Junctional kyphosis could be the resulting compensatory phenomenon of pathologic lumbar hyperlordosis and inadequate spinal curve harmony, as suggested in a recent study. We present the case of a patient who underwent initial lumbar decompression and thoraco-lumbar fusion, using posteriorly and laterally inserted cages. She developed proximal junctional failure, and despite several revision surgeries, she continued to suffer mechanical complications because of excessive lumbar lordosis. Eventually, we performed a posterior opening wedge osteotomy (POWO) of L3 to correct the hyperlordosis and there were no other mechanical complications. We expose the rationale for this treatment and the surgical procedure of the POWO. We also analyze and warn about the risk of overcorrecting lumbar lordosis and modifying the spinal curves’ harmony in surgery of adult degenerative spine.