title: The Effect of Capitate Position on Coronal Plane Wrist Motion After Simulated 4-Corner Arthrodesis.
abstract: OBJECTIVE
  The objective of this study was to examine the effect of altering the capitolunate relationship on coronal-plane wrist motion after scaphoidectomy and simulated 4-corner arthrodesis. Two positions of different capitolunate alignments were compared: "anatomic" (unchanged from pre-fusion) and "lunate-covered" (capitate translated to cover the lunate). We hypothesized that wrist resting posture would be altered and radial-ulnar motion would diminish after 4-corner arthrodesis in the lunate-covered position when compared with normal wrists.
  
  
  METHODS
  Six human cadaveric limbs were disarticulated at the elbow and mounted on a custom jig. The resting position of the wrist was recorded with no load applied, followed by a load of 44 N applied to the flexor carpi radialis, extensor carpi radialis longus, and extensor carpi radialis brevis tendons to simulate radial deviation and to the flexor carpi ulnaris and extensor carpi ulnaris tendons to simulate ulnar deviation. Scaphoidectomy was performed and 2 methods of 4-corner arthrodesis with different capitolunate coronal alignments were studied in random order. Range of motion was compared using one-way analysis of variance and Bonferroni correction.
  
  
  RESULTS
  The "lunate covered" wrist demonstrated significantly greater radial resting posture than that of the preoperative wrist. Under a 44 N load, the lunate-covered position had significantly greater radial motion than the preoperative radial motion. Wrists fused in the "anatomic" position did not differ significantly from the preoperative wrists in posture or range of motion.
  
  
  CONCLUSIONS
  In this cadaveric model, complete covering of the capitate head by the lunate placed the wrist in increased radial deviation compared with the anatomic posture. Changes induced in the resting tension of the extrinsic wrist ligaments serve as a reasonable explanation for the increased radial posture and motion. In a clinical setting, these changes may affect postoperative wrist posture and function.
  
  
  CONCLUSIONS
  Maintaining anatomic lunate position leads to preservation of greater wrist motion and anatomic alignment in a patient undergoing 4-corner arthrodesis.
authors.affiliation: Department of Orthopaedic Surgery, Hospital for Special Surgery, New York, NY.
authors.forename: Alexia
authors.initials: A
authors.lastname: Hernandez-Soria
authors.affiliation: Department of Orthopaedic Surgery, Hospital for Special Surgery, New York, NY.
authors.forename: Soumen
authors.initials: S
authors.lastname: Das De
authors.affiliation: Department of Orthopaedic Surgery, Hospital for Special Surgery, New York, NY.
authors.forename: Zina
authors.initials: Z
authors.lastname: Model
authors.affiliation: Department of Orthopaedic Surgery, Hospital for Special Surgery, New York, NY.
authors.forename: Steve K
authors.initials: SK
authors.lastname: Lee
authors.affiliation: Department of Orthopaedic Surgery, Hospital for Special Surgery, New York, NY. Electronic address: WolfeS@HSS.edu.
authors.forename: Scott W
authors.initials: SW
authors.lastname: Wolfe
mesh_terms: D001174:Arthrodesis / Q000379:methods*; D002102:Cadaver; D051224:Capitate Bone / Q000033:anatomy & histology; D006801:Humans; D012667:Lunate Bone / Q000033:anatomy & histology; D016059:Range of Motion, Articular; D021361:Scaphoid Bone / Q000601:surgery*; D014955:Wrist Joint / Q000502:physiology* / Q000601:surgery
keywords: 4-corner arthrodesis; Capitate position; scaphoidectomy; wrist range of motion