Imaging Techniques





Computerized diagnostic imaging techniques applied to the field of radiology has contributed more to medicine than any other method in diagnosing diseases, injuries, and other conditions. The computer is an indispensable tool for managing information and recording programs from various scanning devices that are retrieved and analyzed by a central computer bank. This technology has provided computer graphics and anatomic color images, has changed diagnostic procedures, and given medical specialists a more accurate diagnostic picture. In addition, imaging technology enables physicians to see detailed images of the body in multiple planes without surgery.


The standard radiographic technique depicts a body part as a simple two-dimensional structure portrayed on a radiographic film. Today, imaging technology creates two- and three-dimensional views from any angle. The types of diagnostic imaging are as follows:




  • Nuclear medicine studies —Tests that use radioisotopes; examples are positron emission tomography (PET) and bone scan (scintigraphy) ( Fig. 3-1 ). These studies require an intravenous injection of radio isotopes.






    Fig. 3-1Bone scan image with areas of more active bone formation brighter at knee joint with arthritis.



  • Magnetic resonance imaging (MRI) —Non­invasive technology that combines radio waves and a strong magnetic field with the hydrogen atoms in the body to produce images of bone and soft tissue structures. Some imaging studies require intravenous injection of contrast (gadolinium).



  • Ultrasound (sonography, ultrasonography), digital color Doppler, pulsed Doppler, or power Doppler —Noninvasive forms of imaging that use a small transducer (transmitter/receiver) that is in contact with the area being examined to produce high-frequency sound waves that penetrate the area involved and reflect back to the receiver.



  • Computed axial tomography (CAT scan, CT) and radioisotope imaging (RII) —In musculoskeletal imaging the majority of studies are obtained without contrast, some will require intravenous injection of iodinated contrast. Scans can now be obtained in a continuous helical motion and not just by a single slice at a time. These and other radiographic techniques have been updated and defined in this edition.



Whilst radiography has been an integral part of the orthopaedic examination, new diagnostic imaging techniques enable the orthopaedic surgeon to not only identify the anatomic site but to evaluate the physiologic conditions within and surrounding this site. Specifically, bone density, pathologic changes (necrosis of bone tissue, tumors, infections), spur formation, joint space narrowing, synovial inflammation, nerve impingements, and soft tissue changes can be evaluated. A computer compiles vast amounts of digital data during an examination, and the data are turned into radiology images, including in some cases dedicated videos.


The radiologist , a board-certified physician and specialist in radiology, is often consulted by the orthopaedist and other physicians to give interpretations of imaging technology and of more complicated pathologic conditions. Using image guidance and minimally invasive techniques to gain access to bone, organs, vessels, and other soft tissues, interventional radiologists can diagnose and treat certain conditions that may otherwise require surgery. The radiologist is assisted by qualified technologists who have learned the fundamentals of working with the radiographic and imaging equipment, developing film, and positioning patients. These specialists are challenged to meet the ever-changing technologic demands in their field to capably assist all branches of medicine.


This chapter presents the specialized terminology of radiology, new imaging technology, and its application to orthopaedics.


General Radiologic Terms





  • baseline radiograph: radiograph taken at time of first examination and compared with those taken later.



  • Bennett lesion: seen in baseball players, mineralization of the posterior band of the inferior glenohumeral ligament resulting from posterior capsular avulsion injury.



  • catheter: a thin plastic tube inserted through the skin and into an artery or vein for the injection of contrast material in a vascular arteriography procedure. An example is femoral arteriography.



  • cathode ray tube: vacuum tube that, with a high enough voltage, will produce x-rays.



  • contrast (iodinated): a radiopaque medium that appears of increased density (white) on x-ray image and can be given intravenously, intraarterially, intrathecally, orally, rectally, or into a joint to aid visualization of internal structures; also called contrast radiography, contrast study. New nonionic contrast agents have been developed. Advantages over standard ionic agents are that there are fewer serious allergic reactions in patients at risk for allergic reactions; nonionic agents should be used.



  • contrast (gadolinium): a contrast agent given intravenously for some MR examinations. Gadolinium shortens the T1 time and displays increased signal on T1-weighted sequences.



  • echogenic: tissue or structure that reflects sound waves and give rise to ultrasound echoes. Examples are bone, metal, and air; produce white (hyperintense) areas on ultrasound images. Also called hyperechoic.



  • Hounsfield unit: a measure of radiodensity relative to water, with air being –1000, water 0, and bone between 700 and 3000.



  • hypoechoic: Tissue or structure that reflects few ultrasound waves. Examples are fluid, muscle, and cartilage; produce dark (hypointense) areas on ultrasound images.



  • oscilloscope: instrument that displays computer data of electrical variations on the fluorescent screen of a cathode-ray tube.



  • Pantopaque: trade name for an iodinated oil (radiopaque contrast medium) used in a contrast radiographic procedure (i.e., myelography). It is no longer used due to its lack of resorption, which required complete removal through aspiration at the end of the procedure. This was usually not possible, and the residual material occasionally resulted in chronic irritation and arachnoiditis. Also called iodophenylundecylic acid.



  • rad: measure of r adiation a bsorbed d ose, 100 erg/g (energy per gram).



  • radiograph: image produced on a film by means of ionizing radiation. X-ray , as in a chest x-ray, is a commonly used synonym.



