The Evaluation of Sagittal Pelvic‐Femoral Kinematics in Patients with Cam‐Type Femoracetabular Impingement

Objective To investigate the sagittal hip‐pelvic kinematics in symptomatic cam‐type femoroacetabular impingement (FAI) patients in the process of sitting down and compare their difference between patients with sitting pain complaint and those without. Methods Twenty‐nine symptomatic cam‐type FAI patients were recruited from our clinic between May 2018 and October 2018. Patients were categorized into two groups depending on whether they complain of pain in prolonged sitting or not. The pelvic‐femoral measurements were assessed with a set of lateral pelvic radiography in sitting and standing respectively. Pelvic incidence (PI), sacral slope (SS), and proximal femoral shaft angle (PFSA) were measured on lateral pelvic radiography, and then pelvic tilting, apparent hip flexion, true hip flexion, and the pelvic‐femoral ratio were calculated to investigate the kinematic change from standing to sitting position. Demographic measurements, hip morphology measurements, functional measurements, visual analog scale (VAS), and pelvic‐femoral measurements were compared between the two groups. Results Thirteen cases without sitting pain complaint and 16 cases with sitting pain complaint were stratified to Group N and Group P respectively. No was significant difference in age, body mass index (BMI), and gender between the two groups. Hip morphology measurements (α angle and lateral center‐edge angle) and functional measurements (iHOT‐12) showed no significant difference between the two groups. However, the mean VAS of pain while sitting was 0.5 ± 0.4 and 1.6 ± 0.6 in Group N and Group P respectively (P = 0.005). Patients with sitting pain complaint have increased pelvic PI compared to those without (50.1° ± 6.5° and 44.2° ± 7.6°, P = 0. 042). The changes in SS (pelvic tilting) from standing to sitting in Group N was significantly larger than that in Group P (21.8° ± 7.0° and 15.1° ± 6.5°, P = 0.012). Although no significant difference in apparent hip flexion and true hip flexion was found. Patients without sitting pain complaint demonstrated a higher pelvic‐femoral ratio (22.8% ± 7.9% and 16.1% ± 7.5%, P = 0.010) compared to those with sitting pain complaint. Conclusion Sagittal pelvic‐femoral kinematics could have an influence on the symptomology of cam‐type FAI. The small PI and insufficient sagittal pelvic tilting in the process of sitting down could be related to the complaint of sitting pain in patients with symptomatic cam‐type FAI. What is the true hip flexion duri