Comparison of the screw fixation stability and examination of the surface contact area of first metatarsal shaft osteotomies and their newly defined modification(biomechanical study)

Hallux valgus is a disease defined as lateral deviation of first toe and medial deviation of first metatarsal. It is the most seen disease of foot. For surgical treatment, providing the soft tissue balance is not enough in every case, so metatarsal osteotomies needed.Metatarsal shaft osteotomies have known for long years but they become popularized nowadays. Some studies emphesizes that these osteotomies are superior for reduction and stability but they also have some weak points.To overcome some disadvantages of well-known shaft osteotomies, we define a new osteotomy that can provide high contact surface area, more correction and more stable fixation. When the current examined, the new osteotomy thought as a new modification of Mau osteotomy.In our study we use Sawbones metatarsal bone models and we compare relationship between the contact area, fixation technique obligation and the bending stabilities in four well-known metatarsal shaft osteotomy and the new modification. We perform Ludloff osteotomy for the first, Mau for the second, Scarf for the third, Ofset V for the fourth and the new Mau modification for the fifth group. The osteotomies preformed by the originally defined technique and the digital images obtained for the contact surface area. After that, 10° correction done and the osteotomies fixated by two interfragmanter acutrak headless compression screws. With a digital image analyzer software, the contact surface areas calculated before fixation. After fixation the three point bending test performed. The results are analysed by the Mann-Whitney U test.When we compared the results, Mau group was found the highest stiffness value, Ofset V and the new Mau modification groups were significantly stiffer than the Scarf group. Ludloff group was found significantly less stiff than all the other groups.When the examination of the contact areas, Scarf osteotomy had the highest contact area before fixation. New Mau osteotomy had higher contact area than Ludloff and Mau osteotomies before fixation. We could not calculate the contact areas after fixation.According to our experience, the linear osteotomies were easily performed but the notched osteotomies were more technical demanding. Mau osteotomy found more stable in bending test because of its distal intrinsic stability but its contact area was less as well.We know that healing of osteotyzed site be effected by many biological factors, so it is suitable that this study may be correlated with clinical studies.Key words: Hallux valgus, metatarsal shaft osteotomy, stiffness, biomechanics