Tobias J. Dietrich

How Useful Is the Alpha Angle for Discriminating between Symptomatic Patients with Cam-type Femoroacetabular Impingement and Asymptomatic Volunteers?

PURPOSE To compare the alpha-angle measurements in volunteers and patients with femoroacetabular impingement (FAI) and to develop potential threshold values. MATERIALS AND METHODS This study was approved by the institutional review board; all individuals signed informed consent. Magnetic resonance (MR) images at 1.5 T in 106 individuals (ages 20-50 years) were analyzed in 53 patients (33 cam- and 20 mixed-type FAI) and 53 age- and sex-matched asymptomatic volunteers. Alpha angles were measured on radially reformatted MR images of the proximal femur by two independent readers. Intraclass correlation coefficient (ICC) and receiver operating characteristic (ROC) were calculated. RESULTS Mean alpha angles were highest in the anterosuperior segment: 65.4° ± 11.5 [standard deviation] and 65.2° ± 7.3 for readers 1 and 2 in patients and 53.3° ± 9.6 and 55.0° ± 8.8 in volunteers, respectively (P < .001, patients vs volunteers). Alpha angles greater than 55° were measured in 20 (38%) and 33 (62%) of 53 volunteers for readers 1 and 2, respectively. Maximal alpha angle in any segment was substantially different (P < .001) in patients and volunteers (70.3° ± 11.2 vs 57.9° ± 10.5 for reader 1; 69.4° ± 8.8 vs 58.7° ± 8.9 for reader 2), with a large overlap. Overall interobserver agreement was good (ICC, 0.712). ROC showed the largest area under the curve at the anterosuperior segment: 0.791 and 0.824 for readers 1 and 2, respectively (P < .001). A 55° alpha-angle threshold value gave a sensitivity and specificity of 81% and 65% for reader 1 and of 90% and 47% for reader 2, respectively. A 60° alpha-angle threshold value gave a sensitivity and specificity of 72% and 76% for reader 1 and 80% and 73% for reader 2, respectively. CONCLUSION There is substantial overlap in the alpha-angle measurements between volunteers and patients with cam-type deformities. Discrimination is best at the anterosuperior segment. Increasing the alpha-angle threshold value from 55° to 60° reduces false-positive results while maintaining a reasonable sensitivity.

Femoral Antetorsion: Comparing Asymptomatic Volunteers and Patients with Femoroacetabular Impingement

PURPOSE To assess the range of femoral antetorsion with magnetic resonance (MR) imaging in asymptomatic volunteers and patients with different subtypes of femoroacetabular impingement (FAI) because abnormal femoral antetorsion might be a contributing factor in the development of FAI. MATERIALS AND METHODS This study was institutional review board approved; all individuals provided signed informed consent. Sixty-three asymptomatic volunteers and 63 patients with symptomatic FAI between age 20 and 50 years were matched for age and sex. They underwent standard MR imaging with two additional rapid transverse sequences over the proximal and distal femur for antetorsion measurement. Twenty volunteers underwent a second MR imaging examination in the same leg. Two readers independently measured femoral antetorsion. The time for the additional sequences was tabulated. Interobserver agreement was calculated; differences in antetorsion were assessed by using analysis of variance and the unpaired t test. RESULTS Femoral antetorsion can be assessed with MR imaging in about 80 seconds, with high interobserver agreement (intraclass correlation coefficient [ICC] = 0.967) and high agreement between different MR examinations (ICC = 0.966). Women had a significantly larger antetorsion than men (P < .001 for both readers), and antetorsion of the left femur was significantly larger than that of the right femur (P = .01 for reader 1, P = .02 for reader 2). Overall, antetorsion was similar in volunteers and in patients for reader 1 (12.7° ± 10.0 [standard deviation] vs 12.6° ± 9.8, respectively; P = .9) and reader 2 (12.8° ± 10.1 vs 13.5° ± 9.8, respectively; P = .7). Femoral antetorsion was significantly higher in patients with pincer-type FAI than in those with cam-type FAI for reader 1 (18.3° ± 9.8 vs 10.0° ± 9.1, P = .02) and reader 2 (18.7° ± 10.5 vs 11.6° ± 8.8, P = .04). CONCLUSION Femoral antetorsion can be measured rapidly and with good reproducibility with MR imaging. Patients with pincer-type FAI had a significantly larger femoral antetorsion than patients with cam-type FAI.

