Musculo_skeletal Imaging

·         "Y" view: It is a special radiographic view of the shoulder that shows the head of the humerus sitting between the two projections off the scapula, namely the acromion and the coracoid process, forming a Y. This view is helpful in determining the relative position of the humeral head and the glenoid fossa and aids in the diagnosis of shoulder (glenohumeral) dislocation.

·         The posterior fat pad and sail signs indicate the presence of an intra-articular elbow fracture. Fat is normally present between the synovium and capsule of the elbow joint, which is normally not radiographically visible, with the exception of occasional normal anterior fat pad that may be seen as a small lucency immediately adjacent to the anterior cortex of the distal humerus. With intra-articular fracture, however, subsequent hemarthrosis distends the synovium and causes displacement of this fat. The posterior fat pad becomes visible as a radiolucency and the anterior fat pad is lifted away from the bone as a triangular radiolucency, causing it to resemble a sail.

·         Scapholunate dissociation results from ligamentous disruption between the scaphoid and lunate. This is manifested by widening of the space between the scaphoid and lunate on the AP view of the wrist and is known as the Terry-Thomas sign. Terry Thomas (1911-1990) was a gap-toothed British comic actor.

·         DISI (dorsal intercalated segmental instability) and VISI are terms used to describe carpal instability based on the tilt of lunate on the lateral radiograph of the wrist. With DISI, the lunate tilts dorsally. With VISI, the lunate tilts in a volar direction.

·         Segond fracture: It is an avulsion fracture of the proximal lateral tibia at the site of attachment of the lateral ligament. The fracture fragment may be very small. Even though it may not look so terrible on a radiograph, it is commonly associated with anterior cruciate ligament tear and meniscal injury.

·         tibial plafond fracture: It is an intra-articular fracture of the distal tibia caused by impaction of the talus and is often comminuted.

·         A swimmer's view is obtained when the lower cervical vertebrae cannot be seen on the lateral view, usually due to a patient's inability to cooperate or a large shoulder girdle obscuring the view. This view is obtained by having the patient, in the supine position, raise his or her arm over the head while lowering the other arm.

·         Chance fracture: There is horizontal splitting of the posterior elements extending anteriorly to involve the vertebral body and/or intervertebral disc space. It is often associated with tearing of the posterior ligament complex. It is also called a "seat belt fracture" after acute hyperflexion. Presence of this fracture should alert the clinician to the existence of significant intra-abdominal injury.

·         Risser classification: It is a gross measure of skeletal maturity as determined by the amount of ossification of the iliac apophysis. The apophyseal ossification begins laterally and progresses medially with increasing skeletal maturity. The Risser classification is significant in scoliosis because the likelihood of progression is high in low Risser stages (e.g., skeletal immaturity) and decreases once the patient reaches skeletal maturity

·         radiographic signs of degenerative disc disease: Disc space narrowing; osteophyte formation; end-plate sclerosis; Schmorl's nodes; vacuum disc phenomenon; facet osteoarthritis; neural foraminal narrowing; and in the cervical spine, uncovertebral joint hypertrophy.

·         A Schmorl's node is a herniation of intervertebral disc material through the vertebral end plate, resulting in a lucent area at the end plate with surrounding sclerosis on radiographs and computed tomography (CT) and possibly surrounding edema on magnetic resonance imaging (MRI)

·         TERMINOLOGY OF DEGENERATIVE DISC PATHOLOGY

1.       Disc bulge: diffuse, symmetric extension of the disc beyond the end plate.

2.       Disc protrusion: more focal extension of the disc. It may be central, left/right paracentral, or left/right lateral. The "neck" is wider than the more distal portion.

3.       Disc extrusion: herniation of a portion of the disc. The "neck" is the narrowest part. The extrusion often extends superiorly or inferiorly along the long axis of the spinal canal.

4.       Disc sequestrum: free disc fragment in the epidural space that has lost its connection to the disc.

·         THE C8 NERVE ROOT

1. C8 is a nerve root without a vertebral body. It exits between C7 and T1.
2. As a result of C8 exiting between C7 and T1, cervical nerve roots exit above the pedicles of the same-numbered body.
3. As a result of C8 exiting between C7 and T1, thoracic and lumbar nerve roots exit below the pedicles of the same-numbered body.

