Large Protrusion at L3/4 but …..???

Hi All, would really appreciate some guidance, not necessarily what to do (though feel free), but more on what is going on with my back. A quick history:-

I am mid fifties.
In my early thirties I did something to my back that from time to time erupted, once or twice a year. It took the form of something seeming to ‘twang’ in my back. It would be leave me in quite a bit of pain, walking lop sided for a couple of days with movement very difficult. However a couple of days of NSAID’s always sorted it.
The pain would nearly always be in my back and a couple of inches to the right of my spine just above the buttock.
So I have been like that for twenty odd years.
Have seen the Doctor from time to time during that period, but apart from referral to a Physio from time to time all I found out was that it was called Non Specific Lower Back Pain, which I realised means they haven’t got a clue!

Towards the end of last year (2009) my back ‘twanged’ again but this time the consequences were quite different. There was no stiffness but for the first time ever I suffered from severe sciatic pain in my right thigh and knee, numbness in my inside thigh and weakness in my leg.
Interestingly a numbness in the middle of my right knee cap that I had ignored for years was replaced by pain during this episode. The numbness in the inner thigh came on slowly over a couple of weeks.
An MRI scan identified a large disc protrusion between L3 and L4 and a couple of minor bulges in the two disc’s below.
**However it is interesting that at the time of the MRI scan I was almost pain free and well on the road to recovery having seen and tried a Piriformis Stretch exercise.** That exercise was basically pulling the right knee up and across the chest. I’m not exaggerating when I say that the day that I discovered that exercise was the night that I had my best nights sleep for weeks and it was the start of my recovery. I also saw an Osteopath but to be frank got more out of the conversations we had than any manipulation.
So by a couple of months or so after the initial episode I was fully recovered. The numbness in my inside thigh had slowly disappeared and the numbness on my knee cap that I had had for years had not returned. I am doing some Gym Ball exercises as prescribed by my Physio (who has now signed me off) and I also do a couple of Robin McKenzie exercises.

It is my experience during those McKenzie exercises that I would like some advice on because they are a bit scary at times.

When I do Flexion in Sitting I sometimes get a very sharp pain that shoots right across my lower back. The first time it happened I thought my back had gone again, but it hadn’t. As instructed I always follow this exercise by Extension in Lying. I really would like to understand what is going on with that occasional pain when in Flexion. I suspect it is muscular or ligament rather than disc related but can anyone confirm or otherwise please?

When I do the Extension in Lying I sometimes get a sort of clunk (not a click) from my back after which any preceding stiffness and slight pain disappears. Its similar to the experience sometimes during manipulation with the Osteopath. Again I really would like to understand what is going on here. Is it just similar to cracking your knuckles which I believe is air popping, or is it disc related and is it ok to carry on? I do get benefit from the exercise.

In medical terms the wheels have slowly turned and next week I am going to see an Orthopaedic Surgeon at Musgrove Park in Taunton (UK). I presume their part in all this will be to consider surgery. I don’t consider myself to be candidate for surgery and I hope they won’t too, but I am hopeful that I might get some explanation too because for me understanding what is happening is key. Which is the reason for this post.

Any advice will greatly appreciated.

Oggy.