Journal ofSpinal DisordersVol. 9. No. 3. pp 246-250© 1996 Lippincott-Ravcn Publishers, Philadelphia

Anatomic Position of a Herniated Nucleus PulposusPredicts the Outcome of Lumbar Discectomy

Barbara M. Knop-Jergas, James F. Zucherman, Ken Y. Hsu, and Bradford DeLong

St. Mary's Spine Center, St. Maiy's Hospital and Medical Center, San Francisco, California, U.S.A.

The purpose of this study was to determine whether the anatomic position of a lumbardisc hemiation has any significant effect on the clinical outcome of lumbar discectomy.Between January 1988 and March 1993, 80 patients with simple disc hemiations underwent lumbar discectomy for herniated nucleus pulposus. We reviewed preoperativecomputed tomography scans after discography and magnetic resonance imaging of thelumbar spine. Disc hemiations were classified as central, paracentral, intraforaminal, ex-traforaminal, or multiregional broad-based protmsions. The Smiley-Webster evaluationscale, which divided patients into groups with excellent, good, fair, and poor clinicaloutcome and evaluated the long-term need for pain medication, was applied. The postoperative evaluation period ranged from 6 to 48 months. The clinical outcome was thencorrelated with the different positions ofhemiations. The frequencies of the clinical outcomes were compared using the x' test. We found a poorer clinical outcome that wasstatistically significant in patients with central hemiations and with multiregional protrusions. Most hemiations occurred at the L4-L5 level (58.7%). However, the level ofdisc hemiation was not found to be a predictor ofclinical outcome. Form and anatomicposition of the lumbar disc hemiation are of prognostic value for the outcome of lumbar discectomy. Further studies are required to confirm our preliminary results and eventually help improve surgical indications for lumbar discectomy. Key Words: Nucleuspulposus—Lumbar discectomy—Anatomic position—Computed tomography scan—Magnetic resonance imaging.

Many clinical factors influencing the success rate oflumbar disc surgery have been determined in the past.Studies have been performed to evaluate the appearanceof disc hemiations histomorphologically on computedtomography (CT) scans with and without contrast material and on magnetic resonance (MR) imaging scans.The shape of a herniated disc has been described regarding the integrity or disruption of the posterior an-nulus and the posterior longitudinal ligament. However, there is little information about the shape and position

Manuscript received September 5, 1995; accepted February 15.1996.

Address correspondence and reprint requests to Dr. Barbara M.Knop-Jergas, St. Mary's Spine Center. 4th Floor, One Shrader Street,San Franci.sco. CA 94127. U.S.A.

of a hemiation in the spinal canal with respect to theclinical outcome. The purpose of this study was to evaluate the anatomic position of a disc hemiation with regard to the postoperative success rate.

MATERIALS AND METHODS

Between January 1988 and March 1993, 170 patientswere treated surgically for lumbar disc hemiations. Fromthese, 80 consecutive patients were chosen for this retrospective study. Patients with additional pathologicalfindings of the lumbar spine, such as central canal stenosis, foraminal stenosis, subarticular stenosis, spondy-lolisthesis, or reherniation after previous surgery wereexcluded. There were 24 women and 56 men. Women

ranged in age between 23 and 67 years (mean, 37.7

246

OUTCOME OF LUMBAR DISCECTOMY 247

years), andthemen were between 25 and80years (mean,40.9years). Legpainwasthemajor complaint of all patients; sometimes thiswasassociated withlowbackpain(5%). The durationof symptoms ranged from 3 to 120months. Many patients (57.1%) reported a slow onsetof symptoms that increased overtime, whereas otherpatients reported a particular event suchas lifting or twistingwith a suddenonsetof clinical sjmiptoms. Thirtypatients had a history ofpathological electromyographicfindings, and25.7®/o of allpatients hadneurological fmd-ingssuchas reduced dermatomal sensitivity, absent deeptendon reflexes, or motor weakness (Table 3). Thestraight legraising testwasfound to be positive in 75.7%with reproduction of typical leg pain <70°. Every patient failedto improve underconservative treatmentwithphysical therapy, epidural or selectivenerve root blocks,and pain medication given orally.

For diagnostic purposes, a CT scan had been performed in 33 patients, and 47 patients received an MRscan for diagnosticevaluation. All these scans had beenreviewedby an independent physicianobserver and thedemonstrated hemiations had been classified as central,paracentral, intraforaminal, extraforaminal, and as mul-tiregional, broad-based disc herniation (Figs. 1 and 2).

All operations had been performed by the same operating team as a small laminotomyor partial laminec-tomy and partial discectomy under loop magnification.Each patient was placed prone in a kneeling position.Anesthesia was general with intubation. Forty-one patients had disc herniation at the L4-L5 level (51.2%),and 39 had herniation at L5-S1. Five patients requireda two-level discectomy at the L4-L5 and L5-S1 levels,one required it at L3-L4 and L4-L5, and in another patient a discectomy at L3-L4, L4-L5, and L5-S1 had tobe performed. On the 1st postoperativeday, all patientswere allowed to start walking with a physical therapist,using a lumbar corset.

