Advances in Bone Plating
World Small Animal Veterinary Association World Congress Proceedings, 2013
Don Hulse, DVM, DACVS, ECVS
Texas A&M University, College Station, TX, USA

Bone plates have been used effectively for treatment of fractures in dogs and cats for over 30 years. Over the years, different designs of plates have become available, including DCP (dynamic compression plates), LC-DCP (limited contact dynamic compression plates) and special situation plates (veterinary cuttable plate, acetabular plates). The most recent plate design to become available is the locking compression plate. The unique feature of the locking plate is the presence of a threaded plate hole that couples with a threaded screw head or alternate locking mechanism. A number of companies have developed locking plates. One of the most recognizable locking plates is the Synthes LCP.

The Synthes LCP features a combi hole; this is a plate hole through which the surgeon can apply compression using a standard cortical screw or apply a locking screw. Using a locking screw, threads in the head of the screw engage threads in the plate hole, locking the screw to the plate. The ability to lock the screw to the plate increases the stiffness of the construct and the pull out strength of the bone plate and screws. Standard plates do not have threaded holes; stability is achieved through compression applied between the plate and bone surface when tightening the screws. The friction between the plate and the bone provides the stability to the bone-implant construct. In contrast, the locking plate achieves stability through the concept of a fixed-angle construct. The locking plate is not pressed firmly against the bone as the screws are tightened. The locking screws and plate function more like an external fixator. The plate functions as a connecting bar and the screw functions as a threaded fixator pin. The threads in the head of the locking screw engage the hole of the plate, similar to the clamp of an external fixator.

Equipment and Application

Many of the same instruments used for application of traditional plates are used for locking plates. The 3.5 mm locking plate and screws are most commonly used in small animals. The 3.5 mm locking plate will accommodate 3.5 mm cortical screw, 4.0 mm cancellous screws or 3.5 mm locking screws. A 2.8 mm drill bit is used when applying 3.5 mm locking screws. A guide is screwed into the intended hole to center the hole when drilling. The locking screw is self-tapping and is placed with a hand or power driver.

TraumaVet system is a locking system for internal fixation. It consists of a steel support, with threaded holes where threaded inserts can be secured. The inserts are externally threaded and are to be screwed into the support. The inner hole of the insert is conical to lodge the head of the screw. The support together with the inserts forms the plate. The screw is a self-tapping with angular stability. The screw head is conical, coupling with the insert to achieve the locking mechanism.

The unique conical screw-plate locking system ensures the distribution of force throughout the structure, virtually eliminating the risk of implant breakage and screws backing out.

The locking system allows easy locking of the screw in the plate and eliminates the possibility of cross-threading the screw head in the plate.

The plate thickness ranges from 1.2 mm to 2.0 mm in the mini-series and from 1.5 mm to 3.0 mm in the medium series.

The Fixin bone plate system is ideal for minimally invasive fracture repair, direct fracture reduction, indirect fracture reduction and corrective osteotomy to treat angular limb deformities.

Traditional locking plates use a threaded screw-plate locking system. TraumaVet screws have a 2° conical head which locks into a corresponding 2° tapered cone in the bushings, which are pre-assembled on the plate. This coupling eliminates the risk of cross threading between the screw and plate and ensures a simple operative technique. It also permits easy removal of the screws. It is an extremely stable coupling, which effectively transfers loads through the structure and reduces the risk of screws backing out or plate breakage.

Indications for Application of Locking Plates

Locking plates are particularly useful when screw pull-out is at a greater risk. Screws may be susceptible to pull-out failure in the metaphyseal region of bones where the bone cortex is thin, in osteoporotic bone, older patients, patients having slow bone healing conditions and patients that have poor compliance to restricted activity during the postoperative period. A locking plate is also useful with the presence of a limited proximal or distal target (epiphyseal or metaphyseal fracture). Minimally invasive plate osteosynthesis (MIPO) is best accomplished with the application of a sliding plate technique. MIPO is usually accomplished with small proximal and distal portals where one applies 2–3 screws in each fracture segment.

Minimally invasive technique is an open technique whereby direct or indirect fracture reduction is achieved with small exposure portals. Each portal is strategically located to allow proper reduction of the fracture and application of an implant. An incision (1–2 cm) is made overlying the metaphyseal-epiphyseal area of the proximal and distal parent bone. Soft tissue is reflected to expose the bone surface where the implant will be applied. An additional small portal may be necessary to expose the transverse (short oblique) fracture site. A periosteal elevator is used to create an avenue on the surface of the bone for positioning the implant. The fracture is visually aligned and the implant applied. With bone plates and screws, the implant is slid beneath the soft tissue into the previously created avenue on the surface of the bone. One proximal and one distal screw are applied to hold fixation while alignment is examined. The remainder of the screws are then inserted. As a generally rule, 2–3 screws are inserted into each fragment.

  

Speaker Information
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Don Hulse, DVM, DACVS, DECVS
Texas A&M University
College Station, TX, USA


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