Hip dysplasia, a prevalent skeletal anomaly, necessitates accurate and early diagnosis to ensure effective treatment. This study presents a novel phantomfree autocalibration technique for 3D reconstruction of 2D ultrasound sweeps, evaluated for infant hip anatomy. By refining the probe-to-image transformation directly on anatomical structures, our approach eliminates the reliance on calibration phantoms, enhancing accessibility and accuracy in clinical settings. We demonstrate that our method improves alignment accuracy compared to traditional calibration methods as well as an existing autocalibration approach. By optimising the alignment of extracted surface keypoints from automatic segmentations, our results demonstrate superior performance, as evidenced by reduced Hausdorff (1.76 mm) and average surface distances (0.38 mm) between sweep reconstructions.