| Objectives:Malunion of tibial fractures is a potential,underestimated postoperative complication of intramedullary nailing,which can lead to long-term arthritis in patients with dysplasia and unstable knee joint.In order to improve the treatment effect of curing lower limb fracture and reduce the risk of long-term arthritis,many scholars have conducted a large number of basic and clinical studies.This study made a model,which is the upper middle section of tibial fracture respectively in different rotation deformity condition,in order to consider tibial rotation deformity caused by different levels of knee weight-bearing area under vertical load,the degree of change with the stress distribution and the relationship between the rotation and the force line offset for providing the biomechanical tibial fracture reduction quality of clinical evaluation.Methods: 12 cadaver specimens were selected excluding rheumatism,tuberculosis,tumor,other pathological changes anatomical changes and osteoporosis.The structure of femur,tibia and knee is structurally complete.Being without visible deformity of knee joint,articular cartilage integrity,unrestricted knee flexion and extension,retaining the joint capsule,ligament and patella retinacula tissue,femoral head four tendon and patellar tendon and removing all muscular tissue are prerequisite.Taking good specimens of standby packages to prevent dehydration,keeping in-20 ? cryopreservation and 12 h at room temperature before the start of the experiment are necessary.The contact characteristics of normal knee joint under vertical load were measured and the window was opened in the joint capsule.The pressure sensitive film placed under 600 n vertical pressure was measured under different deformation stress of the knee joint between inside and outside room(measuring the mean stress,the unit for Mpa)and stress distribution.Then,the model of one third of the tibia was prepared and the models of 5 degrees,15 degrees,5 degrees,10 degrees and 15 degrees of internal rotation deformity were produced respectively after being amputated.The models were fixed by the plate screw system.The last two steps were repeating the experimental steps above and measuring the different deformation stress including both the stress distribution and the statistical analysis of the knee joint between inside and outside room(measuring the mean stress,the unit for Mpa)under 600 n vertical pressure.Results: A completely randomized analysis of variance showed that there was a statistically difference between the medial and lateral stresses on the knee joint,which is medial stress on knee joint significantly higher than the lateral stress(P<0.05).It also revealed that a significantly difference between the medial stress on knee joint at different rotational deformities(including the neutral position of 0 degrees here)was observed(P<0.01).There were statistically significant differences among the rotational deformities of neutral 0 degree,external rotation of 5 degree,external rotation of 10 degree,external rotation of 15 degree and the medial stress of the knee joint gradually increased as the degree of external rotation increased(P<0.05);There were statistically significant differences between the rotational deformities of neutral 0 degree,internal rotation of 5 degree,internal rotation of 10 degree,internal rotation of 15 degree and the medial stress of the knee joint gradually decreased as the degree of external rotation increased(P<0.05).There was no statistically differences among the different rotational deformities(including the neutral 0 degree)in terms of lateral stress of knee joint.Conclusions: In this study,pressure sensitive films were used to quantitatively analyze the stress in the gap of knee joint in middle and lower 1/3 of tibia fracture.Our study indicated that the stress on the medial knee joint was significantly higher than that of the lateral knee joint.Both the external and internal rotation deformity help contribute to the increase of the medial stress on knee joint.In addition,the medial stress on the knee joint increased with the increase of external rotation deformity,while the medial stress on the knee joint decreased with the increase of internal rotation deformity.The lateral stress on the knee joint increased with the increase of external rotation deformity,while the lateral stress on the knee joint decreased with the increase of internal rotation deformity.These to some extent reveal the pathogenesis that knee osteoarthritis occurs in the knee medial compartment and also provide a theoretical basis for the surgeon to choose what degree of rotational deformity as an indicator of osteotomy,a biomechanical basis and a quantitative standard for evaluating the quality of femoral fracture reduction. |
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