Plates form and function

plate form and function dr. gaurav deshwar

1. PLATES: FORMS & FUNCTIONS Dr. Gaurav Deshwar Junior resident III Department of orthopaedics Sarojini Naidu Medical College, Agra

2. History Plates for fixation of long bone fractures were first recorded by Hansmann , of Heidelberg University, Germany in 1886.One of his original plate sets is seen below .Already then the instruments where listed. the white label says: Attention Do not lose anything .

3. History Hansmann’s plates were: Bent at the end to protude through the skin Attched to bone by screw with long shanks that projected outside the soft tissues.

4. History Since 1958, AO has devised a family of plates for long bone fractures, starting with a round holed plate. In 1969 the Dynamic Compression Plate was developed. In 1994 LC DCP was created. In 2011 LCP with combination holes has come into use.

5. Principle of AO 1. Anatomical Reduction. 2. Stable internal fixation. 3. Preservation of Blood supply 4. Early active pain free mobilisation

6. Biomechanical Aspect of AO Technique Neutralization Plate or Protection Plate Compression Plating Lag screw Tension Band Principle Intra Medullary Nailing External Fixation.

7. Plates : Introduction Bone plates are like internal splints holding together the fractured ends of a bone. A bone plate has two mechanical functions. It transmits forces from one end of a bone to the other, bypassing and thus protecting the area of fractures. It also holds the fracture ends together while maintaining the proper alignment of the fragments throughout the healing process.

8. Plate : Form and Function To understand how changes in the design of plates has evolved to meet the needs of the patient To understand how you can use a plate in several different ways to achieve different types of fixation

9. Plate : Form DCP 4.5 narrow and broad types DCP 3.5 LC-DCP 3.5 and 4.5 LCP Reconstruction plate 3.5 and 4.5 mm Semitubular - 1/3 rd Tubular Plate PC-FIX (Point contact fixator ) LISS

10. Orthopaedic alloy

11. DCP - 3.5 and 4.5 First introduced in 1969 by Danis Revolutionary concept of compression plating Featured a new hole designed for axial compression Broad 4.5 for Femur & Narrow 4.5 for Humerus & Tibia DCP 3.5 for Forearm, Fibula, Pelvis & Clavicle

12. Problems with DCP Unstable fixation leads to fatigue & failure Strict adherence to principles of compression Compromised blood supply due to intimate contact with underlying cortex “Refractures” after plate removal

13. LC-DCP Represents a design change Overcome problems with DCP Plate footprint reduced Minimized kinking at screw holes, more countourable , reduced plate fatigue at hole Allows more inclination of screw in longitudinal plane and transverse plane.

14. Tubular plates 3.5 system - 1/3 rd Tubular 4.5 system - Semitubular Limited stability Collared hole Lateral malleolus Distal ulna / Olecranon Distal humerus

15. Reconstruction plates Deep notches between holes Accurate contouring in any plane Pelvis Acetabulum Distal humerus Clavicle Olecranon

16. LCP – Locking Compression Plate

17. LCP Latest in the evolution “ Internal fixator ” Combination of locking screw with conventional screw Extraperiosteal location of plate

18. LCP Combines advantages of DCP principle and locking head principle. Flexibility of choice within a single implant. Screw hole have been specially designed to accept either: cortical screw and locking screw

19. Traditional plating techniques produced stability by: Compression the plate to the bone surface Engaging both cortices.thereby producing a rectangular hoop with two bicortical screws.

20. The locking screws, by achieving angular stability within the plate holes are able to produce a similar hoop with just two unicortical screws.

21. Shown – LCP used as internal fixator to bridge multifragmentary diaphyseal fracture zone. In this example : Locking compression plate is used. Standard cortical and cancellous screws are used as a traditional plate.

22. LISS System Preshaped plates with self drilling self tapping screws with threaded heads. Through a small incision (using this jig ) plate is slid along the bone surface. position of plate and wire are checked radiologically before insertion of metaphyseal screw .

