Radiologic Pitfalls. Pelvis/ Hip Hip DL Femoral neck Another ring fracture Sacrum Acetabulum

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Radiologic Pitfalls Michelle Lin, MD UCSF Associate Professor of Clinical Emergency Medicine San Francisco General Hospital (Michelle.Lin@emergency.ucsf.

1 Radiologic Pitfalls Michelle Lin, MD UCSF Associate Professor of Clinical Emergency Medicine San Francisco General Hospital ERRORS IN RADIOGRAPH INTERPRETATION Commonly missed, high-risk injuries on radiographs can be remembered by using my mnemonic DOH. (similar to what your response might be when a patient is recalled for your incorrect radiology interpretation ) D islocations O ccult fracture H alf of injuries missed Wrist Scapholunate DS Scaphoid Galeazzi Perilunate DL and Lunate DL Triquetrum Distal Radius Fx + Carpal Injury Elbow Radial head DL Radial head Monteggia Pelvis/ Hip Hip DL Femoral neck Another ring fracture Sacrum Acetabulum Knee Knee DL Tibial plateau Maisonneuve Segond Patella Foot Lisfranc injury Calcaneus Thoracolumbar + Calcaneus fx Talus Abbreviations: DL dislocation, DS dissociation, Fx fracture

Ortho Radiography (Lin) 2 Normal Anatomy WRIST PA (R Wrist): ü 3 smooth arcs along carpals ü Intercarpal distance < 3 mm PA

metacarpal ü Scapholunate angle < 30-60 degrees Lateral D islocation 1.

Rotatory subluxation of scaphoid into more transverse orientation.

2 Ortho Radiography (Lin) 2 Normal Anatomy WRIST PA (R Wrist): ü 3 smooth arcs along carpals ü Intercarpal distance < 3 mm PA Lateral (Right Wrist): ü Alignment: Smooth articulation of distal radius to lunate, lunate to capitate, and capitate to 3 rd metacarpal ü Scapholunate angle < degrees Lateral D islocation 1. SCAPHOLUNATE DISSOCIATION Most common and significant ligamentous injury of wrist. Rotatory subluxation of scaphoid into more transverse orientation. Mechanism: Fall on outstretched hand (FOOSH) ü PA view: >4 mm widening of scapholunate space ( Terry Thomas sign ) ü PA view: Scaphoid has signet ring sign ü Lateral view: Scapholunate angle > 60 deg PA of R Wrist 2. PERILUNATE DISLOCATION Mechanism: Hyperextension of the wrist

3 Ortho Radiography (Lin) 3 ü Lateral view: Capitate is not vertically aligned with the lunate and radius. ü PA view: Smooth middle arc alignment of carpal bones is disrupted. Complications: Median nerve injury, SLAC 3. LUNATE DISLOCATION Mechanism: Fall backwards on outstretched hand ü Lateral view: Lunate is rotated out of alignment into spilled teacup position ü PA view: Smooth proximal arc of carpal bones is disrupted ü PA view: Lunate appears triangular (rather than quadrilateral) Complication: Median nerve injury, SLAC O ccult Fracture Lateral of R Wrist Lateral of R Wrist 1. SCAPHOID FRACTURE 2 nd most common fractured bone of the wrist [#1=distal radius] At a teaching hospital ED, the miss rate was greatest for scaphoid fractures (13%) (Freed and Shields) Mechanism: FOOSH Exam: Tenderness to snuffbox area of wrist ü Normal in up to 20% cases (Waeckerle) Ulnar deviated AP ü Consider obtaining additional scaphoid views of R Wrist ü Teaching Pearl: Apply thumb spica splint to all wrists with snuffbox tenderness regardless of normal xrays Complication: ü Avascular necrosis (AVN) ü Nonunion rate increases 5-45% when treatment is delayed > 4 weeks (Langhoff and Andersen) ü SLAC (Scapholunate Advanced Collapse) Scaphoid and/or lunate undergoes AVN and collapses 2. TRIQUETRUM FRACTURE Accounts for 10% of carpal bone fractures Mechanism: FOOSH Exam: Tenderness to ulnar aspect of dorsal wrist Most easily seen on lateral since triquetrum is most dorsal carpal bone

