Posterolateral percutaneous endoscopic lumbar foraminotomy, with instruments or laser, for foraminal or lateral exit zone stenosis

Purpose

Our purpose was to determine the efficacy of posterolateral percutaneous endoscopic lumbar foraminotomy for foraminal or lateral exit zone stenosis of the last lumbar levels in the awake patient, and to discuss the indications which are modified since the advent of laser Holmium YAG of third generation.

Osteoligamentous foraminoplasties or foraminotomies are a usual part of conventional surgery of an osteoarthritic spine, as described Farfan and Kirkaldy-Willis. It is easy to conceive analogue procedures by an endoscopic transforaminal way, through a working channel, by the use of trephines or a motorised reamer. These 2 techniques have to be done without direct vision of the working tool, the lonely control being radioscopic AP and/or lateral picture.

The advent of endoscopes with multiple channels was a progress, permitting a direct vision. It authorized the passage of a laser fiber and the direct control of the laser shot. The lateral shot realized another technical improvement and made the Osteoligamentous enlargement of the foramen. There were two systems to get a lateral shot: the first system, with mirror, reflected perpendicularly the laser beam to the foramen walls; the other system was a curved sheath with memory form, bracing the laser fiber.

The paces to be resected for enlarging the foramen are made of the degenerative discal bulging in the antero-inferior part of the foramen, the anterior capsule of the zygapophyses and the adjacent thickened ligamentum flavum, the osseous tissue of the anterior wall of the homolateral posterior articular zygapophysis, osteoarthritic calcifications of discal or capsular origin, and the osteophytes.

Material and methods

Our technique of endoscopic foraminotomy is done in the surgical theatre, under local anaesthesia and neuroleptanalgesia, on lateral position, under C arm control. The approach is calculated between 10 and 20 centimetres of the midline, depending of patient weight, so that you penetrate at 30° of the coronal plane in the inferior part of the foramen, avoiding the exiting root. The marking on the patient skin of the aimed foramen projection, AP and lateral, permits to choose the best cutaneous penetration point.

A first 18G needle is followed by a 22G coaxial needle for testing the sensibility of the disc to the injection of pressured liquid and to make eventually a discography with iodine and indigocarmin. When you have retrieved the 22 G needle, a small Kirschner wire in passed through the first 18G needle. It will guide the dilation tubes. They are passed progressively, until the 7 mm tube with oblique extremity. Its longer side will be positioned to protect the exiting root.

The motorized reamer of Kambin, with suction, at the beginning of our series, and now the trephines, abrade the osteoligamentous wall, which is narrowing the posterior part of the foramen, and then the laser Holmium-YAG, curved for side fire, fragments the zygapophyses. Larger tools can be progressively passed in the inferior part of the foramen, with protection of the exiting root, which is staying in the subpedicular groove, until sufficient enlargement of the foramen.

Ablation with forceps, trephine, laser, of the other stenosing elements, osteophytes, degenerative discal bulging or hernia, and calcifications, will complete the decompression.

Discectomy is associated if needed.

T the end of the procedure, you verify the exiting root, the dura mater or its epidural fat and the traversing root, their good mobility and the absence of all compressing factor.

All patients got a check up: standard static and dynamic radiographies, TDM, RMI, and where clinically examined before and after operation.

Inclusion criteria's of the patients are: lomboradiculalgia with well localised radiculalgia, picture of foraminal stenosis by hypertrophic posterior zygapophyses, with or without discal hernia, failure of conservative treatment. Exclusion criteria's were: segmental instability, spondylolisthésis with isthmic lysis, painless motor deficiency, or cauda equine syndrome.

All patients of this series had an osteoligamentous foraminoplasty, or foraminotomy, which took off a part of the posterior osseous wall of the foramen, made of the superior zygapophysis of the underlying vertebra.

Since May 1996, we had 76 foraminotomies for foraminal stenosis on 62 patients. Mean age was 52 (26 to 83), sex ratio is 27/35. L5S1 level was operated 26 times, L4L5 20 times, L3L4 5 times. Two levels 8 times, 3 levels 3 times. Procedures were achieved 35 times on the right side, and 27 times on the left.

