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.