Percutaneous laser nucleotomy for lumbar disc herniation: Preliminary report of early results and MRI findings

J Orthop Sci (1996) 1:102-112

~

Journalof

th0paedic Science The lapaneseOrthopaedicAssociation

Original articles Percutaneous laser nucleotomy for lumbar disc herniation: Preliminary report of early results and MRI findings RIYA KOSAKA1, TOSHINOBU O N OMURA I, TAKUMI YONEZAWA:~, YOSHINORI ICHIMURA1, and K o u IMACHI2 1Department of Orthopedic Surgery, Osaka Medical College, 2-7 Daigaku-machi, Takatsuki, Osaka 569, Japan 2Department of Medical Electronics, Faculty of Medicine, University of Tokyo, 3-1, Hongo 7-chome, Bunkyo-ku, Tokyo 113, Japan

Abstract: Early therapeutic results and magnetic resonance imaging (MRI) findings were serially evaluated for 34 consecutive patients with lumbar disc herniation treated by percutaneous laser nucleotomy (PLN), a minimally invasive technique for reducing intradiscal pressure, in which a neodymium:yttrium-aluminum-garnet (Nd:YAG) laser was used. At the mean follow up 13.8 months after PLN, successful results were obtained in 20 patients (58.8%). No serious complications were encountered. In patients with contained disc herniation, the improvement rate was significantly higher than that in patients with non-contained disc herniation (P < 0.05). Sagittal magnetic resonance (MR) images obtained during the time sequence after PLN demonstrated a relationship between MR signal intensity patterns and clinical recovery. No measurable change in the size of the herniated mass was confirmed on axial images immediately after PLN, while, in contrast, reduced signal intensity inside the disc was observed in 12 of 20 patients with successful results in the early postoperative period. Postoperative T2-weighted MRI can be used to predict the prognosis of patients treated with PLN. Key words: lumbar disc herniation, intradiscal therapy, laser, magnetic resonance imaging

Introduction

For symptomatic lumbar disc herniation, a variety of percutaneous procedures, t e r m e d "intradiscal therapy,"

Offprint requests to: R. Kosaka Received for publication on July 5, 1995; accepted on Oct. 23, 1995 This work was presented, in part, at the 68th Annual Meeting of the Japanese Orthopaedic Association, Y o k o h a m a , 9-11 April, 1995

have b e e n developed as alternatives to open surgery. The concept of intradiscal therapy for decompression of a herniated disc was first described by Smith in 1963 as chemonucleolysis. 21 Chemonucleolysis with chymopapain, however, has been used less often in recent years because of potential complications? Instead, percutaneous nucleotomy with manual instruments was introduced by Hijikata et al. in 1975. 7 A n automated cutter and suction system developed by Onik et al. 15 in 1985 o p e n e d a new era in the application of this less invasive technique, and an increasing n u m b e r of reports involving percutaneous nucleotomy have b e e n published, with satisfactory results being seen in up to 88% of patients. ~s Laser techniques were introduced to this field in the 1980s. s Several types of lasers and devices have been developed. 6,x4,2~ Since 1986, we have studied a new intradiscal therapy in which a neodymi u m : yttrium-aluminum-garnet ( N d : Y A G ) laser is used, and we have developed a new technique called percutaneous laser nucleotomy (PLN).23 The N d : Y A G laser has a wavelength of 1064nm. Energy at this wavelength, in the near infrared spectrum, is minimally absorbed by water and is efficient for coagulation. ~ In addition, energy from the N d : Y A G laser can be transmitted via a flexible fiberoptic system. We considered these characteristics of the N d : Y A G laser suitable for percutaneous removal of the disc material, and began clinical application of this technique, using newly developed devices, in February 1992. In the current study, we reviewed the early results of PLN in 34 consecutive patients with lumbar disc herniation, and we also investigated the serial magnetic resonance imaging ( M R I ) findings after PLN to clarify the relationship between clinical outcome and the morphological changes in the disc.

R. Kosaka et al.: Percutaneous laser nucleotomy Materials and methods

Criteria Indications were restricted to patients who failed to respond to at least 6 weeks of conservative therapy, including activity limitation, bracing, pelvic traction, and/or medication. All patients had sciatica with or without low-back pain. Straight leg raising was restricted to less than 70 degrees because of buttock or leg pain in each patient. The neurological impairment (sensory deficits, reflex abnormalities, and/or m o t o r weakness) in all patients was consistent with the level of disc abnormality, determined using preoperative myelography, discography, and MRI. If the symptomatic level of the lesion was not determined in patients with multi-level disc herniations, provocative testing with discography and/or selective root block was employed. In this study, patients with any evidence of sequestrated disc, canal stenosis, or segmental instability on roentgenograms or MRI were excluded. Patients with signs of severe neurological deficits or cauda equina syndrome and patients with a history of back surgery were also excluded. Informed consent was given by each patient.

