Development and validation of a bone quality measurement method integrated into the freehand drilling process

Abstract

Background: Low bone quality associated with osteoporosis is an increasing health issue. The reduction in bone quality increases the risk of bone fractures and implant failure in osteosynthesis. Implant failure can be avoided by adapting the surgical procedure and postoperative care to the bone quality. This requires knowledge of the local bone quality at the implant site. Currently, surgeons can only assess bone quality based on their experience. Therefore, a routinely available and objective bone quality method is needed.
This thesis aims to develop and validate a bone quality measurement method integrated into the freehand drilling process. A new bone quality score was proposed, normalised work (𝑛𝑊𝑜𝑟𝑘), which can be measured during freehand drilling with a sensor module placed between the drill bit and the drilling machine.
Methods: The relationship between 𝑛𝑊𝑜𝑟𝑘 and bone quality and the effect of drill diameter on 𝑛𝑊𝑜𝑟𝑘 was analysed in an in vitro experiment and in an in situ pilot experiment. Drilling was done with a handheld surgical drilling machine and double fluted surgical twist drill bits. A sensor module was placed between the drill bit and the drilling machine to measure the axial drilling force, drilling torque, and drill position.
In an in vitro experiment, freehand drilling was performed in synthetic bone models. Low, medium and high-density bone models were used to simulate bone quality. In addition, three drill bit diameters were used to evaluate the effect of drill diameter on the proposed quality score.
In an in situ pilot experiment, an experienced trauma surgeon performed freehand drilling in a human cadaver’s femoral shaft and tibial plateau. The femoral shaft (cortical bone) and tibial plateau (cancellous bone) were used to simulate high and low-quality bone, respectively.
Results: The bone quality score, 𝑛𝑊𝑜𝑟𝑘, was calculated from the measured axial drilling force, drilling torque, and drill position. In vitro, 𝑛𝑊𝑜𝑟𝑘 differed significantly between the bone model densities for all drill diameters. Furthermore, the 𝑛𝑊𝑜𝑟𝑘 differed between drill diameters. In situ, 𝑛𝑊𝑜𝑟𝑘 was significantly different between the femoral shaft and tibial plateau. 𝑛𝑊𝑜𝑟𝑘 in the tibial plateau and femoral shaft compared well with 𝑛𝑊𝑜𝑟𝑘 in the medium and high-density bone model, respectively.
Conclusion: The in vitro experiment and in situ pilot experiment showed that normalised work (𝑛𝑊𝑜𝑟𝑘) is related to bone quality. This suggests that 𝑛𝑊𝑜𝑟𝑘 can be used to detect low bone quality and develop a new bone quality scoring system. 𝑛𝑊𝑜𝑟𝑘, however, differed between drill bits. Future work should focus on establishing threshold values and making the bone quality score independent of the drill bit geometry. Additionally, the presented method should be evaluated in a multi-user study. Ultimately, the proposed method could routinely provide bone quality measurements to guide surgeons in surgical fracture treatment and postoperative care protocols.