Introduction Current concepts in the treatment of degenerative disc disease include disc replacement. Disc replacement may restore height and lordosis while maintaining motion. This paper reviews the design criteria, biomechanical and biological (wear and safety) testing of the Maverick total disc arthroplasty. The surgical technique and early clinical results of the initial implantations were reviewed (Mathews HH, et al; Spine J. 2004).

Methods The Maverick total disc arthroplasty is a semi-constrained, chrome cobalt metal-on-metal, ball and socket design prosthesis designed to resist shear forces. Various prosthetic sizes allow precise end plate coverage to help prevent subsidence and selective restoration of lordosis and disc height. The posterior location of the ball-and–socket articulation approximates the normal centre of rotation.

The Maverick disc was subjected to axial compression, cadaveric motion, wear testing, and shock transmission studies. Early clinical outcomes were reviewed.

Results Biomechanical testing resulted in no failures, cracks, loss of height or other mechanical damage after subjecting the components to 10 million loading cycles. Cadaveric testing showed maintenance of a range of motion in all planes with no statistically significant (p=.05) differences between the stiffness or range-of-motion measurements in any mode except for extension. Maverick tested at 10 million repetitions of significant bends, estimated to be equivalent to 31.5 years of clinical use, generated only 12 to 14 mm³ of debris. This represents approximately 9% of the anticipated debris of a metal-on-metal hip arthroplasty. No difference in shock transmission between metal-on-metal and metal-on-polyethylene prosthesis designs was demonstrated.

Clinically at 2 years, at least three-quarters of patients obtained an Oswestry success of 15 points or more usually by 3 months after the procedure. Recovery and improvement was significantly quicker when compared to the historical arthrodesis controls. A few approach-related complications and technical failures have been reported. There have been no implant-related failures.

Discussion The most clinically relevant concept in disc replacement may be restoration of spinal balance rather than preservation of motion. Laboratory testing confirms the design rationale of the Maverick disc. Early clinical results are encouraging. Longer term results and more careful study are needed to confirm its efficacy.

Introduction Lumbar fusion may alter the sagittal balance of the spine, including a decrease in the sacral tilt ST and lumbar lordosis. Postoperative pain following a spinal fusion has been shown to be related to changes in sagittal balance, independent of other factors including pseudarthrosis.

The goal of this radiological study was to prospectively determine the effect of a single-level, total disc replacement on the sagittal balance of the spine, especially on sacral tilt (ST), pelvic tilt (PT), and lumbar lordosis (Le Huec J, et al; Spine J. 2004).

Method 35 patients received a single level disc replacement using the Maverick Total Disc Arthroplasty system (Medtronic Sofamor Danek). The preoperative and postoperative radiographic evaluation included standing anteroposterior and lateral full spine films that included the femoral heads. The parameters studied were ST, PT, global and segmental lordosis, and global kyphosis. The average age of the 35 patients studied was 44.3 years (range 35–57). There were 18 females and 17 males. The disc arthroplasty was performed at the L4–L5 level in 19 patients and at the L5-S1 level in 16 patients. The average follow-up was 14 months (range 6–22 months).

Results The preoperative values of global lordosis, ST, PT and global lordosis were not significantly different at last follow-up. When the groups were compared according to the level operated, there was no statistical difference with regard to the overall lordosis, ST, PT or kyphosis from pre- to postoperative period or when the two groups were compared with each other. The level above the prosthesis has significantly less lordosis.

Discussion In the present study with use of a motion-preserving intervertebral disc prosthesis, it appears that the patient is able to maintain the preoperative sagittal balance. The prosthesis has enough freedom of motion to allow the patient to maintain the natural sagittal and spinopelvic balance needed to prevent potentially undue stress on the muscles and the sacroiliac joint. Although the number of patients is small, this is the first study that evaluates the sagittal balance after motion-preserving total disc arthroplasty.