4 Ortho Radiography (Lin) 4 Oblique of R Wrist Oblique of R Wrist H alf of Injuries Missed 1. GALEAZZI FRACTURE Distal-third fracture of the radius AND disruption of distal radioulnar joint (DRUJ) Mechanism: FOOSH with forearm hyperpronated Signs of DRUJ: ü Lateral view: Ulna does not overlie radius ü Lateral view: Ulnar styloid is not aligned with dorsal triquetrum ü PA view: Ulnar styloid fracture ü PA view: Widening of DRUJ Complication: Chronic disability when DRUJ disruption is missed > 10 wks Lateral view of R forearm 2. DISTAL RADIUS FX + CARPAL INJURY Because of the same FOOSH mechanism of injury, scapholunate dissociation may also be present. In a small retrospective study of 52 patients, 69% of distal radius fractures were associated with scapholunate dissociation (Lee et al.) Radial styloid fractures are associated with scaphoid / lunate fractures & ligamentous injury.

Ortho Radiography (Lin) 5 ELBOW Normal Anatomy Capitellum: Portion of distal humerus which articulates with the radial head LATERAL VIEW Fat

$subtle indicator of a fracture or dislocation ü Radiocapitellate line: On both the AP and lateral views, a longitudinal line drawn through the$ midshaft radius should bisect the capitellum. An abnormal alignment suggests a radial head dislocation.

midshaft radius should bisect the capitellum. An abnormal alignment suggests a radial head dislocation.

5 Ortho Radiography (Lin) 5 ELBOW Normal Anatomy Capitellum: Portion of distal humerus which articulates with the radial head LATERAL VIEW Fat pads: Collections of fat tissue adjacent to elbow joint capsule (appears black on xrays) ü Anterior fat pad Can be normal If displaced and elevated, is pathologic (sail sign) ü Posterior fat pad Always abnormal if visualized AP VIEW Lines: Misalignment of normal structures can be a subtle indicator of a fracture or dislocation ü Radiocapitellate line: On both the AP and lateral views, a longitudinal line drawn through the midshaft radius should bisect the capitellum. An abnormal alignment suggests a radial head dislocation. ü Anterior humeral line: On the lateral view, a longitudinal line drawn along the anterior aspect of the humerus should bisect the capitellum. An abnormal alignment suggests a supracondylar fracture.

$Ortho Radiography (Lin) 6 D islocation RADIAL HEAD DISLOCATION When identified, must look for a proximal ulnar fracture (see Monteggia Fracture ) O ccult Fracture RADIAL HEAD FRACTURE At a teaching$

6 Ortho Radiography (Lin) 6 D islocation RADIAL HEAD DISLOCATION When identified, must look for a proximal ulnar fracture (see Monteggia Fracture ) O ccult Fracture RADIAL HEAD FRACTURE At a teaching hospital ED, the miss rate was 2 nd greatest for elbow fractures at 10.8%. In adults, these fractures were primarily missed radial head fractures. (Freed and Shields) Mechanism: FOOSH Lateral view of R elbow ü Cortical break in the radial head may be very subtle or even absent in a nondisplaced fx ü Large anterior fat pad ( Sail sign ) ü Any posterior fat pad ü In the study by Freed and Shields: >80% had an associated fat pad and >40% had ONLY a fat pad sign as indicator of a fracture. Pearl: Sling patients with elbow pain and abnormal fat pads despite no obvious fracture. H alf of Injuries Missed MONTEGGIA FRACTURE Proximal ulna fracture AND radial head dislocation Missed in 50% pediatric population importance of alignment of radiocapitellate line (Gleeson and Beattie) Mechanism: FOOSH with rotational forces ü Obvious proximal ulna fracture ü Misalignment of radiocapitellate line Pearl: Beware of diagnosis of isolated proximal ulna fx! Lateral view of R elbow

$FEMORAL NECK FRACTURE Most commonly missed hip fracture Sometimes elderly patients can weight-bear despite a fx.$

