ASSESSMENT OF ACETABULAR COVERAGE IN BORDERLINE ACETABULAR DYSPLASIA: ARE PLAIN RADIOGRAPHIC PARAMETERS ACCURATELY ESTIMATES OF THREE-DIMENSIONAL COVERAGE?

Introduction: Assessment of anterior acetabular coverage is commonly done with measurement of the anterior center edge angle (ACEA) or anterior wall index (AWI). This is particularly important in cases of borderline acetabular dysplasia where it may influence treatment decisions. However, the ACEA and AWI has been poorly validated. Purpose: The purpose of the current study was to investigate the correlation between plain radiographic measurements and three-dimensional femoral head coverage on low-dose CT in borderline acetabular dysplasia. Methods: Seventy consecutive hips with borderline acetabular dysplasia (LCEA 20-25°) were included in the current study. Radiographic evaluation was performed prospectively including LCEA, acetabular inclination, and AWI on AP pelvis radiographs, and ACEA on false profile radiographs. The mean LCEA was 22.1±1.4°, while the mean acetabular inclination was 10.3±3.3. All patients underwent low-dose pelvic CT assessment for preoperative planning. The radial acetabular coverage was calculated according to the standardized clock-face position [measured at 12:00 (lateral), 1:00, 2:00, 3:00 (anterior), and 4:00] as described by Larson et al. Statistical analysis determined the correlation between ACEA and radial coverage. Results: The mean ACEA in the group was 25.3±5.8° (range 10.1-43.9), with 16% having ACEA≤20° and 50% having ACEA≤25°. The mean radial coverages were 63.5%±1.7 (12:00), 60.7%±2.2 (1:00), 50.8%±3.2 (2:00), 37.0%±3.3 (3:00), and 27.9%±3.1 (4:00). The ACEA had poor correlation with radial coverage at all positions from 12:00 to 4:00 (range –0.068-0.173). The AWI had moderate correlation with radial coverage at 3:00 (PCC 0.499) and 4:00 (PCC 0.573). Comparing hips with an ACEA <20° versus >20°, there was no difference between the mean radial acetabular coverage at any position 12:00-4:00 (p=0.18-0.95). Comparing hips with an ACEA <25° versus >25°, there was no difference between the mean radial acetabular coverage at any position 12:00-4:00 (p=0.12-0.71). No significant difference in AWI was present between subgroups with normal and deficient radial coverage from 12:00 to 4:00 (p=0.09-0.72). Discussion: The current study demonstrates poor correlation of the ACEA measurement with true anterior femoral head coverage as evaluated at clock-face positions from 12:00 to 4:00. The AWI demonstrated moderate correlation for 3:00-4:00 coverage but fails to differentiate hips with normal and deficient coverage. In the setting of borderline acetabular dysplasia, anterior and anterolateral femoral coverage should be assessed via low-dose CT rather than ACEA or AWI.

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BORDERLINE ACETABULAR DYSPLASIA: THREE-DIMENSIONAL DEFORMITY PREDICTORS OF THE DIAGNOSIS OF SYMPTOMATIC INSTABILITY TREATED WITH PERIACETABULAR OSTEOTOMY

Orthopaedic Journal of Sports Medicine ◽

10.1177/2325967121s00160 ◽

2021 ◽

Vol 9 (7_suppl3) ◽

pp. 2325967121S0016

Author(s):

Elizabeth Graesser ◽

Maria Schwabe ◽

Cecilia Pascual Garrido ◽

John C. Clohisy ◽

Jeffrey J. Nepple

Keyword(s):

