title: Wrist salvage procedures alter moment arms of the primary wrist muscles.
abstract: BACKGROUND
  Proximal row carpectomy and scaphoid-excision four-corner fusion are salvage procedures that relieve pain by removing arthritic joint surfaces. While numerous studies have examined how these procedures affect joint motion, few have examined how they influence muscle mechanical actions. This study examines whether muscle moment arms change after these procedures.
  
  
  METHODS
  Moment arms of primary wrist muscles were measured in 8 cadaveric specimens using the tendon excursion method. In each specimen, moment arms were measured for two degrees of freedom (flexion-extension and radial-ulnar deviation) and three conditions (nonimpaired, scaphoid-excision four-corner fusion, and proximal row carpectomy). For each muscle and degree of freedom, moment arm versus joint angle curves for the three conditions were statistically compared.
  
  
  RESULTS
  Wrist salvage procedures significantly alter moment arms of the primary wrist muscles. Proximal row carpectomy primarily alters flexion-extension moment arms, while scaphoid-excision four-corner fusion primarily alters radial-ulnar deviation moment arms. Both procedures also alter the balance between agonist and antagonist wrist muscles. Following proximal row carpectomy, wrist extensors have smaller moment arms in extended postures. Following scaphoid-excision four-corner fusion, radial deviators have larger moment arms throughout radial-ulnar deviation.
  
  
  CONCLUSIONS
  Different moment arms indicate that different forces are required to complete the same tasks in nonimpaired and surgically altered wrists. The altered muscle moment arms likely contribute to post-operative impairments. Understanding how salvage procedures alter muscle mechanical actions is a critical first step toward identifying the cause of post-operative impairments and is necessary to develop effective interventions to augment deficient muscles and improve overall function.
authors.affiliation: Department of Biomedical Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208, USA; Sensory Motor Performance Program, Rehabilitation Institute of Chicago, 345 E Superior Street, Chicago, IL 60611, USA; Edward Hines, Jr. VA Hospital, 5000 S, Fifth Avenue, P.O. Box 5000 (151), Hines, IL 60141, USA. Electronic address: jnichols@u.northwestern.edu.
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Nichols
authors.affiliation: Edward Hines, Jr. VA Hospital, 5000 S, Fifth Avenue, P.O. Box 5000 (151), Hines, IL 60141, USA; Department of Orthopaedic Surgery and Rehabilitation, Stritch School of Medicine, Loyola University - Chicago, Maguire Building - 1700, 2160 South 1st Ave, Maywood, IL 60153, USA. Electronic address: mbednar@lumc.edu.
authors.forename: Michael S
authors.initials: MS
authors.lastname: Bednar
authors.affiliation: Edward Hines, Jr. VA Hospital, 5000 S, Fifth Avenue, P.O. Box 5000 (151), Hines, IL 60141, USA; Department of Orthopaedic Surgery and Rehabilitation, Stritch School of Medicine, Loyola University - Chicago, Maguire Building - 1700, 2160 South 1st Ave, Maywood, IL 60153, USA. Electronic address: Robert.Havey@va.gov.
authors.forename: Robert M
authors.initials: RM
authors.lastname: Havey
authors.affiliation: Department of Biomedical Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208, USA; Department of Physical Medicine & Rehabilitation, Northwestern University Feinberg School of Medicine, 303 Chicago Ave., Chicago, IL 60611, USA; Department of Physical Therapy & Human Movement Sciences, Northwestern University Feinberg School of Medicine, 303 Chicago Ave., Chicago, IL 60611, USA; Sensory Motor Performance Program, Rehabilitation Institute of Chicago, 345 E Superior Street, Chicago, IL 60611, USA; Edward Hines, Jr. VA Hospital, 5000 S, Fifth Avenue, P.O. Box 5000 (151), Hines, IL 60141, USA. Electronic address: w-murray@northwestern.edu.
authors.forename: Wendy M
authors.initials: WM
authors.lastname: Murray
mesh_terms: D000328:Adult; D000368:Aged; D002102:Cadaver; D002348:Carpal Bones / Q000601:surgery*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000503:physiopathology*; D010003:Osteoarthritis / Q000503:physiopathology / Q000601:surgery; D011184:Postoperative Period; D021361:Scaphoid Bone / Q000601:surgery*; D014953:Wrist / Q000503:physiopathology* / Q000601:surgery*
keywords: Four-corner fusion; Moment arm; Proximal row carpectomy; Wrist
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