·         DISH stands for diffuse idiopathic skeletal hyperostosis (also known as "Forestier disease"). DISH has many manifestations throughout the body, including calcification and ossification of ligamentous and tendinous insertion sites, particularly involving the pelvis and patella (known as "whiskering"); enthesophyte formation on the calcaneus and olecranon processes; and para-articular osteophyte formation, particularly around the hip joints. However, its most common manifestation is in the spine, where it is associated with calcification and ossification of the anterior longitudinal ligament and large bridging osteophytes anteriorly and laterally, sometimes interrupted by linear lucencies due to herniation of intervertebral disc material. OPLL can occur in DISH as well.

·         Kümmell's disease: Compression fracture of the vertebral body with intraosseous vacuum phenomenon. This is believed to represent osteonecrosis of the vertebral body with secondary fracture.

·         Sites for DEXA: The lumbar spine, from L1 or L2 to L4, and the proximal femur (regions of interest are the femoral neck, trochanteric region, and Ward's triangle). Ward's triangle is a site at the proximal femur where bone mineral loss is thought to occur first

·         DIFFERENTIATING ARTHRITIS ON HAND X-RAY

1.       Symmetric erosive change of the metacarpophalangeal and proximal interphalangeal joints of both hands suggests RA.

2.       Extensive productive osteophyte changes of the distal interphalangeal joints, with less severe changes of the proximal interphalangeal and metacarpophalangeal joints, or a thickened "sausage-digit," suggests psoriatic arthritis.

3.       Osteophyte production and joint-space narrowing without marginal erosions of the distal interphalangeal and proximal interphalangeal joints, with little or no involvement of the metacarpophalangeal joints, suggests degenerative joint disease.

4.       A soft tissue mass with an overhanging rim of bone, adjacent to a joint space, suggests gout.

5.       Calcifications within the soft tissues of the fingertips and/or resorption of the cortex of the finger tufts suggest scleroderma or polymyositis.

·         Both cellulitis and osteomyelitis demonstrate high soft tissue uptake of the radiotracer in the blood flow and blood pool phases. Differentiation between the two types of infection occurs in the delayed phase. In cellulitis, there is mild, diffuse bone uptake on delayed images. In osteomyelitis, there is focal, intense radiotracer uptake of the infected bone.

·         Phemister's triad refers to the classic radiographic findings of tuberculous arthritis:

1.       Periarticular osteoporosis

2.       Peripherally located osseous erosions

3.       Gradual narrowing of the joint space

Preservation of the joint space is the hallmark of tuberculous arthritis and helps to distinguish it from the rapid joint destruction of pyogenic (bacterial) arthritis.

·         NOF & FCD Both are benign, usually asymptomatic, well-defined cortical-based lesions with sclerotic borders seen in the metaphysis or diametaphysis of long bones and are identical in their histology. They differ only in their size. Fibrous cortical defects are smaller (<2 cm), whereas NOFs are larger (>2 cm) and are usually detected incidentally on radiographs in children and often subsequently heal with sclerosis.

·         A bone island, or enostosis, is a benign lesion that appears radiographically as an oval or round sclerotic focus that may have radiating bone spicules from the center of the lesion. Bone islands are typically asymptomatic, incidentally discovered, and usually do not show increased radiotracer uptake on a nuclear medicine bone scan.

·         SHOULDER MRI

1.       There are three primary diseases that can be seen on MRI of the shoulder: osteoarthritis, rotator cuff tears, and abnormal structures related to the clinical diagnosis of instability.

2.       Radiographs should be obtained before MR images. Many times, rotator cuff tears can be diagnosed by the narrowing of the distance between the undersurface of the acromion and humeral head.

·         SLAP is a type of glenoid labral tear that extends anteriorly and posteriorly. SLAP is an acronym that stands for superior labrum anterior and posterior. It is usually seen in athletes who throw or after shoulder trauma. Subtle SLAP lesions may be difficult to diagnose on routine MRI. MR arthrography increases the sensitivity for detecting these abnormalities.

·         Calcific tendinitis is a type of tendon pathology seen about the shoulder. It is formally known as calcium hydroxyapatite (HA) deposition disease. The shoulder is the most common site of involvement. On MRI, the nodular calcium deposits show low signal intensity on all pulse sequences. The involved rotator cuff tendons may show focal thickening related to the calcified nodules. It can be difficult to appreciate calcific tendonitis on MRI, but this diagnosis can be clearly seen on radiographs.

