title: The midtarsal joint locking mechanism.
abstract: BACKGROUND
  The midtarsal joint, consisting of the talo-navicular and the calcaneocuboid joints, is presumed to be responsible for the foot being both flexible and rigid during different parts of the stance phase of gait. However, this mechanism has never been well quantified. This study explores the midtarsal joint locking mechanism by comparing the effect of hindfoot inversion and eversion on midfoot and forefoot mobility.
  
  
  METHODS
  Motion of the tibia, talus, calcaneus, navicular, cuboid and the first, second, and fifth metatarsals were measured in nine cadaver feet using Polhemus Fastrak electromagnetic sensors (EST GmbH and Co. KG, Kaiserslautern, Germany). The talus was fixed to the tibia, and then the forefoot was maximally dorsiflexed, plantarflexed, inverted, and everted, with the hindfoot in maximal eversion and inversion, for a total of eight test positions. The range of motion of the individual bones between maximal forefoot dorsiflexion and plantarflexion and between maximal forefoot inversion and eversion was calculated for the hindfoot in maximal eversion and inversion.
  
  
  RESULTS
  For the range of motion from maximal dorsiflexion to maximal plantarflexion there was significantly increased movement of the first, second, and fifth metatarsals in the sagittal plane (p-value = 0.003, 0.007, and 0.002, respectively) when the calcaneus was maximally everted compared to when the calcaneus was maximally inverted. No significant differences were detected for the range of motion from forefoot inversion to eversion for the two hindfoot positions.
  
  
  CONCLUSIONS
  This study demonstrated that motion in the forefoot is influenced by hindfoot position through the midtarsal joint. Specifically, the sagittal plane range of motion of the metatarsals is increased when the hindfoot is in valgus.
authors.affiliation: Department of Veterans Affairs RRD Center of Excellence for Limb Loss Prevention and Prosthetic Engineering, VA Puget Sound Healthcare System, Seattle, WA 98108, USA.
authors.forename: C Brian
authors.initials: CB
authors.lastname: Blackwood
authors.forename: Tracy J
authors.initials: TJ
authors.lastname: Yuen
authors.forename: Bruce J
authors.initials: BJ
authors.lastname: Sangeorzan
authors.forename: William R
authors.initials: WR
authors.lastname: Ledoux
mesh_terms: D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D002102:Cadaver; D055590:Electromagnetic Phenomena; D005260:Female; D005528:Foot / Q000502:physiology*; D005529:Foot Bones / Q000502:physiology*; D006801:Humans; D008297:Male; D009068:Movement / Q000502:physiology; D016059:Range of Motion, Articular / Q000502:physiology*; D013640:Tarsal Joints / Q000502:physiology*; D013977:Tibia / Q000502:physiology