Low Dose ◽

Acetabular Dysplasia ◽

Periacetabular Osteotomy ◽

Alpha Angle ◽

Three Dimensional ◽

Acetabular Coverage ◽

Low Dose Ct ◽

Femoral Version ◽

Center Edge ◽

Hip Morphology

Introduction: Borderline acetabular dysplasia is classically defined as a lateral center edge angle (LCEA) of 20-25 degrees. The optimal treatment strategy in this patient group remains controversial, with some patients having primarily hip instability-based symptoms, while others have primarily impingement-based symptoms (non-instability). The purpose of the current study was to define the 3D characteristics on low-dose CT that differentiate patients with instability symptoms from those without instability in the setting of borderline acetabular dysplasia. Methods: Seventy consecutive hips with borderline acetabular dysplasia undergoing surgical treatment were included in the current study. All patients underwent low-dose pelvic CT with femoral version assessment for preoperative planning. CT measurements included alpha angle and radial acetabular coverage (RAC) at standardized clockface positions (9:00-posterior to 3:00-anterior), central and cranial acetabular version. RAC was assessed in three sectors (anterior, superior, and posterior) and defined (relative to published normative data) as normal (-1 SD, +1 SD), undercoverage (<-1 SD), or overcoverage (>+1 SD). Statistical analysis was performed to compare the CT characteristics of the symptomatic instability and non-instability groups. Results: Of the 70 hips, 62.9% had the diagnosis of symptomatic instability, while 37.1% had no instability symptoms. Hips with instability (compared to non-instability) had significantly lower alpha angle (maximal difference at 1:00 - 47.0° vs. 59.4°), increased femoral version (22.3° vs. 15.3°), and decreased radial acetabular coverage (maximal difference at 1:00 – 59.9% vs. 62.2%) (all p<0.001). Multivariate analysis identified femoral version (OR 1.1, p=0.02), alpha angle at 1:00 (OR 0.91, p=0.02), and RAC at 1:00 (OR 0.46, p=0.003) as independent predictors of the presence of instability. The model combining these three factors had excellent predictive probability with a c-statistic 0.92. Conclusion: We found significant differences in the 3D hip morphology of the symptomatic instability and non-instability subgroups within the borderline dysplasia cohort. In the setting of borderline dysplasia, three-dimensional deformity characterization with low-dose CT allowed for differentiation of patients diagnosed with underlying instability vs. non-instability. Femoral version, alpha angle at 1:00, and radial acetabular coverage at 1:00 were identified as independent predictors of diagnosis in borderline acetabular dysplasia. Summary: This study attempts to define 3D CT characteristics to help distinguish between patients with impingement-based vs instability-based symptoms of borderline acetabular dysplasia.

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Defining the Borderline Hip: High Variability in Acetabular Coverage and Femoral Deformity

Orthopaedic Journal of Sports Medicine ◽

10.1177/2325967120s00346 ◽

2020 ◽

Vol 8 (7_suppl6) ◽

pp. 2325967120S0034

Author(s):

Maria Schwabe ◽

Cecilia Pascual-Garrido ◽

John Clohisy ◽

Elizabeth Graesser Jeffrey Nepple

Keyword(s):

Low Dose ◽

Acetabular Dysplasia ◽

Alpha Angle ◽

Acetabular Coverage ◽

Femoral Version ◽

Center Edge ◽

Text Figure ◽

Femoral Deformity ◽

The Mean ◽

Center Edge Angle

Objectives: Borderline acetabular dysplasia is radiographically defined as a lateral center edge angle (LCEA) of 20-25 degrees. It is well accepted that some borderline hips have instability while others have primarily impingement. The optimal management of borderline dysplasia is challenging and particularly complex due to the anatomic variability that exists among patients but has not been well characterized. The purpose of this current study was to investigate the variability in hip deformity present on low-dose CT in a cohort of patients with symptomatic borderline acetabular dysplasia. Methods: Seventy consecutive hips with borderline acetabular dysplasia undergoing surgical treatment were included in the current study. Radiographic evaluation included LCEA, acetabular inclination, anterior center edge angle (ACEA), and alpha angles on AP, Dunn, and frog views. All patients underwent low-dose pelvic CT for preoperative planning. Femoral deformity was assessed with femoral version, alpha angle (measured at 1:00 increments), and maximum alpha angle. Radial acetabular coverage was calculated according to standardized clockface positions [measured from 8:00 (posterior) to 4:00 (anterior)] and defined as normal, undercoverage, or overcoverage relative to 1 SD from the mean of normative values. Results: The mean LCEA was 22.1+1.4, while the mean acetabular inclination was 10.3+3.3. The mean ACEA in the group was 25.3+5.8 (range 10.1-43.9), with 16% having an ACEA < 20 and 50% having an ACEA < 25. The mean femoral version was 17.9° (range -4° to 59°). The mean maximal alpha angle was 57.2° (range 43° to 81°) with 61.4% greater than 55°. Lateral coverage (RAC at 12:00) was deficient in 74.1% of cases. Anterior coverage (RAC at 2:00) was highly variable with 17.1% undercoverage, 72.9% normal, and 10.0% overcoverage. Posterior coverage (RAC at 10:00) was also highly variable with 30.0% undercoverage, 62.9% normal, and 7.1% overcoverage. The three most common patterns of coverage were: isolated lateral undercoverage (31.4%), normal coverage (18.6%), and lateral and posterior undercoverage (17.1%). Conclusion: Patients with borderline acetabular dysplasia demonstrate highly variable three-dimensional deformities including anterior, lateral, and posterior acetabular coverage, femoral version, and alpha angle. Comprehensive deformity characterization in the population is important to guide diagnosis and treatment decisions. [Figure: see text][Figure: see text][Figure: see text]

