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Lumbar Spine (Lower Back) Anatomy and Function

The anatomy of the lumbar spine is quite complex. Here we will attempt to provide a brief overview of lumbar spinal anatomy. The lumbar spine makes up the the lower end of the spinal column. It consists of 5 lumbar vertebra that are numbered 1 through 5 from top to bottom i.e. L1, L2, L3, L4, and L5.  The L5 vertebra is connected to the top of the sacrum (named the S1 segment) through an intervertebral disc.  

To review, the purpose of the spine, as a whole, is to support the body so that we can stand upright. Secondarily, it protects the spinal cord (which is the extension of the brain), and all of the nerves that branch from the spinal cord.  At the level of the lumbar spine, the spinal cord has ended (typically at the L1-2 level in an adult), and at this level exists what is called the cauda equina (latin for horse’s tail), which is a fluid filled sack which houses the nerves that allow you to control your bowel and bladder as well as to move and feel your legs.

For more detailed descriptions of anatomical terminology and spinal cord anatomy, please reference:

Lumbar Spine Anatomy

Bones and disks of lumbar spine

Bones, disks and facet joints of lumbar spine

When looking from behind, in most individuals, the spine looks straight. However, when viewing the spine from the side, there are distinct curves to each part of the spine. The purpose of these curves is to grant some additional flexibility and shock absorbing abilities to the spine. 

In the lumbar region, the spine normally curves backwards.  This curvature is known as a lordosis.  The amount of lordosis an individual has varies, but typically is somewhere in the range of 40-60 degrees. There are many conditions of the spine that may affect the normal curvature of the lumbar spine, resulting in pain and disability. Some of these conditions are listed at the end of this article. 

Similar to the rest of the spine (thoracic and cervical), each of the vertebra of the lumbar spine consists of a body, two pedicles, lamina, and multiple bony projections (called processes). The vertebrae of the lumbar spine are the largest of the spine as they must support the most weight. The vertebral bodies are the major weight bearing portion of the vertebra. The processes serve as attachment points for various ligaments and muscles that are important to the stability of the spine.

The posterior (or back) aspect of the body, and medial (or inside) aspects of the pedicle, and the anterior (or front) lamina form a protective bony ring, called the spinal canal, around the very important dural sac. The dural sac contains all of the important nerves that allow you to control your bowel and bladder as well as to move and feel your legs. Each of these paired spinal nerves exits on both sides of the spine at each level of the lumbar spine.  They exit between the pedicles (in an area called the intervertebral foramen). i.e. there are left and right L1, L2, etc. nerves that exit through intervertebral foramen at each respective level. 

Between each vertebral body is a shock absorbing structure called an intervertebral disc. The intervertebral disc has two distinct components to it. The tough outer ring of the disc is called the annulus fibrosis. The soft, compressible inner portion of the disc is called the nucleus pulposus. The intervertebral disc is, in large part, is made up of water. This trait gives the disc much of its shock absorbing abilities. Unfortunately, as we age, the water content decreases, leading to degenerative disc disease, or more simply put, arthritis of the back. This is also a major reason why we become shorter as we age. 

Spinal Segment

Segment is made of two vertebrae, the intervertebral disk, and two spinal nerves

 

L-5, the 5th lumbar vertebra.

L-5, the 5th lumbar vertebra.

Labeled lumbar vertebra

Labeled lumbar vertebra

Behind the vertebral body are the various processes of the vertebra. These include the spinous process, the two transverse processes, and the paired superior and inferior articulating processes.  As mentioned prior, each of these processes serve as attachment points for various muscles and ligaments which enhance the stability of the spine.  Furthermore, the articulating processes of adjacent vertebra join to form facet joints, which, in the lumbar spine, allow for mainly bending and straightening of the spine. 

Ligaments of the Back

As mentioned previously, the anatomy of the spine is quite complex. There are hundreds of individual ligaments in the spine. Ligaments are strong, tough bands that are typically not very flexible. Ligaments typically joint bones to other bones to stabilize them to one another.  Some of these named ligaments in the spine include: the anterior and posterior longitudinal ligaments (ALL and PLL), interspinous ligaments, supraspinous ligaments, intertransverse ligaments, and ligamentum flavum. 

