Basic And Clinical Study On Biomechanical Stability Of Scaphoid Fractures

The fracture of the scaphoid is a common injury,accounting for 60-80%of all the carpal fractures and over 80% of the fractures occur in the waist of scaphoid.Given the special anatomic location that the scaphoid serves as a major connection in the proximal row of the carpus,it has an important role in the wrist function.Consequently,the nonunion of scaphoid fracture arising from none or inappropriate treatment can compromise the wrist function or even leave the long-term sequela.It is reported that,the risk of nonunion following scaphoid fracture is 5% roughly,and can be up to 15% in selected complex cases,e.g.open fracture,multiple fracture,high body mass index,smoking and alcoholism.Currently,the surgical management of scaphoid waist fractures and nonunion remains a challenge for the hand surgeons and scaphoid waist fractures and nonunion often requires surgical management.Surgical management of scaphoid fractures nonunion included a combination of internal fixation and bone grafting to restore alignment and length of the wrist joint.Inappropriate treatment can lead to scaphoid fracture nonunion,resulting in humpback deformity,avascular necrosis(AVN)and collapse of other carpal bones(SNAC wrist),dorsal intercalated segment instability(DISI),and wrist arthritis,or wrist collapse,affecting the patient’s quality of life seriously.Therefore,in addition to the diagnosis of scaphoid fracture correctly,management of scaphoid fracture properly and timely plays a crucial role in the prevention of the follow potential complications.Through extensive reading of the literatures on scaphoid fractures and fracture nonunion,we found that there were many methods about internal fixation for scaphoid,but no consensus has been reached at present.Although the use of cannulated compression screws is widely accepted,a single screw may not provide absolute stability when considering complex and multidirectional motions,especially for motions during flexion and extension of the rotating wrist,radioulnar migration,and dart-throwing motions.In addition,in cases with significant bone defects and "humpback deformity",additional bone grafting is required to reconstruct the shape and alignment of the scaphoid,and a single screw may not provide a stable internal fixation environment for the bone graft area.To solve the abovementioned problems,many scholars have accomplished plenty of work.Some scholars advocated the use of double headless compression screw,they believe that it can further enhance the torsion resistance of fracture stability,thus increasing the healing rate and improving clinical outcomes.In addition,when it comes to the obvious defects of bone in scaphoid fracture nonunion,some scholars put forward the plate fixation treatment to treat humpback deformities or obvious bone defect of scaphoid fracture and nonunion.They believe it can make up for the deficiency of single screw in this type,at last prevent the gradual collapse and nonunion of scaphoid.Encouraging results have been achieved and reported.Double screws and mini-plates have been proven to have significant biomechanical and clinical advantages,but they also have the following three disadvantages.First,the insertion of double Herbert screws takes up more space that for bone grafting which can reduce the amount of bone graft that can be filled,and affects the fragile blood supply of the scaphoid which is detrimental to fracture healing.Second,when placing a plate,it is necessary to expand the area of dissection around the scaphoid and destroy the blood supply and surrounding tissues,which may also affect bone healing.Third,both of them are technical more demanding and therefore require a longer learning curve.This study put forward “tripod” technique which include a cannulated compression screw and two anti-rotational K-wires to improve the stability of scaphoid fracture.Our study will be divided into three parts.Firstly,the biomechanical advantages of the internal fixation method of cannulated compression screw combined with two K-wires were analyzed by finite element analysis.Secondly,we analyzed the nonunion of scaphoid in patients with “humpbacked deformity”.Tripod internal fixation combined with radial wrist approach in the treatment of humpback deformity has achieved excellent clinical results.Finally,we summarize the comparative study of tripod internal fixation and single cannulated compression screw internal fixation for the treatment of the scaphoid waist fracture nonunion.It is observed that due to the addition of two anti-rotation K-wires,the healing time of fracture is reduced and the early functional exercise can be achieved.Part one Biomechanical stability of three internal fixation devices for scaphoid waist fractures:a finite element analysisObjective: This part aims to compare the biomechanical stability of three internal fixation methods using the method of finite element analysis.These three fixations include single cannulated compression screw and cannulated compression screw combined with one and two K-wires.The hypothesis of our finite element analysis was that cannulated compression screw combined with anti-rotational K-wires can improve the resistance ability of both bending and rotational.Method: One male volunteer was selected,aged 28,175 cm in height and70 kg in weight.CT was used to perform continuous scanning of wrist joint.On the basis of wrist CT data,3-demention model of scaphoid was established by digital software.The scaphoid was designed to simulate waist fracture of scaphoid.Three internal fixation models were performed: single cannulated compression screw,single cannulated compression screw combined with one parallel K-wire,and single cannulated compression screw combined with two parallel K-wires.The same constraints and two kinds of loads(bending and rotation)were applied to the three groups of model,and the