  • radiology: the specialized branch of medicine concerned with the diagnosis of disease utilizing ionizing (e.g., x-rays) and nonionizing (e.g., ultrasound and MRI) radiation; also called roentgenology. A radiologist is a physician specialist who interprets the radiology studies.



  • radiolucent: permitting free passage of ionizing energy (x-ray) through an area, with dark appearance on exposed film.



  • radiopaque: preventing passage of ionizing energy (x-ray), thus allowing the representative area to appear light or white on exposed film.



  • roentgen (R): unit of x- or gamma-radiation exposure; 1 gray = 100 roentgen; 1 centigray = 1 roentgen.



  • roentgenography: the use of x-irradiation to produce either positive or negative film images or fluoroscopic images of objects; also called radiography.



  • scout film: general term for a radiograph prior to the injection of contrast. The purpose is to check the radiographic technique and to look for abnormalities that may be obscured once contrast is given; also called scout radiograph.



  • translucent: allowing some light to pass through but not clearly transparent; for example, soft tissue appears as a light (decreased radiographic density) on a radiograph when compared with bone.



  • wet reading: as implied. Today, films are dried automatically and are read dry. In the past, if an immediate interpretation of the film was required, it was read while still wet. Thus a request for an immediate interpretation may still be called wet reading.



  • x-ray: electromagnetic radiation generally greater than 10 Kev in energy and less than 1 nanometer in wavelength, capable of penetrating tissue; also called roentgen ray.



Orthopaedic Radiographic Techniques and Procedures





  • arthrography: procedure showing interior outline of a joint after contrast (dye) medium or air has been injected intraarticularly; tendon, ligament, or meniscal tears and articular cartilage injuries can be detected in this manner; also called arthrogram. Used in conjunction with imaging modalities MRI, CT, and conventional radiographs.



  • barbotage: typically for calcific tendonitis of the shoulder, using ultrasound and after injection of local anesthetic saline is injected into the calcific area and then withdrawn repeatedly in an attempt to remove the calcium deposits. This term is also used for spinal anesthesia where a portion of local anesthetic in injected into spinal fluid and then aspirated into the syringe, repeating partial injections and aspirations until all of the original contents of the syringe are delivered.



  • bone densitometry: procedure for determining the relative density of bone by using several different radiographic techniques. A density gradient plate can be placed on the film at the same time radiography of the part is being performed. From this plate, a comparative density of the bone can be made, usually of the spine. Photons from a single emitting source can be used to directly measure the density of bone, such as that of the distal radius and lumbar spine. These studies can then be compared with age-matched normal values. This procedure is called photon densitometry.




    • dual photon densitometry (DPD), dual photon absorptiometry (DPA): the use of two different emitting sources to help correct for soft tissue density.



    • dual x-ray absorptiometry (DEXA): the use of two different x-ray voltages to correct for soft tissue density.



    • quantitative computed tomography (QCT): another method of measuring bone density by using computerized tomographic images through lumbar vertebral bodies and comparing the measured density with age-matched normal values.




  • bone marrow pressure: measurement taken to detect bone necrosis. The pressure is taken while intraosseous venography and core decompression are performed to aid in diagnosis of ischemic necrosis of the femoral head, forming an early basis for treatment.



  • bursography: injection of radiopaque dye to show a bursa such as a retrocalcaneal bursa.



  • diskography: visualization of the cervical and lumbar intervertebral disks after direct injection of a radiopaque contrast medium into the disk; also called diskogram.



  • femoral arteriography: radiographic examination in which the femoral artery of the groin is catheterized. Through the femoral artery, the catheter can be directed to arteries throughout the body, including the brain, chest, abdomen, and legs. Contrast is injected through the catheter to identify abnormalities in the arterial system or can be useful in outlining extent of a tumor; also called arteriogram. In some cases, a vascular abnormality can be treated through the catheter (e.g., by angioplasty).



  • fluoroscopy: direct visual radiographic procedure with the use of x-ray tube, fluoroscopic screen, and television monitor for intensification, that is, continuous monitoring showing organ function that can be videotaped; used in gastrointestinal studies, arthrography, and angiography.



  • kidneys, ureters, bladder (KUB): plain frontal supine radiograph of the abdomen, generally not an orthopaedic radiographic procedure, but taken occasionally to study the abdominal wall or suspected masses.



  • lopamidol (Isovue) myelography: this and iohexol (Omnipaque) are water-soluble contrast agents used for myelography after injection of an iodine-based water-soluble contrast medium. The material does not have to be withdrawn after completion of the study, giving some advantages over the oil-based material that must be withdrawn.



  • lymphangiography: radiographic examination after introduction of radiopaque contrast medium into peripheral lymphatic vessels to determine presence of blockage or tumor in proximal lymphatic vessels.



  • myelography: radiographic examination with contrast medium injected into the subarachnoid space under fluoroscopy to examine the spinal cord and canal for possible disk protrusions or lesions; also called myelogram.



  • orthoroentgenography: for measuring limb-length disparity; three separate exposures are taken of the hip, knee, and ankle (or shoulder, elbow, and wrist) to produce an image of the entire limb; also called orthoroentgenogram.



  • pneumoarthrography: injection of air into a joint before radiographic examination to determine internal outline, as in meniscal tear or other injuries and abnormalities; also called pneumoarthrogram.



