# Postoperative X-ray and CT measurement of mounting parameter accuracy for hexapod external fixator in treating tibial fractures: a retrospective study

## TL;DR

This study compares X-ray and CT scans for measuring hexapod external fixator accuracy in tibial fracture treatment, finding CT more efficient but not better for final outcomes.

## Contribution

Demonstrates that CT improves early correction efficiency for hexapod fixators without affecting final outcomes, offering a practical clinical insight.

## Key findings

- CT measurements required fewer prescriptions and less time to achieve fracture reduction compared to X-ray.
- No significant differences were found in fracture union time, radiological outcomes, or functional scores between CT and X-ray groups.
- X-ray remains a robust standard for routine cases despite CT's efficiency in early correction.

## Abstract

The hexapod external fixator (HEF) allows for precise three-dimensional reduction of tibial fractures, but its therapeutic efficacy is highly dependent on the accuracy of postoperative mounting parameters. Currently, X-ray and computed tomography (CT) are the primary imaging modalities, each with distinct trade-offs between accuracy and efficiency in clinical use. This study compares the accuracy of postoperative X-ray and CT in measuring mounting parameters for HEF in tibial fracture treatment and assesses the associated clinical outcomes.

This single-center retrospective cohort study included 71 patients with tibial fractures treated with HEFs at our institution between June 2021 and June 2023. The cohort consisted of 40 males and 31 females, aged 30 to 60 years. Patients were divided into two groups based on the imaging method used for postoperative measurement of the hexapod fixator’s mounting parameters: the X-ray group (n = 34, using 2D measurements from standard anteroposterior (AP) and lateral radiographs) and the CT group (n = 37, using CT scans and 3D reconstruction). Baseline characteristics—including age, sex, mechanism of injury, AO/OTA fracture classification, and Gustilo-Anderson classification—were comparable between groups (all P > 0.05). Primary outcomes were the number of electronic prescriptions, time to fracture reduction (from the first postoperative electronic correction prescription to radiographic confirmation of satisfactory reduction), and measurement operation time. Secondary outcomes included final radiological outcome, time to fracture union, and Johner-Wruhs score at final follow-up.

All 71 patients were followed up for a mean of 24.5 months (range: 18–36 months). The number of electronic prescriptions was lower in the CT group (median [IQR]: 1 [1]-[1]) than in the X-ray group (2 [1-2]). Time to fracture reduction was shorter in the CT group (3.3 ± 0.6 days vs. 4.8 ± 0.8 days). Measurement operation time was shorter in the X-ray group (12.9 ± 2.1 min vs. 14.1 ± 1.5 min). All these between-group differences were statistically significant. In the CT group, 81.1% (30/37) achieved satisfactory reduction with a single prescription, significantly higher than the 55.9% (19/34) in the X-ray group (P < 0.05). No statistically significant group differences were seen in time to fracture union (X-ray: 26.1 ± 3.2 weeks, CT: 25.7 ± 2.3 weeks), final radiological outcomes (displacement and angulation on AP and lateral views), or Johner-Wruhs scores (excellent and good rate: 82.4% for X-ray, 89.2% for CT; P > 0.05). No severe vascular or nerve injuries occurred in either group.

Not applicable.

Both X-ray and CT can successfully guide hexapod fixator correction for tibial fractures. CT measurement was associated with greater efficiency in the correction process, requiring fewer adjustments and less time to achieve reduction. However, this did not lead to differences in final radiographic or functional outcomes. The decision to use CT should therefore balance its potential for streamlining the early correction phase against considerations of cost, radiation exposure, and local resources. For many routine cases, X-ray-based measurement remains a robust and effective standard approach.