The Acetabular Sector Angle of the Adult Hip Determined by Computed Tomography

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144

Appropriate anatomic concepts for surgery to treat femoroacetabular impingement require a precise appreciation of the native acetabular anatomy. We therefore determined (1) the spatial acetabular rim profile, (2) the topography of the articular lunate surface, and (3) the 3-D relationships of the acetabular opening plane comparing 66 bony acetabula from 33 pelves in female and male pelves. The acetabular rim profile had a constant and regular wave-like outline without gender differences. Three prominences anterosuperiorly, anteroinferiorly and posteroinferiorly extended just above hemispheric level. Two depressions were below hemispheric level, of 9°at the anterior wall and of 21°along the posterosuperior wall. In 94% of all acetabula, the deepest extent of the articular surface was within 30°of the anterosuperior acetabular sector. In 99% of men and in 91% of women, the depth of the articular surface was at least 55°along almost half of the upper acetabular cup. The articular surface was smaller in women than in men. The acetabular opening plane was orientated in 21°± 5°for version, 48°± 4°for inclination and 19°± 6°for acetabular tilt with no gender differences. We defined tilt as forward rotation of the entire acetabular cup around its central axis; because of interindividual variability of acetabular tilt, descriptions of acetabular lesions during surgery, CT scanning and MRI should be defined and recorded in relation to the acetabular notch. Acetabular tilt and pelvic tilt should be separately identified. We believe this information important for surgeons performing rim trimming in FAI surgery or performing acetabular osteotomies.

Section: Discussionsupporting

confidence: 91%

Acetabular Morphology: Implications for Joint-preserving Surgery

Köhnlein¹,

Ganz

Impellizzeri³

et al. 2009

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144

“…Previous studies using CT of human hips have measured the contours of the bony acetabulum [13], the relative coverage of the femoral head by the acetabulum in developmental dysplasia of the hip [1,2,5,7], and the contact pressure between the acetabulum and the femoral head [12]. However, these studies have focused on normal and dysplastic hips and did not directly visualize the articular cartilage using MR. Steppacher and colleagues [27] used MR radial sequences to examine protrusio, deep, and retroverted acetabula, finding that retroverted acetabula had smaller cartilage surfaces than deep and protrusio acetabula.…”

Section: Introductionmentioning

confidence: 99%

Is Increased Acetabular Cartilage or Fossa Size Associated With Pincer Femoroacetabular Impingement?

Pun

Hingsammer

Millis

et al. 2017

Background Surgical treatment for pincer femoroacetabular impingement (FAI) of the hip remains controversial, between trimming the prominent acetabular rim and reverse periacetabular osteotomy (PAO) that reorients the acetabulum. However, rim trimming may decrease articular surface size to a critical threshold where increased joint contact forces lead to joint degeneration. Therefore, knowledge of how much acetabular articular cartilage is available for resection is important when evaluating between the two surgical options. In addition, it remains unclear whether the acetabulum rim in pincer FAI is a prominent rim because of increased cartilage size or increased fossa size. Questions/purposes We used reformatted MR and CT data to establish linear length dimensions of the lunate cartilage and cotyloid fossa in normal, dysplastic, and deep acetabula. Methods We reviewed the last 200 hips undergoing PAO, reverse PAO, and surgical dislocation for acetabular rim trimming at one institution. We compared MR images of symptomatic hips with acetabular dysplasia (20 hips), pincer FAI (29 hips), and CT scans of asymptomatic hips from patients who underwent CT scans for reasons other than hip pain (20 hips). These hips were chosen sequentially from the underlying pool of 200 potential subjects to identify the first 10 male and the first 10 female hips in each group that met inclusion criteria. As a result of low numbers, we included all hips that had undergone reverse PAO and met inclusion criteria. Cartilage width was measured medially from the cotyloid fossa to the lateral labrochondral junction. Cotyloid fossa linear height was measured from superior to inferior and cotyloid fossa width was measured from anterior to posterior. Superior lunate cartilage width (SLCW) and cotyloid fossa height (CFH) were measured on MR and CT oblique coronal reformats; anterior lunate cartilage width (ALCW), posterior lunate cartilage width (PLCW), and cotyloid fossa width (CFW) were measured on MR and CT oblique axial reformats. Cohorts were compared using multivariate analysis of variance with Bonferroni's adjustment for multiple comparisons.Results Compared with control acetabula, dysplastic acetabula had smaller SLCW (2.08 ± 0.29 mm versus 2.63 Clinical Orthopaedics and Related Research ®A Publication of The Association of Bone and Joint Surgeons® ± 0.42 mm, mean difference = À0.55 mm; 95% confidence interval [CI] = À0.83 to À0.27; p \ 0.01), ALCW (1.20 ± 0.34 mm versus 1.64 ± 0.21 mm, mean difference = À0.44 mm; 95% CI = À0.70 to À0.18; p = 0.00), CFH (2.84 ± 0.37 mm versus 3.42 ± 0.57 mm, mean difference = À0.59 mm; 95% CI = À0.96 to À0.21; p \ 0.01), and CFW (1.98 ± 0.50 mm versus 2.77 ± 0.33 mm, mean difference = À0.80 mm; 95% CI = À1.16 to À0.42; p \ 0.0001). Based on the results, we identified two subtypes of deep acetabula. Compared with controls, deep subtype 1 had normal CFH and CFW but increased ALCW (2.09 ± 0.42 mm versus 1.64 ± 0.21 mm; p \ 0.001) and PLCW (2.32 ± 0.36 mm versus 2.00 ± 0.32 mm; p = 0.04). Compared ...

