title: Interpretation of the scarf osteotomy by 10 surgeons.
abstract: BACKGROUND
  The study compared three-dimensional (3D) changes in geometry of the first metatarsal following scarf osteotomy performed on standardised Sawbone® models by consultant foot and ankle surgeons. The study considered the inter-surgeon variances in interpretation and performance of the scarf osteotomy with respect to intra-surgeon variances.
  
  
  METHODS
  The analysis used an accurate digitising system to measure and record points on the Sawbone® models in 3D space. Computer software performed vector analysis to calculate 3D rotations and translations of the first metatarsal head as well as the inter-metatarsal angle. Bone cut lengths and displacements were measured using a digital Vernier caliper. One surgeon performed the osteotomy 10 times to form an intra-surgeon control dataset, while 10 different surgeons each did one scarf osteotomy to form an inter-surgeon test dataset.
  
  
  RESULTS
  Both surgical groups produced reductions in the 3D inter-metatarsal angle with non-significant differences between the groups (p>0.05). In contrast, the test group demonstrated highly significant (p=0.000) greater variance compared with the control dataset for all of the variables associated with surgical technique. In addition, there were highly significant (p=0.02 and 0.002) greater variances in the interpretation of the degree to which the metatarsal head should be translated medially (X) and inferiorly (Z). There was also a significant (p=0.001) increase in variances in the rotations about the dorsi/plantar-flexion (X) axis. The only significant differences (all p=0.000) attributable solely to differences in mean values were in proximal-distal (Y) translation, pronation (Y) rotation and medial (Z) rotation. The test group applied greater medial and plantar-flexion rotation of the metatarsal head than the control surgeon and significantly less (p=0.000) shortening of the first metatarsal than the control surgeon.
  
  
  CONCLUSIONS
  The results of this geometric study demonstrate the versatility of the scarf osteotomy. As a result of the multi-planar nature of the osteotomy, there is a potential risk of producing unintended rotational mal-unions in all three planes. These rotational mal-unions may account for some of the poorer outcomes documented within the literature.
authors.affiliation: Sheffield Foot & Ankle Unit, Department of Orthopaedic Surgery, Sheffield Hospitals NHS Foundation Trust, Sheffield S5 7AU, UK. mark.davies@sth.nhs.uk
authors.forename: Mark B
authors.initials: MB
authors.lastname: Davies
authors.forename: Chris M
authors.initials: CM
authors.lastname: Blundell
authors.forename: Christopher P
authors.initials: CP
authors.lastname: Marquis
authors.forename: Avril D
authors.initials: AD
authors.lastname: McCarthy
mesh_terms: D006215:Hallux Valgus / Q000601:surgery*; D006801:Humans; D008683:Metatarsophalangeal Joint / Q000473:pathology / Q000601:surgery; D008953:Models, Anatomic; D015588:Observer Variation; D010027:Osteotomy / Q000379:methods* / Q000706:statistics & numerical data