Pathomechanics of hallux valgus: Biomechanical and immunohistochemical study

Background: One factor believed to contribute to the development of hallux vaigus is an abnormality in collagen structure and makeup of the medial collateral ligament (MCL) of the first metatarsophalangeal joint (MTPJ). We hypothesized that the mechanical properties of the MCL in feet with hallux valgus are significantly different from those in normal feet and that these differences may be related to alterations in the type or distribution of collagen fibers at the interface between the MCL and the bone. Materials and Methods: Seven normal fresh-frozen cadaver feet were compared to four cadaver feet that had hallux vaigus deformities. The MCL mechanical properties, structure of collagen fibers, and content proportion of type I and type III collagen were determined. Results: The load-deformation and stress-strain curves were curvilinear with three regions: laxity, toe, and linear regions. Laxity of the MCL in feet with hallux vaigus was significantly larger than that of normal feet (p = 0.022). Stiffness and tensile modulus in the toe region in feet with hallux vaigus were significantly smaller than those in normal feet (p = 0.004); however, stiffness and tensile modulus in the linear region were not significantly different. The MCL collagen fibrils in the feet with hallux vaigus had a more wavy distribution than the fibrils in the normal feet. Conclusions: In general, strong staining for collagen III and to a lesser extent, collagen I was observed at the interface between the MCL and bone in the feet with hallux valgus but not in the normal feet. These results indicate that the abnormal mechanical properties of the MCL in feet with hallux valgus may be related to differences in the organization of collagen I and collagen III fibrils.