The aim of this work is to compare the role of CT hip arthrography to MR arthrography in the detection of intra-articular hip pathology.

The hip joint is a ball-and-socket synovial joint designed to allow multi-axial motion while transferring loads between the upper and lower body. The acetabular rim is lined by fibrocartilage (labrum), which adds depth and stability to the femoro-acetabular joint. The articular surfaces are covered by hyaline cartilage that dissipates shear and compressive forces during load bearing and hip motion.

Various anatomical factors make the investigation of suspected intra-articular hip pathology challenging. Lesions of the labrum, cartilaginous lesions, femoro-acetabular impingement (FAI), and intra-articular foreign bodies are the most common intra-articular pathology , others causes of intra-articular hip pain include ligamentum teres rupture, degenerative changes, arthritis (inflammatory, infectious, etc.), and synovial proliferative disorders.

The labrum is a fibrocartilaginous triangular-shaped incomplete ring that surrounds the bony acetabulum. The labrum increases the depth of the acetabulum, thereby assisting hip stability and distributing hip load. It also seals the hip joint, helping to maintain synovial fluid within the central compartment and becoming a mechanical stabilizer. The articular cartilage of the acetabulum has a horseshoe shaped appearance with an opening at the acetabular notch, is not as thick as in other joints such as the knee. Hip cartilage in adults has been estimated to be between 1 and 2 mm in thickness. Thus, plain MRI and CT have limited value in assessing labral and articular cartilage disorders. Acetabular labral tears are a potential source of hip pain in young adults. Many underlying conditions may predispose to labral degeneration and tear including prior trauma, femoroacetabular impingement (FAI), developmental dysplasia of the hip (DDH), capsular laxity, and congenital abnormalities involving the axis of the joint such as acetabular retroversion and anteversion. Labral tears rarely occur in the absence of bony abnormalities and that neglecting these underlying structural abnormalities may result in treatment failure. FAI is defined as an abnormal contact between the femoral head and the acetabulum that limits normal range of motion. Although two types were defined (pincer when focal or general acetabular over coverage occurs and cam when there is an abnormal contact between the femoral head-neck junction and the anterior acetabulum), most patients have mixed types.

Arthroscopy is the gold standard for clarifying diagnostic dilemmas but is an invasive procedure with possible complications and cannot be applied to every patient with suspected but not established hip pathology. Thus, imaging may play an important role in planning joint-preserving treatment options in those cases and thus preventing early hip osteoarthritis.

The diagnosis of a labral tear is made on CT arthrography (CTa) and MR arthrography (MRa) when contrast fluid gets inside the labrum. Fluid-sensitive sequences are needed on MRa to detect intrasubstance labrum changes, especially those that do not extend to the articular surface. Unless calcified, these changes are missed on CTa.

Much of the radiology literature has focused on the use of MRa of the hip to detect labral and cartilage pathology. Both non-contrast MRI and MRa have limitations in terms of spatial resolution, which can make the detection of subtle labral and cartilage pathology challenging.

CT arthrography (CTa) with its superior spatial resolution offers several advantages over plain MRI for the evaluation of articular cartilage. Image acquisition at a submillimeter scale together with the availability of multiplanar reformations can reveal early intraarticular changes that are poorly detected on plain MRI. Although Multidetector Computed Tomography (MDCT) has higher spatial resolution than MR, it has significantly lower contrast resolution, and thus labra and extraarticular pathology are not evaluated to the same extent.

CTa may be indicated in cases of MR incompatibility and MR contraindications. So in our study we try prospectively to evaluate the diagnostic value of CTa in comparison to MRa in detection of intraarticular hip pathology

Inclusion Criteria:

• 60 consecutive patients presenting with clinical and routine imaging suggestive of intraarticular hip pathology.
• patients must be accept the intraarticular hip injection of contrast.

Exclusion Criteria:

• Any general contraindication of MRI in some cases as presence of anti-paramagnetic substance as pacemakers aneurysm clips, metallic cochlear implants
• Severely ill patients or those with claustrophobia
• Any general contraindications to radiation in some cases such as pregnancy at first trimester.

Patients of different sex and age groups presenting to the Radiology department with clinical and routine imaging suggestive of intraarticular hip pathology.