MR Arthrogram of the hip : pathology, pearls and pitfalls

Transcription

1 MR Arthrogram of the hip : pathology, pearls and pitfalls Award: Winner Poster No.: P-0041 Congress: ESSR 2012 Type: Scientific Exhibit Authors: P. A. Tyler, H. Gajjar, D. Fox, L. K. Singh, M. Calleja ; Stanmore/UK, Cape Town/ZA Keywords: Musculoskeletal system, Musculoskeletal joint, MR, Arthrography, Arthritides, Athletic injuries, Congenital DOI: /essr2012/P-0041 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 44

2 Purpose A series of 50 hip MRI Arthrograms have been reviewed with the purpose of demonstrating the following: Indications for an arthrographic study Techniques for performing the arthrogram Technical elements including scanning protocols and parameters Normal anatomical structures Normal variants that may simulate pathology Common pathologies encountered with this technique Methods and Materials Not applicable Results Indications for an MRI Arthrogram: Assessment of anatomical structures poorly visualised without arthrography: Acetabular labrum Articular cartilage Chondrolabral junction Hip joint capsule Ligamentum teres Contraindications for MR Arthrography: Pregnancy Any infection Previous reaction to contrast agents On anticoagulation therapy and INR above 1.2 (see below) Aspirin - those taking a dose of 75mg or under can continue their medication. If the patient is taking a larger dose, they are requested to stop the medication for 1 week prior to the injection. Page 2 of 44

3 Warfarin - The patient is requested to liase with their anticoagulation clinic to obtain an INR of 1.2 or less prior to injection and to bring a copy of a recent INR result (not older than 1 day) to the examination. In these cases, the radiology department appointments are arranged to facilitate compliance with the above recommendations (usually not sooner than 2 weeks from date of request). Clopidogrel - Patients are requested to stop taking the drug for at least 7 days before appointment. Arthrographic Injection Technique: There are numerous techniques described. The route of entry is anterior. The image guidance varies: Fluoroscopy Ultrasound CT Fluoroscopic Guidance: The author's preference is a fluoroscopic guided anterior approach onto the anterior lateral femoral head-neck junction. Written informed consent should be obtained prior to the procedure, following discussion of potential risks including infection, bleeding, discomfort, leg weakness and neurovascular damage. Patient placed in a supine position, with the side to be injected closest to the radiologist performing the procedure. Leg placed in mild internal rotation, with the knee slightly flexed and supported by a foam wedge. The path of the femoral artery is marked on the skin to show the position of the femoral neurovascular structures (to be avoided!). Planning screening for marking of the skin entry site. The entry site may be over the centre of the femoral neck, over the inter trochanteric line or over the lateral head-neck junction. The entry point should be within the center of the field of view to avoid errors of parallax. Strict aseptic technique is observed. 5-10ml 1% lidocaine is injected into the adjacent soft tissues. A 22G spinal needle is inserted until resistance is felt when the needle tip abuts the femoral neck. If the skin entry site is over the centre of the femoral neck, the needle should be inserted vertically onto the femoral neck. If the skin entry point is at the level of the intertrochanteric line, the needle should be advanced slightly obliquely in a caudal-to-cranial direction, with the needle tip contacting bone at the centre of the femoral neck. Page 3 of 44

4 Fig. 1: Correct needle placement. Needle tip on anterior central femoral neck. If the lateral head-neck junction skin entry site is preferred, the needle is advanced vertically until it contacts the bone. Page 4 of 44

5 Fig. 2: Correct needle tip placement. Needle tip is on the anterior femoral neck at the lateral head-neck junction. It is often useful to rotate the hub to ensure capsular penetration. 1-2ml 0.5% levobupivicaine is initially injected followed by 2-3ml Iohexal 300 (Omnipaque). There should be no resistance to flow of injectate, and the intra-articular injection is usually painfree. Some resistance to injection may occur if the needle tip firmly abuts the femoral head. Gentle retraction of 1-2mm should reduce resistance. Confirmation of intra-articular placement is determined by visualisation of contrast filling or outlining intra-articular structures: Page 5 of 44

