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Implant removal for the management of infection after instrumented spinal fusion.

J Spinal Disord Tech. 2010 Jun;23(4):258-65

Authors: Kim JI, Suh KT, Kim SJ, Lee JS

STUDY DESIGN: We operated on 21 patients with a postoperative deep wound infection. All the patients underwent implant removal and wide debridement. One patient lost to follow-up was excluded. OBJECTIVE: To reduce the number of debridements and manage uncontrolled spine infection. SUMMARY OF BACKGROUND DATA: There are a few reports on the treatment for postoperative spinal infection after instrumented spine fusion with implant removal and wide debridement. METHODS: The clinical outcomes were assessed using the Oswestry disability index, visual analog scale of pain and patients' satisfaction. RESULTS: The functional outcomes of the Oswestry disability index were minimal in 13 patients and moderate in 7 at final follow-up. The serial changes of visual analog scale score of pain in the back and leg showed statistically significant decline after operation. Patients' satisfaction outcomes were better in 16 patients and unchanged in 4. Six patients of the preoperative spinal fusion group included the patients that already had fusion mass well developed by the time of implant removal. Bony union was not achieved in any patient of the preoperative nonspinal fusion group (n=14) by the last follow-up. In nonspinal fusion group, mean lordotic angle before the operation was 41 degrees decreasing after the operation to 39 degrees. At the final follow-up it was 30 degrees. Mean disc space height before the operation was 11.1 mm and it decreased to 8.1 mm at the final follow-up. The mean lordotic angle and disc space height at last follow-up was larger in the spinal fusion group than in the nonspinal fusion group. CONCLUSIONS: Our results indicate that implant removal and wide debridement for postoperative infection after posterior instrumented spine fusion can provide satisfactory results and could be one treatment option. However, the collapse of the disc space, loss of normal lordosis, and pseudoarthrosis are inevitable in patients with early postoperative infection.

PMID: 20084022 [PubMed - indexed for MEDLINE]

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Validated finite element analysis of the maverick total disc prosthesis.

J Spinal Disord Tech. 2010 Jun;23(4):249-57

Authors: Le Huec JC, Lafage V, Bonnet X, Lavaste F, Josse L, Liu M, Skalli W

STUDY DESIGN: Combining in vitro tests and finite element analysis to provide a more complete picture of the role that a disc prosthesis implant would play in the biomechanics of the spine. OBJECTIVE: Analysis of the disc function after total disc prosthesis insertion with and without antero-posterior or lateral offset and in combination with adjacent fusion. SUMMARY OF BACKGROUND DATA: To avoid the risk of degenerative cascade the total disc replacement may be considered as an alternative. Few finite element analysis combined with cadaver testing under loading conditions have been published today. MATERIALS AND METHODS: In vitro tests were performed using 6 fresh human cadaver specimens to quantify the load-displacement behaviors before and after insertion of a total disc replacement (Maverick, Memphis) implant. A finite element (FE) spine model was validated with the data from the in vitro tests. This model is built on the basis of ANSYS software. The effect of the prosthesis positioning on the motion behavior at L4-L5 and on the inner loads over facets was evaluated in 4 configurations. RESULTS: The study showed that the motion behavior at the levels adjacent to the Maverick prosthesis remained the same as the intact spine, unlike a single level fusion at L5-S1. In the biomechanical study settings, Maverick prosthesis, once properly positioned, does not modify the motion behavior of the spine as compared with its intact state. The less-than-ideal positioning of the prosthesis, especially with anterior offset, affect significantly the range of motion of the spine segment and cause increase of inner load in the facets. Those results indicated a good reliability of the finite element model in representing both intact and instrumented spine segments. DISCUSSION: The in vitro test results demonstrated that Maverick disc prosthesis provides near physiologic function of a natural disc restores stability of the spine and preserves the segmental motion without undue stress on adjacent segments.To our knowledge, this study suggested for the first time the importance of the prosthesis positioning into the spine model.

PMID: 20068471 [PubMed - indexed for MEDLINE]