Radiographic Identification of Arthroscopically Relevant Acetabular Structures

Defining the Borderline Dysplastic Hip: High Variability in Acetabular Coverage and Femoral Morphology on Low-Dose Computed Tomography

BACKGROUND

Borderline acetabular dysplasia is commonly radiographically defined as a lateral center-edge angle (LCEA) of 20° to 25°. While the variability of plain radiographic assessment of this population has been reported, an understanding of the variability of 3-dimensional (3D) hip morphology remains to be better defined.

PURPOSE

To investigate the variability of 3D hip morphology present on low-dose computed tomography (CT) in the setting of symptomatic borderline acetabular dysplasia and to determine if plain radiographic parameters correlate with 3D coverage.

STUDY DESIGN

Cohort study (diagnosis); Level of evidence, 2.

METHODS

A total of 70 consecutive hips with borderline acetabular dysplasia undergoing hip preservation surgery were included in the current study. Plain radiographic evaluation included LCEA, acetabular inclination, anterior center-edge angle (ACEA), anterior wall index (AWI), posterior wall index (PWI), and alpha angles on anteroposterior, 45° Dunn, and frog-leg views. All patients underwent low-dose pelvic CT for preoperative planning, which allowed detailed characterization of 3D morphology relative to normative data. Acetabular morphology was assessed with radial acetabular coverage (RAC) calculated according to standardized clockface positions from 8:00 (posterior) to 4:00 (anterior). Coverages at 10:00, 12:00, and 2:00 were classified as normal, undercoverage, or overcoverage relative to 1 SD from the mean of normative RAC values. Femoral morphology was assessed with femoral version, alpha angle (measured at 1:00 increments), and maximum alpha angle. Correlation was assessed with the Pearson correlation coefficient (r).

RESULTS

Lateral coverage (12:00 RAC) was deficient in 74.1% of hips with borderline dysplasia. Anterior coverage (2:00 RAC) was highly variable, with 17.1% undercoverage, 72.9% normal, and 10.0% overcoverage. Posterior coverage (10:00 RAC) was also highly variable, with 30.0% undercoverage, 62.9% normal, and 7.1% overcoverage. The 3 most common patterns of coverage were isolated lateral undercoverage (31.4%), normal coverage (18.6%), and combined lateral and posterior undercoverage (17.1%). The mean femoral version was 19.7°± 10.6° (range, -4° to 59°), with 47.1% of hips having increased femoral version (>20°). The mean maximum alpha angle was 57.2° (range, 43°-81°), with 48.6% of hips having an alpha angle ≥ 55°. The ACEA and AWI were poorly correlated with radial anterior coverage (r = 0.059 and 0.311, respectively), while the PWI was strongly correlated with radial posterior coverage (r = 0.774).

CONCLUSION

Patients with borderline acetabular dysplasia demonstrate highly variable 3D deformities, including anterior, lateral, and posterior acetabular coverage; femoral version; and alpha angle. Plain radiographic assessments of anterior coverage are poorly correlated with anterior 3D coverage on low-dose CT.

Prominent Anterior Inferior Iliac Spine Morphologies Are Common in Patients with Acetabular Dysplasia Undergoing Periacetabular Osteotomy

BACKGROUND

The anterior inferior iliac spine (AIIS) prominence is increasingly recognized in the setting of femoroacetabular impingement (FAI). The AIIS prominence may contribute to decreased hip flexion after acetabular reorientation in patients with acetabular dysplasia. AIIS morphologies have been characterized in numerous populations including asymptomatic, FAI, and athletic populations, but the morphology of the AIIS in patients with symptomatic acetabular dysplasia undergoing periacetabular osteotomy (PAO) has not been studied. In acetabular dysplasia, deficiency of the anterosuperior acetabular rim is commonly present and may result in the AIIS being positioned closer to the acetabular rim. Understanding morphological variation of the AIIS in patients with symptomatic dysplasia, and its relationship to dysplasia subtype and severity may aid preoperative planning, surgical technique, and evaluation of postoperative issues after PAO.

QUESTIONS/PURPOSES

In this study, we sought to determine: (1) the variability of AIIS morphology types in hips with symptomatic acetabular dysplasia and (2) whether the differences in the proportion of AIIS morphologies are present between dysplasia pattern and severity subtypes.

