Effect of pelvic tilt on acetabular retroversion: a study of pelves from cadavers

Anatomical landmarks for acetabular abduction in adult hips: the teardrop vs. the inferior acetabular rim

PURPOSE

The purpose of this study is to compare the acetabular teardrop (the structure located inferomedially in the acetabulum, just superior to the obturator foramen. The medial lip is the interior, and the lateral lip is the exterior of the acetabular wall) with the inferior acetabular rim as anatomical landmarks to measure the acetabular abduction angle (AAD) using coronal CT images from different levels.

METHODS

Our retrospective study included 120 pelvic CT scans from patients with non-orthopedic pathologies or stress fractures of the proximal femur. The patients included 60 females with a mean age of 48 years (range 40-66) and 60 males with a mean age of 46 years (range 38-65). Each AAD was measured using coronal plane CT slices from five levels: AAD (+ 10) (10 mm anterior to the femoral head center), AAD (+ 5) (5 mm anterior to the femoral head center), AAD (0) (through the femoral head center), AAD (- 5) (5 mm posterior to the femoral head center), and AAD (- 10) (10 mm posterior to the femoral head center). The measurements were then divided into two groups: teardrop-based AADs [AAD (+ 10), AAD (+ 5), and AAD (0)] and rim-based AADs [AAD (- 5) and AAD (- 10)].

RESULTS

There were no mean significant differences in AAD within the groups, whereas the difference between the groups was significant. The mean teardrop-based AAD was quite significantly different from the mean rim-based AAD due to the use of different anatomical landmarks. Teardrop-based AADs are lower than rim-based AADs, leading to measurement differences of more than 10°.

CONCLUSIONS

AAD measurements considering the inferior acetabular rim can be more accurate than those considering the acetabular teardrop because the inferior rim represents the nearly hemispheric acetabulum better than does the teardrop. It is recommended to differentiate between the teardrop and the inferior acetabular rim when measuring AAD to avoid confusion regarding acetabular abduction.

Correlation between the distance from the pubic symphysis to the sacrum with pelvic incidence

INTRODUCTION

The distance between the pubic symphysis and sacrococcygeal joint has been noted as an important parameter in evaluating pelvic tilt in an anteroposterior (AP) radiograph. Similarly, pelvic incidence measures the sagittal balance of the pelvis and is influenced by pelvic rotation. The relationship between these 2 parameters is unknown and could affect interpretation of pelvic AP radiographs.

METHODS

We reconstructed 248 cadaveric pelvises. Pelvic incidence was measured using a previously validated method. Pubic symphysis-sacrococcygeal joint (PSS) height was measured from the superior pubic tubercle to the sacrococcygeal joint. The pelvises were positioned so that the anterior pelvis lay flush with the surface. A ruler was zeroed on the pubic tubercles and a transverse projecting laser was used to measure the height to the sacrococcygeal joint.

RESULTS

A total of 248 pelvises were reconstructed. Average age of death of the specimens was 33±6.0 years. 80% of the pelvises were male, 56% were Caucasian, and 44% African American. The mean PSS height was 2.2 ± 1.4 cm and mean PI was 44.3° ± 10.6°. Multiple regression analysis found PI and PSS height were not correlated (p = 0.144). Females had a larger PSS height than males (beta = 1.17, p < 0.001) and African Americans a larger PSS height than Caucasians (beta = 0.63, p < 0.001).

CONCLUSIONS

This study provides useful information for clinicians in evaluating AP radiographs of the pelvis in that it supports the use of PSS height to judge the adequacy of a radiograph even in the context of abnormal pelvic incidence.

Femoroacetabular impingement is more common in military veterans with end-stage hip osteoarthritis than civilian patients: a retrospective case control study

BACKGROUND

The purpose of this study was to compare the frequency of femoroacetabular impingement (FAI) between matched groups of military veterans and civilian patients with end-stage hip osteoarthritis (OA).

METHODS

Patients who underwent a primary total hip arthroplasty (THA) between January 1, 2015 and December 31, 2015 at a single Veteran's Affairs Hospital were identified. Veterans were then matched 1:2 with civilian patients from our prospective outcome registry. The alpha angle and lateral center-edge angle (LCEA) were measured by a single evaluator. Independent t-tests were used to compare joint angles, and Fisher exact tests were used to compare the prevalence of cam (alpha angle ≥60°), pincer (LCEA ≥40°), or mixed-type pathologies.

RESULTS

Twenty-one veterans were matched 1:2 with civilian patients. The mean alpha angle did not significantly differ between groups (P = 0.33) nor did the prevalence of cam deformities (P = 0.79). The LCEAs were significantly greater in veterans than in civilians (P = 0.04), and veterans also demonstrated a significantly greater prevalence of pincer and mixed-type deformities than civilians (P = 0.025 and P = 0.004, respectively).

CONCLUSION

These results suggest that FAI is perhaps a more common mechanism in the progression of OA in a veteran population than in a civilian population, as pincer and mixed-type deformities were significantly more common among veterans than civilians. The forces borne by the hip during military training exceed normal physiologic conditions. In addition, the time between symptom onset and surgical correction may be 10-12 months longer for active military personnel than for civilians. The combination of increased physical demands and a protracted time to treatment highlights the need for better recognition of FAI in military members. Future studies are necessary to determine whether earlier intervention may prevent or delay the progression to end-stage OA and the need for total hip arthroplasty.

Interobserver and intraobserver reliability of a new radiological classification for femoroacetabular impingement syndrome

PURPOSE

Radiological evaluation of femoroacetabular impingement is based on single-plane parameters such as the alpha angle or the center edge angle, or complex software reconstruction. A new simple classification for cam and pincer morphologies, based on a two-plane radiological evaluation, is presented in this study. The determination of the intraobserver and interobserver reliability of this new classification is the purpose of this study.

METHODS

We retrospectively reviewed the three-view hip study in patient undergoing hip arthroscopy for FAI syndrome between October 2015 and April 2016. Any case having protrusio acetabuli, coxa profunda or which has undergone previous osteotomic surgery was excluded. Five observers used our proposed classification to identify three different stages for the cam and pincer morphologies. Inter- and intraobserver agreement of classification was determined using average pairwise Cohen's kappa coefficient.

RESULTS

The interobserver agreement for the pincer and cam morphologies was excellent. For the pincer morphology classification, the average Kappa agreement was 0.838 (range 0.764-0.944). For the cam morphology, the average pairwise Cohen's kappa coefficient was 0.846 (range 0.734-0.929). The intraobserver agreement was excellent as well. The average percent pairwise agreement was 0.870 and 0.845 for pincer and cam type, respectively.

CONCLUSIONS

The new classification system shows excellent levels of inter- and intraobserver agreement for both deformities. This classification is demonstrated to be a useful tool in planning hip arthroscopy. Further studies are needed to correlate the classification itself with specific intraoperative findings.

Variation in pelvic radiography practice: Why can we not standardise image acquisition techniques?

INTRODUCTION

Pelvic radiographs remain an essential investigation in orthopaedic practice. Although it is recognised that acquisition techniques can affect image appearances and measurement accuracy, it remains unclear what variation in practice exists and what impact this could have on decision making.

METHOD

This was a cross sectional survey of UK radiology departments utilising an electronic tool. An introductory letter and link was distributed. Responses were received from 69 unique hospital sites within the specified timeframe, a response rate of 37.9%.

RESULTS

There was no consistent technique for the positioning of patients for pelvic radiographs. The distance varied between 90 and 115 cm and 10 different centering points were described. In relation to leg position, the feet are usually internally rotated (65 of 69 [94.2%]). Only 1 teaching hospital (1 of 69 [1.4%]) uses a weight-bearing position as standard. Orthopaedic calibration devices were not in routine use, with only 21 using on pelvic x-rays (30.4%). Further, the type of device and application criteria were inconsistent.

CONCLUSIONS

To our knowledge this is the first study to directly compare radiographic positioning across hospital sites. Our data demonstrated marked variation in technique for pelvis radiographs with associated implications for clinical decision making. Research is required to determine the standard technique and quality outcome measures to provide confidence in diagnostic interpretation particularly for serial radiographs.

"Simple mechanical devices did not improve pelvis positioning in AP pelvis radiographs for reliable assessment of the acetabular orientation"

BACKGROUND

The aim of this study was to develop two simple positioning devices for anteroposterior pelvis radiographs and to evaluate their effect on accuracy of the radiographs for assessment of the acetabular orientation compared with non-instrumented positioning.