6 Initially as a ring around the femoral neck at the redundant distal aspect of the hip joint capsule Contrast may flow around the femoral neck Contrast should not be seen in the iliopsoas muscle or bursa Fig. 3: Incorrect needle placement. Contrast is within the psoas bursa. A mixture of 15ml 2mmol/l prediluted gadolinium and 5ml 0.5% levobupivicaine is prepared and between 10-15ml of this mixture is injected. Injection volume depends on Page 6 of 44

7 the sex of the patient (less for females) and patient size (increased volume for larger patients). Ultrasound Guidance: This is performed with an anterior approach using a linear transducer (17-5MHz). The needle is inserted in the plane of the transducer until the tip abuts the intra-articular femoral head-neck junction. Fig. 4: Longitudinal image of the femoral head-neck junction with fluid in the joint capsule. The path of needle insertion is demonstrated with an arrow. Page 7 of 44

8 Fig. 5: Demonstration of the plane of imaging and needle path in ultrasound guided hip arthrography. Arthrographic Contrast Mixture: Many variations on the arthrogram mixture have been described. Some include the local anaesthetic, iodinated contrast and dilute gadolinium in a single injection, with imaging protocol including T1 weighted fat-suppressed sequences. An injection of saline can be used instead of a gadolinium solution, with the imaging protocol including a T2 weighted fat-suppressed sequence. MRI Protocols and Technical Factors: Our scans are performed on a Philips Achieva 1.5T magnet. The patient lies feet first supine on the table with the SENSE body coil on top and below the hip joints. Our routine protocol includes: Page 8 of 44

9 SEQUENCE FOV SLICE MATRIX THICKNESS/ GAP TE/TR SCAN TIME STIR coronal 4/1 30/ mins x 256 TI 150 (Large FOV to cover both hip joints. PD sagittal / x / mins PD axial 180 oblique 3/ x / mins PD coronal 180 3/ x / min T1 fat sat / x / mins 180 3/ x / mins 180 3/ x / mins sagittal T1 fat sat axial oblique T1 fat sat coronal The axial oblique images are prescribed parallel to the neck of femur. Normal Anatomy: The Acetabulum: Formed from the ilium superiorly, the ischium posteriorly and the pubic bone anteriorly Almost hemispherical in cross section Articular surface has an inverted horse shoe or ¾ moon shape (lunula) Acetabular dimensions are widest posteriorly Covered by hyaline cartilage, thickest anterosuperiorly Outer rim of lunula covered by fibrocartilage of the acetabular labrum Acetabular fossa (pulvinar) in the centre, lined by synovium and containing fibrofatty tissue and branches of the obturator artery and nerve Deficient antero-inferior acetabular rim (acetabular notch), bridged by the transverse acetabular ligament Page 9 of 44

10 Ligamentum teres arises from transverse acetabular ligament and inserts onto the fovea capitis of femoral head. Fig. 6: Coronal diagram of the hip (left) and sagittal diagram of the disarticulated hip (right) demonstrating the normal acetabulum. References: Interactive Hip DVD - Primal Pictures Page 10 of 44

11 Fig. 7: Disarticulated hip joint demonstrating normal anatomy. The right side of the image is anterior and the top of the image is superior. References: David B. Fankhauser, Ph.D. The Acetabular Labrum: Deepens the acetabular socket Consists of fibrocartilage Merges with hyaline cartilage at the transition zone Attached to lunula and acetabular rim Merges with the transverse acetabular ligament inferiorly Thickest posterosuperiorly, thinnest anteroinferiorly Individual variations in shape May be partially absent (up to 14% of patients), most commonly anterosuperiorly Fig. 8: T1FS Coronal image of a normal hip. References: IMAIOS.COM Page 11 of 44

12 Fig. 9: T1FS axial image of a normal hip. References: IMAIOS.COM Fig. 10: T1FS sagittal image of a normal hip. References: IMAIOS.COM Page 12 of 44

