Analyzing Pelvic Asymmetry by Sex and Ancestry: Insights From an Osteological Collection.

INTRODUCTION: Pelvic asymmetry has been noted in pelvic imaging, and might influence the development of various spinal pathologies, most notably scoliosis. There is a limited understanding of the relationship between pelvic asymmetry and sex and ancestry, and limited use of 3D modeling. The purpose of this study was to identify pelvic asymmetry and morphology differences between sex and ancestry utilizing 3D modeling on young adults in an osteological collection. METHODS: Thirty-three osteological pelvic specimens aged 18-25 years (average age 21.4 ± 2.0 years) were scanned to create virtual 3D models for analysis. Pelvic asymmetry and morphology were measured and compared across sex (male and female) and ancestry (European American and African American). Multivariate regression analysis was performed to examine the relationship between the variables measured. RESULTS: Multivariate regression analysis demonstrated statistically significant relationships between innominate-pelvic ring ratio and both sex (p < 0.001) and ancestry (p= 0.003) with larger ratios in male and African American specimens respectively. There was also a statistically significant relationship of greater sacral 1 coronal tilt in European American specimens (p= 0.042). There were no statistically significant differences with sex or ancestry in terms of innominate or sacral asymmetry. CONCLUSION: Although there are differences in overall pelvic shape between sex and ancestry, there is no relationship between these two variables versus pelvic asymmetry in the axial or sagittal planes in young adult osteological specimens.

Interfacet distance at L4 is increased in spines with high-pelvic incidence.

Pelvic incidence (PI) is an angular measurement linked to spinal pathologies. There is an increasing distance between facet joints moving caudally down the sagittal plane of the spine. We defined pedicle divergence (PD) as the ratio of interfacet distance (IFD) between adjacent levels. This study aimed to evaluate the relationship between PI and PD. Two hundred and thirty specimens were obtained from the Hamann-Todd Osteological Collection. Specimens were catalogued for age, sex, race, PI, PD, and lumbar facet angle. Multivariate linear regression analysis was performed to determine the relationship between variables. IRB approval was not required. Average age at death was 57.0 years ±6.2 years. There were 211 (92%) male specimens and 176 (77%) were white. Average PI was 47.1 ± 10.5°. For PD between L3/L4, there was a relationship with PI (ß = -0.18, p = 0.008). For PD between L4/L5, there was an opposite relationship with PI (ß = 0.21, p = 0.003). Regression analyses of the interfacet to body ratio at each level found an association with PI only at L4 (p = 0.008). This study demonstrated that PI has a significant association with IFD in the lower lumbar spine. Increasing PI was associated with increased PD between L3/L4 and decreased PD between L4/L5. These results further support the close relationship between pelvic morphology and the lower lumbar spine, and suggest that L4 may have an important role in compensating for aberrant PI.

Pelvic Incidence in Spines With 4 and 6 Lumbar Vertebrae.

STUDY DESIGN: Anatomical study. OBJECTIVES: This study was conducted to determine the prevalence of abnormal lumbar vertebrae (4 and 6) and note any differences in pelvic incidence (PI) between spines with 4, 5, and 6 lumbar vertebrae. METHODS: We screened 2980 dry cadaveric specimens from an osteological collection. Pelvises were reconstructed by articulating the sacra and innominate bones. PI was measured in all specimens via lateral photographs. L6-pelvic incidence (L6PI) was also measured, by articulating L6 to the sacrum and measuring PI from the superior aspect of the L6 vertebral body. RESULTS: Of the specimens screened, 969 specimens were evaluated. Average age of death for all specimens was 50.4 ± 15.4 years. The prevalence of 6 lumbar vertebrae was 0.8% (n = 23), and the prevalence of 4 lumbar vertebrae was 1.8% (n = 54). PI measured 38.5° in specimens with 4 lumbar vertebrae, and 46.7° and 47.1° in specimens with 5 and 6 lumbar vertebrae, respectively. PI was significantly different between specimens with 4 and 5 lumbar vertebrae (P < .001) but not between specimens with 5 and 6 lumbar vertebrae (P = .38). For specimens with 6 lumbar vertebrae, when L6 was added to the sacrum, mean L6PI was 27.4°. CONCLUSIONS: In our large cadaveric study of full spines, we reported a lower prevalence of spines with 4 and 6 lumbar vertebrae compared to previous studies. PI was significantly decreased in subjects with 4 lumbar vertebrae compared with those with normal spines, and special caution should be taken when managing sagittal balance in these patients.

Pelvic Incidence Is Associated With Sacral Curvature, Sacroiliac Joint Angulation, and Sacral Ala Width.

STUDY DESIGN: Cross-sectional anatomical study in dry cadaveric specimens. OBJECTIVE: This study evaluates how the sacroiliac (SI) joint angulation, midsagittal sacral curvature, and sacral ala width relate to pelvic incidence (PI). SUMMARY OF BACKGROUND DATA: Numerous spinopelvic pathologies have been linked with pelvic incidence; however, the manner in which sacral morphology fits into this association is largely unknown. METHODS: A total of 120 cadaveric sacra and corresponding innominate bones were obtained from an osteological collection. Pelvic incidence was measured in a previously validated method. To gauge ala width, calipers were used to measure the distance between the midpoint of the sacral endplate and the anterolateral aspect of the right and left ala. Sacral curvature was evaluated by measuring the difference of the direct distance and the curved bony distance from the sacral promontory to the inferior aspect of the fourth intervertebral foramen. Three separate angle measurements were made to quantify the angulation of the SI joint, which we divided into an upper and lower limb. Angle 1 approximated the relationship between the upper limb and the sacral endplate; angle 2 between the upper and lower limbs; angle 3 between the lower limb and a tangential line to the fourth sacral foramen. RESULTS: Average age at death for all specimens was 31.9 ±â€Š6.3 years with 63% representation of males and an equal distribution of Caucasian and African Americans. The mean PI of our study population was 45.1 ±â€Š12.6°. Results from our regression showed statistically significant associations between our measured angles evaluating SI joint angulation (angles 1, 2, 3) and PI. Standardized beta for angle 1 was -0.421, angle 2 was 0.419, and angle 3 was -0.439 (all P < 0.001). Additionally, the average endplate-ala distance (beta = -0.254) and average difference between tape-caliper measurements, our measurement for sacral arc, (beta = 0.178) were significantly associated with PI (all P < 0.05). CONCLUSION: Our data supports the theory that increased PI is associated with a highly angulated and curved sacrum, with corresponding changes in the SI joint, and narrowed sacral alae. LEVEL OF EVIDENCE: N/A.