New Design And Clinical Application Of NT Memory Connector For Fracture Of Nonunion Of Distal Radius

l. Design and biomechanical study1.l Rationale of the new apparatus: In accordance with theanatomic and biomechanic characters on the fractUre site of distalradius, a new type of nitinol shaPed memory alIoy connector wasdesigned by taking the advantage of its special mechanics action,which was combined with nickel(50~53%) and titanium. Thickness ofthe counector is l.5~2.5mm. It comprises three functional parts:bone connecting part, bone hoIding part and axial comPressing part.After transformed in icy water, the device is put into the fracture sitesymmetrily. It will be driven to recover its original shaPe by bodytemperature. Then the thIee parts perform their mechanics action. Thedevice is treated one way memory effect, reversion temperature 33l2"C.1.2 Biomechanical Studies: Computer simulation threedimensional finite element analysis with ANSYS software were usedQto make the biomechanical studies. The connector was characteristicof good anti-fatigue and reusable. The initiative memorial boneholding and longitudinal comPressive fOrces were 98.40N~l25.05Nand l52N~l96N correspondingly for maintaining axial stability.2. Clinical application2.1 Clincal data: 25cases were treated by the procedure, of which 5cases fresh fractures and 20 cases nonunion of distal radius.2.2 Preoperative preparation: Sterilized SMC, a box of sterile iceand 40-50"C saline 500ml. A-P and lateral view of X-ray film.2.3 Operative technique:Make a Iongitudinal incision about 7.5 cm long on the radiodorsalaspect of the distal forearm. Develop the plane betWeen the extensorsand retract them to expose the fractUre. Reduce the fracture and. Thennickel- titanium memory cormector may be put in place, which hasbeen preshaPed in 0-4ticy water. No sooner 40-50oCsaline is beingsprayed on the connector than it is driven to recover its original shaPe.Then the fractUre is reduced and the articular surface is restored.2.4 Aftertreatmentf A drainage is necessary for almost all thecases. A light posterior pIaster splint is aPplied. If the patient's woundis satisfactorily healing at 7 days, the posterior plaster splint isremoved periodica1ly, and gentle active and active-assisted exercisesare carried out. By 3 weeks the posterior plaster splint can be removed,active motion is encouraged as pain permits. The cnnector can beremoved 6~l0 months postoperative.3. Results: AIl the cases had primary healing without infection,angulationer and dislocation. Fracture line disaPpeared 9~l4 weekslater postoperatively.4. DiscussionNT memory alloy has special mechanics action. The new deviceconsists of three functional parts f bone connecting part, bone holdingpart and axial comPressing part. It can be preshaPed for easy puttinginto the fractUre site in icy water, and will be driven to recover itsoriginal shape by body temperature. Then the thIee parts perform theirmechanics action on one way memory effect. The compressivedistance of the connector is l~5cm, so it can maintain a compressionstress on the fracture site eventhough the absorption of fractured bone.The procedure of handling the device is so convenient that no specialequipments are needed. It can be utilized on all kinds of fractIJre ornounion. It is important that never make the transformation more than8%, otherwise the connecter will lose its memory mechanics action.According to biomechanics stUdy and clinical results, the newlydesigned NT memory device that matches optimally the anatomy ofthe distal radius. It not only can maintained longitUdinal compressivefOrce continuously, but also has efficacious fixation effect withanti-shearing, bending and distracting stress. It can shorten theduration of bone healing and improve the healing quality of bone. Butthe mechanism still remains unknow, further studies required to betaken to make it clear.