Implant Biomechanics

Design, development and evaluation of implants used in joint replacement, trauma and spinal stabilization.

Scope
In order to develop orthopaedic implants, particularly joint replacements, that will function for the lifetime of the patient, many material and biomechanical design criteria must be considered. The purpose of the research conducted at the Implant Biomechanics Lab of the Luck Research Center is to evaluate existing and prototype implants according to these design criteria, with the ultimate goal of designing better functioning implants and avoiding failures. For example, the implant should have adequate strength to avoid fracture or fatigue failure. Implant geometry and appropriate positioning should allow adequate range of motion, since unintended impingement can damage the implant or lead to loosening. Every implant must have secure fixation to the bony structures, whether achieved by press-fit, cementing, or bone ingrowth, to minimize micromotion and fretting wear between the components of the implant or between the implant and bone.

Research Techniques
The researchers of the Implant Biomechanics Lab develop in vitro models that simulate the mechanical conditions experienced by an implant and the surrounding bone and soft tissues in a patient under various physiological activities. These models are employed to evaluate and improve existing implant designs, surgical treatments, or fixation methods, and to develop new implants. The models can be based on cadaveric specimens and/or soft tissues, or synthetic composite bones. Loads and torques in different planes encountered during specific activities by the patient are simulated using sophisticated, multi-dimensional computer-controlled servo-hydraulic load frames. In conjunction with custom test fixtures that are designed in the Implant Biomechanics Lab, the test equipment permits the evaluation of many types of orthopaedic implants, particularly joint replacements and spinal stabilization devices, under a wide variety of complex loading conditions.

Key Research Equipment
The Implant biomechanics lab is equipped with four MTS Servo-hydraulic load frames, each with independent controllers and data acquisition systems. One of the load frames is an MTS 858 equipped with a spine kinematics testing module, allowing application of eight independent loads and motions, including axial loading and axial rotation/torsion; superior and inferior rotations in the sagittal and coronal planes; and inferior translation in the transverse plane. Three additional load frames can be equipped with custom-built test fixtures, as needed for specific projects. At present, one load frame is equipped with a three-station fretting wear simulator, designed to simulate wear due to unintentional motions at non-articulating interfaces of orthopaedic implants. This device has been used to investigate backside fretting between the polyethylene insert and the tibial tray of total knee replacements, fretting of non-cemented femoral stems against the femoral cortex, and wear of cemented femoral stems against the surrounding cement mantle. An additional, three-station artificial disc simulator can be used to evaluate the fatigue strength of elastomeric artificial discs.

Staff
The faculty of the Implant Performance Laboratory includes Eddie Ebramzadeh, Ph.D., and Sophia Sangiorgio, Ph.D.

Publications

 

  1. Ebramzadeh, E.; McKellop, H.; Dorey, F.; and Sarmiento, A.: Challenging the validity of conclusions based on P-values alone: a critique of contemporary clinical research design and methods. Instr Course Lect, 43: 587-600, 1994
  2. Ebramzadeh, E., Sangiorgio, S.N., Longjohn, D.B., Buhari, C.F., Dorr, L.D.: Initial stability of cemented femoral stems as a function of surface finish, collars, and stem size. J Bone and Joint Surg, Am, 2004. Jan;86-A (1): 106-115.
  3. Ebramzadeh, E., Sangiorgio, S.N., Lattuada, F, Kang, J-S, Chiesa, R., McKellop, H.A., Dorr, L.D.:Accuracy of methods for measurement of polyethylene wear from radiographs of total hip replacements. J Bone and Joint Surg, Am, 2004. Dec; 85-A (12):2378-2384.
  4. Sangiorgio, S.N., Ebramzadeh, E., Longjohn, D.B., Dorr, L.D.: Effects of Dorsal Flanges on Fixation of a Cemented Total Hip Replacement Femoral Stem. J Bone Joint Surg Am. 2004 Apr;86(4):813-820.
  5. Ebramzadeh, E., Sangiorgio, S.N., Clarke, I.C.: Greater Expectations and Greater Joint Loads in Modern Total Joint Arthroplasty Patients, in Core Knowledge in Orthopedics: Adult Reconstruction and Arthroplasty, edited by Jonathan Garino and Pedro Beredjiklian. Published by Elsevier in Philadelphia, 2006.

Contact
The Implant Performance Laboratory welcomes industry-sponsored projects, as well as collaborations with other academic institutions. For additional information, please contact:

Eddie Ebramzadeh, Ph.D., EEbramzadeh@mednet.ucla.edu, tel:             (213) 742-1378       
Sophia Sangiorgio, Ph.D., SSangiorgio@mednet.ucla.edu, tel:             (213) 742-1370