METHODS

The superior anterior iliac spines and the pubic symphysis were used as anatomical landmarks to obtain a horizontal orientation of the pelvis according to the anterior pelvic plane. Anteroposterior pelvis radiographs were taken of 11 human cadaveric pelvic bones with each of the positioning devices and without any device. Defined measurements were carried out to objectify the tilt and rotation of the pelvis and to assess the cross-over sign as well as the presence of the ischial spine sign. Computed tomography scans were performed as a standard of reference. Bland-Altman-Plots were used to compare the continuous measurement values and Cohen's Kappa was applied for the categorical data. Intra- and inter-observer reliability was determined by the intraclass correlation coefficient and Cohen's Kappa.

RESULTS

The mean values of the measurements showed a high variability. A low correlation of the measurement values was found between the radiographs of the different positioning methods and the computed tomography scans. The intra- and inter-observer reliability was good (Cohen's Kappa 0.78 and 0.69; intraclass correlation coefficient 0.99 and 0.98).

CONCLUSION

The use of positioning devices did not lead to more accurate anteroposterior pelvis radiographs compared to non-instrumented positioning. Simple positioning devices do not provide standardized anteroposterior pelvis radiographs for reliable assessment of the acetabular orientation.

Hip Radiograph Findings in Patients Aged 40 Years and Under with Posterior Pelvic Pain

BACKGROUND

Several sacroiliac joint (SIJ) provocative tests used to assess posterior pelvic pain involve moving and stressing the hip. It is unknown if there is a subgroup of patients with posterior pelvic pain who have underlying hip deformity that could potentially influence performance and interpretation of these tests.

OBJECTIVE

To describe the prevalence of radiographic hip deformity and hip osteoarthritis in a group of adults 40 years old and under who met the clinical diagnostic criteria for treatment of posterior pelvic pain with an image guided intra-articular SIJ injection.

DESIGN

Retrospective cohort study.

SETTING

Tertiary university orthopedic department PATIENTS (OR PARTICIPANTS): One hundred and forty-eight patients were evaluated (83% (123/148) female; mean age 31.3 ± 6.2 years). All had completed a trial of comprehensive noninvasive treatment for posterior pelvic pain and had a minimum of three positive SIJ provocative tests on physical examination.

METHODS

Retrospective review identified patients undergoing SIJ injection for pain recommended and performed by seven physiatrists between 2011 and 2017. Hip radiographs were read by a physician with expertise in hip measurements with previously demonstrated excellent intrarater reliability.

MAIN OUTCOME MEASUREMENTS

Percentage of patients with hip deformity findings.

RESULTS

No patients meeting the inclusion criteria had significant radiographic hip osteoarthritis (Tonnis ≥2 indicating moderate or greater radiographic hip osteoarthritis) and 4/148 (3%) were found to have mild radiographic hip osteoarthritis. Prearthritic hip disorders were identified in 123 (83%, 95% CI: 76, 89%) patients. For those patients with prearthritic hip disorders, measurements consistent with femoroacetabular impingement (FAI) were seen in 61 (41%) patients, acetabular dysplasia in 49 (33%) patients, and acetabular retroversion in 85 (57%) patients. Acetabular retroversion was identified in 43% (crossover sign) and 39% (prominent ischial spine) of patients.

CONCLUSIONS

Approximately 57% of adult patients under the age of 40 years with the clinical symptom complex of SIJ pain were found to have radiographic acetabular retroversion. This is a higher percentage than the 5%-15% found in asymptomatic people in the current literature. Further study is needed to assess links between hip structure, hip motion, and links to pelvic pain including peri and intra-articular SIJ pain.

LEVEL OF EVIDENCE

III.

Do Changes in Pelvic Rotation and Tilt Affect Measurement of the Anterior Center Edge Angle on False Profile Radiographs? A Cadaveric Study

BACKGROUND

The false profile radiograph assesses acetabular coverage in prearthritic hip conditions. Precise rotation of this radiograph is difficult to obtain, so the clinician must interpret radiographs with nonstandard pelvic rotation or tilt, despite limited evidence of how this may affect the anterior center edge angle measurement.

QUESTIONS/PURPOSES

(1) Does pelvic rotation alter the measurement of the anterior center edge angle on false profile views? (2) Does pelvic tilt alter the measurement of the anterior center edge angle on false profile views? (3) Is there an objective way to assess appropriate pelvic rotation for the false profile view?

METHODS

Eight cadaver hips (four female, four male; one hip randomly selected per pelvis) were included in the study. Hips with degenerative changes, evidence of previous fracture or trauma, or previous surgical intervention were excluded. Specimens were between 68 to 92 years of age (median, 76 years). The specimens were fixed to a custom jig, and radiographs were taken at 5° intervals of rotation (45-85°) and 5° intervals of pelvic tilt (+10° to -10°). The primary outcome variable, anterior center edge angle, was measured for each rotation and tilt.

RESULTS

Every degree increase in pelvic rotation toward a true lateral resulted in 0.18° increase in the anterior center edge angle (95% confidence interval [CI], 0.07-0.29; p = 0.002). For every degree increase in pelvic tilt, the anterior center edge angle increased 0.65° (95% CI, 0.5-0.8; p < 0.001). We verified that standard pelvic rotation of 65° for a false profile radiograph was present when the space between the femoral heads is 66% to 100% of the diameter of the femoral head being imaged.

CONCLUSIONS

This study shows that the anterior center edge angle increases as pelvic tilt increases, with a 6° increase in anterior center edge angle for each 10° increase in pelvic tilt. Since the false profile radiograph is obtained standing, the patient should be counseled to avoid adopting a forced posture, ensuring the radiograph remains an accurate functional representation of the patient's anatomy. In contrast, pelvic rotation did not influence the anterior center edge angle by an important margin, and while we recommend that radiographs continue to be obtained with standardized pelvic rotation, aberrant pelvic rotation will likely not result in a clinically meaningful difference in anterior center edge angle measurements. In the future, studies to identify the specific regions of acetabular anatomy that constitute the radiographic measurement of the anterior center edge angle would enhance current understanding of the associated radiographic anatomy, and consequently improve the ability of the surgeon to treat the specific area of pathology.

CLINICAL RELEVANCE

In practice, the clinician should pay close attention to pelvic tilt, as a 10° change in tilt may cause 6° of change in the anterior center edge angle. However, false profile radiographs obtained within ± 20° of the targeted 65° of rotation will result in less than 4° change in the anterior center edge angle.

Correlation of radiographic variables to guide safe implant positioning during acetabular surgery and hip replacement: a retrospective observational study

Background

Knowledge of periacetabular anatomy is crucial for prosthetic cup placement in total hip arthroplasty and for screw placement in anterior fixation with acetabular fractures. It is known that degree of hip dysplasia correlates with medial bone stock and that medial bone stock shows a weak correlation to Lequesne’s acetabular index (AI). Aim of this study was to investigate a possible correlation between AI and the newly proposed medial safe zone.

Methods

AI and the medial save zone were measured on 419 hips using a computed-tomography scan of the pelvis. AI was assessed on a 2D reconstructed anterior-posterior view of the pelvis using VOXAR™. Correlation was measured using the Pearson correlation coefficient.

Results

Mean AI was 4.2 degrees (SD 4.9 degrees). Mean medial safe zone was 8.1 mm (SD 1.9 mm). There was a significant correlation between AI and medial save space with a Pearson correlation coefficient r = 0.33 (p = .001).

Conclusion

There is a weak correlation between AI and medial safe zone. AI should not be used to predict medial safe zone. Due to the weakness in correlation AI is not suited for predicting medial safe zone. However, a low or negative AI can be a warning sign for less medial safe zone, prompting surgeons to take care when reaming in THA or placing periacetabular screws.

High frequency of labral pathology in symptomatic borderline dysplasia: a prospective magnetic resonance arthrography study of 99 patients

Labral pathology is seen in both dysplastic and borderline dysplastic hips. Periacetabular osteotomy (PAO) is the treatment of choice for dysplasia. However, some authors have suggested that borderline dysplastic hips with concurrent labral pathology should be treated arthroscopically. The purpose of this study was to investigate the frequency of labral pathology between dysplastic and borderline dysplastic hips, whether centre-edge (CE) angle is associated with labral pathology, and finally if pain and labral pathology are associated. Ninety-nine symptomatic patients (104 hips) scheduled for PAO were examined. Five patients were excluded due to complaints from multiple joints and four failed to show at 2-year follow-up. Five patients did not fill out questionnaires preoperatively. Hips were characterized as dysplastic (CE angle <20°) and borderline dysplastic (CE angle 20° ≤ 25°). A magnetic resonance arthrography was performed, and labral pathology was classified according to the Czerny classification. Association with the CE angle, the acetabular index (AI) and preoperative WOMAC pain score was tested by multiple linear regression. There was no significant difference in frequency of labral pathology when comparing the two groups. Across the cohort, 86 of 99 patients had labral pathology. The CE angle was associated with increasing severity of labral pathology, whereas the AI angle and preoperative pain were not associated with labral pathology. Decreased lateral coverage adversely loads the labrum, predisposing it to tears. We advocate reorienting the biomechanical forces through PAO, not arthroscopic treatment. Level of pain was not associated with labral pathology, suggesting that labral pathology may not alone explain the dysplastic pain complex.

