Objective The aim of this study was to describe a novel technique using a gentamicin-impregnated polymethylmethacrylate (PMMA) plug for the surgical treatment of lumbosacral discospondylitis with concomitant instability. Clinical Report A 7-year-old male German Shepherd dog with lumbosacral (LS) discospondylitis and previously diagnosed with degenerative lumbosacral disease underwent ventral slot and distraction of the L7 to S1 intervertebral space with a gentamicin-impregnated PMMA plug. The lumbosacral joint was accessed via the abdomen. Samples were collected for bacterial culture and sensitivity, fungal culture and histopathological examination. The surgical site was omentalized. Long-term oral antimicrobials were administered. Results Clinical improvement was seen immediately after surgery. Complete return to previous activity level was observed 12 months after surgery. Follow-up radiographs 18 months after the procedure revealed no implant migration. Clinical Significance The gentamicin-impregnated PMMA plug in addition to the surgical debridement seemed to be an effective way for short-term distraction, potentially contributing, along with the appropriate antimicrobial therapy and analgesia, to alleviation of pain immediately after surgery and providing for a good short-term outcome, in this clinical case. The use of cement plugs as sole devices in the LS joint warrants further study.