·         MR SIGNS OF TENDON INJURY

1.       Tendon enlargement

2.       Increased intrinsic signal intensity on T1-weighted, proton density-weighted, and T2-weighted images

3.       Fluid/edema surrounding the tendon

4.       Disruption of the tendon fibers

·         The LUCL is a component of the LCL complex, as previously described, originating from the lateral epicondyle and coursing posterior to the radial head to insert on the lateral aspect of the ulna at the supinator crest. Disruption or laxity of the LUCL results in an entity called posterolateral rotatory instability, which is the most common form of chronic elbow instability.

·         King James lesion: A ganglion cyst. This facetious term was derived from the sometimes used "treatment" for this lesion, which consisted of putting the hand on a hard flat surface and slamming it with a King James version of the Bible. Ganglion cysts most commonly occur on the dorsum of the wrist near the scapholunate ligament but can occur anywhere. The typical patient population is young adults, more commonly women.

·         Fatigue fractures are commonly referred to simply as stress fractures. A fatigue stress fracture results from repeated stress on a normal bone. An insufficiency fracture occurs in abnormal bone that has been weakened by decreased mineralization and fractures under stress of routine or normal activity.

·         Transient osteoporosis of the hip is most common in women in the later stages of pregnancy, although it may also occur in older men (ages 50-70). It presents as sudden onset of pain that is increased with weight bearing. Its cause is unknown, but it generally resolves in 6-12 months with supportive therapy. On MRI, it is depicted as marked increase in marrow signal on STIR imaging and decrease of marrow signal on T1-weighted images, reflecting the presence of marrow edema.

·         A bucket handle tear is a subtype of a traumatic, or vertical, tear that comprises 10% of all meniscal tears. This is usually seen on MRI through the following: (1) absence of the inner body segment, resembling a bow tie, known as the "absent bow tie sign" and (2) identification of a displaced meniscal fragment, which is usually located in the intercondylar notch on coronal images, simulating a third cruciate ligament.

·         The majority of ACL tears occur at the femoral origin. MRI signs of an ACL tear include (1) visible disruption of the ligament, (2) irregular or wavy contour, (3) focal signal abnormality within the ligamentous substance, (4) edema, and (5) "empty notch" sign on coronal images (absence of the ACL in its expected location)

·         MRI OF THE KNEE

1.       Abnormal signal within a meniscus is not sufficient to diagnose meniscal tear on MRI. Abnormal meniscal signal intensity must extend to the meniscal surface to be called meniscal tear on MRI.

2.       Diagnosis of an ACL tear should prompt a search for commonly associated injuries, including medial collateral ligament injury, medial meniscal tear, Segond fracture of the proximal lateral tibia, and bone contusions.

·         SONK stands for spontaneous osteonecrosis of the knee and usually presents in the sixth or seventh decade of life as acute onset of pain without inciting trauma. Recently, SONK has been thought to be a result of subchondral insufficiency fracture, usually involving the lateral aspect of the medial femoral condyle, with resultant localized osteonecrosis. MRI demonstrates subchondral sclerosis, edema, and flattening of the medial femoral condyle with concomitant thinning of the articular cartilage. The appearance on T2-weighted images includes a central zone of low signal intensity with a periphery of high signal intensity.

·         Jumper's knee, also known as patellar tendinitis, is an overuse syndrome that classically occurs in young athletes who kick, jump, and run. These actions place stress on the patellofemoral joint with intrasubstance degeneration and partial tearing of the tendon. This injury is analogous to a rotator cuff tear clinically, pathologically, and radiologically.

·         MRI OF THE FOOT AND ANKLE

1.       Tendon tears are generally related to a progressive sequence of disorders.

2.       MRI can detect fractures that are not appreciated on radiographs or CT scans. This occurs commonly in the foot and ankle.

3.       The deltoid ligament practically never tears. Avulsion fractures of the medial malleolus generally occur before deltoid ligament tears.

4.       Tarsal coalitions are usually seen in children and adolescents.

·         Sinus tarsi syndrome: There is loss of the normal fat within the sinus tarsi. In acute or subacute cases, there is low T1 signal and high T2 signal secondary to inflammation. In chronic cases, there is low T1 and T2 signal secondary to fibrosis. Patients complain of weakness and instability in the ankle with palpable tenderness over the sinus tarsi. Most cases are idiopathic, but some patients have a history of ankle inversion injury. Other causes of sinus tarsi include inflammatory conditions, such as rheumatoid arthritis or gout, and ganglion cysts.

(The tarsal canal extends to the medial aspect of the foot, posterior to the sustentaculum tali. The canal widens to form the sinus tarsi, which is cone-shaped and opens laterally. The sinus tarsi contain fat, blood vessels, and the interosseous and cervical ligaments and branches of the tibial nerve.)