  • roentgen stereophotogrammetry: simultaneous anterior-posterior and lateral radiographic examination performed with the examined part in a calibration cage. Radiographs can be obtained serially over time to study the progression of bony changes. Computer-driven calculations allow for the identification of three-dimensional changes as small as 2 mm. The technique is particularly useful in the study of prosthetic wear and migration over time.



  • scanography: for measuring leg-length discrepancy, a film is moved beneath the patient for three successive exposures of the three pairs of joints, and a radiopaque scale is placed beneath the limbs so that measurements may be made from the scale of the film. A film 43 cm in length may be used rather than a film two to three times longer; also called scanogram.



  • sinography: radiographic examination for sinus tract infection in bone, performed after injection of water-soluble contrast medium, after saline cleanser, to determine the course of a deep draining wound; also called sinogram.



  • teleroentgenography: for measuring limb-length disparity; radiographic examination performed with the x-ray tube 2 to 3 m (6 to 7.5 feet) from the plate to obtain a more parallel roentgenogram. The entire bone is visualized, but the degree of magnification (approximately 10%) is difficult to assess; also called teleroentgenogram.



  • tomography: used to show detailed images of structures lying in a predetermined plane of tissue, while blurring or eliminating details of images of structures in other planes as in polytomography, planography, or zonography. It is used with radiographic magnification to detect abnormalities of the spine (laminography) or joints and in malunion fractures; also called tomogram.



Routine Radiographic Views


The number of views varies and is determined by the history and physical examination. For instance, an anteroposterior (AP) view may be unremarkable, but a lateral view may reveal a fracture or dislocation, depending on the angle of view taken. A complaint of knee pain often arises from a hip disorder, making radiographic (x-ray) views of the knee or hip important in diagnostic evaluation. Asymmetry of two identical bones (comparing femur to femur) can also exhibit an underlying abnormality. More than one view is usually required to diagnose the chief complaint. The terms are defined first and then given in abbreviated form by anatomic region.




  • Alexander v.: lateral view of scapula with shoulders protracted forward.



  • AP v.: anteroposterior view (x-ray beam passes from front to back).



  • apical v.: apex, tip, or point of subject radiographed.



  • apical lordotic v.: usually of the chest for the apices of the lungs, but for the clavicle if a patient’s symptoms suggest an orthopaedic problem.



  • axillary lateral v.: for the shoulder, lateral view through axilla.



  • Breuerton v.: special view of the hand to search for early joint changes in rheumatoid arthritis.



  • Broden v.: for injuries affecting subtalar joint; lateral view of foot with a 45-degree rotation and various tilts.



  • Bura v.: for ulnar side of wrist; a supinated oblique view taken as an AP with 35 degrees supination.



  • Burnham v.: AP hyperextended view of thumb with dorsum on cassette and 15-degree cephalic tilt.



  • Canale v.: for the talus; an AP view with 75-degree cephalic tilt and 15-degree pronation.



  • carpal tunnel v.: for hook-of-hamate fracture; tangential view of volar wrist taken with wrist in dorsiflexion.



  • Carter-Rowe v.: view of the hip taken at a 45-degree oblique angle to determine size of bone fragment in a posterior acetabular hip fracture or other abnormality of the pelvis.



  • clenched fist v.: to demonstrate scapholunate instability; an AP view is taken with the fist clenched.



  • coned-down v.: close-up of a particular area, with radiation shielded from the rest of the patient’s body.



  • cross-table lateral v.: for hip fracture; lateral view obtained with opposite hip in flexion.



  • Dunn v.: for hip dysplasia, an AP of the pelvis centered at the pubic symphysis with hips flexed 90 degrees and abducted 20 degrees.



  • false profile view: standing lateral x-ray of pelvis with the pelvis rotated 65 degrees to the imaging cassette and with the foot of the affected side parallel to the cassette.



  • frog-leg lateral v.: AP view of hip in abduction and external rotation.



  • Garth v.: for acromioclavicular joint injury; apical oblique with 45-degree caudal and AP tilt.



  • Grashey view: projection used to assess the integrity of the glenohumeral joint. It represents a true AP view. This view is obtained with the patient usually upright and roated 35–45 degrees with their back against the radiographic imaging detector.



  • Harris v.: for calcaneus; AP standing with 45-degree tilt.



  • Hobb v.: for sternoclavicular joint; while standing, the patient bends over end of x-ray table and cassette with hands on head, neck parallel to table, and chest approximately 45 degrees to table. The x-ray beam is vertical to the cassette.



  • Holmberg v.: for femoral notch architecture, two views with patient on hands and knees. A PA radiograph is obtained with beam perpendicular to knee and leg, and knee flexed at 45 degrees and 70 degrees.



  • Hughston v.: knee is flexed to 60 degrees, and view is obtained at a 55-degree angle to show a cartilage-osseous fracture of the femoral condyle or subluxing patella.



  • inlet v.: for pelvic injury; 45- to 50-degree caudad; an AP view.



  • inversion ankle stress v.: AP view of the ankle, which is stressed in inversion to test the integrity of the lateral collateral ankle ligaments.



  • lateral v.: view taken side to side, left or right.



  • lateral monopodal stance v.: for anterior cruciate deficiency; lateral x-ray to detect posterior shift of femur on tibia.



  • Lowenstein v.: a frog-leg lateral.



  • lumbosacral series: multiple views of the lumbosacral spine to include AP, lateral, and oblique views.