Muscles of the Back

There are many muscles that help to both move and stabilize the spine. The major muscle group that allows us to stand upright is the erector spinae.  This muscle group includes the iliocostalis, longissimus, and spinalis. Another important stabilizing muscle of the spine is the multifidus. There are many other smaller muscles of the spine and characterizing each one would be tedious and is beyond the scope of this article. 

Lumbar segment, spine, nerves

Lumbar segment, spine, nerves

Vascular structures of the Back

The most important vessels of the spine include the anterior spinal and posterior spinal arteries. These vessels give blood supply to the nervous system within the spine.  Additionally, each spinal unit has segmental vessels that come from the aorta that help to nourish the bony and soft tissue structures as well. 

The Sacrum

Side view of the sacrum and tailbone

Side view of the sacrum and tailbone, the body of the sacrum forms a joint with the 5th lumbar vertebra.

A discussion of the lower back wouldn’t be complete without an overview of the sacrum. At birth, the sacrum is actually made up of several vertebrae. By the time you’re an adult, these individual vertebrae have fused together to form the sacrum. By adulthood, it is a large, triangular bone, that forms the base of the spinal column where it connects to the pelvic bones. The top segment of the sacrum, labeled the S1 segment, connects to the L5 vertebra of the lumbar spine via the L5-S1 intervertebral disc. 

Conditions of the Lumbar Spine

• Osteoporosis
• Osteomalacia
• Arthritis
• Ankylosing Spondylitis
• Sacroiliitis
• Lumbosacral sprain and strain
• Acute Cauda Equina Syndrome
• Intervertebral Disk Disease
• Scoliosis
• Spinal Instability
Herniated Disk
Spondylolysis
Spondylolisthesis
Spinal Stenosis

More About the Back

Back Injury
Lumbar Spinal Fusion Surgery

Comments

  1. i have severe spondylosis to L1 L2and L3 and mild spondylolisthesis to L4and L5 what can i do to improve this i have severe back pain in back on the right and this travels to my bottom and thighs find it very difficult to walk is there any excersises or help please thank you

  2. Mohd ekhlaque says

    I am looking degenerative changes in lumbar spine. Reduced L5-S1 intervertebral disc space. Remaining intervertebral disc spaces appear unremarkable. Plz suggest me. What can

  3. SUNIL UPADHAYA says

    What happens if L1 L2 and L3 are broken or damage is lower part of body work or not

  4. Md.Shakawt hossain says

    I have got osteiphyte lumber L-4,L-5 vertebra. How can I get good treatment and recover from this.

  5. Faiz Alam says

    I am getting leg pain due to L3 and L4 nurves has pressd also loses of fiber protection of nerves pls advise.

  6. What are the reason L1_S1 vertebra disconnected

  7. sheri Clayborne says

    I had an exray and it showed mainley arthritis and mild scholis. The pain starts at the lower spine and lower back. Could a orthopedic help me?

  8. Hennie van Eden says

    If you want problems with your back go to a Doctor. Chiropractors, Physiotherapists and the more of a specialist the Doctor is are all part of a racket. I speak of 40 years of back problems from time to time. Basically every person I met who had an operation done to their back had to stop working or ended up with permanent pain. All my back problems came from wrong postures, lifting heavy items and pushing a lawnmower with my back bend in case of with a straight back and using the legs to do the pushing. After going through all the motions i.e Voltaren which is the biggest racket of all, x-rays, Chiropractors, Physiotherapists and specialists I was being lined up for back surgery. From what I was told by all these experts is that the cause of the pain was the disc pushing against the nerves due to the narrowing of the gap between the two vertebrae over a period of time, in my case as a result of the wrong position when sitting (poor ergonomic work conditions), taking an incorrect position lifting heavy equipment and most probably the main contributor pushing a heavy lawnmower incorrectly, Being of an Engineering background I came to the conclusion to fix it up should be simple, all you have to do is to stretch the gap open again so that the disc can move back in position away from the nerves. I got hold of a tennis ball and started lying on it with my back starting from as low as possible and slowly working my way up. In this specific case the pain was down my left leg and I could hardly walk. This is apparently caused by the 3rd vertebrae from the bottom, The guilty vertebrae becomes sore after a day or so and once this happens the pain start to go away in the leg. I ly on the tennis ball for about 15 minutes a day for 3 days and within a week all pain is gone. Apparently the pain is reflected in the leg and there is no pain at the vertebrae and the pain must come back to the vertebrae. I had the same experience with extensive pain in the left arm, neck etc. After going through all the motions and just short of being cut up, I thought if it works at the bottom it should also work at the top. A week later all the pain was gone. I have given this advice to a number op people and all that could handle the pain of lying on the tennis ball ended up without pain.
    Goodluck

  9. I would like to apologise for all the typos but I suffer fron muscular atrophy,radiculopathy and severe pain and shaking. It often makes typing on a small touch screen near impossible and extremely time consuming so I use word prediction to help speed,avoid mistrikes but instead a often get mis spelling due to my improper use of word prediction or rather in actuality I move way to fast mentally and did not notice the improper prediction. Sorry,I’ll try to slow down. Try to cope? I have too?

