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Statistical shape modeling (SSM) offers the potential to describe the morphological differences in similar shapes using a compact number of variables. Its application in orthopedics is rapidly growing. In this study, an SSM of the intramedullary canal of the proximal femur was built, with the aim to better understanding the complexity of its shape which may, in turn, enhance the preoperative planning of total hip arthroplasty (THA). This includes the prediction of the prosthetic femoral version (PFV) which is known to be highly variable amongst patients who have undergone THA. The model was built on three dimensional (3D) models of 64 femoral canals which were generated from pelvic computed tomography images including the proximal femur in the field of view. Principal component analysis (PCA) was performed on the mean shape derived from the model and each segmented canal. Five prominent modes of variations representing approximately 84% of the total 3D variations in the population of shapes were found to capture variability in size, proximal torsion, intramedullary femoral anteversion, varus/valgus orientation, and distal femoral shaft twist/torsion, respectively. It was established that the intramedullary femoral canal is highly variable in its size, shape, and orientation between different subjects. PCA‐driven SSM is beneficial for identifying patterns and extracting valuable features of the femoral canal. [ABSTRACT FROM AUTHOR]

Large acetabular bone defects are challenging in hip revision surgery. Clinical assessment is crucial to evaluate modern technologies in surgical reconstruction. We aimed to better understand the bone remodeling that occurs following acetabular reconstruction. Our objectives were: (1) To characterize changes in the shape of the pelvis by studying sequential computed tomography (CT) scans collected immediately and 1‐year postoperatively and (2) to identify which part of the pelvis is most susceptible to remodeling. We used the CT scans taken at two timepoints, of 24 patients with acetabular bone defects classified as Paprosky IIIB, treated with three‐dimensional (3D)‐printed custom‐made acetabular implants. Segmented 3D models of the bony pelvis were co‐registered using three different techniques. A global co‐registration of the full pelvis was conducted, followed by the co‐registration of the innominate bone and then ilium only, on the ipsilateral reconstructed side. The relative movements of the ilium, ischium, and pubis were analyzed from visual inspection and using co‐registration metrics (root mean square error and intersection over union). No bone remodeling was found in 14/24 patients (58%). The co‐registration of the innominate bone indicated bone remodeling in five cases (21%), while the remaining five cases (21%) presented remodeling in the global co‐registration but not the innominate bone co‐registration, suggestive of changes occurring at the sacroiliac joint. Changes in the pelvic shape were greatest at the pubis and ischium. Bone remodeling may occur in complex cases of Paprosky type IIIB defects, after acetabular reconstruction (occurrence of 21%, 5/24 cases). Surgeons and engineers should consider this when monitoring implant migration. [ABSTRACT FROM AUTHOR]

In revision total hip arthroplasty, achieving robust fixation is difficult and implant movement may occur over time. Bone may also rearrange around the implant as a result of mechanical loading, making the measurement of migration challenging. The study aimed to quantify changes in bone shape and implant position 1 year following acetabular reconstruction using custom three‐dimensional‐printed cups. This observational retrospective cohort study involved 23 patients with Paprosky type IIIB defects. Postop computed tomography scans taken within 1 week of surgery and at 1‐year postsurgery were co‐registered and analyzed. Three co‐registration strategies were implemented including bone‐to‐bone and implant‐to‐implant. (1) Co‐registration of the ipsilateral innominate bone (diseased anatomy) was used to measure changes in implant position. (2) Co‐registration of the implant was carried out to quantify changes in the ipsilateral innominate bone shape. (3) Co‐registration of the contralateral innominate bone (nondiseased anatomy) was performed to measure changes in the ipsilateral innominate bone shape and implant position. The median centroid distances (interquartile range [IQR]) were 2.3 mm (IQR: 3.7–1.7 mm) for changes in implant position, 2.4 mm (IQR: 3.6–1.6 mm) for changes in ipsilateral innominate bone shape, and 3.7 mm (IQR: 4.6–3.5 mm) for changes in ipsilateral innominate bone shape and implant position. Following acetabular reconstruction, implant movements and periprosthetic bone remodeling are physiological and of a similar extent. Surgeons and engineers should consider this when performing implant monitoring in these patients. [ABSTRACT FROM AUTHOR]