Most early revisions in total hip arthroplasty (THA) are caused by dislocations. It has been established that surgeon experience is a major component in the need for revision surgeries. Currently, no standardised protocol for intraoperative soft tissue tension assessment exists. Furthermore, orthopaedic surgeons do not have a method of preoperative validation of trial implant configurations. To address this problem, the design of a physical simulator of the hip joint with muscle force and strain sensors is proposed, mostly made of widely available materials, manufactured using fusion deposition modeling (FDM) technology. The goal is to create a training tool for orthopaedic surgeons which will reduce the number of revision operations caused by poor hip balance. In addition, the simulator could be used to review the effects of varying implant geometries, which may reduce operation times. The simulator is hypothesised to have a similar joint balance to an in vivo hip, where an increased femoral offset will result in increased tension around the joint. In addition, the increased femoral offset is hypothesised to cause an increased external rotation moment and angle required for subluxation.

A scaling model based on anatomical data is constructed, and an additively manufactured shape is designed which mimics the tensile characteristic of muscle tissue. Sensors are added to almost each phantom muscle, to actively monitor the subjected tension and strain. The simulator is then tested by orthopaedic surgeons, performing two of their preferred movements for hip stability assessment, namely a traction and external rotation test, using three different implant configurations with varying femoral offsets. The muscle strains at the point of subluxation are reported. This experiment is then repeated, but not executed by a specialist, while using an additional implant configuration. During this second traction test, the total traction force at the foot was also measured. During the second external rotation test, the angle and moment required for subluxation were also measured at the foot.

The experiments yielded promising results. Muscle strains were recorded during the traction test for the gluteus maximus, minimus and piriformis which ranged from maxima of 10% to 26% at subluxation. For these muscles, the recorded force and strain were significantly higher (P ≤ 0.05) for the highest femoral offset compared to the lowest offset. During the external rotation test, the gluteus medius and minimus were maximally strained from 12% to 23%, while showing significantly higher force and strain for the highest offset configuration compared to the lowest offset. An increased femoral offset did cause increased tension in the joint, suggesting that the first hypothesis may be valid. In addition, the surgeons were able to correctly answer if there had been an increase or decrease in femoral offset without knowing the current implant configuration. They were enthusiastic about the potential of the simulator as a training tool, both for surgeons becoming more acquainted with the stability assessment movements and as a general method of understanding the mechanics of the hip joint, specifically how an implant configuration can influence these mechanics. This experiment was followed by an experiment where the same movements were performed, but not by a specialist...

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.

Total Hip Arthroplasty (THA) is a procedure where a defective hip joint with pain symptoms or functional impairment is replaced by a hip prosthesis. During this procedure, the optimal hip prosthesis should be chosen and placed in the correct orientation to achieve a stable hip joint. Failure to do so can lead to dislocation, mechanical failure or infection of the hip joint. To improve the outcome of the THA, range of motion (ROM) of the hip joint can be evaluated during the surgery after placement of the hip prosthesis. Current methods of measuring hip ROM have some limitations. For example, there is a low intra- and inter-test reliability between identification of the bony landmarks and goniometric alignment. The goal of this project was to develop an instrument that can measure the ROM during THA without the limitations of current instruments. An instrument was developed that determines its orientation via an inertial measurement unit (IMU). The IMU is connected on the upper leg via a strap and aligned with the bony landmarks via laser beams. A test has been performed to validate the usage of the instrument. The ROM of the hip for flexion and abduction motion was measured with the instrument and compared to a reference measurement made with two video cameras. A significant difference was found: the instrument did not stay aligned with the hip joint. For further development of the instrument, the drift should be minimised and multiple straps should be tested to allow a better fixation. Additionally, the added-value of the laser requires further research.