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Failure of the pedicle screw at the screw-bone interface is a common clinical problem, particularly in the setting of osteoporosis, and poses reconstructive challenges for all orthopaedic surgeons. Pedicle screw failure through screw loosing and pull-out is highly correlated with bone mineral density (BMD) and local bone quality [1]. Pre-operative assessment of BMD via dual x-ray absorptiometry (DEXA) has been shown to help determine the need for screw augmentation. However, patients frequently present without pre-operative DEXA scans. Furthermore, DEXA scans provide a measure of general bone quality, but do not necessarily reflect segmental and local variation in the spine [2]. The ability to assess BMD on a per-vertebrae basis intra-operatively would assist with surgical decisions regarding screw sizing, placement and augmentation.Copyright © 2010 by ASME

The distal radius is a common site of fracture with volar plates and screws as the current clinical practice for fracture fixation [1]. Local measurements of bone quality at the sites of screw insertion aid in providing the most stable fixation with the least amount of hardware, minimizing the risk of construct failure and irritation to soft tissue [2, 3]. The clinical standard for pre-operative bone mineral density (BMD) assessment uses dual x-ray absorptiometry (DEXA). However, DEXA scans provide global BMD values and cannot accurately predict variations in BMD within a given anatomical site [4]. Furthermore, patients frequently present without a pre-operative DEXA scan, so intra-operative assessment would be ideal. We developed a simple sensor system that would be appropriate for assessing local BMD intra-operatively. The system consists of a “smart” Weber clamp instrumented with a single uniaxial strain gage that provides real-time feedback regarding the local BMD.