Lumbar ADR Placement Accuracy: "Routine" X-Rays v. CT-Scan, Spine Nov 2007

[Slackwater]

Net Result: CT scans are suggested for placement accuracy. ADR. TDR . TDA placement is important to clinical outcome and kinematics / biomechanics, per many of the Orthopaedic Research Society abstracts and many Medical Journal articles about in-vitro testing. The authors below use the words "prognostically critical" in regards to ADR placement.

Three (3) excerpts are used verbatim from the Discussion section in the full print-out, with references. Otherwise, my words connecting the data points (dots) between medical journal reports has lesser credibility.


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PMID: 17978641

Spine. 2007 Nov 1;32(23):E661-6

The accuracy and validity of "routine" X-rays in estimating lumbar disc arthroplasty placement.

Marshman LA, MD FRSCN(a), Trewhella M, FRCR(b), Friesem T, MD(a), Rampersaud YR, MD, FRCSC(c), Le Huec JC MD, PhD.(d), Krishna M. FRCS(a)
a: Department of Spinal Surgery, University Hospital of North Tees, Hardwick, Stockton, North Tees
b: Department of Radiology, University Hospital of North Tees, Hardwick, Stockton, North Tees
c: Divisions of Orthopaedic and Neurosurgery, University Health Network, University of Toronto, Spinal Program, Krembil Neuroscience Centre Toronto, ON, Canada
d: Department Orthopédie Pr Chauve-aux, Spine Unit Pr Le Huec, CHU Pellegrin Tripode, Université Bordeaux, France


STUDY DESIGN:
Original study.

OBJECTIVE:
To compare the accuracy of radiograph (XR) estimates of lumbar total disc arthroplasty placement with high-resolution computed tomography (CT).

SUMMARY OF BACKGROUND DATA:
Most lumbar disc arthroplasties are inserted and subsequently analyzed using anteroposterior and lateral XR: XR estimates are often correlated with clinical outcomes. No study has hitherto assessed the relative accuracy of XR estimates with CT.

METHODS:
Patients (N = 36) had recently undergone uncomplicated lumbar total disc arthroplasty for unresponsive discogenic back pain. Interpedicular midline malplacement and vertebral body penetration (VBP) were estimated after surgery, by "blinded" independent review, using computer software on both nonrotated XR and high-resolution CT at the same clinic attendance.

RESULTS:
Results were obtained in N = 36 patients. No significant differences were found between XR and CT in the mean +/- standard error estimation of either midline malplacement (1.7 +/- 0.2 mm vs. 1.8 +/- 0.2 mm, P = 0.86) or VBP (1.5 +/- 0.3 mm vs. 1.6 +/- 0.3 mm, P = 0.79). However, the correlation between XR and CT for midline malplacement appeared strong (r = 0.72, P < 0.001), whereas the correlation between XR and CT for VBP was poor (r = 0.23 P > 0.10). The standard deviation of XR-CT differences for VBP (2.2 mm) was almost twice that for midline malplacement (1.2 mm). XR-CT differences exceeded the 95% limit of agreement in<UL TYPE=SQUARE>6% of midline placement estimates, and in
8% for VBP.[/list]CONCLUSION:
Nonrotated XR permitted an accurate and valid estimate of midline malplacement relative to CT in most cases.

However, the correlation was biased toward XR underestimation of CT-derived malplacement, and highly significant XR-CT differences occurred in 6% of estimates: early postoperative CT is therefore recommended to enhance the estimation of midline placement. XR-CT agreement for VBP was poor: CT is therefore indicated in all cases for this parameter. This is the first study to compare the accuracy of XR in estimating lumbar total disc arthroplasty placement with CT.


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Discussion Excerpts:
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Total disc arthroplasty has been shown to be a viable alternative to fusion for patients wiht discogenic pain otherwise unresponsive to nonoperative management [1-3]. Potential advantages over fusion include a sustain restoration of disc height, a decreased risk of implant VBP, as well as preserved intersegmental function [3].
...

Although studies have demonstrated that incorrect placement may be tolerated in the short-term, [3,4] correct placement (in particular, accurate disc space bisection) is considered critical to ensuring long-term function and optimial clinical outcome with total disc arthroplasty. [2,3] Maplacement [particularly off-center malplacement[3] (figure 3)] potentially predisposes to asymmetric loading with subsequent shifts in axes of rotation.
....

Although one (1) study has used CT to correlate arthroplasty placement with clinical outcome,[4] no study has hitherto assesed the relative accuracy of XR - i.e., the most common measurement modality - with CT in estimating implant placement. In one (1) large multicenter clinical study, lumbar disc arthroplasty midline placement was estimated on XR to be<UL TYPE=SQUARE><LI>"suboptimal" (i.e., 3-5 mm off-center) in 10.7%, and
<LI>"poor" (i.e., greater than 5 mm off-center) in a further 6.2%. [3]{ed: 16.9%}[/list]Such measurements were in fact, prognostically critical; ...


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References
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1. Blumenthal S, McAfee PC, Guyer R, et al. Randomized control trial fo the Charite' artificial disc vs fusion for single level lumbar degenerative disc disease: a two year follow-up study. Spinal Arthroplasty Society, Vienna, May 2004

2. Guyer RD, Burd TA, Hoschschuler SH, et al. Total disc replacement: implants and clinical results. In: Guyer RD, Zigler JE, eds. Spinal Arthroplasty, A New Era in Spine Care

3. McAfee PC, Cunningham B, Holsapple G. et al. A prospective randomized multicentre food and drug administration investigational device exemption study of lumbar total disc replacement with the Charite artificial disc versus lumbar fusion. Part II. Evaluation of radiographic outomes and correlation of surgical technique accuracy with clinical outcomes. Spine 2005;30:1576-83 {PMID: 16025025}

4. Patel VV, Andrews C, Pradhan BB, et al. Computed tomography assessment of the accuracy of in vivo placement of artificial discs in the lumbar spine including radiographic and clinical consequences. Spine 2006;31:948-53 {PMID: 16622387}

12. Marshman LAG, Friesem T, Rampersaud YR, et al. Significantly improved lumbar arthroplasty placement using image guidance. Technical Report Spine 2007;32:2027-30 {PMID: 17700452}
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The above article, hard.copy here, has key learnings for me as a patient:<UL TYPE=SQUARE><LI> Estimating mid-line placement with anatomical features v. biologic variability reinforced, pedicle skew low spine
<LI> Parallax estimation errors due to rotation (geometry)
<LI> Rotational malplacement cannot be assessed on X.Rays at all (only on axial CT),
<LI> etc...[/list]Wonder when PEEK ADR . TDA . TDR's will be introduced.
1.0" = 25.4 mm
1/4" = 6.35 mm
1/8" = 3.175 mm


Slackwater
mva: 2-level lumbar surgical candidate