ExVIVO Joint Simulator


 


The Problem


Single-Cycle Acute Failure

Single-Cycle Acute Failure Setup

In orthopedic studies, it is important that the device being tested is in a clinically relevant environment. While testing done in a non-clinically relevant environment can be beneficial in finding certain points of failure, it does not necessarily correspond to the failures experienced in clinical use.  An example is the current testing done for the stabilization of coxofemoral luxations using toggle rod and suture constructs (TRC). Current methods for effectiveness of TRC’s are a single-cycle acute failure study. This form of testing does not properly reflect TRC failure seen in clinical conditions.


The Solution


In order to properly determine points of failure for orthopedic devices and procedures the Experimental Validation Instrument for Veterinary Orthopedics (ExVIVO) joint simulator was created. The ExVIVO provides motion emulation of flexion-extension as well as abduction-adduction through the primary and secondary yoke respectively. Through the use of a dead load rack system, the ExVIVO allows for the replication of simplified forces which would be present in the joint from ground reaction forces.

The ExVIVO joint simulator is designed to work with cadaver specimens which are contained in the environmental chamber. The environmental chamber allows for the circulation of saline solution which can be heated to the appropriate temperature as well as an open top box and lid which are radio-transparent allowing for x-ray imaging.

 


Testing


The first implementation of the ExVIVO joint simulator is the reproduction of canine hip motion for evaluation of three different TRC’s. Summarized steps for the testing procedure are as follows:

X-ray of hemipelvise in ExVIVO join simulator

X-ray of Hemipelvis in ExVIVO Joint Simulator

  • Parts of the femur and pelvis are surgically removed from canine cadavers and implanted with one of three TRC’s.
  • The prepared hemipelvis is inserted into the environmental chamber and sealed to allow for saline circulation.
  • The free end of the femur is secured using a femoral pot creating a closed environment for the specimen.
  • Weight is added to the device to provide load approximations of ground reaction forces
  • The specimen undergoes repeated flexion-extensions and abduction-adduction motions biased on a physiologically relevant range.

The invention’s feasibility has been proven through this study. In this testing instance, the ExVIVO simulator has been able to recreate the clinical failures seen in TRCs. The ExVIVO simulator can be used to evaluate different methods and devices for treating and repairing dislocation of not just the canine hip but other veterinary species.