Introduction The main objective of this study is to describe the morphology and the mechanism of organization of the lumbar lordosis regarding the both position and shape of the pelvis. According to the orientation of the sacral plate, a classification of the lumbar lordosis is proposed. A symptomatic cohort of patient suffering of low back pain is analysed according to this new classification.

Methods 160 asymptomatic, young adult volunteers and 51 symptomatic low back patients were x-rayed in a standardized standing position. Analysis of the spine and pelvis was performed with the SagittalSpine® software. The pelvic parameters were: pelvic incidence, sacral slope, pelvic tilt. Thoracic kyphosis and lumbar lordosis were divided by the inflexion point. The lumbar lordosis was bounded by the sacral plate and the inflexion point. At the apex, the lumbar curve was divided in two tangent arcs of circle, quantified by an angle and a number of vertebrae. The upper one was geometrically equal to the sacral slope. Regarding the vertical line, a lordosis tilt angle was designed between the inflexion point and the anterior limit of the sacral end. The second group was operated with a disc prosthesis at the degenerated level.

Results The value of the lumbar lordosis was very variable. The best correlation was between lumbar lordosis and sacral slope, then between sacral slope and pelvic incidence in both groups. The upper arc of a circle remained constant, when the lower one changed with the sacral slope. There were good correlations of the sacral slope with the position of the apex, and with the lordosis tilt angle. When restoring the disc height at level L4L5 or L5S1 by a prosthesis insertion the local balance is modified but the global balance is unchanged. The prosthesis insertion at level L5S1 modifies significantly the balance at L4L5 which seems to be the most important level to restore a good lumbar lordosis.

Discussion Regarding the sacral slope, the lumbar lordosis can be classified in four types. When the sacral slope is low, the lumbar lordosis can be short and curved with a low apex and a backward tilt (type 1), either both long and flat with a higher position of apex (type 2). When the sacral slope increases, lumbar lordosis increases in angle and number of vertebrae with an upper apex, and it tilts progressively forward (type 3and 4). Depending of the both shape and position of the pelvis, the morphology of the lumbar lordosis could be the main mechanical cause of lumbar degenerative diseases. Total disc arthroplasty at one level L4L5 or L5S1 can significantly restore a good balance in the lumbar without modification on the global balance of the spine. When two levels are involved in the DDD process, the fusion at L5S1 and a prosthesis at L4L5 do not modify the global balance and the clinical results are similar to one level disc arthroplasty. This has to be underlined because all studies with two levels arthroplasties showed worst clinical outcomes than one level.

Introduction The concept of accelerated degeneration of adjacent disc levels as a consequence of increased stress caused by interbody fusion of the lumbar spine has been widely postulated. Total disc arthroplasty may offer the same clinical benefits as fusion while providing motion that may protect the adjacent level discs from the abnormal and undue stresses associated with fusion. The goal of this study was to prospectively analyse the results of the Maverick Lumbar Disc Prosthesis (Medtronic, USA) at 4 years follow-up.

Methods We conducted a prospective analysis of the Maverick Lumbar Disc Prosthesis implanted in the first 50 consecutive patients for the treatment of degenerative disc disease of the lumbar spine resistant to conservative treatment for more than 1 year. 253 Maverick have been implanted in our spine unit and these 50 have the longest follow-up. The outcome data collected included the Oswestry Questionnaire and Visual Analog Scale (VAS) preoperatively and at routine scheduled follow-ups. Radiographic analysis included sagittal balance parameters on standing full length lateral radiographs of the spine and range of motion on flexion/extension dynamic radiographs. 3 European centres were included in the study. The offset on AP x-rays was calculated for all patients and correlated with clinical outcomes.

Results There were 32 females and 28 males with an average age of 43, 4 years and average follow-up of 3.1 years (22 to 48 months). The Maverick was implanted at L5S1: 20 cases; L4L5: 17 cases; 3 patients had 2 levels arthroplasty and 10 had a fusion at L5S1 and a prosthesis at L4L5. Clinical success, defined by the FDA as improvement of at least 25% on the Oswestry, was 76% and 81%, at 6 months and 1 year follow-up respectively. The VAS showed an improvement in back pain from 7.1 (+/− 2, 1) pre-operatively to 3.0 (+/− 1.8) post-operatively. Leg pain was significantly higher according to VAS when patients have been previously operated for disc herniation (HD).

At the latest follow-up, there was no measurable subsidence of the devices except in one case at L5S1 due to a technical error and no evidence of device migration. The measured range of motion in flexion-extension ranged from 3 to 16 degrees (mean range of motion, 6 +/− 4 degrees). L4–L5 level is more mobile: average 8.4 degrees. With regards to sagittal balance, there was no significant change in any of the variables studied including sacral tilt, pelvic tilt, or overall lordosis after placement of total disc arthroplasty. Only the lordosis at the level above the prosthesis was significantly decreased. The position of the implant on AP and lateral x ray was analyzed and correlated with the clinical results. Less than 19% of offset on AP view had no influence on clinical results. One complication, a ureter injury occurred during the approach in one procedure. One left iliac vein injury occurred per-operatively and treated with vascular clip. One patient with two discs with persistent low back was re-operated for posterior fusion with a significant improvement of pain at two years. This patient had been operated 3 times before for disc herniation and recurrence of HD.

Discussion These results of total disc arthroplasty compare favorably with the mid-term clinical outcomes associated with anterior lumbar discectomy and fusion reported in the literature. Unlike fusion however, it appears that the prosthesis has enough freedom of motion to allow the patient to maintain the natural sagittal and spinopelvic balance with radiographic evidence of normal range of motion. However, these early favorable clinical results in addition to the influence on adjacent motion segments can be assessed only after long term follow-up. Previous surgery for HD isn’t the better indication to restore the motion.