Partial Scaphoid Excision of Scaphoid Nonunions



Partial Scaphoid Excision of Scaphoid Nonunions


Rafael J. Diaz-Garcia

Joseph E. Imbriglia





ANATOMY



  • The scaphoid bone represents the bridge between the proximal and distal rows of the carpus. It is tilted in both the volar and radial planes in respect to the central axis of the forearm, articulating with both rows.






    FIG 1 • Failed ORIF of a scaphoid nonunion (PA and lateral views).


  • The scaphoid is mostly covered in articular cartilage and has important intrinsic and extrinsic ligamentous attachments.


  • Most of the vascular supply to the scaphoid enters the bone distal to the waist and perfuses in a retrograde fashion (FIG 2).6,17



    • The proximal pole is most at risk secondary due to its tenuous blood supply.


  • All of these anatomic features make surgical management complex.


PATHOGENESIS



  • Patients with scaphoid fractures who present with delays (>4 weeks) in both diagnosis and treatment can develop a nonunion. Other risk factors for nonunion include proximal fracture location, comminution, fragment displacement or angulation, and associated carpal instability. As with other fractures, smokers are at increased risk for nonunion.



    • Acute scaphoid fractures with fracture fragment displacement more than 1.0 mm, an intrascaphoid angle more than 45 degrees, or a height-to-length ratio more than 0.65 have a higher incidence of nonunion.18


  • Because the scaphoid serves as a bridge between the proximal and distal carpal rows, a scaphoid fracture can severely disrupt wrist biomechanics and normal loading patterns.



    • Scaphoid fractures disrupt the normal linkage between the two rows, and thus the proximal fragment remains with the lunate via the scapholunate ligament and the distal fragment flexes unimpeded.



      • Scaphoid collapse reduces the carpal height and allows the lunate to rotate in a dorsal intercalated segmental instability (DISI) pattern.


      • Scaphoid nonunion advanced collapse (SNAC) arthritis develops from the altered biomechanics.


NATURAL HISTORY



  • Most patients with scaphoid fractures, and thus nonunions, are young males between the ages of 20 and 30 years.5,7


  • There is controversy regarding the true natural history of patients with scaphoid nonunions given that most studies are biased toward symptomatic patients.8 However, it is widely believed that radiographic signs of posttraumatic arthritis will develop in almost 100% of patients with a scaphoid nonunion. These degenerative changes occur in a predictable pattern, and the process may take 5 to 20 years.8,10,14


  • Arthritis first develops between the distal pole of the scaphoid and the radial styloid (SNAC wrist stage I; FIG 3A).


  • Left untreated, stage I SNAC will progress to involve the midcarpal joint (SNAC stages II and III; FIG 3B,C).







    FIG 2A. Volar intraosseous blood supply to the scaphoid with laterovolar and distal vessels visualized. B. Dorsal intraosseous blood supply to the scaphoid.


  • Many patients present once pain and decreased range of motion in the wrist has become increasingly severe. In these cases, salvage procedures requiring arthrodesis are often the only options left.

Jul 22, 2016 | Posted by in ORTHOPEDIC | Comments Off on Partial Scaphoid Excision of Scaphoid Nonunions
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