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The effect of circular external fixation on limb alignment.
INTRODUCTION: A full-length standing radiograph of the entire lower extremity is the standard imaging modality for assessing lower limb alignment. However, the effect of an overlying circular external fixator on the radiographic alignment of the lower extremity is not well documented.
METHODS: After correction of angular deformity using a circular external fixator, 29 patients (31 limbs) underwent 2 sets of full-length standing radiographs, one done before, and the other, after removal of the fixator. The difference in the measurement of frontal plane alignment, limb lengths, and rotation between the 2 radiographs was analyzed.
RESULTS: The mean absolute difference in the measurement of mechanical axis deviation (MAD) between the 2 radiographs was 11.5 mm (P < 0.0001) for the ipsilateral limb (with the external fixator) and 8.9 mm (P < 0.0001) for the contralateral limb. The mean difference in the radiographic measurement of limb lengths was 20 mm (P < 0.0001) for the ipsilateral and 20.2 mm (P < 0.0001) for the contralateral limb. As the magnitude of MAD and external rotation of the ipsilateral limb increased, a progressive increase in the magnitude of discrepancy in the measurement of MAD between the 2 sets of radiographs was noted. There was no significant effect (P > 0.05) of the patient's age, sex, body mass index, primary diagnosis, duration between the 2 radiographs, and the direction of malalignment found on the discrepancy in the measurement of MAD for both limbs.
CONCLUSIONS: The standing full-length radiograph with an overlying circular external fixator may not be a reliable indicator of limb alignment and length of the operated extremity. Moreover, the presence of the circular external fixator on the lower extremity can affect the alignment and length of the opposite limb. Clinicians using circular external fixators for lower extremity trauma and reconstruction should be aware of the pitfalls of using a full-length standing radiograph for assessing limb alignment and length during osseous healing.
LEVEL OF EVIDENCE: Diagnostic level II.
METHODS: After correction of angular deformity using a circular external fixator, 29 patients (31 limbs) underwent 2 sets of full-length standing radiographs, one done before, and the other, after removal of the fixator. The difference in the measurement of frontal plane alignment, limb lengths, and rotation between the 2 radiographs was analyzed.
RESULTS: The mean absolute difference in the measurement of mechanical axis deviation (MAD) between the 2 radiographs was 11.5 mm (P < 0.0001) for the ipsilateral limb (with the external fixator) and 8.9 mm (P < 0.0001) for the contralateral limb. The mean difference in the radiographic measurement of limb lengths was 20 mm (P < 0.0001) for the ipsilateral and 20.2 mm (P < 0.0001) for the contralateral limb. As the magnitude of MAD and external rotation of the ipsilateral limb increased, a progressive increase in the magnitude of discrepancy in the measurement of MAD between the 2 sets of radiographs was noted. There was no significant effect (P > 0.05) of the patient's age, sex, body mass index, primary diagnosis, duration between the 2 radiographs, and the direction of malalignment found on the discrepancy in the measurement of MAD for both limbs.
CONCLUSIONS: The standing full-length radiograph with an overlying circular external fixator may not be a reliable indicator of limb alignment and length of the operated extremity. Moreover, the presence of the circular external fixator on the lower extremity can affect the alignment and length of the opposite limb. Clinicians using circular external fixators for lower extremity trauma and reconstruction should be aware of the pitfalls of using a full-length standing radiograph for assessing limb alignment and length during osseous healing.
LEVEL OF EVIDENCE: Diagnostic level II.
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