METHODS

Using our hip preservation database, we identified 153 hips (148 patients) who underwent PAO from October 2013 to July 2015. Inclusion criteria for the current study were (lateral center-edge angle [LCEA] < 20°), Tönnis Grade of 0 or 1 on plain AP radiographs of the pelvis, preoperative low-dose CT scan, and no prior surgery, trauma, neuromuscular, ischemic necrosis, or Perthes-like deformity. A total of 50 patients (50 hips) with symptomatic acetabular dysplasia undergoing evaluation for surgical planning of PAO remained for retrospective evaluation; we used these patients' low-dose CT scans for analysis. The median (range) age of patients in the study was 24 years (13 to 49). Ninety percent (45 of 50) of the hips were in female patients, whereas 10% (5 of 50) were in male patients. The morphology of the AIIS was classified on three-dimensional CT reconstructions according to a previously published classification to define the relationship between the AIIS and the acetabular rim. The morphology of the AIIS was classified as Type I (AIIS well proximal to acetabular rim), Type II (AIIS extending to level of acetabular rim), or Type III (AIIS extending distal to acetabular rim). Acetabular dysplasia subtype was characterized according to a prior protocol as either predominantly an anterosuperior acetabular deficiency, a posterosuperior acetabular deficiency, or a global acetabular deficiency. Acetabular dysplasia severity was distinguished as mild (LCEA 15° to 20°) or moderate/severe (LCEA < 15°). To answer our first question, regarding the proportions of each AIIS morphology in the dysplasia population, we calculated proportions and 95% CI estimates. To answer our second question, regarding the proposition of AIIS type between subtypes of dysplasia type and severity, we used a chi-square test or Fisher's exact test to compare categorical variables. A p value of < 0.05 was considered significant.

RESULTS

Seventy-two percent (36 of 50; 95% CI 58% to 83%) of patients had a Type II or III AIIS morphology. Type I AIIS morphology was found in 28% of patients (14 of 50; 95% CI 18% to 42%), Type II AIIS morphology in 62% (31 of 50; 95% CI 48% to 74%), and Type III AIIS/morphology in 10% (5 of 50; 95% CI 4% to 21%). A Type I AIIS was seen in seven of 15 of patients with anterosuperior acetabular deficiency, three of 18 of patients with global deficiency, and four of 17 patients with posterosuperior deficiency (p = 0.08). There was no difference in the variability of AIIS morphologies between the different subtypes of acetabular dysplasia pattern and no difference in AIIS morphology variability between patients with mild versus moderate/severe dysplasia.

CONCLUSIONS

The morphology of the AIIS in patients with acetabular dysplasia is commonly prominent, with 72% of hips having Type II or Type III morphologies.

CLINICAL RELEVANCE

The AIIS is often prominent in patients with acetabular dysplasia undergoing PAO, regardless of dysplasia pattern or severity. Prominent AIIS morphologies may affect hip flexion ROM after acetabular reorientation. AIIS morphology is a variable that should be considered during preoperative planning for PAO. Future studies are needed to assess the clinical significance of a prominent AIIS on intraoperative findings and postoperative status after PAO.

Anatomical variation of the Psoas Valley: a scoping review

Background

This scoping review aimed to investigate the literature on the anatomy of the psoas valley, an anterior depression on the acetabular rim, and propose a unified definition of the anatomical structure, describe its dimensions, anatomical variations and clinical implications.

Methods

A systematic computer search of EMBASE, PubMed and Cochrane for literature related to the psoas valley was undertaken using Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines. Clinical outcome studies, prospective/retrospective case series, case reports and review articles that described the psoas valley and its synonyms were included. Studies on animals as well as book chapters were excluded.

Results

Of the 313 articles, the filtered literature search identified 14 papers describing the psoas valley and its synonyms such as iliopsoas notch, a notch between anterior inferior iliac spine and the iliopubic eminence, Psoas-U and anterior wall depression. Most of these were cross-sectional studies that mainly analyzed normal skeletal hips. In terms of anatomical variation, 4 different configurations of the anterior acetabular rim have been identified and it was found that the curved type was the most frequent while the straight type may be nonexistent. Additionally, the psoas valley tended to be deeper in males as compared with females. Several papers established the psoas valley, or Psoas-U in a consistent location at approximately 3 o’clock on the acetabular rim which may have implications with labral pathology.

Conclusion

This review highlights the importance of the anatomy of the psoas valley which is a consistent bony landmark. The anatomy and the anatomical variations of the psoas valley need to be well-appreciated by surgeons involved in the management of young adults with hip pathology and also joint replacement surgeons to ensure appropriate seating of the acetabular component.

