CT Extremities

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Information about CT Extremities
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Published on December 10, 2008

Author: aSGuest5866

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CT OF THE EXTREMITIES : CT OF THE EXTREMITIES Emily Lucchese FAI : FAI Femoroacetabular impingement Results from friction of the hip joint when there is abnormal abutment of the anterolateral surface of the femoral head on the anterior rim of the acetabulum. Important to diagnose as leads to symptoms of chronic pain, reduced ROM and early degenerative arthritis of the hip. FAI : FAI Two forms of impingement: Cam impingement Pincer impingement Characterisation based on anatomic anomaly contributing to the impingement process. Over 80% patients are shown to have both components of pincer and cam impingement. FAI : FAI Cam impingement Cam = Dutch word meaning “cog” Femoral head and neck relationship non spherical Results in intermittent and consistent stress on the articular cartilage as the femoral head is “jammed” into the acetabulum. Causes damage to the acetabular labrum and the articular cartilage of the femoral head and acetabulum. Osteochondral defect known as Ganz lesion. Most common in young males. FAI : FAI Pincer impingement Pincer = French word “to pinch” Abnormal contact between the femoral neck and the acetabular rim with a spherical femoral head Caused by over coverage of acetabular rim as seen in acetabular retroversion and coxa profunda. Leads to acetabular labrum damage and can exacerbate the impingement by increasing the bone growth in the area. Cartilage damage more focal than with Cam impingement. Older age group and more common in women. FAI : FAI Symptoms: Groin pain Pain over trochanters Pain with flexion, adduction and internal rotation Even have clinical symptoms after surgery. Usually unilateral but can be bilateral in patients who have some hip disorders. FAI : FAI Diagnosis: Clinical history Physical examination Imaging methods X Ray CT MRI Important for preoperative assessment to identify the source of impingement. FAI : FAI Radiographic findings Early onset of degenerative arthritis Acetabular retroversion Decrease of the femoral head-neck junction - known as pistol grip deformity Evidence of impaction in regions of the anterosuperior acetabulum and anterior head-neck junction. FAI : FAI MRI Effective as CT with the added bonus of demonstrating articular cartilage damage and acetabular labral tears. No radiation dose to the patient. FAI : FAI CT Very good at demonstrating bony anatomy seen in patients with FAI. Able to demonstrate acetabular retroversion and prominences of the anterior femoral head-neck junction. Dose to pt gonads is a disadvantage and necessity needs to be considered. FAI : FAI Scanning technique Affected side placed in isocentre with the patient supine (not obliqued). Helical scan performed from above acetabulum to below the lesser trochanter. Two reconstructions: Bone plus algorithm Soft algorithm Reformats performed on the workstation. FAI : FAI A true coronal position is achieved by rotating the axis line so it runs through the femoral neck. Axial, coronal, and sagittal MPRs performed. FAI : FAI A batch of images is created parallel to the neck of femur. An image with the best view of the femoral head is selected. FAI : FAI A circular ROI is placed as close to the articular surface of the femoral head as possible. 2 perpendicular lines are inserted to ensure the ROI is circular. An angle is selected with the point at the centre of the ROI. One of the lines is placed parallel to the femoral neck and the other where the anterior cortical bone exits the ROI. The angle made is called the Alpha angle. FAI : FAI Alpha angle Measurement taken of the femoral head and neck junction to determine how much cam impingement exists. The greater the Alpha angle, the larger the cam impingement lesion. Not essential for the diagnosis of FAI. Normal Alpha angle is around 45º. FAI : FAI 2 images are produced perpendicular to the first batch with the 1st image through the widest part of the femoral head and the 2nd through the thinnest part of the neck FAI : FAI These images are then combined. Able to see the femoral head-neck relationship. Neck should be in the centre of the head with equal amounts of bony head surrounding it. FAI : FAI 3D CT images are produced from the soft algorithm reconstruction. 