“…Accurate assessment of acetabular version and anterior and posterior femoral head coverage can be difficult, and changes in patient positioning can lead to errors in measurement [4,24,45,48]. Two-dimensional CT studies have become an integral part of diagnosis and preoperative planning, especially when assessing deficiencies in the transverse plane [5,26,29,33,41,59].…”

Section: Introductionmentioning

confidence: 99%

“…Two-dimensional CT studies have become an integral part of diagnosis and preoperative planning, especially when assessing deficiencies in the transverse plane [5,26,29,33,41,59]. They allow for assessment of acetabular version and anterior and posterior femoral head coverage, defined by acetabular sector angles [4,7,22]. Patient positioning has the potential to cause errors in measurements on CT studies just as it does with plain radiographs.…”

Section: Introductionmentioning

confidence: 99%

“…Abel et al observed the acetabular anteversion decreased 30°as pelvic tilt was varied from 15°posterior tilt to 35°anterior tilt [1]. Anda et al similarly found a change of 0.5°in anteversion and 0.7°in acetabular sector angles for every 1°-change in pelvic tilt [4,5]. Visser et al noted that pelvic tilt changed measured anteversion, but rotation along the body's longitudinal axis did not [58].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Pelvic Positioning Creates Error in CT Acetabular Measurements

Bosse¹,

Lee

Henderson

et al. 2011

Background CT allows for accurate measurement of acetabular orientation and shape, but malpositioning of the pelvis may lead to measurement variance. Purpose We therefore sought to determine: (1) whether acetabular anteversion measurements using the femoral head centers differed from those using the posterior ischia, and (2) the extent to which changing obliquity, rotation, and tilt of a pelvis in a CT scanner affected the measurement of acetabular variables. Methods A radiopaque human pelvis model with articulated hips was suspended from a plastic sheet as part of an adjustable frame. Changes in the transverse and sagittal planes created rotation and tilt, while rotating the frame in the coronal plane created obliquity. CT scans were obtained, varying the combinations of obliquity, rotation, and tilt by intervals of 5°, up to 20°. Acetabular anteversion (AA), anterior acetabular sector angle (AASA), posterior acetabular sector angle (PASA), and horizontal acetabular sector angle (HASA) were measured. Results The two methods for measuring AA yielded values differing by 1°to 4°but correlated (r = 0.981) across the spectrum of pelvis positioning. Pelvic obliquity and tilt were linearly associated with changes in the measurements. For each 1°-increase in pelvic obliquity, AA changed À0.4°, and AASA, PASA, and HASA changed 1.93°, 0.99°, and 2.80°, respectively. For each 1°-increase in pelvic tilt, AA changed 0.8°, and AASA, PASA, and HASA changed À1.07°, 0.52°, and À0.51°, respectively. Rotation had no affect on the variables. Conclusions Small changes in pelvic obliquity and tilt were associated with variances in acetabular measurements. The measured changes were directly proportional to the changes in obliquity and tilt, and were additive. Pelvic rotation created no changes in measurement. Clinical Relevance Incorrect interpretation of acetabular anteversion and coverage may lead to unsatisfactory acetabular fragment positioning during reorientational surgery. Although intraoperative positioning of an acetabular fragment may not be as precise as the tools for preoperative planning, it is important for a surgeon to have the most precise data available for planning a procedure, and know where error can occur in collecting the data.Each author certifies that he or she has no commercial associations (eg, consultancies, stock ownership, equity interest, patent/licensing arrangements, etc) that might pose a conflict of interest in connection with the submitted article.