Supraacetabular Fossa (Pseudodefect of Acetabular Cartilage): Frequency at MR Arthrography and Comparison of Findings at MR Arthrography and Arthroscopy

PURPOSE To evaluate the frequency of the supraacetabular fossa (SAF) (pseudodefect of acetabular cartilage) at magnetic resonance (MR) arthrography of the hip and to compare the MR findings with those from arthroscopy. MATERIALS AND METHODS All patients gave written permission for anonymized use of their medical data for scientific purposes before the imaging examination. The study was submitted to the institutional review board, and the need to obtain additional approval was waived. A medical student, a radiology fellow, and two senior radiologists reviewed 1002 consecutive MR arthrograms for the presence of an accessory bony fossa in the roof of the acetabulum, or SAF. SAF was classified into two types: type 1, which was filled with contrast material on MR arthrograms, and type 2, which was filled with cartilage. The width of the SAF was measured on coronal and sagittal MR images. MR arthrograms showing SAF were evaluated for subchondral reactions. Findings at MR arthrography were compared with those from arthroscopy in four hip joints with SAF type 1 and 13 with SAF type 2. RESULTS Sixteen of the 1002 hip joints (1.6%; four female and 12 male patients; mean age, 20.1 years) had SAF type 1 (mean width, 5.2 × 4.5 mm). Eighty-nine hip joints (8.9%; 43 female and 46 male patients; mean age, 37.8 years) had SAF type 2 (mean width, 5.1 × 4.7 mm). No subchondral changes were found around the SAF. No cartilage defect was seen at the site of the SAF at arthroscopy. CONCLUSION The high frequency of SAF on MR arthrograms (10.5%), the absence of subchondral reaction, and the absence of cartilage defects at arthroscopy indicate that the SAF of the acetabulum likely represents a variant.

Particulate versus non-particulate steroids for lumbar transforaminal or interlaminar epidural steroid injections: an update

Lumbar transforaminal and interlaminar epidural steroid injections are widely used to treat patients with radicular pain and radiculopathy [1]. These lumbar spine procedures are reported to be clinically effective for short-term and longterm pain relief by some studies [2–5]. However, a relative lack of randomized and controlled clinical trials and as well as variability of the employed study methods were noted [6]. Thus, some controversy concerning the effectiveness of lumbar transforaminal and interlaminar epidural steroid injections still remains [6, 7]. Moreover, it should be emphasized that these indications and use are often performed on an off-label basis. The question arises whether just formal approval is lacking or whether extensive medical literature provides sufficient evidence-based efficacy and safety data for this offlabel use. An image-guided therapeutic injection of both the cervical and lumbar spine is a minimally invasive technique, however rare serious adverse events such as brainstem, cerebellum and cervical, thoracic and lumbar spinal cord infarction have occurred [8–26]. The present article discusses serious complications associated with epidural steroid injections after injections at the level of the lumbosacral spine. FDA safety announcement and off-label use

PROPELLER Technique to Improve Image Quality of MRI of the Shoulder

OBJECTIVE The purpose of this article is to evaluate the use of the periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) technique for artifact reduction and overall image quality improvement for intermediate-weighted and T2-weighted MRI of the shoulder. SUBJECTS AND METHODS One hundred eleven patients undergoing MR arthrography of the shoulder were included. A coronal oblique intermediate-weighted turbo spin-echo (TSE) sequence with fat suppression and a sagittal oblique T2-weighted TSE sequence with fat suppression were obtained without (standard) and with the PROPELLER technique. Scanning time increased from 3 minutes 17 seconds to 4 minutes 17 seconds (coronal oblique plane) and from 2 minutes 52 seconds to 4 minutes 10 seconds (sagittal oblique) using PROPELLER. Two radiologists graded image artifacts, overall image quality, and delineation of several anatomic structures on a 5-point scale (5, no artifact, optimal diagnostic quality; and 1, severe artifacts, diagnostically not usable). The Wilcoxon signed rank test was used to compare the data of the standard and PROPELLER images. RESULTS Motion artifacts were significantly reduced in PROPELLER images (p < 0.001). Observer 1 rated motion artifacts with diagnostic impairment in one patient on coronal oblique PROPELLER images compared with 33 patients on standard images. Ratings for the sequences with PROPELLER were significantly better for overall image quality (p < 0.001). Observer 1 noted an overall image quality with diagnostic impairment in nine patients on sagittal oblique PROPELLER images compared with 23 patients on standard MRI. CONCLUSION The PROPELLER technique for MRI of the shoulder reduces the number of sequences with diagnostic impairment as a result of motion artifacts and increases image quality compared with standard TSE sequences. PROPELLER sequences increase the acquisition time.

Imaging of Individual Anatomical Risk Factors for Patellar Instability

This review article presents several pitfalls and limitations of image interpretation of anatomical risk factors for patellar instability. The most important imaging examinations for the work-up of patients with patellar instability are the true lateral radiograph and transverse computed tomography (CT) or MR images of the knee. Primary anatomical risk factors are an insufficient medial patellofemoral ligament (MPFL), patella alta, trochlear dysplasia, increased distance from the tibial tuberosity to the trochlear groove (TTTG), and torsional limb parameters. Limitations of the Caton-Deschamps index are related to the clear identification of the patellar and tibial articular margin. Classification of trochlear dysplasia according to the Dejour system on radiographs and MR images revealed a weak reliability. The comparability of TTTG values obtained on CT and MR images at various flexion angles and different varus alignments of the knee is limited. Thus MRI performed with a dedicated knee coil may underestimate the TTTG distance compared with CT images. Increased lateral patellar tilt is a consequence of primary anatomical risk factors rather than an independent anatomical risk factor for patellar instability. The pretest likelihood of a torn MPFL on MR images is very high after an acute episode of lateral patellar dislocation. Surgical restoration of the patellofemoral joint stability addresses the complex multifactorial biomechanics by a custom-made management such as MPFL reconstruction, sulcus-deepening trochleoplasty, as well as medialization and distalization of the tibial tubercle. Quantification of anatomical risk factors for patellar instability in each person is important for highly individual treatment.

