Non-tuberculous mycobacteria (NTM) are an unusual cause of osteomyelitis. Mycobacterium farcinogenes is an uncommon cause of human disease. We describe here the first case of M. farcinogenes osteomyelitis in a 49-year-old man who underwent left knee anterior cruciate ligament and medial meniscal repair which was complicated by recurrent septic arthritis and surgical site infection. As a consequence, he underwent multiple surgical debridements. Ultimately, left proximal tibial osteomyelitis was diagnosed and M. farcinogenes was recovered from the tissue biopsy culture. Clinical improvement was achieved following surgical removal of the prosthesis along with prolonged combination antimicrobial therapy.

Case: A 20-year-old man carried a 33-cm diaphyseal femoral defect after childhood osteosarcoma and three failed reconstructions — distraction osteogenesis, autografting and the induced-membrane (Masquelet) technique. As a final limb-salvage attempt, a patient-specific 3D-printed polycaprolactone–tricalcium phosphate (PCL-TCP) scaffold was implanted over an intramedullary nail and bioactivated with iliac-crest bone marrow aspirate, followed at nine months by reamer-irrigator-aspirator autograft. Biopsy at that second procedure confirmed new osteoid and thick-walled vessels at the scaffold interface, yet radiographic consolidation never followed. Four weeks later Staphylococcus haemolyticus infection supervened, and after serial debridement the scaffold was explanted. At four years the limb is preserved and the patient walks independently with a mild limp and a radiographically fused knee. Conclusion: Histological osteogenesis without radiographic union indicates a construct that was biologically alive but biologically outpaced. Three determinants — a defect roughly twice the length at which scaffold-guided regeneration has succeeded, a scarred and hypovascular host bed, and a staged bioactivation protocol whose repeated open re-entries were themselves the infective exposure — argue that defect length, host vascularity and cumulative infection risk, rather than scaffold chemistry alone, should govern candidate selection for this technology.