Assessment of Bone Material Strength by Microindentation in vivo after Fracture or Surgery-related Immobilization

The process of bone remodelling provides means of maintaining a
constant mineral content and bone microarchitecture. The response of bone
remodelling to loading and unloading has been extensively studied in animal
models that demonstrated profound changes in bone mass and microarchitecture.
In clinical practice, bone loss is documented in patients with a stroke, spinal
cord injury and after prolonged bed rest or immobilization. It has become clear
that low bone mass is not the only determinant of bone fragility and that the
strength and integrity of the skeleton also depend on other properties of bone
tissue, collectively termed bone quality. We hypothesize that patients also
experience a significant loss of bone quality during immobilization after a
recently sustained fracture or arthrodesis. Whereas Bone Mineral Density (BMD)
could be investigated with absorptiometry and microarchitectural changes with
High Resolution peripheral Quantitative Computer Tomography (HRpQCT),
techniques for the assessment of material properties of bone in vivo were
unavailable. Recently, a minimally invasive technique for the measurement of
micro-hardness of bone was introduced. With this technique, an indenter is
impressed into the surface of the tibia of the test specimen using a known low
applied load and the hardness of the specimen is thereby calculated. This
microindentation in vivo technique is currently tested in patients with and
without a fracture in our hospital.
There is no information on the effect of immobilization and mobilization on BMS
as measured by the microindentation in vivo technique.

To compare Bone Material Strength of the tibia at the side of a fracture or
arhtrodesis with that of the opposite tibia in patients who had been
immobilized for at least 6 weeks after a recently sustained fracture of the
ankle of calcaneus or after arthrodesis surgery.
To assess whether Bone Material Strength recovers by mobilization in patients
who had been immobilized for at least 6 weeks after a recently sustained
fracture of the ankle of calcaneus or after arthrodesis surgery

Prospective study, case-control study

The time required for each measurement is 10-15 minutes. There is a small
chance that the measurements may resul in a haematoma or local infection at the
measurement site.