Effects Of Fibrous Capsule On The Long-time Retraction Rate And Biomechanical Properties Of Expanded Flap

Objective:To investigate the effects and mechanisms of the fibrous capsule on the long-term retraction rate and biomechanical properties of the expanded flap, and discuss whether to resect the fibrous capsule of the expanded flap in clinical practice.Methods:Four guinea pigs were given expander implantation with three100ml rectangular expanders in the subcutaneous tissue on each side of chest and abdomen symmetrically. The expansion was completed as clinical practice. When the expanders were extracted, the capsule of the flaps was removed on one side as test, but retained on the other side as control. The normal unexpanded skin was blank control. The expanded skin and capsule was harvested at3weeks,6weeks,3months,6months after the operation, for histologic and biomechanical test, including expanded rate, instant and long-term retraction rate, the amount of collagen fiber, elastic fiber and α-SMA in derma anda-SMA in capsule, stress-strain relationship, stress relaxation and creep.Results:1. There was no significant difference in expanded rate between test group and control group (P>0.05). The instant retraction rate of flap in experimental group was smaller than the control group (P<0.05).2. The expanded flap retracted significantly in the first three weeks, stretched at the6th week. At the6th month, the area of the flaps was approximately equal to that before operation. The long-term retraction rate of the control group decrease faster than the experimental group.3. The relative content of collagen and elastic fiber increased obviously, and decreased gradually over time. There was no significant difference between two groups (P<0.05).4. α-SMA-positive myofibroblast (MF) can be observed in derma and capsule of the expanded flaps. The integral optic density (IOD) of α-SMA showed no significant difference (P<0.05).5. There was a positive correlation between the IOD of α-SMA in capsule and the long-term retraction rate of expanded flap, with the correlation coefficient (r)0.962(P<0.01). 6.The biomechanics properties in experimental group, such as stress-strain relationship, stress relaxation and creep, were similar to the blank control group.Conclusions:1. The fibrous capsule of the expanded flap can significantly increase the instant retraction rate of the flap.2.The long-term retraction rate of the flap can be influenced by content and structure of collagen and elastic fiber, and α-SMA-positive myofibroblast.3. It is suggested that the fibrous capsule should be resected on the promise of the flaps’ blood supply to reduce the instant and long-term retraction rate of the flap, so that to lower the hyperplasia of scar and enhance the long-term effect of operation.4. The biomechanics properties can reflect the structural changes of the expanded flaps.5. The fibrous capsule can influence the biomechanics properties of the expanded flap.