Prediction of angular correction following first metatarsal-phalangeal joint arthrodesis.

The literature has established that the first metatarsal-phalangeal joint arthrodesis procedure will provide some correction of the first intermetatarsal and hallux valgus angles. But while this has previously primarily been investigated as a simple association (i.e. comparison of pre-operative to post-operative values), the objective of this investigation was to consider angular change as a continuous variable and to specifically correlate it with pre-operative values. Radiographs from 100 consecutive first metatarsal-phalangeal joint arthrodeses meeting selection criteria were evaluated. A negative Pearson correlation coefficient was observed between the pre-operative first intermetatarsal angle and intraoperative change in the first intermetatarsal angle (Pearson -0.547; p<0.001). In other words, with progressively increased levels of pre-operative intermetatarsal angle deformity, one should expect greater intermetatarsal angle correction. The relationship is described by the equation Y = 2.82 - 0.38X indicating that for every one degree of pre-operative intermetatarsal deformity over approximately 7 degrees, 0.38 degrees of post-operative correction might be expected. A negative Pearson correlation was observed between the pre-operative hallux valgus angle and the intraoperative change in the first hallux valgus angle (Pearson -0.806; p<0.001). In other words, with progressively increased levels of pre-operative hallux valgus angle deformity, one should expect greater hallux valgus correction. The relationship is described by the equation Y = 5.5 - 0.63X indicating that for every one degree of pre-operative hallux valgus angle deformity over approximately 9 degrees, 0.63 degrees of hallux valgus angle post-operative correction might be expected. Results of this investigation demonstrate a statistical correlation between pre-operative radiographic deformity and intermetatarsal angle and hallux valgus angle post-operative correction, and might provide foot and ankle surgeons with a degree pre-operative prediction of expected angular correction following the procedure. LEVEL OF EVIDENCE: 3.