To obtain the postoperative results, data of the clinical evaluation during die postprocedure follow-up werecollectedby an independentphysicianobserver. The follow-up period was at least 6 months, with a maximumof48 months (mean, 12.9 months). Patients were clas

sified into four groups, according to their postoperativeclinical results. A modified Smiley-Webster evaluationscale (6), including information about theneed for regular painmedication, had beenused. The% test hadbeen used to determinethe significanceof our fmdings.

RESULTS

According to our postoperative evaluation scale, 39patients hadan excellent result(53.4%), 9 patients hada goodresult (12.2%), 7 patients hada fair result (9.8%),and 18 had a poor outcome (24.6%). Patients with excellentand good results wereconsidered satisfactory intheir outcome, and those with fair or poor results wereconsidered to have an unsatisfactory outcome (Table 1).Finally the five different anatomical types of disc her-niations were correlated with the results of the evaluation scale. There was only one patient who had an extraforaminal herniation, with a poor outcome. This hasnot been considered in further evaluations. Excellentpostoperative results weremorefrequently found in patients with a paracentral or intraforaminal herniation(Fig. 3; Table 2).

In patientswith a centraldisc herniation, 52.6%hadonly a fair or poor outcome. On the other hand, the percentage of patients withparacentral or intraforaminal herniation wifri an unsatisfactory outcome was low (20%).

Statisticalanalysiswith the test shows that the unsatisfactory outcome in patients with a central disc herniation was found to be significant, when compared withparacentral as wellas intraforaminal disc hemiations (p< 0.05 for both).

DISCUSSION

Clinical factors, which can influence the outcomeafter lumbar disc surgery for a herniated nucleus pul-posus, have been well described, but there is little information about the shape and position of the herniated disc within the canal with respect to the clinicaloutcome. When the location ofa lumbar disc hemiationwas taken into account, it was correlated with the clin-

j( }[ FIG. 1. Anatomic position of disc hemiations.

central intraforaminal multiregional

paracentral extraforaminal

J Spinal Disord, Vol. 9, No. 3. 1996

B. M. KNOP-JERGASETAL.

FIG. 2. Disc herniations, diagnosed on computed tomography scan/magnetic resonance Imaging as (A) central, (B) paracentral, (C) in-traforaminal, or (D)muitiregional to determine the anatomic positionof the hemiated nucleus pulposus.

ical pain reproduction by the straight leg raising test (5)or was chosen as a criterion to select a patient for percutaneous nucleotomy (3).

Our findings show that patients with central discherniations have a significantly worse postoperativeoutcome after a discectomy. The same procedure is associated with a good clinical outcome in the majorityof patients with paracentral or intraforaminal herniations.

In 1993, Mochida et al. (3) published their data concerning the clinical results after percutaneous nucleotomy. Their patients had been preoperatively evaluated with discogram CT as well as myeiogram CT.Thedisc herniations in the imaging studies were classifiedas median, paramedian, intraforaminal, and ex-traforaminal. They found a significantly poorer outcomein patients after nucleotomy, when they had presentedwith a median or with an intraforaminal disc hemiation.

Patients with paramedian protrusions were more likelyto have satisfactory results. They concluded that patientswith a centralhemiation are candidatesfor open surgeryrather than nucleotomy.

TABLE 1. Clinical rating scalefor assessmentofpostoperative results

I; Excellent

Patient returned to full-time work/activity as before onset ofsymptoms; no pain medication required

II: Good

Patient returned to full-time work/activity; occasionalconsumption of pain medication

III: Fair

Patient not able to return to former level of work/activity;occasionally pain medication;improved over preoperativc status

IV: Poor

Patient not able to return to work/former activity level;regular consumption of pain medication

Most patients in our study with intraforaminal herniations had excellent or good clinical results after theprocedure. These results are in contrast to the percutaneous nuclectomy study by Mochida et al. (3). One reason for these divergent results might be that during nucleotomy, it is technically difficult to remove nucleusmaterial from an intraforaminal area. The tip of the nu-cleotome cannot be directed into the foramen because

of the entrance point of the nucleotome through the an-nulus. Furthermore, there is the close proximity of thenerve root, which could easily be damaged. The intraforaminal hemiation can be addressed in an open procedure more easily, because herniated material can beremoved ifom the foramen under direct vision and the

foramen can be probed to determine the intraforaminalspace. However, our results show that those patients witha central disc hemiation did not present with a betteroutcome in an open procedure, as suggested by Mochida et al. Although technically the hemiation can be addressed, our results suggest that there may be an underlying pathological change, for which discectomyalone is an inadequate procedure.

