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BACKGROUND Metallic implants, which are inserted into the patient's body during trauma interventions, are the main cause of heavy artifacts in 3D X-ray acquisitions. These artifacts then hinder the evaluation of the correct implant's positioning, thus leading to a disturbed patient's healing process and increased revision rates. PURPOSE This problem is tackled by so-called metal artifact reduction methods (MAR). This paper examines possible advances in the inpainting process of such MAR methods to decrease disruptive artifacts whilst simultaneously preserving important anatomical structures adjacent to the inserted implants. METHODS In this paper, a learning-based inpainting method for cone-beam computed tomography is proposed that couples a CNN with an estimated metal path length as prior knowledge. Further, the proposed method is solely trained and evaluated on real measured data. RESULTS The proposed inpainting approach shows advantages over the inpainting method used by the currently clinically approved frequency split metal artifact reduction method (fsMAR)as well as the learning-based SOTA method PConv-Net. The major improvement of the proposed inpainting method lies in the ability to correctly preserve important anatomical structures in those regions adjacent to the metal implants. Especially these regions are highly important for a correct implant's positioning in an intraoperative setup. Using the proposed inpainting, the corresponding MAR volumes reach a mean SSIM score of 0.9974 and outperform the other methods by up to 6 dB on single slices regarding the PSNR score. Furthermore, it can be shown that the proposed method can generalize to clinical cases at hand. CONCLUSIONS In this paper, a learning-based inpainting network is proposed that leverages prior knowledge about the metal path length of the inserted implant. Evaluations on real measured data reveal an increased overall MAR performance, especially regarding the preservation of anatomical structures adjacent to the inserted implants. Further evaluations suggest the ability of the proposed approach to generalize to clinical cases. This article is protected by copyright. All rights reserved.