Quote:
Originally Posted by Slackwater
reference Activ-L documents, LINK
DEL.TEXT noted -> minimum disc height of 8.5mm. |
An interruption made me post before finishing the draft response above.
The minimum disc height ~may be of interest depending on a patient's MRI translation into a metric measurement. There is talk of over distraction pain that I acknowledge. Maybe the posterior longitudinal ligamet is innervated. The facet joints need to line up is a major factor.
The footprint Anterior-Posterior (AP) and Lateral is ~important so the ADR / TDR sits on cortical bone, not the cancellous (or trabecular, soft porous interior) bone.
Small or incorrectly sized implants will lead to subsidence, sinking into the vertebrae. Subsidence will mean the facet joints will not line up correctly. Subsidence will be a reason for re-operation and defaulting to Fusion.
Subsidence was listed as a significant factor in the early ADR / TDR operations. "Complications of Artificial Disc Replacement: A Report of
27 Patients with the SB Charite´ Disc" van Ooij et al,
2003 Journal of Spinal Disorders & Techniques, Vol. 16, No. 4, pp. 369–383.
"subsidence of the prosthesis in 16" © 2003 Lippincott Williams & Wilkins, Inc., Philadelphi
A personalized disc replacement is a good concept. Biologic variabillity is normal. Subsidence does not appear to be a major ADR / TDR issue today because of surgical training or awareness created with the earlier patients where the literature comments by surgeons mentioned "size mis-match".
The latest Canadian study published 2010 (?)
Link mentioned subsidence: average 1.7 mm (range 0-4.8 mm). Full text of the Canadian study is available (
LINK).
Figure 1 showing subsidence and radiographic disc size illustrates a ~possible footprint mismatch to my "untrained eye". The device sizes may be limited and that was the best match.
Subsidence was present in 44 of 53 (83%) patients at the L5–S1 level and was exclusively seen at the posterior part of the inferior end plate of L5. The mean subsidence was 1.7 (range 0– 4.8) mm, meas ured at 3 months after surgery. Although there was a marginal progression of subsidence beyond this time point, it was not statistically significant. Subsidence had no effect on the range of motion at the replaced segment and did not correlate with clinical outcome. In patients who underwent an L4–5 TDA, subsidence occurred at both end plates: mean subsidence was 0.9 mm at the inferior end plate of L4 and 1.75 mm at the superior end plate of L5.
The Chinese study Oct 2010, Zhonghua Yi Xue Za Zhi
LINK, on 1 and 2 level Charite' for up to 60 months listed "no subsidence".
activ-L
"
Clinical results show, that in approx 47.5 % the application of a small height (less then 9 mm) is indicated." (The activL quote is directly from the BBraun literature / pdf, this requires a look-up on pubmed for clinical reference? I believe the numbers on are on the hard disk)
S = (26 x 31)
M = (28 x 34.5)
L = (30 x 39)
XL = (33 x 40)
ProDisc II L (LINK) Product Insert
10 mm minimum height
m = (27 x 34.5)
L = (30 x 39)
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LINK-Full Text
Eur Spine J. 2008 Nov;17(11):1470-5. Epub 2008 Sep 13.
Footprint mismatch in lumbar total disc arthroplasty.
Gstoettner M, Heider D, Liebensteiner M, Bach CM.
Department of Orthopaedic Surgery, Medical University Innsbruck, Innsbruck, Austria
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Clin Biomech (Bristol, Avon). 1997;12 Suppl 1:S1-S63.
Precision measurement of disc height, vertebral height and sagittal plane displacement from lateral radiographic views of the lumbar spine.
Frobin W, Brinckmann P, Biggemann M, Tillotson M, Burton K.