4 images are obtained: True coronal position 45° anterior rotation from the coronal position A lateral image A superior lateral image. FAI : FAI FAI : FAI Treatment Non-operative Arthroscopy Surgical hip dislocation-arthroscopy Periacetabular osteotomy PFJs : PFJs Importance Patella is the largest sesamoid bone in the body and improves the extension capacity of the quadriceps muscle. Knee pain most common complaint in contact sports. Patella tracking abnormalities major cause of anterior knee pain. PFJs : PFJs Injuries of the patellofemoral joint occur in two ways: Abrasive wear Disruption of deep cartilage by force. Signs and symptoms mimic other knee problems. PFJs : PFJs Abnormalities of the PFJ: Patella Alta - Patella too high in the vertical plane. Patella Baja - Low vertical position of the patella. Trochlear dysplasia - Femoral Trochlear Angle > 150°. PFJs : PFJs Patella Alta Increased risk of patella dislocation as more flexion is needed for articulation with the trochlear groove. Associated with small patella, excessive patellar tilt, a dysplastic condyle, a dysplastic trochlea and ligamentous laxity. PFJs : PFJs Patella baja Main culprit for chronic patellofemoral pain and joint stiffness. Is common after trauma or operations to the knee due to a weakened quadriceps muscle. Other causes also include quadriceps muscle rupture or muscular diseases such as poliomyelitis. PFJs : PFJs Trochlear dysplasia One of the main causes for patellofemoral instability. Four grades described Grade A - morphology still preserved Grade B - flat or convex trochlea with a supratrochlear spur. Grade C - asymmetric trochlear facets with a convex lateral and a hypoplastic medial facet. Grade D - grade C dysplasia as well as an over-sized lateral spur of the convex medial trochlear facet. PFJs : PFJs Diagnosis X-ray CT MRI Arthroscopy - gold standard PFJs : PFJs X-ray Skyline patella view - at least 25° flexion required. Cannot assess at important range from 30° flexion to full extension. Difficult to position. Lateral allows measurement of the vertical position of the patella. PFJs : PFJs MRI Amount of possible knee flexion dependant on size of the patient and bore of magnet. Maximum amount of flexion is 30 - 45°. Active imaging is also possible. PFJs : PFJs CT Introduced in 1979. Allows assessment of PFJs in extension and flexion with and without contraction. According to research can perform assessment during active joint motion using multi-slice CT scanner. Measurements are operator dependent and therefore very subjective. PFJs : PFJs Contact stress within the PFJ gradually increases during knee flexion. Studies have been undertaken to assess the best flexion to determine patella tilt. Patella instability best evaluated in the first 20-30 degrees of knee flexion. A subluxated patella returns to a normal position when flexion is >30º. PFJs : PFJs Chance of dislocation greater in full extension as lateral forces of the quadriceps muscle stronger than the medial and the patella not in the trochlear groove. CT allows evaluation in extended position. Muscle contraction included to simulate the effect of weight bearing on the patella. PFJs : PFJs CT Technique Pt is positioned supine with the knees flexed on a 20° sponge. Quads are relaxed with the knees touching so as to reduce FOV. 1st scan from above the patella to below the tibial tuberosity. 2nd scan planned from above patella to top of tibia. Pt contracts quads without changing angle of flexion. PFJs : PFJs PFJs : PFJs Both knees measured. Reconstruction - Bone Plus algorithm. Axial and coronal MPRs are performed. Measurements are performed from the workstation to assess if any morphologic abnormalities. PFJs : PFJs From the raw data the best axial images showing the patella, femoral trochlea and the tibial tuberosity are found for both the left and right knees. The same is done for the contracted series for the patella and femoral trochlea. PFJs : PFJs The two images showing the femoral trochlea and the tibial tuberosity are superimposed. PFJs : PFJs A horizontal line placed parallel to the condylar line. Perpendicular lines are placed through the mid point of the femoral trochlear angle and the mid point of the tibial tuberosity where the tendon insertion sits. Distance between the two lines is the tubercle lateralisation. (N < 9mm) PFJs : PFJs The relaxed axial images for both knees displaying the patella and femoral condyles are superimposed. 