TDR - Resect or Not Posterior Longitudinal Ligament: European Spine Journal epub 2009

[Slackwater]

pubmed: 19882178
European Spine Journal, epub © 2009 Springer

Resect or not to resect: the role of posterior longitudinal ligament in lumbar total disc replacement

Balkan Cakir1 , Marcus Richter2, Werner Schmoelz3, René Schmidt4, Heiko Reichel1 and Hans Joachim Wilke5
(1) Department of Orthopaedic Surgery, University of Ulm, Oberer Eselsberg 45, 89081 Ulm, Germany
(2) Spine Unit, St. Josefs Hospital, Wiesbaden, Germany
(3) Trauma Surgery and Sports Medicine, Medical University of Innsbruck, Innsbruck, Austria
(4) Department of Orthopaedic and Trauma Surgery, University Medical Center Mannheim, Mannheim, Germany
(5) Institute of Orthopaedic Research and Biomechanics, University of Ulm, Ulm, Germany

Received: 25 May 2009 Revised: 18 August 2009 Accepted: 12 October 2009 Published online: 31 October 2009

Abstract
With regard to the literature, several factors are considered to have an impact on
postoperative mobility after lumbar total disc replacement (TDR). As TDR results
in a distraction of the ligamentous structures, theoretically the postoperatively
disc height and ligamentous integrity have also an influence on biomechanics
of a treated segment.

The purpose of the study was to evaluate the influence of posterior longitudinal ligament (PLL)
resection and segmental distraction on range of motion (ROM).

Six human, lumbar spines (L2–L3) were tested with pure moments of ±7.5 Nm
in a spine loading apparatus. The ROM was determined in all three motion planes.
Testing sequences included:
(1) intact state,
(2) 10 mm prosthesis (PLL intact),
(3) 10 mm prosthesis (PLL resected),
(4) 12 mm prosthesis (PLL resected).

The prosthesis used was a prototype with a constrained design using the ball-and-socket
principle. The implantation of the 10 mm prosthesis already increased the disc height significantly

(intact: 9.9 mm;
10 mm prosthesis: 10.6 mm;
12 mm prosthesis: 12.7 mm).

Compared to the intact status, the implantation of the 10 mm prosthesis resulted in an
increase of ROM for

flexion/extension (8.6° vs 10.8°; P = 0.245) and
axial rotation (2.9° vs 4.5°; P = 0.028),

whereas lateral bending decreased (9.0° vs 7.6°; P = 0.445).

The resection of the PLL for the 10 mm prosthesis resulted in an increase of ROM
in all motion planes compared to the 10 mm prosthesis with intact PLL

(flexion/extension: 11.4°, P = 0.046;
axial rotation: 5.1°, P = 0.046;
lateral bending: 8.6°, P = 0.028).

The subsequent implantation of a 12 mm prosthesis, with resected PLL,
resulted in a significant decrease of ROM in all motion planes compared
to the 10 mm prosthesis with intact PLL

(flexion/extension: 8.4°, P = 0.028;
axial rotation: 3.3°, P = 0.028;
lateral bending: 5.1°, P = 0.028).

Compared to the intact status, the 12 mm prosthesis with resected PLL
only decreased lateral bending significantly while the 10 mm prosthesis
with intact PLL increased axial rotation significantly.

The resection of the PLL during TDR results in a significant increase of ROM
in all three principle motion planes. But it still remains unclear if this increase
which is in median not more than 1° may alter the clinical results. Moreover,
the destabilizing effect of PLL resection can be reversed using a higher implant.

The prosthesis height seems more crucial than PLL preservation
to maintain the primary stability after TDR.

Keywords: Lumbar disc replacement - Range of motion - Posterior longitudinal ligament - Biomechanics



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