Why Is Lumbar Fusion at L4-L5 So Common?

Lumbar fusion at L4-L5 is a fairly common procedure. It involves the permanent fusion of the fourth and fifth lumbar vertebrae, and in most cases, the surgery is performed in an attempt to relieve chronic lower back pain caused by degenerative spine conditions that many people experience due to age and/or overexertion. Traditional open spine fusion is irreversible, highly invasive and usually involves a fairly lengthy and arduous rehabilitation. Needless to say, it is not something to be taken lightly.

However, some patients with conditions of the lower back like sciatica or spinal stenosis are so plagued by painful symptoms that open spine lumbar fusion may seem like their best option. That brings us to the question of why the lower back, and particularly the last two vertebrae of the lower spine – L4 and L5 – are so susceptible to injury and degeneration.

The anatomy of the lumbar spine

The spine is a complex structure comprised of vertebrae, intervertebral discs, ligaments, facet joints, muscles, and of course, the spinal cord. Many of these components play vital roles within the spine:

  • Vertebrae – These small bones make up the structure of the spinal column and help to protect the delicate spinal cord. There are 33 vertebrae, five of which are in the lumbar spine.
  • Intervertebral discs – These spongy pads of cartilage separate adjacent vertebrae, absorb shock and help facilitate flexibility in the spine.
  • Ligaments – Ligaments connect bone to bone. Several ligaments in the spine hold vertebrae together and help with spinal stability.

The degenerative process

Like any other part of the body, the components of the spine begin to degenerate over time due to age, repetitive stress and a variety of other factors. Intervertebral discs can bulge or herniate; ligaments can calcify and buckle; vertebrae can develop fractures or bone spurs; and joints can become arthritic. The lumbar spine is especially susceptible to degeneration because it supports more than half of the body’s weight and undergoes such a large amount of stress in our day-to-day movements. For this reason, lumbar fusion at L4-L5 is one of the most common surgeries performed on the spine.