Ptosis of the hip: a new radiographic finding in patients undergoing femoroacetabular osteoplasty

Ptosis is a newly described phenomenon appearing on AP radiographs of patients undergoing femoroacetabular osteoplasty (FAO), and refers to a reverse break down in Shenton’s Line. Thorough characterization of this phenomenon is needed to better understand the hip morphology and pathologic ramifications. Our goal was to define the radiographic hip parameters accompanying a break down in Shenton’s Line and to determine how these values compare with standard values in normal hips. Using two independent readers, we retrospectively reviewed the medical records and preoperative supine radiographs of 630 patients (1260 hips) who underwent FAO by a single surgeon between 2003 and 2016. Prevalence of hip pathology and 28 radiographic parameters in ptosis hips was measured, as well as a comparison between unilateral ptosis hips and contralateral normal hips. Of the 53 patients (106 hips) who fulfilled the criteria for the study, 94 hips had a Shenton’s Line break down of at least 5 mm. Sixty-nine percent of ptosis hips had femoroacetabular impingement (FAI), 70.2% had coxa profunda, and 52.1% had partial joint space narrowing. Ptosis hips had 1.05 mm less lateral subluxation (P = 0.012), 2.28° larger Center-edge angle (P = 0.046), 2.59° smaller Sharp angle (P = 0.011) and 2.49% smaller extrusion index (P = 0.016) compared with contralateral normal hips. FAI is prevalent in patients with a positive ptosis sign. The high prevalence of partial joint space narrowing could suggest eventual osteoarthritis. We believe our results demonstrate the importance of further investigation of a positive ptosis sign on AP pelvic radiographs.

The Berbeo-Sardi Angle (BSA): An Innovative Method to Effectively Estimate Pelvic Retroversion in Anteroposterior Radiographs-A Correlation With Traditional Parameters

STUDY

Design: Diagnostic studies-concordance between diagnostic tests.

OBJECTIVES

The purpose of this study was to develop a novel spinopelvic parameter (Berbeo-Sardi angle [BSA], the angle formed at the intersection of a line that connects the inferior margin of the sacroiliac joint to the midpoint of a horizontal line joining both femoral heads) measurable in anteroposterior radiographs that indirectly estimates pelvic retroversion and correlates with traditional measurements like pelvic tilt (PT).

SUMMARY

Sagittal balance appraisal and surgical planning rely on the interpretation of spinopelvic parameters. An increased PT reflects pelvic retroversion as a compensatory mechanism to limit sagittal imbalance and correlates with increased pain and disability. However, poor imaging techniques and incorrect patient positioning frequently hamper landmark identification in lateral radiographs, and with no measurable angles in anteroposterior radiographs, it is often impossible to determine PT and pelvic retroversion.

METHODS

Whole-spine radiographs from 105 consecutive patients were used to retrospectively measure conventional spinopelvic parameters and the BSA. Intraclass correlation coefficient was used to assess a quantitative correlation between the PT and BSA as indirect measures of pelvic retroversion.

RESULTS

Average values for pelvic incidence, lumbar lordosis, sacral slope, PT, and BSA were 46.5° (±10.23), 48.56° (±12.30), 29.97° (±9.77), 16.94° (±8.03), and 54.47° (±4.05), respectively. We encountered a moderately strong correlation (r = -0.66) between PT and BSA. Receiver operating characteristic plot analysis revealed that a BSA threshold of 46° has a sensitivity of 90% to identify pathologic PT values (>20°), whereas a BSA ≥60° has a specificity of 90% to rule out pelvic retroversion using anteroposterior radiographs.

CONCLUSIONS

There is a moderately strong correlation between the BSA, an innovative spinopelvic parameter measurable in anteroposterior radiographs, and PT. BSA seems to show great promise in simplifying spinopelvic appraisal by easily estimating pelvic retroversion associated with sagittal imbalance, while avoiding image-quality issues often encountered in lateral radiographs.

LEVEL OF EVIDENCE

Level III.

Acetabular retroversion: Diagnosis and treatment

Acetabular retroversion (AR) consists of a malorientation of the acetabulum in the sagittal plane. AR is associated with changes in load transmission across the hip, being a risk factor for early osteoarthrosis. The pathophysiological basis of AR is an anterior acetabular hyper-coverage and an overall pelvic rotation.

The delay or the non-diagnosis of AR could have an impact in the overall management of femoroacetabular impingement (FAI). AR is a subtype of (focal) pincer deformity.

The objective of this review was to clarify the pathophysiological, diagnosis and treatment fundaments inherent to AR, using a current literature review.

Radiographic evaluation is paramount in AR: the cross-over, the posterior wall and ischial spine signs are classic radiographic signs of AR. However, computed tomography (CT) evaluation permits a three-dimensional characterization of the deformity, being more reliable in its recognition.

Acetabular rim trimming (ART) and periacetabular osteotomy (PAO) are the best described surgical options for the treatment of AR.

The clinical outcomes of both techniques are dependent on the correct characterization of existing lesions and adequate selection of patients.

Cite this article: EFORT Open Rev 2018;3:595-603. DOI: 10.1302/2058-5241.3.180015

Anterior Inferior Iliac Spine Morphology: Comparison of Symptomatic Hips With Femoroacetabular Impingement and Asymptomatic Hips

OBJECTIVE

The objective of our study was to compare anterior inferior iliac spine (AIIS) morphology in symptomatic hips with femoroacetabular impingement (FAI) and in asymptomatic hips, determine the prevalence of impingement morphology in patients with a radiographic "crossover" sign, and identify potential risk factors for having impingement morphology.

MATERIALS AND METHODS

For this retrospective study, we identified consecutive symptomatic hips with FAI (n = 54) and asymptomatic hips (n = 35) in patients who underwent CT from 2015 to 2017. Two radiologists blindly and independently evaluated 3D CT images of each hip and graded the AIIS morphology according to the Hetsroni classification scheme. The prevalence of AIIS morphology types was calculated. Associations of AIIS morphology types with symptoms and the crossover sign were evaluated with a chi-square test. A multivariable logistic regression determined risk factors for abnormal AIIS morphology (i.e., type 2 or 3).

RESULTS

There was no difference in the prevalence of AIIS morphology types for symptomatic hips with FAI versus asymptomatic hips (p = 0.44) or for hips with a positive versus those with a negative crossover sign (p = 0.21). There was moderate interobserver agreement (κ = 0.44) and good-to-excellent intraobserver agreement (κ = 0.67 and 0.90) for grading AIIS morphology. Age, sex, femoral version, acetabular version, alpha angle, lateral center edge angle, and the crossover sign were not significant risk factors for abnormal AIIS morphology in patients with FAI (p = 0.11-0.79).

CONCLUSION

There is no difference in AIIS morphology between symptomatic hips with FAI versus asymptomatic hips or between hips with and those without the radiographic crossover sign. Age, sex, and other FAI parameters are not risk factors for developing AIIS impingement morphology.

Variability of Pelvic Orientation in the Lateral Decubitus Position: Are External Alignment Guides Trustworthy?

BACKGROUND

The position of the acetabular component in total hip arthroplasty (THA) is critical for success. However, this remains the most variable aspect of the surgery. We hypothesized that there is wide variation in pelvic orientation in the lateral decubitus position. We sought to determine the variability in pelvic positioning and the frequency of pelvic malposition during THA in lateral decubitus with regard to pelvic tilt and pelvic rotation.

METHODS

We analyzed preoperative standing and intraoperative anteroposterior pelvis X-rays in 248 consecutive THAs performed in lateral decubitus by one surgeon. Pelvic tilt and rotation were determined for preoperative and intraoperative X-rays. Proper intraoperative positioning was defined as less than 10° change in tilt or rotation between preoperative and intraoperative X-rays.

RESULTS

With regard to pelvic tilt, the intraoperative position was proper in 188 (76%) cases. There was a pelvic tilt discrepancy of 10°-20° in 43 (17.5%) cases and greater than 20° in 16 (6.5%) patients. With regard to pelvic rotation, the intraoperative position was proper in 202 (81%) cases. There was a pelvic rotation discrepancy of 10°-20° in 38 (15.4%) cases and greater than 20° in 7 (2.8%) cases. In 248 cases, only 154 (62.1%) had intraoperative positioning within 10° of preoperative tilt and axial rotation. Pelvic malposition occurred in 38% of cases overall.

