Vascular Damage in Fracture Plating: An Introduction
In the late seventies and early eighties, in vivo experimental animal studies produced convincing evidence that early temporary porosis, commonly observed under conventional bone plates, resulted from an insult to periosteal blood circulation caused by implant-bone contact. Deprived of blood perfusion, the bone turned necrotic, then sclerotic, before undergoing remodelling through neovascularization. The result was early, frequently persistent porosis. While in most cases, the end result was still bony union, many of the major complications of internal fixation can be linked to the vascular damage caused by surgical intervention and the implants used. Infection tops the list.
Reducing Vascular Damage: Methods
Two engineering proposals from the Straumann Institute, Waldenburg, provided early leads:
(i) Brunner proposed to increase dynamic compression plate (DCP) deformation tolerance in fatigue by transverse undercuts between the screw holes, evening out longitudinal variation in plate stiffness;
(ii) Sutter developed a mandibular reconstruction locking plate system.
In vivo testing of the Brunner plate provided some of the most convincing evidence linking bone remodelling to perfusion damage. Sutter’s in vitro testing of the locked vs. conventional plates demonstrated the mechanical advantages of locked screws.
Research & Development: PC-Fix to LC-DCP
Combining the two proposals with a novel technique, locking the screw by means of friction between a conical head and a conical hole in the plate, Dr. Slobodan Tepic initiated the development of a new plating system, PC-Fix, or Point Contact Fixator, by AO.
Approximately eight years of testing on animals demonstrated some anticipated and some surprising advantages of PC-Fix when compared to conventional plating:
• Significantly increased resistance to infection;
• Faster, more consistent, healing;
• Reduced impact on bone remodelling.
PC-Fix was then taken into the clinical setting in both human and veterinary applications. A large, multi-centre clinical trial on forearm fractures largely met the expectations, but the system was never commercialized.
Elucidation, of the role played by vascular damage resulting from internal fixation plates, provided fertile ground for innovation in the past three decades. A spur of activity, in R&D and marketing in the eighties, resulted in the release of the Synthes LC-DCP system. LC-DCP featured a modification in design and established titanium as the metal of choice, but the surgical principles of application remained the same. While the PC-Fix system was never commercialized, the locking screw principle caught the attention of both the industry and the surgical community. Within a very short period of time, locking has become a standard feature on just about every internal fixation system. Technical solutions also proliferated, but the main message of the research that started it all — the crucial role of blood perfusion in the process of healing – was still looking for an audience.
Moving Forward: The Advanced Locking Plate System (ALPS)
Dr. Tepic, who conducted the research on PC-Fix, developed the Advanced Locking Plate System (ALPS) as a “biological internal fixation”  system, designed from conception to preserve the vascular supply, increase resistance to infection and accelerate healing. “Biological internal fixation” involves the use of locked internal fixators, which have minimal implant-to-bone contact, long-span bridging and fewer screws for fixation.
ALPS has not been used on any experimental animals, nor has it been tested in a clinical trial, but its main features related to the bone contact and fixation method are very similar to PC-Fix, suggesting that most, if not all of the observations from the PC-Fix project are highly relevant to ALPS, and specifically those related to infection.
The ALPS plate is a combination of Shermann (1907) and Brunner plates, with holes, providing for use of either conventional or locking screws. The shape of the plate allows for bending in both planes. The plate material is c.p. titanium; for the screws, titanium alloy. Finite Element Analysis was used to optimize the shape of the plate. Three sizes, designated by the width of the plate (5, 8 and 10mm), suitable for small animals are currently available, with additional sizes coming soon. Since ALPS’ commercial release in the spring of 2007, 50 surgeons have used ALPS on over 1,000 clinical cases. Anecdotal evidence is positive. Increased resistance to infection and faster, more consistent healing are all but certain benefits to come from further clinical applications.
Currently, an in vitro study, comparing ALPS plates with other plates, is ongoing at the Cummings School of Veterinary Medicine at Tufts University. Results will be referenced once the study is complete and published.
Advanced Locking Plate System is patented/patent pending
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