Calculating the hip center of rotation using contralateral pelvic anatomy

Abstract

Failure to place an artificial hip in the optimal center of rotation results in poor hip function and costly complications. The aim of this study was to develop robust methodology to estimate hip center of rotation (hCoR) from preoperative computed tomography (CT) scans, using contralateral anatomy, in patients with unilateral diseased hips. Ten patients (five male, five female) with normal pelvic anatomy, and one patient with a unilateral dysplastic acetabulum were recruited from the London Implant Retrieval center image bank. 3D models of each pelvis were generated using commercial software. Two methods for estimation of hCoR were compared. Method 1 used a mirroring technique alone. Method 2 utilized mirroring and automatic alignment. Predicted versus actual hCoR co-ordinates were compared using intraclass correlation coefficients and paired T-tests. Both methods predicted hCoR with excellent agreement to original co-ordinates (>0.9) in all axes. Both techniques allowed prediction of the hCoR within AE 5 mm in all axes. Both techniques provided useful clinical information for planning acetabular reconstruction in patients with unilateral defects. Method 1 was less complex and is suitable for patients with developmental and degenerative pathologies. Method 2 may provide greater accuracy in a discrete group of patients with normal development prior to pathology (e.g., acetabular fractures). ß

Determination of the hip rotation centre from landmarks in pelvic radiograph

“… 23 However, this distance might be quite variable in terms of gender, race, community and even dependent upon the technique in which the radiograph was taken. 10 , 12 , 18 , 24 The difference between genders is already clearly shown in the present study too (p < 0.05). There are also some other studies, which reported the pelvic dimensions to be quite variable in the Japanese, African and Western populations.…”

“…In these conditions, the normal opposite hip can be used successfully. 10 But in the cases with unavailable reference points on the opposite hip, as in the bilaterally affected hips, we need more solid references points. For this intent various references points and methods have been described in the literature.…”

Can custom 3D printed implants successfully reconstruct massive acetabular defects? A 3D‐CT assessment

“…To generate 3D models of the patients’ postoperative anatomy, each patient's DICOM series was imported into ScanIP. Following importation into the 3D software, a threshold‐based extraction method was performed to select two meshes: one of the pelvis and the other of the implanted 3D printed component 18 . Each mesh was subsequently saved as an STL file.…”

“…Following importation into the 3D software, a threshold-based extraction method was performed to select two meshes: one of the pelvis and the other of the implanted 3D printed component. 18 This resulted in the Z-axis being the anterior-posterior (AP) axis, assuming 0 degrees of pelvic tilt. A sphere matching technique was used to determine the CoR of the components.…”

“…A sphere matching technique was used to determine the CoR of the components. 18,19 The coordinates of the CoR for the planned and achieved center rotation were recorded and compared in all axis. The limit for translation of CoR, beyond which components were labeled malpositioned, was 10 mm in any plane.…”