7 Ortho Radiography (Lin) 7 Normal anatomy PELVIS / HIP AP D islocation HIP DISLOCATION Most commonly posterior from dashboard injuries in MVA s. Posterior: Affected leg is shortened and internally rotated Anterior: Aftected leg is shortened and externally rotated Since hip dislocations are associated with femoral head / acetabular fx s, consider a CT for unsuccessful reduction to assess for intraarticular bone fragments. O ccult Fracture AP view of L Hip 1. FEMORAL NECK FRACTURE Most commonly missed hip fracture Sometimes elderly patients can weight-bear despite a fx. Mechanism: From direct blunt trauma (fall) ü Can be very subtle ü Cortical disruption or impacted hyperlucency ü Loss of smooth cortical transition from femoral neck to head. ü Trabecular disruption AP view of R hip Delay in Diagnosis: ü Radiographically occult hip fx s occur in 2-9%. ü One study had 16/825 missed hip fractures. 15/16 were initially nondisplaced but became displaced secondary to the delayed diagnosis. (Parker) Additional Imaging: Consider MRI (CT is ok alterative, but less sensitive) if still clinically suspicious because of the risk of missing a nondisplaced fracture and having the patient return with a displaced fracture. MRI sensitivity and specificity = 100%.

8 Ortho Radiography (Lin) 8 2. SACRAL FRACTURE In one study: 72% of sacral alar fractures were missed initially. (Jackson et al.) Subtle break in smooth sacral alar lines Additional Imaging: ü Pelvic outlet views improve visualization of the sacrum and rami. ü CT required to assess severity of sacral fracture and additional fx s. AP view of sacrum 3. ACETABULAR FRACTURE Anterior acetabular fracture: Detected by break in iliopubic line Posterior acetabular fracture: Detected by a break in the ilioischial line; look specifically behind superimposed femoral head Additional Imaging: ü Can get additional Judet views to assess for clinically suspicious cases ü Requires CT assessment to assess severity and because 40% of associated intraarticular bone fragments and 50% of femoral head fractures are missed initially. (Lipman) AP of R hip H alf of Injuries Missed PELVIC RING DISRUPTION Because of the inflexible, ring-like structure of the pelvis, pelvic bone injuries are often found in multiples. In addition to the already mentioned injuries, also beware of subtle rami fractures and sacroiliac dissociation.

9 Ortho Radiography (Lin) 9 Normal Anatomy KNEE AP Lateral

$Requires angiography Lateral view of R knee O ccult Fracture 1. TIBIAL PLATEAU FRACTURE 32% of all knee fractures Mechanism: Valgus force with axial load (knee vs.$

10 Ortho Radiography (Lin) 10 D islocation KNEE DISLOCATION Not a subtle clinical or radiographic finding 40% have associated popliteal artery injury regardless of pedal pulses and reducibility. Requires angiography Lateral view of R knee O ccult Fracture 1. TIBIAL PLATEAU FRACTURE 32% of all knee fractures Mechanism: Valgus force with axial load (knee vs. car bumper) Sensitivity of radiographs: 79% for 2-view, 85% for 4-view (Gray et al.) Pearl: When a patient with knee pain from blunt trauma can not walk, be sure that oblique views are obtained to assess for a tibial plateau fracture. Consider CT despite radiographically negative findings in a patient. Additional Imaging: ü Oblique views (plain radiographs), CT to assess for severity AP view of R knee 2. SEGOND FRACTURE Small proximal lateral tibial avulsion fx Often associated with an ACL tear 3. PATELLA FRACTURE 40% of all knee fractures Additional Imaging: Sunrise view AP of L knee Lateral of R knee H alf of Injuries Missed MAISONNEUVE FRACTURE ü Proximal fibula fracture AND medial malleolus (or deltoid ligament) fracture ü Mechanism: Abduction and external rotation of ankle PLUS AP of R Knee AP of R Ankle

Ortho Radiography (Lin) 11 Normal Anatomy FOOT Lateral PA PA : The

Lateral : ü Bohler s angle (generated by a line bordering the

connecting the superior subtalar articular surface and superior

$ü A Bohler s angle < 20 degrees implies an occult calcaneal fracture.$

11 Ortho Radiography (Lin) 11 Normal Anatomy FOOT Lateral PA PA : The medial edges of the 2 nd metatarsal and 2 nd cuneiform should align. Lateral : ü Bohler s angle (generated by a line bordering the superior aspect of the posterior calcaneal tuberosity and a line connecting the superior subtalar articular surface and superior aspect of the anterior calcaneal process) normally is degrees. ü A Bohler s angle < 20 degrees implies an occult calcaneal fracture. Oblique Oblique : The medial edges of the 3 rd metatarsal and 3 rd cuneiform should align.

