Israel Ziv

Ultrasound velocity and broadband attenuation over a wide range of bone mineral density.

Ultrasound velocity (UV) and broadband ultrasound attenuation (BUA) were studied in human and bovine bone with a wide range of bone mineral density (BMD). The BMD of 98 fresh specimens was measured by quantitative computed tomography: 42 cancellous specimens from women in the age group of 64±4 years; 51 bovine cancellous and 5 bovine cortical. BMD values ranged from 90 to 400 mg/cm3 for the human cancellous bone, 310 to 870 mg/cm3 for the bovine cancellous bone, and 1750 to 1780 mg/cm3 for the bovine cortical bone. BMD showed a strong linear correlation with apparent density over the entire range of density (r=0.979). UV of human and bovine cancellous bone was 1480 –2650 m/s and 2880–3100 m/s for bovine cortical bone. BUA values were 1–61 dB/MHz/cm for the cancellous specimens and 5–12 dB/MHz/cm for cortical specimens. UV was found to be linear with BMD for all specimens; however, BUA was linear with BMD only for the specimens from elderly women. A quadratic relationship between BUA and BMD was found when the bovine samples were included.

Changes in human knee ligament stiffness secondary to osteoarthritis

Stiffness of the medial (MCL) and lateral (LCL) collateral ligaments was compared between a group of 10 patients undergoing total knee arthroplasty for varus degenerative osteoarthritis (OAP), a group of 10 osteoarthritic cadaveric knees (OAC), and a group of 10 non‐osteoarthritic cadaveric knees (NOA). A load‐elongation curve was obtained for the medial and lateral compartments of each knee using an instrumented Moreland spreader. A strain gage (SG) was attached to the spreader handle and strain was calibrated to load applied against the spread distance. In extension, medial compartment stiffness of the OAP, OAC, and NOA groups was 60.7 ± 16, 52.8 ± 9.3 and 21.4 ± 5.0 N/mm, respectively. Lateral compartment stiffness in extension was 29.2 ± 9.2, 33.3 ± 10.3 and 19.5 ± 5.3 N/mm, for OAP, OAC, and NOA, respectively. Differences in stiffness between the OAP and OAC groups were not statistically significant (p > 0.05). However, the osteoarthritic groups (OAP and OAC) demonstrated a statistically significantly (p < 0.05) increase in ligament stiffness when compared to the NOA group. Following knee arthroplasty, stiffer medial structures in extension may lead to flexion contracture and accelerated polyethylene wear. Adequate bone resection, in conjunction with soft tissue release may alleviate the threefold increase in stiffness observed in the medial compartment secondary to OA without jeopardizing joint stability.

Orientation and loading condition dependence of fracture toughness in cortical bone

The fracture toughness at crack initiation were determined for bovine cortical bone under tension (mode I), shear (mode II), and tear (mode III). A total of 140 compact tension specimens, compact shear specimens and triple pantleg (TP) specimens were used to measure fracture toughness under tension, shear, and tear, respectively. Multiple-sample compliance method was utilized to measure the critical strain energy release rate (G c ) at the a/W = 0.55 (crack length, a, to specimen width, W, ratio). The critical stress intensity factor (K c ) was also calculates from the critical loading (P c ) of the specimens at the a/W=0.55, The effect of the anisotropy of bone on its resistance to crack initiation under shear and tear loading was investigated as well. Fracture toughness of bone with precrack orientations parallel (designed as longitudinal fracture) and vertical (designed as transverse fracture) to the longitudinal axis of bone were compared. In longitudinal fracture, the critical strain energy release rate (G c ) of cortical bone under tension, shear, and tear was 644 ± 102, 2430 ± 836, and 1723 ± 486 N/m, respectively. In transverse fracture, the critical strain energy release rate (G c ) of cortical bone under tension, shear, and tear was 1374 ± 183, 4710 ± 1284, and 4016 ± 948 N/m, respectively. An unpaired t-test analysis demonstrated that the crack initiation fracture toughness of bone under shear and tear loading were significantly greater than that under tensile loading in both longitudinal and transverse fracture (P < 0.0001 for all). Our results also suggest that cortical bone has been designed to prevent crack initiation in transverse fracture under tension, shear, and tear.

