title: An anatomical study of the watershed line on the volar, distal aspect of the radius: implications for plate placement and avoidance of tendon ruptures.
abstract: OBJECTIVE
  The watershed line is a useful surgical landmark for positioning a volar locking plate. Implants placed on or distal to it can impinge on flexor tendons and cause injury. However, the details of the anatomy of this line are unclear. We studied macroscopically and histologically the structures of the volar aspect of the distal radius.
  
  
  METHODS
  We studied 20 distal forearm regions of 10 cadavers (5 males and 5 females; mean age, 79 y [range, 56-88 y]) to clarify the details of the watershed line. In 16 specimens, we investigated the macroscopic appearance of the volar aspect of the radius and the relationships among the bone, the volarradiocarpal ligaments, and the pronator quadratus. Histological analyses were performed in 4 specimens of 2 cadavers to examine the morphology of the margin of the bony structures.
  
  
  RESULTS
  In the medial half of the distal volar radius, 2 lines were identified by direct macroscopic visualization; one was the proximal line that corresponded to the distal ridge of the pronator fossa, and the other was the distal line, which was more prominent. A medial bony prominence was situated on the distal line. In the lateral half, the distal and proximal lines of the medial half merged to form a single line. A lateral prominence was situated on this line.
  
  
  CONCLUSIONS
  The watershed line might not be a distinct line, and it corresponds to the distal margin of the pronator fossa in the lateral half of the volar radius and to a hypothetical line between the distal and proximal lines in the medial half. The medial and lateral bony prominences on the volar radius should be key structures for accurate plate placement to avoid flexor tendon injury.
  
  
  CONCLUSIONS
  The present study suggests bony landmarks for positioning a volar locking plate.
authors: Department of Orthopaedic Surgery, Okayama Saiseikai General Hospital, Okayama, Japan. imatani@saiseidr.jp
authors: Junya
authors: J
authors: Imatani
authors: Keiichi
authors: K
authors: Akita
authors: Kumiko
authors: K
authors: Yamaguchi
authors: Hirotaka
authors: H
authors: Shimizu
authors: Hidenori
authors: H
authors: Kondou
authors: Toshifumi
authors: T
authors: Ozaki
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001860:Bone Plates; D002102:Cadaver; D005260:Female; D005593:Fracture Fixation, Internal / Q000379:methods; D006801:Humans; D008297:Male; D008875:Middle Aged; D053401:Palmar Plate / Q000033:anatomy & histology* / Q000601:surgery; D011884:Radius / Q000033:anatomy & histology* / Q000601:surgery; D011885:Radius Fractures / Q000601:surgery; D013708:Tendon Injuries / Q000517:prevention & control