Evaluation of Union Rates Between Two Fixation Constructs with Use of an Allograft Bone Wedge in the Lapidus Procedure

CATEGORY: Bunion; Midfoot/Forefoot INTRODUCTION/PURPOSE: The Lapidus procedure is used to treat a painful bunion deformity by decreasing motion and aligning the first ray of the foot. Although structural allograft has been previously described as acceptable practice for reconstructive foot and ankle surgery, outcomes following the addition of an allograft bone wedge at the Lapidus arthrodesis site are unknown. The biomechanical properties of various internal fixation constructs for Lapidus have been evaluated in cadaveric models with no consensus on the superiority of a single fixation method. Our objective was to report union rates for the Lapidus procedure with and without the use of an allograft bone wedge and to determine if fixation construct influenced the rates of union. METHODS: Lapidus patients with fixation constructs of 2 crossed compression screws (CS) and a medial locking plate with single intra-articular screw (LPS), with and without use of an allograft bone wedge were retrospectively analyzed. Inclusion required a postoperative CT scan which evaluated union status, with greater than 50% bony bridging across the arthrodesis site used as determination of bony union. Exclusion criteria included age younger than 18 years, prior midfoot surgery, concomitant surgical procedures which may alter the normative healing process, neuropathy and inflammatory disease. Demographic and radiographic outcomes were analyzed between the wedge and no wedge groups. Pre and post operative radiographic measurements included intermetatarsal angle (IMA), first cuneiform-metatarsal length (CML) and relative length of the 1st metatarsal (RLM). Two sample t tests were used to evaluate the radiographic measurements and risk differences were calculated to evaluate rates of union. All analyses were executed using SAS Studio version 9.04. RESULTS: A total of 81 cases were included with 54 cases in the wedge group and 27 cases in the no wedge group. Preoperative IMA, CML and RLM measurements were not significantly different between the groups (p >0.05 for each). An overall union rate of 92% was found, with a significant difference (p=0.01) between the wedge group with 87.5% union and the no wedge group with 100% union (Table 1). With LPS fixation, there was no significance difference (p>0.05) in rates of union between the wedge (N=25) and no wedge (N=21) groups. With CS fixation, there was a significant difference (p=0.014) in rates of union between the wedge (N=29) and no wedge (N=6) groups. Postoperative radiographic comparisons between the wedge and no wedge groups were not significant for IMA (p=0.89), CML (p=0.16) and RLM (p=0.32) measurements. CONCLUSION: With LPS fixation, rates of union were not significantly different between the wedge (96% union) and no wedge groups (100% union). This finding highlights the importance of a robust fixation construct which is an important predictor of union in Lapidus procedures. Use of an allograft wedge can facilitate intraoperative decisions on the appropriate amount of bony resection and decrease the risk of metatarsalgia due to shortening. Lapidus arthrodesis with an allograft bone wedge fixated with a medial locking plate and intra-articular compression screw provides the ability to maintain first ray length and achieve greater corrections with satisfactory union rates.