#76 Five-year Follow-up of a Prospective, Randomized FDA IDE Trial Comparing Two Lumbar Total Disc Replacements: Clinical Outcome and Serum Ion Level Analysis for a Metal-on-Metal Device

General Session: Lumbar Therapies Motion Preservation

Presented by: R. Guyer

Author(s):

R.D. Guyer (1)
K. Pettine (2)
T. Dimmig (3)
D. Coric (4)
A. Cappuccino (5)
J. Roh (6)

(1) Texas Back Institute, Plano, TX, USA
(2) Rocky Mountain Associates, Loveland, CO, USA
(3) Triangle Orthopaedic Associates, Durham, NC, USA
(4) Carolina Neurosurgery and Spine Associates, Charlotte, NC, USA
(5) Buffalo Spine Surgery, Lockport, NY, USA
(6) Orthopedics International Spine, Seattle, WA, USA

Abstract

Introduction: Results at 24-month follow-up in this prospective, randomized FDA IDE trial directly comparing two lumbar total disc replacements (TDR)s, found that both treatment groups improved significantly, with no significant differences when comparing the two. One of the devices was a metal-on-metal implant. The purpose of this study was to compare clinical outcomes of the two TDR designs at 5-year follow-up and secondly, report results analyzing serum ion levels in a subgroup of these patients.

Methods: The study included 204 patients receiving Kineflex-L (Investigational group; Spinal Motion) and 190 randomized to the Charité (Control group; DePuy). Five-year follow-up rates were 66.0% in the Investigational group and 70.9% in the Control group. In 32 patients assigned to the Investigational group, blood samples were evaluated for serum ion levels of cobalt and chromium, with 48 month follow-up available of 20 of these patients. These values were compared to the Medicines and Healthcare Products Regulatory Agency (MHRA) value determined to merit following total hip replacement patients more closely for potential problems related to wear.

Results: Mean Oswestry scores in both groups improved significantly by 6 weeks and remained improved throughout 5-year follow-up (Figure 1; p< 0.01).

VAS scores assessing pain followed a similar pattern and were also significantly improved throughout the study (p< 0.01). Approximately 11% of both groups underwent re-operation or revision surgery by 5-year follow-up. Results of serum ion level evaluation in the Investigational group found the greatest mean value at any point during the 4-year follow-up was less than 20% of the minimum value recommended by the MHRA to merit following total hip replacement patients more closely for potential problems related to wear (Figure 2). By 48 months, the values were less than 10% of the recommended monitoring threshold.

Conclusions: The results of this prospective, randomized trial found no significant differences in outcomes during 5-year follow-up when comparing the two TDRs. Both designs provided statistically significant improvement 6 weeks post-operatively and significant improvements were maintained. These results further support findings from multiple studies involving other TDR designs that this technology provides significant improvement with very stable multi-year outcomes. Although there may be concern about the use of metal-on-metal hip replacements due to wear, the serum ion levels measured in these TDR patients were well below the level recommended as the threshold to merit closer patient monitoring and in fact, many individuals without metallic implants have levels higher than these patients.

Figure 1. Mean ODI scores.

Figure 2. Serum ion levels- Investigational device