ABSTRACT: Part two of this series of articles covers the more common plates in use, describes classification of plates by form and function, and shows how to measure and identify different types of bone screw.

The term implant is used to describe, amongst other things, plates and screws used for fracture repair. This article will cover common types of plate and screw used for osteosynthesis or fracture repair.

Bone plates

Bone plates come in many shapes and sizes. They can be divided broadly into compression (DCP) and non-compression (round hole and locking) plates.1'2-3

Non-compression plates

Non-compression plates can be described as buttress plates, which are used to bridge an unreconstructed comminuted fracture. Used in this way, the plate repair maintains length and orientation of the bone, while transferring the weight of the patient from the proximal to the distal segment. The chosen plate must be strong enough for this.

Neutralisation plates

A neutralisation plate is one that is used to protect an oblique fracture that has been repaired using lag screws. Lag screws alone are not strong enough for long-bone repair.2 The neutralisation plate shares the load on the bone, transmitting torsion, compression and bending forces from the proximal section to the distal, thus protecting the weaker lag repair.

Locking plates

Locking plates effectively act as internal external fixators.1 Stability of the repair is provided by the rigid screw/plate interface. The plate does not have to be contoured as closely to the bone as with a conventional plate, which is held on to the bone by the head of the screw, which in turn is dependent on the security of the bone/screw interface.

This reduction of contact with locking plates has beneficial implications for the blood supply to the periosteum and bone. Anything which reduces damage to the blood supply can help to improve the rate of bone healing.1

Other plates

There are ‘hybrid’ compression plates which combine locking holes and separate compression holes in one plate (Hybrid Locking Pancarpal Arthrodesis Plates, VILock TPLO plates, Veterinary Instrumentation) and holes which accept cortical screws to create compression or locking screws to fix the plate and screw relative to one another (Locking Compression Plate LCP, Synthes).

Both of these hybrid styles allow the veterinary surgeon to apply compression to a repair and then take advantage of the angular rigidity of locking plate fixation to increase the rigidity of the construct.

There are also plates that use standard cortical screws with a specially modified plate to create a locking effect (SOP, Orthomed).

In addition plates can be described by their function, for example TPLO plates or arthrodesis plates. Round hole, locking and compression plates can be used for buttress and neutralisation plates, but if compression plates are used they are used only with the screws placed in neutral mode. Figure 1 shows a selection of bone plates.

Figure 1: Examples of different kinds of plate: A – dynamic compression plate IDCP) front and back; B – limited contact compression plate front and back; C – supracondylar plate 2.0mm; D – Slocum-style TPLO plate; E – pancarpal arthrodesis plate; F – round-hole plate; G – biological healing plate; H – cuttable malleable plate; I – cuttable plate;

So how to tell the plate holes apart?

Compression holes

Viewed from the back of a bone plate, standard compression holes are oval (Figure 1A). Looking into the hole from the front, it is possible to see the specially engineered slope which, when combined with the hemispherical head of a cortical screw and drill placement using the load end (offset drill hole placement) of a double-ended load and neutral drill guide, allows compression to be applied to a fracture.

This may be important close to joint surfaces or the end of fracture fragments. Compression holes also allow a greater range of screw angulation. These holes are complicated and expensive to produce, which is reflected in the cost of compression plates.

Round holes

Compression is not appropriate for every fracture, so it would make economic sense to use simple round-hole plates where compression is not desirable. As the name would indicate, these holes, when viewed from the back of the plate, are round (Figures IF & 1G).

The front of the plate shows some countersinking round the hole to allow the head to seat into the plate, and the hole is smooth within the plate. These plates will accept cortical/cortical self-tapping screws or the older-style Sherman self¬tapping screws (see Bone screws below).

Locking-plate holes

Standard locking holes are also round, but have rings of fine thread visible within the screw hole that – when gripped by the fine thread of locking- screw heads – create angular rigidity between the plate and screw. They may also be keyhole-shaped as in the LCP (Synthes), with locking threads at one end that do not engage the full circumference of the screw head. Locking holes are very expensive to produce because of the high level of accuracy required in their manufacture.

Plate shape

Plate shape is also variable. The commonest is the straight plate, used for long bone repair (Figures 1A, IB, IF & 1G).

Also available are T plates, which are often used for distal radius repairs. A variation with three head screws is used in the proximal tibia, both for fracture repair and TPLO (Figure 1L). Radial-cut TPLO has its own plates shaped to fit the curved osteotomy (Figures ID & IK).

Supracondylar plates are hockey stick¬shaped, and used in distal femoral fractures (Figure 1L). The layout of holes in the distal plate allows as many screws as possible in the distal fragment. A special curved plate is available for placement round the rim of the acetabulum for fracture repair (Figure 1J). The notched reconstruction plate is another option for pelvic repairs, as it can be contoured to fit the pelvis more accurately (Figure 1H).

