Lumbosacral Spine: Structure and Muscles

The lower back makes itself known first — when you lift a bag of groceries or sit for a long time at a laptop. Below is a breakdown of the anatomy: where the lumbar region is located, what the lumbar and sacral sections consist of, and which muscles support the lower back.

Where the lumbar region is located and what the lower back is

The lumbar region is the area of the back between the lower ribs and the pelvis. "Lower back" or "the lower part of the back" — is the same thing: the lumbar spine and the muscles surrounding it.

Back pain is one of the most common medical problems: 8 out of 10 people encounter it at least once in their life.

Lumbar section: how many vertebrae and how they are structured

There are five lumbar vertebrae — from the 20th to the 24th, counting from the top, L1–L5. At the top, L1 connects to the last thoracic vertebra (Th12); at the bottom, L5 connects to the first sacral vertebra (S1). The wording "6 lumbar vertebrae" does not exist in standard anatomy: the norm is five. These are the most massive vertebrae in the entire spine; their size increases from the first to the fifth. The fifth is wedge-shaped and tilted forward because the sacrum is directed backward. Together they form the lumbar lordosis — a curve that forms when a child begins to stand and walk.

Lumbosacral section: what it is and where the border is

The lumbosacral spine is the transition zone from the lumbar region to the sacrum, the L5–S1 level and the sacrum itself. The sacrum is a fused bone, not a set of movable vertebrae; together with the pelvis it supports the body's weight. The five lumbar vertebrae and the sacrum form five spinal motion segments: they make it possible to rotate the torso and bend. Intervertebral hernias are most often found precisely here — in 48% of cases at the L5–S1 level and in 46% at the L4–L5 level.

Muscles of the lumbar region and load

The lumbar region is surrounded by muscles involved in torso movements. Strong lumbar muscles help perform movements even with additional load.

Why the lower part of the back bears the greatest load

The lumbar section bears the most pronounced shock-absorbing function, and it weakens with age. Above is the relatively immobile thoracic section, below are the sacrum and pelvis, so the mobility of the torso falls on the five lumbar vertebrae. This also explains their size: the vertebrae increase from L1 to L5 along with the load. A common cause of problems is incorrect load distribution, when additional weight is lifted with a single lever in the lumbar region. Among the causes of pain are a disc hernia, sciatica, ankylosing spondylitis; rarely — a fracture, oncological disease, or infection.

Why lower back pain requires a doctor's consultation

Acute back pain usually lasts from several days to several weeks; it is called chronic when it lasts more than three months. You should see a doctor if the pain does not go away within several weeks, interferes with everyday activities, does not improve after rest or is worse at night, as well as with unexplained weight loss, swelling, or a change in the shape of the back.

The following should also be cause for concern:

• fever, chills, or general malaise;
• sharp pain that began suddenly or rapidly increases;
• numbness, weakness, or tingling in the legs;
• loss of sensation in the genital and anal area;
• problems with urination or defecation.

The lower back alone is not a reason to call an ambulance. Call 103 or 112 if, with back pain, weakness, tingling, or numbness appears in both legs; loss of sensation in the genital and anal area; problems with urination or defecation, including incontinence; changes in sensation during sex or problems with erection; chest pain; the pain began after a serious accident.

This material is for reference: it explains the structure but does not replace a doctor's consultation — it is better to deal with your back together with a doctor.

This content is for reference and does not replace a doctor's consultation. Medical disclaimer