N. J. Wachter

Correlation of bone mineral density with strength and microstructural parameters of cortical bone in vitro

The aim of this study was to evaluate the influence of microstructural parameters, such as porosity and osteon dimensions, on strength. Therefore, the predictive value of bone mineral density (BMD) measured by quantitative computed tomography (QCT) for intracortical porosity and other microstructural parameters, as well as for strength of cortical bone biopsies, was investigated. Femoral cortical bone specimens from the middiaphysis of 23 patients were harvested during total hip replacement while drilling a hole (dia. 4.5 mm) for the relief of the intramedullary pressure. In vitro structural parameters assessed in histological sections as well as BMD determined by quantitative computed tomography were correlated with yield stress, and elastic modulus assessed by a compression test of the same specimens. Significant correlations were found between BMD and all mechanical parameters (elastic modulus: r = 0.69, p < 0.005; yield stress: r = 0.64, p < 0.005). Significant correlations between most structural parameters assessed by histology and yield stress were discovered. Structural parameters related to pore dimensions revealed higher correlation coefficients with yield stress (r = -0.69 for average pore diameter and r = -0.62 for fraction of porous structures, p < 0.005) than parameters related to osteons (r = 0.60 for osteon density and average osteonal area, p < 0.005), whereas elastic modulus was predicted equally well by both types of parameters. Significant correlations were found between BMD and parameters related to porous structures (r = 0.85 for porosity, 0.80 for average pore area, and r = 0.79 for average pore diameter in polynomial regression, p < 0.005). Histologically assessed porosity correlated significantly with parameters describing porous structures and haversian canal dimensions. Our results indicate a relevance of osteon density and fraction of osteonal structures for the mechanical parameters of cortical bone. We consider the measurement of BMD by quantitative computed tomography to be helpful for the estimation of bone strength as well as for the prediction of intracortical porosity and parameters related to porous structures of cortical bone.

First histological observations on the incorporation of a novel calcium phosphate bone substitute material in human cancellous bone

Calcium phosphates are frequently used as bone substitute materials because of their similarity to the mineral phase of bone, absence of antigenicity, and excellent osteoconductivity. However, in most currently available mineral substitutes, resorption occurs slowly if at all. In contrast, calcium phosphate cements have shown rapid resorption and remodeling in animal studies. In two prospective studies, a novel amorphous calcium phosphate cement (Biobon) was implanted in human patients for the first time. After 2-12 months, ten biopsies were obtained from nine individuals during secondary surgical interventions, for example, for implant removal. In all specimens, partial replacement of the material by new bone was observed, while residues of the cement were still visible. Undecalcified sections revealed extensive bone formation in immediate contact to the cement without fibrous interface. Polynucleated cells and superficial lacunae were indicative of resorptive activity, but inflammatory tissue response was absent. The new bone displayed regular trabecular and osteonal patterns. The histologic findings are in accordance with the excellent biocompatibility observed in the clinical follow-up. Though still incomplete, the resorbability of this cement appears superior to sintered calcium phosphates in these biopsy specimens. Presumably this is due to its amorphous crystalline structure. Biobon merits further studies as a promising substance for bone defect reconstruction in non-stress-bearing areas.

Prediction of cortical bone porosity In Vitro by microcomputed tomography

The high importance of intracortical porosity for mechanical strength of cortical bone has been established. The contribution of other parameters of microstructure such as osteon dimensions for strength is in discussion. The aim of this study was to evaluate the predictive value of microcomputed tomography (µCT) for porosity and other microstructural parameters of cortical bone in cortical bone biopsies. Femoral cortical bone specimens from the middiaphysis of 24 patients were harvested during the procedure of total hip replacement at the location where normally one hole (Ø 4.5 mm) for the relief of the intramedullary pressure is placed.In vitro intracortical porosity and bone mineral density (BMD) measurements by µCT were compared with structural parameters assessed in histological sections of the same specimens. A strong correlation was found between intracortical porosity measured by µCT and histological porosity (r=0.95,P<0.0001). Porosity measured by µCT was also a strong predictor for other parameters describing dimensions of porous structures. BMD−1 was associated with osteonal area (r=−0.76,P<0.0001). We consider the measurement of porosity by µCT as a very potent procedure for assessing intracortical porosity and parameters related to porous structures of cortical bone nondestructivelyin vitro.