  10. Tim Marks says

    “Speak your mind?” I have multiple sever spine injuries almost exclusively from blunt force traumas from accidents through my entire life from age 5 – through the current age of 53. These injuries involve and include broken vertebrae, sacrum,13 herniated discs in all,7 severe and some even grossly and unbelievably so. Broken and distroyed IS and facet joints of the spine, all combined injuries uniformly span the entire length of the spine and all its segments or say sections,cervical through the sacrum ! So yes,I’ll gladly speak my mind for you an if I have your attention I hope to keep it and that you give me and what i say ear? The first thing i will mention to you is ive never seen a pain killer yet in my life other than over the counter meds and home remedies and “self conducted physical therapy!” Do i have your attention? I hope? These injuries were no secret to me,believe me! And it took up to 35 years to get some of them finally imaged and genuinely diagnosed! And no,they have never truely been treated by the medical profession. Why? Many reasons! I want to warn you that if you genuinely have prominent spin injuries that you might as well settle in and make yourself at home! Its a long and very rough road to hoe and often gets worse no matter what and can even become a never ending down hill battle! And despite all the nonsense out there from everyone especially medical arenas and all the expenses, it often does regardless. So first come to grips with that your life is changing and you will one way or another to some extent change with it! We have no choice,”not a game!” Though apparently many think so in all walks of life. This is really all up to you,always has been,always will be. I had not money enough,nor were any willing because of that. So each time when I healed and used exercise to get back to able to work while I lived on and exhausted savings,credit cards ect. I went to the medical profession with pains,symptoms etc that did not go away. When asked what did I do,what happened,how was I injured. Well I explained in great detail and as you see I’m a fair hand at the English language. When I explained that my back bad been broken and how grossly it was done the year before I was laughed at and told,”nonsense,you wouldn’t be walking!” MRI by requisition only from my doctors were refused by my doctors to prescribe! As they told impossible,I think I know everything and tried to blame symptoms of everything but which almost led to my death in 1996. And irreversible kidney damage and a heart attack at 31 yrs old in perfect athletic,muscular shape! Did you know spine injuries can cause multiple kidney stones no matter what your diet is? I know and did but know one would listen,said my diet of fresh raw and cooked vegetables,meat,bread,juice wasn’t perfect and that’s why I had 47 stone come out in a day ,that plagued me for 11 years on and off under their care, when I could afford it. Said it must have been the ketchup? Thats is baby,no more ketchup for me! Uh huh! When the lawers and disability came down on them we finally got answers in 2009! But the drink driver hit me when i was 7? Do some math people!! My first advice to you is check into good lawyers and disability attorney and don’t be afraid to put any medical personnel or institutions butt on the spot or even the 6 o’clock news! I don’t care if the government is paying for it and helping you, that’s all of our money and our system gives blank checks in advance with no avenue of recourse should they play with it or be ignorant. Other than that do your best to survive,”did ya here that families of the injured?” Help them survive and file grievances if necessary! Anyone can,even friends. By gosh and golly absolutely get an MRI if at all posible,and the right kind with dye or what ever is needed! “If you possibly can?” Do I lot of research on the spine and injuries on the internet especially things related to your problems. Get your own copies of xrays and MRI cds that you have in your possession to take for other opinions. You can,it’s the law,they are your records!
    All my vegetables came from the farm where I grew the beef,pork,chicken,turkey ect. Funny thing is when those animals were hurt or sick the spoke no human tongue of any kind? But I still had to treat and help them? And did,often by symptoms and reading sign cause they can not speak with words! Here I was speaking perfect English and “nope,we can’t have any of that around here!” I wouldn’t let one of those nuts trim my nails let alone cut my spine. Come on it took 1/3 century to get a diagnosis and I spoke English. You can do what you want but I will do what I will. But we all need a proper diagnosis so any one can begin to do anything. So I’m cool with getting that if possible,but really that’s about all for me. Had to have been the ketchup,they said that 1400 lb herferd that smashed me through the barn wall had no real effect? I wish you the best of luck. I have and am doing as good or better and much more peaceful than any I’ve encountered that have had any spine surgeries and I know of hundreds having worked construction ect. My secret is sit ups or anything I can pull of that resembles one,it duplicates the fetal position and let’s my spine realign naturally with as little pain as possible. Yes I’m in great pain and have been for years and years but I still some how smile when I think of how close to dead I was. Every moment is a blessing. No I don’t stand or walk far or long and it is pain intense and not pretty,but everyone else is the same or worse with my type injuries and usually far worse and had surgery at least once,some 3 & 4 Times. Sure I’m still disabled but so are they,and I haven’t cost my country 3 million in surgeries ,treatment and therapy . So go figure? Bless ya!

