Biomedical subjects

Joyce H Keyak

Publications and source records attributed to Joyce H Keyak.

8 recordsLinked to original sources

PubMed2006

Feasibility of a percutaneous technique for repairing proximal femora with simulated metastatic lesions.

Fracture of the proximal femur due to metastatic disease is a significant cause of morbidity and mortality among breast cancer patients. Prophylactic surgical fixation is advised for patients at risk of fracture and typically involves placement of an orthopaedic implant. We propose that some proximal femora with metastases can be repaired by removing the lesion and filling the resulting defect with bone cement (polymethylmethacrylate), a procedure that could be performed percutaneously without the use of hardware. We studied the strengths of 12 matched pairs of cadaveric proximal femora under single-limb stance loading. One femur from each pair remained intact, while a simulated metastatic lesion, measuring approximately 75% of the neck diameter, was burred into the neck of the contralateral femur. The defects were repaired using a procedure similar to the one proposed. Femoral strength was measured via mechanical testing to failure. The strengths of the repaired femora averaged 94.7% of the strength of their respective contralateral intact femur (standard deviation, 8.7%). These findings suggest that the proposed procedure may be useful for some patients with metastases in the femoral neck. If the proximal femur could be safely repaired using the proposed technique in place of conventional surgical fixation, the patient would benefit from a shorter and less invasive surgical procedure, less pain and discomfort, greatly reduced recovery time, and a shorter hospital stay-all at a much lower cost.

Aged↗

PubMed2005

Predicting proximal femoral strength using structural engineering models.

Hip fracture related to osteoporosis and metastatic disease is a major cause of morbidity and mortality. An accurate and precise method of predicting proximal femoral strength and fracture location would be useful for research and clinical studies of hip fracture. The goals of this study were to develop a structural modeling technique that accurately predicts proximal femoral strength; to evaluate the accuracy and precision of this predicted strength on an independent data set; and to evaluate the ability of this technique to predict fracture location. Fresh human cadaveric proximal femora with and without metastatic lesions were studied using computed tomography scan-based three-dimensional structural models and mechanical testing to failure under single-limb stance-type loading. The models understated proximal femoral strength by an average of 444 N, and the precision of the predicted strength was +/- 1900 N. Therefore, the ability to predict hip strength in an individual subject is limited primarily by the level of precision, rather than accuracy. This level of precision is likely to be sufficient for many studies of hip strength. Finally, these models predict fractures involving the subcapital and cervical regions, consistent with most fractures produced experimentally under single-limb stance-type loading.

Aged↗

PubMed2005

Predicting the strength of femoral shafts with and without metastatic lesions.

To evaluate a potential tool for assessing the risk of a pathologic fracture of the femoral shaft, we examined whether fracture loads computed by our computed tomography scan-based finite element models are predictive of measured fracture loads. We also evaluated whether the precision of the computed fracture loads for shafts with metastases is altered if models are generated using mechanical property-density relationships for bone without metastases. We investigated whether femoral shafts with a hemispheric defect and shafts with metastases have qualitatively similar structural behavior. Using identical four-point bending loading conditions, we computed and measured fracture loads of femoral shafts with and without metastases and with a burred hemispheric defect to simulate a tumor. Finite element model fracture loads were strongly predictive of the measured fracture loads (range, 0.92-0.98) even when the models of bones with metastases used mechanical property relationships for bone without metastases. Specimens with hemispheric defects behaved structurally differently than specimens with metastases, indicating that these defects do not accurately simulate the effects of metastases. Results of our study show that these computed tomography scan-based finite element models can be used to estimate the strength of femoral shafts with and without metastases. These models may be useful for assessing the risk of pathologic fractures of femoral shafts.

Aged↗

PubMed2004

Differences in hip quantitative computed tomography (QCT) measurements of bone mineral density and bone strength between glucocorticoid-treated and glucocorticoid-naive postmenopausal women.

