Optimum loading mode for axial stiffness testing in limb lengthening

Abstract

ABSTRACT:The axial stiffness of the regenerate is an indicator of bone healing after fracture or distraction osteogenesis. The axial stiffness may be assessed clinically by measuring the sharing of load between fixator and limb during loading. The aim of this study was to find out how to perform the stiffness test in order to minimize the influence of confounding factors to the test result. We investigated whether the test score was influenced by two factors: 1) the magnitude of the external load applied to the limb during the test; and 2) the patient's position during the test. The problem was approached by both a clinical study and by theoretical calculations. Thirty-three patients undergoing leg lengthening were tested regularly during the consolidation period. The stiffness test was executed with both high and low load, and in a standing and sitting position. There were significant differences in results between both the tests with high and low load, and between the standing and sitting tests. This indicated that both the magnitude of force and patient position during the test influenced the test result. Accordingly, these factors represent sources of error and must be taken into consideration when performing an axial stiffness test. The result of the theoretical calculations confirmed the result. We recommend performing the test while the patient is sitting, and to apply no more than 20% of the individual's body weight. It is also recommended that the same load be used in every test, when testing a patient several times during the treatment period. ß

In Vivo Mechanical Characterization of the Distraction Callus During Bone Consolidation

“…The increase of the stiffness of the callus with time was modeled with a linearized exponential correlation according to the trend observed in results below and in the literature 1,8,16,45 :…”

Assessment of distraction callus in rabbits by monitoring of the electrical impedance of bone

“…Examples of methods previously reported for evaluation of distraction callus in animal studies include quantitative computed tomography (CT) (Harp et al 1994, Reichel et al 1998), dual-energy X-ray absorptiometry (DEXA) (Eyres et al 1993, Reichel et al 1998, Tselentakis et al 2001), ultrasound (Eyres et al 1993, Bail et al 2002), and bone stiffness testing (Dwyer et al 1996, Windhagen et al 2000, Aarnes et al 2006). CT (particularly with multiple examinations) is associated with additional radiation and is costly, and both CT and DEXA may be associated with artifacts attributable to external fixation.…”

In vivo axial load-share ratio measurement using a novel hexapod system for safe external fixator removal

“…Prolonged utilization of the external fixator results in an uncomfortable lifestyle for patients and amplifies their psychological distress. Moreover, the fixator’s stress shielding during fracture healing will impact the bony callus formation [ 3 , 4 ]. Nevertheless, premature removal of the external fixator may cause refracture [ 5 – 7 ].…”

“…Currently, Aarnes’ approach is still utilized for clinical assessment of LS [ 3 , 6 , 19 ], although it is hindered by operational difficulties and imprecise results. Thus, we have developed a novel hexapod system to overcome the discussed limitations of Aarnes’ device.…”