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.

Surgical treatment of degenerative disc disease (DDD) has been widely modified in the last decade. The clinical evaluation of back pain has been improved by the use of functional scores and VAS. The discography is an adjunct for decision-making, but CT scan and MRI are the keys to evaluate the aging process.

The conservative treatment with physiotherapy and exercise programs is always the first and very useful treatment. Percutaneous therapy like facets injection, laser, IDET, radiofrequency in the disc can be a solution in some specific cases. Their efficacy has been evaluated in different studies and is sometimes controversial but there aren’t contraindications for further treatment and their complication rate is low. Dynamic posterior stabilization devices using pedicular screws and ligament tension band are proposed to try to put the disc in rest and some histological analyzes confirmed this hypothesis. Interspinous devices have been evaluated since many years but there indications need to be established as the literature available doesn’t provide clear indication criteria. Partial disc replacement is a new challenge for DDD. Many devices have in clinical evaluation but only few have prospective studies demonstrating their efficacy. The PDN was the pioneer and as the other in the evaluation process it has to solve the problem of the stability of the device. The last products on the market are promising. The total disc replacement is the last solution before fusion. Many studies including prospective and randomized have demonstrated the efficacy of total disc replacement. The indication is the key point of success. The training to perform the approach safely is mandated. Finally the fusion: anterior, posterior or combined is the ultimate solution to treat DDD. This was the gold standard and is still the most widely used treatment. As a dead end fusion is used only if other solutions cannot be proposed or used. DDD therapy has to be considered with the help of an algorithm including all motion preservation treatment before fusion.

Purpose: The objective of this study was to examine the shock absorption capacity of two currently marketed lumbar disc prostheses, a metal-polyethylene prosthesis and a metal-metal prosthesis. Shock absorption capacity, which could be a useful parameter for choosing between implants, has not been examined in the literature.

Material and methods: Two types of implants were tested: the Maverick prosthesis marketed by Medtronic, and the Prodic proposed by Spine Solution. Five implants of each type were tested. The disc prostheses were mounted on a testing device designed to analyse shock transmission by application of a constant force. Force captors were positioned on the upper and lower parts of the implant being tested. The force delivered and the force perceived on the opposite side of the implant were recorded simultaneously. The implant was submitted to a static loading force of 350 N to which was added a 100 N oscillating vibration force delivered at a frequency varying from 0 to 100 Hz. A supplementary 250 N shock was also applied every 10 s. The spectrum and frequency of each input and output were recorded. Vibration and transmission of the shock though the implant were defined as the ratio of the output over input spectra. Measurements were taken for all frequencies between 0 and 100 Hz. Phase deviation was calculated to characterise the shock absorption effect.

Results: The phase deviation between the input and the output signal was less than 10 for both prostheses. Under loaded oscillating vibration, shock transmission was greater than 99.8% for both implants. In the 1–100 Hz frequency interval, the difference in shock transmission was less than 0.3±0.1% between the two implants. More than 98% of the supplementary 250 N shocks were transmitted by both implants. The difference between the two implants was thus less than 0.8% and can be considered negligible since the machine’s test sensitivity was 0.5%.

Conclusion: The two implants tested exhibited the same capacity to absorb and transmit vibration and shocks. Shock absorption capacity was close to zero or at least less than the sensitivity threshold of the testing device. This degree of freedom is not sufficient to use shock absorption capacity as an argument for choosing between the two implants currently available.

Purpose: Intersomatic L5-S1 arthrodesis is a common procedure in orthopaedic surgery of the spine. Two approaches are generally proposed: the anterior trans or retroperitoneal approach and the posterior approach via the spinal canal or laterally. We conducted an anatomic animal study to examine the feasibility of a new approach to the L5–S1 disc.

Material and methods: Five anatomic specimens were used. The approach consisted in introducing via posterior laterosacral access a blunt 5 mm trocar into the sacrococcygeal joint. A 2 cm incision was made to identify the anterior aspect of the sacrum. Anterior and lateral scopic control was used to follow the progression of the trocar. The guide was medialised and slid into the median part of the sacrum. A larger tube with an oblique end was slid over the guide and impacted on the inferior border of the S1–S2 disc. The blunt trocar was then removed and the tube was impacted into the S2 bone under scopic control. A hollow bit was then inserted into the tube to perforate S2 and reach the L5-S1 disc. Angled instruments allowed nucleoctomy without injuring the annulus. All specimens were then explored anteriorly. The technique was tested on five 40–50 kg living pigs. After inserting the hollow bit, laparoscopy was performed to visualise the trajectory of the tube and search for possible complications.

Results: The anatomic study was conducted with the animals placed in a ventral position. The blunt trocar easily detached the presacral infraperitoneal region without any perforation of the neighbouring organs (sigmoid, colon). The presacral membrane was fragile in two cases but appeared to have been weakened by prior intra-peritoneal surgery due to the presence of pseudomembranes. It was possible to achieve perforation of S1 and partial L5–S1 discectomy in all cases. Nucleoctomy was difficult due to insufficient instrument design. There was no problem in inserting the trocar and reaching the L5–S1 disc in any of the piglets.It was sometimes difficult to impact the tube into the S1 bone because of the small angle between the sacrum and the lumbar spine. Laparoscopy revealed a small pre-sacral haematoma in four cases without significant bleeding. In one case, the haematoma was much larger and related to arterial or venous bleeding from presacral vessels. Insertion of the trocar was difficult. The instrument slid toward the promontory probably causing injury to a branch of the sacral vessels which have a large diameter in the piglet.

Discussion: This anatomic study demonstrated the feasibility of a new approach to the L5–S1 disc. This approach could be an interesting alternative in several indications: revision surgery for nonunion after other methods, treatment of certain types of spondylolisthesis. For partial prosthetic replacements (nucleoplasty) this approach would have the advantage of avoiding the need to open the annulus, the principal element of disc stability. Other trials would be necessary to design adequate instrumentation, but this new approach appears promising because it involves a minimally vascularised area. Video assistance for the trocar would help optimise presacral dissection.