Research On The Movement Mode Of The Elbow Joint Based On Three-dimensional Motion Analysis Technique

Objective(1)To observe and study the elbow joint movement mode of normal subjects and to measure the carrying angle(CA)of the elbow joint through three-dimensional motion analysis system(3DMAS);(2)To compare different passive movement models of 2 human elbow joints specimens with different CA.(3)To investigate the effect of the rotational displacement in humeral supracondylar fracture on the motion carrying angle(MCA),and to discuss the feasibility of reducing the cutting angle of osteotomy by correcting the rotational deformity actively.Methods(1)Fifteen healthy subjects were enrolled.Motion capture system NDI Optotrak Certus(Northern Digital Inc.)was used to collect the static data of each subject.Then subjects were guided to complete elbow flexion/extension(F/E)movement at a cycle of 4 seconds,and the data acquisition was carried out for 20 seconds while the upper arm was fixed in the horizontal position.The elbow joint motion trajectory was simulated and analyzed by Visual3 D software(Visual 3D v6 Professional,C-Motion,Inc.).Euler angle components of the forearm relative to the upper arm position were calculated to get the maximal F/E angles and the change of CA during elbow movement.Bilateral motion data was acquired to compare with each other and with the standard normal range.Seven subjects of all were retested and analyzed for consistency.(2)Two right upper extremity specimens of adult male with different CA were taken.All the soft tissues except the elbow capsule were removed,and the positive X-ray images were taken at F/E positions.The passive F/E motion data of 2 specimens were collected and compared with each other,and with healthy subjects.(3)A humeral supracondylar fracture model was made on a corpse's upper extremity.A rotatable fixator which was designed in computer and 3D printed was used to collect the passive elbow F/E movements under different rotation angles of the distal fracture.Under different rotation angles,changes in MCA and joint trajectories were compared.One case of cubitus varus was selected for computer-aided design,simulating conditions that the rotational deformity was corrected or not,respectively.The feasibility of reducing cutting angle on the coronal plane during osteotomy through correcting rotational deformity was discussed.Results(1)Elbow movement trajectory of normal subjects formed a fan-shaped curved surface.The paired T-test showed that there was no significant difference in F/E angles between left and right elbow joint,nor the CA of fully extended elbow joint(CAE)(P = 0.493)and CA of elbow joint forming a right angle(CAR)(P = 0.298).With respect to the CA of fully flexed elbow(CAF),the right side of the movement was significantly larger than the left side(P = 0.006).When the single sample T-test was performed with the standard range of motion(ROM)of 0-140 °,only the right flexion angle conformed to this standard(P = 0.435),while bilateral extension angles differed by about 10° from this standard.Repeated measurement of the maximum flexion angle of right elbow joints indicated that difference between 2 independent measurements was no more than 7%,showing a higher consistency.(2)Although CAE of 2 specimens were all in normal range of 0-15°,showing no varus or valgus changes,motion data of the specimen with larger CA was significantly different from those of normal subjects and of the specimen with smaller CA,showing an outward shift of the movement trajectory,which was consistent with the X-ray performance.Three-dimensional motion capture can measure the MCA,and then speculate the varus/valgus changes in the elbow joint.(3)When the distal part of the fracture is rotated,the absolute value of the CAE gradually decreases to 0,while the absolute value of the CAF gradually increases.The rotation angle and the variation of CA are functionally related,and the overall movement trajectory moves inwards.Correcting rotational deformity actively is helpful to reduce the cutting angle during osteotomy in orthopedic surgery.Conclusion(1)Elbow movement trajectory of normal subjects formed a fan-shaped curved surface where individual differences existed,which is related to anatomical structure of the humeral trochlea and the effect of the upper arm muscle.3DMAS can simulate and visualize the elbow movement trajectory,providing an effective method to measure the MCA.(2)Measurement of MCA can be used as a way to identify elbow varus/valgus deformity.Through analyzing a variety of sports data using 3DMAS,non-complex elbow deformities can be speculated.(3)The rotational displacement of the humeral supracondylar fractures causes the overall elbow movement trajectory to deflect towards the direction of rotation,and the rotation angle and the variation of CA are functionally related.For cases of humeral supracondylar fracture complicated with cubitus varus needing orthopedic surgery,correcting rotational deformity actively is helpful to reduce the cutting angle during osteotomy to a certain extent.