The Strain/stress Analysis Of The Medial Parapatellar Retinacular Approach And Guide For Wound Suture

Background: There have been a lot of methods of wound strength analysis, such as Instron tensiometer (INSTS),air insufflated positive pressure device (AIPPD) and vacuum-controlled wound chamber device (VCWCD). But all of these methods contain some defects. Especially that there are no cases reported about complex incisions, such as medial parapatellar retinacular approach.Objective: Improve the methods of strength analysis, and analyze the strain and stress distribution of the site of medial parapatellar retinacular approach before dissection, after suture and early movement, as a guide to improve the suture techniques and early postoperative rehabilitation.Methods:10 fresh pretreated hind porcine legs from pigs weighing 90-100KG were fixed on an order-made device which could imitate the passive movement of the knee. And then recorded the deformation of the marked tissue with a hd video camera before operation, after operation, and after 100 flexions-extensions. After image manipulation, strain at different degree of flexion was got. A tensile test was executed to get the strain-stress curve.Results: strain distributions, degree of flexion -strain curves and strain-stress curves were obtained. Under continuous suture technique, the strains of"after operation"is different from that of"after 100 flexions-extensions",the level of significance was P=0.032<0.05.Under the interrupted suture technique, the strain of"after operation"is not different from that of"after 100 flexions -extensions"the level of significance was P=0.698>0.05. Just after operation , the strain of continuous suture technique was not different from interrupted suture technique, P=0.549>0.05. After 100 flexions-extensions, the strain of continuous suture technique was different from interrupted suture technique, P=0.012<0.05. Under the interrupted suture technique, coefficient correlation between strain distribution curve of"after operation"and"after 100 flexions and extensions"was bigger than that under continuous suture technique, P=0.003<0.05.Conclusion: The strain of different part of knee enlarges with the increment of flexion, except the two ends of the marked area, that is to say strain near tibial tubercle and the superior part of muscular mantle is not influenced by the flexion movement. After transforming the strain into stress with the strain-stress curve, the increase is more significant. That means that during early postoperative rehabilitation, on the premise of enough range of motion, the degree of flexion should be limited as small as possible, as exceeding certain degree the stress will increase sharply. The strain distributions of wound, it'lateral area and it's medial area are not similar. In lateral area of the wound, the strains descend in the order of parapatellar area, patellar ligament and muscular area. And the strains of parapatellar area are much bigger, so we should make a reinforced suture there to prevent the sliding of the surgical suture. In the wound area, the strains descend from tibial part to the femoral part, and in the medial of the wound, it has the same tendency except for some fluctuation. Just from the standpoint of biomechanics, interrupted suture technique is more liable than continuous suture technique, and the enlongation of time for operation is acceptible. And junctional zone of muscle and retinacula should make a reinforced suture to prevent the slide of the surgical suture.