  • Merchant v.: tangential superior to inferior patellar view taken with the knee flexed at 45 degrees; also called Knuttson v.



  • mortise v.: view of the ankle rotated internally until medial and lateral malleoli are parallel to film; demonstrates the talus, tibia, and fibula without superimposition; used for comparison with normal AP view and to detect joint abnormalities.



  • Neer transscapular v.: posterior oblique scapular projection to help obtain a lateral view of the shoulder in trauma; also called Neer lateral v.



  • notch v.: prone view of knee with 45-degree caudal from vertical.



  • oblique v.: any view that is off angle from AP, PA, or lateral.



  • odontoid v.: specific for the odontoid process of C2 vertebra; AP view obtained with mouth open; also called open-mouth v.



  • outlet v.: for pelvic injury; 45-degree cephalad AP view.



  • PA: posteroanterior view (from back to front).



  • plantar axial v. of foot: offers visualization of the plantar aspect of the metatarsal heads.



  • prayer v.: for wrist instabilities; lateral view of both wrists at same time with palms pressed together to bring about maximum wrist extension.



  • push-pull ankle stress v.: lateral view of the ankle, which is stressed in an attempt to evaluate the anterior talofibular ligament.



  • Robert v.: AP hyperextended view of thumb with dorsum on cassette.



  • Rosenberg v.: for osteoarthrosis knee; weight-bearing PA with knee at 45-degree flexion and x-ray tube positioned 10 degrees above the horizontal.



  • serendipity v.: for sternoclavicular dislocation or proximal-third fracture of the clavicle; AP view taken with patient supine and tube angled upward 40 degrees from the vertical position.



  • Slomann v.: for tarsal coalition; a 45-degree oblique view of the foot.



  • Stagnara derotation v.: for sever scoliosis rotation deformity, plane of x-ray beam is perpendicular to vertebra in question.



  • Stryker notch v.: for scapular notch an Hill Sachs impaction fracture; view taken with patient supine, hand on head, and camera with 10-degree cephalic tilt.



  • sunset v.: view of patella with knee bent at 120 degrees to permit a profile view; used for examination of patella and adjacent femoral surfaces; also called sunrise v. and tangential v.



  • Supraspintus outlet view: for shoulder impingement by acromion; scapular lateral with a 10-degree caudal tilt; also called supraspinatus outlet v.



  • swimmer’s v.: for lower cervical spine injuries; lateral view obtained with one arm held overhead while other arm is pulled down.



  • transthoracic lateral v.: for proximal humeral fracture or dislocation; view obtained with one arm held overhead and x-ray beam directed through chest.



  • trauma v.: for shoulder injuries; true AP, 45-degree oblique, and Y scapular (tangential) or axillary views.



  • true lateral v.: perfectly positioned lateral projection without rotation.



  • tunnel v.: view of tibia, fibula, and femur only with patella out of the way; a knee notch or intercondylar view; the radiographic examination is done with the tibia and fibula straight and the femur at a 45-degree angle.



  • von Rosen v.: view of the hips in 45 degrees abduction and internal rotation for determining dislocation of the hip(s) in developmental dysplasia.



  • West Point v.: for shoulder (glenoid) injuries; prone axillary lateral view with 25-degree lateral and posterior tilt to camera.



  • Y scapular v.: lateral view of scapula taken at an angle to view scapular blade such that it appears as the stem of a Y with coracoid and spine as the branches of the Y.



  • Zanca v. : for distal-third clavicle fractures or acromioclavicular joint, a 10-degree cephalad view.



Radiographic Views by Anatomic Region


Thoracic Region





  • chest: PA, lateral



  • clavicle: AP, apical lordotic, tangential



  • ribs:




    • anterior: PA, obliques



    • posterior: AP, obliques




  • scapula: AP, oblique, lateral



  • shoulder: AP, internal rotation; AP, external rotation; axillary lateral; transthoracic lateral



  • sternum: right anterior oblique, lateral



Upper Limbs





  • elbow: AP, lateral, oblique



  • hands/fingers: PA, lateral, oblique



  • humerus: AP, lateral, transthoracic lateral



  • radius/ulna: AP, lateral



  • wrist: PA, lateral, oblique, PA with ulnar and radial deviation (for scaphoid fracture), carpal tunnel



Spinal Region





  • C-spine: AP, lateral, both obliques, open-mouth odontoid



  • coccyx: AP, lateral



  • L-spine: AP, lateral, both obliques, coned-down L-5 to S-1 lateral



  • pelvis: AP, inlet, outlet



  • SI joints: AP, both obliques



  • sacrum: AP, lateral



  • T-spine: AP, lateral



Lower Limbs





  • ankle: AP, lateral, and mortise oblique



  • calcaneus: lateral, plantodorsal, axial



  • femur: AP, lateral



  • foot/toes: AP, lateral, oblique



  • hip: AP, frog-leg, and/or cross-table lateral



  • knee: AP, lateral, tunnel, Hughston



  • patella: tunnel, sunset, lateral, PA, merchant



  • tibia/fibula: AP, lateral



Additional views requested may be views in flexion and extension, special views of the skull, push-pull films of hips for piston sign, and cine (movies) of x-ray images.


Radiographic Angles, Lines, Signs, and Methods


Angles


The anatomic description is taken directly from points using the intersection of two straight lines to form the angle.




