Stiffness Measurements to Assess Healing During Leg Lengthening

Abstract

We describe a technique for measuring the stiffness of regenerate bone after leg lengthening. This allows early identification of slow healing by reference to normal patterns. We determined the time of removal of the fixator from clinical and radiological information independent of the stiffness result.In a series of 30 leg lengthenings there were no refractures when the tibial stiffness had reached 15 Nm/° or the femoral stiffness 20 Nm/°. Three refractures occurred at lower stiffness values. The technique is simple to perform, will allow a reduction in plain radiography and is recommended for routine postoperative management.

Stiffness measurements to assess healing in bone transport: a preliminary report

“…As in those studies [4,6], the stiffness rise in our study was approximately exponential. Moreover, the median healing time was 17 weeks for the callotasis segment, similar to the 20 weeks for tibial lengthening reported previously [6]. The median healing time for the docking site was 26 weeks, similar to the 22 weeks observed in the tibial fracture healing study [4].…”

“…The rise of stiffness in the callotasis segment and docking site resembled the rise in stiffness recorded in studies of leg lengthening [6] and fracture healing [4], respectively. As in those studies [4,6], the stiffness rise in our study was approximately exponential.…”

“…Even though other Authors have reported problems with re-fracture [9, 10], we did not and 15 Nm/d stiffness provided a safe level for fixator removal. The studies of tibial lengthening [6] and fracture healing [4] also found a value of 15 Nm/d as a safe level of bone stiffness at which to remove the fixator. Therefore, our small series of bone transports confirms the suggestion that it would be acceptable to use a figure of 15 Nm/d as a safe level of bone healing for fixator removal.…”

“…An average of 5 readings was recorded at regular outpatient follow-up visits. When the stiffness reached 15 Nm/d, the fixator was modified to leave the relevant site unprotected; this defined the healing time [6].…”

“…Assessment of healing currently relies on plain radiographs and clinical examination. Bending stiffness has been used as an objective measure to define healing in knee arthrodesis, tibial fractures, and limb lengthening [4][5][6]. The purpose of the present study was to determine the normal pattern of increasing stiffness during bone transport, and to compare the relative rates of healing of the callotasis segment with the docking site in the same individual.…”