Sixty-four patients were included in this prospective study and operated in one center by one surgeon. All patients had been suffering from chronic back pain resistant to conservative treatment for at least l year and had received medical and rheumatologic follow-up and rehabilitation physiotherapy.

Contraindications for disc arthroplasty were the following: previous spinal surgery other than discectomy at the painful level, lumbar fracture, permanent symptomatic disc hernia, narrow lumbar canal or isthmic spondylolisthesis, scoliosis greater than 15-degrees Cobb angle, spinal tumor, general or local infection, evolving autoimmune disease, pregnancy, morbid obesity, psychiatric disturbances, and major bone disease.

Inclusion criteria were as follows: age between 20 and 60 years irrespective of gender, symptomatic degenerative lumbar discopathy as evidenced by radiography and magnetic resonance imaging (MRI), failure of conservative treatment given for longer
than 12 months, Oswestry score > 30%, predominant chronic back pain, and absence of permanent nerve root compression.

There were 64 patients, mean age 44 years (SD 7), measuring a mean height of 1.68 m (SD 0.09) and weighing 68 kg (SD 12). There were 39 women and 25 men, all of Caucasian type. Thirty percent were smokers and 9% had back pain associated with a work accident. Professionally, 20 were attending work, 21 were absent on account of their back pain, and 23 were no longer able to work. Eighteen patients had had previous spinal treatment: 3 isolated rhizolysis of the posterior facets and disc annuloplasties by radiofrequency at the painful level, one of which was followed by discectomy. There were also 8 patients who had received disc nucleolysis with chymopapain, one of which was followed by discectomy. Twenty-four had a history of abdominal surgery as follows: 13 appendicectomies, 2 extrauterine pregnancies, 6 cesarean sections, 3 surgeries for groin hernia, 2 cholecystectomies, 4 tubal ligations under coelioscopy, and 2 hysterectomies.

Levels to be operated were the following: disc prosthesis L5-S1 (35 cases), L4-5 (14 cases) and arthrodesis L5-S1 with disc prosthesis at L4-5 (13 cases), and prosthesis at L3-4 (2 cases).

All had received radiologic, static, dynamic, and load-bearing evaluation, in addition to MRI. Preoperative MRI was used to assess the state of the disc. Disc degeneration was measured on T2-weighted sagittal slices and classified as described by Fujiwara (8): grade 1, normal disc; grade 2, normal height with median transversal dark band; grade 3, normal height but with hypointensity; grade 4, slightly decreased height accompanied by inhomogeneous hypointensity; and grade 5, clearly diminished hypointense heterogeneous disc with hyperintense transversal lines. High intensity zone (HIZ) was noted. For facet arthrosis, we used the MRI classification described by Fujiwara (9): grade 1, normal facets; grade 2, moderately compressed facets with small osteophytes; grade 3, facets with subchondral sclerosis and moderate osteophytes; and grade 4, facets lacking articular joint space and with large osteophytes. For muscle degeneration, Goutallier’s scale was applied (10): grade 1, normal muscle; grade 2, muscle interspersed with some fat; grade 3, as much muscle as fat; and grade 4, more fat than muscle.

Radiography was used to examine mobility during flexion-extension around the device and the two adjacent levels. Sagittal equilibrium was assessed by radiography in standing anteroposterior (AP) and lateral position. Measurements performed by an independent radiologist on AP and lateral radiographs were accurate to 3 degrees for angles and 3 mm for distances.

The prosthesis is inserted by a mini-invasive anterior approach (11) with complete discectomy and release of the discal space. The patient is positioned supine in the so-called French position, with legs bent and open laterally (12,13). The surgeon stands between the legs facing the lumbar spine in the cephalad-caudal direction, which is ergonomic for checking the midline of the spine when approaching the L5-S1 and L4-5 levels. The assistant stands on the right or left side of the patient. The incision is longitudinal or horizontal crossing the midline, 7 to 8 cm long. A Pfannenstiel incision is more cosmetic for one-level surgery. After vertical incision of the rectus abdominis sheath, the muscle is retracted laterally to reach the common fascia of the external oblique muscle. The retroperitoneal space is reached and the peritoneal sac retracted. The peritoneal sac is pushed to the contralateral side with the ureter and the hypogastric plexus. The vessel bifurcation is now exposed and analyzed. To reach L5-S1, the left iliac vein must be carefully retracted and the medial sacral vessels ligated. An opening to the anterior part of the L5-S1 disc of least 32 mm must be exposed. At the L4-5 level, the left approach is commonly used. The surgeon must pay attention to the ascending lumbar vein, which is located at the corner of the psoas belly and the left iliac vein. This
important collateral must be ligated. The segmental vessels at L4 and L5 must also be ligated to allow retraction of the aorta and vena cava. Traction on the left iliac vein must be controlled throughout the procedure. The anterior part of the disc is opened according to the size of the templates. The anterior annulus and nucleus are removed using disc rongeur, Kerrison, curettes, and a scraper. The posterior annulus must be opened to free the disc space and to allow good restoration of the disc height. It is not necessary to open the posterior longitudinal ligament, but it must be detached from the posterior border of the endplates using the specific instruments. The mobility of the disc space is tested with a spreader under C-arm control. The midline is checked with AP fluoroscopy. A dedicated instrument is introduced in the disc space and makes it possible to create a parallel distraction of the disc, thus restoring the disc height. The upper or the lower keel cutter is slid onto a guide and impacted into the vertebral body to prepare the bed for the fin of the prosthesis. The prosthesis is impacted into the prepared disc space under fluoroscopic control. The retractors are carefully removed and bleeding is controlled. The rectus abdominis fascia and subcutaneous fat are closed with drainage.

The implant used is a metal on metal disc prosthesis Maverick (Medtronic, Memphis, TN) made of cobalt chrome, with a ball and socket design. The prosthesis has a fixed posterior center of rotation located below the lower endplate. The production of wear debris is very low without epidural reaction on animal studies (3,12,14).

All patients were seen at 1, 3, and 6 months, then 1 and 2 years, and each year after this point with assessment of pain, according to a visual analogue scale (VAS), neurologic function, Oswestry scores, and the SF36 (15). Clinical success was taken to be a 25% improvement on the Oswestry score, that is, the success rate defined by the U.S. Food and Drug Administration (FDA) in a randomized prospective study concerning the SB Charité prosthesis (16). Degree of patient satisfaction was noted, as were need of antalgics and duration of treatment with antalgics or anti-inflammatory agents. All patients received postoperative physiotherapy from 1 week postoperative and wore a supple girdle for 6 weeks. Statistical analysis was with the t test and the chi-square test.

All the patients underwent follow-up examinations. Oswestry score preoperative and at 4-years’ follow-up was 43.8 and 24.1, respectively. Low back pain improved from a mean VAS of 7.6 ± 1.7 preoperatively to 3.3 ± 1.7 at 4 years. Mean VAS leg pain score decreased from 3.9 to 2.2 at 4 years (p < 0.05). Mean daily duration of back pain decreased from 70% to 42% (p < 0.05). Daily duration of leg pain decreased from 36% to 23% (p < 0.05). According to the FDA criteria (>25% improvement of Oswestry score) (17), the success rate was 75.6% (p < 0.05). Improvement in back pain directly affected the improvement in Oswestry score (p = 0.008) (Table 18.1).