Pelvic incidence is not associated with the development of hip osteoarthritis

Aims Pelvic incidence (PI) is considered an important anatomical parameter for determining the sagittal balance of the spine. The contribution of an abnormal PI to hip osteoarthritis (OA) remains controversial. In this study, we aimed to investigate the relationship between PI and hip OA, and the difference in PI between hip OA without anatomical abnormalities (primary OA) and hip OA with developmental dysplasia of the hip (DDH-OA). Methods In this study, 100 patients each of primary OA, DDH-OA, and control subjects with no history of hip disease were included. CT images were used to measure PI, sagittal femoral head coverage, α angle, and acetabular anteversion. PI was also subdivided into three categories: high PI (larger than 64.0°), medium PI (42.0° to 64.0°), and low PI (less than 42.0°). The anterior centre edge angles, posterior centre edge angles, and total sagittal femoral head coverage were measured. The correlations between PI and sagittal femoral head coverage, α angle, and acetabular anteversion were examined. Results No significant difference in PI was observed between the three groups. There was no significant difference between the groups in terms of the category distribution of PI. The DDH-OA group had lower mean sagittal femoral head coverage than the other groups. There were no significant correlations between PI and other anatomical factors, including sagittal femoral head coverage, α angle, and acetabular anteversion. Conclusion No associations were found between mean PI values or PI categories and hip OA. Furthermore, there was no difference in PI between patients with primary OA and DDH-OA. From our evaluation, we found no evidence of PI being an independent factor associated with the development of hip OA. Cite this article: Bone Joint J 2021;103-B(11):1656–1661.

The association between femoral neck shaft angle and degenerative disease of the hip in a cadaveric model

Background: While the influences of acetabular dysplasia and overcoverage on hip arthritis have been studied, the impact of femoral neck-shaft angle on hip arthritis is much more poorly understood. The purpose of this study is to determine if a relationship exists between neck shaft angle and the development of osteoarthritis, a better understanding of which would be useful to surgeons planning osteotomies about the hip. Methods: 533 cadaveric femora and acetabulae (1066 total) from the Hamann-Todd Osteological Collection (Cleveland, OH) were acquired. We measured true neck shaft angle using an AP photograph with the femoral neck parallel to the table. Femoral head volume to acetabular volume ratio, representing femoral head coverage, as well as femoral version were utilised. Correlation between neck shaft angle, femoral version, femoral head coverage and osteoarthritis were evaluated with multiple regression analysis. Results: The mean age and standard deviation was 56 ± 10 years. There were 64 females (12%) and 469 males. There were 380 Caucasians (71%) and 153 African-Americans. Mean femoral version was 11° ± 12° and mean true neck shaft angle was 127.7° ± 5.9° There was a strong correlation between age and arthritis (standardised beta 0.488, p < 0.001). There was a significant correlation between increasing true neck shaft angle and decreasing hip arthritis (standardised beta -0.024, p = 0.038). In the femoral head overcoverage subset, increasing true neck shaft angle was still significantly associated with decreasing hip arthritis (standardised beta −0.088, p = 0.018), although this relationship was not significant with femoral head undercoverage subset. Conclusions: With sufficient acetabular coverage, a relative increase in femoral neck shaft angle within the physiologic range is associated with decreased hip osteoarthritis. Clinical relevance: An understanding of the relationship between femoral neck shaft angle and hip osteoarthritis could be useful for surgeons planning pelvic or proximal femur osteotomies in children.

What is the pelvic tilt in acetabular dysplasia and does it change following peri-acetabular osteotomy?

To quantify the pelvic tilt (PT) in patients with symptomatic acetabular dysplasia and determine if it represents a compensatory mechanism to improve femoral head coverage, we studied a cohort of 16 patients undergoing 32 bilateral staged PAOs for acetabular dysplasia and compared this to a matched cohort of 32 patients undergoing PAO for unilateral acetabular dysplasia all with &gt;1 year follow-up. The change in PT was determined with two validated methods, namely, the sacro-femoral-pubic (SFP) angle and the pubic symphysis to sacroiliac index (PS-SI). Despite an improvement in the lateral centre-edge and Tönnis angles to within normal limits following PAO, patients with unilateral and bilateral acetabular dysplasia have similar PT pre-operatively (8° ± 5°) and post-operatively (9° ± 5°). A change of &gt;5° was observed in only six patients (13%) using the SFP angle, and five patients (10%) using the PS-SI, all increased (posterior rotation of the pelvis). No patients were observed to have a change in PT &gt;10°. The observed PT in our study group is equivalent to that found in the normal population and in patient with symptomatic acetabular retroversion. These findings all suggest that PT is morphological rather than a result of a compensatory mechanism, and even if it was compensatory, it does not appear to reverse significantly following PAO. The target for acetabular reorientation, therefore, remains constant.

