Introduction. Dual x-ray absorptiometry (DEXA) scan has been the gold standard for assessing bone mineral density prior to spinal instrumentation surgery. DEXA scans, on the other hand, can produce falsely elevated measurements in patients with severe degenerative changes, compression fractures, and aortic calcification, which can lead to incorrect patient selection and failed interbody fusion. Materials and methods. Detailed anamnesis of disease development, thorough clinical examination, patient-reported outcome measures (pain VAS, ODI, SF-12), preoperative and postoperative bone-window CT of the spine (interbody fusion status assessment), vertebral bone mineral density assessment by DEXA scan, vertebral bone density measurement in Hounsfield units by computer tomography, and the review of published literature were analysed. Results. A 67-year-old woman was diagnosed with L4-L5 degenerative spondylolisthesis. DEXA scan revealed normal bone mineral density in the lumbar vertebrae. The patient underwent midline lumbar interbody fusion (MIDLIF). The postoperative course was complicated by the occurrence of clinical and radiographic signs of pseudarthrosis. She refused revision surgery and was lost to follow-up. Three years postoperatively, she presented in good physical condition, with significant improvement in pain and functional disability. A CT scan showed delayed successful interbody fusion with complete resolution of radiolucency around implants. Conclusions. This case report summarizes some of the possible errors in diagnosis and surgical treatment in patients with degenerative pathology associated with severe vertebral osteoporosis.