The role of mechanical deformation in lumbar radiculopathy: an in vivo model.
METHODS
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.


BACKGROUND
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.
Winkelstein
Beth A
BA
Department of Anesthesiology , Dartmouth-Hitchcock Medical Center, Lebanon, New Hampshire 03756, USA. Beth.A.Winkelstein@Dartmouth.EDU
Weinstein
James N
JN
DeLeo
Joyce A
JA
D000818:Animals; D001522:Behavior, Animal; D001696:Biomechanical Phenomena; D004195:Disease Models, Animal; D006614:Hindlimb / Q000294:innervation / Q000503:physiopathology; D006930:Hyperalgesia / Q000209:etiology / Q000473:pathology / Q000503:physiopathology; D007091:Image Processing, Computer-Assisted; D008026:Ligation; D008161:Lumbosacral Region; D008297:Male; D010147:Pain Measurement; D017288:Pain Threshold; D010812:Physical Stimulation; D011843:Radiculopathy / Q000209:etiology* / Q000473:pathology* / Q000503:physiopathology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012720:Severity of Illness Index; D013314:Stress, Mechanical