Detecting a Disruption of Blood Flow to the Femoral Head After Ischemic Injury Using 4 Different Techniques: A Preliminary Study

Background: Disruption of blood flow to the femoral head can have a detrimental effect on the clinical outcome after a closed or open reduction for the treatment of developmental dysplasia of the hip and after a treatment of slipped capital femoral epiphysis. Availability of a clinically reliable and easy-to-use technique to monitor the blood flow before, during, and after a therapeutic intervention may allow early detection and more effective management of this complication. An experimental investigation was performed to evaluate 4 different sensors/techniques for their ability to detect an acute disruption of blood flow to the immature femoral head. Methods: Under general anesthesia, the femoral heads of 10 immature pigs were exposed and total head ischemia was induced by ligating the femoral neck and transecting the ligamentum teres. Blood flow was assessed before and after the induction of ischemia using 1 of 4 techniques. The following sensors/techniques were evaluated: fiber optic pressure (FOP), piezoelectric pressure, partial pressure of oxygen, and laser Doppler flowmetry (LDF). The time taken to observe a 50% reduction of the preischemia level was determined and the sensor outputs were monitored until each reached a steady level. Results: All techniques demonstrated a reduction in their respective measurements after a disruption of blood flow to the femoral head. However, the response time differed, even between the 2 pressure sensors (FOP and piezoelectric pressure at 3 and 15 min, respectively). The fastest response time for a 50% reduction was observed with the LDF (2 min) and the FOP (3 min) sensors. The partial pressure of oxygen was the slowest to change, taking over 30 minutes. Technique-dependent advantages and disadvantages were seen. The FOP sensor was fragile and susceptible to the positioning of the sensor tip. The LDF sensor was susceptible to motion artifact. Conclusions: The LDF and the FOP sensors demonstrated a rapid decline in their respective measurements after the induction of ischemia. Clinical Relevance: These techniques may prove to be useful in the assessment of an acute disruption of the femoral head blood flow.