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.

Does Pelvic Rotation Alter Radiologic Measurement of Anterior and Lateral Acetabular Coverage?

PURPOSE

The purpose of this study was to determine the radiologic tolerance of the lateral center edge angle (LCEA) and anterior center edge angle (ACEA) to pelvic rotation.

METHODS

Eleven dry cadaveric pelvises from an osteological collection were reconstructed and placed in anatomic position with corresponding bilateral proximal femurs. Conventional anteroposterior (AP) and false-profile (FP) pelvic radiographs were taken at 5° increments with fluoroscopy from 0° to 25° of rotation. LCEA and ACEA were measured for conventional and rotated AP and FP fluoroscopic views, respectively. Statistical analysis was conducted to determine the error in ACEA and LCEA with pelvic rotation.

RESULTS

The mean LCEA was 29.1° (95% confidence interval [CI], 25.5°-32.7°). Mean ACEA was 38.9° (95% CI, 34.1°-43.8°). There was significant change in the LCEA past 10° of rotation (P = .041). There was significant change in the ACEA with 5^o or more of rotation (P < .001). The FP view rotated 40° from an AP view produced 6.8° (95% CI, 4.7-8.9) of error, whereas one rotated 90° from an AP view produced 13.2° (95% CI, 11.2°-15.3°) of error in the ACEA. An AP view rotated 25° toward the x-ray beam produced 2.3° (95% CI, 1.1°-3.4°) error, whereas one rotated 25° away from the beam produced 2.6° (95% CI, 1.5°-3.8°) of error.

CONCLUSIONS

Rotation of AP and FP radiographs significantly affects the measured values of the LCEA and ACEA, respectively. The ACEA experiences more dramatic changes with rotation of the FP view compared with the LCEA with the same amount of rotation of an AP view. This study illustrates the importance of verifying the quality of the FP radiograph when using ACEA to guide therapy for hip pathology.

CLINICAL RELEVANCE

This study emphasizes the importance of evaluating pelvic rotation when using the center edge angle to assess femoral head coverage.

Revisiting the Anteroinferior Iliac Spine: Is the Subspine Pathologic? A Clinical and Radiographic Evaluation

BACKGROUND

Subspine impingement is a recognized source of extraarticular hip impingement. Although CT-based classification systems have been described, to our knowledge, no study has evaluated the morphology of the anteroinferior iliac spine (AIIS) with plain radiographs nor to our knowledge has any study compared its appearance between plain radiographs and CT scan and correlated AIIS morphology with physical findings. Previous work has suggested a correlation of AIIS morphology and hip ROM but this has not been clinically validated. Furthermore, if plain radiographs can be found to adequately screen for AIIS morphology, CT could be selectively used, limiting radiation exposure.

QUESTIONS/PURPOSES

The purposes of this study were (1) to determine the prevalence of AIIS subtypes in a cohort of patients with symptomatic femoroacetabular impingement; (2) to compare AP pelvis and false profile radiographs with three-dimensional (3-D) CT classification; and (3) to correlate the preoperative hip physical examination with AIIS subtypes.

METHODS

A retrospective study of patients undergoing primary hip arthroscopy for femoroacetabular impingement syndrome was performed. Between February 2013 and November 2016, 601 patients underwent hip arthroscopy. To be included here, each patient had to have undergone a primary hip arthroscopy for the diagnosis of femoroacetabular impingement syndrome. Each patient needed to have an interpretable set of plain radiographs consisting of weightbearing AP pelvis and false profile radiographs as well as full documentation of physical findings in the medical record. Patients who additionally had a CT scan with 3-D reconstructions were included as well. During the period in question, it was the preference of the treating surgeon whether a preoperative CT scan was obtained. A total of 145 of 601 (24%) patients were included in the analysis; of this cohort, 54% (78 of 145) had a CT scan and 63% (92 of 145) were women with a mean age of 31 ± 10 years. The AIIS was classified first on patients in whom the 3-D CT scan was available based on a previously published 3-D CT classification. The AIIS was then classified by two orthopaedic surgeons (TGM, MRK) on AP and false profile radiographs based on the position of its inferior margin to a line at the lateral aspect of the acetabular sourcil normal to vertical. Type I was above, Type II at the level, and Type III below this line. There was fair interrater agreement for AP pelvis (κ = 0.382; 95% confidence interval [CI], 0.239-0.525), false profile (κ = 0.372; 95% CI, 0.229-0.515), and 3-D CT (κ = 0.325; 95% CI, 0.156-0.494). There was moderate to almost perfect intraobserver repeatability for AP pelvis (κ = 0.516; 95% CI, 0.284-0.748), false profile (κ = 0.915; 95% CI, 0.766-1.000), and 3-D CT (κ = 0.915; 95% CI, 0.766-1.000). The plane radiographs were then compared with the 3-D CT scan classification and accuracy, defined as the proportion of correct classification out of total classifications. Preoperative hip flexion, internal rotation, external rotation, flexion adduction, internal rotation, subspine, and Stinchfield physical examination tests were compared with classification of the AIIS on 3-D CT. Finally, preoperative hip flexion, internal rotation, and external rotation were compared with preoperative lateral center-edge angle and alpha angle.

