title: Intraoperative mechanical bone strength determination in tibiotalocalcaneal fusion: a biomechanical investigation.
abstract: BACKGROUND
  Bone strength is currently measured with indirect techniques. We investigated the use of an intraoperative mechanical measurement for local bone strength determination and prediction of intramedullary-nail fusion failure. We investigated whether intraoperative local bone strength determination may be useful to the surgeon in predicting intramedullary nail hindfoot fusion performance.
  
  
  METHODS
  In seven human specimens, bone mineral density (BMD) was determined with qCT. A device (DensiProbe) specially devised for nailed tibiotalocalcaneal arthrodesis (TTCA) was inserted at the intended calcaneal screw sites of an intramedullary nail, and the cancellous break-away torque was measured. The constructs were then cyclically loaded to failure in dorsiflexion-plantarfexion.
  
  
  RESULTS
  The BMD range was wide (42.8 to 185.9 mg HA/cm(3)). The proximal-screw site peak torque was 0.47 to 1.61 Nm; distal-screw site peak torque was 0.24 to 1.06 Nm. The number of cycles to failure correlated with peak torque both proximally (p = 0.021; r(2) = 0.69) and distally (p = 0.001; r(2) = 0.92). Proximally, peak torque did not correlate with BMD (p = 0.060; r(2) = 0.54); distally, it correlated significantly (p = 0.003; r(2) = 0.86).
  
  
  CONCLUSIONS
  DensiProbe measurements can be used in the hindfoot to assess bone strength. In this study, specimens that failed early could be identified. However, in clinical practice fusion failure is multifactorial in origin, and failure prediction cannot be based upon peak torque measurements alone.
  
  
  CONCLUSIONS
  The technique described here may be of use to give an intraoperative decision aid to predict intramedullary nail hindfoot fusion performance.
authors.affiliation: AO Foundation, Clavadelerstrasse 8, 7270 Davos Platz, Switzerland. kajetan.klos@aofoundation.org
authors.forename: Kajetan
authors.initials: K
authors.lastname: Klos
authors.forename: Markus
authors.initials: M
authors.lastname: Windolf
authors.forename: Karsten
authors.initials: K
authors.lastname: Schwieger
authors.forename: Philipp
authors.initials: P
authors.lastname: Kuhn
authors.forename: Markus
authors.initials: M
authors.lastname: Hänni
authors.forename: Boyko
authors.initials: B
authors.lastname: Gueorguiev
authors.forename: Gunther O
authors.initials: GO
authors.lastname: Hofmann
authors.forename: Thomas
authors.initials: T
authors.lastname: Mückley
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000843:Ankle Joint / Q000601:surgery*; D001174:Arthrodesis; D001696:Biomechanical Phenomena; D015519:Bone Density; D001858:Bone Nails; D002102:Cadaver; D002111:Calcaneus / Q000601:surgery; D005260:Female; D006801:Humans; D007432:Intraoperative Period; D008297:Male; D013314:Stress, Mechanical; D013628:Talus / Q000601:surgery; D013640:Tarsal Joints / Q000601:surgery*; D013977:Tibia / Q000601:surgery; D019415:Torque