13 Appearance of the Acetabular Labrum at MR arthrography: Triangular in cross section, but some individual variation in labral morphology, especially in older patients (?degenerative) It measures 3-11 mm in width and 2-5 mm in height Normal labrum is hypointense on all sequences Increased signal intensity may represent labral tears or myxoid degeneration Intra-articular gadolinium solution is hyperintense on T1 weighted images and may extend into sub-labral sulci/recesses Fig. 11: T1FS coronal image demonstrating a normal anterosuperior labrum (arrow). Page 13 of 44

14 Fig. 12: T1FS axial image demonstrating the normal anterior and posterior labrum (arrows). Page 14 of 44

15 Fig. 13: PD sagittal image demonstrating the anterior labrum (arrowhead), acetabular notch (arrow) and posterior sulcus (double arrow). Sublabral Sulci: Normal recesses adjacent to labrum that fill with contrast May be mistaken for labral tears/detachments Anterosuperior Posterinferior Anteroinferior Posterosuperior A tear generally has irregular edges and extends more than 50% across the depth of the labrum Page 15 of 44

16 Fig. 14: T1FS sagittal image demonstrating a normal posterior labroligamentous sulcus (arrow). Page 16 of 44

17 Fig. 15: PD axial image demonstrating a posterior sublabral recess (arrow). Page 17 of 44

18 Fig. 16: T1FS sagittal image demonstrating an anterior sublabral recess (arrowhead). Labral Pathology - Labral Tears: MR arthrography has a sensitivity of 92 percent and a specificity of 100 percent for the detection of labral tears. Aetiology: Page 18 of 44

19 1) Post-traumatic hyperextension, external rotation: anterosuperior labrum axial loading of flexed hip: posterior labrum 2) Degenerative 3) Associated with acetabular dysplasia 4) Following posterior hip dislocation Staging of Labral Pathology: Stage 0: normal labrum, hypointense, triangular, normal perilabral recess Stage 1: increased intralabral signal intensity not reaching the articular surface (no tear) Stage 2: contrast extending into the labrum and involving the articular surface Stage 3: labrum detached from the acetabulum Further subdivided into type A (no labral hypertrophy) and type B (labral hypertrophy and loss of perilabral recess) The Acetabular Labrum can be divided into 4 quadrants: Anterior Anterosuperior Posterosuperior Posterior Most labral pathology occurs in the anterosuperior quadrant. Labral Tears - Imaging Features: Extension of contrast into the labral tissue Associated features include labral blunting, deformity and hypertrophy Look for bucket handle tears, especially in cases of labro-acetabular separation Classification of Labral Tears and MRA Appearance: Type 1: Detached labrum from the articular cartilage Occurs at the transition zone between the fibrocartilaginous labrum and the articular hyaline cartilage Page 19 of 44

20 Is perpendicular to the articular surface May extend down to the subchondral bone Fig. 17: T1FS axial image demonstrating labro-acetabular separation (arrow). Page 20 of 44

21 Fig. 18: PD sagittal image demonstrating labro-acetabular separation (arrow). Page 21 of 44

22 Fig. 19: PD image demonstrating a tear at the chondro-labral junction (arrow). Type 2: Torn labrum Consists of one or more cleavage planes of variable depth within the substance of the labrum Extends perpendicular to the surface of the labrum Extension of contrast into the labral tissue Associated features include labral blunting, deformity and hypertrophy Page 22 of 44

23 Fig. 20: T1FS axial imaging demonstrating an anterosuperior type 2 labral tear extending within the labrum (arrow). Page 23 of 44

24 Fig. 21: PD axial image demonstrating a type 2 anterosuperior labral tear (arrow). Page 24 of 44

25 Fig. 22: T1FS axial oblique image demonstrating a type 2 anterosuperior labral tear (arrow). Page 25 of 44

26 Fig. 23: T1FS axial image demonstrating labral blunting (arrow). A further classification system may be used: Radial flap tear: Involves the free margin of the labrum Radial fibrillated tear: Irregularity of the labral surface, associated with degenerative change Peripheral longitudinal tears (unstable): Occurring at the junction of the labrum and acetabular rim Bucket-handle tear: Unstable and displaced Page 26 of 44