Predictive value of bone mineral density and morphology determined by peripheral quantitative computed tomography for cancellous bone strength of the proximal femur.

Peripheral quantitative computed tomography (pQCT) is an established diagnostic method for assessment of bone mineral density in the diagnosis of osteoporosis. However, the capacity of structural parameters of cancellous bone measured by high-resolution computed tomography remains to be explored. In 33 patients, bone mineral density (BMD) of the proximal femur was measured in vitro by pQCT using cylindrical biopsies from the intertrochanteric region harvested before the implantation of an artificial hip joint. By digital image analysis of CT scans, parameters derived from histomorphometry describing the microarchitecture of cancellous bone were measured. The biopsies were also loaded to failure by an uniaxial compression test to determine the biomechanical parameters, Youngs modulus, strength, and maximum energy absorption (E(max)). Strong correlations were found for BMD vs. mechanical parameters (r = 0.73 for Youngs modulus, r = 0.82 for strength, and r = 0.79 for E(max); p < 0.001, n = 29). The morphological parameters, bone volume per trabecular volume (BV/TV), apparent trabecular thickness (app.Tb.Th), apparent trabecular separation (app.Tb.Sp), and trabecular number (Tb.N), correlated significantly with all mechanical parameters. The combination of morphological parameters with BMD in a multivariate regression model led to an overall, but only moderate, increase in R(2) in all cases. Our data confirm the high predictive value of BMD for the mechanical competence of cancellous bone of the intertrochanteric region. However, quantification of cancellous bone structure by image analysis of CT scans may provide additional qualitative information for the analysis of bone strength.

Difference in metallic wear distribution released from commercially pure titanium compared with stainless steel plates

IntroductionStainless steel and commercially pure titanium are widely used materials in orthopedic implants. However, it is still being controversially discussed whether there are significant differences in tissue reaction and metallic release, which should result in a recommendation for preferred use in clinical practice.Materials and methodsA comparative study was performed using 14 stainless steel and 8 commercially pure titanium plates retrieved after a 12-month implantation period. To avoid contamination of the tissue with the elements under investigation, surgical instruments made of zirconium dioxide were used. The tissue samples were analyzed histologically and by inductively coupled plasma atomic emission spectrometry (ICP-AES) for accumulation of the metals Fe, Cr, Mo, Ni, and Ti in the local tissues. Implant corrosion was determined by the use of scanning electron microscopy (SEM).ResultsWith grades 2 or higher in 9 implants, steel plates revealed a higher extent of corrosion in the SEM compared with titanium, where only one implant showed corrosion grade 2. Metal uptake of all measured ions (Fe, Cr, Mo, Ni) was significantly increased after stainless steel implantation, whereas titanium revealed only high concentrations for Ti. For the two implant materials, a different distribution of the accumulated metals was found by histological examination. Whereas specimens after steel implantation revealed a diffuse siderosis of connective tissue cells, those after titanium exhibited occasionally a focal siderosis due to implantation-associated bleeding. Neither titanium- nor stainless steel-loaded tissues revealed any signs of foreign-body reaction.ConclusionWe conclude from the increased release of toxic, allergic, and potentially carcinogenic ions adjacent to stainless steel that commercially pure Ti should be treated as the preferred material for osteosyntheses if a removal of the implant is not intended. However, neither material provoked a foreign-body reaction in the local tissues, thus cpTi cannot be recommend as the ‘golden standard’ for osteosynthesis material in general.

