Lumbar facet joint compressive injury induces lasting changes in local structure, nociceptive scores, and inflammatory mediators in a novel rat model

Abstract

Objective. To develop a novel animal model of persisting lumbar facet joint pain. Methods. Sprague Dawley rats were anaesthetized and the right lumbar (L5/L6) facet joint was exposed and compressed to ~1 mm with modified clamps applied for three minutes; sham-operated and naïve animals were used as control groups. After five days, animals were tested for hind-paw sensitivity using von Frey filaments and axial deep tissue sensitivity by algometer on assigned days up to 28 days. Animals were sacrificed at selected times for histological and biochemical analysis. Results. Histological sections revealed site-specific loss of cartilage in model animals only. Tactile hypersensitivity was observed for the ipsi- and contralateral paws lasting 28 days. The threshold at which deep tissue pressure just elicited vocalization was obtained at three lumbar levels; sensitivity at L1 > L3/4 > L6. Biochemical analyses revealed increases in proinflammatory cytokines, especially TNF-α, IL-1α, and IL-1β. Conclusions. These data suggest that compression of a facet joint induces a novel model of local cartilage loss accompanied by increased sensitivity to mechanical stimuli and by increases in inflammatory mediators. This new model may be useful for studies on mechanisms and treatment of lumbar facet joint pain and osteoarthritis.

Figure 1

An axial section of the facet joint from L5/L6 stained with Safranin-O (4  wk post-surgery). (a)   Left side: sham control facet joint with exposed after open surgery, and right side: intact side of facet joint. (b) Left side: facet joint L5/L6 with open surgery followed by compression, and right side: intact side of facet joint (20x).

Figure 2

A larger magnification (100x) to examine structural changes in the facet joint L5/L6. Facet joints with and without compression were stained with Safranin-O (4 wk postsurgery) followed by microscopic examination.

Figure 3

(a) von Frey data comparing tactile threshold between ipsilateral foot (■) with the contralateral foot (□) in animals after facet joint compression on day 5, 7, 14, 21, and 28. (b) Comparison of tactile sensitivity in the three groups: naïve (•; n = 6), sham (▲; n = 6) and model (■; n = 6) animals. The model animals showed a statistically significant difference from the sham and the naïve animals on all test days (P < 0.001).

Figure 4

Pressure sensitivity measured by algometer in naive (n = 6), sham (n = 6) and model (n = 6) rats at lumbar levels 6, 3/4 and 1. (a) At L6, model animals showed a difference in sensitivity only on day 7 compared to either sham or naïve animals (P < 0.05). (b) At L3/4, model animals showed a higher sensitivity compared to sham animals on days 7 and 28 (P < 0.01) and compared to naïve animals on days 7, 14 and 28 (P < 0.01). (c) At L1, model animals showed a higher sensitivity to pressure on all test days compared to sham and naïve animals (P < 0.001).

Figure 5

Cytokine array (all P values less than 0.05).

Figure 6

(a) Total dorsal horn TNF-alpha RNA. Sham control (gray, open surgery is performed as in the experimental group, but without facet joint compression) and the experimental group (black, open surgery followed by facet joint L5/L6 compression) during a time course (day 7, 14, and 28). Real-time PCR results were normalized by using β-actin as an internal control. (b) Total dorsal horn TNF-alpha RNA. Experimental group in a time course (day 7, 14, and 28), left versus right sides of lumbar spinal dorsal horn. Real-time PCR results were normalized by using β-actin as an internal control. (c) Total dorsal horn IL-1beta RNA. Sham control (gray, open surgery is performed as in the experimental group, but without facet joint compression) and the experimental group (black, open surgery followed by facet joint L5/L6 compression) during a time course (day 7, 14, and 28). Real-time PCR results were normalized by using β-actin as an internal control. (d)Total dorsal horn IL-1beta RNA. Experimental group in a time course (day 7, 14, and 28), left versus right sides of lumbar spinal dorsal horn. Real-time PCR results were normalized by using β-actin as an internal control.

Figure 7

Entire rat spinal cords were ejected and lumbar dorsal horns were dissected from intact control (naïve tissue), sham control (upper panel, open surgery is performed as in the experimental group, but without facet joint compression) and the experimental group (lower panel, open surgery followed by facet joint L5/L6 compression) in a time course (day 7, 14, and 28). Tissue lysates of spinal cords were prepared and equal amount of protein (25 μg each) was analyzed for the activation of ERK MAP kinase 1/2 (44 and 42 kDa, resp.) by using phosphospecific anti-ERK1/2 antibody. Nonphosphospecific total anti-ERK antibody was used for internal control for normalization of the western blotting analyses. All immunoblotting experiments were repeated at least three times.