Twenty-Eight-Day Pain Trajectories After Standardized Three-Position Coccygeal Infiltration: A Prospective Observational Study of 274 Patients.

OBJECTIVE

To characterize daily pain trajectories after standardized three-position coccygeal infiltration and explore differences by clinical and radiographic subgroups.

DESIGN

Prospective, single-arm observational cohort study.

SETTING

Specialized orthopedic and spine care setting.

SUBJECTS: Patients had chronic coccygodynia with symptomatic coccygeal instability confirmed clinically and on paired standing and seated lateral radiographs. Of 668 treated patients receiving a diary, 274 returned complete diaries and were analyzed (41.0%); 394 did not return a diary (59.0%).

METHODS

Patients were treated prone without procedural imaging guidance. Through one skin entry, a 23-gauge needle was directed sequentially to the symptomatic mobile segment, coccygeal tip, and immediately lateral to the coccyx. The standard injectate was mepivacaine 1% (5 mL) plus triamcinolone 40 mg. NRS pain was recorded before infiltration (day 0) and daily through post-injection day 27. Responder thresholds were ≥30%, ≥50%, and, supplementarily, ≥2-point improvement.

RESULTS

Mean NRS was 5.55 at baseline, increased transiently on post-injection days 1 and 2, and was below baseline on day 3. By day 27, mean NRS was 1.99 (paired change, -3.56; 95% CI, -3.90 to - 3.22; P < 0.001; Cohen dz = 1.24); 220 patients (80.3%) achieved ≥30% improvement and 192 (70.1%) achieved ≥50% improvement. Mean pain decreased further from 3.51 in diary week 3 to 2.73 in diary week 4 (change, -0.78; 95% CI, -0.95 to - 0.61; P < 0.001; Cohen dz = 0.55). More than half of day-20 nonresponders achieved responder status by day 27.

CONCLUSIONS

Three-position coccygeal infiltration was followed by substantial pain reduction through day 27, including further improvement during diary week 4. Causal efficacy cannot be established without a comparison group, and responder estimates may not represent the entire treated population because 59.0% did not return diaries.