Perfusion of muscle flaps independent of the anatomical vascular pedicle: Pedicle autonomy.

INTRODUCTION: Free muscle flaps are being used more commonly for complex lower limb reconstruction. Up to 33% of flaps used to reconstruct lower limb trauma will require an orthopaedic procedure after reconstruction. To date there have been only case reports detailing the variable survival of muscle flaps after actual or simulated pedicle injury and the process and timeframe of neovascularisation remains undefined. We aim to show that perfusion of a muscle flap is possible after injury to its anatomical vascular pedicle.

METHODS: Pedicled muscle flaps were raised and transposed to a cutaneous inset on the chest wall in a rodent model. Each flap was subjected to simulated pedicle injury at a variable time. Allocation was by computer randomisation. Flap perfusion was assessed before and after pedicle injury followed 48 h later by sacrifice of the animal and static angiography of the flaps.

RESULTS: By the 21st day after inset, all flaps survived simulated pedicle injury. Prior to this, flap survival was significantly lower (p = 0.017, Fisher's Exact Test). Clinical signs at the time of pedicle injury did not predict flap survival. Most new vessels form at the distal part of the inset (p < 0.01, ANOVA). The total number does not change with time (p = 0.82, ANOVA). New vessels anastomose preferentially with skin. The fall in perfusion after pedicle ligation was significant for all groups except the day 35 group (p = 0.53).

CONCLUSIONS: Muscle flaps can perfuse after an injury to the anatomical vascular pedicle through neovascularisation at the inset. These new vessels are evident early but may not function adequately to perfuse the flap. Regional variations in neovascularisation suggest that a gradient of ischaemia drives this process. Inset at the cutaneous level is important, which has implications for buried muscle flaps. The correlation between change in flap perfusion after pedicle injury and flap necrosis suggests a role for the former in determining the capacity of a muscle flap to tolerate a pedicle injury and thereby the approach to re-raising it.