Now it is time to speak about the fourth lumbar segment – I will keep this simple…it is implicated in pretty much any condition in the pelvic viscera, reproductive organs, and lower limbs. Obviously this will not be easy to keep simple but I think I can manage!
We will start with the nerve roots that L4 is involved in: femoral nerve (L2-L4), obturator nerve (L2-L4), superior gluteal nerve (L4-S1), sciatic nerve (L4-S3), common fibular/common peroneal nerve (L4-S2), tibial nerve (L4-S3), as well as the medial and lateral plantar nerves (L4-S3). These nerves cover the majority of the musculature of the lower body as well as the vasomotion of the lower body. It is safe to say that the fourth lumbar segment is extremely important. This can be seen through dermatomes as well – L4 covers a very large area.
The biggest deal, when using the Osteopathic lens, is the iliolumbar ligament. The iliolumbar ligament joins L4 (and L5) directly to the ilium from the transverse processes. Any issue with the ilium/innominate complex will cause problems at L4 – group lesioning. In principle, that is why the pelvis is addressed first (it is the base). If you have the time read my thoughts on sacral mechanics and on innominate lesions. As a result of the mechanical issues related to the iliolumbar ligament there is also strain that happens through the innominate complex, under the inguinal ligament, and in the soft tissues of the lower limb that will also cause reflex lesions in other lumbar segments (and likely even farther away). When there is an issue in the lumbar spine, the innominate complex, or the lower limb the fourth lumbar segment will likely pick up the trouble via mechanical strains that seem to present as coupled side bends and rotations.
As far as the pelvic viscera are concerned I don’t know that a lesion of L4 is directly related through the nerves (Marion Clark notes this and states that there is a clinical connection) but through related mechanics. As part of a group lesion L4 will be accompanied by the innominates that will also throw the sacrum in to lesion. When these areas are all in lesion there is a mechanical strain through the pelvic viscera that upset soft tissue, hard tissue, nerves, arteries, veins, and lymphatics.
I know I am not spending a lot of time speaking about L4 specifically – it is because I want it to be clear that the issues with an L4 lesion are much more global. Osteopathy requires that we look globally first and I believe (so far) that L4 is primarily a more global lesion. From what I know now (my knowledge is ever evolving) L4 is an area that will pick up trouble from almost anywhere as well as send trouble almost anywhere. Students of the CAO know that the pelvis is the first adjustment and that adjustment will often correct L4, if it does not immediately correct L4 it definitely sets the stage for it.