Long biceps tendon: normal position, shape, and orientation in its groove in neutral position and external and internal rotation.

PURPOSE To characterize the position, shape, and orientation of the long biceps tendon (LBT) on transverse magnetic resonance (MR) images acquired in neutral position and in maximal external and internal rotation of the shoulder in asymptomatic volunteers. MATERIALS AND METHODS Informed consent was obtained from all volunteers for this institutional review board-approved study. Fifty-three asymptomatic volunteers (mean age, 33 years; age range, 21-58 years) were included. The position of the LBT with respect to the bicipital groove was measured by two musculoskeletal radiologists on three levels along the bicipital groove on axial MR images in neutral position and in external and internal rotation of the shoulder. The shape of the LBT was classified as round, oval, flat, or comma shaped, and the orientation of the LBT was measured. RESULTS The position of the LBT changed significantly at the entrance into the bicipital groove in the mediolateral and anteroposterior directions (P < .01). The changes of LBT position in external rotation and internal rotation compared with the neutral position were markedly small (< 1.5 mm). Medial eccentricity of the LBT was greatest in the neutral shoulder position at all measurement levels. Differences in LBT shape and orientation were found between the neutral position and external or internal rotation and between the three measurement levels. CONCLUSION The position of the LBT is only slightly dependent on shoulder rotation. LBT eccentricity is maximal in the neutral position. Rotational misplacement during image acquisition does not increase LBT eccentricity.

Postoperative Imaging in Femoroacetabular Impingement

Femoroacetabular impingement (FAI) has been recognized as a common cause of pain, limited range of motion, and development of early osteoarthritis of the hip in adolescents and adults. Current surgical approaches include femoral osteochondroplasty, acetabular rim resection, and reattachment of torn labrum as either open surgical or arthroscopic techniques as well as periacetabular osteotomy. Conventional radiographs are routinely obtained in the postoperative setting. In addition, MRI serves for work-up in patients with persistent or recurrent groin pain after surgery. Inappropriate correction of the underlying femoral or acetabular osseous abnormality, insufficiency fractures of the femoral neck due to bone resection, intra-articular adhesions, ongoing joint degeneration including advanced cartilage damage, iatrogenic cartilage injury, retear of the labrum, rarely avascular necrosis of the femoral head, defects of the hip joint capsule, or heterotopic ossification might be observed after surgery for FAI.

Imaging-Guided Subacromial Therapeutic Injections: Prospective Study Comparing Abnormalities on Conventional Radiography With Patient Outcomes

OBJECTIVE The purpose of this study was to compare abnormalities detected on conventional shoulder radiography with improvement in pain and shoulder function after subacromial injections. SUBJECTS AND METHODS We conducted a prospective outcomes study including 98 consecutive patients after fluoroscopy-guided subacromial injections who returned outcome questionnaires and who underwent routine shoulder radiography. Numeric pain rating scale (NRS) data were collected before and, along with patient global impression of change (PGIC) data, at 1 week and 1 month after injection. Outcome differences were assessed using the Student t test and Mann-Whitney U test. Logistic regression analysis was done, including radiographic variables compared with the outcome improvement. The odds ratios with 95% CIs were identified for the significant predictors. RESULTS A significant difference in overall improvement was found depending on the posterior acromial slope. Patients with a slope of more than 36° had significantly lower NRS and PGIC scores at 1 week and 1 month (p < 0.025) compared with those with a slope of 36° or less, with 86.4% of patients with a slope of more than 36° reporting significant improvement at 1 month. This was the only variable linked with improvement in the logistic regression analysis, with an odds ratio of 2.16 (95% CI, 1.11-4.22). Patients with calcific tendinitis had significantly lower NRS scores at both 1 week and 1 month (p = 0.03 and 0.05, respectively) and PGIC scores at 1 week (p = 0.05). CONCLUSION A posterior acromial slope of more than 36° and the presence of calcific tendinitis on conventional shoulder radiography are associated with better outcomes. Patients with a slope of more than 36° showed the best improvement.

Hip MRI: Prevalence of articular cartilage defects and labral tears in asymptomatic volunteers. A comparison with a matched population of patients with femoroacetabular impingement.

To prospectively compare defects of the articular cartilage and labrum in asymptomatic volunteers and in patients with femoroacetabular impingement (FAI) matched for age and gender.