Mcguire and Amundson (2) published the results ofa study evaluating the postoperative instability after central L4-L5 discectomy with either a central or a bilateral laminotomy approach. This proved significant forthe development of an instability, when compared with

TABLE 2. Anatomic position ofdisc herniations

Anatomic positionof disc hemiation

Central

Paracentral

Intraforaminal

Extraforaminal

Muitiregional

No. of patients

OUTCOME OF LUMBAR DISCECTOMY

TABLE 3. Clinical data ofpatients involvedin the study

Data No. (%)

Sex

Male 56 (70)Female 24 (30)

Clinical symptomsLeg pain 76(95)Leg pain with lower back pain 4(5)

Onset of symptomsinjury 34 (42.9)Spontaneous 46 (57.1)

Clinical-diagnostic findingsNeurological impairment 20 (25.7)Pathologicalelcctromyographic Findings 30 (37.5)

Positive straight leg raising test (<70°) 60 (75.5)

the outcome of patients treated with a unilateral approach for a posterolateral disc herniation. Eighty-twopercent of the patients aftercentral discectomy requireda fusion of the operated segment within 11 months afterthe initial procedure. The authors recommended a bilateral lateral fusion of the segment for all patients undergoingL4-L5 central discectomy usingeither a central or bilateral laminotomy approach to the disc. In ourseries with both L4-L5 and L5-S1 discectomies, thelevelof the herniation was not a prognostic indicator ofsurgical outcome.

Our results indicate an unsatisfactory outcome for mostpatients with a central disc herniation undergoing discectomy. Surgically, the same approach had been madein all patients included in this study. No patient had undergone a central decompression, whichis a moredestabilizingprocedurethan a laminotomy. If instability is themain reason for the unsatisfactory outcome after discectomy for a central herniation, the reason mayrather bean unstable segment presentingwith a central herniationin the first place than the surgicalapproach itself. It may

be that a nucleus pulposus protrudingthrough the central portion of the annulus fibrosus weakens the architecture of the disc more than any other type of protrusiondoes. Another explanation may be that theinner disc derangement that leads tocentral disc herniation isprecededby a higher degree of internal disc disruption, becausethe centralposteriorportion of the disc is normally stabilized by theposterior longitudinal ligament. Ninomiyaand Muro (4) introduceda classification for disc protrusions, basedon the degree of general degeneration of thediscs, range of disc herniation, anddegree of protrusionin patients who underwent discography/disco-CT, followed by corticosteroid or chymopapain injection. Thepostprocedure outcome in this study hadnot beencorrelated with the pathologydescribed.

Hirabayashi andco-workers (1) analyzed the data oftheir patient population who required surgeryfor her-niated discs. The herniations were classified as protruded, extruded, or sequestered. None of the patientswith a sequestration showed a poor outcome, whereasin the group with the protrusion-type herniation, a significant pooroutcome hadbeen documented. This grouprequired a high incidence of second operations, whichled the authors to the conclusion that the pathology ofa contained protruded disc remains deep to the intactannulus fibrosus and is difficult to localize underneaththe longitudinal ligament. During a surgical procedure,disc material and elastic annulus fibrosus are inadequately removed andcompression of nerve roots wouldpersist after the operation.

CLINICAL SIGNIFICANCE ANDCONCLUSION

The anatomicposition of a lumbardisc herniationisof predictive value for the clinical outcome of lumbar

Bexcellent/good outcome

•fair/poor outcome

E 150)

X2

ES 10

central intraforaminal muitiregionalparacentral extraforaminal

Anatomic position of disk herniation

FIG. 3. Correlation between clinicaloutcome after lumbar discectomy andanatomic position of disc herniations.

J Spinal Disord. Vol. 9. No. 3. 1996

250 B. M. KNOP-JERGAS ETAL

discectomy.This has to be considered, when a decisionfor a surgical intervention is made. Other surgical andnonsurgical treatment options have to be taken into account to prevent unsatisfactory postoperative results.

REFERENCES

1. Hirabayashi S, Kumano K, Ogawa Y, Aota Y, Maehiro S: Mi-crodiscectomy and second operation for lumbar disc hemia-tion. Spine 18:2206-2211, 1993.

2. Mcguire R, Amundson G: The outcome of surgically treated

J Spinal Disord, Vol. 9, No. 3. 1996

of L4/5 central dischemiation. J BoneJoint Surg[Br] Suppl74:280,1992.

3. Mochida J, Toh E, Nishimura K, Nomura T, Arima T: Percutaneous nucleotomy in lumbar disc hemiation. Spine 18:2212-2217,1993.

4. NinomiyaM, MuroT: Pathoanatomyof liunbardisc hemiationas demonstrated bycomputed tomography/discography. Spine17:1316-1322, 1992.

5. Tibreval S, Pearcy M, Portek 1,SpiveyJ: A prospective studyof lumbar spinal movements before andafterdiscectomy usingbiplanar radiography. 5p/«e 10:455-460, 1985.

6. WebsterF, SmileyD: Evaluation of an operativeseriesof lumbar-disc hemiations.J BoneJoint Surg [Am]39:688,1957.