February 7,1991 GRAND ROUNDS-DEPT OF ORTHOPEDICS-U. MAIMI/JMH

ADVANCED ORTHOPEDIC IMAGING

Jeffrey C. Allard M.D., Chief Of Musculoskeletal Radiology, UMiami

I. Ultrasound-- best modality for differentiating cystic from solid structures. Also for subtle textural differences in tissue.

1. Congenital dislocated hip-- prior to 6 months the femoral head is not ossified and can be clearly seen on US relative to location within acetabulum. Femoral head coverage (Graf) and subluxability also can be evaluated

2. Fluid detection-joint effusion, Bakers cyst, hematoma, osteomyelitis

3.Early ossification-Ilizarov, myositis

4. Neoplasm-cystic versus solid

5. Tendon-Achilles, supraspinatus

6. Muscle-tears and ruptures

7. Post_op_DVT, abscess

8. Spine- intraoperative disc fragment, dysraphism, tumor or syrinx localization

II. Computed tomography-- axial plane only, good for flat bones or complex anatomy. Best for detection of calcium and fat

1.Pelvis-sacrum, SI joint, acetabulum, hematoma

2. Shoulder post-arthrography visualization of glenoid labra

3. Knee-complex tibial plateau fractures, reconstruction in sagittal and coronal planes.

4. Foot and ankle- triplane (Tillaux) fractures, subtalar dislocations, calcaneal fractures, tarsal coalition

5. Spine-C1 or lateral mass fractures, bony stenosis 

III. Magnetic resonance- premier modality for marrow and soft tissue imaging. Protons (hydrogen) are flipped by electromagnetic waves. T1 weighted image- water=black, fat=white. T2 weighted image- water=white, fat=not as white- Always black- tendon, calcium, air, hemosiderin, fibrocartilage

1. Spine- sagittal imaging, disc herniation, dysraphism, neoplasm (gadolinium), postoperative (scar versus disc, need gadolinium)

2. Knee- most commonly imaged joint-

a. menisci_ normally seen as a bowtie configuration and homogeneously black. Posterior horn of medial meniscus should normally be largest. Lateral meniscus should not be larger or else consider discoid meniscus (prone to tear).

Degeneration- grade 1- central white signal

grade 2- central signal that extends to nonarticular surface and more extensive than grade 1-95% of grade 1 or 2 menisci correlate with an arthroscopically intact meniscus, except when clinically suspicious grade 2 lesions are vigorously probed

Tear_grade 3- signal that extends to articular surface grade 4- no recognizable meniscus, usually macerated or severely degenerated-95% arthroscopic correlation

b. cruciate ligaments -Anterior cruciate- attaches to lateral femoral condyle, should be taut as usually imaged

-Posterior cruciate- attaches to medial femoral condyle. Blacker than anterior cruciate (more tightly packed fibers) and tends to have curve.

c. collateral ligaments- need coronal sections, T2 images show abnormal fluid. If black line (ligament) is discontinuous a complete tear can be diagnosed.

d. cartilage- hyaline cartilage is grey on T1 weighted images and white on gradient echo images. Axial gradient echo images are useful for evaluating chondromalacia patella, patella tracking abnormalities, and integrity of patellar retinacula.

f. Fluid- joint, Bakers cyst, meniscal cyst, muscle tear.

3. Shoulder-- oblique coronal image plane parallel to supraspinatus tendon most useful for rotator cuff.

Tendonitis- thickening of tendon

Partial tear- white signal within tendon without discontinuity

Complete tear- tendon discontinuity. May see fluid in subacromial or subdeltoid bursae.

Impingement- either due to acromioclavicular hypertrophy or acromial spurring [type 3]. Predisposes to tear.

Axial images demonstrate subscapularis and infraspinatus muscles.Capsule, ligaments, and glenoid labra seen well. Biceps tendon.

4. Ankle or Foot --Mortons neuroma or other neoplasm anatomically defined. Ligamentous injury, occult fractures, avascular necrosis, and osteomyelitis can be diagnosed. Achilles tendon, peroneal tendon, and posterior tibial tendons are seen well. Diabetic foot- to diagnose osteomyelitis MRI is much more definitive than bone scan.

5. Hand or Wrist- Carpal tunnel well delineated. Ganglions or other soft tissue masses. Triangular fibrocartilage better seen than intercarpal ligaments. Avascular necrosis of lunate or scaphoid. Extent of pannus formation in arthritis can be assessed prior to synovectomy

6. Neoplasms-Plain films still very helpful for differential diagnosis of bone tumors. MRI is needed for preoperative staging. Masses that enhance with gadolinium are more likely to be vascular or aggressive.

a. Osteosarcoma- beware of the skip lesion. Soft tissue tumors prior to MRI were poorly imaged. Lipomas can be accurately predicted preoperatively. Simple cysts and hematomas can be differentiated from solid neoplasms. Benign versus malignant- 90-95% predictive value (synovial sarcomas can look benign and aggressive fibromatosis can look malignant).

Tumor mapping- neurovascular invasion -relation to joint and bone -relation to muscle