Modifying an Angular Hinge for Transarticular Use
Occasionally we see customers doing something with a product that merits bringing it to the attention of others. Several customers have been utilizing the angular hinge of the circular external skeletal fixation system to construct a simple, non-locking hinged fixator for temporary use across joints. When used in this fashion, the resulting fixator is a linear transarticular frame. An article published in 2005 documents case experience (Jaeger, et.al. Use of hinged transarticular external fixation for adjunctive joint stabilization in dogs and cats: 14 cases (1999-2003). JAVMA, Volume 227, No. 4, August 15, 2005.)
A hinged external fixator is constructed by screwing hybrid rods with 6mm threads into each end of the angular hinge. Small or large SK™ hybrid rods can be used, but small are by far more commonly utilized. Hybrid rod length for each end of the fixator is chosen based on patient size and joint involved. Hybrid rods are available in overall length increments of 50mm (approximately 2 inches.) 6mm hex nuts are utilized to lock the hybrid rods into the hinge and are the same hex nuts used with the large SK™ clamps and the IMEX™ CESF system. The appropriate sized SK™ clamp is then utilized to hold ESF pins onto the selected hybrid rods.
The angular hinge (part# 2.60001) is normally utilized in pairs with the CESF device to treat limb deformities. In CESF use, the angular hinge is not dynamic but slowly moved over a period of days. The modified hinge becomes very dynamic when utilized as a transarticular hinge. One potential complication of dynamic use is the tendency for the bolt that holds the two hinge halves together to loosen and back out.
To eliminate potential bolt loosening, IMEX™ now supplies a longer bolt to replace the factory hinge bolt. The longer bolt will traverse the hinge body with enough length to support two 5 mm hex nuts, which can be locked together to maintain bolt position. These 5mm hex nuts are the same as those on the small SK™ ESF clamp. There is a nylon bushing in the hinge assembly that must not be lost when modifying the angular hinge. Hinge modification should be performed prior to surgery to establish length and fit. It is recommended that the hinge bolt and 5 mm locking nuts be loosened prior to steam sterilization and tightened at surgery.
Modifications to this hinge are a great example of the modular nature of IMEX™ SK™ linear and CESF components, which is one reason the SK™ ESF device is depended on by more academic institutions and surgical referral practices than any other fixator.