ULTRASOUND VELOCITY AND BROADBAND ATTENUATION AS PREDICTORS OF LOAD-BEARING CAPACITIES OF HUMAN CALCANEI

The main purpose of this study was to determine whether calcaneal ultrasound parameters, measured in the mediolateral direction, reflect load-bearing capacities of human calcanei. Broadband ultrasound attenuation (BUA) and ultrasound velocity (UV) were measured in 20 cadaveric calcanei with a mean age of 74.1 (SD 8.8). Normalized BUA (nBUA) was determined by dividing BUA by the calcaneal thickness obtained using a pulse-echo technique. The bone mineral density (BMD) of each calcaneus was measured by quantitative computed tomography. The calcanei were embedded in PMMA to simulate the midstance physiologic orientation during compressive testing in the load-bearing direction. The failure load, stiffness, and energy absorption were determined for each calcaneus. It was shown that BMD was well correlated with all ultrasound parameters (P < 0.0001). BMD, BUA, nBUA, and UV were all significantly associated with calcaneal failure load, stiffness, and energy absorption capacity (P < 0.05). nBUA was found to be the strongest predictor of all compressive properties. BUA and BMD demonstrated similar predictability of stiffness and energy absorption capacity, however, BUA showed a more significant relationship to the failure load of the calcaneus than did BMD. UV was found to be inferior to BMD, as well as BUA or nBUA, in assessing failure load, stiffness, and energy absorption capacity. It was also shown that nBUA was superior to BUA in the assessment of load-bearing capacity, but not in the prediction of BMD. Multivariate regression analysis showed that the combination of BUA or nBUA with UV did not improve the predictability of failure load, stiffness, and energy absorption capacity over that of BUA or nBUA alone (P > 0.5).

The ability of quantitative ultrasound to predict the mechanical properties of trabecular bone under different strain rates

The ability of quantitative ultrasound to predict the mechanical properties of trabecular bone under different strain rates was investigated. Ultrasound velocity (UV) and broadband attenuation (BUA) were measured for 60 specimens of human trabecular bone. Samples were divided into two equal groups and loaded in compression at the strain rates of 0.0004 and 0.08 s-1. The ultimate strength, elastic modulus, and energy absorption capacity were determined for each specimen. Specimens tested at 0.08 s-1 had a mean value of strength 63% higher than the specimens tested at 0.0004 s-1. The elastic modulus and energy absorption capacity were 82% and 42% higher, respectively, for the higher strain rate. UV and BUA were significantly associated with most mechanical properties at both strain rates. All mechanical properties were also correlated strongly with a linear combination of UV and BUA for both the low and high loading rates. The use of ultrasound parameters may provide good clinical means for assessing the resistance of trabecular bone to both low and high energy trauma.

Cerclage wiring technique after proximal femoral fracture in total hip arthroplasty

Cerclage wires have been used to stabilize proximal femoral cracks after stem insertion in cementless total hip arthroplasty. The objective of this study was to determine the optimal number and orientation of cerclage wires necessary to prevent stem subsidence and crack propagation. The crack was stabilized by 1, 2, or 3 wires placed either normal to the femoral neck axis or normal to the crack. The femora were compressed to 2,670 N while measuring crack opening and stem subsidence. Wires placed normal to the crack allowed less stem subsidence by 3.17 mm and less crack opening by 1.55 mm compared with wires placed normal to the neck. The addition of multiple wires reduced subsidence by 50% and reduced crack opening to <1 mm. Medial and anterior calcar cracks are best stabilized by at least 2 cerclage wires that are placed normal to the crack.