Fig. 1. Devices for percutaneous laser nucleotomy. All devices were manufactured by Osada Electric Co. (Tokyo, Japan). The instruments consist of the following: (1) an outer needle (17 gauge, 1.5mm in diameter • 150ram in length); (2) an inner needle (22 gauge, 0.6ram in diameter • 150mm in length), which includes a bare optical fiber 200 btm in diameter; and (3) a guide pin (1.2 mm in diameter • 250 mm in length). The specific feature of our devices is the double-lumen structure. The suction channel is connected to the inner needle

103

Patients The subjects comprised 34 patients who underwent PLN for symptomatic lumbar disc herniation between February 1992 and July 1994. Age at PLN ranged from 14 to 62 years (mean, 26.8 years). There were 21 men and 13 women. The period from the onset of low-back pain and/or leg pain to PLN ranged from 6 weeks to 7 years (mean, 13.8 months). T h e level of herniation was L 4 - L 5 in 19 patients, L5-L6 in 2 patients, and L 5 - $ 1 in 13 patients. The type of disc herniation, based on findings of discography, computed tomography (CT)discography and MRI, and according to Macnab and McCulloch's classification, 12 were: protrusion in 6 patients, subligamentous extrusion in 16, and transligamentous extrusion in 12. Protrusion-type disc herniation was defined as a contained disc, while the other types were defined as non-contained discs (extrusion).

Procedures All devices for PLN were developed by the authors and manufactured by Osada Electric Co. (Tokyo, Japan) (Fig. 1). The procedures are: (1) The patient is placed in

(arrowhead) and allows vaporization products to escape simultaneously during irradiation through the inner space of the double-lumen, thereby preventing excessive build-up of heat and pressure at the needle tip and decreasing the scattering of the laser beam for uniform laser irradiation. The outer needle has a surface coating of Teflon (du Pont, Wilmington, Del.) to protect the surrounding tissue from thermal damage

104 a prone position on an operating table. After a subcutaneous injection of 1% lidocaine is given, a guide pin is inserted into the center of the disc, under biplanar fluoroscopic guidance. The insertion is performed through a posterolateral route, as in lumbar discograp h y . (2) Once the pin is positioned in the disc, a 17-gauge outer needle is inserted over the guide pin into the disc. The guide pin is then removed. (3) After power calibration of the laser to produce an output of 10W at the fiber tip, an inner needle, including a 200-~,m bare fiber, is inserted into the disc space through the outer needle, and 0.3-s pulses of the N d : Y A G laser are applied repeatedly at 1.7-s intervals until the total irradiation energy reaches approximately 1500J for each disc. This amount of laser energy has been proven to achieve sufficient ablation of the nucleus pulposus. 23 Irradiated disc tissues are removed by suction through the double-lumen channel. (4) During the procedure, the laser fiber is frequently withdrawn and the intradiscal pressure is measured, using a needle-tip type pressure transducer (Tokai Rika Electric Co., Aichi, Japan). This device enables intraoperative measurem e n t of intradiscal pressure. Comparative changes in pressure before and after laser irradiation can be examined, indicating that an adequate volume of disc material has been vaporized with thermal energy. Irradiation is completed when adequate decompression of intradiscal pressure is attained. (5) The inner and outer needles are r e m o v e d together, and a small bandage is applied. After bed rest for a day, patients are allowed to walk with a soft brace, which is employed for 6 - 8 weeks. They are discharged several days after PLN, and allowed to resume back muscle exercise 1 or 2 months later.

