【Abstract】 Objective To develop a new internal fixator Ni-Ti shape memory alloy scaphoid arc nail (NT-SAN)for fracture of the scaphoid waist and to test the biomechanical characteristics of NT-SAN so as to provide the biomechanicalproofs for cl inical appl ication. Methods According to the acquired measurements and anatomic features of the scaphoid in Chinese population, a special internal fixator—— NT-SAN was designed. The biomechanical intensity experiment: The 32 specimens of fractures of the waist of scaphoid were divided randomly into 4 groups (n =8). Reduction and internal fixation were carried out in each specimen, with Kirschner wires (Group A), with Kirschner wires stapl ing (Group B), with screw (Group C) and with NT-SAN (Group D). Their fixed strength was tested by a hydrol ic pressure biomechanical system AG-1. The biomechanical fatigue experiment: The models of 24 waist scaphoid fracture of adult upper l imbs specimens were made and randomly divided into 3 groups (n =8). Fracture was fixed with Kirschner wire stapl ing (Group E), with screw(Group F) and with NTSAN(Group G). Wrist joint was vertically pressured load of 98 N, palmar flexion and dorsal extension motion was simulated;the range of movement was from palmar flexion 5° to dorsal extension 30° and the frequency was 2 000 cycles. Displace data offragment were measured at every 500 cycles. Finally, the biomechanical features of NT-SAN were evaluated according to thetested data. NT-SAN was used to treated 1 patient with fracture of the waist of scaphoid, who was typed as Ⅱ b according to Herbert classification. Results The biomechanical tests showed that the traction forces were (15.18±3.55), (36.04±4.30),(64.88±11.62), (65.84±12.22) N and (20.28±12.09), (75.95±47.64), (120.91±26.68), (130.21±31.55) N when the displacements of the fracture l ines distracted in 1 mm/min were 1 mm and 2 mm; showing significant differences between Group D and groups A, B (P lt; 0.05), and showing no significant difference between Group D and Group C (P lt; 0.05). The biomechanical fatigue experiment showed that there were significant differences between Group G and groups E, F(P lt; 0.05) according to the measuredresults of the displacements of the fracture l ines. When wrist joint were circularly moved; showing significant differences between Group G and Group E(P lt; 0.05) after 500 circular movements, and showing significant differences between Group G and Group F(P lt; 0.05) after 1 500 circular movements according to the measured results of the “stage-shape” displacements in the fracture position. Incision healed by first intention and the X-ray films showed good NT-SAN fixation 3 months after followup.Conclusion The design of NT-SAN is in accordance with the anatomic features of the scaphoid. The fixed strength can meet the demand of the biomechanics and the range of fatigue strength can meet the demand of bony union.
ObjectiveTo summarize the effectiveness of bone transport with unilateral external fixator combined with locked plate internal fixation in treatment of infected tibial nonunion.MethodsBetween January 2010 and December 2014, 23 patients with infected tibial nonunion were treated with bone transport with unilateral external fixator combined with locked plate internal fixation. There were 19 males and 4 females with an average age of 37.8 years (range, 19-54 years). The mean length of the bone defect was 6.5 cm (range, 5.2-8.1 cm). The number of previous operations ranged from 2 to 4 times, with an average of 2.5 times. The time from injury to this treatment was 7-23 months, with an average of 11.8 months. The time of bone transport, time of the external fixation, fracture healing time, external fixation index, healing index, and complication were recorded; and the Association for the Study and Application of the Methods of Ilizarov (ASAMI) bone healing and function scores were used to evaluate the effectiveness.ResultsAll patients were followed up 3-6 years with an average of 4.8 years. Wounds and bone defects healed in all patients. No complication such as infection recurrence, nonunion, re-fracture, malunion, iatrogenic nerve paralysis, or stiffness of knee and ankle joints occurred. Five patients had needle infections which were treated by local care and no deep infection occurred. The time of bone transport was 65-120 days (mean, 75.6 days); the time of the external fixation was 75-145 days (mean, 97.8 days); the fracture healing time was 4-17 months (mean, 8.7 months); the external fixation index was 18-28 days/cm (mean, 22.4 days/cm); and the healing index was 31-52 days/cm (mean, 40.2 days/cm). At last follow-up, according to ASAMI criteria, the result of bone healing was excellent in 15 cases and good in 8 cases, and the result of function was excellent in 18 cases and good in 5 cases, all with the excellent and good rate of 100%.ConclusionFor infected tibial nonunion, bone transport with unilateral external fixator combined with locked plate internal fixation can reduce the time of external fixation and related complications, with a satisfactory effectiveness.