Bone ingrowth into a shoulder prosthesis

Elise van Aken

Site of the project:

start of the project: October 2006

In February 2007 the Interim Thesis has been appeared and a presentation has been given.

The Master project has been finished in September 2007 by the completion of the Masters Thesis and a final presentation has been given. For working address etc. we refer to our alumnipage.

Summary of the master project:
After a long period of functioning a joint (such as a shoulder, hip or knee) may fail due to mechanical wear and tear, osteoporosis (decrease of the bone-density), osteoarthritis or rheumea (decay of cartilage). As a consequence, the patient is faced with a lot of pain and mobility limitations. In some cases this problem can be solved by the replacement of the glenoid (which is the cavity of the shoulderblade in which the upper arm fits) of the shoulder joint with a prosthesis. The prosthesis consists of porous material on the bone-side. After positioning of this prothesis, by replacement of the cavity of the shoulder joint, bone is supposed to grow into the prosthesis such that the prosthesis becomes integrated with the shoulderblade. This enhances a stable position of the cavity of the shoulder prosthesis in the shoulderblade. A crucial aspect is the stress distribution in the shoulderblade, since the human body has been constructed such that growth of bone takes place if a threshold mechanical stress has been exceeded. If the stress is lower than this threshold, then, no bone ingrowth will occur and even the present bone will decay ( bone resorption). Of course, the latter case is undesirable. The mechanism is logically sound: At those positions without mechanical loading, no bone is needed and hence the present bone will disappear. If the body is loaded, then, bone has to be reinforced. A crucial question is here: Does the mechanical loading / stress exceed the threshold necessary for bone ingrowth into the prosthesis and will the bone of the shoulderblade remain intact?


To answer these questions, the stress distribution over the shoulderblade and prosthesis is computed. The contact between the prosthesis and the shoulderblade and the difference in material properties are dealt with in the simulation. A further assumption in the simulation is that the arm of the patient moves up and down. This gives a boundary condition for the computation of the stress of the prosthesis and shoulderblade. For the relation between the stresses and strains, Hooke's Law is used. The set of governing partial differential equations is solved using a finite element procedure.

In the present three-dimensional simulations a coupling between the solution of the mechanical equations for the stress and the equations for bone ingrowth is currently lacking. The ingrowth of bone provides a change of the bone density. This change influences the solution of the mechanical equations. Besides the medical / mechanical interest of this project, the largest mathematical challenges are provided by the solving the three-dimensional problem and the nonlinear coupling between the mechanical equations and the models for bone ingrowth.

Contact information: Kees Vuik

Back to the home page or the Master students page of Kees Vuik