Influence of screw insertion order on compression generated by bone plates in a fracture model

Effects of Angled Dynamic Compression Holes in a Tibial Plateau Levelling Osteotomy Plate on Cranially Directed Fragment Displacement

OBJECTIVE

 To compare angled dynamic compression holes in a tibial plateau levelling osteotomy (TPLO) plate to a commercially available TPLO plate in an ovine cadaveric model.

STUDY DESIGN

 Ovine tibias (40 bones) were mounted on a custom-made securement device and radiopaque markers were placed to aid radiographic measurements. A standard TPLO procedure was performed on each tibia with either a custom-made six-hole 3.5 mm angled compression hole plate (APlate) or a six-hole 3.5 mm standard commercial plate (SPlate). Radiographs were obtained before and after tightening of the cortical screws and evaluated by an observer blinded to the plate. Measurements of cranio-caudal displacement (CDisplacement), proximo-distal displacement (PDisplacement) in relation to the long axis of the tibia, and change in tibial plateau angle (TPA) were determined.

RESULTS

 CDisplacement was significantly greater in APlate (median 0.85 mm, Q1-Q3: 0.575-1.325 mm) compared to SPlate (median 0.00 mm, Q1-Q3: -0.35-0.50 mm, p < 0.0001). There were no significant differences in the PDisplacement (median 0.55 mm, Q1-Q3: 0.075-1.00 mm, p = 0.5066) or TPA change (median -0.50°, Q1-Q3: -1.225-0.25°, p = 0.1846) between the two plate types.

CONCLUSION

 APlate increases cranially directed displacement of the osteotomy in a TPLO procedure without causing TPA change. The reduced interfragmentary distance across the whole osteotomy could improve osteotomy healing compared to standard commercial TPLO plates.

Tibial Plateau Leveling Osteotomy Plate Contouring and Proximal Load Screw Angulation Affect Osteotomy Compression

OBJECTIVE

To evaluate the effect of contouring a tibial plateau leveling osteotomy (TPLO) plate, the associated angulation of the dynamic compression plate (DCP) hole relative to the long axis of the tibia, and angulation of the screw relative to the DCP hole on the osteotomy compression generated by load screws in a TPLO model.

STUDY DESIGN

In vitro biomechanical study.

STUDY POPULATION

Polyoxymethylene (POM) rod and synthetic cortical bone substitute model (n = 9).

METHODS

The distal portion of a Slocum TPLO plate was attached to a horizontally positioned POM rod that was connected to a load cell. A segment of synthetic cortical bone substitute was attached to the end mount of the testing frame and adjusted to conform to the angle of the proximal portion of the TPLO plate. A 3.5 mm cortical bone screw was inserted in the proximal DCP hole and tightened to 1.5 Nm. The peak longitudinal load (N) was recorded. Screw insertion and data collection were repeated for proximal plate angles of 0-40° at 5° increments.

RESULTS

A significant increase in the compression generated was observed as the plate angle was increased from 0° to 10°. The compression ceased to significantly increase until the plate was bent more than 20°, after which a significant decrease in compression was noted. A marked reduction in the compression generated occurred at plate angles greater than 30°.

CONCLUSION

Angulation of the DCP hole and screw insertion angle can have deleterious effects on the magnitude of osteotomy compression.