3-D acetabular morphology of the neuromuscular hip: implications for preoperative planning.

The importance of precisely understanding the pathoanatomy of acetabular dysplasia prior to surgical treatment has long been recognized. Acetabuloplasties for neuromuscular hip dysplasia have typically aimed to improve the acetabulum by increasing posterior-superior coverage, as previous three-dimensional (3-D) computed tomography (CT) studies have shown that acetabular dysplasia in neuromuscular hips is primarily in the direction of posterior-superior subluxation or dislocation. The purpose of this study was to identify differences in 3-D morphology between normal hips and dysplastic neuromuscular hips, specifically to identify areas of acetabular deficiency to guide preoperative decision-making. Patients treated for neuromuscular hip dysplasia at a single institution between 2009 and 2017 with a preoperative high-resolution pelvic CT scan (28 hips) were evaluated with custom software to measure acetabular morphology. Acetabuli were divided into equal octants; coverage angles were measured for each octant of interest. Variables were compared with age- and sex-matched normal controls (56 hips). We found a wide range of hip pathology in our study cohort. Five hips had no sectors with abnormal coverage. One hip (4%) was overcovered anteriorly. The remaining pathology was undercoverage located anteriorly [n = 7 (25%)], superiorly [n = 6 (21%)], posteriorly [n = 4 (14%)] or globally [n = 5 (18%)]. Our findings indicate that individual patients with neuromuscular acetabular dysplasia have unique deformities that do not uniformly conform to a specific area of acetabular deficiency. It is imperative to define the specific 3-D acetabular deficiency location and magnitude for accurate preoperative planning. Level of evidence: Level III.

3D cone-beam tomosynthesis provides axial imaging of the spine with lower radiation compared to computed tomography.

STUDY DESIGN: Three imaging techniques were compared using porcine spines. OBJECTIVES: To compare image acquisition time, radiation exposure, pedicle width measurement, assessment of screw breach, and image artifact between cone-beam tomosynthesis (CBT) single mode, CBT dual mode (stereotactic CBT), and computed tomography (CT) imaging with and without spinal implants. CT is the standard for axial imaging of orthopedic procedures. CBT technology is being developed, allowing real-time intraoperative imaging and 3D surgical guidance. CBT may deliver useful axial imaging quicker with less radiation than current technologies. METHODS: Six porcine spines were instrumented with bilateral pedicle screws at six levels connected with 5.5 mm rods. Dosimeters were attached to four surfaces of spines. CT, CBT single and CBT dual images were acquired pre-implant and post-implant. Image acquisition and 3D reconstruction times were recorded. Pedicle widths were measured before and after instrumentation. Screw medial breaches were graded (0: no breach, 1: < 2 mm, 2: 2-4 mm, 3: > 4 mm). Artifact and/or distortion of each image was ranked (0 = none, 1 = mild, 2 = moderate, 3 = large). Image acquisition and reconstruction times, radiation dose, pedicle width, screw breach and artifact were compared between techniques. RESULTS: Total image acquisition and reconstruction times of CBT was significantly less (single: 9.9 ± 0.2 s, p < 0.001; dual: 60.0 ± 8.7 s, p < 0.001) than CT (250.3 ± 36.7 s). CBT had significantly less radiation exposure than CT (CT: 0.7 ± 0.1 rad, single: 0.03 ± 0.02 rad, dual: 0.07 ± 0.03 rad; p < 0.001). No difference in pedicle width change pre-implant to post-implant was found (CT: p = 0.449, single: p = 0.430, dual: p = 0.528). Pedicle width (pre-implant: p > 0.5, post-implant: p > 0.9) and pedicle width change (p > 0.4) was similar amongst all techniques. Breach assessment was not different between groups (p = 0.257). CBT images had consistently lower artifact grades than CT. CONCLUSIONS: Although CBT axial image quality appeared subjectively inferior to CT, it enabled consistent assessment of pedicle width and screw breach, at half time and 10× lower radiation exposure. With continued refinements, CBT technology may allow for adequate intra-operative axial imaging using low radiation exposure.

Three-dimensional Analysis of Acetabular Morphology and Orientation in Patients With Slipped Capital Femoral Epiphysis.

BACKGROUND: Previous studies analyzing the acetabuli in patients with slipped capital femoral epiphysis (SCFE) have not definitively addressed the relationship between SCFE and acetabular shape. Femoral head overcoverage and acetabular version are thought to contribute to SCFE. The purpose of this study was to determine the acetabular morphology and orientation in hips with SCFE and compare them with normally developing children. METHODS: Pelvic computed tomography (CT) images of patients with SCFE were compared with pelvic CTs of patients without orthopedic abnormalities (normal controls). Three-dimensional (3-D) reconstructions were created from each CT examination. Custom software uniformly aligned the pelvis then determined acetabular measures from the reconstructions including acetabular version, acetabular tilt, articular surface area, and acetabular coverage angle measured in a radial manner dividing the acetabulum into octants. RESULTS: Two-hundred forty-four hips were included (53 SCFE, 31 unaffected contralateral hips in patients with SCFE, and 160 controls). The acetabular version was similar among SCFE hips, unaffected contralateral hips, and normal controls (P=0.48). Control hips had higher acetabular tilt than SCFE-affected hips (P=0.01) and unaffected contralateral hips (P=0.04). The acetabular surface area was higher in SCFE-affected hips compared with controls (P<0.05). SCFE-affected hips and the unaffected contralateral hips in patients with SCFE had increased acetabular coverage compared with controls in all 5 acetabular octants. CONCLUSIONS: Contrary to some previous studies, the authors did not find the acetabulum to be retroverted in patients with SCFE compared with controls. Both affected and unaffected hips of patients with SCFE have decreased acetabular tilt. Acetabular surface area is higher in hips with SCFE compared with normal controls, and both the SCFE-affected hips and unaffected hips had increased acetabular coverage compared with controls in all 5 octants of the acetabulum. The shared morphology of affected and unaffected hips in patients with SCFE suggests that their acetabular anatomy may predispose them to slip. LEVEL OF EVIDENCE: Level III.

Assessment of three-dimensional acetabular coverage angles.

The purpose of this article is to report the inter- and intra-observer reliability of a computerized objective technique to quantify patient-specific acetabular morphology. We describe the use of and provide the software code for a technique to better define the location and magnitude of acetabular pathology. We have developed software code that allows the end user to obtain detailed measurements of the acetabulum using traditional computed tomography data. We provide the code and detailed instructions on how to use it in this article. The methodology was validated by having an unbiased observer (that was not involved in this project but has been trained in this software measurement methodology) to perform the entire acquisition, reconstruction and analysis procedure and compare their measurements to the measurements of one of the authors. The author then repeated the procedure 2 months later to determine intra-observer reliability. Inter- and intra-observer reliability for version, tilt, surface area and total acetabular coverage angles ranged from an intra-class correlation coefficient of 0.805 to 0.997. The method provided in this manuscript gives a reproducible objective assessment of three-dimensional (3D) acetabular morphology that can be used to assist in the diagnosis of hip pathology and to compare the morphological parameters of subjects with and without hip pathology. It allows a surgeon to understand the 3D shape of each individual's acetabulum, share these findings with patients and their parents to demonstrate the magnitude and location of the clinical abnormality and perform patient-specific surgical corrections to optimize the shape and coverage of the hip.