ASSESSMENT OF CANCELLOUS BONE STRENGTH IN THE LUMBAR SPINE USING A 'SMART' BALL-TIP PROBE

摘要

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 pervertebrae basis intra-operatively would assist with surgical decisions regarding screw sizing, placement and augmentation. We have developed a simple device for an intra-operative, local bone strength assessment in the pedicle. The device consists of a ball-tip probe instrumented with an in-line load cell. The objective of this study is to determine the in situ performance of the newly developed "smart" ball-tip probe in predicting local bone strength. Specific aims include: 1) to quantify the intra and inter-rater variability in local bone strength measurements made using this device, 2) to assess spatial variability in bone strength along the path of screw insertion and compare probe-measured bone strength with DEXA scores, and 3) to compare screw pull-out force with probe-measured bone strength.