R. Kosaka et al.: Percutaneous laser nucleotomy Table L The scoring system proposed by the Japanese Orthopaedic Associations for the assessment of treatment for lowback pain (JOA score) with some modifications 1. Symptoms (9 points) A. Low back pain None (3), occasional mild pain (2), frequent mild or occasional severe pain (1), frequent or continuous severe pain (0) B. Leg pain and/or tingling None (3), occasional slight symptoms (2), frequent slight or occasional severe symptoms (1), frequent or continuous severe symptoms (0) C. Gait Normal (3), able to walk farther than 500m, although this results in pain, tingling, and/or muscle weakness (2), unable to walk farther than 500m because of leg pain, and/or muscle weakness (1), unable to walk farther than 100m because of leg pain, and/or muscle weakness (0) 2. Clinical signs (6 points) A. Straight-leg raising test (including tight hamstrings) Normal (2), 30-70 degrees (1), less than 30 degrees

(0) B. Sensory disturbance None (2), slight disturbance (not subjective) (l), marked disturbance (0) C. Motor disturbance (MMT) Normal (grade 5) (2), slight weakness (grade 4) (1), marked weakness (grade 3-0) (0) Improvement rate =

Postoperative JOA score - Preoperative JOA score

• 100 (%). 15 - Preoperative JOA score MMT, manual muscle testing; grade 5, normal, 100%; grade 4, good, 75%; grade 3, fair, 50%; grade 2, poor, 25%; grade 1, trace, 10%; grade 0, 0%.

J O A score, and MRI findings, were compared in the successful group and the unsuccessful group.

MRI study Clinical evaluation T h e patients were examined immediately after PLN, and i week and 1, 3, and 6 months after the procedure, and every 6 months thereafter. The therapeutic outcome on serial follow up was evaluated using the scoring system for low-back pain proposed by the Japanese Orthopaedic Association 8 ( J O A score) with some modifications. With this system, there is a maximum of 15 points, consisting of points for symptoms and clinical signs (Table 1). The improvement rate in the J O A score was calculated by the formula shown in Table 1. The final response to treatment was judged by Macnab's criteria, lj and excellent or good results were defined as successful. For patients who received subsequent open surgery after PLN, final follow up examinations were performed the day before open surgery. The mean follow up period was 13.8 months. Several clinical variables; age, gender, duration of symptoms, preoperative

MRI was performed on a 1.5 Tesla General Electric Medical Systems Signa Unit (General Electric, Milwaukee, Wis.) with a surface coil for spine imaging. Images were taken on the sagittal and axial planes with a 6-ram slice thickness. Tl-weighted images (pulse repetition time [TR], 500ms; echo time [TEl, 20ms), T2weighted images (TR, 2000; TE, 80ms), and proton-density images (TR, 2000; TE, 30ms) were obtained, using the spin echo technique. The matrix elements numbered 256 • 192. We analyzed the morphological changes in irradiated discs On axial Ti-weighted images. The anteroposterior height of the herniated mass from the posterior margin of the disc and sagittal diameter of the spinal canal were measured on t h e axial plane, and the percentage of the hernia height to canal diameter was defined as the hernia to canal ratio (HCR). The signal intensity in the central area of the disc was evaluated on sagittal T2-

R. Kosaka et al.: Percutaneous laser nucleotomy weighted images. The hydration status of the disc was classified, according to Schneiderman's classification, 19 as: normal, intermediate, marked, and absent (Fig. 2). All patients underwent MRI within 1 month prior to PLN and within 1 month (2-4 weeks) after PLN. For patients who did not undergo subsequent open surgery, M R I was performed serially 3, 6, and 12 months after the PLN procedure. Overall, 130 images were available for evaluation; 34 images before PLN, 34 within 1 month postoperatively, 25 after 3 months, 22 after 6 months, and 15 after i year. The relationship between the improvement rate in the J O A score and postoperative changes in MRI parameters was investigated.

Statistical analysis Success rates and other qualitative data were compared, using the ~2 test for independence or Fisher's exact probability test. The mean values, with their SD, of

105 several clinical parameters were compared in the successful and unsuccessful groups, using Student's t-test or the Mann Whitney test, at a 5 % level of significance.

Results

Clinical evaluation The total amount of applied energy per disc was 1440J, on average. Approximately 40-50 rain was required to complete the laser irradiation at the L4-5 disc level, and the entire procedure was completed in 60min. According to Macnab's criteria, 11the final outcome of PLN was excellent in 6 patients, good in 14, fair in 5, and poor in 9. Successful outcome was obtained in 20 patients (58.8%). The preoperative J O A scores were 9.7 _+ 2.2 points (range, 4-13), and the postoperative scores 12.2 _+ 2.2 points (range, 8-15). The improvement rate in the J O A score was 47.4%, on average. The average

d Fig. 2a-d. Classification of preoperative hydration status of the herniated disc (Schneiderman, 1987) 19.a Normal; normal height and signal intensity, b Intermediate; speckled pattern or heterogeneously decreased signal intensity, c Marked; diffuse loss of signal, d Absent; signal void

