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Dynamic compression plate
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A dynamic compression plate (DCP) is a metallic plate used in orthopedics for internal fixation of bone,[1] typically after fractures. As the name implies, it is designed to exert dynamic pressure between the bone fragments to be transfixed. Dynamic compression is achieved either by attaching a tension device to a plate or by using a special dynamic compression plate. However, compression plating requires a longer surgical incision to allow insertion of the tension device and the possibility of refracture after the plate is removed. A neutralization plate is used to bridge a comminuted fracture; it also transmits bending or torsional forces from the proximal to the distal fragment. Plates used for buttressing prevent collapse by supporting an area of thin cortex or cancellous bone graft.[citation needed]
When plates are used, atrophy of the bone beneath the plate may predispose the bone to fracture. After removal of plates, fractures may occur through the screw holes.
Sliding screw plate
[edit]The sliding screw plate (dynamic compression screw, dynamic hip screw) may be used to treat intertrochanteric fractures as well as other injuries. This device consists of a lag screw and a side plate with a barrel. The sliding screw telescopes and provides fixation while allowing impaction to occur at the fracture during healing and weight bearing. Among the complications of sliding screw plate fixation are "cutting out" of the nail, penetration of the screw into the joint, bending or breaking of the nail, and disengagement of the screw from the barrel and even protrusion of the screw into the vertebrae.[citation needed]
See also
[edit]References
[edit]- ^ Cohn, M. R.; Unnanuntana, A.; Pannu, T. J.; Warner, S. J.; Lane, J. M. (1 January 2017). "7.16 Materials in Fracture Fixation☆". Comprehensive Biomaterials II. Elsevier. pp. 278–297. ISBN 978-0-08-100692-4. Retrieved 29 January 2022.
Dynamic compression plate
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History and Development
Origins
The origins of compression plating trace back to early 20th-century efforts in internal fracture fixation, which initially relied on rigid plates without mechanisms for interfragmentary compression. In 1909, Belgian surgeon Albin Lambotte introduced one of the first practical metal plates for bone stabilization, featuring a thin, round design tapered at both ends to minimize soft tissue irritation; this plate used screws for attachment but provided absolute rigidity, limiting its ability to promote direct bone healing.[7] Similarly, in 1912, American surgeon William O. Sherman developed a plate system with self-tapping screws, emphasizing secure fragment alignment through rigid immobilization, though it too lacked dynamic features to apply controlled compression across the fracture site.[7] These innovations marked a shift from earlier wire-based methods but were constrained by material limitations and design simplicity. Early rigid plate designs encountered significant clinical challenges, including high rates of infection, delayed union, and non-union, primarily due to inadequate compression that failed to achieve stable interfragmentary contact. The absolute stability provided by these plates often resulted in excessive rigidity, leading to stress shielding, cortical porosis, and micromotion at the fracture interface, which compromised healing and increased susceptibility to postoperative infections from poor vascularity and biofilm formation on hardware.[8] Non-union rates were notably elevated in long bone fractures treated with such systems, as the lack of compression hindered primary bone healing and allowed for excessive strain that disrupted callus formation.[7] A pivotal advancement occurred in 1956 when George W. Bagby, working at the Mayo Clinic, modified the existing Collison plate by incorporating oval-shaped holes, enabling eccentric screw placement to generate dynamic interfragmentary compression during insertion. This design allowed the plate to slide slightly along the screw axis, applying controlled force to approximate fracture fragments without excessive rigidity, and was rigorously tested in canine femoral fracture models, where it demonstrated accelerated healing rates compared to non-compression controls.[9] Bagby's approach addressed prior deficiencies by promoting primary bone union through precise compression, reducing the shear forces that contributed to complications in earlier systems. Throughout the 1950s, several key publications and designs underscored the critical need for interfragmentary compression in fracture fixation, building on Bagby's prototype. Bagby and colleague J.M. Janes detailed the oval-hole mechanism in their 1956 work, highlighting its role in achieving compression via screw head eccentricity, which influenced subsequent engineering efforts.[10] These contributions emphasized that effective plating required not just stability but active fragment apposition to minimize healing time and complications, paving the way for formalized advancements in the following decade.[11]AO Introduction and Evolution
The Association for the Study of Internal Fixation (AO), founded in 1958 by a group of Swiss surgeons led by Maurice E. Müller, aimed to standardize and advance fracture treatment through rigorous scientific research and education.[7] The organization's core principles emphasized anatomical reduction of fractures, stable internal fixation to promote primary bone healing without callus formation, preservation of vascular supply to the bone, and early functional rehabilitation to minimize complications like stiffness.[12] These tenets shifted the paradigm from conservative casting to operative intervention, focusing on rigid fixation that allows direct osteonal remodeling across the fracture gap under absolute stability. Building on these principles, the AO introduced the Dynamic Compression Plate (DCP) in 1969 as a major advancement in plating technology.[13] The DCP featured oval-shaped screw holes that enabled eccentric screw insertion to generate interfragmentary compression, paired with self-tapping cortical screws for secure anchorage without predrilling taps.[2] This design, inspired by earlier concepts like Bagby's 1956 oval hole plate for compression, allowed for precise control of fracture site stability while adhering to AO's rigid fixation goals.[7] In the 1990s, the AO evolved the DCP into the Limited Contact Dynamic Compression Plate (LC-DCP) to address concerns over periosteal blood supply disruption from broad plate-bone contact.[14] The LC-DCP incorporated undercuts along the plate's underside, reducing contact area to approximately 50% and minimizing vascular impairment and cortical atrophy.[13] Titanium alloys have been used for DCP and LC-DCP implants since the early 1970s alongside stainless steel, offering superior biocompatibility, a modulus of elasticity closer to bone, and reduced risk of allergic reactions.[15] Early clinical studies in the 1970s validated the DCP's efficacy, reporting primary bone healing rates of 80-90% in stable fractures treated with compression plating, with union times averaging 12-16 weeks and low complication rates when principles were followed.[2] These outcomes, documented in prospective series of long bone fractures, underscored the DCP's role in achieving direct healing without external support, influencing global adoption of AO techniques.[16]Design Features
