COMPARISON OF A MEDIAL LOCKING PLATE AND COMPRESSION SCREW CONSTRUCT VERSUS A TWO CROSSED SCREW CONSTRUCT FOR LAPIDUS ARTHRODESIS IN HALLUX VALGUS SURGERY: A BIOMECHANICAL INVESTIGATION

Abstract

Background: Lapidus (first metatarsocuneiform joint) arthrodesis is an established procedure for the management of hallux valgus. This study investigated the utility of fixation with a medial locking plate with adjunct compression screw versus fixation with two crossed screws.

Methods: Eight pairs of fresh-frozen human specimens were used in a matched paired test. Bone mineral density (BMD) was measured with peripheral quantitative computed tomography (pQCT). Fixation with two 4-mm-diameter crossed screws was compared versus a medial locking plate (X-Locking Plate 2.4/2.7; Synthes, Solothurn, Switzerland) with adjunct 4-mm-diameter compression screw. The specimens tested in a four-point bending test. Parameters obtained were initial stiffness; plantar joint-line gapping after one cycle, 100 and 1000 cycles; and number of cycles to failure. Failure was defined as ≥ 3 mm plantar gapping displacement.

Results: The groups did not differ significantly with regard to BMD (p = 0.866) and initial stiffness (p = 0.889). The plate-and-screw construct showed significantly less movement during testing, and significantly (p = 0.001) more cycles to failure than did the crossed-screw construct. There was a significant correlation (crossed-screw construct: p = 0.014; plate-and-screw construct: p = 0.010) between BMD and the number of cycles to failure.

Conclusions: Under cyclic loading conditions, the construct using a medial locking plate with adjunct compression screw was superior to the construct using two crossed screws.

Clinical Relevance: The medial locking-plate technique described holds promise for shortening the time off weight-bearing and for reducing the risk of non-union.