106

R. Kosaka et al.: Percutaneous laser nucleotomy

J O A score increased significantly in 34 patients after P L N (P < 0.0001). O f 20 patients judged as successful, 13 showed gradual relief of s y m p t o m s beginning a few days after PLN. In 7 patients, rapid relief of symptoms was achieved during or immediately after PLN. Fourteen patients (43.3%) failed to respond immediately to treatm e n t or experienced only minimal relief of pain. Eight patients with fair or p o o r results underwent subsequent partial laminectomy to r e m o v e the herniation 2-3 weeks after PLN. In 6 (75.0%) of these patients, perforation of the posterior longitudinal ligament with extruded disc herniation was confirmed. Three patients were treated with a smaller amount of applied laser energy (500-700J/disc) because of local pain at the insertion point. These three patients showed no significant recovery of symptoms after P L N and the outcomes were judged as unsuccessful. No serious complications were encountered in any patients. We studied the relationships between therapeutic outcome and several clinical parameters; gender, age, preoperative J O A score, the period f r o m onset of symp-

toms to PLN, and total irradiated energy. However, no significant difference was observed between the successful and unsuccessful groups in any factors (Table 2). The analysis of preoperative M R I characteristics also demonstrated no significant difference between the two groups (Table 3). With respect to the type of disc herniation, the P L N technique was effective in 83.3% (5/6) of patients with contained discs and in only 53.6% (15/28) of those with non-contained discs, but no significant association was found between clinical results and the type of disc herniation. The final i m p r o v e m e n t rate in the J O A score was significantly higher in patients with contained disc (average, 72.6%) than that in patients with noncontained disc (average, 42.0%) (P < 0.05). Hernia to canal ratio

The H C R was 29.2% on average (range, 13.8%-55.8%) before PLN, and 28.4% (range, 11.4%-57.6%) within 1 m o n t h after PLN. There was no significant difference between these findings. T h e imagings immediately after

Table 2. Clinical characteristics in successful and unsuccessful groups Macnab's criteria 11 Factor

Excellent/Good (n = 20)

Fair/Poor (n -- 14)

Significance

6/14 30.4 +- 13.8 16.4 + 18.6 9.9 + 2.4 1473 + 359

6/8 21.7 +_ 5.0 10.1 _+ 7.5 9.5 _+ 1.8 1383 +_ 574

NS NS NS NS NS

Gender: Men/Women (no of patients) Age at PLN (years) Duration of symptoms (months) Preoperative JOA score (points) Irradiated energy (J) Mean • SD. NS, not significant (P > 0.05).

Table 3. Preoperative MRI characteristics in successful and unsuccessful groups Macnab's criteria H Factor Herniation level L4-L5 L5-L6 L5-$1 Herniation type" Protrusion Subligamentous extrusion Transligamentous extrusion Herniation size b <25% ==_25% Disc signal c grade 1 2 3 4

Excellent/Good (n = 20)

Fair/Poor (n = 14)

Significance

11 2 7

8 0 6

NS

5 10 5 6 14 0 15 5 0

1 6 7 6 8 2 11 1 0

NS, not significant (P > 0.05). "Determined based on preoperative discography and computed tomography-discography. bHernia to canal ratio (%) measured on axial magnetic resonance (MR) images. cSchneiderman's classification.19

NS NS NS

R. Kosaka et al.: Percutaneous laser nucleotomy P L N demonstrated no measurable changes in size (greater than 5% change in H C R ) in 30 (88.2%) of the patients. Three patients showed reduction of the herniated mass (less than 10% change in H C R ) , and one showed a slight increase (less than 10% change in HCR). T h e r e was no change in the height of the disc on M R ! in any patients. For 15 patients who underwent all M R I examinations (preoperatively and 1, 3, 6, and 12 months postoperatively), serial changes in disc morphology were evaluated. These 15 patients included 11 judged as successful and 4 as unsuccessful. Postoperative MRI showed no significant difference in the size of the herniated mass until 6 months after PLN; however, the H C R after 12 months was significantly reduced in comparison with the preoperative value (P < 0.05) (Fig. 3). In contrast, the 11 patients with successful results continued to show clinical improvement of symptoms in the early postoperative period, irrespective of the lack of morphological changes in the discs. The clinical results were also examined in relation to changes in H C R between preoperative and postoperative measurements. On serial observation of 34 patients, 10 patients showed a decrease in H C R greater than 5% on the final MRI, and 8 of the 10 patients were judged to have successful results on the final follow up examina-

107 tion. All three patients who showed shrinkage greater than 10% demonstrated successful results (Fig. 4). However, there was no correlation between the change in H C R and clinical results.