RESULTS

The prevalence of AIIS was 56% (44 of 78) Type I, 39% (30 of 78) Type II, and 5% (four of 78) Type III determined from the 3-D CT classification. For the plain radiographic classification, the distribution of AIIS morphology was 64% (93 of 145) Type I, 32% (46 of 145) Type II, and 4% (six of 145) Type III on AP pelvis and 49% (71 of 145) Type I, 48% (70 of 145) Type II, and 3% (four of 145) Type III on false profile radiographs. False profile radiographs were more accurate than AP pelvis radiographs for classification when compared against the gold standard of 3-D CT at 98% (95% CI, 96-100) versus 80% (95% CI, 75-85). The false profile radiograph had better sensitivity for Type II (97% versus 47%, p < 0.001) and specificity for Types I and II AIIS (97% versus 53%, p < 0.001; 98% versus 90%, p = 0.046) morphology compared with AP pelvis radiographs. There was no correlation between AIIS type as determined by 3-D CT scan and hip flexion (rs = -0.115, p = 0.377), internal rotation (rs = 0.070, p = 0.548), flexion adduction internal rotation (U = 72.00, p = 0.270), Stinchfield (U = 290.50, p = 0.755), or subspine tests (U = 319.00, p = 0.519). External rotation was weakly correlated (rs = 0.253, p = 0.028) with AIIS subtype. Alpha angle was negatively correlated with hip flexion (r = -0.387, p = 0.002) and external rotation (r = -0.238, p = 0.043) and not correlated with internal rotation (r = -0.068, p = 0.568).

CONCLUSIONS

The findings in this study suggest the false profile radiograph is superior to an AP radiograph of the pelvis in evaluating AIIS morphology. Neither preoperative hip internal rotation nor impingement tests correlate with AIIS type as previously suggested questioning the utility of the AIIS classification system in identifying pathologic AIIS anatomy.

LEVEL OF EVIDENCE

Level III, diagnostic study.

Comprehensive Clinical Evaluation of Femoroacetabular Impingement: Part 3, Magnetic Resonance Imaging

Radiologic imaging is an essential supplement to the physical examination in the evaluation of a patient with femoroacetabular impingement. Plain radiographs are the initial modality of choice for the evaluation of bony anatomy and pathology. Magnetic resonance imaging supplements the physical examination and standard radiographs by enabling qualitative and quantitative evaluation of both articular cartilage and soft tissues about the hip. Magnetic resonance imaging also provides improved 3-dimensional characterization of the bony anatomy owing to the multiplanar nature of this technique. This article describes a comprehensive approach to interpretation of magnetic resonance examination of the hip.

Three Patterns of Acetabular Deficiency Are Common in Young Adult Patients With Acetabular Dysplasia

BACKGROUND

Detailed recognition of the three-dimensional (3-D) deformity in acetabular dysplasia is important to help guide correction at the time of reorientation during periacetabular osteotomy (PAO). Common plain radiographic parameters of acetabular dysplasia are limited in their ability to characterize acetabular deficiency precisely. The 3-D characterization of such deficiencies with low-dose CT may allow for more precise characterization.

QUESTIONS/PURPOSES

The purposes of this study were (1) to determine the variability in 3-D acetabular deficiency in acetabular dysplasia; (2) to define subtypes of acetabular dysplasia based on 3-D morphology; (3) to determine the correlation of plain radiographic parameters with 3-D morphology; and (4) to determine the association of acetabular dysplasia subtype with patient clinical characteristics including sex, range of motion, and femoral version.

