Mechanical testing of 3.5 mm locking and non-locking bone plates
Locking plate technologies are being developed in order to provide the surgeon with advantages over previous bone plate systems (both locking and non-locking). Locking plate systems possess inherent biological advantages in fracture fixation by preserving the periosteal blood supply, serving as internal fixators. It is important to consider the strength of each orthopaedic implant as an important selection criterion while utilizing the reported advantages of locking plate systems to prevent catastrophic fracture failure. Mechanical testing of orthopaedic implants is a common method used to provide a surgeon with insight on mechanical capabilities, as well as to form a standardized method of plate comparison. The purpose of this study was to demonstrate and to quantify observed differences in the bending strength between the LCP (Limited Contact Plate), LC-DCP, 3.5 mm Broad LC-DCP (Limited Contact Dynamic Compression Plate), and SOP (String of Pearls) orthopaedic bone plates. The study design followed the ASTM standard test method for static bending properties of metallic bone plates, which is designed to measure mechanical properties of bone plates subjected to bending, the most common loading encountered in vivo. Single cycle four point bending was performed on each orthopaedic implant. The area moment of inertia, bending stiffness, bending strength, and bending structural stiffness were calculated for each implant. The results of this study demonstrated significant differences (p<0.001) in bending strength and stiffness between the four orthopaedic implants (3.5 Broad LC-DCP>SOP>LCP=LC-DCP). The 3.5 mm LCP should be expected to provide in vivo strength and stiffness similar to a comparable LC-DCP. The SOP should provide strength and stiffness that is greater than a comparable LC-DCP but less than a 3.5 mm Broad LC-DCP.
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ABSTRACT: The advent of internal fixation with bone plates and screws represents a tremendous advancement in the methods of fracture fixation. During this era, the emphasis was on anatomic reconstruction and rigid internal fixation. Although these principles are applicable to a great number of fractures, not all can be treated in this manner. In fact, the disruption of the soft tissue envelope required to perform an anatomic reconstruction of a highly comminuted fracture and ensuing disruption of healing potential can contribute to nonunion. Gradually, a shift in philosophy has occurred, and now the emphasis is on preservation of fracture biology, with spatial realignment of the major bone segments; this technique is known as biological osteosynthesis. LCP IMPLANT DESIGN The LCP features a uniquely designed combination hole that accepts standard bone screws as well as locking screws, and allows the plate to be used as a conventional plate (compression), a locking plate (internal fixator principle) or as a combination of both principles. The ends of the plate have a "slipper toe" design that facilitates tunneling the bone plate under soft tissues in a minimally invasive manner. The underside of the plate has scalloped undercuts similar to the LCDCP, which creates a uniform area moment of inertia to minimize stress concentration at the plate hole, as well as mitigate disruption of extraosseous blood supply. The locking screws are designed to tolerate the shear loads resulting from angle stable fixation. The core (diameter of the screw between threads) is larger than standard bone screws, with a smaller thread profile. In addition, the pitch of the screw is smaller, and matches the pitch of the thread on the head of the screw. The smaller pitch minimizes the distance the screw travels prior to the threads of the screw head engaging the bone plate; this diminishes plate compression onto the bone surface. Finally, the locked screw has a conical, double-lead thread design that facilitates alignment with the threaded plate hole, and ensures that the screw thread engages the plate thread with no more than one-half turn. Figure 1. Locking plate combi-hole with locked screw (center) and standard screw (right).
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ABSTRACT: Locking plates are becoming increasingly popular in veterinary orthopaedics. The SOP is a novel locking plate system, which can be contoured with 6 degrees of freedom and which utilises standard bone screws. The purpose of this work was to investigate the mechanical consequences of contouring the 3.5 SOP plate to support the formulation of clinical guidelines. The implants were loaded in four point bending using an industry standard protocol. The uncontoured SOP was found to be significantly stiffer and stronger than the uncontoured 3.5 DCP. Bending, and to a lesser extent, twisting, diminished the SOP's stiffness and strength but the contoured SOP remained at least as stiff and strong as the untouched DCP.
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ABSTRACT: To describe a technique for treating Y-T humeral fractures using paired string of pearls (SOP) plates and to review the outcome in 13 cases.
A series of 13 consecutive Y-T humeral fractures, otherwise known as distal humeral dicondylar fractures, were treated according to a surgical protocol which involved combined medial and lateral surgical approaches, accurate reduction and fixation of the condylar fracture with a single transcondylar lag screw, and then re-alignment and fixation of the diaphyseal fracture using two SOP plates and screws.
Functional outcome was recorded as excellent in 10 dogs, good in two and poor in one. Six of the 13 patients were working dogs and of these, five returned to pre-injury levels of activity, including work. Complications requiring additional surgery were seen in four of the 13 cases, and three of these cases had a sub-optimal functional outcome.
The results following repair of Y-T fractures using SOP locking plates, placed via combined medial and lateral incisions, compared favourably with those reported for other techniques.
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