INTERPRETATION OF THE SCARF OSTEOTOMY BY TEN SURGEONS.

Abstract

The study evaluated and compared the three-dimensional (3-D) changes in geometry of the first metatarsal following scarf osteotomy. All osteotomies were performed on standardised Sawbone® models by consultant orthopaedic surgeons with a sub-specialist interest in foot and ankle surgery. The study considered the inter-surgeon variances in interpretation and performance of the scarf osteotomy with respect to intra-surgeon variances. The analysis used an accurate digitising system to measure and record points on the Sawbone® models in 3-D space. Computer software performed vector analysis to calculate 3-D rotations and translations of the first metatarsal head as well as the inter-metatarsal angle. Bone cut lengths and displacements were measured using a digital Vernier caliper. One surgeon performed the osteotomy ten times to form an intra-surgeon control dataset, while ten different surgeons each did one scarf osteotomy to form an inter-surgeon test dataset. Both surgical groups produced reductions in the 3-D inter-metatarsal angle with non-significant differences between the groups (p> 0.05). In contrast, the test group demonstrated highly significant (p=0.000) greater variance compared with the control dataset for all of the variables (bone cut length, proximal and distal metatarsal displacements plus angulation of the distal fragment) associated with surgical technique. In addition, there were highly significant (p=0.02 and p=0.002) greater variances in the interpretation of the degree to which the metatarsal head should be translated medially (X) and inferiorly (Z). There was also a significant (p=0.001) increase in variances in the rotations about the dorsi/plantarflexion (X) axis. The only significant differences (all p=0.000) attributable solely to differences in mean values were in proximal-distal (Y) translation, pronation (Y) rotation and medial (Z) rotation. The test group applied greater medial and plantarflexion rotation of the metatarsal head than the control surgeon and significantly less (p=0.000) shortening of the first metatarsal than the control surgeon. The results of this geometric study demonstrate the versatility of the scarf osteotomy. In addition, it indicated notable out-of-plane metatarsal head rotations and translations effected by the scarf osteotomy. As a result of the multi-planar nature of the osteotomy, there is a potential risk of producing unintended rotational mal-unions in all three planes. These rotational mal-unions may account for some of the poorer outcomes documented within the literature.