Background: Bone conduction devices (BCD) are indicated for rehabilitation in conductive or mixed hearing loss or single-sided deafness when conventional hearing aids are unsuitable. This systematic review evaluated BCD efficacy, specifically assessing the correlation between bone conduction overclosure and word recognition outcomes. Methods: Following PRISMA guidelines, a systematic search of PubMed, Embase, and Cochrane databases was conducted for English articles published until 2009. Included studies featured patients with conductive, mixed, or single-sided hearing loss using BCDs, with pre- and post-operative audiological assessments and patient-reported outcomes. A narrative synthesis focused on bone conduction (BC) overclosure, pure tone thresholds, sound field threshold (SFT), and word recognition score (WRS). Risk of bias was assessed using ROBINS-I. Results: Eighteen studies (459 patients) met the selection criteria. Audiological outcomes revealed significant SFT improvements, with average functional gains ranging from 23.4 to 42 dB. Mean BC overclosure (0.5 to 4 kHz) was 14.5 dB for Bonebridge and 10.4 dB for Osia. Although a positive trend was observed, the correlation between bone overclosure and WRS improvement was not statistically significant due to data variability. Patient-reported outcomes indicated high satisfaction, despite heterogeneity in reporting. Conclusions: BCDs demonstrate significant improvements in audiological outcomes and high patient satisfaction. However, no statistically significant correlation was found between bone overclosure and speech recognition. The review emphasises the need for standardised reporting and larger, high-quality studies to better guide clinical decision-making.