Background <p><i>Capnocytophaga sputigena</i> (<i>C. sputigena</i>), a species of bacteria resident in the human oral cavity. Here, to the best of our knowledge, this is the first reported case of a post-arthroscopic knee infection caused by this organism in an anemic patient. We described the clinical characteristics, therapeutic intervention and outcome associated with knee joint infection induced by this bacterium. Furthermore, the treatment approaches and challenges in managing this particular pathogen were explored.</p> Case presentation <p>A 58-year-old female patient presented with a knee infection following arthroscopy, caused by <i>C. sputigena</i>. The species <i>C. sputigena</i> was confirmed on the basis of the results of the joint fluid culture and metagenomics next-generation sequencing (mNGS). The infection was treated with arthroscopic debridement, in addition to intravenous and intra-articular meropenem irrigation. The initial therapy with meropenem resulted in clinical improvement, and was subsequently de-escalated to amoxicillin-clavulanate potassium. Following a period of observation, the patient was discharged, as her condition was stable.</p> Conclusions <p>The case of a post-arthroscopic knee infection caused by <i>C. sputigena</i> in an anemic patient resulted in surgeons developing a more profound clinical understanding of infections induced by the bacterium. The combination of arthroscopic debridement with meropenem therapy (subsequently followed by de-escalation to amoxicillin-clavulanate potassium) yielded favourable clinical outcomes, thereby establishing a practical reference point for the management and prognosis of such infections.</p>