Correlation of Patient-Reported Outcomes After Periacetabular Osteotomy With Femoral Head Coverage and Acetabular Orientation: A Single-Center Cohort Study

Background: Gaining a better understanding of the underlying pattern of acetabular dysplasia 3-dimensionally can help better guide treatment and optimize clinical outcomes after periacetabular osteotomy (PAO). Purpose: (1) To examine the relationship between femoral head coverage before and after PAO for dysplasia and patient-reported outcome measure (PROM) scores and (2) to assess if the direction/orientation of correction of the acetabulum can be predicted based on the Ottawa classification. Study Design: Cohort study; Level of evidence, 3. Methods: A retrospective analysis of a prospectively collected database from a single-center institutional registry of PAO was conducted, and PROM scores at a minimum of 2 years were analyzed. A total of 79 hips (67 patients [56 female]; mean age at surgery, 27.5 years [range, 15.8-53.7 years]) were available for inclusion. According to the Ottawa classification, 54 hips (68.4%) had global deficiency, 15 hips (18.9%) had posterior deficiency, and 10 hips (12.7%) had anterior deficiency. Hip2Norm software was used to analyze the 3-dimensional coverage of the femoral head. Statistical analysis was conducted to look at significant predictors of improvements in PROMs using the minimal clinically important difference (MCID) for the Hip disability and Osteoarthritis Outcome Score (HOOS) Activities of Daily Living subscale. Results: At a mean follow-up of 3.1 years (range, 2.0-7.4 years), all functional outcome scores improved significantly. A postoperative total femoral coverage <75.7%, posterior coverage (PC) <45.2%, and femoral head extrusion index >15.5% were all associated with not reaching the MCID for the HOOS Activities of Daily Living subscale. Multivariate analysis showed that PC was the single most important significant modifier influencing functional outcomes after PAO for the treatment of acetabular dysplasia, with an odds ratio of 6.0 (95% CI, 1.8-20.4; P = .004). One-way analysis of variance showed a significant difference comparing the mean change in radiographic measurements, that is, anterior coverage, PC, and total femoral coverage, per the Ottawa classification ( P < .001). Conclusion: Our study demonstrated that postoperative femoral head coverage and acetabular orientation were significant predictors of PROM scores. Classifying acetabular dysplasia into 3 groups based on the plane of instability could optimize the planning of PAO by giving a better understanding of the 3-dimensional deformity.

Change in 2D and 3D femoral head coverage after curved periacetabular osteotomy

Femoral head coverage in patients with hip dysplasia (DDH) is often quantified using 2D parameters, including the lateral center edge angle (LCEA) and anterior center edge angle (ACEA). However, only moderate correlations have been observed between the 2D coverage and 3D coverage. The purposes of this study were to: 1) quantify the change in 3D head coverage after curved periacetabular osteotomy (CPO), and 2) analyze the relationship between 2D and 3D head coverage preoperatively and postoperatively. Forty-three hips of 39 female cases (age: 37±10 years) who underwent CPO were analyzed. 2D coverage was quantified using the LCEA and ACEA from CT images. 3D coverage was quantified in the anterior, superior, posterior, inferior head regions. 3D measurements were performed both pre- and post-operatively and were correlated to the measurements of 2D coverage to study interactions. Preoperative 3D percent coverage in each head region was 17.8±6.7%, 36.2±7.7%, 57.6±10.2%, and 15.3±6.4% for the anterior, superior, posterior, and inferior region, respectively. Postoperatively, 3D coverage in the anterior and superior regions increased to 23.4% and 53.7%, respectively while a significant decrease was found for the posterior and inferior regions (all p&lt;0.01). When 3D and 2D coverage was correlated, significant positive correlation was found between the 3D superior coverage and the LCEA both preoperatively (r=0.72, p&lt;0.01) and postoperatively (r=0.67, p&lt;0.01). However, no correlation was found between the 3D anterior coverage and the ACEA, which became significant in the postoperative period (r=0.69, p&lt;0.01). Results indicate that preoperative anterior coverage for patients with DDH should be evaluated three-dimensionally.

LOW DOSE CT SCAN FOLLOWING PERIACETABULAR OSTEOTOMY: ASSESSMENT OF REDUCTION AND CORRELATION WITH RADIOGRAPHIC MEASURES

Introduction: Periacetabular osteotomy (PAO) has become a favored treatment for symptomatic acetabular dysplasia worldwide. Nevertheless, the parameters for optimal correction to avoid residual instability or iatrogenic impingement have not been defined. Purpose: The purposes of this study were (1) to assess the ability of PAO to correct femoral head coverage to normal ranges as measured by 3D CT scan and (2) to determine if postoperative radiographic parameters of dysplasia are accurate markers of optimal acetabular correction. Methods: A total of 43 hips (in 38 patients, mean 27.7 years, 88.4% female) were enrolled in this prospective cohort study at minimum 1 year after PAO. Postoperative femoral head coverage was assessed via low-dose CT and compared to normative data of asymptomatic hips from the literature. Anterior (3:00-1:15), lateral (1:00-11:00), and posterior (11:25-9:00) sector coverage was defined by averaging the coverage at 15 minute increments in each zone. Postoperative radiographs were utilized to measure lateral center edge angle (LCEA), anterior wall index (AWI), posterior wall index (PWI), and anterior center edge angle (ACEA). Good correction for each sector was defined as coverage from 1 SD below mean to 2 SD above mean. Results: Postoperatively, the anterior sector was normalized in 84% of hips, lateral sector in 84% of hips, and posterior sector in 86% of hips. Sixty-seven percent of hips were corrected to normative range in all three sectors and 19% were corrected in two sectors (86% in at least two sectors). LCEA and PWI showed the highest correlation with lateral and posterior sector coverage with Pearson’s correlation coefficients of 0.67 and 0.71 (p < 0.001), respectively. Weaker correlations were found between anterior coverage and the AWI and ACEA coverage (-0.16 and 0.15, respectively). Good correction was best correlated with the following target values for acetabular correction: LCEA 28°, AI 1°, AWI 0.37, ACEA 32°, and PWI 1.0. Conclusion: PAO can effectively normalize femoral head coverage compared to normative data. Good correction of each sector coverage ranged from 84-86% of cases. The proposed set of radiographic parameter targets were found to be reliable markers of femoral head coverage.