Plate Construction
The dynamic compression plate (DCP) is primarily constructed from biocompatible materials such as 316L stainless steel or titanium alloys, selected for their high corrosion resistance, biocompatibility, and mechanical strength suitable for load-bearing orthopedic applications.[17][18] These materials ensure durability in physiological environments while minimizing adverse tissue reactions.[19] DCP plates are available in narrow and broad profiles tailored to specific anatomical regions. The narrow profile, intended for the upper extremities and forearm, accommodates 3.5 mm screws and features a thickness of 2.0–3.3 mm and width of 10 mm.[20][21] In comparison, the broad profile, designed for the lower leg and thigh, uses 4.5 mm screws with a thickness of 4.8 mm and width of 16 mm to provide enhanced stability for larger bones.[22] Plates are produced in various lengths corresponding to 3–18 holes, enabling adaptation to different fracture spans.[23] Factory prebent options are available for certain DCP variants to approximate bone contours, such as a slight S-curve for femoral applications, though intraoperative contouring with bending tools is often required for precise fit.[24] Hole configurations consist of a combination of compression (oval-shaped) and round (neutral) holes, with center-to-center spacing typically ranging from 12–18 mm depending on plate size.[25][26] Plate thicknesses vary by system size, typically from ~2.0 mm for small fragment (3.5 mm screws) to ~5.0 mm for large fragment (4.5 mm screws), optimizing contact with bone while maintaining structural integrity.[26] An evolution to the limited-contact DCP (LC-DCP) incorporates undercuts in the plate undersurface to reduce bone contact area and preserve periosteal vascularity.[26]Screw and Hole Mechanics
The holes in a dynamic compression plate (DCP) are oval-shaped, elongated along the longitudinal axis of the plate to accommodate eccentric screw placement that facilitates controlled fracture compression.[27] Each hole features a sloped edge, formed as part of an inclined cylinder on the side distant from the fracture, allowing the screw head to slide and generate axial compression as it tightens.[13] This design contrasts with round holes, which provide neutral fixation without such movement.[13] DCP systems utilize self-tapping cortical screws, typically 3.5 mm or 4.5 mm in diameter, with lengths ranging from 6 mm to 70 mm in 2 mm increments, and featuring hexagonal heads for precise torque application using a screwdriver.[26] These screws are designed for bicortical purchase, threading fully into the far cortex while the head seats against the plate hole.[27] In neutral position, screws are placed centrally in either oval or round holes, securing the plate to bone without inducing motion or compression.[13] For load or compression mode, eccentric placement in the oval hole positions the screw head against the sloped edge, causing the plate to glide relative to the bone fragment as the screw tightens, thereby drawing the fragments together.[27] This interaction relies on a specialized drill guide to offset the drill hole by about 1 mm from the center.[26] A key aspect of this mechanics is the recoil effect, where the plate's elastic deformation during screw tightening results in an additional 1-2 mm of fragment approximation after the screw head fully seats, enhancing interfragmentary contact.[1] The oval hole design also permits angulation tolerance of up to 20-25 degrees off-axis in the longitudinal direction and about 7 degrees transversely, allowing adaptive insertion while maintaining effective compression.[26]Biomechanical Principles
Compression Mechanism
The dynamic compression plate (DCP) generates axial compression through eccentric loading of non-locking screws within its specialized oval holes. When a screw is inserted into the compression hole and positioned eccentrically toward the fracture site, tightening causes the screw head to engage the inclined surface of the hole, translating the plate laterally by up to 1 mm relative to the underlying bone fragment. This action induces a slight temporary bowing of the plate, followed by elastic recoil that draws the bone ends together, achieving interfragmentary compression across the fracture gap.[28][1] To optimize compression, particularly at the far cortex and prevent gapping at the near cortex, surgeons employ a pre-bending technique by contouring the plate 1-2 mm away from the bone surface over the fracture line prior to fixation. Upon screw insertion and tightening, the plate flattens against the bone, leveraging its elastic properties to produce additional compressive force through recoil. This method shifts pressure distribution toward the far cortex and enhances overall stability at the fracture interface.[28][1] The resulting interfragmentary pressure at the fracture site provides the rigid environment necessary for primary bone healing without callus formation. Pre-bending improves pressure distribution across a larger contact area.[1] The dynamic nature of the DCP allows limited interfragmentary micromotion following implantation, which supports bone remodeling under physiological loads while minimizing shear at the fracture site. This controlled motion arises from the plate's elastic deformation limits and the non-locking screw interface, contrasting with fully rigid systems.[28][1] The underlying mathematical basis for compression relies on a simplified application of Hooke's law, where the compressive force $ F $ is given by
with $ k $ representing the plate's axial stiffness (typically 100-150 N/mm for standard DCP constructs) and $ \delta $ the deflection from pre-bending or recoil. This model approximates the spring-like behavior during flattening, with forces of approximately 160-520 N under clinical torque levels up to 4 Nm.[1][29]