CONCLUSION

There is wide variation in pelvic orientation in lateral decubitus and frequent discrepancy in pelvic tilt and rotation between preoperative and intraoperative anteroposterior X-rays. Anatomic landmarks should be used to guide acetabular component positioning.

LEVEL OF EVIDENCE III

Diagnostic.

Acetabular morphology in slipped capital femoral epiphysis: comparison at treatment onset and skeletal maturity

PURPOSE

To investigate changes in acetabular morphology during the follow-up of slipped capital femoral epiphysis (SCFE) and search for factors associated with acetabular dysplasia at skeletal maturity.

METHODS

We evaluated 108 patients with unilateral SCFE (mean age at slip, 12.3 years sd 1.7) to skeletal maturity, with a minimum follow-up of two years (median 4.5 years; interquartile range 3.2 to 6.2). Acetabular parameters obtained from initial and most recent radiographs included the lateral centre-edge angle (LCEA), Tönnis angle (TA) and acetabular depth-width ratio (ADR). Acetabular dysplasia was considered for LCEA < 20° or TA > 10°. Femoral parameters consisted of the most recent head diameter, neck-shaft angle, neck length, articulotrochanteric distance and alpha angle.

RESULTS

At SCFE onset, the affected hip showed a slightly lower LCEA (26.4° sd 6.1° versus 27.3° sd 5.7°; p = 0.01) and ADR (330 sd 30 versus 340 sd 30; p < 0.001) compared with the uninvolved hip. At final follow-up, the affected hip showed lower LCEA (24.5° sd 7.6° versus 28.8°sd 6.6°; p < 0.001) and ADR (330 sd 40 versus 350 sd 40; p < 0.001), and TA was larger (5.5° sd 5.4° versus 2.3° sd 4.2°; p < 0.001) compared with the uninvolved hip. Acetabular dysplasia was observed in 27 (25%) of 108 hips with SCFE. Femoral head overgrowth, age at slip and SCFE severity were independent factors associated with acetabular dysplasia (p < 0.05).

CONCLUSION

Acetabular coverage and depth are not increased in SCFE, and the acetabular coverage tends to decrease up to skeletal maturity. A potential disturbance in the acetabular growth and remodelling exists mainly for young children with severe SCFE, and a potential for acetabular insufficiency may be observed at the diagnosis and follow-up of SCFE.

LEVEL OF EVIDENCE

Prognostic Level IV.

Pinnacle polyethylene liner dissociation: a report of 3 cases

We describe 3 cases of DePuy Pinnacle polyethylene dissociations, their presentations, and treatment. A 34-year-old female with arthritis secondary to dysplasia, a 51-year-old male with avascular necrosis of the femoral head, and a 57-year-old female with osteoarthritis were treated with total hip arthroplasty. Acute nontraumatic polyethylene liner dissociations occurred at 31, 42, and 2 months postoperatively. They were treated with component retention and modular femoral head and liner revision. The 51-year-old male subsequently developed a prosthetic joint infection requiring explant of his components. Although dissociation of polyethylene liners from the DePuy Pinnacle acetabular components is an uncommon complication, this problem may increase in prevalence with longer term follow-up, and vigilance is recommended.

Hemi-pelvic slope is correlated with the acetabular depth in adults-a radiological study

OBJECTIVE

The purpose of this study was to determine if there is an anatomic relationship between pelvic geometry and acetabular depth.

MATERIALS AND METHODS

One hundred and fifty-one anteroposterior pelvic radiographs (157 hip joints) were selected and analyzed in a retrospective fashion. Six parameters, including iliac offset, ischial offset, acetabular offset, pelvic height, center-edge (CE) angle of Wiberg, and acetabular index (AI) angle of Tönnis were measured for each of the hip joints. Based on the defined variables, three formulas (formulas 1, 2, and 3) were calculated to represent the hemi-pelvis slope.

RESULTS

There was a strong relationship between the hemi-pelvis slope and probability of acetabular dysplasia. Wider upper pelvis was associated with deeper acetabulum and wider lower pelvis was associated with dysplastic acetabulum.

CONCLUSIONS

Pelvic anatomic dimensions and the relationship between them are strongly correlated with hip dysplasia indices. Dysplastic hips tend to be found in pelvises with lower slope (low width of the upper pelvis at the level of iliac crest and high width of the lower part at the level of ischium).

Correct Assessment of Acetabular Component Orientation in Total Hip Arthroplasty From Plane Radiographs

BACKGROUND

Correct positioning of the cup is an important factor in total hip arthroplasty. Assessing its position from a plain anteroposterior pelvic radiograph is known to be hampered by systemic errors. This study focuses on developing a correction method to adjust for these potential sources of error and to eliminate them based on a 3D geometric analysis.

METHODS

Computed tomography scans of 113 (66 male, 47 female) pelvices were reconstructed and virtually projected onto a plain radiograph with varying rotational and translational positions. Thus cup inclination and anteversion as measured on a 2D-radiograph and in the 3D environment were correlated. Projected offset of the symphysis from the mid-sacrum served as a mean to measure pelvic right/left-rotation. Pelvic tilt was determined from the projected height of the contour of the small pelvis. Correction formulas were verified by projecting a gimbal-mounted artificial pelvis with a cup implanted in a known position.

RESULTS

We found gender-specific formulas that correct for malrotated and off-centered radiographs. Applying these formulas cup inclination was assessed as close as 1.3° (±1.90°) to the true 3D value and cup anteversion as close as 1° (±1.91°) although deviations between directly measured plain values and corrected values rose up to 18°.

CONCLUSION

Inherent effects of central projection and malrotations due to pelvic tilt, pelvic rotation, and noncentered radiographs are corrected. Evaluation of radiographic inclination and anteversion of acetabular cups from plain 2D-radiographs show improved precision. Real values are approached better than 1.3° when applying our correction formulas.

Validation of CT image-based software for three-dimensional measurement of acetabular coverage profile

BACKGROUND

Plain radiography, 2-dimensional (2D) magnetic resonance imaging (MRI), and computed tomography (CT) do not precisely display morphology and acetabular coverage in developmental dysplasia of the hip or pincer-type femoroacetabular impingement. Pelvic position and pelvic tilt affect assessment of the acetabular parameters, leading to misinterpretation.

OBJECTIVE

We tested a 3-dimensional (3D) CT evaluation script to calculate the crossover sign (COS), acetabular coverage and morphology.

METHODS

To test the method, we constructed a phantom pelvic model, in which the acetabulum was mounted at different coverages of the femoral head, and simulated a COS and the acetabular morphology. Additionally we examined the reliability and objectivity of this method in ten patients with CT scans of the pelvis for conditions unrelated to hip disorders.

RESULTS

We obtained an average accuracy of the 3D CT evaluation script of -0.37∘ (range -3.84 to 3.88; SD ± 1.43) for morphology, and 0.002% (range -7.28% to 6.90%; SD ± 1.60%) for coverage of the femoral head. Significant correlation between the expected and calculated COS (p= 0.01) was found.

CONCLUSIONS

Our 3D CT evaluation script permits precise evaluation of the acetabular coverage profile, the presence or absence of a COS and acetabular morphology, independent of patient positioning or pelvic tilt.

The influence of patient factors on femoral rotation after total hip arthroplasty

Background

A postoperative change in femoral rotation following total hip arthroplasty (THA) might be the cause of dislocation due to the change in combined anteversion. However, very few studies have evaluated the femoral rotation angle following THA, or the factors that influence femoral rotation. We aimed to evaluate changes in femoral rotation after THA, and to investigate preoperative patient factors that influence femoral rotation after THA.

Methods

This study involved 211 hips treated with primary THA. We used computed tomography to measure the femoral rotation angle before and one week after THA. In addition, multiple regression analysis was performed to evaluate preoperative patient factors that could influence femoral rotation after THA.

Results

The femoral rotation angle was 0.2 ± 14° externally before surgery and 4.4 ± 12° internally after surgery (p < 0.001). Multiple regression analysis revealed that sex (β = 0.19; p = 0.003), age (β = 0.15; p = 0.017), preoperative anatomical femoral anteversion (β = − 0.25; p = 0.002), and preoperative femoral rotation angle (β = 0.36; p < 0.001) were significantly associated with the postoperative femoral rotation angle. The final model of the regression formula was described by the following equation: [postoperative femoral rotation angle = 5.41 × sex (female: 0, male: 1) + 0.15 × age - 0.22 × preoperative anatomical femoral anteversion + 0.33 × preoperative femoral rotation angle - 10.1].

