Rapid design and fabrication of custom artificial semi-knee joint and its clinical application

Minglin SUN

ABSTRACT

BACKGROUND:

During semi-knee arthroplasty,only the design and fabrication performed according to patient's injury can implement the good matching between prosthesis and joint surface,which is difficult to perform by conventional design and fabrication.

OBJECTIVE:

To develop a custom design and rapid fabrication method for artificial semi-knee joint based on computer aided design (CAD) and rapid prototyping (RP) techniques,and to evaluate the clinical application value of semi-knee arthroplasty and the role of CAD/RP in the design and fabrication of prosthesis.DESIGN,TIME AND

SETTING:

A custom design and fabrication of prosthesis and its clinical application was performed in the Xijing Hospital Affiliated to Fourth Military Medical University of Chinese PLA & Institute of Advanced Manufacturing Technology,Xi'an Jiaotong University & the State Key Laboratory of Materials and Mechanics,College of Mechanical Engineering,Xi' an Jiaotong University between January 2002 and December 2005.

PARTICIPANTS:

A 14-year-old male patient with osteosarcoma in the lower segment of the right femur was recruited into this study due to recurred osteosarcoma one year after surgery.Tumorectomy,large allogenic bone transplantation,and custom-made semi-knee arthroplasty were to be performed in this patient.A written informed consent was obtained from his relatives.

METHODS:

Clinical imageological data of the patient in terms of CT scanning and three-reconstruction were taken as data source.Data regarding joint shape were acquired by image processing technique.Joint contour was reconstructed by NRRBS algorithm using Surfacer software.Through the use of computer,the three-dimensional design of semi-knee joint prosthesis and its auxiliary devices was conducted.Subsequently,prosthetic prototype was fabricated by RP technique and prosthetic products were made by precise casting methods.Finally,the manufactured prosthesis was installed into the allogenic bone with the help of aiming device and was transplanted into the affected limb following distal locking.MAIN OUTCOME

MEASURES:

Error analysis of joint contour reconstructed using the Surfacer software; assembling of manufactured joint prosthesis and auxiliary devices; X-ray examination results,joint space status,and range of motion of joint in flexion and extension positions following prosthesis replacement.

RESULTS:

All procedures were conducted within 1 week.The maximum difference between CAD model-related data and original data was less than 1 mm.In the flexion,extension,and rotation positions,joint prosthesis well matched tibial joint surface,with evenly distributed stress.The prosthesis and auxiliary manufactured by RP and precise casting techniques met the requirements of design and could be installed into large segment of allogenic bone.Prosthesis was precisely placed into the affected knee and could well match contralateral tibial joint surface with normal joint space.No adverse reactions were found and the patient could implement functional exercise.One-year follow-up results revealed that the patient acquired satisfactory therapeutic effects without dislocation and chronic pain.

CONCLUSION:

Semi-knee joint individually fabricated by CAD and RP techniques provides some clinical application vilues in specific cases.