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Acetabular Dysplasia: Three-Dimensional Deformity Predictors of the Diagnosis of Symptomatic Instability Treated with Periacetabular Osteotomy

Orthopaedic Journal of Sports Medicine ◽

10.1177/2325967120s00426 ◽

2020 ◽

Vol 8 (7_suppl6) ◽

pp. 2325967120S0042

Author(s):

Maria Schwabe ◽

Cecilia Pascual-Garrido ◽

John Clohisy ◽

Elizabeth Graesser ◽

Jeffrey Nepple

Keyword(s):

Low Dose ◽

Acetabular Dysplasia ◽

Periacetabular Osteotomy ◽

Alpha Angle ◽

Three Dimensional ◽

Acetabular Coverage ◽

Low Dose Ct ◽

Femoral Version ◽

Center Edge ◽

Hip Morphology

Objectives: Borderline acetabular dysplasia is classically defined as a lateral center edge angle (LCEA) of 20-25 degrees. The optimal treatment strategy in this patient group remains controversial, with some patients having primarily hip instability-based symptoms, while others have primarily impingement-based symptoms (non-instability). The purpose of the current study was to define the 3D characteristics on low-dose CT that differentiate patients with instability symptoms from those without instability in the setting of borderline acetabular dysplasia. Methods: Seventy consecutive hips with borderline acetabular dysplasia undergoing surgical treatment were included in the current study. All patients underwent low-dose pelvic CT with femoral version assessment for preoperative planning. CT measurements included alpha angle and radial acetabular coverage (RAC) at standardized clockface positions (9:00-posterior to 3:00-anterior), central and cranial acetabular version. RAC was assessed in three sectors (anterior, superior, and posterior) and defined (relative to published normative data) as normal (-1 SD, +1 SD), undercoverage (<-1 SD), or overcoverage (>+1 SD). Statistical analysis was performed to compare the CT characteristics of the symptomatic instability and non-instability groups. Results: Of the 70 hips, 62.9% had the diagnosis of symptomatic instability, while 37.1% had no instability symptoms. Hips with instability (compared to non-instability) had significantly lower alpha angle (maximal difference at 1:00 - 47.0° vs. 59.4°), increased femoral version (22.3° vs. 15.3°), and decreased radial acetabular coverage (maximal difference at 1:00 – 59.9% vs. 62.2%) (all p<0.001). Multivariate analysis identified femoral version (OR 1.1, p=0.02), alpha angle at 1:00 (OR 0.91, p=0.02), and RAC at 1:00 (OR 0.46, p=0.003) as independent predictors of the presence of instability. The model combining these three factors had excellent predictive probability with a c-statistic 0.92. Conclusion: We found significant differences in the 3D hip morphology of the symptomatic instability and non-instability subgroups within the borderline dysplasia cohort. In the setting of borderline dysplasia, three-dimensional deformity characterization with low-dose CT allowed for differentiation of patients diagnosed with underlying instability vs. non-instability. Femoral version, alpha angle at 1:00, and radial acetabular coverage at 1:00 were identified as independent predictors of diagnosis in borderline acetabular dysplasia.

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DEFINING THE BORDERLINE HIP: HIGH VARIABILITY IN ACETABULAR COVERAGE AND FEMORAL DEFORMITY

Orthopaedic Journal of Sports Medicine ◽

10.1177/2325967120s00210 ◽

2020 ◽

Vol 8 (4_suppl3) ◽

pp. 2325967120S0021

Author(s):

Elizabeth Graesser ◽

Maria Schwabe ◽

Cecilia Pascual-Garrido ◽

John C Clohisy ◽

Jeffrey J Nepple

Keyword(s):

