Histopathological Changes Of Articular Cartilage On Knee Joint During Tibial Lengthening:an Experimental Study

ObjectiveTo establish the rabbit model of tibial lengthening using the monolateral external fixatior: To observe the histopathological changes of the different distraction length and mineralized times on the articular cartilage of knee joint during tibial lengthening. To analaysis the impact factors that could be the theoretical basis to prevent the damage of articular cartilage in clinic.MethodsFifty rabbits were divided into experimental group and control group, five for control group and forty-five for experimental group. According to the distraction degree, the experimental group was divided into three groups, the10%group (A group),20%group (B group) and30%group (C group). Every group was subdivided into three groups based the mineralized times after the lengthening process, including the0day group (Ao、Bo、C0group), the four weeks group (A1、B1、C1group) and the eight weeks group (A2、B2、C2group). Every subgroup was five rabbits. The experimental group was performed the tibial osteotomy fixed the monolateral external fixator and began distraction at five days after surgery in a rate of lmm/d for twice a day. The distraction degrees were10%,20%and30%. The rabbits were killed at the Od,4w and8w after the lengthening process was completed. The control group was not performed anything. To observe the distraction degrees, callus and the changes of knee joint by the X-ray. The changes of cartilage were observed by the general observation and the light microscopy using HE staining, safranin-O staining and the immunohistochemical staining of type Ⅱ collagen. The changes were assessed by the Mankin pathological scores.Results1. X-ray:every group was observed the accomplishment of distraction degree and there were not observed any changes of the cartilage surfaces and the joints.2. General observation:the pale and rough surface of cartilage on tibial plateau was observed in C group and there were not any changes in the other groups.3. The Mankin scores:the C group got the higher scores than the A and B groups in the same mineralized times (P<0.05), while the C2group got the lower scores than the C1and Co groups (P<0.05).4. The immunohistochemical staining of type II collagen:there was positive staining in all groups. The staining was heavy in the cytoplasm of cartilage cells and aroud the cartilage lacuna. The staining was obvious heavier with the increased distraction length, especially in the superficial zone of cartilage on the C group. The stainng in heavier site is lighter in the longest mineralized times of C groups.ConclusionIt is well that the rabbit model of tibial lengthening using the monolateral external fixation can imitate the clinical lengthening process in this study. There are not any changes of articular cartilage in low distraction degree (<20%) and some abnormal histopathological changes in the greater distraction degree (30%). There is a trend of less damage of cartilage with the increased mineralized times which is related to the self-recovery of cartilage.