First Metatarsophalangeal Contact Properties are Similar Following Proximal Opening Wedge and Scarf Osteotomies

Abstract

Category: Bunion Introduction/Purpose: Proximal opening wedge osteotomy (POWO) is an established correctional procedure for moderate to severe hallux valgus. A common concern of this procedure is that it results in lengthening of the metatarsal which could cause increased intra-articular pressure of the first metatarsophalangeal joint (MTP), and may ultimately lead to arthritis due to these altered mechanics. The purpose of this study was to use cadaveric models to compare intra-articular pressures and articulating contact properties of the MTP joint following either scarf osteotomy or POWO. These were compared to normal cadaveric specimens. Our hypothesis was that the intra-articular pressure of the first MTP joint would be greater following the POWO compared to the scarf osteotomy. Methods: Fresh-frozen cadaveric below knee specimens with pre-existing hallux valgus (n=12) and specimens without arthritis or hallux valgus (n=6, control group) were used. The hallux valgus specimens were stratified into two groups (n=6 each): POWO or scarf osteotomy. The groups were matched based on the degree of deformity. Peak intra-articular pressure, force, and area were measured in all normal, preoperative and postoperative specimens. These measurements were made with a pressure transducer (Tekscan, Boston, Massachusetts) while a 50 N dorsiflexion load was applied via a wired loop on the first toe over 5 seconds and then released. Secondary outcomes included range of motion (ROM) and radiographic measurements. ROM was measured pre and postoperatively under fluoroscopy. 1-2 intermetatarsal angle (1-2 IMA), hallux valgus angle (HVA), and metatarsal length were measured on simulated weight-bearing radiographs. Statistical analyses were performed using unpaired Student’s t-test, paired Student’s t-test, and ANOVA with Bonferroni correction for post-hoc analysis. Results: Postoperatively, although POWO group had slightly higher contact forces and pressures compared to the scarf group, they were lower than those of the normal group. These comparisons had no statistically significant differences (P>0.05). Normal specimens had significantly higher force (P=0.012) and pressure (P=0.007) but similar contact area (P>0.05) compared to the preoperative hallux valgus specimens. Contact area were similar in normal, POWO, and scarf groups. There was no significant difference in ROM between all three groups. The first metatarsal was lengthened 1.36 mm +/- 1.39 mm in the POWO group and lengthened 1.54 mm +/- 2.27 mm in the scarf osteotomy group. Conclusion: The results from this study show that after surgical correction, contact properties of the fist MTP joint among normal, POWO, and scarf osteotomy groups revealed no significant differences. First MTP joints in those with hallux valgus have significantly lower contact force and pressure compared to those without hallux valgus. Our results provide biomechanical evidence that first MTP joint biomechanics are similar after POWO and scarf osteotomy.