Tim Clijmans

A custom-made guide for femoral component positioning in hip resurfacing arthroplasty: development and validation study

In the field of hip resurfacing arthroplasty, accurate femoral component placement is important to achieving a positive outcome and implant survival in both the short and long term. In this study, femoral component placement was defined preoperatively using virtual computed tomography-based surgical simulation of a classical posterior surgical approach. Custom-made surgical drill guides were produced to reproduce the surgical plan in the operating room. We first developed a custom-made guide for guide-wire placement to position the femoral resurfacing component. Then, to assess the accuracy in vivo, the custom-made guide was evaluated in five patients with normal anatomy. The first hypothesis of this patient study was that the use of custom-made neck guides would allow for an average accuracy within the range of ±4° for the drill path and ±4 mm for the entry point of the guide-wire. A second hypothesis was that three-dimensional preoperative planning would enable the prediction of an implant size differing by a maximum of one size from the size eventually implanted. The presented hip resurfacing guide performed well in terms of fit, stability and accuracy. The in vivo accuracy study revealed an accuracy of 4.05 ± 1.84° for the drill path and 2.73 ± 1.97 mm for the entry point of the guide-wire. The predicted component sizes and the implanted component sizes differed maximally by one size, confirming our hypothesis. We conclude that these preliminary data are promising, but require further validation in a full clinical setting in larger patient groups.

Computer-aided planning of reconstructive surgery of the innominate bone: Automated correction proposals

Objective: In cases of complex reconstructive surgery of the innominate bone, it is difficult to draw up a good surgical plan; manual planning of a 3D reconstruction is highly demanding and time-consuming. This paper presents and validates methodology to automatically generate 3D correction proposals for reconstructive surgery of the innominate bone, and illustrates its use with clinical applications. Materials and Methods: The developed Matlab® methodology starts from CT-based outer surface representations of the patients bone, which allow straightforward mirror and matching implementations for automated reconstruction procedures. The validation on 9 cadavers was two-fold: the geometrical deviations of the intact original with respect to the reconstructed surface meshes were assessed, and the characteristics of both original and reconstructed acetabular cup regions were determined. Results: Eighteen healthy and thus, it was assumed, spherical acetabula were automatically reconstructed with mean accuracies of 3.2 ± 2.2 mm, 0.1 ± 1.0 mm and 3.8 ± 2.9° for the hip joint centerpoint, joint radius and cup orientation, respectively. As a demonstration, a triflange cup acetabular implant was rapidly designed, starting from the correction proposal. Conclusions: A highly automated, computer-aided approach to surgical planning for pelvic bone defects was developed and sample applications demonstrated. Validation results for healthy acetabula were superior to those obtained in real surgery. The generated virtual correction proposals can be used as targets in surgical planning and cup navigation applications, or in the design of customized implants with complex shapes.

Skull reconstruction planning transfer to the operation room by thin metallic templates: clinical results.

INTRODUCTION Craniofacial malformations implicate a risk of medical complications and a negative psychological impact on the patient. In order to correct functional and aesthetic aspects of these malformations, skull reconstruction is required. Because of the complexity of the surgery, pre-operative planning is unavoidable. Current and previously developed planning environments often lack the opportunity to transfer the simulated surgery to the operation room on a cheap but accurate, and easy to handle basis. MATERIALS AND METHODS This study applies an automated filter procedure, implemented in Matlab, to generate a set of adapted contours from which a surface mesh can be directly deduced. Skull reconstruction planning is performed on the generated outer bone surface model. For each resected/osteotomized bone part, the presented semi-automatic Matlab procedure generates surface based bone cutting guides, also denoted bone segment templates. Autoclaved aluminium templates transfer the surgical plan to the operation room. RESULTS The clinical feasibility is demonstrated by the successful pre-operative planning and surgical correction of three skull reconstruction cases in which the proposed procedure leads to considerable reduction in surgery time and good results. CONCLUSION A cost-efficient and planning-environment-independent solution is generated for an accurate and fast transfer of a complex cranial surgery plan to the operation room.

Creating a normative database of age-specific 3D geometrical data, bone density, and bone thickness of the developing skull: a pilot study

OBJECT Finite element models (FEMs) of the head are used to study the biomechanics of traumatic brain injury and depend heavily on the use of accurate material properties and head geometry. Any FEM aimed at investigating traumatic head injury in children should therefore use age-specific dimensions of the head, as well as age-specific material properties of the different tissues. In this study, the authors built a database of age-corrected skull geometry, skull thickness, and bone density of the developing skull to aid in the development of an age-specific FEM of a childs head. Such a database, containing age-corrected normative skull geometry data, can also be used for preoperative surgical planning and postoperative long-term follow-up of craniosynostosis surgery results. METHODS Computed tomography data were processed for 187 patients (age range 0-20 years old). A 3D surface model was calculated from segmented skull surfaces. Skull models, reference points, and sutures were processed into a MATLAB-supported database. This process included automatic calculation of 2D measurements as well as 3D measurements: length of the coronal suture, length of the lambdoid suture, and the 3D anterior-posterior length, defined as the sum of the metopic and sagittal suture. Skull thickness and skull bone density calculations were included. RESULTS Cephalic length, cephalic width, intercoronal distance, lateral orbital distance, intertemporal distance, and 3D measurements were obtained, confirming the well-established general growth pattern of the skull. Skull thickness increases rapidly in the first year of life, slowing down during the second year of life, while skull density increases with a fast but steady pace during the first 3 years of life. Both skull thickness and density continue to increase up to adulthood. CONCLUSIONS This is the first report of normative data on 2D and 3D measurements, skull bone thickness, and skull bone density for children aged 0-20 years. This database can help build an age-specific FEM of a childs head. It can also help to tailor preoperative virtual planning in craniosynostosis surgery toward patient-specific normative target values and to perform objective long-term follow-up in craniosynostosis surgery.

Quantitative Computerized Assessment of the Degree of Acetabular Bone Deficiency: Total radial Acetabular Bone Loss (TrABL)

A novel quantitative, computerized, and, therefore, highly objective method is presented to assess the degree of total radical acetabular bone loss. The method, which is abbreviated to “TrABL”, makes use of advanced 3D CT-based image processing and effective 3D anatomical reconstruction methodology. The output data consist of a ratio and a graph, which can both be used for direct comparison between specimens. A first dataset of twelve highly deficient hemipelves, mainly Paprosky types IIIB, is used as illustration. Although generalization of the findings will require further investigation on a larger population, it can be assumed that the presented method has the potential to facilitate the preoperative use of existing classifications and related decision schemes for treatment selection in complex revision cases.