Grading system for articular surface degeneration of zygapophysial (Z) joints following induced segmental hypomobility in the rat

Articular surface degeneration (ASD) of the Z joint cephalad articular facets (CAFs) is characterized by roughening, pitting, and remodeling. These changes have been previously found in hypomobile Z joints of rats. Our objective was to refine the method of grading ASD for use in large scale studies. Left and right L4‐S1 CAFs of 6 randomly selected spines (45 CAFs) of control and experimental rats were assessed. The experimental animals had undergone 8 weeks of fixation, using an established, IACUC approved, rat model, in which 3 contiguous segments (L4, L5, L6) were fixed with a specially engineered, surgically implanted, vertebral fixation device. Using a decision tree developed to score overall CAF degeneration, the CAFs were graded under dissection microscopy by 2 observers (blinded to each other and to their own initial scores) to determine: number of regions and size of remodeling; number, location, and depth of pits; and severity and size of roughening. The observers scored the spines on 2 occasions separated by at least 7 days. Weighted kappa showed substantial intra‐observer (k=0.77, SE 0.1) and inter‐observer agreement (first measurement, k=0.72, SE 0.14; second measurement k=0.71, SE 0.14), indicating that the grading system can be used in future studies assessing ASD of CAFs. Support: NIH/NCCAM (Grant #s 1R21 AT00784 and U19 AT002006).