstruction, the Kotz modular femoral tibial replacement (KMFTR; Howmedica, Rutherford, New Jersey). A total of 23 patients was entered into the study which had four parts: 1) 17 patients were scanned three times on both the implant and contralateral legs to determine whether the precision of DEXA measurements was adequate to estimate bone loss surrounding the anchorage piece of the KMFTR; 2) in 23 patients the bone mineral density (BMD) in different regions of interest surrounding the diaphyseal anchorage was compared with that of the contralateral femur at the same location to test whether there was consistent evidence of loss of BMD adjacent to the prosthetic stem; 3) in 12 patients sequential studies were performed about one year apart to compare bone loss; and 4) bone loss was compared in ten patients with implants fixed by three screws and in 13 without screws. The mean coefficients of variation (SD/mean) for the 17 sets of repeated scans ranged from 2.9% to 7.8% at different regions of interest in the KMFTR leg and from 1.4% to 2.5% in the contralateral leg. BMD was decreased in the KMFTR leg relative to the contralateral limb and the percentage of BMD loss in general increased as the region of interest moved distally in the femur. Studies done after one year showed no consistent pattern of progressive bone loss between the two measurements. The ten patients with implants fixed by screws were found to have a mean loss of BMD of 42% in the most distal part of the femur, while the 13 without screw fixation had a mean loss of 11%. DEXA was shown to have adequate precision to evaluate loss of BMD around the KMFTR. This was evident relative to the contralateral leg in all patients and generally increased in the most distal part of the femur. In general, it stabilised between two measurements taken one year apart and was greater surrounding implants fixed by cross-locking screws

In a prospective study of 14 patients undergoing total hip replacement we have used dual-energy X-ray absorptiometry (DEXA) to investigate remodelling of the bone around two different designs of cementless femoral prosthesis. The bone mineral density (BMD) was measured at 12-weekly intervals for a year. Eight patients (group A) had a stiff, collarless implant and six (group B) a flexible isoelastic implant. Patients in group A showed a decrease in BMD from 14 weeks after operation. By 12 months, the mean loss in BMD was 27%, both medially and laterally to the proximal part of the implant. Those in group B showed an overall increase in BMD which reached a mean of 12.6% on the lateral side of the distal portion of the implant. Our results support the current concepts of the effects of stem stiffness and flexibility on periprosthetic remodelling

We examined the effect on bone mineral density (BMD) of a single dose of 3 mg/kg of the bisphosphonate, pamidronate (Novartis) in distraction osteogenesis in immature rabbits. Seventeen rabbits (9 control, 8 given pamidronate) were examined by dual-energy x-ray absorptiometry. There was a significant increase in the BMD in the pamidronate group compared with the control animals. The mean areal BMD (g/cm. 2. ) in the bone proximal and distal to the regenerate was increased by 40% and 39%, respectively, compared with the control group (p < 0.05). The BMD of the regenerate bone was increased by a mean of 43% (p < 0.05). There was an increase of 22% in the mean area of regenerate formed in the pamidronate group (p< 0.05). Histological examination of bone in nine rabbits (5 control, 4 pamidronate) showed an increase in osteoblastic rimming and mineralisation of the regenerate, increased formation of bone around the pin sites and an increase in the cortical width of the bone adjacent to the regenerate in the rabbits given pamidronate. Pamidronate had a markedly positive effect. It reduced the disuse osteoporosis normally associated with lengthening using an external fixator and increased the amount and density of the regenerate bone. Further study is required to examine the mechanical properties of the regenerate after the administration of pamidronate

The operative treatment of fractures of the proximal humerus can be complicated by poor bone quality. Our aim was to evaluate a new method which allows prediction of the bone quality of the proximal humerus from radiographs. Anteroposterior radiographs were taken of 19 human cadaver humeri. The cortical thickness was measured at two levels of the proximal humeral diaphysis. The bone mineral density (BMD) was determined for the humeral head (HH), the surgical neck (SN), the greater tuberosity (GT) and lesser tuberosity (LT) using dual-energy x-ray absorptiometry. The mean cortical thickness was 4.4 ± 1.0 mm. Specimens aged 70 years or less had a significantly higher cortical thickness than those aged over 70 years. A significant positive correlation was found between cortical thickness and the BMD for each region of interest. The cortical thickness of the proximal diaphysis is a reliable predictor of the bone quality of the proximal humerus