Signal intensity Before PLN, signal intensity in 34 discs was grade 1 in 2 discs (5.9%), grade 2 in 26 (76.5%), grade 3 in 6 (17.6%), and grade 4 in 0 (0%). Within 1 month after PLN, 9 discs (8 of grade 2 and 1 of grade 3) showed a one-grade decrease compared with the preoperative signal. Three months after PLN, although only 25 images were available for this study, an additional 6 patients showed a one- or two-grade decrease, and the proportion of grade 3 and grade 4 discs increased to 52.0% and 16.0%, respectively (Table 4). W e studied the relationship between final outcome of PLN and signal reduction on MRI retrospectively in serial follow up. O f 34 patients, 15 showed signal reduction of more than one grade 1 or 3 months after PLN. Twelve Of the 15 patients with decreased intensity were classified as successful and only 3 as unsuccessful. Of the remaining 19 patients, who demonstrated no decreased intensity until 3 months postoperatively, in contrast, 8 were classified as successful. The mean improvement

Hernia to Canal Ratio (%) 3432I

30282624

N=15

22-; i

before 3 mos. PLN after PLN < 1 too. after PLN

6 mos. after PLN

Fig. 3. Serial changes in the hernia to canal ratio (HCR) on sagittal images over the course of 1 year after PLN in 15 patients. In 15 patients who underwent postoperative magnetic resonance imaging (MRI) four times, the preoperative ratio was 31.2 _+ 10.0% (mean _+SD). Postoperative HCR was 30.3 _+ 10.2%, 30.6 +_ 9.7%, 30.7 + 9.2%, and 26.1 § 8.4%, respectively. There was no significant difference in HCR until 6 months postoperatively. The HCR after 12 months was sig-

i

12 mos. after PLN

nificantly reduced in comparison with preoperative HCR (Wilcoxon signed-rank test, P < 0.05). The Japanese Orthopaedic Association (JOA) score ~ in the 15 patients at each follow up was 9.5 + 2.5 points preoperatively, and 11.6 _+ 1.7, 12.6 -+ 1.6, 12.5 -+ 1.4, and 12.5 +_ 1.6 points postoperatively. Significant improvement in the JOA score was attained in the early postoperative period, and the outcome was maintained over the course of 1 year. Mos, Months

108

R. Kosaka et al.: Percutaneous laser nucleotomy

Fig. 4a-e. Tl-weighted axial images in a 15-year-old woman with left sciatica, a Preoperative axial scan demonstrates a transligamentous extrusion type disc herniation at L5-$1 (arrow). The HCR was 56%. b Three weeks after percutaneous laser nucleotomy (PLN). Note a slight reduction in the herniated mass (arrow). e One year after PLN. Significant reduction of L5-$1 disc herniation was demonstrated (arrow). The HCR 1 year after PLN was 25%. The patient experienced gradual pain relief over the 3 months after the procedures, attaining a 62.5% recovery rate in the JOA score at follow up 2 years after PLN

Table 4. Serial changes in signal intensity

Number of discs examined Before PLN <1 Month 3 Months 6 Months 12 Months Total

34 34 25 22 15 130

Grade of signal intensity 19 2 3

1 Normal 5.9% 5.9% 0% 0% 0%

(2) (2) (0) (0) (0)

Intermediate 76.5% 52.9% 32.0% 27.3% 13.3%

Marked

(26) 17.6% (6) (18) 38.2% (13) (8) " 52.0% (13) (6) 63.6% (14) (2) 66.7% (10)

Absent

0% (0) 2.9% (1) 16.0% (4) 9.1% (2) 20.0% (3)

Figures in parentheses indicate number of discs. PLN, Percutaneous laser nucleotomy.

rate in the J O A score in the positive degradation group was 65.4%, and this value was significantly higher than that in the negative degradation group, 31.9% (P < 0.05) (Fig. 5). T h e r e was a significant correlation between the reduced signal intensity up to 3 months after P L N and the final clinical outcome (P < 0.05) (Table 5). For patients with unsuccessful results, measurable changes were not detected in either H C R or the grade of signal throughout the follow up period. Two patients

experienced an increase of low-back pain after PLN; the pain was reduced spontaneously during the following 3 months. One of the two patients d e m o n s t r a t e d postoperative signal change in the vertebral b o d y m a r r o w adjacent to the end plate on MRI. This signal change also recovered spontaneously after 3 months (Fig. 6). N o n e of the patients followed by M R I showed increased signal intensity in comparison with that shown before PLN.