  11. Luana Guzman says

    I was told I have l3/4 disk compressing my nerve roots “mildly” but my feet are burning really bad and numb from arch to toes on bottom. But I had a cervical fusion posterior, as soon I I woke up from surgery my feet was on fire. I’m confused it the burning and numbness come from my cervical or lumbar?

  12. I find going to the doc for a back problem is similar to taking my car to the garage, it’s trial and error. You get the doctor they choose for you and you will probably get the assistant that is not a real doctor but could luck up and make the correct diagnosis. When you get older, expect problems. I have had spinal surgery for scoliosis with rods and fusion. No problems until I had an accident. Take care of your back and don’t do stupid stuff, like lifting heavy objects. Know your limits and don’t let anyone talk you into doing anything you know is going to be a risk. You will suffer for it.

  13. There is a back pain along with a line like pain along the left leg that gets increase on walking. This is becoming difficult for me even to sleep. How could i overcome this problem by doing what kind of excersices. Please suggest me.

  14. We are asking questions, but we are really supposed to make comments.
    Hamisi Nuhu, you need to have an X-ray or scan of some sort. You need a diagnosis. No good doctor should give you medication and send you on your way without trying to discover what your problem is.

  15. what causes the spinous process to move over to the left or right?

  16. June Tomlinson says

    What part(S) of of the body is served from the nerves coming out of L3,4 & 5. Thank you

  17. Laurie spicer says

    Hi there, could you please tell me which nerves coming our at L1 serve which parts of the body?
    Many thanks
    Kindest regards
    yours

    Laurie spicer

  18. Patricia a Lynch says

    I would like to know if you can get drop foot from the spinal surgery in the LS 5 area.

  19. Cindy Schmidler says

    I am so sorry for your pain. Please, immediately see your doctor and get a second opinion or recommendation for a specialist. There are many other things this could be and finding out quickly from a qualified back specialist or neurologist is important.

  20. GIllian Snyders says

    I would like to know my husband was at the doctor they said it is Arthrirtis in the spine he has severe lower back pain and even now at the moment pins and needles in his leg and the leg is lame from the hip and cannot feel anything in that area if you pinch it. what can it be. he do not sleep his whole body shakes because of the pain, Help what do we do. tabletts prescribed do not help. what next.

  21. i have a lower back for about two months,i have been given medication but there is NO remarkable change,please help.

  22. Media Partners says

    Joann, There are many fibrous tissues around muscles, and nerves. It could just be a “sleeve” around the muscle, etc. It’s hard to say exactly which fibrous tissue was involved.

  23. I had a desectomy at L5, S1. After the surgery the doctor talked to my husband (very quickly and breifly) and said the piece of bone causing the pain had origined higher up the spine, dropped down perforated a “fibrous tissue” surroundding the neve and was pressing hard directly onto the nerve. He also said this tissue was very inflated but went down once the bone was removed. What is the firbous tissue called?

  24. Media Partners says

    I think you are describing a herniated disk that is causing pressure on the nerve and pain down the leg. We do not offer medical advice. We just try to help you learn about health problems so you can better talk with your doctor or health care team about your own problem.

  25. i think the doctor told,my father problem is loss of the fiber protection of the ligament,the liquid is out and pressure to the nerve. what type surgery is better to this time. father occuring leg pain and very difficult to move

  26. thomas mullen says

    im looking for a picture from the back view showing the lower lumbar region of the back can you help ?

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