The spinal canal encloses the spinal cord and, in the lower back, the nerve fibres that run to the legs. Over the years, the intervertebral discs lose height, the ligaments between the vertebral arches thicken and bony outgrowths form on the small facet joints. Together, these changes can narrow the canal so much that the nerves and blood vessels have too little space. This usually affects the lumbar spine in later life.
The key symptom shows up when you are out and about: after a certain distance, the legs become heavy, ache, tingle or go numb, and you have to stop. Sitting down or bending forward brings relief because the canal widens slightly; walking downhill often makes the symptoms worse. Specialists call this neurogenic claudication. Most people affected also have low back pain.
The diagnosis is based on the description of the symptoms, the examination and an MRI scan. Similar symptoms can be caused by poor circulation in the legs, nerve disorders such as polyneuropathy, or hip osteoarthritis – these need to be ruled out. What matters is whether the narrowing seen on the scan matches the symptoms: a pronounced finding does not necessarily mean severe symptoms.
If there is no paralysis, treatment starts conservatively, with physiotherapy to relieve the strain, painkillers and injections if needed. If this is not enough for a satisfactory everyday life, decompression becomes an option. What it achieves compared with good conservative treatment varies from person to person – which is why the decision deserves a thorough discussion.