R. Kosaka et al.: Percutaneous laser nucleotomy

109

Table 5. Signal degrgdation on serial MRIs in successful and unsuccessful groups (number of discs) Signal degradation on MRI Positive Postoperative period Up to 1Month 3Months 6Months 12Months

Negative

Successful

Unsuccessful

Successful

Unsuccessful

P value

7 12 12 13

2 3 5 5

13 8 8 7

12 11 9 9

0.25 <0.05 0.16 0.13

For patients who did not receive repeated postoperative MRI, degradation of signal intensity was judged based on findings of the latest MRI after PLN.

a

b

c

Fig. 5a-c. T2-weighted sagittal images in a 34-year-old man with left sciatica, a Preoperative sagittal scan shows protruded disc herniation at L5-6. A slight signal loss of the disc was demonstrated, indicating mild degeneration, b Three weeks after PLN; speckled decrease of disc signal was detected, c Six months after PLN; the signal intensity of the L5-L6 disc was

further decreased. Symptoms recovered immediately after PLN and further improved over time, with the patient attaining a 75.5% recovery rate on follow up 1 year after PLN. There were no measurable changes in the size of the herniated mass on postoperative axial images

Discussion

surgical invasion is minimal and there is less soft tissue damage. Postoperative adhesions around the spinal nerve roots or the caudal sac can be avoided. Stability of the spinal segment can also be preserved. The procedure requires only a few days of postoperative hospitalization, or it can even be done on an outpatient basis, thereby decreasing total medical cost. In our devices for PLN, in addition, there are m a n y advantages over other percutaneous instruments: (1) the external needle is flexible and has a smaller diameter (1.5 m m ) than that used in previous studies. 7,9,15,16,18 The smaller diameter allows a less invasive approach and easier access to the L 5 - $ 1 interspace. (2) The P L N method accomplishes thermal nucleolysis without the risk of anaphylaxis, unlike chemonucleolysis with

A f t e r the first clinical report of percutaneous removal of herniated nucleus pulposus with the aid of a laser syst e m in 1987, 5 a considerable n u m b e r of clinical and experimental studies on the use of lasers was enthusiastically conducted. 6,14,2~Despite the increasing n u m b e r of clinical applications in recent years, the mechanism of action involved in the pain relief obtained after P L N remains hypothetical and there has b e e n little literature comparing preoperative and postoperative imaging of discs treated by PLN. Percutaneous removal of lumbar discs has recently b e e n employed as an alternative to open procedures. Because it can be p e r f o r m e d under local anesthesia,

110

Fig. 6 a - e . TR 2000ms/TE 80ms, and TR 500ms/TE 20ms sagittal images in a 34-year-old woman with left sciatica, a Preoperative T2-weighted sagittal scan shows protruded disc herniation at L5-S1. No specific change is observed in the $1 body. b Postoperative T2-weighted scan obtained 3 weeks after PLN shows increased signal intensity in the S1 vertebral body marrow adjacent to the end plates (arrow). Note the moderately decreased signal in the L5-$1 disc. e Postoperative Tt-weighted scan demonstrates a decreased signal in the

R. Kosaka et al.: Percutaneous laser nucleotomy

same region (arrow). d Three months after PLN. Abnormal marrow signal has disappeared, e One year after PLN. Note marked degradation of disc signal in L5-S1. Body marrow signal of $1 seems to be normal. This patient experienced a transient increase in low-back pain immediately after PLN; the pain spontaneously recovered to the preoperative condition during the next 3 months. She was judged unsuccessful at the final examination 1 year after PLN

