A PROSPECTIVE STUDY OF INCIDENTAL DURAL TEARS IN MICROENDOSCOPIC LUMBAR DECOMPRESSION SURGERY: INCIDENCE AND OUTCOMES

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1 A PROSPECTIVE STUDY OF INCIDENTAL DURAL TEARS IN MICROENDOSCOPIC LUMBAR DECOMPRESSION SURGERY: INCIDENCE AND OUTCOMES Takahiro Tsutsumimoto, Mutsuki Yui, Masashi Uehara, Hiroki Ohba, Hiroshi Ohta, Hidemi Kosaku, Hiromichi Misawa Spine Center, Yodakubo Hospital, Nagawa, Japan

2 Background Incidental dural tear (DT) is a bothersome complication of microendoscopic lumbar surgery because primary repair of the dura is difficult owing to the limited surgical field offered by a tubular retractor. However, the knowledge about the influence of DTs on surgical outcomes is limited.

3 Purpose To prospectively examine the incidence of DTs and their influence on the surgical outcomes of microendoscopic lumbar decompression surgery (MELD).

4 Methods We prospectively examined 641 consecutive patients who underwent MELD from January 1, 2006 to December 31, Surgical procedures: Under fluoroscopic guidance, an incision 16 mm to 18 mm long was made corresponding to the appropriate spinal level. Sequential dilation was used to allow placement of the tubular retractor (16 mm or 18 mm) (METRx lumbar endoscopic system; Medtronic Sofamor Danek, Memphis, Tennessee). In patients with radiculopathy, an ipsilateral laminotomy and removal of the ligamentum flavum was performed using a high-speed drill and a Kerrison punch under endoscopic visualisation. In those patients with disc herniation, a discectomy was performed by retracting the traversing nerve root medially, followed by removal of the herniated fragments of the disc. In patients with central lumbar canal stenosis, the tubular retractor was moved medially, so that the base of the spinous process, the contralateral lamina and the medial facet, could be undercut. The ligamentum flavum was then separated from the underlying dura and removed from both sides using a Kerrison punch and an angled curette.

5 Summary Summary of patients of patients characteristics Mean age at surgery (y) 47.9 (13 89) Gender (Female:Male) 237:404 Diagnosis (n) Lumbar disc herniation 483 Lumbar canal stenosis 107 Degenerative spondylolisthesis 42 Spondylolysis 4 Facet cyst 5 Reoperation (n) 6 Disc level (n) L L L5-S 273 L3-4 + L4-5 1 L4-5 + L5-S1 14 Surgery (n) UD 510 UD 2 26 BD 95 LF 8 UD + LF 1 BD + LF 1 UD, unilateral decompression with or without discectomy; BD, bilateral decompression from a unilateral approach; LF, lateral fenestration with or without discectomy

6 Methods Dural tear: Any disruption of dural integrity recognized during surgery was considered a DT. Visualization of the arachnoid and/or outpouching of the arachnoid associated with a loss of dural integrity was also counted as a DT irrespective of CSF leakage. The occurrence and the details, including the repair method of the DT, were recorded at the time of the surgery on a computerized research database by an attending surgeon. Radiographical and clinical evaluation: Patients were followed up for a minimum of 6 months after surgery. All patients underwent magnetic resonance imaging (MRI) 6 months after surgery. The clinical outcomes were evaluated using the Oswestry disability index (ODI) and the Japanese Orthopedic Association (JOA) scores for management of low back pain.

7 Result 1: Incidence of Dural Tears and Risk Factors The overall incidence of DTs was 5.1% (33 of 641). The mean age of these 33 patients (13 women, 20 men) was 54.3 years (range, years). The age of the patients in the group with DTs was significantly higher than that of the patients in the group with no DTs (mean age, 47.5 years; range, years) (P =.023). No statistical difference in gender was observed between the 2 groups (P =.85). No. of DTs (No. of DTs in primary MELD) Total no. of cases (Total no. of primary MELDs) Incidence (%) (Incidence in primary MELD) Diagnosis Lumbar disc herniation 22 (22) Lumbar canal stenosis Degenerative spondylolisthesis Spondylolysis Facet cyst Surgery type UD 23 (23) BD LF DT, dural tear; MELD, microendoscopic lumbar decompression; UD, unilateral decompression with or without discectomy; BD, bilateral decompression from a unilateral approach; LF, lateral fenestration with or without discectomy 483 (477) 563 (557) 4.6 (4.6) 4.1 (4.1)

8 Results of univariate logistic regression analysis of risk for dural tears Variable OR 95% CI P Age Gender Female 1 Male Diagnosis Lumbar disc herniation 1 Lumbar canal stenosis Degenerative spondylolisthesis Spondylolysis Facet cyst Surgery UD 1 BD UD, unilateral decompression with or without discectomy; BD, bilateral decompression from a unilateral approach There was no occurrence of DT in the revision MELD cases (n = 6).

9 Result 2: Clinical Results of Patients with Dural Tears The DTs in 5 cases were repaired primarily with an additional incision. In another 28 cases with no dural repair, 9 patients presented with symptoms related to low cerebrospinal fluid (CSF) pressure after surgery, which subsided in several days. One patient had a neurologic deficit at L5 that was caused by an associated root injury. No other complications were observed, including wound infections and subcutaneous fluid collection, and no revision surgery was needed. The MRI at 6 months after surgery revealed no pseudomeningoceles; however, 4 patients had recurrent or residual disc herniation and 2 patients had a facet cyst at the surgical level.

10 A comparison of the surgical results of 2 groups of patients, one with DT (n = 33) and another without DT (n = 33) but matched in age, gender, and procedure, was performed. Mean age at surgery (y) Dural tear (n = 33) 54.3±15.2 (29 81) No dural tear (n = 33) 52.3±15.3 (21 79) Gender (Female:Male) 13:20 14:19 >0.99 Diagnosis Lumbar disc herniation Lumbar canal stenosis 7 7 Degenerative spondylolisthesis 3 3 Cyst 1 1 Surgery type UD BD UD, unilateral decompression with or without discectomy; BD, bilateral decompression from a unilateral approach P.60

11 Comparison of clinical outcomes between patients with and those without dural tears Dural tear (n = 33) No dural tear (n = 33) P JOA score Preoperation 11.4±4.7 (1 20) 12.2±4.7 (1 20).48 Postoperation 24.9±3.8 (16 29) 26.8±1.8 (22 29).009 Recovery rate (%) 76.5±20.1 ( ) 86.7±12.5 ( ).016 ODI (%) Preoperation Postoperation 53.8±23.8 (0 98.0) 15.7 ± 14.0 (0 57.8) JOA, Japanese Orthopedic Association; ODI, Oswestry disability index 50.5±17.2 ( ) 8.7 ± 9.2 (0 36.0)

12 Conclusion The overall incidence of DT in MELD was 5.1%. The risk factors for DTs were the age of the patient and the performance of the BD procedure. Small DTs can be managed without dual repair; however, symptoms of low CSF pressure should be given adequate care. Clinical outcomes were significantly lower in patients with than in those without DT. None of the authors has any potential conflict of interest.