Fifth Metatarsal Stress Fractures: Unlocking the Clues

Stress fractures of the 5th metatarsal (M5) can be frustrating. Unlike other traumatic fractures, stress fractures often lead to complications such as delayed healing, nonunions, or recurrence. The key question is whether we can identify the anatomic factors that increase the risk of these poor outcomes. 

Study design

A retrospective case-control analysis approved by the Institutional Review Board (IRB), was conducted to analyze 15 feet with M5 stress fractures and 15 matched controls based on age and sex. The study evaluated weightbearing CT scans taken between February 2022 and May 2024.

The methods of the study involved these steps:

• A total of 74 M5 fracture patients were initially reviewed, but only 15 were included in the final analysis after exclusions for metal artifact.

• The control group consisted of individuals with no foot disorders or prior interventions.

• The analysis focused on foot alignment, the orientation of the M5, bone density measured in Hounsfield Units (HU), and the HU ratios between M5 and the talus.

• Receiver Operating Characteristic (ROC) analysis was performed using the Youden index to identify predictive thresholds.

Results

Following is a summary of the key findings:

• The M5 base height was lower at 9 ± 3 mm compared to 12 ± 3 mm (p = 0.045).

• Ground contact increased notably, observed in all 11 of 15 cases versus none in controls (p < 0.001).

• The MS was longer, with an M5/M4 ratio of 1.06 compared to 1.01 (p = 0.04).

• Fractures were linked to alignment factors like hindfoot varus and forefoot adductus.

• Bone density showed a 50% higher HU M5/HU talus ratio (1.52 vs 1.02, p < 0.001).

• An HU ratio of 1.2 or more predicted fractures with 80% sensitivity ad 94% specificity.

M5 stress fractures correlate with hindfoot varus, forefoot adductus, reduced base height, increased plantarflexion, a longer M5, and higher bone density. An HU ratio of 1.2 or greater could be useful in identifying high-risk patients for early preventative measures.