R. Kosaka et al.: Percutaneous laser nucleotomy chymopapain, and repetitive treatment is possible if necessary. (3) Needle insertion is conducted in a simple manner, the entire procedure is easy to perform, and there is a short duration of X-ray exposure (approximately 15 min). There were no serious complications in any patients in the current series. No patient showed narrowing of disc height of more than 2 mm and/or segmental instability of the irradiated disc after PLN on roentgenographic examinations. We encountered one patient with transiently increased low-back pain after PLN. In this patient, postoperative MRI showed abnormal signal intensity in the vertebral body marrow adjacent to the end plates. Although the pattern of changes on MR signal, i.e., the decreased intensity on Tl-weighted images and the increased intensity on T2-weighted images, was similar t o findings in vertebral osteomyelitis, there were no laboratory data to indicate the presence of infection in this patient. This finding on MRI seems to correspond to the Type 1 degenerative changes described by Modic et al., ~3 which show vascularized fibrous tissue histopathologically. We speculate that the abnormal intensity in marrow resulted from the thermal effect of Nd:YAG laser energy. In this patient, because of a technical problem, placement of the needle was too close to the end plate of the $1. Our previous experimental study, using therm0graphy,23 documented the safety of this method when needle insertion was correctly performed and an adequate amount of energy was applied; therefore, to achieve good results with PLN, the importance of careful technique in placing the needle and appropriate setting up of the irradiation conditions is strongly emphasized. Although the mechanism of action involved in pain relief after PLN is still unclear, we speculate that the intradiscal pressure is reduced after PLN. 23This mechanism of action in PLN would be fundamentally similar to that operating in percutaneous nucleotomy (PN). 7 In the present study, 88% of herniated discs showed no measurable shrinkage immediately after PLN; in contrast, 15 patients showed a rapid decrease in disc signal intensity in the early postoperative period up to 3 months after PLN, and such a finding of signal intensity appeared to be closely related to clinical improvement. The successful group could be characterized as showing an early reduction in signal intensity in the central area of the disc on T2-weighted images. The decrease in signal intensity most likely reflects dehydration of the disc tissue resulting from thermal coagulation and subsequent scarring. Dehydration of the central area of the disc should result in a reduction of intradiscal pressure, due to a bulk-modulus effect,22

111 thus diminishing the inflammatory interface around the disc and nerve roots. We speculate that the rapid degradation of signal intensity after PLN is one of the characteristic MRI findings specific to successful patients, in contrast to findings in the unsuccessful group, and we therefore suggest that T2-weighted sagittal MRI can be used to predict the prognosis of patients treated with PLN. On follow up examination 1 year after PLN, a significant reduction in the mean HCR was observed in 15 patients, although no significant correlation with clinical improvement was observed. Our preliminary experimental study with rabbits revealed that the tissue of the intradiscal space was vaporized by laser irradiation and was gradually replaced by cartilaginous fibrous tissue, with a proliferation of cartilaginous cells and fibrous tissue, 6-8 weeks after treatment. 23A possible explanation for the reduction in size is that proliferation of cartilaginous fibrous tissue may lead to contraction of the central area of the disc as a process of scar formation, thereby causing the peripheral mass to reduce in size after 1 year. The phenomenon of shrinkage of the herniated mass was previously reported with conventional intradiscal therapies, 2,1~ and in the natural history of lumbar disc herniation. 4a7 Therefore, a controlled follow up study is required to evaluate the true mechanism responsible for the shrinkage of the herniated mass after PLN. The reported success rate of PN varies within a range of 37%-88%. 2,9,15,1~,1~ The results of the present study show that the improvement rate in patients with protrusion-type disc herniation was significantly higher than the rate in patients with subligamentous or transligamentous extrusions (P < 0.05). In 75% of the patients who failed to recover and received subsequent open exploration, perforation of the posterior longitudinal ligament with extruded disc herniation was confirmed. These observations demonstrate that the preoperative anatomical type of disc shows some relationship with the clinical results of PLN. Because of the small number of patients with protrusion-type disc herniation in the present series, further clinical investigation is warranted to determine the relationship between the anatomical appearance of the disc and the outcome of PLN. We consider, however, that the relatively low rate of success in this series (58.8%) was primarily due to the high proportion of non-contained discs. If we had limited candidates to those with contained discs, PLN would have been indicated in only 6 patients in this series, and 5 (83.3 %) of these 6 patients were judged as successful, showing a mean improvement rate in JOA score of 72.6%. In conclusion, the early series of PLN provided a relatively low rate of success. The procedure, however, is simple to perform, and is associated with fewer post-

112

operative complications than those reported in conventional intradiscal therapiesY 6 If patients are carefully selected, PLN is effective and safe, and is less invasive than conventional methods. This procedure may become a practical choice of treatment for contained lumbar disc herniation in future. Review of the preoperative and postoperative MRIs showed no measurable change in the size of the herniated mass immediately after treatment; however; the reduced signal in the disc in the early postoperative period, resulting in decompression of the nerve root, may be correlated with the relief of symptoms.

