The straight leg raise test has demonstrated high levels of sensitivity in the research (.88 in pooled data). The cross straight leg raise test has high levels of specificity (.91 in pooled data). These tests cost about $.03 to perform and provide more clinical utility than an MRI outside of a cauda equina (medical emergency). As far as a disc herniation goes, the medical and scientific research has been quite clear; MRI FINDINGS DO NOT MEAN OR SHOW BACK PAIN. The MRI is sensitive, not specific. It can rule out a problem but is poor at ruling one in.
What does this all mean?
If the straight leg raise is negative without provoking symptoms, it is good at ruling out a symptomatic disc herniation. If the crossed-straight leg raise is positive it is good at ruling in a symptomatic disc herniation.
Disc bulges, herniations and protrusions are all common. The only disc injury that correlates to symptoms/disability are extrusions, which are also present in a smaller asymptomatic populations.
On to your next question: what can the PT, DO, DC do about the disc…nothing…
There is nothing in the scientific research that demonstrates changes in the disc with manual therapy, exercise, traction, ,etc that correlates to symptom resolution or outcomes. It doesn’t matter because MRI confirmed disc herniations are the norm and do not correlate to patient related pain or disability (unless there is an extrusion).
This is the unfortunate misunderstanding of neurosurgeons, orthopedic spine surgeons, anasthesiologists, disc-head PTs (i.e. McKenzies), etc. For those that don’t agree, lets look at what is done for ‘discogenic’ pain: fuse it, replace it, snip it out, burn it, inject it, suck it in, suck it out, medicate it, etc. Guess what, they all have one thing in common…none are better than the next. They all have one more thing in common: the are no better than exercise and appropriate movement/active interventions.
Discs don’t cause pain.