  • acetabular a.: angle created by the intersection of a line from the inferior margin to the superior margin of the acetabulum and a line horizontal to the pelvis (connecting two inferior acetabuli; Fig. 3-2 ).






    Fig. 3-2Radiographic measurements for hip dysplasia. 1, horizontal Y line (Hilgenreiner line); 2, vertical line (Perkins line); 3, quadrants (formed by lines 1 and 2); 4, acetabular index (Kleinberg and Lieberman); 5, Shenton line; 6, upward displacement of femoral head; 7, lateral displacement of femoral head; 8, U figure of teardrop shadow (Kohler); 9, Y coordinate (Ponseti); 10, capital epiphyseal dysplasia ( a, delayed appearance of center of ossification of femoral head; b, irregular maturation of center of ossification); 11, bifurcation (furrowing of acetabular roof in late infancy [Ponseti]); 12, hypoplasia of pelvis (ilium); 13, delayed fusion (ischiopubic juncture); 14, adduction attitude of extremity. (Modified from Kelly DM: Congenital and developmental anomalies of the hip and pelvis. In Canale ST and Beaty JH, editors: Campbell’s operative orthopaedics, ed 12, Philadelphia, 2013, Elsevier, Fig. 30-4B.)



  • acetabular index: angle formed between lateral margin of acetabular roof and inferior aspect of the pelvic “teardrop” and horizontal line between the inferior aspect of both pelvic “teardrops.”



  • acromial a.: measured in patients with shoulder impingement by drawing a line along the inferior acromial cortex on either side of the apex, resulting in anterior and posterior lines that cross to form an angle.



  • alpha a (α angle): a measure for femoral acetabular impingement on an axial MR image, angle made by the intersection of a line from the center line of the femoral neck to the central part of the femoral head, to a line from the central femoral head to a point where the contour of the femoral head-neck junction exceeds the radius of the femoral head. An angle greater than 55 º is considered CAM impingement.



  • anatomic femorotibial a. (FTA): angle created by the intersection of lines through the shaft of the tibia and the shaft of the femur.



  • Baumann a.: there are two angles: in children an angle between a line parallel to the longitudinal axis of the humeral shaft subteneded by a line drawn along the growth plate of the lateral epicondyle. The normal range is 70–75 degrees. The second is the angle between the line perpendicular to the long axis of the humerus and the growth plate of the lateral condyle. Normal is 9 to 26 degrees. Also known as the humeral-capitellar a.



  • bimalleolar a.: angle drawn by bisection of line horizontal to ankle joint with line crossing medial and lateral malleolar tips. This angle is typically 23 degrees.



  • Böhler a.: angle formed by intersection of a line drawn from the cephalic aspect of the anterior calcaneal tuberosity to the superior point of the posterior facet with a line drawn from the superior point of the posterior facet to the superior posterior calcaneus, normally 20 to 40 degrees.



  • carrying a.: for the AP angle of the extended elbow, that is, the angle of the forearm when arm is extended.



  • center edge (CE) a.: created by two lines drawn from the center of the femoral capital epiphysis, one line being vertical and the other extending to the acetabular edge. Also called Wiberg a.



  • critical shoulder angle: for rotator cuff impingement and repair durability, on an anterior posterior radiograph an angle made by the intersection of a vertical line drawn from the edge of the inferior to superior glenoid and a line from the inferior glenoid to the lateral acromion.



  • Codman a.: discrete angle at edge of the bone cortex produced by periosteal elevation and reactive bone in the area of a tumor; also called Codman triangle.



  • condylar-plateau a. (CPA): angle created by the intersection of a line parallel to the tibial plateau surfaces and the distal femoral condyles.



  • congruence a.: bisecting angle of the patella intersecting with vertical angle from trochlea ( Fig. 3-3 ).






    Fig. 3-3Radiographic measurements to evaluate patellar instability. A, Insall-Salveti ratio, LT–LP, normally 0.8 to 1.2. B, Measurements of patellofemoral congruence described by Merchant et al. F, facet; L, lateral condyle; M, medial condyle; P, patellar ridge; S, sulcus. Angle MSL is sulcus angle (average, 137 degrees; standard deviation, 6 degrees). Line SO is zero reference line bisecting sulcus angle. Angle PSO is congruence angle (average, –8 degrees; standard deviation, 6 degrees). Line PF (lateral facet) and line ML form patellofemoral angle that should diverge laterally. Ratio of lateral height at L to medial height at M is normally 1.65. (Modified from Phillips BB: Recurrent dislocations. In Canale ST and Beaty JH, editors: Campbell’s operative orthopaedics , ed 12, Philadelphia, 2013, Elsevier, Figs. 47-4 and 47-10.)



  • coronal femoral component a.: for knee replacement positioning, the angle of distal femoral cut to the anatomic line through the femur seen on AP projection.



  • coronal tibial component a.: for knee replacement positioning, the angle of proximal tibial cut to the anatomic line through the tibia seen on AP projection.



  • costophrenic a.: angle formed at the junction of the costal and diaphragmatic parietal pleura.



  • costovertebral a.: angle made between the twelfth thoracic rib and the T12 vertebra at the posterior inferior margin of the thoracic cage on each side.



  • crucial angle of Gissane: seen on lateral radiograph of foot; angle created by posterior facet of calcaneus and the superior anterolateral surface of the calcaneus.