Conclusion

The current study showed the mean internal change of 4.6° in the femoral rotation angle one week after THA. Sex, age, preoperative anatomical femoral anteversion and preoperative femoral rotation were associated with postoperative femoral rotation. The patients who were male, older, and who exhibited lesser preoperative anatomical femoral anteversion or greater preoperative femoral rotation angles, tended to demonstrate an externally rotated femur after THA. Conversely, patients who were female, younger, and who exhibited greater preoperative anatomical femoral anteversion or lesser preoperative femoral rotation angles, tended to demonstrate an internal rotation of the femur after THA.

Is anatomic acetabular orientation related to pelvic morphology? CT analysis of 150 healthy pelvises

BACKGROUND

Links between sagittal spinal alignment and acetabular orientation attract considerable research attention with the goal of optimising prosthetic cup position. However, whether pelvic incidence (PI) is related to anatomic acetabular orientation remains unknown. We therefore conducted a radiological study with the following objectives: to look for correlations between PI and anatomic acetabular parameters; to describe the sacro-pubic angle (SPA), defined by fixed bony pelvic landmarks, and its relations with acetabular anteversion; and to determine whether anatomical parameters (PI and SPA) correlate with demographic characteristics.

HYPOTHESIS

PI correlates with anatomical acetabular parameters.

MATERIALS AND METHODS

We conducted a computed tomography (CT) study of the pelvises of 150 patients free of degenerative disease. Three parameters were measured: anatomic acetabular orientation in the Lewinnek reference plane, PI, and the SPA subtended by the line connecting the midpoint of the sacral endplate to the pubic symphysis and the anterior pelvic plane. Statistical tests were performed to look for correlations among these parameters.

RESULTS

Intra-observer and inter-observer reproducibility was considered highly satisfactory (inter-class correlation coefficient, >86% and >82%, respectively). Mean PI was 58.6°±10.2° (range, 32.8°-97.6°), with no significant differences between genders or across age groups. Mean SPA was 34.7°±5.5° (range, 18.3°-49.8°). Mean anatomic acetabular anteversion (AAA) was greater in females (23.4°; range, 11.5°-34.5°) than in males (20°; range, 7.5°-34.5°) (P<0.001). PI did not correlate with any of the acetabular parameters (PI/AAA, r=0.8 and P=0.33; PI/acetabular inclination on the horizontal, r=-0.96 and P=0.24). SPA correlated significantly with both PI (r=0.33 and P<0.001) and AAA (r=0.33 and P<0.001).

DISCUSSION

This CT study of normal pelvises showed that AAA was significantly greater in females and that SPA correlated significantly with both PI and acetabular anteversion. SPA could serve to define the "theoretical" AAA of each individual patient and could thus be incorporated into surgical planning protocols or intra-operative guidance methods for hip replacement surgery.

LEVEL OF EVIDENCE

IV, retrospective study with no control group.

Impact of vertical and horizontal malrotation on measurements of anteroposterior radiographs of the scapula: need for standardized images in modern omometry

BACKGROUND

An increasing number of parameters measured on anteroposterior radiographs are used for the evaluation of the bony geometry of the scapula. Inhomogeneous acquisition of images is common because of the lack of standardization in radiographic positioning. Images with malrotation around the horizontal axis of the scapula are particularly frequent. We hypothesized that malrotated images would result in large variations in measured radiographic parameters and that image standardization using qualitative and semiquantitative "omometric" criteria would decrease these variations in measurements. "Omometry" is a newly introduced umbrella term that contains all standardized measurements on plain radiographs of the shoulder, analogous to the term "coxometry," which is widely used for the radiographic assessment of the osseous pelvis and hip.

METHODS

In this experimental, cadaveric radiographic study, 7 dry-bone human scapula cadaveric specimens from anonymous donors were used to obtain 210 radiographs. We incrementally rotated (steps of 3°) every scapula around its horizontal and vertical axis, with a total range of 42° per each axis. Then, we measured 5 radiographic parameters on every image and observed their change with malrotation. Furthermore, we introduced 4 omometric criteria defining an appropriate (presence of ≥3 criteria) radiographic image to improve standardization of scapular image acquisition.

RESULTS

Overall, measured values remained stable within a narrow range of ±9° of malrotation. Beyond this range, values of all parameters significantly deviated (>±2°) from the initial value. Measurements on appropriate images were significantly less prone to deviation. Within the appropriate images, those with 4 criteria showed a higher specificity than those with 3 criteria.

CONCLUSION

There is significant variation in values of measured radiographic parameters on anteroposterior radiographs of the scapula with substantially malrotated images. With the use of the 4 newly introduced semiquantitative and qualitative omometric criteria, which define an appropriate image, reliability of the measured parameters can be significantly improved.

Prevalence and morphological features of acetabular dysplasia with coexisting femoroacetabular impingement-related findings in a Japanese population: a computed tomography-based cross-sectional study

The coexistence of acetabular dysplasia (AD) and femoroacetabular impingement (FAI) has not been well discussed. This study was performed to elucidate the prevalence and morphological features of AD with coexisting FAI-related findings in a Japanese population. Computed tomography images were retrospectively evaluated. AD was classified as definite or borderline. The morphological findings that defined cam deformity were an α angle of ≥55°, head–neck offset ratio (HNOR) of <0.13, pistol grip deformity positivity and herniation pit positivity. The morphological findings that defined pincer deformity were acetabular index of ≤0° and a retroverted acetabulum. In total, 128 hips (male, 64; female, 64) were analyzed. The prevalence of coexistence of AD and FAI-related findings was detected in 23.4% of hips (definite AD and FAI, 7.8%; borderline AD and FAI, 15.6%). The percentages of hips with AD containing cam or pincer deformities among all were 54.3% and 4.3%, respectively. The percentage of AD with coexisting cam and that of AD with coexisting combined deformities was significantly higher in men, respectively. On the other hand, the most major morphological feature of FAI detected in hips with AD was a HNOR of <0.13. The coexistence of AD and FAI-related findings was common in a Japanese population, and 65.2% of hips with AD had some FAI-related findings. In discussing and managing AD, we recommend paying attention to the coexistence with FAI-related findings, especially in men and in borderline AD. In such hips, the most notable parameter as a morphological feature of FAI is a reduced HNOR.

Pelvic Tilt Displacement Before and After Artificial Hip Joint Replacement Surgery

BACKGROUND

Prediction of pelvic displacement before total hip arthroplasty (THA) is important for accurate acetabular implant placement. This study aimed to evaluate the effect of contralateral joint conditions on pelvic displacement after THA.

METHODS

A total of 355 cases that underwent computed tomography before and after THA for osteoarthritis due to developmental dysplasia were assessed. The pelvic plane was based on preoperative and postoperative day 1 computed tomography images. The displacement in the anteversion direction was expressed as +. Subjects with a minimal joint space <2 mm in the contralateral hip joint were in group N; subjects with ≥2 mm were in group W; subjects with THA were in group P; and subjects who underwent THA simultaneously on both sides were in group B. The Bartlett test was used when conducting the equal variance test among the groups. The F test was used for pairwise comparison. A P value <.01 was considered statistically significant.

RESULTS

Groups N, W, P, and B had 49, 227, 55, and 24 cases, respectively, and their displacements were -0.2° ± 2.7°, 0.8° ± 3.9°, 0.5° ± 2.6°, and 1.1° ± 4.0°, respectively; the variance between the groups was significantly different (P = .0001). The differences between groups W and N (P = .0020), between groups W and P (P = .0003), and between groups P and B (P = .0086) were statistically significant.

CONCLUSION

When the contralateral joint space is wide, the variance of the displacement is high. The contralateral joint affects pelvic displacement.

Digital Radiography in Total Hip Arthroplasty: Technique and Radiographic Results

BACKGROUND

Obtaining the ideal acetabular cup position in total hip arthroplasty remains a challenge. Advancements in digital radiography and image analysis software allow the assessment of the cup position during the surgical procedure. This study describes a validated technique for evaluating cup position during total hip arthroplasty using digital radiography.

METHODS

Three hundred and sixty-nine consecutive patients undergoing total hip arthroplasty were prospectively enrolled. Preoperative supine anteroposterior pelvic radiographs were made. Intraoperative anteroposterior pelvic radiographs were made with the patient in the lateral decubitus position. Radiographic beam angle adjustments and operative table adjustments were made to approximate rotation and tilt of the preoperative radiograph. The target for cup position was 30° to 50° abduction and 15° to 35° anteversion. Intraoperative radiographic measurements were calculated and final cup position was determined after strict impingement and range-of-motion testing. Postoperative anteroposterior pelvic radiographs were made. Two independent observers remeasured all abduction and anteversion angles.

