In the context of urinary infections, tenderness in the lower back is most indicative of:

Tenderness in the lower back, particularly in the area where the kidneys are located, is most indicative of an upper urinary tract infection, often described as pyelonephritis. This condition involves the kidneys and is typically characterized by inflammation and infection that can result in pain radiating to the lower back or flank area. The presence of tenderness signifies possible involvement of the renal parenchyma, which is more common in infections affecting the upper urinary tract rather than the lower.

In contrast, conditions like kidney trauma may cause back pain but are usually associated with additional symptoms related to injury or trauma. Lower urinary tract infections primarily affect the bladder and urethra, leading to symptoms such as painful urination and urgency, but not typically back tenderness. Bladder prolapse is a structural issue that may lead to urinary symptoms, but it does not commonly present with back tenderness as a symptom. Thus, tenderness in the lower back points more specifically to an upper urinary tract infection rather than these other conditions.