Introduction Minimally invasive lumbar discectomy using the METRx™ System (MAST discectomy) has been advocated as an alternative to open microdiscectomy for symptomatic posterolateral lumbar disc herniation. This paper presents a quality assurance dual surgeon retrospective study with independent observer minimum twelve month follow-up.

Methods This study was approved by the Ethics Committee of the Princess Alexandra Hospital prior to commencement. All patients who underwent MAST discectomy using the METRx™ System for the management of radiculopathy caused by posterolateral lumbar disc herniation under the care of two surgeons (AN and RK) more than twelve months prior to the commencement of assessment were included in the study. The patient demographic data was collected contemporaneously, operation performance data was collected retrospectively from hospital databases and outcome data was collected by telephone interview by independent observers (PL, SO and JP) a minimum of twelve months after discharge from hospital.

Results 101 patients (53 males, 48 females) (average age 43 years, range 17 to 83 years) underwent 102 procedures between July 2001 and December 2004. Surgery was performed on the right side in 63 cases and was either at L4/5 (30%) or more commonly L5/S1 (70%). 21 were public patients and 80 private patients with 59 episodes of surgery occurring in a public hospital. 46 operations were performed with the METRx™ MED System and 56 with the METRx™ MD System. The average duration of surgery for patients at the Princess Alexandra Hospital (n = 48) was 88 minutes with an average length of post-operative hospital stay of 22 hrs 35 mins. 16 of these cases were performed as day surgery. Perioperative complications were: conversion to open (3), urine retention (7), nausea and vomiting (3), durotomy (5), wound haematoma not requiring surgery (1) and incorrect level surgery identified and rectified during surgery (1). The average length of time from surgery to independent follow-up was 679 days (range: 382 to 1055) with 78% successful contact. On the Modified McNabb Outcome Scale, 83% reported an excellent or good outcome, 9% reported a fair outcome and 8% a poor outcome. The time until return to work was identified as less than two weeks in 28% and between 2 weeks and 3 months in 39%. Patients whose surgery was funded by Workers Compensation were over-represented in both the poor outcomes and delayed return to work. 4 patients reported progressive severe low back pain, 10 patients reported ongoing lower limb pain (severe in 1 and mild in 9) and 1 patient underwent surgery for a recurrent disc prolapse. Further disc prolapse at different sites was identified in five patients.

Discussion The retrospective data in this study forms class IV evidence for efficacy. As a quality assurance exercise it suggests an acceptable level of safety and efficacy to allow further technique development and study. A prospective randomized controlled study is proposed. The high incidence of urine retention early in the series of one surgeon is considered to be related to the practice of placing depot morphine in the operative bed. The reduction in complications in general and the improvement in duration of surgery over the series is evidence of the learning curve for this procedure.