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

Background: 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.

Objectives: In this study, we aimed to explore the anatomy of the gastrocnemius muscle and adjacent structures as intramuscular and subcutaneous recipient sites. Additionally, we sought to analyze pressure-volume relationships and fat migration patterns during posterior calf grafting.

Methods: Eight cadaveric lower extremities were examined. A prosection was performed to better understand the vascular complex around the gastrocnemius. Ultrasound-guided fat injections were then performed into both the subcutaneous and intramuscular layers; dynamic pressures were measured with a manometer. Last, dyed-injectant was injected subcutaneously to better elucidate subcutaneous anatomy.

Results: Anatomic prosection demonstrated the proximity of the gastrocnemius muscle to the popliteal venous system that arborized (>1 mm) intramuscularly. In the 3 specimens that underwent intramuscular fat grafting, the peak intramuscular pressures plateaued at 21 mmHg (19.5-23 mmHg); there was no observed extrafascial migration of the injectant. With subcutaneous injectant in 1 specimen, pressures in the subcutaneous space increased (125 mmHg) with additional injectant (240 mL) while pressures in the intramuscular space remained relatively constant (4 mmHg).

Conclusions: Intramuscular gastrocnemius fat grafting should be done with caution: its proximity to critical veins and sustained increased intramuscular pressures following grafting increases risks of embolus and thrombosis, respectively. Subcutaneous injection may be safer in that increased pressures are not communicated to deep structures. Last, we present a novel description of posterior calf subcutaneous compartments that may better allow surgeons to direct and predict subcutaneous injectant.