Predictive value of bone mineral density and Singh Index for the in vitro mechanical properties of cancellous bone in the femoral head

OBJECTIVE The purpose of this study was to assess the validity of two methodically different radiological parameters, bone mineral density and Singh Index, for the prediction of mechanical properties in femoral cancellous bone. DESIGN Coherence between in vitro evaluation of mechanical properties and bone mineral density on a femoral bone slice, combined with clinical determination of Singh Index on ordinary X-rays. BACKGROUND It is accepted that bone densitometry yields excellent prediction of mechanical bone quality, but is considered to be an expensive and not widely available method for routine diagnostics in clinical practice. In contrast, determination of Singh Index is an inexpensive and simple technique, but its predictive value for bone mechanics is still controversially discussed. METHODS We used cortically confined bone slices from 33 femoral heads. Bone mineral density was measured using quantitative computed tomography. Strength and elastic modulus were assessed by mechanical testing in up to 39 circular positions on each slice. Singh Index was evaluated on ordinary X-rays of the hip by two independent readers. RESULTS Bone mineral density showed strong correlations with strength (r=0.86) and good correlations with elastic modulus (r=0.68). Singh Index correlated well with strength (r=0.70), but only moderately with elastic modulus (r=0.52). CONCLUSIONS The strong validity of bone mineral density in predicting mechanical bone quality was confirmed. Singh Index assessment permits a rough estimation of mechanical strength in particular and can therefore be used for first estimations of mechanical bone quality, provided that readings were performed by experienced clinicians. RELEVANCE Reduced mechanical bone quality induces an increase in fracture risk. Whenever performed, bone mineral density measurement allows an excellent evaluation of the mechanical properties of cancellous bone in the hip and can be recommended for screening evaluations. The assessment of Singh Index on ordinary X-rays of the hip is an inexpensive and simple method, and allows a rough estimation of the mechanical quality of the femur. However, due to its subjective character, its predictive value for the mechanical quality of bone in individual patients remains uncertain.

Prediction of strength of cortical bone in vitro by microcomputed tomography

OBJECTIVE The aim of this study was to evaluate the predictive value of bone mineral density and intracortical porosity measured by microcomputed tomography for the strength of cortical bone biopsies. DESIGN Experimental study comparing the predictive value of bone mineral density and of intracortical porosity determined in vitro by microcomputed tomography for the mechanical properties of cortical bone cylinders. BACKGROUND The assessment of cortical bone strength might be relevant for the prediction of fracture risk or the choice of suitable therapy strategies in orthopaedic surgery. The predictive value of cortical density for the mechanical properties is discussed controversially. The relevance of intracortical porosity measured by histomorphometry has been established, but the predictive value of porosity determined by microcomputed tomography remains to be explored. METHODS Femoral cortical bone specimens from the mid diaphysis of 24 patients were harvested during total hip replacement procedure at the location, where a diaphyseal hole (diameter 4.5 mm) was drilled in order to reduce the intramedullary pressure. In vitro intracortical porosity and bone mineral density measurements by microcomputed tomography were compared with strength and elastic modulus assessed by a compression test transverse to the Haversian systems of the same specimens. RESULTS Significant negative correlations were found between porosity measured by microcomputed tomography scans and yield stress, stiffness and elastic modulus (P<0.001), however, the positive correlations between bone mineral density and mechanical parameters were stronger (P<0.0001). The mechanical parameter best predicted by mineral density as well as by porosity was yield stress (r=0.72,P<0.0001;r=-0.64,P<0.001). CONCLUSIONS Bone mineral density determined by microcomputed tomography imaging in vitro may be a potent method to predict mechanical properties of cortical bone non-destructively. The application in vivo remains to be explored.

