The plantar gap: another prognostic factor for fifth metatarsal stress fracture

There have been diverse results, even in the same Torg type classification, in cases with fifth metatarsal stress fracture.

The "plantar gap" is correlated with the time for bone union and complications. It might be used for a prognostic factor.

Cohort study; Level of evidence, 3.

Seventy-five cases with a fifth metatarsal stress fracture treated with modified tension band wiring from January 2003 to December 2008 were evaluated retrospectively. This consecutive series of patients included 71 male and 2 female patients with a mean of 19.8 years of age at the time of surgery. All of the enrolled patients were elite-level athletes. Each case was classified according to Torg classification and the degree of plantar gap was also measured. After the surgery, bone union was determined by computed tomography findings. Statistical analysis of the Torg classification and time for bone union, as well as plantar gap and time for bone union, was performed.

The mean time for bone union for each Torg type was 71.05 ± 21.77 days for type I, 104.48 ± 54.62 days for type II, and 122.92 ± 51.75 days for type III. There was a significant difference in the time for bone union among the 3 Torg types (P = .008). The mean time for bone union in group A (plantar gap <1 mm) was 71.21 ± 29.95 days and it was 126.4 ± 51.99 days for group B (plantar gap ≥1 mm) (significantly different; P < .001). In addition, there was a positive correlation of the time for bone union with the degree of plantar gap (ρ = .661, P < .001). In cases with Torg type II classification, there was a significant difference in the time for bone union between groups A and B (P < .001) In addition, there was a strong correlation between the time for bone union and the degree of plantar gap (ρ = .657, P < .001). There were 8 cases of nonunion in Torg type II, and 1 case in Torg III. With regard to the plantar gap, there was 1 case of nonunion in group A, and 8 cases in group B.

The results of this study suggest that the plantar gap might be used for prognosis in cases with a fifth metatarsal stress fracture, even in patients with the same Torg classification.