Standardized radiologic protocol for the study of common coccygodynia and characteristics of the lesions observed in the sitting position. Clinical elements differentiating luxation, hypermobility, and normal mobility.

STUDY DESIGN: Ninety-one patients with common coccygodynia and 47 control subjects prospectively underwent dynamic radiographic imagery.

OBJECTIVES: To standardize the radiologic protocol to better define normal and abnormal mobility of the coccyx, and to study clinical parameters useful in classifying and differentiating the lesions.

SUMMARY OF BACKGROUND DATA: In a previous study, comparison of films taken in the sitting and standing positions allowed to individualize two distinct coccygeal lesions: luxation and hypermobility. Measurement technique was precise and reproducible, but the control group was not pain-free. No specific clinical features were described.

METHODS: Standing films were made first. Control subjects were healthy volunteers. The following items were recorded: presence of an initial traumatic event, elapsed time before investigation, body mass index, presence of an acute pain when passing from sitting to standing, effect of intradiscal steroid injection, and angle of the coccyx with respect to the seat.

RESULTS: Hypermobility was defined as a flexion of more than 25 degrees, luxation by displacement of more than 25% of the coccyx. The base angle is a good predictor of the direction in which the coccyx moves when sitting. In the "luxation" group, a history of initial trauma, a shorter clinical course, pain when standing up, increased body mass index, and satisfactory results with intradiscal injection were found more frequently than in the "normal" group. The "hypermobility" group had characteristics between these two groups.

CONCLUSION: Common coccygodynia is associated in 48.4% of patients with a luxation or hypermobility of the coccyx. A distinct clinical presentation was found in individuals with luxation of the coccyx.