Effect of ovariectomy and calcium deficiency on the ultrasound velocity, mineral density and strength in the rat femur

Abstract Objective. Ultrasound transmission velocity (UTV) and bone mineral density (BMD) were examined as possible predictors of the bending strength of osteoporotic long bones in ovariectomized rats treated with calcium-depleted diet. Background. Changes in cancellous bone quality due to osteoporosis have been well documented, but only a few studies described non-invasive assessment of the biomechanical quality of long bones. Methods. Forty-three rats were divided into three groups: ovariectomized and calcium-depleted diet, ovariectomized and standard diet, and untreated controls. All femora were scanned by quantitative computed tomography (QCT) to measure BMD and cortical dimensions at the mid-diaphysis. Bending strength was determined from the maximum bending moment and the femoral cortical dimensions at the mid-diaphysis. The UTV of cortical bond at the mid-disphysis of the femur was measured in the proximal/distal direction. Results. It was found that bending strength was significantly different among the groups (p

Combined models of ultrasound velocity and attenuation for predicting trabecular bone strength and mineral density.

Three quantitative ultrasound parameters and their combinations were examined as possible predictors of the bone mineral density and compressive strength of human cancellous bone. Seventy-three trabecular bone cubes obtained from female cadaveric tibiae were measured by quantitative computed tomography. Measurements of the ultrasound velocity, ultrasound attenuation at 0.5 MHz and broad-band ultrasound attenuation were made in three orthogonal anatomical directions. The specimens were then tested to failure in compression, 38 in the anterior/posterior direction and 35 in the superior/inferior direction. The apparent density of all specimens was also found. Linear regressions showed that bone mineral density and strength were significantly correlated with each ultrasonic parameter in each direction (P < 0.05). Linear combinatinations of two ultrasound parameters were significantly better predictors than single parameters, although the optimum pair of parameters differed with direction. Three parameter models did not further improve predictability.

THE ACCURACY OF COMPUTED TOMOGRAPHY-BASED LINEAR MEASUREMENTS OF HUMAN FEMORA AND TITANIUM STEM

RATIONALE AND OBJECTIVES The authors investigate the accuracy of computed tomography linear measurement of femora with titanium stem, and the effect of the stem on these measurements. MATERIALS AND METHODS Two embedded cadaveric femora, one of them containing a titanium stem, and two cortical bone parallelepipeds were scanned. Thirty-six cross-sections were studied, each measured in two linear directions by the profile window technique. A half-maximum height method was used to determine the cortex-gap-titanium sizes from the computed tomography (CT) images. The accuracy of the measurements from the parallelepipeds, femora, and titanium stem taken from the CT was compared with those taken by a digital caliper of anatomical sections at the same level of the same bone. RESULTS Computed tomography measurements of the parallelepipeds were similar to the anatomical size (mean relative error 0.04% +/- 0.63%). The mean error and mean relative error of the cadaveric femora CT with and without the stem were similar to the control parallelepipeds. Higher values of error were found for the titanium stem. CONCLUSIONS The half-maximum height method in the profile window provides an accurate measurement of the femoral cortex and the titanium stem. The presence of the titanium stem in the medullary cavity of the femur did not interfere with the measurements of cortical dimensions.

A Cartilage Matrix Deficiency Experimentally Induced by Vitamin B6 Deficiency

Abstract A vitamin B6-deficiency-induced disorder in avian articular cartilage resembling osteoarthritis has been further characterized. We measured several parameters of proteoglycan (PG) metabolism, i.e., fixed charge density and sulfated glycosaminoglycans (S-GAG) content in PN-deficient versus control articular cartilage and synovial fluid from the knee joint. Statistically significant changes were: 1) decreased content and increased extractability of total sulfated PGs from articular cartilage with guanidine HCI; 2) elevation of S-GAG concentration in synovial fluid; 3) increased plasma cystathionine (sulfur amino acid) levels. PG synthesis as assessed by 35SO4 incorporation into S-GAGs was not impaired. A lack of cartilage swelling in 0.15 M saline and the normal water content indicated that although disturbed, the collagen network was not disrupted. This finding was in agreement with a previous microscopic study that revealed no fissures in the articular cartilage. Previous findings of a normal aggregating PG size-distribution and absence of elevated metallo-proteases made a disturbance of aggregating PG metabolism unlikely. Escape into the synovial fluid of small PGs, normally bound to articular collagen, was believed to result from an alteration in collagen molecular organization that could be secondary to elevated circulating SH-compounds.