Strength reductions from metastatic cortical defects in long bones

Abstract

The purpose of this investigation was to measure the reduction in bone strength resulting from drill holes in diaphyseal bone and to compare this with finite element and theoretical predictions for stresses in a tubular structure. Fifty-two pairs of canine femora were tested to failure in four-point bending. One bone of each pair was used as the control; the other femora had holes of variable size drilled in the lateral cortex. At a ratio of drill hole diameter to bone diameter of 0.2, the bone retained only 62% of its expected strength. A linear regression between the area fraction (the ratio of the cross-sectional area of the drilled specimen to the control specimen) and the percentage of expected strength yielded a strong positive correlation (R2 = 0.79). The average cross-sectional properties were used as the basis for linear orthotropic and nonlinear elastic-plastic finite element models of idealized geometry. The linear models proved insufficient for prediction of failure loads. The nonlinear models, which accounted for both material plasticity and the stress concentration effects of the defect, yielded good correspondence with the experimental data. While the influence of irregular borders and adaptive remodeling of the bone adjacent to the defect requires further investigation, our results suggest the possibility of prediction of fracture risk based on geometric properties of metastatic lesions. Prophylactic fixation remains a matter of clinical judgement based on the functional demands and expected strength of the affected bones.

Dynamic Stabilization with Active Locking Plates Delivers Faster, Stronger, and More Symmetric Fracture-Healing

“…Moreover, the callus strength in active locking plate group specimens was likely greater than the reported strength results, as failure occurred by spiral fracture through screw holes outside the callus zone. Extrapolating from a cadaveric study on the effects of screw holes on diaphyseal strength 35 , a 4.5-mm screw hole will reduce the strength of the ovine tibia by 15% to 30%, which would fully account for the observed strength loss in active locking plate group specimens compared with contralateral tibiae. In contrast, the finding that half of all standard locking plate group specimens recovered <10% of their native strength, and none recovered more than 43% of their native strength, provides further evidence that excessively stiff fixation suppresses healing.…”

Surgical Revascularization in Structural Orthotopic Bone Allograft Increases Bone Remodeling

“…In larger animal models the effect of the size of cortical holes on biomechanical properties has been determined. McBroom et al [20] determined the biomechanical properties with variable cortical hole sizes in canine femurs. They performed fourpoint bending and concluded that a ratio of drill hole diameter to bone diameter of 0.2 leads to a 38% strength reduction.…”

Torsional strength estimates of femoral diaphyses with endosteal lytic lesions: Dual‐energy x‐ray absorptiometry study

“…Several previous studies have analyzed the effect of transcortical holes. 26,44,[53][54][55][56][57][58][59] We suspect that inclusion of a stress concentration factor would improve our strength estimates. However, the clinical setting was more closely replicated by not correcting for this.…”

“…Structural properties, such as bending and torsional strength, have been estimated using crosssectional information obtained from radiographs, absorptiometry (single and dual energy), and computed tomography (CT). 26,27,[33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48] The weakness of radiograph-based estimates is that they require assumptions of cross-sectional shape and measurements of often indistinct inner cortical boundaries. Dual-energy X-ray absorptiometry (DXA), a convenient and economical method for accurately measuring bone mass and density, has been used to estimate strength.…”