  • femoral tibial a.: angle created by anatomic axis of the femur and tibia (line drawn from midpoint of proximal and distal shaft). Average is 6 degrees of valgus.



  • Ferguson’s a.: represents the angle of the lumbosacral junction as measured by the inclination of the superior surface of the first sacral vertebra to another line parallel to the ground (usually measured from a standing lateral film); also called sacral base a.



  • Fick a.: standing foot angle or Fick’s angle represents the amount of toeing in ( decreased foot a. ) or toeing out ( increased foot a. ) observed during stance.



  • Fowler-Phillip a.: to measure degree of pump bump; angle created by intersection of a line from the posterior surface and the plantar surface of the calcaneus.



  • hallux valgus a.: angle created by intersection of a longitudinal line through shaft of first metatarsal and the shaft of the proximal first phalanx.



  • head-shaft a.: for slipped capital femoral epiphysis; angle between the femoral head physis and a vertical line drawn through the femoral shaft seen on frog-leg projection; also called Southwick a.



  • Hibbs a.: two angles created by intersection of a longitudinal line of first metatarsal and the line of the plantar surface of the calcaneus.



  • Hilgenreiner a.: angle of the acetabular slope to the Y-line (horizontal line drawn through both acetabular centers); also called acetabular index a.



  • Hilgenreiner epiphyseal a.: for coxa vara or slipped epiphysis angle of intersection of Y-line with line drawn through femoral physis.



  • Kager triangle: triangular space anterior to the Achilles tendon normally visible on radiographs as a radiolucent area.



  • Kerboul a.: for determining extent of osteonecrosis of the femoral head on radiograph or MRI, angle created by extending lines from the center of the femoral head to the subchondral margin. margin of extent of osteonecrosis. Coronal and sagittal images can be used for a combined Kerboul a.



  • Konstram a.: for gibbus deformity; the obtuse angle created by the intersection of the two lines drawn parallel to the surface of the superior vertebral body above and inferior surface of vertebral body below the deformed segment.



  • lateral distal femoral a.: angle of a line from the femoral head to the tibial spine to a horizontal line across the two femoral condylar surfaces; measured in the superolateral of the four quadrants obtained.



  • Laquena and Deseze a.: for acetabular coverage of femoral head in developmental hip dysplasia; using a lateral x-ray view, the angle between a line seen in the shaft of the femur and from the center of the femoral head to the anterior acetabular rim; also called ventral inclination a. (VCA).



  • Laurin a. (lateral patellofemoral a.): acute angle created by intersection of line drawn from medial to lateral condylar points and a line parallel to the lateral undersurface of the patella. The angle is positive when it opens laterally.



  • Levine Drennan a.: angle that lies between a line drawn through the most distal points of the medial and lateral beaks of the metaphysis and a line perpendicular to the lateral cortex of the tibia; also called metaphyseal-diaphyseal a.



  • Lewinnek safe zone: for positioning of the acetabular cup in total hip arthroplasty, cup inclination and anteversion of 40° ± 10° and 15° ± 10°, respectively, represent a “safe zone.” This can be affected by spino-pelvic inclination.



  • lumbosacral a.: angle between the inferior plate of L5 to line of superior plate of sacrum. Typically the sacrum is inclined such that the sacral line opens anteriorly in reference to the lumbar line.



  • Meary a.: angle formed between the long axis of the talus and the first metatarsal on a lateral weight-bearing view. This line is used as a measurement collapse of the longitudinal arch. An angle that is greater than 4 degrees convex downward is considered pes planus.



  • mechanical axis: line created between the center of the femoral head and the center of the talus. In a normal knee, this axis passes close to the center of the joint; also called Maquet line.



  • medial proximal tibial a.: for tibial plateau slope; the angle created by a vertical tibial shaft line and a line across the tibial plateaus; measured in the inferomedial of the four quadrants drawn.



  • Merchant a.: created on a Merchant view by intersection of two lines, one drawn from the intracondylar apex of patella to center and a line perpendicular to plane of condyles.



  • Mikulicz a.: angle of declination of the proximal femur formed by the neck of the femoral epiphysis and diaphysis center lines. It is the same as the neck shaft angle.



  • neck shaft a.: created by intersection of a line drawn through the femoral shaft and a line through the femoral head and neck.



  • Pauwels a.: of a femoral neck fracture in reference to the horizontal line of a standing patient.



  • pelvic femoral a.: of inclination formed by a line parallel to the tilt of the pelvis with line of femoral shaft.



  • physeal a.: for Legg-Calvé-Perthes disease; the angle created by intersection of a line drawn vertically though the femoral shaft and the line of femoral head physis; also called physeal slope.



  • pitch a.: a line is drawn from the plantar-most surface of the calcaneus to the inferior border of the distal articular surface. The angle made between this line and the transverse plane of the floor is the calcaneal pitch angle. A decreased pitch is consistent with pes planus. Also called calcaneal inclination a.



  • Q angle: made by intersection of lines drawn from anterosuperior iliac spine to midpatella and from midpatella to anterior tibial tuberosity.



  • radial inclination a.: measured by drawing a perpendicular line to the radial axis through the distal sigmoid notch and by drawing another line joining the tip of the radial styloid and the distal sigmoid notch. These two lines form the radial inclination angle (normal angle 21–25 degrees).



