Introduction

In daily clinical practice, progression of spinal fusion is typically monitored during clinical follow-up using conventional radiography and Computed Tomography scans. However, recent research has demonstrated the potential of implant load monitoring to assess posterolateral spinal fusion in an in-vivo sheep model. The question arises to whether such a strain sensing system could be used to monitor bone fusion following lumbar interbody fusion surgery, where the intervertebral space is supported by a cage. Therefore, the aim of this study was to test human cadaveric lumbar spines in two states: after a transforaminal lumbar interbody fusion (TLIF) procedure combined with a pedicle-screw-rod-construct (PSR) and subsequently after simulating bone fusion. The study hypothesized that the load on the posterior instrumentation decreases as the segment stiffens due to simulated fusion.

In orthopedic surgeries, it is critical to reduce the risks of drilling complications during bone fracture fixation, especially around critical organs such as in acetabula-pelvic procedures. Either over-drilling or x-ray overuse shall be avoided to reduce potential complications to the surrounding critical organs or tissues. Toward recognising perforation process during bong drilling, we employed drilling vibration signal analysis based on the measurements from miniature inertial sensors. Time-frequency analysis is used for features extractions, which show that information from drilling vibration measurements could reveal the drilling process, hence help doctors track the drilling process and avoid over-drilling.

We addressed the aforementioned challenges through inertial sensor development, vibration measurements, and time-frequency signal analysis. In the preliminary ex-vivo bone drilling experiment setup, an inertial sensor is mounted on a pig femur bone with two fixing nails and can capture 3-axes acceleration data during drilling procedures. A cordless drill is used with Kirschner wires (K-wires) and the diameter of the pin is 3.5 mm. The mounting locations of inertial sensors are close to actual drilling entries without affecting normal procedures. The recorded vibration signals indicate how the drill is interacting with surrounding bone tissues, which shall have different patterns along the deep drilling process. After normalisation, the power spectral density (PSD) is calculated to examine the frequency domain representation of the time series during drilling process. As the drilling vibration process along the bone is non-stationary, we further employ wavelet transform for more localised time-frequency analysis.

When the bone substance interacts with drill bits, compact substance and spongy substance have different bone densities and structures, thus inducing different vibration waveform patterns. In our preliminary experiments, we recorded acceleration data from the pig femur drilling process, where a surgical drill penetrates from compact substance, spongy substance and then to compact substance again. The article shows the feasibility study of estimating femur bone drilling process based on vibrations signals captured from low-cost miniature inertial sensors. Through a preliminary animal ex-vivo bone study, the proposed framework of time-frequency wavelet analysis indicates the drilling interface between compact substance and spongy substance. It shows potentials in perforation recognition along drilling process and more clinical studies will be performed for validating its capability in over-drilling avoidance.