The external fixator: a tool for evaluation of complex low back pain problems

The selection of patients with low back pain for fusion is especially difficult when previous surgical interventions failed and/or invasive tests (discograms, facet blocks) do not allow or do not clearly identify the painful motion segment. Test fixation with an external fixator may mimic a definite internal fixation, such as a fusion, and may help select patients for a more favorable result. The purpose of the study was to clarify if temporary back pain relief by external fixation is predictive for back pain relief after final internal fixation and fusion.

A retrospective study of 63 patients up to 6 years after evaluation of low back pain problems with an external fixator (index operation) was conducted. The data were collected from the charts based on a protocol that patients had to fill in during evaluation, and the actual state was checked during a clinical investigation at the outpatient clinic. The protocol monitored pain (Visual Analog Scale), pain medication, and work status. Based on the first two parameters, the effect of external fixation was defined as a general estimation as positive, doubtful, or negative. The same parameters were reassessed at follow-up control.

In 38 patients, the immobilization test did improve the pain situation, in 11 it remained unchanged, and in 14 the pain got worse. Thirty-eight patients (not identical with the above) underwent definitive fusion afterward, whereas 25 were not operated on. Twenty-one of 30 patients with a positive effect undergoing surgery showed an improved situation after fusion, and 8 of 22 patients without further operation were improved at follow-up. Nine of 12 patients with a negative immobilization test did stay in a bad situation at follow-up.

The external fixator as a tool for evaluation of patients with low back pain is an expensive measure with a considerable complication risk and only justified in selected patients when any other measure fails to assess and evaluate a patient's situation. If the test fixation reveals no benefit, the patients will remain in a bad situation whatever the therapeutic measure will be. Therefore the main value of the external fixator assessment is the selection of these patients that should not undergo surgery. A positive test fixation means a 72% chance for a satisfactory outcome at least two years after surgery, whereas without surgery the chance for some spontaneous improvement is 57% if the test immobilization did show some improvement. With respect of the "negative" selection of this group of patients (complex history, previous interventions) in our as well as in others series, the obtained results seem acceptable and the use of this invasive diagnostic measure in this group of patients seems justified. Statistical analysis did not show differences of significance as the numbers in the individual groups was too small.