We have studied the effect of hydroxyapatite (HA) coating in 15 ovariectomised and 15 normal rats which had had a sham procedure. Twenty-four weeks after operation, HA-coated implants were inserted into the intramedullary canal of the right femur and uncoated implants into the left femur. The prostheses were removed four weeks after implantation. Twelve specimens in each group had mechanical push-out tests. Sagittal sections of the other three were evaluated by SEM. The bone mineral density (BMD) of the dissected left tibia was measured by dual-energy x-ray absorptiometry. The difference in BMD between the control and ovariectomised tibiae was 35.01 mg/cm. 2. (95% CI, 26.60 to 43.42). The push-out strength of the HA-coated implants was higher than that of the uncoated implants in both groups (p < 0.0001), but the HA-coated implants of the ovariectomised group had a reduction in push-out strength of 40.3% compared with the control group (p < 0.0001). Our findings suggest that HA-coated implants may improve the fixation of a cementless total hip prosthesis but that the presence of osteoporosis may limit the magnitude of this benefit

We carried out limb lengthening in rabbits and then transplanted osteoblast-like cells derived from the tibial periosteum to the centres of distracted callus immediately after distraction had been terminated. Two weeks later the transaxial area ratio at the centre of the distracted callus and the bone mineral density (BMD) were significantly higher in the transplanted group, by 21% and 42%, respectively, than in the non-injected group or the group injected with physiological saline (p < 0.05). Callus BMD as a percentage of density in uninvolved bone was also significantly higher in the transplanted group (p < 0.05) than in the other two groups, by 27% and 20% in the second and fourth weeks, respectively (p < 0.05). Mechanically, the callus in the transplanted group tended to be stronger as shown by the three-point bending test although the difference in fracture strength was not statistically significant. Our results show that transplantation of osteoblast-like cells promotes maturity of the distracted callus as observed at the second and fourth weeks after lengthening. The method appears promising as a means of shortening the consolidation period of callus distraction and decreasing complications during limb lengthening with an external fixator

We investigated the effects of low-intensity pulsed ultrasound on distraction osteogenesis in a rabbit model. Callotasis of the right tibia was performed in 70 male Japanese white rabbits using mini-external fixators. In the first part of the study in 64 animals using normal distraction (waiting period seven days; distraction rate 0.5 mm/12 hours; distraction period ten days), we evaluated the distraction site by radiography, measurement of the bone mineral density (BMD), mechanical testing, and histology. In the second part in six rabbits using fast distraction (waiting period 0 days; distraction rate 1.5 mm/12 hours; distraction period seven days) the site was evaluated radiologically. Half of the animals (35) had received ultrasound to their right leg (30mW/cm. 2. ) for 20 minutes daily after ceasing distraction (ultrasound group), while rigid fixation only was maintained in the other half (control group). With normal distraction, the hard callus area, as shown by radiography, the BMD, and the findings on mechanical testing, were significantly greater in those receiving ultrasound than in the control group. Histological analysis showed no tissue damage attributable to exposure to ultrasound. With fast distraction, immature bone regeneration was observed radiologically in the control group, while bone maturation was achieved in the ultrasound group. We conclude that ultrasound can accelerate bone maturation in distraction osteogenesis in rabbits, even in states of poor callotasis

