title: Precision of surface measurements for below-knee residua.
abstract: OBJECTIVE
  To determine the absolute and relative precision of geometric measurements made of below knee (BK) residua and their BK plaster positive casts using calipers, electromagnetic digitizer, optical surface scanner (OSS), and spiral x-ray computed tomography (SXCT).
  
  
  METHODS
  The experimental measurement protocol for a single measurement session was as follows: Dot markers were placed on the residuum, and volume and distances were measured using water displacement and calipers; residuum was measured using electromagnetic digitizer; residuum was scanned using three-dimensional (3D) OSS; a negative plaster cast of subject's residuum was made; the residuum was scanned using SXCT scanner. These steps were repeated at a second measurement session. Plaster positive casts were constructed and subsequently measured using the same protocol.
  
  
  METHODS
  Thirteen adult below-knee amputee volunteers (subjects) participated in the study, and nine subjects returned for a second measurement session. The study group consisted of 9 men and 4 women; 10 Caucasians and 3 African Americans.
  
  
  RESULTS
  Distance measurements for all measurement devices were repeatable within 1% in vivo and within 0.5% on plaster casts; and volumes were within 1% in vivo and within 0.1% on plaster casts. Distance measurements for each device were precise within 3% in vivo and within 1% on plaster casts; and volumes were within 5% in vivo and within 6% on plaster casts when compared with caliper and water displacement measures.
  
  
  CONCLUSIONS
  These measurement systems were found to be substantially equivalent in terms of repeatability and precision for measurement of lower extremity residua.
authors.affiliation: Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, MO 63110, USA.
authors.forename: P K
authors.initials: PK
authors.lastname: Commean
authors.forename: K E
authors.initials: KE
authors.lastname: Smith
authors.forename: J M
authors.initials: JM
authors.lastname: Cheverud
authors.forename: M W
authors.initials: MW
authors.lastname: Vannier
mesh_terms: D000328:Adult; D000368:Aged; D000672:Amputation Stumps; D005260:Female; D006801:Humans; D007866:Leg / Q000033:anatomy & histology*; D008297:Male; D008875:Middle Aged; D008953:Models, Anatomic; D017755:Prosthesis Fitting / Q000295:instrumentation* / Q000379:methods; D015203:Reproducibility of Results; D014057:Tomography, X-Ray Computed