METHODS

Using our hip preservation database, we identified 153 hips (148 patients) that underwent PAO from October 2013 to July 2015. Among those, we noted 103 hips in 100 patients with acetabular dysplasia (lateral center-edge angle < 20°) and who had a Tönnis grade of 0 or 1. Eighty-six patients (86%) underwent preoperative low-dose pelvic CT scans at our institution as part of the preoperative planning for PAO. It is currently our standard to obtain preoperative low-dose pelvic CT scans (0.75-1.25 mSv, equivalent to three to five AP pelvis radiographs) on all patients before undergoing PAO unless a prior CT scan was performed at an outside institution. Hips with a history of a neuromuscular disorder, prior trauma, prior surgery, radiographic evidence of joint degeneration, ischemic necrosis, or Perthes-like deformities were excluded. Fifty hips in 50 patients met inclusion criteria and had CT scans available for review. These low-dose CT scans of 50 patients with symptomatic acetabular dysplasia undergoing evaluation for surgical planning of PAO were then retrospectively studied. CT scans were analyzed quantitatively for acetabular coverage, relative to established normative data for acetabular coverage, as well as measurement of femoral version. The cohort included 45 females and five males with a mean age of 26 years (range, 13-49 years).

RESULTS

Lateral acetabular deficiency was present in all patients, whereas anterior deficiency and posterior deficiency were variable. Three patterns of acetabular deficiency were common: anterosuperior deficiency (15 of 50 [30%]), global deficiency (18 of 50 [36%]), and posterosuperior deficiency (17 of 50 [34%]). The presence of a crossover sign or posterior wall sign was poorly predictive of the dysplasia subtype. With the numbers available, males appeared more likely to have a posterosuperior deficiency pattern (four of five [80%]) compared with females (13 of 45 [29%], p = 0.040). Hip internal rotation in flexion was significantly greater in anterosuperior deficiency (23° versus 18°, p = 0.05), whereas external rotation in flexion was significantly greater in posterosuperior deficiency (43° versus 34°, p = 0.018). Acetabular deficiency pattern did not correlate with femoral version, which was variable across all subtypes.

CONCLUSIONS

Three patterns of acetabular deficiency commonly occur among young adult patients with mild, moderate, and severe acetabular dysplasia. These patterns include anterosuperior, global, and posterosuperior deficiency and are variably observed independent of femoral version. Recognition of these distinct morphologic subtypes is important for diagnostic and surgical treatment considerations in patients with acetabular dysplasia to optimize acetabular correction and avoid femoroacetabular impingement.

Comparison of Radiographs and Computed Tomography for the Screening of Anterior Inferior Iliac Spine Impingement

PURPOSE

To compare radiographic and 3-dimensional (3D) computed tomography (CT) imaging modalities for the screening of anterior inferior iliac spine (AIIS) impingement by establishing imaging measurement related to the AIIS.

METHODS

Anteroposterior and false-profile radiographs and 3D CT scans were obtained on 10 human cadaveric pelvises. On the anteroposterior view for each methodology, 2 measurements were calculated: distance to the most lateral AIIS from the 12 o'clock position on the acetabular rim, and the angle between the lateral AIIS and the sagittal plane. On the false-profile view for each methodology, 2 measurements were calculated: distance to the anterior AIIS from the 12 o'clock position on the acetabular rim, and the angle between the anterior AIIS and the sagittal plane. Inter-rater and intrarater reliability analyses were performed for both methods in addition to an intermethod analysis.

RESULTS

The radiographic false-profile view was the most repeatable orientation, with intraclass correlation coefficients showing excellent reproducibility in both inter-rater (angle: 0.980, distance: 0.883) and intrarater (angle: 0.995, distance: 0.995) analyses. The mean distance from the 12 o'clock position of the acetabular rim to the most anterior/lateral aspect of the AIIS was 41.4 mm and 16.0 mm on the radiographic false-profile and anteroposterior views, respectively. Intermethod analysis showed a systematic, quantitative bias between modalities (anteroposterior view: -4.1 mm, 6.7°; false-profile view: -0.1 mm, 8.3°), which will remain relatively consistent as evidenced by the strong individual reproducibility of each measurement.

CONCLUSIONS

AIIS morphology in relation to the acetabular rim 12 o'clock position and its angle relative to the sagittal plane can be quantitatively determined using either radiographic or 3D CT imaging modalities.

CLINICAL RELEVANCE

Radiographic evaluation may be a valuable tool in the screening of AIIS impingement.