The Effect of Rotational Guided Growth With Flexible Tethers on the Distal Femoral Bone: An Experimental Study in a Porcine Model

New and innovative surgical techniques, using a flexible tether to correct rotational deformities of the growing femur have recently emerged, but are lacking radiographic validation of desired rotation and adverse effects in the frontal and sagittal planes. We, therefore, investigated this new technique in an established large animal model. Eight skeletally immature pigs were included in the study in a paired (left vs. right leg) design. Mean (range) observation time was 83 days (77-90). CT-scans and X-rays were performed immediately after insertion of the tethers and again at euthanasia after 12 weeks. From the CT-scans, 3D-models of the left and right femora were generated and analyzed for intended external rotation and unintended effects in other planes and bone morphology. One pig was excluded due to surgical site infection. Average change in rotation between the operated and non-operated femora was 7.2° (CI: 5.9-8.6) external rotation. We also found unintended valgus deformity in the coronal plane (7.8° (CI: 3.9-12.0) and unintended extension in the sagittal plane (3.9° (CI: -1.8 to 8.7). Unintended changes to the joint morphology were also observed. Rotation by guided growth was achieved with this surgical technique, confirmed by radiological measurements. Clinical Significance. While this large animal study has shown that this new surgical technique reliably corrected rotational deformities by guided growth, it has also revealed adverse effects that need further investigation before clinical use.