The Effectiveness of ADCON-T/N, a New Anti-Adhesion Barrier Gel, in Fresh Divisions of the Flexor Tendons in Zone II

In a prospective randomized clinical trial, ADCON-T/N was investigated with regard to its effectiveness in fresh traumatic injuries of the flexor tendons in Zone II of the hand. Thirty patients participated in the trial. Following a standardized technique of tendon repair, the total active motion (TAM) and total extension lag (TEL) were determined after 12 weeks and evaluated according to the Buck-Gramcko score. Excellent results were achieved in 15 out of 16 patients in the ADCON-T/N group and 12 out of 14 in the control group. However, no statistically significant difference was found between the mean TAM and TEL in the two groups.

Predictive value of Singh index and bone mineral density measured by quantitative computed tomography in determining the local cancellous bone quality of the proximal femur

OBJECTIVE The purpose of this study was to assess the predictive value of the Singh index as well as quantitative computed tomography for the in vitro local mechanical competence of the cancellous bone of the proximal femur. DESIGN An experimental study examining the relation between mechanical properties and bone mineral density of the femoral neck determined in vitro and the clinical estimated Singh index on X-rays. BACKGROUND Evaluation of the predictive value of the Singh index, an inexpensive and simple technique for the mechanical properties of the cancellous bone of the proximal femur. METHODS The bone quality of the proximal femur of 34 patients undergoing total hip replacement was estimated by roentgenography using the Singh index. Bone mineral density was quantified by quantitative computed tomography using cylindrical cancellous bone biopsies harvested during the total hip replacement procedure by a new biopsy method. The mechanical properties of the bone specimens (Youngs modulus, strength and maximum energy absorption E(max)) were measured by mechanical testing of the bone biopsies. RESULTS A strong correlation of the Singh index versus material properties of cancellous bone was noted (r=0.66 for Youngs modulus, r=0.73 for strength and r=0.69 for E(max), P<0.0001). The correlations of bone mineral density measured by quantitative computed tomography versus Youngs modulus, strength and energy absorption E(max) were significant. Strength was predicted best (r=0.82; P<0.0001), followed by E(max) (r=0.79; P<0.0001) and Youngs Modulus (r=0.73; P<0.0001). CONCLUSIONS We conclude, that assessment of bone mineral density by quantitative computed tomography is a reliable and precise method for the estimation of cancellous bone material properties. The Singh index provides a rough estimate for the mechanical competence of the proximal femur. It is inexpensive, simply to assess and can in some cases replace the measurement of bone mineral density, notably in cases of marked decrease in bone density.

Influence of preoperative mechanical bone quality and bone mineral density on aseptic loosening of total hip arthroplasty after seven years

OBJECTIVE To test mechanical bone quality and bone mineral density of the femoral head at the day of implantation as indicators for femoral prosthesis loosening. METHODS Mechanical bone quality of a femoral head slice was assessed by destructive compression testing combined with bone mineral density measurements using peripheral quantitative computed tomography. Fourteen patients with walking pains were attainable for a radiographical follow-up mean 7.1 years after implantation. RESULTS Radiolucent lines along the stem were evident in 11 of 14 femurs, most of them seen in Gruen zones 7, 6, 1, 3, 14, and showed strong correlations to preoperative bone strength (r=-0.80; P<0.001) and axial stiffness (r=-0.75; P=0.002), yet not to bone mineral density (r=-0.67; P=0.009). Slight varus deviations <3 degrees were noted in six femurs. Preoperative strength was reduced in this femurs to 54% (P=0.006), and stiffness to 61% (P=0.038), while bone mineral density did not differ significantly. CONCLUSIONS Femoral prosthesis loosening after seven years can be predicted by mechanical bone quality of the femoral head at the time of implantation. Bone mineral density measurements may also indicate future stem loosening but have to interpreted carefully, keeping in mind a poorer predictive value. RELEVANCE Indications and choice of type of hip arthroplasty should be balanced in osteoporotic bones in particular. While preoperative bone mineral density measurement allows the prediction of mechanical bone quality, its relevance in predicting failure in arthroplasty treatment remains unclear.