title: Relative Contribution of the Subsheath to Extensor Carpi Ulnaris Tendon Stability: Implications for Surgical Reconstruction and Rehabilitation.
abstract: OBJECTIVE
  To identify the varying contributions of the proximal and distal portions of the subsheath of the extensor carpi ulnaris (ECU) to its stability, evaluate the correlation of ulnar groove depth and ECU subluxation, and observe the effect of forearm and wrist positions on ECU stability.
  
  
  METHODS
  Extensor carpi ulnaris tendon position relative to the ulnar groove was measured in 10 human cadaveric specimens with the subsheath intact, partially sectioned (randomized to distal or proximal half), and fully sectioned. Measurements were obtained in 9 positions: forearm supinated, neutral, and pronated and wrist extended, neutral, and flexed. Ulnar groove depth was measured on all specimens.
  
  
  RESULTS
  In 7 of 10 specimens with an intact subsheath, the ECU tendon subluxated out of the groove in at least 1 forearm-wrist position. We noted the subluxation of the ECU tendon in all wrist-forearm positions with the exception of pronation-extension in at least 1 specimen. For partial subsheath sectioning, tendon displacement markedly increased after distal subsheath sectioning but not after proximal sectioning. For full subsheath sectioning, wrist flexion produced subluxation in all forearm positions, and forearm supination produced subluxation in all wrist positions. Maximum displacement occurred in supination-flexion. There was no correlation between ulnar groove depth and ECU subluxation.
  
  
  CONCLUSIONS
  Mild tendon subluxation occurred in the intact specimens in most tested positions. Two positions were remarkable for their consistency in maintaining the tendon within the groove: pronation-neutral and pronation-extension. In fully sectioned specimens, the greatest subluxation occurred in supination-flexion, with supination and flexion independently producing subluxation. Partial sectioning demonstrated that the distal portion of the subsheath played a more important role than the proximal portion in stabilizing the ECU.
  
  
  CONCLUSIONS
  Subsheath repair or reconstruction should target the distal portion of the subsheath. During postinjury rehabilitation or following surgical reconstruction, combined forearm supination and wrist flexion should be avoided.
authors.affiliation: Hospital for Special Surgery, New York, NY.
authors.forename: Andrew C
authors.initials: AC
authors.lastname: Ghatan
authors.affiliation: Hospital for Special Surgery, New York, NY.
authors.forename: Sameer G
authors.initials: SG
authors.lastname: Puri
authors.affiliation: Hospital for Special Surgery, New York, NY.
authors.forename: Kyle W
authors.initials: KW
authors.lastname: Morse
authors.affiliation: Hospital for Special Surgery, New York, NY.
authors.forename: Krystle A
authors.initials: KA
authors.lastname: Hearns
authors.affiliation: Hospital for Special Surgery, New York, NY.
authors.forename: Caroline
authors.initials: C
authors.lastname: von Althann
authors.affiliation: Hospital for Special Surgery, New York, NY. Electronic address: carlsonm@hss.edu.
authors.forename: Michelle G
authors.initials: MG
authors.lastname: Carlson
mesh_terms: D000368:Aged; D002102:Cadaver; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011403:Pronation / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology*; D013484:Supination / Q000502:physiology*; D013708:Tendon Injuries / Q000503:physiopathology*; D014955:Wrist Joint / Q000503:physiopathology*
keywords: ECU; Extensor carpi ulnaris; ligament; subsheath; wrist