| Objective: Recently, with the rapid development of transportation andindustrial production, fracture in distal femur caused by high energy inducedtrauma has seen a gradually uprising tendency. Fractures in distal femur areusually caused by direct or indirect violence and manifest as open, segmental,multi-segmental and comminuted fractures with severe soft tissue damage.The wounds are generally complex and complications such as healing withlimb deformity, delayed healing and pain are usually seen after surgery.Antegrade or retrograde interlocking intramedullary nailing and locked plateare the mostly used treatments for distal femoral fractures by orthopedicsphysicians due to its obvious advantages in reduction of soft tissue damage byprotection of blood supply to fracture site, fixed axis,and early functionalexercise after surgery. Orthopedic physicians face severe challenges withdistal femoral fractures as during which bone loss, severe soft tissue injury,wide and large medullary cavity in distal femur and muscular stretching caninduce swinging of intramedullary nail in medullary cavity which affect therestoration of bones, healing process of fracture and functional exercise ofaffected extremity. With the promotion of poller screw technology which canreduce the width of metaphyseal marrow cavity and increase the stability ofthe broken ends, clinical reports on the correction of angular deformity indistal femur with a combination of poller screws and intramedullary nail areaccumulating.In this study, the biomechanical effects of using pure antegradeintramedullary nail, antegrade intramedullary nail plus poller screw orretrograde intramedullary nail in fixation of AO：33-A3were compared so asto provide more evidences for clinical application.Methods:6adult lower limb specimens with anticorrosion (provided bythe department of anatomy of Hebei medical university), including5males,1 females with a mean age of29(31-45years old) and the mean length of femurwas42cm (40-46cm). The section between hip joint and knee joint wasselected and only thigh was kept. Soft tissues such as skin and muscle on thesurface were removed to expose femur. Skeletal diseases such as fracture,bone cancer and osteoporosis were checked under naked eye and X-rayexaminations. According to AO classification, establish the femurs to AO：33-A3. Specimens were randomly divided into group A, B and C. group A wasfixed with retrograde intramedullary nail; group B was fixed with antegradeintramedullary nail; group c was fixed with antegrade intramedullary nail pluspoller screws. Fixed specimens were embedded into denture resin with femurupward and femoral condyle downward. Femoral condyle was maintained in ahorizontal position and a valgus angle of7degree was produced betweenfemoral shaft axis and vertical axis. Specimens were then fixed onBOSE3520-AT biomechanical machine and then the three-point bending test,vertical compression test and rotation test were performed. All data wereprocessed with SPSS19.0software by using one way ANOVA analysis and avalue of P <0.05was considered significant.Results: In three-point bending test, the bending, flexion, anteflexion andretroflexion displacement under400N vertical load in group A, B and C wererespectively,the displacement of group A was1.3652±0.1587mm、1.9522±0.1785mm、1.2136±0.1453mm、1.6358±0.1208mm；group B was2.1624±0.1552mm、2.8025±0.1058mm、2.1781±0.1433mm、2.1236±0.1825mm；group C was0.9157±0.1444mm、1.4261±0.1368mm、2.0758±0.1366mm、2.0756±0.1497mm。 There were significant differencesamong three groups（P <0.05） in distances of displacement and load bearingcapacity of bones during anteflexion and retroflexion in group A were largerthan those in group B and C while the loading bearing capacity of bone duringflexion and bending in group C were larger than group A and group B.In vertical compression test, under the vertical load of500N, thedisplacement for group A was0.4130±0.0235mm； for group B was0.5090±0.0241mm；for group C was0.4613±0.0343mm。 the displacement for group A was for group B and for group C. There were significantdifferences among three groups in distances of displacement（P<0.05）.Distances of displacement between group A and B（P<0.05）, Aand C（P<0.05） and B and C （P<0.05）were significantly different. GroupA had the largest load bearing capacity, followed with group C while group Bhad the poorest load bearing capacity.In the rotation test, under3Nm torque, the torsional angle for group Awas3.1967±0.2151； for group B was3.3320±0.2120°；and for group C was2.4907±0.2085. There were significant differences among three groups intorsional angle（sP<0.05）. torsional angles between group A and B（P<0.05）,A and C（P<0.05） and B and C （P<0.05）were significantly different. GroupC had the largest load bearing capacity while group A and C were similar.Conclusion: AO：33-A3fixed with retrograde interlockingintramedullary nail had better resistance to vertical compression and bendingand flexion than those with antegrade intramedullary nailing which showedexcellent biomechanical effects; poller screw could strengthen the stability ofbroken ends and when combined with antegrade intramedullary nailingmethod, it showed better resistance to rotation and anteflexion andretroflexion when compared with retrograde intramedullary nailing method inthe treatment of AO：33-A3. Fixation of AO：33-A3with pure intramedullarynailing showed poorer resistance to bending, rotation and compression whencompared with the other two groups. |
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