  • sacrovertebral a.: obtained by junction of lines through lateral projection of sacrum and lumbar spine.



  • sagittal femoral component a.: for knee replacement positioning, the angle of distal femoral cut to the anatomic line through the femur seen on lateral projection.



  • sagittal tibial component a.: for knee replacement positioning, the angle of proximal tibial cut to the anatomic line through the tibia seen on lateral projection.



  • Sharp a.: defined by intersection of lines from inferior acetabulum (bottom of teardrop) to superolateral acetabulum and a horizontal line.



  • slip a.: angle of the line of the inferior body of L5 to the line of the superior body of S1. As L5 slips forward on S1, this angle reverses.



  • Southwick a.: for slipped capital femoral epiphysis, on lateral radiograph of the hip the angle created by a line through the center of the shaft of the femur to a perpendicular line to a line through the base of the epiphysis. The angle is compared to the normal side. If both sides affected at an angle greater that 12 degrees is considered abnormal, less than 30 degrees is mild, 30 to 50 degrees is moderate, and more than 50 degrees is severe; also called posterior slip a. and epiphyseal shaft a.



  • sternal a: angle formed by the junction of the manubrium and the body of the sternum; also called the angle of Louis.



  • sulcus a.: on Merchant view, lines drawn from apex of medial and lateral condyles to lowest point in groove to create this obtuse angle.



  • T1 pelvic a.: On sagittal spinal projection, angle created by a line from the center of the femoral head to the center of the vertebral body of T1 and a line from the femoral head to the middle of the superior plate of S1.



  • talocrural a.: angle created by intersection of lines, one drawn parallel to the tibial plafond, the other across the tips of the medial and lateral malleoli; normally 8 to 15 degrees.



  • thoracic lumbar spinopelvic inclination: for spinal hip relationships, on sagittal spinal projection, angle created by a line from the center of the femoral head to the center of the vertebral body of T1 and a line from the femoral head to the most anterior part of a lumbar vertebral body. Also known as TL spinopelvic inclination



  • Tönnis a.: on an AP projection of the pelvis, the angle created by the intersection of a line parallel to the ischial tuberosities and the slope of the sourcil, which is the dense subchondral bone of the roof of the acetabulum.



  • Ward triangle: relatively radiolucent area of bone in the intertrochanteric area of the femur.



Lines, Indices, and Ratios


A line is defined as that seen or drawn directly on the film to help in the interpretation of the radiograph or an anatomic line of reference.




  • acetabular coverage: may be expressed as distance from lateral lip of acetabulum to lateral edge of the femoral head, or as a ratio of the width of the femoral head divided into distance from the lateral lip of acetabulum to the lateral edge of the femoral head.



  • acetabular depth: depth of the longest possible vertical line drawn perpendicular to a line crossing the superior and inferior acetabular margins.



  • acetabular head quotient: for hip dysplasia; the ratio of the radius of the femoral head divided by the distance from the femoral head center to a vertical line drawn from the acetabular lip.



  • acetabular l.: line drawn from superolateral tip of both acetabuli for measuring femoral head or prosthetic migration.



  • Akagi line: for plate position in total joint replacement, a line connecting medial edge of the patellar tendon attachment and the middle of the PCL. This line is typical perpendicular to the surgical epicondylar axis in normal knees.



  • anteversion: descriptive of axial rotation. For example, the normal relationship of femoral head is 20 degrees anterior to axis of femur.



  • Blackburne-Peel ratio: for a patella alta, the distance from the inferior articular margin of the patella to the line parallel to the tibial surface is divided by the length of the articular surface. Normal range is 0.54 to 1.06.



  • Blumensaat l.: line parallel to superior part of intercondylar notch as seen on lateral radiographs; used to judge the relative height of the patella.



  • canal bone ratio: the ratio between the endosteal and outer diameters of the proximal femur at 10 cm below the lesser trochanter.



  • canal calcar ratio: the fraction of the isthmus canal width divided by the calcar canal dimension.



  • canal flair index: ratio of the canal width at 10 cm below the lesser trochanter over the canal width at 2 cm above the lesser trochanter.



  • canal-to-calcar isthmus ratio: for proximal femoral canal cylindrical configuration; two vertical lines are drawn from points on the inner cortex, one 10 cm from the mid-lesser trochanter and the other 3 cm from the mid-lesser trochanter. The ratio is the width of the space between these two lines at the mid-lesser trochanter divided by the width of the canal 10 cm distal to that point.



  • carpal height ratio: for capitate instability in the wrist; the ratio of the length of the third metacarpal to the length of the wrist from the base of the third metacarpal to the distal radius. The revised carpal height ratio is the width of the wrist from the base of the third metacarpal divided by the length of the capitate.



  • Caton-Deschamps ratio: for patella baja or alta, from a lateral projection of the knee. The ratio of a line drawn from the anterior corner of the tibial surface to the lower articular margin of the patella divided by the length of the patellar ­articular ­surface. Normal range is 0.6 to 1.2.



  • central sacral l.: the vertical line on a frontal radiograph that passes through the center of the sacrum.



  • cervico-obturator l.: a curve that can be drawn on an AP view of the pelvis. This line continues from the inferior border of the femoral neck to the inferior border of the pubic ramus. An interruption in the line is suggestive of an abnormal position of the femoral head. Also called Shenton l.



