Mechanical effects of high density polyethylene Dynamic Compression Plate hole inserts on bone-plate constructs

Summary

This study was conducted in order to investigate the mechanical effects of high density polyethylene screw hole inserts in 4.5 mm Dynamic Compression Plate (DCP) – synthetic bone constructs. A mid-shaft ‘osteotomy’ was created in synthetic bone cylinders. The bisecting ‘osteotomy’ was reduced using six-hole broad DCPs and 4.5 mm cortical bone screws. The screws adjacent to the ‘osteotomy’ were placed using a loadguide. The remaining screws were placed in neutral position. High density polyethylene DCP screw hole inserts were incorporated with each screw in neutral position, in the experimental group. The bone plate constructs were tested in four point cyclical bending with the plates loaded at 2,000 Newtons, for a total of 6,000 cycles. Osteotomy gap was measured at 3,000 and 6,000 cycles. Screw head deflection adjacent to the osteotomy was measured. Kruskal-Wallis non-parametric testing was used for statistical comparisons. There was significantly less gapping at the osteotomy site in the treatment group after 3,000 cycles (0.49 +/- 0.18 mm [control] vs. 0.06 +/- 0.14 mm [treated], P=0.02) and 6,000 cycles (0.6 +/- 0.18 mm [control] vs. 0.1 +/- 0.22 mm [treated], P=0.02). The screws adjacent to the gap were significantly more deformed in the control group than those in the treated constructs (3.63 +/- 1.81 [control] vs. 1.06 +/- 1.55 [treated], P=0.0002). The polyethylene inserts improved the interface between bone plate and screw head, resulting in decreased relative movement of the implant and bone. The polyethylene inserts also resulted in less bending of the loaded screws.

Keywords

Hdpe inserts - bone construct - cyclical fatigue

• References

• 1 Cheal EJ, Hayes WC, White AA. et al. Three-dimensional finite element analysis of a simplified compression plate system. J Biomech Eng 1984; 106: 295-301.
• 2 Frigg R. Locking Compression Plate (LCP): An osteosythesis plate based on the Dynamic Compression Plate and the Point Contact Fixator (PC-Fix). Injury 2001; 32: 63-6.
• 3 Nunamaker DM. On bone and fracture treatment in the horse. Proceedings: 46th Annu Meet AAEP 2002; 90-101.
• 4 Nunamaker DM, Richardson DW, Butterweck DM. Mechanical and biological effects of plate luting. J OrthopTrauma 1991; 5: 138-45.
• 5 Nunamaker DM, Bowman KF, Richardson DW. et al. Plate luting A preliminary report. Vet Surg 1986; 15: 289-93.
• 6 Perren SM, Klaue K, Pohler O. et al. The limited contact dynamic compression plate (LC-DCPj. Arch Orthop Trauma Surg 1990; 109: 304-10.
• 7 Richardson DW, Nunamaker DM. Evaluation of plate luting, using an in vivo ovine osteotomy model. Am JVet Res 1991; 52: 1468-73.
• 8 Staller GS, Richardson DW, Nunamaker DM. et al. Contact area and static pressure profile at the plate-bone interface in the nonluted and luted bone plate. Vet Surg 1995; 24: 299-307.
• 9 Texhammar R, Colton C. (eds) AO/ASIF Instruments and Implants. Berlin: Springer-Verlag; 1994
• 10 Turner AS, Smith FW, Nunamaker DM. et al. Bone cement around the screw heads improves plate fixation with insufficient bony support. Proceedings: 37th Annu Meet Orth Res Soc. 1991: 449.
• 11 Wroblewski BM. Wear of high-density polyethylene on bone and cartilage. J Bone Joint Surg Br 1979; 61-B (4) 498-500.