Bone Fracture Fixation Overview (3/3)
previous page...the limb anatomy for the healing period and act as a splint that shares the load with the bone. The advantages of internal fixators are excellent control over the position of the bone segments, early stability/rigidity and early usage of joints and muscles. Stress shielding, commonly experienced due to high plate stiffness, may lead to delayed union and poor bone formation. The stiff plate may also act as a 'stress raiser', causing a new fracture at the end of the plate. Primary cortical healing is often the mechanism by which fracture heals when plates are used. Hidaka and Gustilo  have shown that removal of plates introduces risks of re-fracture of the healed bone. Intramedullary nails (IMN) have an unassailable place in the management of fractures of the femoral shaft. This however is only true for the femur due to the anatomy of the blood supply to the shaft. For other bones, the IMN with or without reaming can interfere with the blood supply, which may negatively influence healing. Furthermore, it is not possible to perform bone transport, shortening, lengthening and postoperative deformity correction, unless a special IMN is used at a specialist treatment centre. The common healing mechanisms when the IMN is used, are external bridging and later medullary callus formation.
The other group of the invasive fixators is external. These invade minimally human anatomy during treatment periods. The majority of the external fixator's structure (exoskeleton) is located outside the human anatomy. The exoskeleton is connected to the bone segments via fine wires and half/full pins. Axial external fixators (uniaxial / biaxial / monolateral), of which the geometry is normally parallel to the axis of the bone, are connected using pins. Advantages of the axial fixator are simple structure and simple kinematics. However, such fixation has low overall bending stiffness, which is significant since the main axis of the fixator is offset from the load axis of the bone. In addition, it is very complicated (even if possible at all) to perform deformity correction in more than one plane using such fixators. The axial fixators are simple in structure and suitable mainly for stabilising fractured bone segments where low loads are exhibited during treatment. It was observed by Khalily et al  that the stiffness of axial fixators decreases with increasing load. Since this type of fixator allows micromotion, the typical bone healing is by formation of external bridging callus.
In the present research, all attention is paid to ring fixators, as they are highly versatile, allowing post-operative adjustments. They, contrary to the axial fixators, become stiffer with increasing load . The vertical axis of the ring fixator is aligned with the bone load axis, minimising unwanted bending effects observed in axial fixators. Subject to frame design, it is possible to change the mechanical properties of the frame during the treatment period. Since the exoskeleton of the fixator is located a few inches away from the anatomy, access to the skin and soft tissues is maintained, allowing access of fresh air and post-operative treatment of any damage or infection. Frames can be applied with minimal blood loss or soft tissue damage, due to small diameters of half-pins and fine wires. This in turn provides pain relief and early mobility.
The main disadvantages of the ring fixators are size, form, weight, pin tract infections, lack of means of assessing the fracture stability with the fixator in situ and high cost. Few types of ring fixators are available commercially to date. An Ilizarov fixator [4, 5] is one of the more popular ring fixators. It was pioneered by the Prof. Ilizarov in 1950s in the former USSR and has been used over the last 10 years in Europe and the USA. The Taylor Spatial Frame (TSF)  is a recent introduction. Details of it are discussed in the dedicated section.Discuss this article, in our forum.
Fracture fixation references
1. Hidaka S and Gustilo RB. Refracture of bones of the forearm after plate removal. Journal of Bone & Joint Surgery - American Volume, 1984. 66(8): p. 1241-3.
2. Khalily C, Voor MJ, and Seligson D. Fracture site motion with Ilizarov and "hybrid" external fixation. Journal of Orthopaedic Trauma., 1998. 12(1): p. 21-6.
3. Hillard PJ, Harrison AJ, and Atkins RM. The yielding of tensioned fine wires in the Ilizarov frame. Proc Instn Mech Engrs, 1998. 212: p. 37-47.
4. Ilizarov GA. The tension-stress effect on the genesis and growth of tissues: Part II. The influence of the rate and frequency of distraction. Clinical Orthopaedics & Related Research, 1989(239): p. 263-85.
5. Ilizarov GA. The tension-stress effect on the genesis and growth of tissues. Part I. The influence of stability of fixation and soft-tissue preservation. Clinical Orthopaedics & Related Research, 1989(238): p. 249-81.
6. Taylor HS and Taylor JC, Orthopaedic fixation device, Patent No: 5,702,389. 1997, Smith & Nephew Richards, Inc.: USA. p. 1-24.