Gert Krischak

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.

Survival trends and predictors of mortality in severe pelvic trauma: Estimates from the German Pelvic Trauma Registry Initiative

STUDY OBJECTIVE To determine longitudinal trends in mortality, and the contribution of specific injury characteristics and treatment modalities to the risk of a fatal outcome after severe and complex pelvic trauma. METHODS We studied 5048 patients with pelvic ring fractures enrolled in the German Pelvic Trauma Registry Initiative between 1991 and 1993, 1998 and 2000, and 2004 and 2006. Complete datasets were available for 5014 cases, including 508 complex injuries, defined as unstable fractures with severe peri-pelvic soft tissue and organ laceration. Multivariable mixed-effects logistic regression analysis was employed to evaluate the impact of demographic, injury- and treatment-associated variables on all-cause in-hospital mortality. RESULTS All-cause in-hospital mortality declined from 8% (39/466) in 1991 to 5% (33/638) in 2006. Controlling for age, Injury Severity Score, pelvic vessel injury, the need for emergency laparotomy, and application of a pelvic clamp, the odds ratio (OR) per annum was 0.94 (95% confidence interval [CI] 0.91-0.96). However, the risk of death did not decrease significantly in patients with complex injuries (OR 0.98, 95% CI 0.93-1.03). Raw mortality associated with this type of injury was 18% (95% CI 9-32%) in 2006. CONCLUSION In contrast to an overall decline in trauma mortality, complex pelvic ring injuries remain associated with a significant risk of death. Awareness of this potentially life-threatening condition should be increased amongst trauma care professionals, and early management protocols need to be implemented to improve the survival prognosis.

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.

Can Computer-assisted Surgery Reduce the Effective Dose for Spinal Fusion and Sacroiliac Screw Insertion?

BackgroundThe increasing use of fluoroscopy-based surgical procedures and the associated exposure to radiation raise questions regarding potential risks for patients and operating room personnel. Computer-assisted technologies can help to reduce the emission of radiation; the effect on the patient’s dose for the three-dimensional (3-D)-based technologies has not yet been evaluated.Questions/purposesWe determined the effective and organ dose in dorsal spinal fusion and percutaneous transsacral screw stabilization during conventional fluoroscopy-assisted and computer-navigated procedures.Patients and MethodsWe recorded the dose and duration of radiation from fluoroscopy in 20 patients, with single vertebra fractures of the lumbar spine, who underwent posterior stabilization with and without the use of a navigation system and 20 patients with navigated percutaneous transsacral screw stabilization for sacroiliac joint injuries. For the conventional iliosacral joint operations, the duration of radiation was estimated retrospectively in two cases and further determined from the literature. Dose measurements were performed with a male phantom; the phantom was equipped with thermoluminescence dosimeters.ResultsThe effective dose in conventional spine surgery using 2-D fluoroscopy was more than 12-fold greater than in navigated operations. For the sacroiliac joint, the effective dose was nearly fivefold greater for nonnavigated operations.ConclusionCompared with conventional fluoroscopy, the patient’s effective dose can be reduced by 3-D computer-assisted spinal and pelvic surgery.Level of Evidence Level II, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

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.

Physiotherapy After Volar Plating of Wrist Fractures Is Effective Using a Home Exercise Program

OBJECTIVE To determine the effect of 2 different postoperative therapy approaches after operative stabilization of the wrist fractures: treatment by a physical therapist with 12 sessions and an unassisted home exercise program. DESIGN Randomized controlled cohort study. SETTING Hospital-based care, primary center of orthopedic surgery. PARTICIPANTS Volunteers (N=48) with fractures of the distal radius after internal fixation with locking plates. There were 46 patients available for follow-up after exclusion of 2 participants due to physiotherapy sessions in excess of the study protocol. INTERVENTIONS Not applicable. MAIN OUTCOME MEASURES Evaluation of grip strength using a Jamar dynamometer, range of motion (ROM), and Patient Related Wrist Evaluation (PRWE). RESULTS After a 6-week period of postoperative treatment, the patients (n=23) performing an independent home exercise program using a training diary showed a significantly greater improvement of the functionality of the wrist. Grip strength reached 54% (P=.003), and ROM in extension and flexion 79% (P<.001) of the uninjured side. Ulnar and radial abduction was also higher in this group. In contrast, patients who were treated by a physical therapist achieved grip strength equal to 32%, and ROM in extension and flexion of 52% of the uninjured side. Patients who were performing the home training after operation recorded an improved wrist function with a nearly 50% lower value (P<.001) in the PRWE score. CONCLUSIONS In the postoperative rehabilitation of wrist fractures, instructions in a home exercise program are an effective alternative to prescribed physical therapy treatment.

Effects of high-frequency, low-magnitude mechanical stimulus on bone healing.

Recent studies have shown osteogenic effects of high-frequency mechanical stimuli. The purpose of this study was whether externally applied, high-frequency, low-magnitude interfragmentary movements affect the process of bone healing. In 12 sheep, a transverse osteotomy with a 3-mm gap was created in the right metatarsus and externally stabilized by a rigid circular fixator. External stimulation was performed in six sheep with the use of ground-based vibration. The sheep were standing with their hind limbs on a platform that produced vertical movements resulting in interfragmentary movements of approximately 0.02 mm magnitude at 20 Hz frequency. The other six sheep remained rigidly stabilized by external fixation during the 8-week study and served as a control group. Healing was assessed postmortem by densitometric and mechanical examinations. No significant differences were found between the two groups, although callus formation was slightly enhanced (11%) in the stimulated group compared with the control group. Mechanical stimuli attributable to weightbearing in the control group were sufficient enough to initiate callus formation even under rigid, external fixation. Thus, external mechanical stimulation with the stimulation design described in the current study might not be indicated for improvement of bone healing.

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.