23. LISS-Less Invasive Stabilization System

24. LISS

25. Plate: Function Each time a plate is used the surgeon determines how a plate will function. Plates can be used in four different ways: Neutralization/protection Compression Buttress Tension Band

26. Neutralization Plate A neutralization plate acts as a ""bridge". It transmits various forces from one end of the bone to the other, bypassing the area of the fracture. Its main function is to act as a mechanical link between the healthy segments of bone above and below the fracture. Such a plate does not produce any compression at the fracture site.

27. A plate used with combination with lag screw is also a neutralisation plate lag screw produce compression and stability. neutralisation plate merely protects the lag screw, allowing mobilization of the extremity. Lag screw generates forces of 3000 N. Term protection plate expresses the true function.

28. it is crucial to use a plate that is long enough so that at least three bicortical screw can be inserted in to each main fragment.

29. The most common clinical application of the neutralization plate is to protect the screw fixation of a short oblique fracture, a butterfly fragment or a mildly comminuted fracture of a long bone, or for the fixation of a segmental bone defect in combination with bone grafting.

30. Compression plate A compression plate produces a locking force across a fracture site to which it is applied. The effect occurs according to Newton's Third Law (action and reaction are equal opposite). The plate is attached to a bone fragment. It is then pulled across the fracture site by a device, producing tension in the plate. As a reaction to this tension, compression is produced at the fracture site across which the plate is fixed with the screws. The direction of the compression force is parallel to the plate

31. Role of compression Reduction of the space between the bone fragments to decrease the gap to be bridged by the new bone. Compaction of the fracture to force together the interdigitating spicules of bone and increase the stability of the construct. Protection of blood supply through enhanced fracture stability. Friction, which at the fracture surfaces resists the tendency of the fragments to slide under torsion or shear. This is advantageous as plates are not particularly effective in resisting torsion.

32. Static compression between two fragments maintained over several weak and does not enhance bone resorption and necrosis. Interfragmentary compression leads to absolute stability but has no direct influence on bone biology or fracture healing.

33. METHODS OF ACHIEVING COMPRESSION With tension devise By overbanding With dynamic compression principle (DCP/LC-DCP) By contouring plate Additional lag screw thro plate

34. Compression with external devise it is recommended for fractures of the femur or humeral shaft, when the gap to be closed exceeds 1–2 mm, as well as for the compression of osteotomies and nonunions .  After fixation of the plate to one main fragment, the fracture is reduced and held in position with a reduction forceps. The tension device is now connected to the plate and fixed to the bone by a short cortex screw.and then after comression another fragment is fixed to plate.

35. Application of the articulated tension device In oblique fractures the tension device must be applied in such a way that the loose fragment locks in the axilla if compression is produced. This figure demonstrates the tension device applied in the wrong position

36. Compression with overbanding If a straight plate is tensioned on a straight bone, a transverse fracture gap will open up due to the eccentric forces acting on the opposite side .

37. If the plate is slightly prebent prior to the application (a), the gap in the opposite cortex will disappear as compression is built up (b), so that finally the whole fracture is firmly closed and compressed (c).

38. Compression plating Compression through plate - DCP / LC-DCP

39. Dynamic compression principle: a  The holes of the plate are shaped like an inclined and transverse cylinder. b–c  Like a ball, the screw head slides down the inclined cylinder. d–e  Due to the shape of the plate hole, the plate is being moved horizontally when the screw is driven home. f  The horizontal movement of the head, as it impacts against the angled side of the hole, results in movement of the plate and the fracture fragment already attached to the plate by the first screw (1). This leads to compression of the fracture.

40. After insertion of one compressing screw, it is only possible to insert one further screw with compressing function in the same fragment. Movement of the plate pushes the first compression screw against the side of the screw hole and prevents further movement. When the second screw is tightened, the first has to be loosened to allow the plate to slide on the bone, after which it is retightened .

41. Screw holes allow 1mm compression Additional compression with 1 more eccentric screw before locking first screw

42. The oval shape of the holes allows 25° inclination of the screws in the longitudinal plane, and up to 7° inclination in the transversal plane

43. Contouring Plates Straight plates often need to be contoured prior to application to fit the anatomy of the bone. This is best done with hand-held bending pliers, the bending press, or bending irons . Special flexible templates are available that can be modeled to the bone surface. Repeated bending back and forth should be avoided, as this weakens the plate.

