Quantitative Radiographic Morphology of Posterior Calcaneal Spurs Independently Predicts Patient-Centered Outcomes...

Background/Objectives: Insertional Achilles tendinopathy (IAT) is frequently associated with posterior calcaneal spurs; however, the prognostic significance of spur morphology for patient-centered treatment outcomes remains unquantified. This study aimed to establish treatment-specific minimal clinically important difference (MCID) and patient acceptable symptom state (PASS) thresholds after extracorporeal shockwave therapy (ESWT) and to determine whether quantitative spur morphology independently predicts achievement of these patient-centered endpoints. Methods: In this retrospective cohort study, 201 patients with IAT and radiographically confirmed posterior calcaneal spurs received standardized ESWT (three weekly sessions, 0.20 mJ/mm², 8 Hz). Spur length and angle were measured on calibrated weight-bearing lateral radiographs. MCID and PASS thresholds for VISA-A, AOFAS, and VAS scores were determined using anchor-based receiver operating characteristic (ROC) analyses. Optimal spur morphology thresholds were derived from ROC curves using PASS achievement as the outcome criterion and the Youden index for cut-off selection. Multivariable logistic regression analyses, adjusted for age, sex, and body mass index, were performed to assess the independent prognostic value of spur morphology. Results: MCID thresholds were: ΔVISA-A ≥ 16.5 (AUC = 0.886), ΔAOFAS ≥ 11.5 (AUC = 0.830), and ΔVAS ≥ 2.5 (AUC = 0.897). PASS thresholds were: VISA-A ≥ 70.5 (AUC = 0.712), AOFAS ≥ 72.5 (AUC = 0.842), and VAS ≤ 3.5 (AUC = 0.753). While significant mean improvements occurred (all p < 0.001), only 36.8-43.3% of patients achieved MCID and 38.3-53.2% achieved PASS. ROC analysis identified spur length > 8.7 mm (AUC = 0.713) and spur angle > 16° (AUC = 0.738) as optimal thresholds predictive of PASS failure. In multivariable analysis, increased spur length (adjusted OR = 0.23-0.24, p < 0.001) and angle (adjusted OR = 0.16-0.23, p < 0.001) independently reduced the likelihood of achieving both MCID and PASS. Conclusions: This study provides the first anchor-based MCID and PASS thresholds for ESWT in IAT and demonstrates that posterior calcaneal spur morphology-specifically length > 8.7 mm and angle > 16°-independently predicts patient-defined treatment success. These findings support the integration of quantitative spur assessment into clinical decision-making for personalized management of IAT.