Diameter is the key element in determining the stiffness or resistance to bending of a fixation pin. Hybrid (and circular frame) fixation wires are of small diameter, but placing them under tension can enhance their mechanical performance. IMEX® provides a wire-tensioning device for this purpose. When the distance the wire spans is short (small diameter rings) or the patient is small (mini rings), wire tensioning is not necessary. When ring diameters or patients are large, wires must be tensioned to achieve adequate mechanical stability.
Assuming one is knowledgeable and experienced with linear external skeletal fixation, the learning curve is relatively short for fracture repair using hybrid frames. The necessary details to master are proper wire placement, wire tensioning, and frame component selection. One should be well versed with linear fixators before attempting hybrid ESF. Many consider hybrid ESF a simpler alternative to growth deformity correction than true circular ESF frames.
True circular ESF frames are built with three or four threaded rods spanning the length of the involved bone and supporting the ring in several places. Hybrid frames often mimic a Type I-a or Type I-b frame and only support the ring at one or two locations. With 35mm, 45mm or occasionally 50mm rings, a single support may result in a stable frame. When larger rings are used or unstable scenarios are encountered, it is mandatory to use struts or additional sidebars to stabilize the ring in two or more locations. Larger ring diameters are most secure with a construct of three or more supports (rods and struts).
Most hybrid conversations begin with the assumption that the surgeon owns basic SK® linear external fixation components. Therefore, only a minimum of circular fixation components are necessary compared to a complete circular external fixation frame. Hybrid frame cost is significantly less than a complete CESF frame. The modular nature of the IMEX® system allows one to upgrade to a true CESF frame with the same components.
Since use of small diameter wires allows the capture of small bone fragments, hybrid ESF frames are popular for fixation of fractures with a short juxta-articular bone fragment where standard ESF pins or bone plating might be difficult. In addition, many referral practices utilize hybrid frames for correction of growth deformities.
No, it is especially common to use standard full-pins and half-pins when repairing juxta-articular fractures of the distal humerus or distal femur. In these locations it is difficult to obtain wire divergency because of the patient anatomy. When wires do not have divergency, less stability is achieved. Attempts to increase wire divergency in these locations results in unacceptable soft-tissue morbidity. Threaded ESF pins perform well in these locations.
Small diameter wires are not threaded and therefore are subject to micromotion. When four or more smooth wires are used with good divergency, stability is adequate. When wire number is reduced or divergency is not adequate, surgeons choose to place stopper wires (also called olive wires) to reduce micromotion and enhance stability. Stopper wires have a centrally located expanded bead designed for placement against the bone. Most situations where hybrid frames are chosen will benefit from the added stability provided by stopper wires.
Mini and small SK® clamps can be utilized to construct hybrid frames. The SK® ESF System is the most modular veterinary fixator available. The small SK® is the most commonly used hybrid frame due to its ability to cover a wide patient range.