Some plate suppliers produce actual-size clear acetates of plates to place over radiographs, to aid planning of fracture fixation (Plate Acetates, Veterinary Instrumentation). These come in handy for identifying stray plates!

Bone screws

Last but not least! There are four main types of screw, which are differentiated by their head and/or thread pitch.3 The pitch of a thread is the distance between each ridge in the spiral thread (Figure 2). A selection of screws is shown in Figure 3.

Figure 2: Measurement of screw pitch

Figure 3: Examples of different kinds of screw: A – 2.0mm cortical; B – 2.4mm cortical self-tapping; C – 2.7mm cortical; D – 3.5mm cortical; E – 3.5mm Sherman; F – 3.5mm locking; G – 4.0mm cancellous; H – k.0mm part thread cancellous

Cortical and cancellous

Cortical and cancellous screws both have the hemispherical head required to create compression with a DCP, and are placed using a hexagonal-head screwdriver. The difference between them is their pitch.

Cancellous screws have a wider, deeper pitch, designed to grip in the looser, trabecular structure of cancellous bone, while cortical screws have a finer, shallower pitch, which allows more rings of thread to grip in the thinner, denser cortical bone of the diaphysis of long bones.1


Sherman self-tappin
g screws have a conical head and take either a flat blade or, in the 3.5mm diameter size, a cruciate screwdriver. The thread pitch is shallower than that foimd on cortical screws. They can be used with round-hole plates but cannot be used to create compression with DCPs.2 These are cheaper than cortical screws and have been around for a long time!


Locking screws also have a conical head and are self-tapping, but have a very fine thread on the head, as well as a fine thread to engage the bone on the screw shaft. The industry standard thread for the head of a locking screw is a double helix, twin-start thread. This means that there are, in fact, two threads on the head, running side by side.

This allows the pitch of each thread to be the same as that on the shaft, allowing the screw head to move into the plate at the same speed as the screw shaft moves into the bone. A drill guide is screwed into the plate to make sure the screw is placed centrally, which is a critical element of placement.

Tapping or not self-tapping?

The tip of the screw will give a clear indication which type it is (Figure 4). Cortical and cancellous screws are available in both variants.

Figure 4: Screw tips

Self-tapping screws have one or more flutes cut into the tip of the screw. These flutes cut a thread in the drill hole as the screw is inserted. This type of self¬tapping tip is found on cortical, Sherman and locking screws. Self-tapping cancellous screws have a sharp-pointed ‘pigtail’ tip that is more suitable for softer cancellous bone. Non-self-tapping screws have a blunter, rounded tip.

Measuring screws

There are two ways of measuring bone screws (Figure 5).

Figure 5: Measuring screw lengths. Drawings courtesy of Veterinary Instrumentation

The majority of screws are measured including the whole head, i.e. the entire length of screw is measured. Sherman screws are the odd ones out, as they are measured from the top of the conical section of the head to the tip.

Most diameters of screw are length-sized in 2mm increments, increasing to 5mm increments in some longer sizes. The exceptions to this are the 2.7mm (7/64") and 3.5mm (9/64”) Sherman screws, which are in 3mm increments.

Screw diameters are now available from 1mm to 5.5mm in cortical thread patterns, and up to 6.5mm in cancellous.

An electronic measuring calliper, which is widely available from hardware or electronic stores, is invaluable in measuring screws, as well as pins and wires. A flow chart to help with screw identification is shown in Figure 6. Although this is not exhaustive, it will give a useful guide.


Of course, in addition to the implants and equipment described above, there are also many other implants used in veterinary orthopaedics. Alongside pins, wires and external fixators there are specialist cruciate surgery implants such as TTA plates/cages/forks.

Suppliers catalogues are invaluable as a reference and source for identification. 


Linda Capewell VN

Linda qualified in 1988 after 10 years in practice with the PDSA in Sheffield, as one of the first group of the charity's VNs. She spent a total of 26 years with the PDSA, and then in 2004. she left and joined Veterinary Instrumentation as veterinary technical support manager. She now deals with a wide range of queries every day.

To cite this article use either

DOI: 10.1111/j.2045-0648.2012.00193.x or Veterinary Nursing Journal Vol 27 pp 260-263


1.   JOHNSON, A. J„ HOULTON, J. E. F. and VANNINI. R. [2005] Principles of Fracture management in the Dog and Cat AO Publishing, Switzerland.

2.   DENNY, H. R. and STEVEN, J. A. (2008) Guide to Canine & Feline Orthopaedic Surgery 4th edition Butterworth Blackwell Scientific, Oxford

3.   COUGHLAN. A. and MILLER. A. [1998] Manual of Small Animal Fracture Repair and Management, BSAVA Cheltenham,


Thanks to Veterinary Instrumentation for implants and instruments shown.


Veterinary Nursing Journal • VOL 27 • July 2012 •