Low Dose ◽

Acetabular Dysplasia ◽

Alpha Angle ◽

Acetabular Coverage ◽

Edge Angle ◽

Femoral Version ◽

Center Edge ◽

Femoral Deformity ◽

The Mean ◽

Center Edge Angle

Introduction Borderline acetabular dysplasia is radiographically defined as a lateral center edge angle (LCEA) of 20-25 degrees. It is well accepted that some borderline hips have instability while others have primarily impingement. The optimal management of borderline dysplasia is challenging and particularly complex due to the anatomic variability that exists among patients but has not been well characterized. Purpose The purpose of this current study was to investigate the variability in hip deformity present on low-dose CT in a cohort of patients with symptomatic borderline acetabular dysplasia. Methods Seventy consecutive hips with borderline acetabular dysplasia undergoing surgical treatment were included in the current study. Radiographic evaluation included LCEA, acetabular inclination, anterior center edge angle (ACEA), and alpha angles on AP, Dunn, and frog views. All patients underwent low-dose pelvic CT for preoperative planning. Femoral deformity was assessed with femoral version, alpha angle (measured at 1:00 increments), and maximum alpha angle. Radial acetabular coverage was calculated according to standardized clock-face positions [measured from 8:00 (posterior) to 4:00 (anterior)] and defined as normal, under-coverage, or over-coverage relative to 1 SD from the mean of normative values. Results The mean LCEA was 22.1±1.4, while the mean acetabular inclination was 10.3±3.3. The mean ACEA in the group was 25.3±5.8 (range 10.1-43.9), with 16% having an ACEA ≤ 20 and 50% having an ACEA ≤ 25. The mean femoral version was 17.9° (range -4° to 59°). The mean maximal alpha angle was 57.2° (range 43° to 81°) with 61.4% greater than 55°. Lateral coverage (RAC at 12:00) was deficient in 74.1% of cases. Anterior coverage (RAC at 2:00) was highly variable with 17.1% under-coverage, 72.9% normal, and 10.0% over-coverage. Posterior coverage (RAC at 10:00) was also highly variable with 30.0% under-coverage, 62.9% normal, and 7.1% over-coverage. The three most common patterns of coverage were: isolated lateral under-coverage (31.4%), normal coverage (18.6%), and lateral and posterior under-coverage (17.1%). Discussion Patients with borderline acetabular dysplasia demonstrate highly variable three-dimensional deformities including anterior, lateral, and posterior acetabular coverage, femoral version, and alpha angle. Comprehensive deformity characterization in the population is important to guide diagnosis and treatment decisions.

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

Orthopaedic Journal of Sports Medicine ◽

10.1177/2325967120s00213 ◽

2020 ◽

Vol 8 (4_suppl3) ◽

pp. 2325967120S0021

Author(s):

Clarabelle DeVries ◽

Jeffrey J Nepple ◽

Lucas Fowler ◽

Sean Akers ◽

Gail Pashos ◽

...

Keyword(s):

Femoral Head ◽

Normative Data ◽

Low Dose ◽

Periacetabular Osteotomy ◽

Femoral Head Coverage ◽

Edge Angle ◽

Center Edge ◽

Two Sectors ◽

Posterior Sector ◽

Center Edge Angle

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.

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Comparison of four parameters to assess acetabular dysplasia and acetabular dysplasia rates in primary hip osteoarthritis patients: A study in Turkish population

Journal of Orthopaedic Surgery ◽

10.1177/2309499018768032 ◽

2018 ◽

Vol 26 (2) ◽

pp. 230949901876803 ◽

Cited By ~ 1

Author(s):

Oktay Adanir ◽

Gazi Zorer

Keyword(s):