deformation peaks and stress peaks of the three groups of model under the action of two kinds of the same load(rotational force and bending force)were compared.Results: In the deformation and stress cloud diagrams under 50 N bending load state of the three internal fixation devices,the peak deformations of fracture side of single screw and screw combined with one and two K-wires were 0.2448 mm,0.20075 mm and 0.19436 mm,respectively.The peak stresses were 28.939 MPa,38.272 MPa and 15.951 MPa,respectively.The Von Mises stress distribution of internal fixation were 298.29 MPa,242.51 MPa and221.12 MPa,respectively.In the deformation and stress cloud diagrams under50 N rotational load state of the three internal fixation devices,the peaks deformation at the fracture side of the single screw and screw combined with one and two K-wires were 0.020324 mm,0.011651 mm and 0.010709 mm,respectively.The peak pressures were 1.1969 MPa,0.91448 MPa and0.95722 MPa,respectively.The Von Mises stress distribution of internal fixation were 39.403 MPa,53.062 MPa and 48.725 MPa,respectively.Part two A preliminary study of "tripod" technique combined with radial approach of wrist for the treatment of scaphoid nonunion with "humpback deformity"Objective: The aim of this part was to introduce the “tripod” technique combined with the radial approach of wrist for the surgical management of the scaphoid nonunion with "humpback deformity".The “tripod” technique used a cannulated compression screw and two anti-rotational K-wires.We also reported the surgical outcome in this technique to evaluate its clinical efficacy.Method: From January 2016 to January 2020,15 eligible patients with "humpbacked deformity" of scaphoid nonunion were included,with an average age of 33.4 years and an average time after injury was 11.5 months.Preoperative X-ray and computed tomography(CT)confirmed scaphoid waist nonunion with "humpback deformity".After the "humpback deformity" was corrected by open reduction through radial approach of wrist,volar wedge bone grafting was performed,and finally fixation was performed with the "tripod" internal fixation technique.They were told to return to the clinic every two weeks and were followed up every three months after bone healing until 12 months at least postoperatively.The minimum follow-up was 12 months.The healing status,healing time and deformity of each patient were recorded.LISA,DASH score and Mayo Score of each patient were recorded before and after surgery.Results: Postoperative follow-up was 12-22 months(mean 16.5 months).All fractures were confirmed to be healed by postoperative imaging,with an average of 14.5 weeks.The "humpback deformity" was satisfactorily corrected in all patients.The LISA was 74.8±3.5 before surgery and 35.7±4.0after surgery.DASH score,and Mayo score were all improved after surgery.Part three Cannulated compression screw with versus without two K-wire fixation for treatment of scaphoid waist fracture nonunionObjective: This part aims to introduce the “tripod” technique using cannulated compression screw and two anti-rotational K-wires for treatment of unstable scaphoid waist fracture nonunion,and to compare it with the single cannulated screw fixation technique in term of scaphoid union and surgical outcomes.Method: It was a retrospective study.From January 2014 to March 2020,103 consecutive patients with scaphoid waist fracture nonunion treated with the tripod fixation and bone grafting(n=45)or with single cannulated compression screw and bone grafting(n=58)were included.All the procedures were performed by the same hand surgery team,and autologous cortico-cancellous radius bone graft was used for bony reconstruction.The minimal follow-up period was 12 months.The union rate and the time to union,range of motion(ROM),grip strength,Visual Analogue Scale(VAS),Quick Disabilities of the Arm,Shoulder and Hand(DASH)score and modified Mayo Scores at the last visit were compared.Results: In tripod fixation group,bony union was achieved in all patients at the mean of 14.8±3.8 weeks,while in the single cannulated screw fixation group the bony union rate was 94.8%(55/58)and the time to union was17.6±3.6 weeks.The difference of time to union was statistically significant(P=0.027),but not for bony union rate(P =0.122).At the last visit,no significant difference was found with respect to any clinical and radiographic outcome measures(all P >0.05).The overall rate of complications was not significantly different between two groups(15.6% vs 10.3%,P =0.430).Conclusion:1.By comparing the biomechanical stability of three internal fixations using the method of finite element analysis(FEA),we can conclude that cannulated compression screw combined with two K-wires was a more stable internal fixation method for scaphoid waist fracture compared with the other two internal fixation methods,which could provide a certain biomechanical basis for its clinical application2.Through the radial approach of wrist,the exposure of scaphoid“humpback deformity” is relatively superficial.It can be fully exposed directly,and can reduce the operation time;Secondly,the radial wrist approach can reduce the destruction of trophoblast vessels of scaphoid,and provide a clear surgical field for the exposure of humpback deformity,and provide convenience for bone grafting to achieve normal alignment of wrist.3.Tripod fixation technique combined with the structural bone grafts can make up for the shortage of the single screw rotation resistance and can correction of scaphoid humpback deformity firmly,thereby avoiding the collapse of scaphoid,avoiding the happen of the scaphoid malunion,and reducing the surgical complications to the large extent.4.Tripod fixation technique with headless compression screw and two K-wires is a safe and effective technique for treatment of scaphoid nonunion fixation and can be considered to use in practice,especially for those potentially rotationally unstable cases.