UNLABELLED: Chronic treatment with glucocorticoids (GCs) leads to significant bone loss and increased risk of fractures. In chronically GC-treated patients, hip fracture risk is nearly 50%. The purpose of this investigation was to determine if there are differences in the quantities of trabecular and cortical bone and bone strength of the hip between GC-treated osteoporotic patients and controls. METHODS: Study subjects were GC-treated osteoporotic postmenopausal women, and controls were postmenopausal women, recruited for separate clinical trials. Quantitative computed tomography (QCT) and dual-energy X-ray absorptiometry (DXA) of the hip were obtained from all subjects. QCT outcome variables measured included total, cortical, and trabecular BMD of hip subregions (femoral neck and trochanter) and total hip. In addition, finite element modeling (FEM) was performed on a subset of 19 cases and 38 controls, matched on age (+/- 5 years), weight (+/- 5 kg), and history of hormone replacement (> 1 year use) to assess failure load in stance and fall loading conditions. Generalized linear models were used to adjust the QCT variables for covariates between groups. Multiple regression was performed to identify independent predictors of bone strength from the QCT variables. RESULTS: Compared with controls, GC-treated subjects were significantly (p < 0.05) younger, weighed less, and had more years of hormone replacement. QCT of the hip in GC-treated subjects for total femoral integral, cortical, and trabecular BMD averaged 4.9-23.2% (p < 0.002) less than controls, and similar results were seen by hip subregion including the trochanter and femoral neck. DXA of the total hip was 17% lower in GC subjects than controls (p < 0.05). Compared with controls, FEM failure load in GC subjects was 15% (p<0.05) and 16% (p = 0.07) lower for stance and fall loading conditions, respectively. Multiple regression analysis demonstrated that a combination of QCT measures was correlated with bone strength as measured by FEM. CONCLUSIONS: Chronic GC treatment in postmenopausal women resulted in significantly decreased BMD of the hip, measured by QCT, with loss of both trabecular and cortical bone. In addition, GC treatment decreased bone strength as determined by FEM. The reduced cortical and trabecular bone mass in the hip may contribute to the disproportionately high hip fracture rates observed in GC-treated subjects.

Absorptiometry, Photon↗

PubMed2004

Mechanical properties, density and quantitative CT scan data of trabecular bone with and without metastases.

Pathologic fracture of the hip due to metastatic lesions in bone is a serious problem. This study examined the effect of metastatic lesions on the material properties and quantitative computed tomography (QCT) data of trabecular bone. Twelve distal femora were obtained, four with lytic and/or blastic metastatic lesions (group L), four without lesions but from donors who died from breast, prostate, or lung cancer (group NL), and four from donors with no cancer (group NC). Each specimen was CT scanned, and 56, 15x15x15-mm cubes of trabecular bone were cut. QCT density (rho(QCT)), compressive elastic modulus (E), compressive yield and ultimate strengths (S(y) and S(u)), and ash density (rho(ash)) of each cube were determined. Regression analysis was performed between rho(ash) and E, S(y), S(u) and rho(QCT), and analysis of covariance was used to identify differences between groups. Power relationships that did not depend on group (p >/= 0.1) were found between E and rho(ash) (0.74 </= r </= 0.84; p<0.001) and between strength (S(y) and S(u)) and rho(ash) (r >/= 0.94; p<0.001). rho(ash) was strongly related to rho(QCT) (r >/= 0.99; p<0.001). These results indicate that metastatic disease does not significantly impair the ability of QCT to provide an accurate and precise estimate of rho(ash) that can be used to estimate mechanical properties of trabecular bone with and without metastases.

Aged↗

PubMed2003

Relationships between material properties and CT scan data of cortical bone with and without metastatic lesions.

