Stability of unicortical locked fixation versus bicortical non-locked fixation for forearm fractures

Abstract

Locking plate fixation is being widely applied for fixation of forearm fractures and has many potential advantages, such as fixed angle fixation and improved construct stability, especially in osteoporotic bone. Biomechanical data comparing locking devices to commonly used Low Contact Dynamic Compression (LCDCP) plates for the fixation of forearm fractures has been lacking. The purpose of this study was to compare the fixation stability of a 3.5-mm unicortical locked plate with bicortical non-locked LCDCP plates. Six matched pairs of fresh frozen cadaveric forearms were randomly assigned to unicortical locked and bicortical unlocked groups. Non-destructive four-point bending and torsional test was performed on the ulna and radius separately, using a servohydraulic testing system to obtain construct stiffness of the intact specimens and specimens after osteotomy and plating. The specimens were then loaded to failure to test the fixation strength. The locked unicortical fixation showed significantly higher bending stiffness than the unlocked bicortical fixation, but with significantly lower stiffness and strength in torsion. Fixation strength was comparable between the two groups under bending, but significantly greater in the bicortical non-locked group under torsion. Findings from this study suggest that postoperative rehabilitation protocols may need modification to limit torsional loading in the early stage when using locked unicortical fixation. The study also points out the potential advantage of a hybrid fixation that combines locked unicortical and unlocked bicortical screws.

Fractures: Fixing forearm fractures

A new type of surgically implanted plate for fixation of broken bones is stronger and reduces bone damage from screws. The older screws pass straight through a bone, contacting the hard outer layer (cortex) on both sides (bicortical). Newer screws penetrate only one side of a bone (unicortical) and are held at the correct angle by their threaded heads. Unicortical screws are becoming more common but few data are available comparing the two types of screw. Steven Grindel from the Medical College of Wisconsin, USA and co-workers tested whether unicortical or bicortical screws provide better stability for fixation of broken forearms, using matched pairs of forearm bones from donated cadavers. The unicortical screws led to greater bone density following plate removal and were more resistant to bending but were weaker under twisting loads.

References

[1] Jain R, Podworny N, Hearn T et al Effect of stainless steel and titanium low-contact dynamic compression plate application on the vascularity and mechanical properties of cortical bone after fracture. J Orthop Trauma, 1997, 11: 490-495

[2] Jain R, Podworny N, Hupel TM et al Influence of plate design on cortical bone perfusion and fracture healing in canine segmental tibial fractures. J Orthop Trauma, 1999, 13: 178-186

[3] Perren SM, Cordey J, Rahn BA et al Early temporary porosis of bone induced by internal fixation implants. A reaction to necrosis, not to stress protection? Clin Orthop Relat Res, 1988, 232: 139-151

[4] Leung F, Chow SP. Locking compression plate in the treatment of forearm fractures: a prospective study. J Orthop Surg, 2006, 14: 291-294

[5] Sommer C, GautierE, Muller M, Helfet DL, Wagner M. First clinical results of the Locking Compression Plate (LCP). Injury, 2003, 34: B43-B54

[6] Miranda MA. Locking plate technology and its role in osteoporotic fractures. Injury, 2007, 38: S35-S39

[7] Lochmuller E, Lill CA, Kuhn V, Schneider E, Eckstein F. Radius bone strength in bending, compression, and falling and its correlation with clinical densitometry at multiple sites. J Bone Mineral Res, 2002, 17: 1629-1638

[8] Yamada H, Evans FG. Aging rate for the strength of human organs and tissues. Strength of biological materials, 1970 Baltimore Williams & Wilkins 272-280

[9] Kellam JF, Jupiter JB, Browner B. Diaphyseal fractures of the forearm. Skeletal Trauma, 1998 Philadelphia, PA WB Saunders 1421-1454

[10] Marti A, Fankhauser C, Frenk A et al Biomechanical evaluation of the less invasive stabilization system for the internal fixation of distal femur fractures. J Orthop Trauma, 2001, 15: 482-487

[11] ElMaraghy AW, ElMaraghy MW, Nousiainen M et al Influence of the number of cortices on the stiffness of plate fixation of diaphyseal fractures. J Orthop Trauma, 2001, 15: 186-191

[12] Jain R, Podworny N, Hearn T et al A biomechanical evaluation of different plates for fixation of canine radial osteotomies. J Trauma, 1998, 44: 193-197

[13] Jones DJ, Henley MB, Schemitsch EH et al A biomechanical comparison of two methods of fixation of fractures of the forearm. J Orthop Trauma, 1995, 9: 198-206

[14] Sanders R, Haidukewych GJ, Milne T et al Minimal versus maximal plate fixation techniques of the ulna: the biomechanical effect of number of screws and plate length. J Orthop Trauma, 2002, 16: 166-171

[15] Deluca PA, Lindsey RW, Ruwe PA. Refracture of bones of the forearm after the removal of compression plates. J Bone Joint Surg Am, 1988, 70: 1372-1376

[16] Langkamer VG, Ackroyd CE. Removal of forearm plates. A review of the complications. J Bone Joint Surg Am Br, 1990, 72: 601-604

[17] Perren SM. Minimally invasive internal fixation history, essence and potential of a new approach. Injury, 2001, 32: SA1-SA3

[18] Frigg R. Locking Compression Plate (LCP). An osteosynthesis plate based on the Dynamic Compression Plate and the Point Contact Fixator (PC-Fix). Injury, 2001, 32: 63-66

[19] Frigg R, Appenzeller A, Christensen R et al The development of the distal femur Less Invasive Stabilization System (LISS). Injury, 2001, 32: S24-S31

[20] Krettek C, Muller M, Miclau T. Evolution of minimally invasive plate osteosynthesis (MIPO) in the femur. Injury, 2001, 32: S14-S23