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The Role of Mechanical Deformation in Lumbar Radiculopathy: An In Vivo Model

Winkelstein, Beth A., PhD,*; Weinstein, James N., DO, MS,†; DeLeo, Joyce A., PhD*

Basic Science

Study Design.  In vivo strain techniques were used in an animal radiculopathy model.

Objective.  To quantify the severity of compressive nerve root injury and characterize its effect on resultant mechanical allodynia in a lumbar radiculopathy model.

Summary of Background Data.  Clinical and experimental work indicate many factors contributing to radicular pain mechanisms, including mechanical injury. Although it has been suggested that the degree of mechanical injury to the nerve root affects the nature of the pain response, no study has quantified local in vivo injury biomechanics, nor have such measures been linked with the resulting magnitude of mechanical allodynia or other clinical symptoms.

Methods.  Male Holtzman rats were divided into a sham group with only nerve root exposure or a ligation group in which the nerve root was tightly ligated with a single silk suture. Using image analysis, nerve root radial strains were calculated at the time of injury and after surgery. The animals were grouped according to ligation strain for analysis. Mechanical allodynia was continuously assessed throughout the study.

Results.  Compressive strains in the nerve root ranged from 7.8% to 61% (mean, 30.8% ± 14.5%). Animals undergoing larger ligation strains exhibited heightened mechanical allodynia after injury. This was significant using a 12-g von Frey filament (P = 0.05). After surgery, the nerve roots displayed tissue swelling, which was relatively uniform in the low-strain group and less so in the high-strain group.

Conclusions.  For the first time, in vivo biomechanical analysis of tissue deformations was used to investigate the role of mechanics in radicular pain. Overall mechanical allodynia was greater for more severe nerve root injuries (greater strains) in an animal model, suggesting that mechanical deformation plays an important role in the pain mechanism. Continued work is underway to understand the complex interplay between mechanics and the physiology of radicular pain.

From the *Departments of Anesthesiology and Pharmacology and the

†Department of Orthopedic Surgery, Dartmouth–Hitchcock Medical Center, Lebanon, New Hampshire.

Supported by National Institute of Arthritis and Musculoskeletal and Skin Diseases (AR 44757), Bristol-Myers Squibb/Zimmer Orthopedic Foundation.

Acknowledgment date: November 29, 2000.

Acceptance date: May 21, 2001.

Device status category: 1.

Conflict of interest category: 15.

Address reprint requests to

Beth A. Winkelstein, PhD

Departments of Anesthesiology and Pharmacology

Dartmouth–Hitchcock Medical Center

HB 7125 One Medical Center Drive

Lebanon, NH 03756

E-mail: Beth.A.Winkelstein@Dartmouth.EDU

© 2002 Lippincott Williams & Wilkins, Inc.