Effectiveness of Microdiscectomy for Lumbar Disc Herniation: A Randomized Controlled Trial With 2 Years of Follow-up

Heikki Österman, MD; Seppo Seitsalo, MD, PhD; Jaro Karppinen, MD, PhD; Antti Malmivaara, MD, PhD

Disclosures

Spine. 2006;31(21):2409-2414. 

In This Article

Materials and Methods

The study was conducted from November 1996 to December 1999 at the Jorvi Hospital (a primary referral center with a catchment population of 220,000 inhabitants situated in Espoo in southern Finland) and at the Finnish university hospitals of Kuopio, Tampere, and Oulu.

Patients

Eligible patients had been referred to elective orthopedic consultation because of sciatica. They were 20 to 50 years of age and had to have radiating pain below the knee with clinical findings suggestive of nerve root compression. At the first visit, the patients were informed of the aims and content of the study, and a minimum follow-up of 2 weeks was organized to rule out eventual spontaneous resolution of the symptoms. If the symptoms were not resolving at the follow-up visit, enrollment into the study was considered. Inclusion criteria were 1) below knee radicular pain of 6 to 12 weeks' duration at randomization, 2) a CT finding of intervertebral disc extrusion or sequester, and 3) at least one specific physical finding (a positive straight leg raising test <70°, muscle weakness, altered deep tendon reflex, or a dermatomal sensory change). Exclusion criteria were 1) previous back surgery, 2) spondylolisthesis, 3) symptomatic spinal stenosis, 4) over 3 months' continuous sick leave because of low back pain or leg pain preceding randomization, 5) a condition confounding evaluation of treatment outcomes (vascular claudication, symptomatic osteoarthritis, previous major trauma, diabetic polyneuropathy), or 6) a contraindication to conservative treatment (cauda equina syndrome, progressive neurologic deficit, or intolerable pain).

One patient assigned to the surgical group was withdrawn because he did not fulfill the inclusion criteria.

All the participants gave their written consent in accordance to the Helsinki Declaration.[11] The study was approved by the ethical research committees of all the participating hospitals and by the Finnish National Research and Development Centre for Welfare and Health.

Protocol

Patients completed a baseline questionnaire gathering data on demographic characteristics, potential confounders, and factors related to sciatica ( Table 1 ).

Clinical examinations throughout the study were carried out by an independent research physiotherapist. Straight leg raising was recorded with a goniometer to the nearest 5°. Lumbar flexion (modified Schober 15 cm) and lateral bendings were measured. Great toe and ankle extension strengths were estimated on a standard scale from 0 to 5. Deep tendon reflexes and sensation were tested and Waddell tests performed.[12] The physiotherapist encouraged early physical activity within pain limits and gave instructions on isometric muscle exercises.

Plain radiographs and a CT scan of the lumbar spine were obtained. Disc findings in the CT were graded as normal, protrusion, extrusion, or sequester.

A research assistant at the National Research and Development Centre for Welfare and Health performed randomization based on computer generated random blocks of variable size and placed the assignments in sealed opaque envelopes with running numbers. Every participating center had its own series of envelopes. Randomization took place after the baseline examination and questionnaires were completed. The treating physician phoned the central office, gave the identification data, and received the concealed treatment allocation.

A microdiscectomy by a spinal orthopedic surgeon was performed within 2 weeks of randomization in the surgical group.[13] The operation was carried out under general anesthesia in a genupectoral position with fluoroscopic control of the spinal level before draping. The patients were usually discharged from the hospital on the second or third postoperative day. Sick leave and analgesia were prescribed according to individual requirements. Surgical patients were advised to continue with isometric exercises while waiting for the operation and also after discharge from the hospital. At follow-up visits, this group received active physiotherapeutic instructions, including stretching, bending, and muscle strengthening exercises. Passive forms of treatment were not recommended.

The control group received similar physiotherapeutic instructions initially and continued with isometric exercises after randomization. At follow-up visits, as with the surgical group, activity was encouraged. Patients in the control group were informed of symptoms meriting operation, and they were advised to contact the treating physician if the symptoms should get worse.

Clinical follow-up took place at 6 weeks, 3 months, and 1 year. At 6 months and 2 years, the patients received a mailed questionnaire.

Outcome Measures

Leg pain intensity was the primary outcome measure. Secondary outcomes measured at every follow-up included back pain and work ability (100 mm visual analog scales [VAS]), a generic health-related quality of life measure 15D, and the Oswestry Low Back Disability Score.[14,15] Risk of depression was assessed at 6 weeks, 3 months, 1 year, and 2 years.[16] Satisfaction with treatment (100 mm VAS) was assessed at every follow-up. Global assessment of healing was recorded at 6 weeks, 3 months, and 1 year. Clinical examinations similar to the baseline examination took place at 6 weeks, 3 months, and 1 year.

Statistical Analysis

Power calculations to obtain a power of at least 0.80 at a significance level of 0.05 were done assuming a standard deviation of 20 mm for leg pain intensity (the primary outcome measure). Considering a clinically significant difference in pain intensity to be 10 or15 mm would necessitate a sample size of 80 to 56 patients, respectively.

Change in outcome measures from baseline during the entire follow-up was assessed with a general linear model for repeated measures (SPSS, version 12.0.1). The baseline measurement of the outcome variable was entered as a covariant into the model, which included group and time effects and their interaction. Efficacy variables were analyzed on an intention-to-treat basis. The last observation was carried forward for patients who did not complete the study or who had missing values at follow-up. Differences between the groups at different times of follow-up were checked for with the Mann-Whitney U test, χ2 test, or Fisher's exact test. Additional analyses included an on-treatment analysis according to the actual treatment and subgroup analyses based on gender, age, intensity of sciatica at baseline, and spinal level of disc herniation. Differences between subgroups were tested with one-way analysis of variance using the Bonferroni method for multiple comparisons.

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