Femoral Head ◽

Acetabular Dysplasia ◽

Hip Prosthesis ◽

Hip Osteoarthritis ◽

High Rate ◽

Femoral Head Coverage ◽

Coverage Ratio ◽

Total Hip ◽

Center Edge ◽

Age At Surgery

Introduction: Hip osteoarthritis is an important orthopedic problem frequently observed in the elderly. Acetabular dysplasia (AD) is one of the pathologies that cause coxarthrosis. Nearly 20–45% of primary or idiopathic hip osteoarthritis is linked to AD. In our country, there are few studies on this topic. We measured the center–edge (CE) angle, Sharp’s angle, acetabular depth, and femoral head coverage ratio on pelvis anteroposterior radiographs of patients with primary coxarthrosis and calculated the dysplasia rates. Patients and method: Age at surgery and sex of the patients; and CE angle, Sharp’s angle, acetabular depth, and femoral head coverage ratio for both operated and opposite hips were evaluated in 223 total hip prosthesis–performed patients with coxarthrosis. Also the distribution of mean age at surgery, sex of patients, dysplasia rates of operated hips, and bilateral dysplasia rates were calculated. Results: The right to left ratio of operated hips was 104/119. Female to male ratio was 163/60 (2.7/1), for those with CE angle below 20° it was 123/30 (4.1/1), and it was 40/30 (1.3/1) with CE angle above 20°. Mean age of patients at surgery was 56.9 (±11.4) years. CE angle less than 20° was found in 68.6% of patients, acetabulum depth less than 9 mm was found in 75.3%, Sharp’s angle was more than 45° in 65.9%, and femoral head coverage ratio was less than 70% in 70.3% of patients. Conclusions: We identified a high rate of AD in primary coxarthrosis patients undergoing total hip arthroplasty in the study population.

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Three-Dimensional Evaluation of Anterior Acetabular Coverage of the Femoral Head.

Orthopedics & Traumatology ◽

10.5035/nishiseisai.42.328 ◽

1993 ◽

Vol 42 (1) ◽

pp. 328-331 ◽

Cited By ~ 1

Author(s):

Etsuo Chosa ◽

Naoya Tajima ◽

Yoshitaka Nagatsuru

Keyword(s):

Femoral Head ◽

Three Dimensional ◽

Acetabular Coverage

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A novel protocol for three-dimensional rotational venography with low-dose contrast media in preoperative angiography of brain tumours

The Neuroradiology Journal ◽

10.1177/1971400919873894 ◽

2019 ◽

Vol 32 (6) ◽

pp. 452-457

Author(s):

Kimiaki Kashimoto ◽

Katsunori Asai ◽

Manabu Kinoshita ◽

Yoshiko Okita ◽

Shogo Tanabe ◽

...

Keyword(s):

Contrast Media ◽

Brain Tumours ◽

Low Dose ◽

Cerebral Arteries ◽

Three Dimensional ◽

Preoperative Assessment ◽

Mr Venography ◽

Time To Peak ◽

The Mean ◽

Time Density

Aim The most appropriate imaging protocol for three-dimensional rotational venography (3D RV) has not been established. The aim of this study was to optimise the protocol for 3D RV with low-dose contrast media using time–density curve analysis. Methods Twenty-five consecutive patients with brain tumours who received preoperative assessment with 3D RV were retrospectively collected and included in this study. To optimise the imaging delay time of 3D RV with low-dose contrast media, time–density curve analysis was performed on two-dimensional conventional angiography. The image quality for depicting cortical veins and venous sinuses was compared to that of magnetic resonance (MR) venography in five cases. Results A total of 27 3D RVs were performed in 25 patients. The time–density curves of cortical veins were different from those of cerebral arteries or sinuses. The mean time to peak of cortical veins was significantly longer than the time to peak of cerebral arteries (2.47 ± 0.35 seconds vs. 6.44 ± 1.14 seconds; p < 0.0001) and shorter than the time to peak of venous sinuses (6.44 ± 1.14 seconds vs. 8.18 ± 1.12 seconds; p < 0.0001). The optimal imaging delay time could be determined as the phases in which cortical arterial opacities disappeared and cortical veins started to appear. The mean dose of injected contrast media was 5.3 mL. The image quality of cortical veins in 3D RV was superior to that in MR venography in all cases. Conclusions Three-dimensional RV with low-dose contrast media was useful for the preoperative assessment of cortical veins in patients with brain tumours.

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ACETABULAR VERSION INCREASES DURING ADOLESCENCE SECONDARY TO A REDUCTION IN ANTERIOR FEMORAL HEAD COVERAGE

Orthopaedic Journal of Sports Medicine ◽

10.1177/2325967119s00014 ◽

2019 ◽

Vol 7 (3_suppl) ◽

pp. 2325967119S0001

Author(s):

Sasha Carsen ◽

George Grammatopoulos ◽

Paul Jamieson ◽

Kawan Rakhra ◽

Johanna Dobransky ◽

...

