Introduction

Evaluation of low back pain for prolapsed intervertebral disk (PID) is based on history, physical findings and im-aging examination such as Computerized Tomography (CT) scan or Magnetic Resonance Imaging (MRI). In pa-tients with recurrent low back pain, reflex sciatica, strik-ing tenderness on spinal processes or beside vertebrae, possible knocking pain transmitted to lower limbs and positive straight leg raising test are hallmark findings (1, 2). Ergonomic factors, age, familial predisposition, trau-ma, hypertension and cigarette smoking are implicated risk factors (3, 4) but their contribution is often under-mined in patients’ history. The straight leg raising test (SLRT) is not only diagnostic, but is also prognostic in evaluating patients with back pain for possible PID (2, 5). MRI is the standard radiological test for diagnosis of a herniated disk. Its use vis-à-vis CT scan, however, var-ies between centers (6). In spite of their value and need for consistent recording, the extent of use of clinical and MRI findings in accurate diagnosis of PID in a Kenyan setting is not documented. The study therefore aimed at evaluating the diagnostic protocol of PID among low back pain patients at Kenyatta National Hospital.

 

 

Patients and Methods

Files of patients with entry and exit diagnosis of low back pain and PID respectively seen at Kenyatta National Hospital from January 1997 to December 2007 were re-trieved from the records department. Ethical approval was obtained from Kenyatta National Hospital/Univer-sity of Nairobi – Ethics and Research Committee (KNH/ UON-ERC). Biodata, history of presenting complaints, risk and co-morbid factors, physical findings and imag-ing methods were recorded. Files with incomplete docu-mentation were excluded.

 

Data collected were analyzed using SPSS® version 16.0 of Windows®. Tables and histograms were used to illus-trate the findings.

 

Results

Six hundred and three patient files with low back pain were evaluated. There were 267 (44.3%) males and 336 (55.7%) females. The onset of pain was sudden or in-sidious in 15% and 49% of patients respectively. Risk/ co-morbid factors were recorded in 238 (39.5%) of the cases. Of these one hundred and fifty eight (66.4%) were due to trauma, while 80 (33.6%) were associatedwith non traumatic co-morbidities. In the majority (60.5%) of the patients, risk/co-morbid factors were not recorded. In 47.8% of the patients, the clinicians did not document performing the straight leg raising test. Where performed, the test was negative in 61.5% of casesThe spectrum of radiological investigations ordered in these patients included MRI (44.1%), lumbosacral X-ray (38.5%) and CT scan (9.1%). In 50 patients (8.3%) no imaging test was done. The lumbosacral X ray was con-sistently requested throughout the period while the MRI services were popular in the recent years (Figure 1).

 

Most (82%) patients with sciatica had MRI features con-sistent with prolapsed intervertebral disk.

 

Discussion

Prolapsed intervertebral disk is diagnosed on history of back pain, sciatica, positive straight leg raising test and positive imaging finding consistent with prolapsed inter-vertebral disk (7). In the present study, 37% of patients had sciatica while 21% had a positive SLRT. Risk/co-morbid factors were recorded in 39.5% of the patients. Family history, young age, male gender, ergonomic en-vironmental factors, trauma and cigarette smoking have been associated with PID (3, 4). This calls for detailed history of low back pain especially family predisposition and predisposing factors.

 

Two hundred and twenty two (47.8%) of the patients in the present study did not have the SLRT done. In a meta-analysis from 1965 to 1994 Vroomen et al found that pain distribution and the Lasegue test (SLRT) seemed to be the only useful clinical item in the diagnosis of PID (7). The pooled sensitivity and specificity values of the Lasegue test are 89% and 52%, respectively (7, 8). Fur-ther, SLR has utility as a screen of lumbar spine stability, and can assess control of lumbar rotational movements and when used with imaging, it ameliorates accu-racy (10). Another significant observation of the present study is that while the crossed straight leg raising test has a relative higher specificity of 84% (7), it was not per-formed in any of the patients. Accordingly, it is probable that accuracy of clinical diagnosis is often undermined in patients at KNH and irrational treatment instituted.

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While MRI is the gold standard diagnostic test for pro-lapsed disk worldwide (7, 11), it is used in less than half of our patients. This could be attributed to high cost and low availability of this useful tool. Although a few pa-tients had disc prolapse or herniation with a non-degen-erated disc, there is a relationship between the presence of disc degeneration and prolapse or herniation on MRI Unfortunately, MRI is so sensitive that frequently it over diagnoses PID (12).

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Plain X-ray was done in 38.5% of all the patients. The consensus based on guidelines issued by the Royal Col-lege of Radiologists, however, is that plain lumbar spine X-rays are not indicated routinely in cases of possible PID. In fact during conservative management, there is no justification for it in the absence of other indications Its use in KNH should therefore be reduced. Ob-servations of the current study reveal that CT scan was ordered in less than 10% of the patients. In many places, because of its wider availability, lower cost, patient ac-ceptability and effectiveness CT scan is the investigation of choice (13). It is carried out in most places especially where MRI may not be done due to non availability, high cost, claustrophobia on the part of the patient or contraindication due to metal implants (6). Further the

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use of CT is of considerable value in determining the size, position and volume of sequestration and extent of excavation of spinal cord (14,15). Accordingly, greater use of this imaging modality may reduce the cost and increase diagnostic rate at KNH.

 

 

In conclusion, the evaluation of low back pain for pro-lapsed intervertebral disk at Kenyatta National Hospital is incomplete; the history of risk factors is not always taken, and the straight leg raising test, magnetic reso-nance imaging or computerized tomography scans are not routinely done. History of sciatica, SLRT, crossed SLRT and MRI use are recommended in evaluation of low back pain for PID.

 

Acknowledgements

We are grateful to Dr. Pamela Mandela for her critique, the KNH registry staff for availing the records and Mrs. Cath-erine Chinga for typing the manuscript.

 

References

 

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