44. Plate contouring steps Twisting the plate -The anteromedial surface of the tibial shaft twists internally approximately 20° as it approaches the medial malleolus . The first step of plate contouring is to twist the plate so it matches the tibial surface upon which it will lie.  If the plate is bent before it is twisted, the process of twisting will alter the bend that has been created.

45. Matching the curvature Depending upon the plate location, more or less bending of the plate will be required to match the contour of the intact (or reduced) bone. Much of the medial tibial shaft is quite straight, so that little bending is required. However, the distal medial surface has a significant concavity, with a typical radius of curvature of 20 cm as illustrated. Such a 20 cm radius can be drawn on a sterile drape and used as a template for plates to be used in this location.

46. Bending the plate The plate can be bent with bending irons alone, but it is preferable to bend with a bending press, because the press gives more control. In either case, the bending is done in small steps to produce a smooth contour. Contouring only takes place over the distal 10-12 cm of the plate. When finished, the plate should match the 20 cm radius of curvature.

47. Buttress Plate A buttress is a construction that resists axial load by applying force at 90° to the axis of potential deformity Used in metaphyseal / epiphyseal shear or split fractures For application of a buttress plate, the first screw must be eccentric to prevent sliding of the plate.

48. Tension band principle Frederic Pauwels observed that a curved, tubular structure under axial load always has a compression side as well as a tension side. Under vertical pressure the curved femur creates a tension force laterally and a compression force medially A plate positioned on the side of tensile forces neutralizes them at the fracture site provided there is cortical contact opposite to this plate. In case of a cortical defect, the plate will undergo bending stresses and eventually fail due to fatigue.

49. Dynamic and static tension band a) tension band principle on a fracture of the patella. Upon knee-flexion the distraction forces are converted to compression.  In the olecranon fracture the figure-of-eight wire loop acts as a tension band upon flexion of the elbow tension band principle at the proximal humerus with an avulsion of the greater tubercle Tension band principle to the medial malleolus example of static tension band

50. Tension band principal The following prerequisites are essential: a) Bone or a fracture pattern that is able to withstand compression. b) An intact cortical buttress on the opposite side of the tension band element. c) Solid fixation that withstands tensile forces.

51. Antiglide Concepts In this model black plate is secured by three white screws distal to the blue fracture line. The fracture is oriented such that displacement from axial loading requires the proximal portion to move to the left. The plate acts as a buttress against the proximal portion, prevents it from “sliding” and in effect prevents displacement from an axial load. If this concept is applied to an intraarticular fracture component it is usually referred to as a buttress plate , and when applied to a diaphyseal fracture it is usually referred to as an antiglide plate.

52. Bone-implant composite Interdependence of bone and implant in contributing to stability Intact femur- support axial load of 850 kg Transverse fracture of mid shaft, with plate on lateral, tension cortex – withstand upto about 800 kg. Similar fixation with gap in medial cortex will fail under a load of about 60 kg Plated gap in shaft- buckle under a 20 kg load.

53. Fixation with an empty screw hole directly leval with a single plane fracture resulted in early fatigue failure due to Movement Stress concentration at the weak point. If a single plane fracture is spilnted with a plate even with axial interfragmentary compression,the fracture will open at the cortex oppsite to plate due to elasticity of the plate. This instability is avoided by-lag screw and prestressd by overbending and by incorporate bone graft medially.

54. Relative stability : Biological osteosynthesis In multiplaner fracture complex,use of technique to achieve absolute rigid stability can jeopardize the fragment biology and failure of healing and fixation. Application of plate over top of wedge can damage the vascularity . To avoid these complication of absolute stability has developed the concept of relative stability .

55. In such a fraacture if the comminuted zone is bridged in a manner that the main diaphyseal fragments are: Aligned Correctly matched for rotation Out of length Undisturbed intermediate fragments heal rapidly by formation of external callus in response to interfragmentary motion. Addition of bone graft will ensure rapid bone healing.

56. AO Organisation Philosophies and techniques of treatment will change with time The philosophy that we exist to improve the care given to our patients will last forever

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