Diagnosis of Low Back Pain
The diagnosis of low back pain is difficult and simply relying on an MRI to diagnose low back pain is expensive and can be misleading. While one can estimate the age of an individual by examining an MRI of the low back, one cannot say whether the subject has pain or not.
By way of background, I am a neurologist trained before the advent of CT scanning. In large part, we had to rely on what we could hear, feel, and see when we analyzed patients with a stroke, for example. Nowadays, no neurologist would attempt to diagnose and treat a stroke patient without an MRI, yet one can still examine and sometimes treat patients with low back pain the “old fashioned” way.
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Low back pain doesn’t always come from the back. Physical diagnosis techniques exist to help differentiate back pain originating from other than the lumbar spine.1 The best example of this is when assessing back patients for pain arising in and around the sacroiliac joints.
Assessing the Sacroiliac Joints
If one defines “sciatica” as any back pain radiating down the back of a lower extremity, then sacroiliac sprain may account for 15%-20% of sciatica and nerve root compression and irritation for 3% or 4%. An MRI of the lumbar spine does not assist in the diagnosis of sacroiliac sprain. I advise surgeons to examine the sacroiliac joints if their patient returns with a “failed back.”2
The standing flexion test is done as follows: With the patient standing upright, one places the thumbs on the posterior superior iliac spines and he can feel the buttocks rotate downward or not.3 Whether the sacroiliac joint in question actually moves or not is uncertain, but with a little practice, it can easily be felt and is a useful sign.
What else? With the patient supine, internally rotating the thigh distracts the sacroiliac joint on that side and may cause pain. If the patient says it reproduces the pain, then the examiner has learned a bit more about that joint. The patient learns something, too. This sign is also present with arthritis of the hip joint. The examiner can also sometimes reproduce the pain by pushing the flexed knee down and laterally while the hip is flexed and internally rotated. Next, with the patient lying prone, one may be able to palpate fullness and tenderness over a ligament. Deep pressure may also reproduce the patient’s pain. Studies indicate that rating is fairly reliable if three or more provocative tests are in agreement.2,4-7
What about the space inside the sacroiliac joint? I don’t have fluoroscopy and so I confine my injection to ligaments I can get at: iliolumbar, posterior interosseous, sacrotuberous and long and short dorsal ligaments. What I have found in the literature are accounts of injecting the posterior interosseous ligament at a particular site,8 but the others can easily be identified. One must locate the sacral tubercle by palpation to find the sacrotuberous ligament, the iliolumbar ligament is in the angle between the lumbar spine and the ilium, the posterior interosseous ligament is along the joint, and the long and short dorsal ligaments are near the posterior superior iliac spine. They offer the examiner an injection site by reproducing the patient’s pain complaint by deep palpation. On inserting the needle, I ask the patient if I am in the right place. Following the injection of 1 or 2ml of lidocaine 1%, I ask the patient to stand up and see if pain is gone with the postures or movements that ordinarily reproduce the pain. A nearby myofascial trigger point in longissimus dorsi or multifidi can mimic pain from a ligament such as iliolumbar. Radiation of pain is the same whether it arises from a joint, a ligament, or a muscle.9,10
Why would the examiner think of looking at the sacroiliac joint in the first place? If the patient limps into the room, is seen to sit with his weight shifted to one buttock, and complains of pain on standing on the same lower extremity he avoids sitting on, he probably has a sprained sacroiliac joint. He may also complain of painless “giving out” weakness of that lower extremity. The sacroiliac joint winds up like a spring in the after-following leg. If the sacroiliac joint is dysfunctional, the leg doesn’t move far enough forward and the patient may trip.
One besetting difficulty about this is the question of inter-rater reliability. Without a “gold standard” such as a MRI, would five experienced physicians examine such a patient and agree? One might argue for a “gold standard” for an intra-articular injection, perhaps, but a few minutes examining a patient is likely to be much cheaper than an MRI or an intra-articular injection with fluoroscopic control. If some depot methylprednisolone of prolotherapy injected in a sprained ligament gives the patient pain relief then and there, then the matter is settled.
Greenman’s textbook11 provides information about examining the zygapophyseal joints of the lumbar spine. This is fairly straightforward. With the thumbs placed on the transverse processes of the lumbar vertebrae in a fully erect patient, they can be felt to rotate on side-bending. If a facet joint is “stuck,” it is readily apparent. Facet arthropathy is a common concomitant of advancing age, especially in a working man or someone obese, so the demonstration of a fact arthropathy is not prima facie evidence of a pain generator. Provoking pain by pressing downward on the facet joints has better inter-rater reliability, but the gold standard remains competent block of the lumbar facet.8,12 The reader is likely familiar with the straight leg raising test and its variants.
Nerve Root Exam
I also have some preferences regarding muscle stretch reflexes. One is to examine the patient supine. Muscle tone changes in the upright seated position and so this can be a confounding factor. I distract the patient by repeating some nonsense and use the same phrase each time so I don’t have to think about what I am saying while performing the maneuver on the patient. Since the medial hamstring reflexes are useful for the L5 root, I support both knees of the relaxed lower extremities, place my index finger over the tendon of the medial hamstrings at the knee and strike my finger. A contraction is readily felt. I prefer to examine the ankle jerks with the patient prone and the knees flexed. I grasp both feet with one hand to facilitate comparison and use the reflex hammer with the other. It is easier to obtain the reflex and they can be easily compared.