The properties of impacted morsellised bone graft (MBG) in revision total knee arthroplasty (TKA) were studied in 12 horses. The left hind metatarsophalangeal joint was replaced by a human TKA. The horses were then randomly divided into graft and control groups. In the graft group, a unicondylar, lateral uncontained defect was created in the third metatarsal bone and reconstructed using autologous MBG before cementing the TKA. In the control group, a cemented TKA was implanted without the bone resection and grafting procedure. After four to eight months, the animals were killed and a biomechanical loading test was performed with a cyclic load equivalent to the horse’s body-weight to study mechanical stability. After removal of the prosthesis, the distal third metatarsal bone was studied radiologically, histologically and by quantitative and micro CT. Biomechanical testing showed that the differences in deformation between the graft and the control condyles were not significant for either elastic or time-dependent deformations. The differences in bone mineral density (BMD) between the graft and the control condyles were not significant. The BMD of the MBG was significantly lower than that in the other regions in the same limb. Micro CT showed a significant difference in the degree of anisotropy between the graft and host bone, even although the structure of the area of the MBG had trabecular orientation in the direction of the axial load. Histological analysis revealed that all the grafts were revascularised and completely incorporated into a new trabecular structure with few or no remnants of graft. Our study provides a basis for the clinical application of this technique with MBG in revision TKA

This study was designed to test the hypothesis that the sensory innervation of bone might play an important role in sensing and responding to low-intensity pulsed ultrasound and explain its effect in promoting fracture healing. In 112 rats a standardised mid-shaft tibial fracture was created, supported with an intramedullary needle and divided into four groups of 28. These either had a sciatic neurectomy or a patellar tendon resection as control, and received the ultrasound or not as a sham treatment. Fracture union, callus mineralisation and remodelling were assessed using plain radiography, peripheral quantitative computed tomography and histomorphology.

Daily ultrasound treatment significantly increased the rate of union and the volumetric bone mineral density in the fracture callus in the neurally intact rats (p = 0.025), but this stimulating effect was absent in the rats with sciatic neurectomy. Histomorphology demonstrated faster maturation of the callus in the group treated with ultrasound when compared with the control group. The results supported the hypothesis that intact innervation plays an important role in allowing low-intensity pulsed ultrasound to promote fracture healing.

Medial open-wedge high tibial osteotomy has been gaining popularity in recent years, but adequate supporting material is required in the osteotomy gap for early weight-bearing and rapid union. The purpose of this study was to investigate whether the implantation of a polycaprolactone-tricalcium phosphate composite scaffold wedge would enhance healing of the osteotomy in a micro pig model. We carried out open-wedge high tibial osteotomies in 12 micro pigs aged from 12 to 16 months. A scaffold wedge was inserted into six of the osteotomies while the other six were left open. Bone healing was evaluated after three and six months using plain radiographs, CT scans, measurement of the bone mineral density and histological examination.

Complete bone union was obtained at six months in both groups. There was no collapse at the osteotomy site, loss of correction or failure of fixation in either group. Staining with haematoxylin and eosin demonstrated that there was infiltration of new bone tissue into the macropores and along the periphery of the implanted scaffold in the scaffold group. The CT scans and measurement of the bone mineral density showed that at six months specimens in the scaffold group had a higher bone mineral density than in the control group, although the implantation of the polycaprolactone-tricalcium phosphate composite scaffold wedge did not enhance healing of the osteotomy.

We investigated several factors which affect the stability of cortical screws in osteoporotic bone using 18 femora from cadavers of women aged between 45 and 96 years (mean 76). We performed bone densitometry to measure the bone mineral density of the cortical and cancellous bone of the shaft and head of the femur, respectively. The thickness and overall bone mass of the cortical layer of the shaft of the femur were measured using a microCT scanner. The force required to pull-out a 3.5 mm titanium cortical bone screw was determined after standardised insertion into specimens of the cortex of the femoral shaft.

A significant correlation was found between the pull-out strength and the overall bone mass of the cortical layer (r² = 0.867, p < 0.01) and also between its thickness (r² = 0.826, p < 0.01) and bone mineral density (r² = 0.861, p < 0.01). There was no statistically significant correlation between the age of the donor and the pull-out force (p = 0.246), the cortical thickness (p = 0.199), the bone mineral density (p = 0.697) or the level of osteoporosis (p = 0.378).

