Continuing on our sequence of stories from neuroanatomy …
Clinicians know that persistent pain experienced around the ischial tuberosity and sub gluteal space can sometimes be tricky to sort out. There is a fear factor here too – the athlete pondering if their hammie is going to go and those who google “piriformis syndrome” will find many treatments offered for something not fully understood.
Over the years, I have thrown every manual test known to manual therapy at the bum (or butt for our American friends) in an attempt to find local culprits, though in recent years, the introduction of central sensitisation into reasoning has lessened the need for relentless testing.
A recent paper by Bäumer et al. (2015) excited my clinical pattern memory book. I have noted that in the presence of bum area pain, that while a straight leg raise may not show much, if you do it with ankle plantarflexion inversion (ie load fibular divisions), the problem appears to be elicited. However, in the same person, if you do the SLR with ankle dorsiflexion/eversion (ie loading tibial divisions) it all seem fine. And vice versa too – a tibial division loaded SLR can reproduce bum area pain, but not the fibular loaded SLR.
The Bäumer et al. (2015) paper provides in-vivo evidence of a distinct somatopic pattern within the sciatic nerve. In other words, the nerve bundles from the L5 and S1 roots were separate in the nerve. While there is a bit of nerve fibre intermingling, the nerve topography is more cable like than a mixed plexiform structure. L5 bundles are more anterolateral within the nerve and S1 posteromedial (see image below). So the nerve is more like a sheath around separate bundles (fascicles). It’s not all twisted up inside the nerve as many of us may have thought.
So what can we take from these observations and the experimental findings:
- In the case of buttock pain, especially where there are hints of neurogenic involvement, it is worth performing tests via both divisions of the sciatic nerve – try DF/eversion and PF/inversion while in SLR
- Pathology leading to mid axon discharge could come from one division and not the other
- The divisions/bundles can move in relation to each other. Maybe a bleed or inflammation within the sciatic sheath can hinder this movement.
- maybe you can perform a sciatic interfascicular mobilisation (sounds sexy, eh?). That is what I thought I was doing in one of my patients. In hip flexion, work knee extension in plantar flexion/inversion and then work it in dorsiflexion/eversion (as in the image above).
Happy mobilising, share your thoughts.