WEIGHT BEARING AFTER TIBIAL FRACTURE AS A GUIDE TO HEALING

Abstract

Tibial fractures represent a heterogeneous group of fractures that are difficult to treat and vary widely in their time to union. Judging when it is safe to remove an external fixator or plaster cast requires clinical and radiological assessments both of which are subjective. Any errors in determining when a fracture has healed can lead to a prolonged treatment time or to refracture. Many methods have been employed to attempt to define clinical union in an objective manner including ultrasound, DEXA scanning, vibration analysis, and fracture stiffness measurements. Stiffness measurements are however time consuming to perform, of debatable clinical significance, and applicable only to fractures treated with external fixators. It has been previously observed^1,2 that weight bearing increases with time post-fracture. It has also been suggested³ that the ability of a patient to weight bear on the fractured limb is controlled by a biofeedback mechanism of biological self-control of fracture site strain that will be related to the stiffness of the fracture. We hypothesised that weight-bearing will be closely related to fracture healing and could be used as an alternative measure of healing where other objective measures of healing are not available or are impracticable.

A group of ten patients with tibial fractures treated by external fixation were studied. Using a Kistler force plate set into the floor, ground reaction forces for both lower limbs (fractured and non-fractured) were measured during normal walking at three weekly intervals. Concurrent fracture stiffness measurements were made using the Orthofix Orthometer.

In 8 patients who made good recoveries, the fixator was removed between 15–20 weeks post injury when the fracture stiffness had reached a minimum of 15 Nm/deg. Weight-bearing through the injured leg was seen to approach 90% of that through the uninjured leg in the 3 weeks prior to fixator removal. Two patients with delayed union achieved weight bearing of less than 40% of normal between 15–20 weeks. They also demonstrated low values of fracture stiffness (< 5 Nm/deg.) and subsequently required operative intervention to achieve union.

In this small study of 10 patients, weight bearing appears to correlate well with clinical union. It is quicker and easier to assess than stiffness and potentially has relevance to other fixation methods. We are continuing these measurements on conservatively treated, intra-medullary nailed, and externally fixed tibial fractures.