Comparison Of Three Cannulated Compression Screws With AO Kirschner Wires Tension Band In Patella Transverse Fracture: A Cadaveric Biomechanical Study

Background: The incidence of patella fractures has been increasing in recent years,and more than half of them are transverse fractures(AO-34-C).The indication for transverse patella fracture surgery is displacement of more than 2mm or comminuted fracture.The patella can transmit the tensile force of the quadriceps muscle,which plays an important role in extending the knee and maintaining the stability of the knee joint.This requires surgical treatment to preserve the complete anatomical shape of the metatarsal bone as much as possible,restore the flatness of the articular surface and the continuity of the knee extension structure.At present,the AO Kirschner wire tension band method is still widely used in clinical treatment of patella fractures.However,due to the strict early rehabilitation exercise and the high incidence of postoperative displacement,failure,pain and secondary surgery,orthopedist has been searching for the best alternative for many years.The purpose of this study was to compare the stability of three cannulated compression screws and AO Kirschner wire tension bands for the fixation of a transverse patella fracture model,and to objectively and quantitatively evaluate the feasibility of alternative solutions..Methods: A total of 15 patella specimens were used for biomechanical testing.The standard trauma model of the patella transverse fracture(AO-34-C)was made by transacting the patella transversely.It was fixed with three cannulated compression screws(N = 9)and AO Kirschner wire tension band(N = 6).A custom platform was used to simulate knee flexion at 90 °.The quadriceps tendon was loaded with 25-275 N force to simulate knee extension.The displacement of fracture(mm)and the number of loading cycles were both continuously recorded during the 1000 cycles and 10,000 cycles of dynamic fatigue testing of the two fixation methods.Fixation failure was defined as a displacement of more than 2 mm or structural damage.Statistical analysis was performed using Mann-Whitney U test and Fisher’s exact test.Results: 1.Early in the low-cycle test,we can observe that the separation gap of the AOKW group increases rapidly,and then the increasing rate gradually slows down and stabilizes.During the TCCS loading cycle,the growth rate of the separation gap remained stable.The early growth rate of the AOKW group was significantly higher than that of the TCCS group(P = 0.005,P <0.05),and the difference was statistically significant.After the low cycle test,the separation gap of the AOKW group was 0.77 ±0.59 mm.All six samples passed the low cycle fatigue test with a 100% pass rate.The separation gap of the TCCS group was 0.31 ± 0.69 mm.Eight samples passed the low cycle fatigue test.The pass rate of the test was 89%.The separation gap of the fracture low cycle test in the TCCS group was much smaller than that in the AOKW group(P =0.012,P <0.05),and the difference was statistically significant.2.During the high cycle test,after the AOKW group was loaded to 3149 ± 1706 cycles,the separation gap reached 2mm in succession and the fixation failed.None of the 6samples passed the high cycle fatigue test,and the pass rate was 0%.One sample of the TCCS group failed,and the remaining eight samples entered high cycle testing,and the separation gap of TCCS group is only 0.69 ± 0.42 mm when it is loaded to 10,000 cycles.TCCS group is still effective,and the pass rate is 89%.The pass rate of the high cycle fatigue test in the TCCS group was significantly higher than that in the AOKW group(P= 0.000,P <0.05),and the difference was statistically significant.3.In addition,after the high-cycle dynamic fatigue test was terminated,it was also observed that the fracture separation gap of the TCCS group became smaller or even disappeared with stress unloading,while the fracture separation gap of the AOKW group remained with stress unloading and there is an irreversible separation gap appeared.Conclusion: Both the TCCS and AOKW methods can endure early simulated rehabilitation exercise.However,the TCCS fracture separation gap is smaller and thenumber of tolerable loading is more.TCCS method has obvious advantages in initial stability and long-term stability when used to fix transverse patella fractures.The biomechanical properties of TCCS in the treatment of simple transverse patellar fractures are significantly better than AOKW.