On these 76 levels, we had 14 very narrow osseous stenosis by hypertrophy of articular zygapophyses (fig 1). Of these 14, 11 are associated with a moderated paramedian discal bulging, 1 with a foraminal hernia, and 2 with a major discoostephytic hernia (fig. 2 and 3); 62 narrow foraminal stenosis (9 associated with a foraminal hernia, and 33 with a paramedian hernia, whose 3 presented a migration of more than 6 millimetres). Two patients suffered of a fibrosis secondary to a previous open surgery.

Comorbidity was important for 15 patients. Seven suffered of neurological localized disorders. Among these 7, 6 because a mechanical compression (3 quadricipital amyotrophies, 3 paresis of tibialis anterior and extensor proprius), and 1 because of associated sequels of zona. Three patients had general neurological disorder: one Parkinson disease, one multiple sclerosis, one by hemiplegia by brain vascular stroke. Five patients entered in the general comorbidity frame: we note insulin dependant diabetes mellitus, one coronaritis under anticoagulation, and two depressive syndromes.

In the OP room, the patient was installed 24 times prone, 38 times in lateral position.

The foraminotomy technique used different instruments : 24 patients had motorized reamer (fig 4 and 5), 20 had trephine alone particularly pressed, 18 the Holmium YAG laser of third generation with a memory form curved extremity, and variable parameters (pulse duration of 650µs, 15 Hertz, 23 Watts, 1.5 Joules/pulse), by completing osseous fragmentation with a trephine.

Mean follow up of clinical examination in surgeon's office was 18.5 (6 to 84) months

Macnab criteria's were put down during visit

Results

There was no conversion from endoscopic to open procedure

Complications were: transient quadriceps paresis: 1, temporary dysesthesia: 5, thrombophlebitis: 1, pulmonary embolism: 1

On 62 procedures, 11 were too recent, 1 was lost of view. We count 16 (32%) very good results, 21 (42%) good results, 6 (12%) fair, and 7 (14%) failures. In the 6 fair results, 2 patients had a second procedure for treatment of remaining lumbalgia to complete the relief of radicular pain obtained by the foraminotomy: one surgical treatment of associated central stenosis, one arthrodesis. Among the 7 failures, 3 necessitated a subsequent arthrodesis. Globally, it makes 86% of improved patients, and 14% failures.

The motor disorders ( 3 quadriceps paresis, 3 incomplete foot drops) have all recovered with a normal strength.

Discussion

The for amen L5S1 is most frequently wounded for several facts: shift of L5 root nearer of horizontal (40° instead of 60°), greater length of the foramen, occupation of 30 to 40% of foraminal section area (instead of 20% at the other levels), weight of 60% of body weight on the corresponding tripod.

Our technique improves the procedures of foraminotomy: its very low morbidity, its efficiency enlarges the indications in skilled hands. Aged and weak patients, for whom a general anesthesia in prone position would be contra-indicated, patients under anticoagulation and/or with heavy comorbidity for whom the indications for open surgery would be a borderline indication, are the first beneficiaries.

The recent technique, with the laser Holmium-Yttrium Aluminium Garnet of third generation, has the advantage to fragment the bone with the lowest energetic parameters, so as to minimize the risk of radicular wound, because of two particular properties: very weak thermal dissipation, and minimal depth of shot, 50 µ, on one nerve.

Th. Hoogland made systematically in a transforaminal approach for discal hernia a foraminoplasty by osteoligamentous abrasion, blindly, with a trephine, controlled with his endoscope.

Other surgeons used different lasers and tools: M. Knight (5) and A. Yeung (6) had a single use "reflecting mirror" which dissipated the laser beam and required more energy.

Y. Ahn and S.H. Lee and W.M. Park (1), in a technical note showing the feasability at the level L5S1 of the PELD (Posterolateral Endoscopic Laser Discectomy), published 12 L5S1 foraminotomies with ten good results.

J.C. Chiu used multiple techniques used all new technologies (3).

G.D. Casper (2), in a preliminary revue of 21 patients, who had a laser foraminotomy for foraminal stenosis (ELF), counted 75% of success after 2 years. On 5 failures, 3 had open decompression, and 2 were medically treated.

Conclusions

The indication for endoscopic foraminotomy has to be considered for all isolated and well localised foraminal stenosis, especially in weak patients with high comorbidity, where the open surgery in supine position is contra-indicated.

Third generation Holmium-YAG laser and its reusable tool for side fire is a promising treatment for the discal, ligamentous and particularly osseous component of foraminal stenosis under direct vision, with optimized energetic capacity and minimum risk of radicular wounds.