27 Fig. 24: PD sagittal image demonstrating a radial flap tear (arrow). Page 27 of 44

28 Fig. 25: PD coronal image demonstrating a radial fibrillated tear (arrow). Page 28 of 44

29 Fig. 26: T1FS sagittal image demonstrating a peripheral longitudinal tear (arrow). Page 29 of 44

30 Fig. 27: T1 coronal image demonstrating a bucket-handle tear detachment associated with developmental hip dysplasia. Arrows show contrast interposed along the entire superior acetabular labral interface (arrowheads). References: Petersilge CA. Radiographics 2000;20:S43-S52 Associated Findings: Paralabral cysts: Associated with osteoarthritis, acetabular dysplasia and trauma Page 30 of 44

31 Usually extra articular, occurring when a labral tear extends through the adjacent joint capsule Commonly associated with labral detachment May erode adjacent bone and compress neurovascular structures May contain mucinous / gelatinous material May fill with contrast May demonstrate continuity with the adjacent labral tear Cysts located lateral to iliopsoas tendon (iliopsoas bursal fluid is typically located medial to the tendon) Associate chondral pathology is seen in 30% of labral detachments or tears. Fig. 28: T1FS sagittal (left), PD axial (middle) and PD coronal (right) images depicting paralabral cysts (arrows). Page 31 of 44

32 Fig. 29: T1FS axial image demonstrating a paralabral cyst (arrow) lateral to the iliopsoas bursa (double arrow) and iliopsoas tendon (arrowhead). Pitfalls: Sublabral sulci/recesses may be mistaken for labral tears/detachments Cleft at attachment of transverse acetabular ligament and inferior labrum may be mistaken for a labral tear Relatively hyperintense hyaline cartilage at chondrolabral junction undercuts the labrum mimicking a labral tear. No contrast should extend into an intact chondrolabral junction Iliopsoas tendon adjacent to anterior labrum on axial imaging may mimic a labral tear Intra-osseous tracking of contrast material in a nutrient foramen in the acetabular fossa may be mis-interpreted as acetabular pathology Page 32 of 44

33 The Articular Cartilage of the Hip: Subtle early changes not visible on standard plain MRI may be seen on MR arthrography. Changes may affect acetabular and femoral head articular cartilage Classification or chondral pathology: Grade 0: normal Grade 1: chondral softening, no contour defect Grade 2: cartilage defect, less than 50 % depth of cartilage thickness Grade 3: cartilage defect > 50% depth Grade 4: Full thickness defect, with subchondral bone involvement Advanced chondromalacia : subchondral cyst formation. MRA findings: Oedema, fibrillation of chondral surface Contrast extending into fissures or defects Fig. 30: The PD coronal image on the right demonstrates chondral thinning, oedema and fissuring associated with a subchondral cyst. Contrast this with the normal T1FS sagittal image on the left. Page 33 of 44

34 Fig. 31: PD axial images. The image on the left depicts posterior chondral thinning and oedema. The image on the right demonstrates posterior chondral thinning. Page 34 of 44

35 Fig. 32: PD axial image demonstrating diffuse chondral thinning. Acetabular Pathology: Acetabular Dysplasia: Termed acetabular rim syndrome when associated with labral pathology. Type 1: Shallow, vertically orientated acetabulum, resulting in acetabular / femoral head incongruity. Results in the labrum becoming a weight-bearing component of the hip joint. Type 2: Congruent acetabulum and femoral head with a short acetabular roof. Results in stress to the acetabular rim Page 35 of 44

36 MRA findings: Labral hypertrophy and increased labral length Increased labral signal intensity Superolateral labral tear Anterosuperior acetabular chondromalacia (particularly at the chondro-labral junction) Intra-osseous cyst formation Os acetabuli formation Fig. 33: Frontal radiograph demonstrating right sided acetabular dysplasia. The PD coronal image of the same patient demonstrates the associated labral hypertrophy (arrow). Page 36 of 44