4 measurements are made. PFJs : PFJs 4 measurements: Patella tilt angle (PTA) = an angle made by a line parallel to the lateral patella facet and the posterior condylar reference line (N > +4°). Femoral Trochlear Angle (FTA) = formed by the intersection of lines drawn parallel to the medial and lateral trochlear facets (N < 150°). PFJs : PFJs Congruence angle (CA) = made by bisecting the FTA and drawing a second line from the apex of the trochlea to the most posterior point of the patella. If the patella is medial to the bisector, the CA is negative and positive if the patella moves laterally (N < +5°). Measures subluxation. Femoral Trochlear Depth (FTD) = The distance between the most anterior lateral femoral trochlear surface and the femoral condylar line (N > 5mm). PFJs : PFJs The contracted axial images for both knees displaying the patella and femoral condyles are superimposed. This time only the congruence angle and the patella tilt angle are measured. PFJs : PFJs True sagittal images included in the relaxed state with measurements of the patella height and patella tendon length of each knee. PFJs : PFJs Findings 3 patterns of patellar malalignment Type 1 - Patella subluxation without patellar tilting Type 2 - Patella subluxation with patellar tilting Type 3 - Patella tilting without patellar subluxation PFJs : PFJs Treatment Arthroscopic debridement and microfracture technique combined with rehabilitation if a cartilage lesion is present seems to offer great improvement to patients. BERGER PROTOCOL : BERGER PROTOCOL Total knee arthroplasty (TKA) popular treatment for knee disorders. Patellofemoral complications common post TKA. Berger protocol recent CT technique to quantitatively assess malrotation of the femoral and tibial components after total knee arthroplasty. BERGER PROTOCOL : BERGER PROTOCOL Proper axial alignment is essential for a successful TKA. Malrotation of the tibial and femoral components can cause patella: Dislocation Subluxation Tilt Excessive Wear BERGER PROTOCOL : BERGER PROTOCOL Diagnosis Long leg films - used to measure axial alignment but not able to measure rotation. CT Berger protocol - measurements made based on the surgical epicondylar axis and the tibial tubercle. BERGER PROTOCOL : BERGER PROTOCOL CT Values have shown to be a reliable measurement of the tibial and femoral component rotation. Able to determine if revision of either or both components is necessary. Well-tolerated, non-invasive, technology readily available and easy to perform Beam hardening and subjective measurements a problem. BERGER PROTOCOL : BERGER PROTOCOL CT technique Patient positioned supine with the effected knee in the isocentre of the scanner. A helical scan is taken from above the patella to inferior to the tibial tuberosity. Measurements are again made from the workstation. BERGER PROTOCOL : BERGER PROTOCOL An axial image through the surgical epicondylar axis (SEA) which includes the lateral epicondylar prominence and the medial sulcus is found. This is made off an oblique coronal image along the axis of the femur. BERGER PROTOCOL : BERGER PROTOCOL Medial Sulcus Lateral Epicondylar Prominence BERGER PROTOCOL : BERGER PROTOCOL This time a coronal oblique image is angled along the long axis of the tibia. An axial batch of images its made through the tibial component of the knee replacement to below the tibial tuberosity. BERGER PROTOCOL : BERGER PROTOCOL From the axial batch, images containing the tibial component, tibial plateau and the tibial tuberosity are found. The Posterior Condylar Angle is measured from the image of the SEA. BERGER PROTOCOL : BERGER PROTOCOL A line is placed through the SEA and another through the posterior condyles. An angle is placed on the medial side with one line parallel to the SEA and the other parallel to the posterior epicondylar line. A PCA above the posterior epicondylar line is positive and below is negative. BERGER PROTOCOL : BERGER PROTOCOL Normal PCA relative to the SEA Females = 0.3° internal rotation Males = 3.5° internal rotation Normal tibial component angle 18° The resultant malrotation is therefore either x degrees internal or external rotation from this. BERGER PROTOCOL : BERGER PROTOCOL The tibial component axis is found by superimposing the images of the tibial tuberosity and the tibial plateau. The geometric centre of the tibial plateau is found and a line is made from the centre to the tip of the tuberosity. BERGER PROTOCOL : BERGER PROTOCOL The 3 images of the tibial component are then superimposed. An ellipse and line through the tuberosity is placed on the image as similar as possible to the previous one. BERGER PROTOCOL : BERGER PROTOCOL A line is placed parallel to the posterior section of the tibial component. A line perpendicular to that is placed through the centre of the ellipse. The tibial component axis is the angle between the tip of the tuberosity and the line perpendicular to the posterior section of the tibial component. BERGER PROTOCOL : BERGER PROTOCOL The resultant angle is the tibial component axis. N = 18° Any malrotation is either x degrees internal or external rotation from this.

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