$Ortho Radiography (Lin) 12 D islocation LISFRANC INJURY Tarsal-metatarsal (MT) fracture/dislocation pattern 20% are initially missed (Goossens and DeStoop) LisFranc ligament: Attaches 2 nd MT base to$ $Fracture of 2 nd metatarsal base or Lisfranc ligament and subsequent dislocation of MT #2-5 from the midfoot Pearl: An avulsion fracture of the 2 nd metatarsal base alone is a LisFranc fracture$ $CALCANEUS FRACTURE At a teaching hospital ED, the miss rate was 3 rd greatest for calcaneal fractures at 10%.$

12 Ortho Radiography (Lin) 12 D islocation LISFRANC INJURY Tarsal-metatarsal (MT) fracture/dislocation pattern 20% are initially missed (Goossens and DeStoop) LisFranc ligament: Attaches 2 nd MT base to 1 st cuneiform. Fracture of 2 nd metatarsal base or Lisfranc ligament and subsequent dislocation of MT #2-5 from the midfoot Pearl: An avulsion fracture of the 2 nd metatarsal base alone is a LisFranc fracture DESPITE a normal alignment of the metatarsals with the tarsal bones, because the LisFranc ligament inserts at its base. Complications: Compartment syndrome O ccult Fracture 1. CALCANEUS FRACTURE At a teaching hospital ED, the miss rate was 3 rd greatest for calcaneal fractures at 10%. (Freed and Shields) Most commonly fractured tarsal bone Mechanism: Often from fall on heels from a height ü A Bohler s angle < 20 degrees suggests a fracture. Additional Imaging: ü Consider obtaining a calcaneal view ü Often requires CT imaging to assess fragments Complication: Compartment syndrome 2. TALUS FRACTURE Second most commonly fracture tarsal bone The neck is the most common location of a talar fracture. Mechanism: Excessive dorsiflexion of ankle Can be subtle cortical break on lateral view Complications of neck fracture: Avascular necrosis, subchondral collapse, and degenerative arthritis H alf of Injuries Missed CALCANEUS FRACTURES: 10% associated with THORACOLUMBAR FRACTURE because of load on axial skeleton when landing on the heels AP view of R foot Lateral of L foot Lateral of R foot Lateral of Lumbar Spine

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American Academy of Orthopaedic Surgeons Bulletin, Jun 1998; 46(3). George JE, Espinosa JA, Quattrone MS. Legal Issues in Emergency Radiology: Practical Strategies to Reduce Risk. Emergency Medicine Clinics of North America, Feb 1992; 10(1): Gilbert TJ, Cohen M. Imaging of Acute Injuries to the Wrist and Hand. Radiologic Clinics of North America, May 1997; 35(3): Gleeson AP, Beattie TF. Monteggia Fracture-Dislocation in Children. J Accid Emerg Med, Sept 1994; 11(3): Goossens M, DeStoop N. Lisfranc's Fracture-Dislocations: Etiology, Radiology, and Results of Treatment. A Review of 20 Cases. Clinical Orthopaedics & Related Research. 1983; 176: Gratton MC, Salomone JA, Watson WA. Clinically Significant Radiograph Misinterpretations at an Emergency Medicine Residency Program. Ann Emerg Med, May 1990; 19: Gray SD, et al. Acute Knee Trauma: How Many Plain Film s are Necessary for the Initial Examination? Skeletal Radiology, 1997; 26: Harris JH, Harris WH. The Radiology of Emergency Medicine. Philadelphia: Lippincott, Williams, & Wilkins, Henry G, George JE. Specific High-Risk Clinical Presentations. In: Henry G, Sullivan DJ, eds. Emergency Medicine Risk Management: A Comprehensive Review. 2nd ed. Dallas, TX: American College of Emergency Physicians,1997. Jackson H, et al. The Sacral Arcuate Lines and Upper Sacral Fractures. Radiology, 1982; 145: Karcz A, et al. Malpractice Claims Against Emergency Physicians in Massachusetts: Am J Emerg Med, Jul 1996; 14(4): Karcz A, et al. Massachusetts Emergency Medicine Closed Malpractice Claims: Ann Emerg Med, Mar 1993; 22(3): Langhoff O, Andersen JL. Consequences of Late Immobilization of Scaphoid Fractures. J Hand Surg Br, 1998; 13: Lee JS, et al. Signs of Acute Carpal Instability Associated With Distal Radial Fracture. Emergency Radiology, 1995; 2(2): Lipman, JC. Quick Reference to Radiology. New Jersey: Appleton & Lange, Lufkin KC, et al. 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