Basic And Clinical Studies Of The Joint Capsule After Anatomical Repair Of Hip Arthroplasty

Part Ⅰ Anatomical and tensile mechanical analysis of hip joint capsule repairObjective To design an anatomical way of capsule repair,compare the differences of anatomy and tensile mechanics between anatomical and transtrochanteric repair,and provide biomechanical and anatomical evidence for capsule repair in total hip arthroplasty(THA).Methods Six bone–capsule–bone specimens were obtained from posterior hip joint of fresh frozen cadavers.The maximum strain,load,elastic modulus and load-strain curves of the capsule ligament complex specimens were recorded by Instron Universal Material Testing Machine.Twelve cadaveric hip specimens were dissected to the capsule.The anatomical data of the anatomical and reconstructed insertion of the posterior capsule was measured and recorded,and anatomical way of capsule repair was designed.The tensile strain of anatomical and transtrochanteric repaired capsule at 90 degrees of hip flexion were documented.The suture area of the posterior capsule was divided into nine sections,and the thickness of different sections was measured and compared.Posterior capsule of the cadavers was repaired in transtrochantericly way and anatomical way separately and simulated rehabilitation was conducted.The effect of rehabilitation on the repaired capsule was observed.Results The load-strain curve of capsule ligament complex conforms to rheological and viscoelastic characteristics.The maximum tensile strain of the complex was(39.21 ± 5.23)%,the maximum load was(142.06 ± 34.15)N,the tensile strength was(1.65 ± 0.38)Mpa,and the elastic modulus is(14.23 ± 5.62)MPa.The distances from the anatomical insertion to the transtrochanteric reconstructed insertion point is: upper part 7.35±0.38 mm,middle part 11.30±0.60 mm,and lower part 13.24±0.74 mm.Anatomical repair of the capsule is feasible.At 90 ° hip flexion,the tensile strain of repaired capsule was higher than that of normal capsule,and the difference was statistically significant(P<0.05).Tensile strain of transtrochanteric repaired capsule is: upper part(37.0 ± 4.9)%,middle part(53.3 ± 1.1)%,lower part(68.3 ± 6.2)%,tensile strain of normal capsule is: upper part(17.0 ± 2..6)%,middle part(24.1 ± 1.4)%,lower part(26.0 ± 4.3)%.The thickness of the posterior joint capsule in different sections is statistically significant(P<0.05),and capsule at0.5cm-1cm proximal to the femoral insertion is suitable for suture.There the average thickness of capsule is: upper part(3.48 ± 0.11)mm,middle part(2.36 ± 0.09)mm,lower part(1.59±0.24)mm.The posterior inferior joint capsule is thinnest at(1.42 ±0.02)cm proximal to the femoral insertion,and sutures should be avoided here.After simulating rehabilitation,avulsion occurred in the lower part of the posterior capsule repaired transtrochanteric(10/12),and the anatomically repaired capsule remained intact.Conclusion1 The capsular ligament complex has nonlinear material characteristics and uneven thickness.A reasonable way of capsular repair should conform to its mechanical characteristics,that is,the tensile range of the capsule in rehabilitation activities should be in the straight region of the load-strain curve after repair.The line0.5cm-1cm proximal to the femoral neck insertion is the most suitable region for suturing.2 The anatomical insertion of capsule is located at the distal end of the femoral neck osteotomy line,and anatomical repair can be implemented.The transtrochanteric way of repairing the capsule is not anatomical repair.3 The tensile strain of posterior and inferior part of transtrochanteric repair capsule is too high and easy to tear.Anatomical capsule repair is in accordance with the requirements of tensile mechanics and helpful to improve the survival rate of repair.Part Ⅱ Construction and Analysis of Three-dimensional Finite Element Model of Capsule RepairObjective To construct a three-dimensional finite element mechanical model of total hip arthroplasty including joint capsule,and compare the biomechanical differences between two repair methods.Methods Thin-section CT data of pelvis and lower limbs of a volunteer was obtained and imported into Mimics(Materialise’s interactive medical image control system),and three-dimensional model of the hip joint was reconstructed.Digital model of cup,femoral prosthesis and joint capsule was created in CATIA software and imported into Mimics to simulate total hip arthroplasty.Digital geometry model was generated by surface fitting of Geomagic Studio Software,after assembly,data were imported into ABAQUS software.The properties of capsule were set according to the mechanics test,anatomical studies,and constitutive equations.The boundary conditions and loading of the model was set.Anatomical and transtrochanteric repair of capsule was simulated.Difference of mechanics between anatomical repaired and transtrochanteric repaired capsule was compared during hip flexion.Results The finite element model is valid and the stress-strain curve of the finite element model coincides with the mechanical test results of the specimens,which is consistent with the characteristics of capsule.The stress distribution of anatomical repair capsule is even,while that of transtrochanteric repair capsule is uneven,the lower part of transtrochanteric repair capsule reaches the ultimate tensile stress of capsule specimens at 90 degrees flexion.Conclusion The finite element model can be applied to study the dynamic stress distribution of capsule visually and quantitatively,The stress distribution in the lower part of transtrochanteric repaired capsule is concentration and uneven when the hip is flexed,and is prone to avulsion.The anatomical repair stress distribution is even and more biomechanical.Part Ⅲ Clinical Study of Anatomical Repair of Capsule in Total Hip ArthroplastyObjective To compare the clinical data of THA patients received two different repair methods and explore the impact of anatomical repair of the joint capsule on postoperative function and prognosis after performing total hip arthroplasty(THA)via posterolateral approach.Methods Between April 2013 and April 2015,THA was performed on 106 patients with femoral neck fractures by posterolateral approach.According to the different repair methods of the posterior capsule complex,they were divided into 2groups,52 cases in the anatomical repair group(group A)and 54 cases in the transtrochanteric repair group(group B).There was no significant difference in age,gender,cause of injury,fracture classification,prosthesis type,combined medical disease and body mass index(BMI)(P> 0.05).Operation time,ambulation time,blood loss,drainage volume,difference of hemoglobin before and after operation,acetabular cup anteversion and abduction,femoral offset,visual analogue score(VAS),Harris score and early dislocation rate were compared.Results There was no significant difference in intraoperative blood loss,operation time,acetabular cup anteversion,abduction,femoral offset,and leg length discrepancy(P> 0.05).Ambulation time,drainage,and hemoglobin difference of anatomic group was less than transtrochanteric group(P <0.05).The mean follow-up period was 24.6 months,(range 12 months to 48 months).Postoperative VAS and Harris scores in each group were significantly better than those before surgery(P<0.05),and the VAS scores in the anatomic group were better than those in the transtrochanteric group at 3 days,3 weeks and 6 weeks after surgery.(P <0.05).There was no significant difference in VAS scores between the two groups at 6 and 12months(P> 0.05).The Harris score of the anatomic group was better than that of the transtrochanteric group at 3 weeks(P <0.05).The difference of Harris score at 6weeks,6 months and 12 months between two groups was not statistically significant(P> 0.05).One patient in the transtrochanteric group was dislocated 4 weeks after surgery,and no dislocation occurred in the anatomy group during the follow-up period.The difference of dislocation rate between two groups was not statistically significant(P> 0.05).Conclusion Anatomical repair of joint capsule in THA helps is helpful in faster recovery,reducing postoperative pain,and increasing joint stability.