37 Fig. 34: PD coronal image demonstrating an os acetabuli (arrow). Femoroacetabular Impingement (FAI): Cause may relate to acetabular or femoral morphology Is a cause of early onset hip osteoarthritis and labral tears. 1) CAM (femoral) type: Often seen in active young men Causes: DDH; Perthes' disease (Fig 29); AVN; reduced femoral head-neck offset (pistol grip deformity); post-traumatic Prominent bump on contour of femoral head-neck junction Page 37 of 44

38 Results in contact between the femoral head-neck junction and the acetabular rim on hip abduction, flexion-adduction and internal rotation Best seen on oblique axial imaging along the femoral neck Associated with an alpha angle measuring more than 55 degrees on oblique axial image Anterosuperior chondromalacia and anterosuperior labral tear or detachment is present in virtually all cases of Cam-type FAI Associated with a herniation pit in 1/3 of patients A herniation pit is an area of fibrocystic change on the femoral head-neck junction, secondary to repetitive contact with the anterosuperior acetabulum Herniation pits typically measure 3-15mm in diameter Fig. 35: PD axial oblique image demonstrating a prominent head-neck junction bump (arrow). Page 38 of 44

39 Fig. 36: Measurement of the alpha angle is shown. A best-fit circle is drawn over the femoral head. The alpha angle is formed by the axis of the femoral neck (1) and a line (2) drawn from the femoral head centre to the point where the head extends beyond the margin of the best fit circle (arrow). References: Rakhra et al. Clin Orthop Relat Res March;467(3): Page 39 of 44

40 Fig. 37: PD axial oblique image demonstrating a synovial herniation pit (arrow). 2) Pincer (acetabular) type: Often occurs in active middle aged women Causes include: actabular anteversion; acetabular retroversion; acetabular protrusio; coxa profunda Pincer impingement results in: The acetabular rim impinging on the femoral head/neck junction labral degeneration and labral tears (usually anterosuperior, articular side of labrum) Cartilage lesions, most often in a postero-inferior position Page 40 of 44

41 Chondrolabral degeneration or separation (usually anterosuperior or superolateral) Chondromalacia of acetabulum or femoral head Acetabular oedema or sub-chondral cyst formation, usually anterosuperior Acetabular rim osteophyte formation Page 41 of 44

42 Fig. 38: PD coronal image demonstrating ossification of the superior labrum in a patient with pincer FAI (arrow). Fig. 39: Sagittal image demonstrating cartilage damage at the posteroinferior aspect of the acetabulum as seen in pincer impingement. References: Pfirrmann CWA et al. Radiology 2006;240: Pathology of the Joint Capsule: Adhesive Capsulitis: Page 42 of 44

43 Rare Middle aged women Painful and restricted hip movement Fibrotic, thickened and haemorrhagic capsule May be idiopathic, post-traumatic or associated with synovial osteochondromatosis Degenerative changes in labrum or articular cartilage often co-exist Capsular Laxity: Can occur in Marfan's and Ehler's Danlos MRA findings: thickening of the iliofemoral ligament and ligamentum hypertrophy May follow posterior subluxation / dislocation Conclusion MR arthrography is a sensitive and specific method to evaluate the internal structures of the hip joint MRA can reveal pathology not seen on standard non-contrast MR imaging, and alert the surgeon to the site and nature of pathology prior to arthroscopy MR arthrography is an invasive procedure, typically involving the use of ionising radiation for needle positioning, and should be used appropriately. References Saifuddin A. Musculoskeletal MRI. London: Hodder Arnold; 2008 Stoller DW. Magnetic Resonance Imaging in Orthopaedics and Sports Medicine. 3rd Ed. Philadelphia: Lippincott Williams & Wilkins; Chippindale et al. Interactive Hip DVD. Primal Pictures Ltd. Petersilge CA. Chronic Adult Hip Pain: MR Arthrography of the Hip. Radiographics 2000;20: S43-S52 Rakhra KS et al. Comparison of Alpha Angle Measurement Planes in Femoroacetabular Impingement. Clin Orthop Relat Res. 2009;467(3): Pfirrmann CWA et al. Cam and Pincer Femoroacetabular Impingement: Characteristic MR Arthrographic Findings in 50 patients. Radiology 2006;240: Page 43 of 44

44 Personal Information Page 44 of 44