RESULTS

Of the cups, 97.8% were placed within 30° to 50° of abduction, with a mean angle (and standard deviation) of 39.5° ± 4.6°. The 2.2% of cups placed outside the target zone were placed so purposefully on the basis of intraoperative range-of-motion testing and patient factors, and 97.6% of cups were placed between 15° and 35° of anteversion, with a mean angle of 26.6° ± 4.7°. Twenty-eight percent of cups were repositioned on the basis of intraoperative measurements. Subluxation during range-of-motion testing occurred in 3% of hips despite acceptable measurements, necessitating cup repositioning. There was 1 early anterior dislocation.

CONCLUSIONS

Placing the acetabular component within a target range is a critical component to minimizing dislocation and polyethylene wear in total hip arthroplasty. Using digital radiography, we positioned the acetabular component in our desired target zone in 97.8% of cases and outside the target zone, purposefully, in 2.2% of cases. When used in conjunction with strict impingement testing, digital radiography allows for predictable cup placement in total hip arthroplasty.

Acetabular overcoverage in the horizontal plane: an underdiagnosed trigger of early hip arthritis. A CT scan study in young adults

INTRODUCTION

Acetabular overcoverage promotes hip osteoarthritis causing a pincer-type femoroacetabular impingement. Acetabular coverage in the horizontal plane is usually poorly defined in imaging studies and may be misdiagnosed. The goal of this study was to analyze the role of acetabular overcoverage measured in the frontal plane and in the horizontal plane by CT scan and to determine its relationship with other anatomic features in the onset of hip arthritis in young adults.

MATERIALS AND METHODS

We compared prospectively CT scans from two groups of adults of 55 years or younger: the patient group (n = 30) consisted of subjects with diagnosis of early hip arthritis (Tönnis Grade I or II) and the control group (n = 31) consisted of subjects with healthy hips. Two independent observers analyzed centre edge angle (CEA), acetabular anteversion angle (AAA), anterior sector acetabular angle (AASA), posterior sector acetabular angle (PASA), horizontal acetabular sector angle (HASA), femoral anteversion angle (FAVA), alpha angle (AA), and Mckibbin Instability Index (MI).

RESULTS

Angles measuring the acetabular coverage on the horizontal plane (AASA, PASA and, HASA) were significantly higher in the patient group (p < 0.001, p = 0.03 and p < 0.001, respectively). Pearson's correlation coefficient showed a positive correlation between CEA and HASA in patients (r = 0.628) and in controls (r = 0.660). However, a high CEA (> 35º) was strongly associated with a high HASA (> 160º) in patients (p = 0.024) but not in controls (p = 0.21), suggesting that pincer should be simultaneously present in the horizontal and frontal plane to trigger hip degeneration. No significant association was detected between a high alpha angle (> 60º) and a high CEA (> 35º suggesting that a mixed pincer-cam aetiology was not prevalent in our series. Multivariate regression analysis showed the most significant predictors of degenerative joint disease were HASA (p = 0.008), AA (p = 0.048) and ASAA (p = 0.004).

CONCLUSIONS

Acetabular overcoverage in the horizontal plane plays an important role in the onset of early hip arthritis. Considering that this condition is usually underdiagnosed, we suggest the anterior sector acetabular angle, the posterior sector acetabular angle, and the horizontal acetabular sector angles be routinely included in decision-making algorithms in hip conservative surgery to better define hips-at-risk of developing early hip osteoarthritis.

Population-based prevalence of multiple radiographically-defined hip morphologies: the Johnston County Osteoarthritis Project

OBJECTIVE

To provide the first prevalence estimates of different radiographic hip morphologies relevant to dysplasia and femoroacetabular impingement in a well-characterized USA population-based cohort.

METHODS

Cross-sectional data were from the baseline examination (1991-1997) of a large population-based prospective longitudinal cohort study (The Johnston County Osteoarthritis Project). HipMorf software (Oxford, UK) was used to assess hip morphology on anteroposterior (AP) pelvis radiographs. Weighted, sex-stratified prevalence estimates and 95% confidence intervals for four key hip morphologies (AP alpha angle, triangular index sign, lateral center edge angle (LCEA), and protrusio acetabula) were derived and further stratified by age, race and body mass index (BMI).

RESULTS

A total of 5192 hips from 2596 individuals were included (31% African American, 43% male, mean age 63 years, mean BMI 29 kg/m²). Cam morphology was seen in more than 25% of men and 10% of women. Mild dysplasia was present in about 1/3 of men and women, while pincer morphology was identified in 7% of men and 10% of women. Femoral side (cam) morphologies were more common and more frequently bilateral among men, while pincer morphologies were more common in women; mixed morphologies were infrequent. African-Americans were more likely to have protrusio acetabula than whites.

CONCLUSION

We report the first population-based prevalence estimates of radiographic hip morphologies relevant to femoroacetabular impingement (FAI) and dysplasia in the USA. These morphologies are very common, with ¼ men and 1/10 women having cam morphology, 1/3 of all adults having mild dysplasia, and 1/15 men and 1/10 women having pincer morphology in at least one hip.

Assessment of the Relationship between Pelvic Tilt and the Sacro-Femoral-Pubic Angle in Middle-Aged and Elderly Asian Individuals

Study Design

Cross-sectional study.

Purpose

The purpose of this study was to evaluate the correlation between pelvic tilt (PT) and the sacro-femoral-pubic (SFP) angle, which is easier to identify than PT, in middle-aged and elderly Asian subjects from the general population.

Overview of Literature

Measuring PT is important in the diagnosis and treatment of adult spinal deformity. However, identifying femoral heads, which are necessary to determine PT, using sagittal radiographs is often difficult.

Methods

Standing coronal and sagittal pelvic radiographs of individuals aged more than 50 years were taken during a local medical examination. The subjects were divided into female, male, and total groups at the time of evaluation. Linear regression analysis was performed to investigate the relationship between PT and the SFP angle, which were obtained from the X-rays.

Results

The present study included 291 subjects. There were no statistically significant differences between the left and right SFP angles, and there was gender difference regarding the SFP angle. However, a gender difference was observed regarding PT. The correlation between PT and the SFP angle was substantiated in each group. Pearson's correlation coefficients between PT and the SFP angle in the total, female, and male groups were 0.696, 0.853, and 0.619, respectively. In the linear regression analysis, PT was calculated as follows: PT=60.1-0.77×(SFP angle) in the total group, PT=62.8-0.80×(SFP angle) in the female group, and PT=51.5-0.64×(SFP angle) in the male group.

Conclusions

A significant correlation between PT and the SFP angle was observed in middle-aged and elderly Asian subjects from the general population.

Preoperative planning for redirective, periacetabular osteotomies

Redirective, periacetabular osteotomies (PAO) represent a group of surgical procedures for treatment of developmental dysplasia of the hip (DDH) in skeletally mature and immature patients. The ultimate goal of all procedures is to reduce symptoms, improve function and delay or prevent progression of osteoarthritis. During the last two decades, the understanding of the underlying pathomechanisms has continuously evolved. This is mainly attributable to the development of the femoroacetabular impingement concept that has increased the awareness of the underlying three-dimensional complexity associated with DDH. With increasing knowledge about the pathobiomechanics of dysplastic hips, diagnostic tools have improved allowing for sophisticated preoperative analyses of the morphological and pathobiomechanical features, and early recognition of degenerative changes, which may alter the long-term outcome. As redirective, PAO are technically demanding procedures, preoperative planning is crucial to avoid intraoperative obstacles and to sufficiently address the patient-specific deformity. Although conventional radiography has been used for decades, it has not lost its primary role in the diagnostic work-up of patients with DDH. Furthermore, an increasing number of modern imaging techniques exists allowing for assessment of early cartilage degeneration (biochemical magnetic resonance imaging) as well as 3D planning and computer-based virtual treatment simulation of PAO. This article reviews the literature with regard to the current concepts of imaging of DDH, preoperative planning and treatment recommendations for redirective, PAO.

High prevalence of acetabular retroversion in asymptomatic adults

Aims

This study sought to establish the prevalence of the cross over sign (COS) and posterior wall sign (PWS) in relation to the anterior pelvic plane (APP) in an asymptomatic population through reliable and accurate 3D-CT based assessment.

Materials and Methods

Data from pelvic CT scans of 100 asymptomatic subjects (200 hips) undertaken for conditions unrelated to disorders of the hip were available for analysis in this study. A previously established 3D analysis method was applied to assess the prevalence of the COS and PWS in relation to the APP.

Results

Of the 200 included hips, 24% (48) presented a positive COS and 5.5% (11) presented a positive PWS. A combination of COS and PWS was observed in 1% (two) of all hips (1%).

