Locked versus unlocked plating with respect to plate length in an ulna fracture model.

OBJECTIVE

Determine contributions of plate length and locked fixation in an ulna fracture.

METHODS

two groups of six pairs of ulnae were plated with a small-fragment LCP around a 1 cm ostectomy. Control specimens: eight-hole plate, three consecutive unlocked screws on each side. Experimental specimens: 10-hole plate, two screws (Group 1, Unlocked; Group 2, Locked) in near- far configuration on either side.

OUTCOMES

Stiffness in torsion and 4-point bending stiffness and load at yield.

RESULTS

Unlocked: mean torsional stiffness (Ncm/deg) for the experimental and control specimens, 7.57 and 7.73, respectively (p > 0.05); mean bending stiffness (kN/m), 88.50 and 90.76, respectively (p > 0.05); and mean yield strength (kN), 1.06 and 0.89, respectively (p < 0.05). Locked: mean torsional stiffness for the experimental and control specimens, 7.10 and 8.27, re- spectively (p > 0.05); mean bending stiffness, 72.96 and 79.20, respectively (p > 0.05); and mean yield strength, 1.23 and 1.03, respectively (p > 0.05). Mean differences between the experimental and control specimens in tor- sion: Unlocked, 0.17; Locked, 1.17 (p > 0.05). Mean differences in bending stiffness: Unlocked, 2.25; Locked, 6.24 (p > 0.05). Mean differences in yield strength: Unlocked, 0.17; Locked, 0.21 (p > 0.05).

CONCLUSIONS

Locked plating provided no mechanical advantage over unlocked plating. The use of a longer plate with unlocked screws increased yield strength.