L5S1

L5S1 refers to the lumbosacral junction between the fifth lumbar vertebra (L5) and the first sacral vertebra (S1). It is a transition zone between the mobile lumbar spine and the rigid sacrum and bears substantial loads during standing and locomotion. The intervertebral disc between L5 and S1, along with the facet joints at this level, helps absorb shock and guide motion, which commonly includes flexion, extension, and limited axial rotation.

Pathology at L5S1 is common, particularly disc herniation and degenerative disc disease. The most frequent clinical problem involves compression of the traversing S1 nerve root by a herniated disc or foraminal stenosis at L5-S1; patients often present with lower back pain radiating into the buttock and posterior leg, weakness on plantar flexion, and decreased ankle reflex. Because the exiting L5 nerve root travels at this level, radiculopathy can classically match the S1 distribution rather than L5.

Imaging usually begins with MRI to assess disc and neural structures; CT can help with bone detail. Plain radiographs evaluate alignment and degenerative changes. Treatment ranges from conservative measures (physical therapy, NSAIDs, activity modification) to injections like epidural steroids. Surgery may be considered for persistent, disabling radiculopathy or progressive neurological deficit and includes discectomy or, less commonly, fusion.

Prognosis varies by pathology and response to treatment but many L5S1 disc problems improve with nonoperative care. In persistent or severe cases, surgical outcomes are generally favorable when indicated.