Conclusion

The high incidence of acetabular retroversion, determined by the COS, shows that this anatomic configuration may not differ in frequency between asymptomatic individuals and patients with symptomatic femoroacetabular impingement (FAI). Patients presenting with hip pain and evidence of FAI should be subjected to strict diagnostic scrutiny and evaluated in the sum of their clinical and radiological presentation. In our cohort of asymptomatic adults, the COS showed a higher incidence than the PWS or a combined COS/PWS. Cite this article: Bone Joint J 2017;99-B:1584–9.

Hip shape is symmetric, non-dependent on limb dominance and gender-specific: implications for femoroacetabular impingement. A 3D CT analysis in asymptomatic subjects

OBJECTIVE

To determine the reference intervals (RefInt) of the quantitative morphometric parameters of femoroacetabular impingement (FAI) in asymptomatic hips with computed tomography (CT) and determine their dependence on age, side, limb dominance and sex.

METHODS

We prospectively included 590 patients and evaluated 1111 hips with semi-automated CT analysis. We calculated overall, side- and sex-specific parameters for imaging signs of cam [omega and alpha angle (α°)] and pincer-type morphology [acetabular version (ACvers), lateral centre-edge angle (LCEA) and cranio-caudal coverage].

RESULTS

Hip shape was symmetrical and did not depend on limb dominance. The 95% RefInt limits were sex-different for all cam-type parameters and extended beyond current abnormal thresholds. Specifically, the upper limits of RefInt for α° at 12:00, 1:30 and 3:00 o'clock positions were 56°, 70° and 58°, respectively, and 45° for LCEA. Acetabular morphology varied between age groups, with a trend toward an LCEA/ACvers increase over time.

CONCLUSION

Our morphometric measurements can be used to estimate normal hip morphology in asymptomatic individuals. Notably they extended beyond current thresholds used for FAI imaging diagnosis, which was most pronounced for cam-type parameters. We suggest the need to reassess α° RefInt and consider a 60° threshold for the 12:00/3:00 positions and 65-70° for other antero-superior positions.

KEY POINTS

• Hip shape is symmetrical regardless of limb dominance. • Pincer/cam morphology is frequent in asymptomatic subjects (20 and 71%, respectively). • LCEA and acetabular version increases with age (5-7° between opposite age groups). • Femoral morphology is stable after physeal closure (in the absence of pathology). • Alpha and omega angle thresholds should be set according to sex.

Comprehensive Clinical Evaluation of Femoroacetabular Impingement: Part 2, Plain Radiography

The use of hip arthroscopy to treat various forms of hip pathology continues to grow. As part of a standard evaluation for eligibility for hip arthroscopy, we routinely obtain standard radiographs to assess the hip joint. These include orthogonal projections of the acetabulum and proximal femur, which can be obtained with a standing false profile, supine anteroposterior pelvis, and a lateral view of the proximal femur (either Dunn 45° or 90°, frog-leg lateral, or cross-table lateral). A comprehensive analysis of the radiographs is of utmost importance in order to indicate a patient for hip arthroscopy, for preoperative planning, and to determine prognosis. The purpose of this Technical Note is to provide a comprehensive guide of how our group performs qualitative and quantitative analysis of hip radiographs in a potential candidate for hip arthroscopy.

Sports Injuries about the Hip: What the Radiologist Should Know

Injuries of the hip and surrounding structures represent a complex and commonly encountered scenario in athletes, with improper diagnosis serving as a cause of delayed return to play or progression to a more serious injury. As such, radiologists play an essential role in guiding management of athletic injuries. Familiarity with hip anatomy and the advantages and limitations of various imaging modalities is of paramount importance for accurate and timely diagnosis. Magnetic resonance (MR) imaging is often the modality of choice for evaluating many of the injuries discussed, although preliminary evaluation with conventional radiography and use of other imaging modalities such as ultrasonography (US), computed tomography, and bone scintigraphy may be supplementary or preferred in certain situations. Stress fractures, thigh splints, and posterior hip dislocations are important structural injuries to consider in the athlete, initially imaged with radiographs and often best diagnosed with MR imaging. Apophyseal injuries are particularly important to consider in young athletes and may be acute or related to chronic repetitive microtrauma. Femoroacetabular impingement has been implicated in development of labral tears and cartilage abnormalities. Tear of the ligamentum teres is now recognized as a potential cause of hip pain and instability, best evaluated with MR arthrography. Greater trochanteric pain syndrome encompasses a group of conditions leading to lateral hip pain, with US playing an increasingly important role for both evaluation and image-guided treatment. Muscle injuries and athletic pubalgia are common in athletes. Lastly, snapping hip syndrome and Morel-Lavallée lesions are two less common but nonetheless important considerations. ^©RSNA, 2016.

Radiographic cup anteversion measurement corrected from pelvic tilt

The purpose of this study was to develop a novel technique to improve the accuracy of radiographic cup anteversion measurement by correcting the influence of pelvic tilt. Ninety virtual total hip arthroplasties were simulated from computed tomography data of 6 patients with 15 predetermined cup orientations. For each simulated implantation, anteroposterior (AP) virtual pelvic radiographs were generated for 11 predetermined pelvic tilts. A linear regression model was created to capture the relationship between radiographic cup anteversion angle error measured on AP pelvic radiographs and pelvic tilt. Overall, nine hundred and ninety virtual AP pelvic radiographs were measured, and 90 linear regression models were created. Pearson's correlation analyses confirmed a strong correlation between the errors of conventional radiographic cup anteversion angle measured on AP pelvic radiographs and the magnitude of pelvic tilt (P < 0.001). The mean of 90 slopes and y-intercepts of the regression lines were -0.8 and -2.5°, which were applied as the general correction parameters for the proposed tool to correct conventional cup anteversion angle from the influence of pelvic tilt. The current method proposes to measure the pelvic tilt on a lateral radiograph, and to use it as a correction for the radiographic cup anteversion measurement on an AP pelvic radiograph. Thus, both AP and lateral pelvic radiographs are required for the measurement of pelvic posture-integrated cup anteversion. Compared with conventional radiographic cup anteversion, the errors of pelvic posture-integrated radiographic cup anteversion were reduced from 10.03 (SD = 5.13) degrees to 2.53 (SD = 1.33) degrees. Pelvic posture-integrated cup anteversion measurement improves the accuracy of radiographic cup anteversion measurement, which shows the potential of further clarifying the etiology of postoperative instability based on planar radiographs.

A Contemporary Definition of Hip Dysplasia and Structural Instability: Toward a Comprehensive Classification for Acetabular Dysplasia

Hip dysplasia has long been known to be a risk factor for pain and degenerative changes in the hip joint. The diagnosis of dysplasia has historically been based on assessments of acetabular anatomy on the anteroposterior pelvic radiograph, most commonly the lateral center-edge angle. Recent advances in imaging of the dysplastic hip with computerized tomography scans have demonstrated that hip dysplasia is in fact a 3-dimensional (D) deformity of the acetabulum and that multiple patterns of hip instability exist that may not be completely assessed on 2D imaging. A more thorough understanding of acetabular anatomy permits an evolution away from vague terms such as "borderline dysplasia." A 3D assessment of the acetabulum and the resultant patterns of instability may be more appropriate since this would allow more accurate treatment to correct the structural instability with acetabular reorientation. With this information, we propose a diagnostic framework that groups symptomatic dysplastic hips into one of 3 categories based on the primary direction of instability: (1) anterior, (2) posterior, and (3) global. This framework may aid the clinician in developing a differential diagnosis for the assessment of hip pain and suspected instability, and for planning an appropriate surgical management.

Bony Morphology of Femoroacetabular Impingement in Young Female Dancers and Single-Sport Athletes

BACKGROUND

Femoroacetabular impingement (FAI) is a painful and limiting condition of the hip that is often seen in young athletes. Previous studies have reported a higher prevalence of this disorder in male athletes, but data on the structural morphology of adolescent and young adult female athletes, specifically those involved in dance, are lacking.

PURPOSE

(1) To investigate the radiographic morphology of FAI deformities in adolescent and young adult female single-sport dance and nondance athletes and (2) to examine the differences in the radiographic findings between these 2 groups.

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

METHODS

A retrospective chart review of 56 female single-sport athletes 10 to 21 years of age with a diagnosis of FAI within a single-sports medicine division of a pediatric academic medical center was performed. Acetabular index (AI), lateral center-edge angle (LCEA), crossover sign, and ischial spine sign were measured bilaterally on anteroposterior radiographs; alpha angle (AA) was measured on lateral films, and anterior center-edge angle (ACEA) was measured on false-profile films. Independent t tests and Mann-Whitney U tests were used to compare mean angle measurements between dance and nondance athletes. Dichotomized categorical variables and crossover and ischial spine signs were analyzed between dance and nondance athletes by applying a chi-square test. Statistical significance was set as P < .05 a priori.

