The Fifth Lumbar Vertebrae

As with the innominate, and most other structures Marion Clark wrote about, I will not go in to the same depth as he does, my aim is to bring out some relevant information to share with everyone. Before going any further I would like to postulate that L5, and L4, are part of the innominates due to the iliolumbar ligament.

Due to the location of L5 it can be called a transitional vertebrae as it is wedged between the sacrum and L4. It sits anterior to to L4 and its superior portion is built like a standard lumbar vertebrae while its inferior surface is very different as it articulates with the much wider sacrum.

The nerves that will show affects of a lesion of L5 are: the superior gluteal nerve (L4-S1), inferior gluteal nerve (L5-S2), sciatic/common fibular nerve (L4-S3), tibial nerve (L4-S2), nerve to obturator internus and superior gemellus (L5-S2), and nerve to quadratus femoris and inferior gemellus (L4-S1). Considering the motor effects of these nerves L5 is clearly important to extension of the leg at the hip, internal and external rotation of the leg at the hip, flexion of the knee, as well as most movements of the foot and ankle. Instead of going on ad nauseum I will say that knowing dermatomes is a big deal here.

According to Clark the most common lesion is anterior displacement of L5 (as it sits anterior to the rest of the vertebrae) with the possibility of a torsion (may be a Fryette’s type 2 lesion – this is how your Osteopath might know you have been having some rougher carnal relations 😉 as well as posterior displacement (from flexion with a strain – such as improper lifting mechanics). The thing to keep in mind with L5 is that is at the mercy of the innominates, the sacrum, and L4 due to connective tissue so it is almost always involved in a group lesion. The idea of a group lesion is important in that it will determine the way that treatment is applied – do not waste time on corrections of each individual lesion when you can affect them all with one treatment option (check out the innominate article where I mention group lesions). Also note that due to L5 being more anterior it is the most common site for a spondylolysthesis.

Not to completely ignore Marion Clark, here are some interesting points he makes:

– Morton’s toe (in Clark’s time this would be what we know as Morton’s Neuroma) occurs on the sciatic nerve and its divisions in the foot often in relation to a lesion of L5 (there are mechanical implications possible here due to altered pelvic positioning in relation to the leg and the foot – that is why the centre of gravity is checked)

– Disorders of the rectum, vesicles seminales (think premature ejaculation, nocturnal emission, imperfect emission, aka male sexual disorders), uterus (think dysmenorrhea, reflex backache, inflammatory conditions, relaxation of the uterine walls), prostate, bladder (think painful urination), and urethra (think pain, congestion, alteration in size of the urethra)

L5 is pretty important for sexual health as well as fluid excretion!

Take home messages here?

– L5 is part of the innominate group lesion pattern due to connection with the innominates (iliolumbar ligament), the sacrum (lumbosacral ligaments), and L4

– L5 gives nerve tone to much of the pelvic viscera

– L5 influences vasomotion to the pelvic viscera and the legs

– L5 gives motor tone to a large amount of leg muscles

– L5 is the most likely lumbar vertebrae to suffer a lesion (that doesn’t mean a lot though as L5 is part of a group lesion pattern and will affect the rest of the body – Osteopathy, you are so full of connections and grey areas!)

Correct the pelvic lesion first then see what is happening with other lesions such as L5 – stick with the principles!


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