Functional Acetabular Orientation Varies Between Supine and Standing Radiographs: Implications for Treatment of Femoroacetabular Impingement

Abstract

Background Often, anteroposterior (AP) pelvic radiographs are performed with the patient positioned supine. However, this may not represent the functional position of the pelvis and the acetabulum, and so when assessing patients for conditions like femoroacetabular impingement (FAI), it is possible that standing radiographs better incorporate the dynamic influences of periarticular musculature and sagittal balance. However, this thesis remains largely untested. Questions/purposes The purpose of this study was to determine the effect of supine and standing pelvic orientation on (1) measurements of acetabular version and common radiographic signs of FAI as assessed on two-and three-dimensional (3-D) imaging; and (2) on terminal hip range of motion (ROM). Methods Preoperative pelvic CT scans of 50 patients (50 hips) who underwent arthroscopic surgery for the treatment of FAI between July 2013 and October 2014 were analyzed. The mean age of the study population was 29 ± 10 years (range, 15-50 years) and 70% were male. All patients had a standing AP pelvis radiograph, a reconstructed supine radiograph from the CT data, and a 3-D model created to allow manipulation of pelvic tilt and simulate ROM to osseous contact. Acetabular version was measured and the presence of the crossover sign, prominent ischial spine sign, and posterior wall sign were recorded on simulated plain radiographs. Measurements of ROM to bony impingement were made during (1) simulated hip flexion; (2) simulated internal rotation in 90°of flexion (IRF); and (3) simulated internal rotation in 90°of flexion and 15°adduction (FADIR), and the location of bony One or more of the authors has received funding outside of submitted work from Smith & Nephew (Andover, MA, USA) (JJN); Smith & Nephew and A3 Surgical (La Tronche, France) (CML); and Smith & Nephew, A3 Surgical, and Pivot (Sunnyvale, CA, USA) (BTK, AB). During the study period, an amount less than USD 10,000 was received. One or more of the authors has stock/stock options in A3 Surgical (CML, AB) and A3 Surgical and Pivot (BTK Clin Orthop Relat Res (2015) 473:1267-1273 DOI 10.1007/s11999-014-4104-x Clinical Orthopaedics and Related Research ® A Publication of The Association of Bone and Joint Surgeons®contact between the proximal femur and acetabular rim was defined. These measurements were calculated for supine and standing pelvic orientations. A paired Student's t-test was used for comparison of continuous variables, whereas chi square testing was used for categorical variables. A p value of \ 0.05 was considered significant. Results When changing from supine to the standing radiographs, both mean cranial and central version increased by 2°± 4°(95% confidence interval [CI], 1°-3°) and 2°± 3°(95% CI, 1°-3°), respectively (both p \ 0.001). However, with the numbers available, there were no changes in the proportion of positive crossover, posterior wall, and prominent ischial spine signs. Standing pelvic position tilt resulted in an increased hip flexion of 3°( 95% CI, 2°-4°) as well as an i...

The Warwick Agreement on femoroacetabular impingement syndrome (FAI syndrome): an international consensus statement

“…For example, the spatial orientation of the acetabulum may be affected by the position of the pelvis. Posterior tilt increases in standing position and the parameters that describe anterior and posterior acetabular coverage, which are important in describing pincer morphology, may change 50 53. Also, two orthogonal views of the femoral neck may not be sufficient to identify all instances of cam morphology 21.…”

Supine and Standing AP Pelvis Radiographs in the Evaluation of Pincer Femoroacetabular Impingement

“…With increased pelvis tilt causing increased pincer impingement findings being well known, the true functional tilt of a pelvis and how this affects pincer FAI is less known. More recently, in an attempt to study supine and standing changes, Ross et al [8] studied reformatted preoperative CT scans and compared them with standing AP radiographs. They measured percentage of anteversion, ischial spine signs, crossover sign, and posterior wall sign and showed only a significant difference in the amount of cranial and central anteversion measurements.…”

“…In a comparison of supine CT versus standing radiographs, Ross et al [8] found an increase in anteversion in the supine reconstructed CT scans; however, they were unable to show a difference in crossover sign, ischial spine sign, and posterior wall sign. They did not measure LCE angle or inclination [8]. A cadaveric laboratory study showed differences in LCE angle, inclination, and crossover sign with increasing pelvic tilt [4].…”

“…Standing radiographs may represent a more natural, functional pelvic position and may be more clinically relevant in the diagnosis and treatment of FAI, more specifically in patients who may have pincer impingement. The difference between supine and standing AP pelvis radiographs on pelvic tilt and these effects on the evaluation of pincer impingement have been studied in patients with dysplasia and more recently in patients with FAI [4,8]. In a comparison of supine CT versus standing radiographs, Ross et al [8] found an increase in anteversion in the supine reconstructed CT scans; however, they were unable to show a difference in crossover sign, ischial spine sign, and posterior wall sign.…”

“…The difference between supine and standing AP pelvis radiographs on pelvic tilt and these effects on the evaluation of pincer impingement have been studied in patients with dysplasia and more recently in patients with FAI [4,8]. In a comparison of supine CT versus standing radiographs, Ross et al [8] found an increase in anteversion in the supine reconstructed CT scans; however, they were unable to show a difference in crossover sign, ischial spine sign, and posterior wall sign. They did not measure LCE angle or inclination [8].…”