  • Chamberlain l.: for developmental basilar skull impression onto cervical spine; a line drawn from the posterior edge of the foramen magnum to the posterior edge of the hard palate, on a lateral projection.



  • demarcation l.: zone between normal and abnormal tissue, most commonly used to denote area or line of normal-appearing tissue next to gangrenous tissue in a devitalized limb. This term is also used in describing radiographic evidence of disease that shows a clear line or zone of activity.



  • Dorr ratio: for proximal femoral canal cylindrical configuration; width of the canal at the mid-lesser trochanter divided by the width of the canal 10 cm distal to that point.



  • double line s.: seen on MRI in osteonecrosis of the femoral head, comprised of both granulation tissue (mixed consistency hyperintense line) and a margin of sclerotic bone (hypointense line).



  • epiphyseal l.: line of fusion of the physeal growth plate.



  • Feiss l.: a line drawn on a standing lateral radiograph between the tip of the medial malleolus and the base of the first metatarsophalangeal joint. The position of the navicular tuberosity is noted, and it should not lie below the line. The Feiss line is used in evaluation of pes planus.



  • femoral cortical index: ratio of the femoral diameter of the outer cortex to the inner cortex 10 cm distal to the mid-lesser trochanter.



  • femoral head neck offset: not to be confused with femoral offset, this measures the ratio of the distance from the outermost margin of the femoral head to the femoral neck to the radius of the femoral head.



  • femoral offset: perpendicular distance from the center line of the femoral shaft to the center of the femoral head.



  • femoral shaft l.: line drawn from midpoint of proximal and distal shaft; also called the anatomic femoral axis.



  • Fischgold and Metzger l.: for basilar skull invagination transverse line on AP projection centered on C1. Also called digastric l. or biventer l.



  • fracture l.: any line thought to be the result of a fracture.



  • Frankel l.: a white line in the physis zone of provisional calcification, which can be seen on a bone radiograph in a patient with scurvy.



  • growth-arrest l.: line of bony density seen on radiograph of a long bone. This may represent a growth-arrest scar from the growth plate as a result of stress (fracture or an illness) during a period of growth; also called Harris l. and Harris-Park l.



  • herniation pit: not a true herniation, but a point of wear in the femoral neck caused by misshaped femoral head or acetabulum leading to impingement on the anterior acetabulum.



  • Hilgenreiner l.: a horizontal line drawn between the two triradiate cartilage centers of the hips defines a horizontal plane and an approximation to the flexion axis of the hips.



  • Hueter l.: line drawn horizontal to the medial epicondyle of the humerus, passing tip of olecranon when elbow is extended.



  • Insall ratio: for patella alta; with the knee flexed at 30 degrees, the ratio is the length of the patella tendon to the height of the patella. A number greater than 1.3 indicates patella alta; also called Insall-Salvati ratio.



  • K line: for cervical kyphosis, a virtual line between the midpoints of the antero-posterior canal diameter at C2 and C7, helps determine surgical procedures for ossification of the posterior longitudinal ligament (OPLL).



  • Klein l.: a line tangential to the superior femoral neck on an AP view of the pelvis. Normally, a portion of the femoral head is above this line. In patients with a slipped capital femoral epiphysis, the femoral head is below this line or a smaller portion of the femoral head is above this line when compared with the contralateral view.



  • Kohler l.: slanted line drawn from the acetabular teardrop to the most lateral tangent of the pelvic ring (commonly the sciatic notch).



  • lead l.: radiopaque (white) thin line in the metaphysis (end region) of bones in a patient with lead poisoning.



  • Maquet l.: line drawn from center of femoral head to midtalus; normally passes through middle of the knee.



  • McGregor l.: for developmental basilar skull impression onto cervical spine; line drawn from base of occiput to posterior edge of hard palate.



  • McRae l.: for developmental basilar skull impression onto cervical spine; a line drawn from anterior to posterior edge of the foramen magnum.



  • medialization ratio: percentage of the horizontal radius of the cartilaginous femoral head medial to vertical line drawn from lateral tip of acetabulum, as seen on an arthrogram with the hip in the position of reduction.



  • morphological cortical index: outer cortical diameter at the lesser trochanter divided by the endosteal width 7 cm below the lesser trochanter



  • necrotic index: for extent of avascular necrosis of the femoral head, MRI midcoronal and midsagittal are measured by the angle created lines drawn from the outer extent of necrotic margins to the center of the femoral head. These angles are each divided by 180, added together, and that sum multiplied by 100. The modified necrotic index uses the MRI images that have the widest extent.



  • Nélaton l.: drawn from the anterosuperior iliac spine to the ischial tuberosity; normally goes through the greater trochanter forming one side of Bryant triangle.



  • obturator/brim l.: drawn from inner pelvic brim to midobturator foramen. It is used in determining the degree of femoral head or prosthetic migration.



  • Ogston l.: drawn from adduction tubercle to intercondylar notch; used as a guide for transection of condyle in osteotomy for knock-knee deformity.



  • patella subluxation ratio: for patellar subluxation; ratio created by the distance of medial femoral condylar margin to apex of patella divided by the depth of the patella groove.



  • Pavlov ratio: for spinal cord space in cervical spine; ratio of vertebral body width to spinal canal diameter ( Fig. 3-4 ).


Dec 24, 2021 | Posted by in ORTHOPEDIC | Comments Off on Imaging Techniques
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