Lapidus arthrodesis in combination with arthrodesis of the first metatarsophalangeal joint-biomechanical cadaver study comparing two methods of fixation

Aims: To assess the results of a biomechanical test of cadaveric specimens, comparing 2 methods of fixation of modified Lapidus arthrodesis in combination with arthrodesis of the first metatarsophalangeal joint.

Methods: A total of 12 cadaveric specimens were used in the test. Arthrodesis of the first MTP joint was in all patients fixed with a Variable Angle LCP 1st MTP Fusion Plate 2.4/2.7. Two methods of fixation of the Lapidus arthrodesis were compared, i.e. fixation with two screws in the PS (plate-screw) version versus fixation with X-Locking Plate 2.4/2.7 in the PP (plate-plate) version. Measurements were obtained with the use of a testing machine ZWICK Z 020-TND with an optical device Mercury RT for measuring deformities. Each specimen was subjected to 3 loading options, a. displacement 5 mm, the support is placed under the proximal phalanx, b. displacement 5 mm, the support is placed under the first metatarsal head and c. load to failure, the support is placed under the first metatarsal head.

Results: In all specimens the PS construct showed a statistically considerably higher stiffness than the PP construct. In all specimens treated with the PP construct the load to failure was lower than in the PS construct. For loading mode a., at a significance level of 0.05 (P<0.05), the P-value was 0.036, for mode b. the P-value was 0.007 and for loading mode c. the P-value was 0.006. In addition, age-related decrease in stiffness of the specimen was proved at a significance level of 5% (P=0.004).

Conclusion: In all the three loading modes, the PS (plate-screw) construct showed a statistically higher stiffness than the PP (plate-plate) construct.