Breast, prostate, lung, and other cancers can metastasize to bone and lead to pathological fracture. To lay the groundwork for new clinical techniques for assessing the risk of pathological fracture, we identified relationships between density measured using quantitative computed tomography (rhoQCT), longitudinal mechanical properties, and ash density (rhoAsh) of cortical bone from femoral diaphyses with and without metastatic lesions from breast, prostate, and lung cancer (bone with metastases from six donors; bone without metastases from one donor with cancer and two donors without cancer). Moderately strong linear relationships between rhoQCT and elastic modulus, strength, and rhoAsh were found for bone with metastases (0.73<r<0.93, P<0.05). After accounting for differences in rhoQCT, the elastic modulus, compressive strength, tensile yield strain, and rhoAsh of bone with metastatic lesions differed from those of bone from donors without cancer (P<0.01). However, differences in tensile strength or compressive yield strain, after controlling for rhoQCT, were not found. Thus, these cancers degrade the elastic modulus and compressive strength, but not the tensile strength, of cortical bone beyond the amount that would be expected from decreased density alone. The rhoQCT-mechanical property relationships reported may be useful for evaluating bone integrity and assessing the risk of fracture of bone with metastases.

Aged↗

PubMed2003

Comparison of in situ and in vitro CT scan-based finite element model predictions of proximal femoral fracture load.

Hip fracture is a serious and common injury that can lead to permanent disability, pneumonia, pulmonary embolism, and death. Research to help prevent these fractures is essential. Computed tomographic (CT) scan-based finite element (FE) modeling is a tool that can predict proximal femoral fracture loads in vitro. Because this tool might be used in vivo, this study examined whether FE models generated from CT scans in situ and in vitro yield comparable predictions of proximal femoral fracture load. CT scans of the left proximal femur of two human cadavers were obtained in situ and in vitro, and three-dimensional FE models employing nonlinear mechanical properties were generated from each CT scan. The models were evaluated under single-limb stance-type loading by applying displacements incrementally to the femoral head. The FE-predicted fracture load (F(FE)) was the maximum femoral head reaction force. F(FE) for the in situ-derived models for the two subjects were 5.2 and 13.3% greater than for the in vitro-derived models. These results demonstrate that using CT scan data obtained in situ instead of in vitro to generate FE models can lead to substantially different predicted fracture loads. This effect must be considered when using this technology in vivo.

Bone Density↗

PubMed2002

Computed tomographic osteoabsorptiometry of the elbow joint in clinically normal dogs.

OBJECTIVE: To evaluate subchondral bone density patterns in elbow joints of clinically normal dogs by use of computed tomographic (CT) osteoabsorptiometry. SAMPLE POPULATION: 20 cadaver forelimbs from 10 clinically normal dogs. PROCEDURE: Each elbow joint was imaged in parasagittal and transverse planes of 1.5-mm thickness. Slice data were converted to dipotassium phosphate equivalent density (PPED) values. Sagittal, parasagittal, and transverse medial coronoid process topographic maps were constructed. Defined zones were created for each of the 3 CT planes, and confluence and peak PPED values were determined. RESULTS: The lowest PPED value was 340 mg/ml (articular and subchondral confluence), and the highest was 1780 mg/ml (peak subchondral density). Detectable effects of joint laterality were not found in the confluence or peak PPED measurements or in the peak-to-confluence PPED ratio for all 3 CT planes. Significant differences were found among zones in all 3 planes for confluence and peak PPED measurements and between sagittal and transverse planes for peak-to-confluence PPED ratios. Subjectively, the pattern of density distribution among dogs was fairly consistent for the sagittal and parasagittal slices. Three specific patterns of density distribution were apparent on the transverse topographic maps of the medial coronoid process that corresponded to conformational differences. CONCLUSIONS AND CLINICAL RELEVANCE: The use of CT osteoabsorptiometry provides a repeatable technique that can be used to noninvasively examine bone density and the effects of stress acting on joints in vivo. Variability in density values for any of the CT planes was not identified among clinically normal dogs.

Animals↗