RESULTS

Significant differences in angle measurements were noted. AA was significantly lower in the dancers compared with the nondance athlete group (49.5° ± 6.0° vs 53.9° ± 7.3°, P = .001). The LCEA and ACEA of dance athletes were significantly greater compared with nondance athletes (33.8° ± 6.7° vs 30.9° ± 5.8° [P = .016] and 36.0° ± 8.1° vs 32.3° ± 7.0° [P = .035], respectively). No significant difference in AI was seen between the 2 cohorts (5.0° ± 4.0° for dancers vs 5.9° ± 3.4° for nondancers, P = .195).

CONCLUSION

Significant differences existed in the radiographic bony morphology of young female single-sport dance athletes compared with nondance athletes with FAI. In dance athletes, symptoms were seen in the setting of normal bony morphology.

Imaging of impingement syndromes around the hip joint

Impingement syndromes are increasingly recognised as significant causes of hip pain and dysfunction. A broad spectrum of intraarticular and extraarticular conditions has been implicated in their pathophysiology. Physical examination is often inconclusive as clinical findings may be unclear or misleading, often simulating other disorders. With current improvements in imaging techniques and better understanding of hip impingement related pathomechanisms, these entities can be accurately diagnosed. In addition, preoperative imaging has allowed for targeted treatment planning. This article provides an overview of the various types of hip impingement, including femoroacetabular impingement, ischiofemoral impingement, snapping hip syndrome, greater trochanteric-pelvic and subspine impingement. Current literature data regarding their pathogenesis, clinical manifestation and imaging work-up are discussed.

Three-dimensional orientation of the acetabulum

This study was designed specifically to determine the normal acetabular orientation and femoral head covering, and whether these are affected by age or sex. Computed tomographic images of normal Japanese hip joints were used (males 60, females 60; mean age 48.3 years, range 15-79 years). Male and female age profiles were matched. The reconstructed 3-D pelvic images were aligned in the anatomical pelvic coordinate system. The acetabular orientation angles and femoral covering angles were measured in the sagittal, coronal, and horizontal planes. In the sagittal plane, the acetabular orientation angle was operative anteversion (O-av), and the femoral covering angles were the anterior and posterior center-edge angles (ACE and PCE). In the coronal plane, they were the Sharp angle (SA) and the lateral center-edge angle (LCE). In the horizontal plane, they were anatomical anteversion (A-av) and the anterior and posterior sector angles (ASA and PSA). The O-av, SA, and A-av were smaller in the male than the female acetabulum (P < 0.01). SA in both males and females was inversely correlated with age (P < 0.01). Both male PCE and PSA were significantly smaller than those of females, while male ASA was larger than female ASA (P < 0.05). The male acetabulum is directed further outward and downward than the female one. However, this does not indicate that the male acetabulum covers the femoral head more, because there is no significant sex difference in the LCE. Femoral coverage is more posteriorly biased in females than in males owing to pelvic inclination. Clin. Anat. 30:753-760, 2017. © 2017Wiley Periodicals, Inc.

Is the evaluation of the anterior inferior iliac spine (AIIS) in the AP pelvis possible? Analysis of conventional X-rays and 3D-CT reconstructions

INTRODUCTION

A hypertrophic AIIS has been identified as a cause for extraarticular hip impingement and is classified according to Hetsroni using 3D-CT reconstructions. The role of the conventional AP pelvis X-ray, which is the first standard imaging step for the evaluation of hip pain, has not been investigated yet.

MATERIALS AND METHODS

AP pelvis X-rays and 3D-CT reconstructions of patients were evaluated regarding their morphology of the AIIS. The conventional X-rays were categorized into three groups according to the projection of the AIIS: above (A) or below (B) the acetabular sourcil or even exceeding the anterior acetabular rim (C). They were compared to the morphologic types in the 3D-CT reconstruction (Hetsroni type I-III).

RESULTS

Ninety patients with an equal distribution of type A, B or C projection in the AP pelvis were evaluated and compared to the morphology in the 3D-CT reconstruction. The projection of the AIIS below the acetabular sourcil (B + C) showed only moderate sensitivity (0.76) and specificity (0.64) for a hypertrophic AIIS (Hetsroni type II + III), but if the AIIS exceeds the anterior rim, all cases showed a hypertrophic AIIS in the 3D-CT reconstructions (Hetsroni type II + III).

CONCLUSIONS

Distinct differentiation of the AIIS morphology in the AP pelvis is not possible, but the projection of the AIIS below the anterior acetabular rim represented a hypertrophic AIIS in all cases and should, therefore, be critically investigated for a relevant AIIS impingement.

Parameters for assessment of the inferior acetabulum morphology in 300 adult hips

The inferior acetabulum (IA) has been studied as a stabilizer of the hip in flexed positions with potential implications in femoroacetabular impingement and hip instability. However, there is a paucity of studies considering the normal morphology and parameters for assessment of the IA. The purpose of this study was to define parameters to assess the IA morphology and their normal range. Specifically, the objectives were to assess: (i) the width of the anterior horn (AH) and posterior horn (PH) of the acetabulum; (ii) the inclination of the articular surface of the AH angle (AHA) and PH angle (PHA) in the axial plane; (iii) the anterior opening angle of the IA and differences between genders. One hundred and fifty adult skeletons were utilized in this study. Measurements were taken directly from acetabula in 300 innominate bones utilizing digital calipers. In sequence, the innominate bones were assembled to sacrum and 150 pelvises were digitally photographed in standardized positions. Angular parameters of the acetabulum were then measured utilizing the Adobe Photoshop software. The mean width of the AH was 14.80 ± 2.35 mm (range 9.44–20.88). The mean width of the PH was 19.72 ± 2.61 mm (range 13.16–25.86). The AHA was on average 43.58 ± 7.10° (range 24.70–64) and the PHA was on average 36.07 ± 7.54° (16.10–53.20). The mean anterior opening angle of the IA was 25.33 ± 5.40° (10.90–43.10). The IA morphology can be evaluated in all anatomical planes through quantitative parameters. The assessment of the osseous morphology of the IA is the first step to elucidate abnormalities of the IA as potential source of hip pain.

Postarthroscopy Imaging in Femoroacetabular Impingement: Persistent Pain May Be Due to an Insufficient Correction of Preoperative Abnormalities

Purpose  The purpose of this study was to evaluate the effect of correction of abnormal radiographic parameters on postoperative pain in a group of patients treated arthroscopically for femoracetabular impingement (FAI).

Methods  A retrospective study was performed on 23 patients affected by mixed-type FAI and treated arthroscopically. There were 11 males and 12 females with a mean age of 46.5 (range: 28–67) years. Center-edge (CE) and α angles were measured on preoperative and postoperative radiographic and magnetic resonance imaging (MRI) studies and were correlated with persistent pain at follow-up.

Results  The mean preoperative CE and α angles were 38.6 ± 5.2 and 67.3 ± 7.2 degrees, respectively. At follow-up, in the 17 pain-free patients, the mean pre- and postoperative CE angle were 38.1 ± 5.6 and 32.6 ± 4.8 degrees, respectively, whereas the mean pre- and postoperative α angles at MRI were 66.3 ± 7.9 and 47.9 ± 8.9 degrees, respectively. In six patients with persistent hip pain, the mean pre- and postoperative CE angles were 39.8 ± 3.6 and 35.8 ± 3.1 degrees, respectively, whereas the mean pre- and postoperative α angles were 70.0 ± 3.9 and 58.8 ± 2.6 degrees, respectively. Mean values of all the analyzed radiological parameters, except CE angle in patients with pain, improved significantly after surgery. On comparing patient groups, significantly lower postoperative α angles and lower CE angle were observed in patients without pain.

Conclusion  In case of persistent pain after arthroscopic treatment of FAI, a new set of imaging studies must be performed because pain may be related to an insufficient correction of preoperative radiographic abnormalities.

Level of Evidence  Level IV, retrospective case series.

Hip Imaging in Athletes: Sports Imaging Series

Hip or groin pain in athletes is common and clinical presentation is often nonspecific. Imaging is a very important diagnostic step in the work-up of athletes with hip pain. This review article provides an overview on hip biomechanics and discusses strategies for hip imaging modalities such as radiography, ultrasonography, computed tomography, and magnetic resonance (MR) imaging (MR arthrography and traction MR arthrography). The authors explain current concepts of femoroacetabular impingement and the problem of high prevalence of cam- and pincer-type morphology in asymptomatic persons. With the main focus on MR imaging, the authors present abnormalities of the hip joint and the surrounding soft tissues that can occur in athletes: intraarticular and extraarticular hip impingement syndromes, labral and cartilage disease, microinstability of the hip, myotendinous injuries, and athletic pubalgia. (©) RSNA, 2016.