Functional modes

Neutralisation plate

• It neutralises torsional and bending forces after lag screw fixation. Because lag screws are required, it is used only for simple patterns (Rockwood, p. 476).
• Usual sequence: reduce, fix with lag screws, then apply the plate. Alternatively, apply the plate first and place a lag screw through it.
• Campbell's adds that for a plate to work as a neutralisation plate it must be contoured exactly. Screws should be inserted from the fracture towards the ends of the plate (Campbell's Operative Orthopaedics, 15th ed, Fig. 58.29).

Compression plate

• Compression comes from eccentric screw placement in the plate holes, which shifts the plate on the bone (Rockwood, p. 477).
• Slightly overcontour ("pretension") the plate for a transverse fracture. Otherwise the far cortex gaps when the near cortex is compressed.
• For an oblique fracture, fix the plate to the correct fragment first. Fixing it to the wrong fragment first causes shear across the fracture.
• Other ways to get compression are a push-pull screw with a tensioning device, or a Verbrugge clamp.

Buttress versus antiglide plate

• Buttress: The plate is deliberately undercontoured and placed across the apex of the fracture. It touches bone only at its proximal and distal margins. An "axillary screw" is placed in the stable segment next to the apex, where the plate is lifted off the bone. Tightening this screw pulls the plate down, which compresses the fracture and blocks longitudinal translation. Lag screws through the plate often add compression.
• Antiglide: The plate mainly prevents shortening in a shear-type fracture. It is usually shorter than a buttress plate and relies on lag screws for compression. The classic example is a posterior antiglide plate on a Weber B distal fibula.
• Both plates are often used together in a bicondylar tibial plateau fracture. A medial buttress plate or a posteromedial antiglide plate holds the shearing medial fragment.

Bridge plate

• Anatomic reduction of each fragment is not attempted. Length, alignment and rotation are restored by indirect reduction. A long plate is fixed proximally and distally, often without exposing the fracture.
• The aim is to preserve biology. Surgeons usually use a long plate with few, well-spaced screws (Rockwood, p. 481).

Plate designs

DCP (dynamic compression plate)

• The screw holes are shaped like an inclined, transverse cylinder. As the screw head slides down the incline, the plate moves horizontally relative to the bone, which produces axial compression (Rockwood, Fig. 12-12).
• It is a conventional plate. The screws have no angular stability and hold by friction between plate and bone.
• The large plate-bone contact area can impair periosteal blood supply.
• It can be used in compression, neutralisation, buttress or bridge mode.

LC-DCP (limited contact DCP)

• This is a DCP with undercuts between the holes. These reduce contact with the bone and give more uniform stiffness along the plate, which lessens stress concentration at the holes (Rockwood, Fig. 12-32).

LCP (locking compression plate)

• It has combination holes that accept either a conventional screw (dynamic compression unit) or a locking screw. This is a standard feature of the design, though the textbook excerpts I retrieved did not describe it in detail.
• A locking screw threads into the plate and forms a fixed-angle device. It does not depend on friction between plate and bone (Rockwood, Fig. 12-10).
• Locked screws work in parallel. To pull out a locked plate, all the screws must loosen together, whereas conventional screws fail one at a time (Rockwood, Fig. 12-31).
• It is useful in osteoporotic bone and short metaphyseal segments. It can be used as an internal fixator for bridging, and it does not need to be contoured precisely to the bone.
• Locked constructs are stiff. This can reduce callus formation, so dynamic or far-cortical locking strategies have been developed (Rockwood, p. 496).

Practical points

• Conventional DCP or LC-DCP plates are best for absolute stability (compression, neutralisation, buttress) in simple fractures. LCPs are best for bridging, for osteoporotic bone and for periarticular fractures.
• Mixing conventional and locking screws in one LCP is acceptable. A common sequence is to place a conventional screw first to pull the plate to the bone, then add locking screws.
• A locked plate cannot reduce a fracture by itself, because the screws do not pull the plate to the bone.

Recent evidence