Hallux valgus: the main risk factor for non union in first MTPJ fusion treated with a dorsal plate

G. Williams, C. Butcher, A. Molloy, L. Mason

Introduction: We aimed to retrospectively identify risk factors for delayed / non-union for first metatarsophalangeal joint fusion.

Methods: Case notes and radiograph analysis was performed for operations between April 2014 and April 2016 with at least 3 months post-operative follow up. Union was defined as bridging bone across the fusion site on AP and lateral radiographic views with no movement or pain at the MTPJ on examination. If union was not certain, CT scans were performed. All patients operations were performed/supervised by one of three consultant foot surgeons. Surgery was performed through a dorsal approach using the Anchorage compression plate. Blinded pre-operative AP radiographs were analysed for the presence of a severe hallux valgus angle equal or above 40 degrees. Measurement intra-observer reliability was acceptable (95% CI:1.6-2.3 degrees). Smoking and medical conditions associated with non-union underwent univariate analysis for significance.

Results: 73 patients, 9 male, 64 female with a mean age of 61 years (range, 29 to 81) comprised the patient group. Mean follow up time was 13 months for both union vs non-union groups (range 3 to 24 months). 7 patients were identified as non / delayed union (9.6%). All smokers healed (n = 17), age, diabetes, COPD and rheumatoid arthritis did not show significant associations with non-union. Pre-operative hypothyroidism (relative risk 6.9, p = 0.05) and severe hallux valgus (relative risk 9.9, p = 0.002) were significantly associated with non / delayed union.

Conclusion: Although overall bone mineral density is unaffected, studies have demonstrated abnormal bone remodelling in patients with hypothyroidism which may account for this unexpected finding. A dorsally placed locking plate with a dorsal to plantar placed compression screw is at a biomechanical disadvantage to resist lateral force when trying to hold a corrected severe hallux valgus. These patient groups may benefit from supplementary fixation techniques.