Clinical Implications of Fat Grafting in the Posterior Calf: A Dynamic Cadaver-based Study.

Abstract

Intramuscular fat grafting in extremity muscles, especially the gastrocnemius, has become increasingly popular. However, while safety in truncal muscle fat grafting has been well-studied, research on extremity muscles is lacking. This study aims to explore the anatomy of the gastrocnemius muscle and adjacent structures concerning intramuscular and subcutaneous recipient sites. Additionally, it seeks to analyze pressure/volume relationships and fat migration patterns during posterior calf grafting. Eight cadaveric lower extremities were examined. A prosection was performed to better understand the vascular complex as it exists about the gastrocnemius. Ultrasound-guided fat injections were then performed into both the subcutaneous and intramuscular layers; dynamic pressures were measured with a manometer. Lastly, dyed-injectate was injected subcutaneously to better elucidate subcutaneous anatomy. Anatomic prosection demonstrated the proximity of the gastrocnemius muscle to the popliteal venous system which arborized (>1mm) intramuscularly. In the three specimens that underwent intramuscular fat grafting, the peak intramuscular pressures plateaued at 21mmHg (19.5-23mmHg); there was no observed extra-fascial migration of the injectate. With subcutaneous injectate into one specimen, pressures in the subcutaneous space increased (125mmHg) with additional injectate (240cc) while pressures in the intramuscular space remained relatively constant (4mmHg). Intramuscular gastrocnemius fat grafting should be done with caution: its proximity to critical veins and sustained increased intramuscular pressures following grafting increases risk of embolus and thrombosis, respectively. Subcutaneous injection may be safer in that increased pressures are not communicated to deep structures. Lastly, we present a novel description of posterior calf subcutaneous compartments that may better allow surgeons to direct and predict subcutaneous injectate.