Keyword(s):

Femoral Head ◽

Acetabular Anteversion ◽

Femoral Head Coverage ◽

Range Of Movement ◽

Patient Factors ◽

Mri Scan ◽

Acetabular Version ◽

The Mean ◽

Sector Angle

The understanding of the underlying mechanisms leading to FAI continues to evolve; it is evident that both the femoral (cam, retroversion) and acetabular (pincer, retroversion) anatomy may contribute to its development. Several studies have demonstrated the development of cam morphology during the growing years of the skeleton and its association with increased activity during the adolescence years. However, considerably less is known about the development of the acetabulum and what changes occur during the adolescent years, which appear to be the key developmental stage. Retrospective cross-sectional studies derived from CT-data (hence missing cartilaginous portions of the growing skeleton) noted that acetabular version increased with skeletal maturity – the authors noted that the posterior rim increased however recognised that this may have to do with the inability to detect the cartilage posteriorly. A recent MRI-based study, with MRIs performed at the 1-year interval of various developmental stages, showed that the acetabular version increases around adolescence, but did not identify how this may occur. Furthermore, none of the above studies accounted for the individual demographic data, the individual’s physical activity, or the femoral-sided anatomy. The aims of this prospective longitudinal study were to determine how 1. Acetabular version and 2. Coverage to the femoral head the acetabulum provides change during the adolescent years. Furthermore, we aimed to determine whether patient factors (BMI, activity levels) or the femoral-sided anatomy contribute to any of the changes observed. METHODS: 19 volunteers (38 hips) were recruited. The mean age of the cohort was 10.5±1.3 years old and 10 patients were female (52%). The volunteers underwent clinical examination (BMI, range of movement assessment) and a MRI scan of both hips. All participants presented for further clinical examination of both hips and a second MRI scan at an interval of 6 ± 2 years. The mean age at follow-up was 16.6 ±1.3. At the follow-up visit, volunteers were also asked to fill in the HSS Pediatric Functional Activity Brief Scale (Pedi-FABS) questionnaire, which reflects the level of physical activity of each volunteer. Assessments of MRI included the status of the tri-radiate cartilage complex (TCC) (Oxford Classification I – III: open – closed), the acetabular anteversion angle at various levels in the axial plane [5 mm below the roof (top), at the middle of the femoral head (middle) and 3 equidistant slices in-between top and middle]. We measured three acetabular sector angles (anteriorly, posteriorly and superiorly) at the middle of the femoral head, reflecting degree of femoral head coverage by the acetabulum. Alpha angles anteriorly and antero-laterally were determined for each hip for each time-point. Outcome measures included how the anteversion changed at each of the five levels and the mean change overall. We also determined how the sector angles changed over time anteriorly, posteriorly and superiorly. Change in anteversion and sector angles were influenced by the BMI, range of movement measurements, the Pedi-FABS or the alpha angle measurements. RESULTS: At the baseline MRI, all hips had a Grade I (open) TCC; the TCC was Grade III (closed) by follow-up MRI in all of the hips. The acetabular anteversion increased moving, caudally, further away from the roof for both time-points (Figure 1). The mean anteversion increased from a mean of 7.4°±3.8 (initial) to 12.2°±4 (follow-up) (p<0.001). The increase in anteversion was 4.7° (range: 0 – 9). The increase in version occurred along all slices, but was greater at the rostral ¼ of the acetabulum (slices 1 and 2); 8/38 the hips had retroversion of the rostral ¼ of the acetabulum at the initial scan, whilst none of the hips had retroversion at follow-up. Females had greater anteversion than males (13.2° Vs 10.6°, p=0.04), however the change that occurred between scans was the same (4.6° Vs 5.0°; p=0.9). The anterior sector angle reduced from 72°±8 to 65°±8 (p=0.002); the posterior sector angle remained unchanged (98°±5° Vs. 97°±5) (p=0.8), whilst the superior sector angle slightly increased from 121°±4 to 124°±5° (p=0.007). The change in the anterior sector angle correlated with the change in version (rho=0.5, p=0.02). The change in version did not correlate with BMI, ROM, Pedi-FABS score or the measured alpha angles of the hip (p=0.1 – 0.6). DISCUSSION: The native acetabulum orientation changes around adolescence, with the version significantly increasing. The version increases as a result of a reduction of the femoral head coverage anteriorly (rather than an increase in posterior femoral head coverage). Therefore, if the normal developmental change did not occur, the associated retroversion would be related to anterior wall over-coverage rather than posterior deficiency. We identified no patient factors (BMI, activity level, range of movement) or proximal femoral anatomical factors (alpha angles) that were associated with this change. The increase in acetabular version may be related with the reduction in femoral version that occurs over the same period and hence further study is necessary.

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