Acknowledgments. This study was supported, in part, by Grants-in-Aid for Scientific Research no. 05671238C from the Ministry of Education, Culture, and Science of Japan.

References 1. Abelow SP. Use of lasers in orthopedic surgery: Current concepts. Orthopedics 1993;16: 551-556. 2. Bernhardt M, Gurganious LR, Bloom DL, et al. Magnetic resonance imaging analysis of percutaneous discetomy: A preliminary report. Spine 1993;18: 211-217. 3. Bouillet R. Treatment of sciatica: A comparative survey of complication of surgical treatment and nucleotysis with chymopapain. Clin Orthop 1990;251 : 144-152. 4. Bush K, Cowan N, Katz DE, et al. The natural history of sciatica associated with disc pathology: A prospective study with clinical and independent radiologic follow-up. Spine 1992; 17 : 1205-1212. 5. Choy DSJ, Case RB, Fielding W, et al. Percutaneous laser nucleolysis of lumbar disks. N Engl J Med 1987;317:771772. 6. Cummings RS, Prodoehl JA, Hermantin FU, et al. Percutaneous laser discectomy using a flexible endoscope: Technical considerations. Spine: State Art Rev 1993;7 : 135-139.

R. K o s a k a et al.: P e r c u t a n e o u s laser n u c l e o t o m y 7. Hijikata S, Yamagishi M, Nakayaka T, et al. Percutaneous nucleotomy: A new treatment method for lumbar disc herniation (in Japanese). J Toden Hosp 1975;5:39-45. 8. Japanese Orthop Assoc. Assessment of treatment for low back pain. J Jpn Orthop Assoc 1986;60:909-911. 9. Kahanovitz N, Viola K, Goldstein T, et al. A multicenter analysis of percutaneous discectomy. Spine 1990;15 : 713-715. 10. Kato F, Mimatsu K, Kawakami N, et al. Serial changes observed by magnetic resonance imaging in the intervertebral disc after chemonucleolysis: A consideration of the mechanism of chemonucleolysis. Spine 1992;17: 934-939. 11. Macnab I. Negative disc exploration: An analysis of the causes of nerve-root involvement in 68 patients. J Bone J Surg 1971;53A : 891-903. 12. Macnab I, McCulloch J. Backache. 2nd ed. Baltimore: Williams and Wilkins, 1990:130-134. 13. Modic MT, Masaryk TJ, Ross JS, et al. Imaging of degenerative disk disease. Radiology 1988;168:177-186. 14. Ohnmeiss DD, Guyer RD, Hochschuler SH. Laser disc decompression: The importance of proper patient selection. Spine 1994;19: 2054-2059. 15. Onik G, Helms CA, Ginsburg L, et al. Percutaneous lumbar diskectomy using a new aspiration probe. Am J Roentgenol 1985;144 : 1137-1140. 16. Revel M, Payan C, Vallee C, et al. Automated percutaneous lumbar discectomy versus chemonucleolysis in the treatment of sciatica: A randomized multicenter trial. Spine 1993;18:1-7. 17. Saal JA, Saal JS, Herzog RJ. The natural history of lumbar intervertebral disc extrusions treated nonoperatively. Spine 1990;15:683 686. 18. Schaffer JL, Kambin P. Percutaneous posterolateral lumbar discectomy and decompression with a 6.9-mm cannula. J Bone J Surg 1991;73-A : 822-831. 19. Schneiderman G, Flannigan B, Kingston S, et al. Magnetic resonance imaging in the diagnosis of disc degeneration: Correlation with discography. Spine 1987;12:276-281. 20. Sherk HH, Rhodes A, Black J, et al. Results of percutaneous lumbar discectomy with lasers. Spine: State Art Rev 1993;7:141 149. 21. Smith L. Enzyme dissolution of the nucleus putposus in humans. J A M A 1964;187 : 137-140. 22. White A A III, Panjabi MM. Clinical biomechanics of the spine. 2nd ed. Philadelphia: JB Lippincott, 1990:446. 23. Yonezawa T, Onomura T, Kosaka R, et al. The system and procedures of percutaneous intradiscal laser nucleotomy. Spine 1990;15 : 1175-1185.