IMPROVING THE SCARF OSTEOTOMY: KNOW YOUR LIMITS

Abstract

Introduction: The high prevalence and associated morbidity of the hallux valgus deformity has lead to a myriad treatment options being developed. These range from conservative to operative interventions, including many different forms of osteotomy. The various interventions have met with mixed success, with some operative options suffering a high level of recurrence or patient dissatisfaction. Both outcomes have been shown to correlate to inadequate correction of one or other component of the deformity. High recurrence rates result most frequently from the failure to correct for both the intermetatarsal (IMA) and the distal metatarsal-articular (DMAA) angles, instead focusing on the IMA alone. In most techniques, the use of a two-dimensional osteotomy with a concentric axis of rotation allows only for the correction of one of the involved angles, therefore is not appropriate for the correction of this geometrically complex condition. This most often results in failure to adequately correct the DMAA. The scarf osteotomy is a triplanar osteotomy with the potential to correct both the DMAA and IMA in the same procedure, thereby performing a more anatomical correction.

Hypothesis: Even in experienced hands the accuracy of the correction can be improved, and the limitations of attainable correction identified, with simple calculations based on pre-operative radiographs.

Methods: We generated a formula to calculate the appropriate proximal and distal translations required for a given length of osteotomy to accurately correct the deformities. Two groups, of 20 patients each, were included in the study. One group prior to introduction of the formula and a second group after the introduction of the formula. Pre and post-operative weight bearing radiographs were assessed by blinded observers pre and post-operatively to determine the accuracy of the formula. Groups were compared using the independent samples T-test.

Results: There were no differences between the pre-operative IM and DMA angles between the groups. Post operative DMAA was improved by 6.1 degrees when using the formula (p=0.02). The frequency of post-operative IMA correction to within normal limits improved from 75% to 100% and the average IMA correction was improved by 2.5 degrees (p=0.003). Post operative IM and DMA angles correlated well with the calculated results from the formula. This formula has altered procedure selection in our institution for certain patients with combined large DMA and IM angles due to the easy pre-operative identification of the limits of correction.

Discussion and Conclusion: The formula allows more precise, reproducible correction of both the IMA and DMAA. The formula also clarifies the limits of the scarf osteotomy and therefore improves appropriate patient selection.