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General Orthopaedics

Ground reaction force calcaneal offset: a new tool for measuring hindfoot alignment

British Orthopaedic Association/Irish Orthopaedic Association Annual Congress (BOA/IOA)



Abstract

Background

Traditional measurements of hindfoot alignment are based on the tibio-calcaneal angle and do not take the forefoot into account. We have developed an algorithm based on standard radiographs to calculate calcaneal offset using Ground Reaction Force (GRF).

Hypothesis

The GRF algorithm measures hindfoot alignment without using the tibial axis

Materials and Methods

Thirty six patients (40 feet) were included (21 female, 15 male). Mean age was 56 (SD:17). Weight bearing orthogonal radiographs were taken. Calcaneal offsets were measured using the tibio-calcaneal angles and the GRF algorithm. The two methods were compared using the Bland-Altman method.

Results

Ground Reaction Force Calcaneal Offset was in agreement with traditional measurement (p< 0.05) but individual discrepancies were found. Mean measured offsets were respectively −11.5 mm (SD:10.2) and −8 mm (SD:9.3) valgus. Mean bias between the two methods was −0.88 mm.

Discussion

The GRF algorithm successfully measured hindfoot alignment, and took into consideration the influence of forefoot position. The absence of a previous gold standard and variability related to radiographic protocols are a limit. Overall, angular measurements underestimated calcaneal offset. Individual discrepancies showed that including data related to forefoot position provided a more accurate assessment. This could be of particular clinical relevance for surgical planning. Unexplained total ankle replacement failures and diffuse arthritis after ankle fusion might be reduced by using this information preoperatively.

Conclusion

Ground Reaction Force could improve assessment of hindfoot alignment and provide useful information for surgical planning.