Comparison of screw-fixation stabilities of first metatarsal shaft osteotomies: a biomechanical study.
OBJECTIVE
Although metatarsal shaft osteotomies have become popular in the surgical treatment of moderate or advanced hallux valgus owing to better reduction and stability, they present fixation problems as the angular correction increases. The purpose of this biomechanical study was to evaluate the effects of widely used metatarsal shaft osteotomies and a newly defined osteotomy modification on the stability of screw fixation at greater angular corrections.


METHODS
Upon evaluation of known problems of shaft osteotomies, a new osteotomy type was designed that might provide an adequate contact area while allowing a greater angular correction, increased stability, and safer osteosynthesis. In our new modification of the Mau osteotomy, the proximal plantar notch that was defined for the Sammarco's modification to increase the contact area was created more proximally making an angle of about 50 degrees with the osteotomy, and the osteotomy was extended until 5 mm to the distal joint surface, aiming to increase the contact area and intrinsic stability. For biomechanical analysis, 30 standard metatarsal bone models (Sawbones) were divided into five groups equal in number for the following osteotomy methods: Myerson's modification of the Ludloff osteotomy, Mau osteotomy, scarf osteotomy, offset V osteotomy, and the new modification of the Mau osteotomy. Osteotomies were performed with a standard correction of 10 degrees in the intermetatarsal angle, followed by appropriate osteosynthesis with fixation by two Acutrak compression screws. The relationship between osteotomies and osteosynthesis in terms of stability was assessed by the three-point bending test.


RESULTS
The mean stiffness of the Ludloff osteotomy was significantly lower than all the other osteotomy groups (p<0.05). Stiffness of the Mau group was significantly greater than three groups (p<0.05), but the difference from the offset V group did not reach significance. Stiffness of the new Mau modification was significantly greater than the scarf group (p=0.016), but did not differ significantly from the offset V group. Osteotomy groups with and without notching had similar stiffness values (p=0.582), whereas single notching was associated with a significantly greater stiffness compared to double notching (p=0.031).


CONCLUSIONS
Our findings suggest that the new modification to the proximal shaft osteotomies moves the center of rotation of angulation more proximally and provides sufficient stability of screw fixation.
Department of Orthopedics, Dokuz Eylül University, Izmir, Turkey. abdmunal@yahoo.com
A Meriç
AM
Unal
Onder
O
Baran
Bora
B
Uzun
Ahmet C
AC
Turan
D001696:Biomechanical Phenomena / Q000502:physiology; D001863:Bone Screws; D004867:Equipment Design; D005593:Fracture Fixation, Internal / Q000379:methods; D006801:Humans; D008682:Metatarsal Bones / Q000033:anatomy & histology / Q000601:surgery*; D010027:Osteotomy / Q000379:methods; D019651:Plastic Surgery Procedures