Cortical Bone Thickness Measurements from CT in the Presence of Metalwork
Category: Biomechanics and Bone Quality
Poster Sessions, Presentation Number: SU0024
Session: Poster Session II & Poster Tours
Sunday, October 11, 2015 12:30 PM - 2:30 PM, Washington State Convention Center, Discovery Hall - Hall 4BC
, UNITED KINGDOM, * Graham Treece, University of Cambridge, Andrew Gee, University of Cambridge, Kenneth Poole, University of Cambridge
Purpose: Measuring bone thickness can be an important tool in assessing fracture healing and investigating other bony pathological processes after hip replacement surgery. Measurements from CT near metallic implants or fixation devices are difficult to obtain due to the high attenuation coefficient of metal. This study therefore proposes and evaluates a method for the measurement of cortical bone thickness in the presence of metal components.
Methods: Four cases with distinct metallic implants at the proximal femur were examined. These include a post-operative CT scan of a hemi-arthroplasty, a dynamic hip screw fixation, a bipolar hemi-arthroplasty and a fixation with cannulated screws. All CT scans were processed using metal artefact removal software (Boas, Radiology 2011). A previously validated technique based on the fitting of a cortical model was used to measure the cortical thickness over selected regions, which results in a colour coded cortical thickness map (Treece, Med Image Anal 2015). This method was adapted to also model metal structures when required. The measurements were compared with the corresponding sections on the un-fractured contralateral bone segment whereby point-to-point correspondences were obtained through the registration of the two cortical maps.
Results: For the proximal femoral sections of the aforementioned cases, the cortical thickness was measured with a mean absolute difference of 0.57, 0.37, 0.44 and 0.52 mm with respect to the contralateral femur. The hemi-pelvis produced thickness differences of 0.47, 0.49, 0.51 and 0.46 mm respectively. There was no noticeable structural over- or under-estimation of the thickness measurements. Cortical thickness maps indicate a reduction of noise by applying metal artefact removal software and more valid cortical measurements with a greater accuracy when modelling metal structures.
Conclusion: A method is proposed for the measurement of cortical bone thickness in the presence of metalwork, with results indicating sub-millimetre accuracy. This new technique might be helpful in assessing fracture healing near implants, and improve the evaluation of periprosthetic bone after hip replacement surgery.
* Presenting Authors(s):
Graham Treece, University of Cambridge