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Scaphoid / Scaphoid Fracture


   - Work Up for Scaphoid Frx: (w/ discussion)    
         - clinical differential diagnosis:
               - distal radius frx
               - transscaphoid perilunate dislocation:
               - scaphoid impaction syndrome 
         - radiographs and determination of stability (CT scan)
               - non diagnostic radiograph  (bone scan)
               - tubercle frx
               - transverse waist frx
               - proximal pole frx
         - treatment:
               - non-displaced fractures
                      - casting of scaphoid frx
                      - percutaneous scaphoid fixation
               - surgical treatment of displaced frx (herbert screw fixation of scaphoid fractures):
         - complications:
               - nonunion of scaphoid (3.5 mm cannulated screw fixation)
                      - non union of proximal pole
                      - bone grafting technique
               - avascular necrosis of the scaphoid
               - SLAC or SNAC wrist
               - degenerative disease of the STT joint:
                      - Degenerative changes at the scaphotrapezial joint following Herbert screw insertion: a radiographic study comparing patients with scaphoid fracture and primary hand arthritis.

 - Discussion:
    - surface of scapoid is largely covered by articular cartilage, & only narrow area of its neck, & even smaller distal portion, are
           accessible to blood vessels;
           - frxs across scaphoid may destroy blood supply to its proximal part;
    - scaphoid represents floor of anatomic snuff box;
    - scaphoid spans both carpal rows and therefore has less mobility than other carpals;
           - scaphoid is principal bony block to dorsiflexion of hand & wrist & is suscepible to frx during fall on outstretched hand;
    - scaphoid (navicular): the most frequently fractured carpal bone (frx occurs in tubercle, waist, or proximal 1/3);
    - biomechanics and scaphoid movement:
           - scaphoid exerts flexion extension control over lunate and distal carpal row; 
           - ulnar side of the wrist exerts rotational control and stability;
           - as wrist rotates from neutral to ulnar deviation, proxomal row dorsiflexes & x-ray profile of the scaphoid appears longer;
                    - in radial deviation, proximal carpal row volar flexes & scaphoid appears foreshortened;
                    - hence, ulnar deviation AP is necessary for visualization of scaphoid;
           - becuase scaphoid crosses both proximal & distal carpal rows, excessive dorsiflexion causes it to be pinned between dorsal lip
                    of radius & palmar sling of the radial capitate ligament;
           - scaphoid flexes with wrist flexion & extends with wrist extension, but it also flexes during radial deviation & extends
                   w/ ulnar deviation;
                    - these factors make immobilization of scaphoid fractures difficult;
                    - w/ scaphoid frx, distal scaphoid tends to flex, & proximal scaphoid extends with the proxmal carpal row; 
                    - because of this, angulation occurs at frx site, which gaps open dorsally & gradually assumes a humpback deformity;
    - mechanism of frx:
           - most injuries to wrist are sustained by a fall on outstretched hand;
           - frx occurs w/ wrist is dorsiflexed & radially deviated;
           - in this position, proximal pole of schaphoid is held by radius & radioscaphocapitate ligament, while distal pole of bone is
                    carried dorsally by trapeziocapitate complex; 
           - radioscaphoid ligament is relaxed by & radial deviation & cannot alleviate tensile stresses accumulating on radiovolar
                    aspect of scaphoid:
           - radioscaphoid ligament:
                    - inserts onto tuberosity of scphoid & is radial expansion of radiocapitate ligament which courses over palmar concavity
                               of scaphoid proximal to tuberosity before inserting on palmar aspect of capitate;
                    - forms a fulcrum over which scaphoid rotates; 
    - incidence:
           - 1 out of 100,000 people per year;
           - ref: Incidence Estimates and Demographics of Scaphoid Fracture in the U.S. Population

- Pediatric Scaphoid Fracture:
   - forms from enchondral ossification
            - forms in males between ages 5-15
            - forms in forms in females 4-13 years;
   - non operative treatment is usually indicated;
   - references:
            - Pediatric fractures of the carpal scaphoid: a retrospective clinical and radiological study 
            - Pediatric scaphoid nonunion

 - References for Scaphoid Frx