We conclude that the overall bone mass, the thickness and the bone mineral density of the cortical layer, are the main factors which affect the stability of a screw in human female osteoporotic cortical bone.

Operative fixation is the treatment of choice for a rupture of the distal tendon of biceps. A variety of techniques have been described including transosseous sutures and suture anchors. The poor quality of the bone of the radial tuberosity might affect the load to failure of the tendon repair in early rehabilitation.

The aim of this study was to determine the loads to failure of different techniques of fixation and to investigate their association with the bone mineral density of the radial tuberosity.

Peripheral quantitative computed tomography was carried out to measure the trabecular and cortical bone mineral density of the radial tuberosity in 40 cadaver specimens. The loads to failure in four different techniques of fixation were determined.

The Endobutton-based method showed the highest failure load at 270 N (sd 22) (p < 0.05). The mean failure load of the transosseous suture technique was 210 N (sd 66) and that of the TwinFix-QuickT 5.0 mm was 57 N (sd 22), significantly lower than those of all other repairs (p < 0.05). No significant correlation was seen between bone mineral density and loads to failure.

The transosseous technique is an easy and cost-saving procedure for fixation of the distal biceps tendon. TwinFix-QuickT 5.0 mm had significantly lower failure loads, which might affect early rehabilitation, particularly in older patients.

The medial periosteal hinge plays a key role in fractures of the head of the humerus, offering mechanical support during and after reduction and maintaining perfusion of the head by the vessels in the posteromedial periosteum. We have investigated the biomechanical properties of the medial periosteum in fractures of the proximal humerus using a standard model in 20 fresh-frozen cadaver specimens comparable in age, gender and bone mineral density. After creating the fracture, we displaced the humeral head medial or lateral to the shaft with controlled force until complete disruption of the posteromedial periosteum was recorded. As the quality of periosteum might be affected by age and bone quality, the results were correlated with the age and the local bone mineral density of the specimens measured with quantitative CT.

Periosteal rupture started at a mean displacement of 2.96 mm (sd 2.92) with a mean load of 100.9 N (sd 47.1). The mean maximum load of 111.4 N (sd 42.5) was reached at a mean displacement of 4.9 mm (sd 4.2). The periosteum was completely ruptured at a mean displacement of 34.4 mm (sd 11.1). There was no significant difference in the mean distance to complete rupture for medial (mean 35.8 mm (sd 13.8)) or lateral (mean 33.0 mm (sd 8.2)) displacement (p = 0.589).

The mean bone mineral density was 0.111 g/cm³ (sd 0.035). A statistically significant but low correlation between bone mineral density and the maximum load uptake (r = 0.475, p = 0.034) was observed.

This study showed that the posteromedial hinge is a mechanical structure capable of providing support for percutaneous reduction and stabilisation of a fracture by ligamentotaxis. Periosteal rupture started at a mean of about 3 mm and was completed by a mean displacement of just under 35 mm. The microvascular situation of the rupturing periosteum cannot be investigated with the current model.

Corticosteroids are prescribed for the treatment of many medical conditions and their adverse effects on bone, including steroid-associated osteoporosis and osteonecrosis, are well documented. Core decompression is performed to treat osteonecrosis, but the results are variable. As steroids may affect bone turnover, this study was designed to investigate bone healing within a bone tunnel after core decompression in an experimental model of steroid-associated osteonecrosis. A total of five 28-week-old New Zealand rabbits were used to establish a model of steroid-induced osteonecrosis and another five rabbits served as controls. Two weeks after the induction of osteonecrosis, core decompression was performed by creating a bone tunnel 3 mm in diameter in both distal femora of each rabbit in both the experimental osteonecrosis and control groups. An in vivo micro-CT scanner was used to monitor healing within the bone tunnel at four, eight and 12 weeks postoperatively. At week 12, the animals were killed for histological and biomechanical analysis.

