Abstract
Introduction: Bone mineral density (BMD) has been shown to correlate well with strength and bending stiffness of bone. Following tibial diaphyseal fracture, reduction in the optical density of cancellous bony regions is apparent throughout the postoperative period. As much as 70% loss in BMD in the distal tibia and 45% in the proximal tibia has been reported. The process influencing the extent of such posttraumatic osteoporosis is multifactorial: the severity of injury, age of the patient, the effects of the regional acceleratory phenomenon (RAP), fixation type and onset of weight-bearing have all been implicated. Such loss in BMD in most cases is not fully recoverable and has been shown to increase subsequent fracture risk in the ipsilateral tibia and femur. It has been estimated that a 50% reduction in bone mineral content is required before changes are radiologically observed. Such changes in BDM however can be calculated post operatively from standardised orthogonal tibial digital images, following image density calibration and the utilisation of soft tissue subtraction techniques. Using these image density quantification techniques, a study was performed to examine and compare the effects of fixation of tibial fractures, with either Ilizarov or Intramedullary nail, on BMD in cancellous bone.
Method: Twenty-nine patients were recruited in the context of a randomised controlled trial assessing the radiological outcome following the treatment of closed tibial diaphyseal fractures with either an Ilizarov fixator (n=15) or an intramedullary nail (n=14). Informed consent was obtained for AP and Lat radiograph examination at selected postoperative time intervals (1, 3, 6, 12, 26 and 52 weeks). At each visit the rotation of the patients’ limb was standardised using a position control device (jig). The exposure and image acquisition parameters were standardised and digital images analysed. Serial BMD values were calculated and changes throughout the postoperative period compared between treatment groups.
Results: This study demonstrated considerable differences in the extent of disuse osteoporosis in the cancellous regions of the tibia following either Ilizarov fixation or intramedullary nailing. In the proximal metaphysic patients treated with a tibial nail displayed a reduction in BMD by 18.8% at 26 weeks and 25.7% at 42 weeks. In contrast, patients managed with Ilizarov fixation actually increased the BMD at this region at 26 weeks by 11.7% but with a final overall loss of 5.2% at 52 weeks. Each group demonstrated decreases in BMD at both the distal metaphysic and medial malleolar regions over 26 and 52 weeks. The BMD of the distal metaphysic decreased by 15.9% at 26 weeks and 35.3% at 52 weeks for patient treated with a nail, and reduced by 11.1% at 26 weeks and 0.76% at 52 weeks in patients treated with Ilizarov fixation. The medial malleolar region demonstrated the greatest decreases of all with a reduction in BDM of 43.1% and 66.4% in the nail group, and 34.9% and 61.6% in the Ilizarov group, at 26 and 52 weeks, respectively.
Conclusion: The magnitude of disuse osteoporosis following tibial diaphyseal fractures treated with intramedullary nailing, calculated using digital image analysis, and demonstrates changes similar to those reported previously in the literature. The use of Ilizarov fixation however maintains proximal metaphyseal BMD throughout the review period and promotes remineralisation in the distal metaphysic. No difference is observed in the medial malleolus between the two groups. The benefits of axial loading, stability and preservation of intraosseus vascularity with the use of the Ilizarov fixator are clearly demonstrated in the results; preservation of BMD was also shown to correlate well with improved clinical outcome and will reduce future ipsilateral tibial and femoral fracture risk.
The abstracts were prepared by Emer Agnew. Correspondence should be addressed to Irish Orthopaedic Association, Secretariat, c/o Cappagh National Orthopaedic Hospital, Finglas, Dublin 11, Ireland.
