Abstract
Introduction: Complex foot and ankle surgery requires accurate preoperative planning. In the foot corrective osteotomies and lengthening procedures are challenging and can be associated with a range of complications. The aim of planning is to correct only the deformity and prevent extensive surgery on adjacent rays while maintaining biomechanical integrity. Knowledge of foot and ankle morphometry is vital to preoperative planning model. A 3D coordinate system is required for accurate morphological analysis. To conduct meaningful comparison between different subjects the coordinate system between subjects must be constant. Coordinate systems have been defined for other joints, however, there has been no previous description of a coordinate system for 3D analysis in the foot and ankle. We present a coordinate system for 3D data analysis in the foot and ankle and apply this to morphological analysis in the forefoot for preoperative planning.
Methods: CT images of ten anatomically normal feet were segmented in Materialise’s Interactive Medical Image Control System 10.1 (MIMICS) a general purpose segmentation program for grey value images. These files were then imported to a shape analysis program for biomechanics, Arthron. A coordinate frame was defined in a 3 × 3 identity matrix using the inter-malleolar axis and a fibular diaphyseal centroidal axis in the construction. Centroidal vectors were defined in the metatarsals enabling 3D analysis of the forefoot. Correlation of metatarsal length, inter-metatarsal angles, inter-malleolar distance and stature was carried out using Pearson product moment correlation coefficient, r.
Results: The morphology of the forefoot was examined in relation to the medial and lateral columns. The length of the metatarsals had a strong mathematical correlation within each column and between the two columns (0.525 – 0.965). There was also a strong correlation in the length between the lesser metatarsals (0.76 – 0.97) The 3rd metatarsal at the column junction correlated well (−0.583) with the inter-metatarsal angles. There was also a strong correlation between the individual’s stature and the metatarsal length and the inter-malleolar distance (0.60 – 0.89). Specifically in relation to the first metatarsal length there was a good correlation with inter-malleolar (0.75) and suture (0.65).
Discussion: We applied our analysis of the forefoot to the well recognised complication of Hallux Valgus surgery, first metatarsal shortening. This may lead to or exacerbate transfer metatarsalgia due to redistribution of force in the forefoot. Osteotomies of the lesser rays aim to relieve symptoms and re-establish the relationship between metatarsal lengths. However, this does not restore the relationship between metatarsal length, stature and inter-malleolar distance which we have shown to be important. Hurst et al proposed distraction osteogenesis of the first metatarsal to re-establishing length. This would return the normal mathematical relationship, which we have described and seems the most probable way to restore normal foot biomechanics and therefore relieve pain.
Conclusion: We have presented a means defining a coordinate system for 3D data analyses in the foot and ankle. We have shown this coordinate system to be effective in the morphometrical analysis of the forefoot. This analysis shows the importance of a proportional metatarsal length within the forefoot but also in relation to stature and the inter-malleolar distance in preservation of a normal biomechanical environment. This coordinate system can now be used for meaningful comparison of anthropological and morphological data between multiple subjects.
Correspondence should be addressed to Mr Richard Wallace at Musgrave Park Hospital, 20 Stockman’s Lane, Belfast BT9 7JB, Northern Ireland.
