This report describes the difference between a type I subtalar arthroereisis device and a type II non-arthroereisis device used to stabilization a talotarsal joint dislocation. Learn more at www.GraMedica.com.

1. Extra-Osseous Stabilization Devices: A New Classification System
Journal of Foot and Ankle Surgery, Volume 51, Issue 5 , Pages 613-619, September 2012
Michael E. Graham, DPM, FACFAS, Nikhil T. Jawrani, MS
Purpose Results/Classification System Parameters
The purpose of this study was to classify the various  Type I Devices:
extra-osseous talotarsal stabilization (EOTTS) devices o Cylindrical (IA) or Conical (IB) in shape.
into categories by design features and biomechanical o Inserted in a lateral-to-medial/oblique
function. These differences may have an impact on the orientation.
success rates of each type. This classification system o Leading anterior edge inserted up to the
will help surgeons appreciate these differences and the longitudinal talar bisection.
associated benefits, which in turn will aid them when o Laterally anchored by soft tissues in the sinus
making patient care decisions. portion of the tarsal sinus.
o Function by an impingement mechanism (block
Background excessive motion).
Many treatment options have been used to correct the  Type II Devices:
partial dislocation of the talus on the tarsal mechanism o Lateral conical and medial cylindrical geometry.
(RTTD), a dynamic deformity that has been shown to be o Inserted anterior-distal-lateral to posterior-
the primary etiology for many pathologies of the foot proximal medial.
and ankle. EOTTS has been a controversial surgical o Leading anterior edge inserted medially beyond
option. It offers improved stabilization over external the longitudinal talar bisection.
measures and is less invasive than traditional hindfoot o Medially anchored by soft tissues within the
reconstructive surgery. Over the years, many subtalar canalis portion of the tarsal sinus.
devices have been introduced, which differ in design, o Function by allowing normal helicoidal motion
materials, orientation and biomechanical function. of the talus on the tarsal mechanism.
Previous classification systems have been published,
however, due to the introduction of a new implant design Clinical Significance & Conclusions
and function, it was thought it would be beneficial to  The partial/recurrent dislocation of the talus on the
present an updated classification system. tarsal mechanism is a triplane deformity.
Displacement on any one of the four articular facets
Methods of the TTM leads to displacement at the other facets.
 Four critical design/function aspects were determined  The ideal method to stabilize the TTM is exactly at
on which to base classification: the axis of triplanar talotarsal motion. In the TTM,
o Device geometry/shape. this is referred to as the “cruciate pivot point” and is
o Anatomic orientation within the sinus tarsi. generally located at the entrance of the canalis tarsi
o Anchoring location within the tarsal sinus. along the longitudinal talar bisection line.
o Mechanism of talar stabilization and  It has been acknowledged that a device that better
biomechanical function. matches the anatomical shape of the tarsal sinus and
 Two major categories were established – Type I and follows its natural orientation would allow for better
Type II devices. Type I devices were further sub- biomechanical functioning.
classified into Type IA and Type IB.  Only Type II devices meet the ideal parameters,
which has an impact on their improved success rates.
 This improved design and function may also
contribute to the success of Type II devices in
decreasing the effects of or even eliminating
secondary pathologies.
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