In the osteonecrosis group all measurements of bone healing and maturation were lower compared with the control group. Impaired osteogenesis and remodelling within the bone tunnel was demonstrated in the steroid-induced osteonecrosis, accompanied by inferior mechanical properties of the bone.

We have confirmed impaired bone healing in a model of bone defects in rabbits with pulsed administration of corticosteroids. This finding may be important in the development of strategies for treatment to improve the prognosis of fracture healing or the repair of bone defects in patients receiving steroid treatment.

The aim of our study was to investigate whether placing of the femoral component of a hip resurfacing in valgus protected against spontaneous fracture of the femoral neck.

We performed a hip resurfacing in 20 pairs of embalmed femora. The femoral component was implanted at the natural neck-shaft angle in the left femur and with a 10° valgus angle on the right. The bone mineral density of each femur was measured and CT was performed. Each femur was evaluated in a materials testing machine using increasing cyclical loads.

In specimens with good bone quality, the 10° valgus placement of the femoral component had a protective effect against fractures of the femoral neck. An adverse effect was detected in osteoporotic specimens.

When resurfacing the hip a valgus position of the femoral component should be achieved in order to prevent fracture of the femoral neck. Patient selection remains absolutely imperative. In borderline cases, measurement of bone mineral density may be indicated.

We investigated the effect of locally administered bisphosphonate on distraction osteogenesis in a rabbit model and evaluated its systemic effect. An osteotomy on the right tibia followed by distraction for four weeks was performed on 47 immature rabbits. They were divided into seven equal groups, with each group receiving a different treatment regime. Saline and three types of dosage of alendronate (low, 0.75 μg/kg; mid, 7.5 μg/kg and high 75 μg/kg) were given by systemic injection in four groups, and saline and two dosages (low and mild) were delivered by local injection to the distraction gap in the remaining three groups. The injections were performed five times weekly during the period of distraction.

After nine weeks the animals were killed and image analysis and mechanical testing were performed on the distracted right tibiae and the left tibiae which served as a control group. The local low-dose alendronate group showed a mean increase in bone mineral density of 124.3 mg/cm³ over the local saline group (analysis of variance, p < 0.05) without any adverse effect on the left control tibiae.

The findings indicate that the administration of local low-dose alendronate could be an effective pharmacological means of improving bone formation in distraction osteogenesis.

The cortical strains on the femoral neck and proximal femur were measured before and after implantation of a resurfacing femoral component in 13 femurs from human cadavers. These were loaded into a hip simulator for single-leg stance and stair-climbing. After resurfacing, the mean tensile strain increased by 15% (95% confidence interval (CI) 6 to 24, p = 0.003) on the lateral femoral neck and the mean compressive strain increased by 11% (95% CI 5 to 17, p = 0.002) on the medial femoral neck during stimulation of single-leg stance. On the proximal femur the deformation pattern remained similar to that of the unoperated femurs.

The small increase of strains in the neck area alone would probably not be sufficient to cause fracture of the neck However, with patient-related and surgical factors these strain changes may contribute to the risk of early periprosthetic fracture.

The aim of this biomechanical study was to investigate the role of the dorsal vertebral cortex in transpedicular screw fixation. Moss transpedicular screws were introduced into both pedicles of each vertebra in 25 human cadaver vertebrae. The dorsal vertebral cortex and subcortical bone corresponding to the entrance site of the screw were removed on one side and preserved on the other. Biomechanical testing showed that the mean peak pull-out strength for the inserted screws, following removal of the dorsal cortex, was 956.16 N. If the dorsal cortex was preserved, the mean peak pullout strength was 1295.64 N. The mean increase was 339.48 N (26.13%; p = 0.033). The bone mineral density correlated positively with peak pull-out strength.

Preservation of the dorsal vertebral cortex at the site of insertion of the screw offers a significant increase in peak pull-out strength. This may result from engagement by the final screw threads in the denser bone of the dorsal cortex and the underlying subcortical area. Every effort should be made to preserve the dorsal vertebral cortex during insertion of transpedicular screws.