An RSA and DEXA Study on Migration of Proximal Interphalangeal (PIP) Joint Prostheses of the Hand

There is a large patient group with primary osteoarthritis (OA) and secondary osteoarthritis due to joint-associated fractures, repeated trauma to the joint and surroundings, congenital joint-deformity, hyper mobility and diabetes. There are 2 preservative surgical treatment alternatives for PIP joint OA; namely arthrodesis and arthroplasty. Arthroplasty is the choice of treatment, when preserving motion is feasible, but patients can have excellent results with arthrodesis. There are several arthroplasty techniques including fibrous interposition, palmar plate advancement, metallic or metalloplastic hinges or one piece polymeric plastic hinge devices.

In this study, we use a 2 part metallic implant designed to minimize bone removal and preserve the collateral ligaments of the PIP joint providing a more stable joint particularly to imposed lateral forces. Preservation of the capsule with this prosthesis allows diversion of some of the transverse forces and axial torques from the prosthesis endosteal interface to the lateral cortices through the collateral ligaments. The semi-constrained design provides a more physiological articulation, and besides this the centered anatomical configuration allows a more reliable restoration of tendon movements to the joint. All of this probably diminishes the mechanical contribution to osteolysis and subsidence at the bone prosthesis interface and prolongs the time of survival of the prosthesis. All of these improvements on prosthetic design are very important and provide a better possibility for the patient to regain near-normal joint conditions.

The prosthesis has two components - one proximal and one distal. The proximal part has a symmetric shallow bicondylar anatomic configuration fixed on a stem for the intramedullary cavity of the proximal phalanx. The distal component is fabricated from polyethylene press-molded on a metal backing with a stem for the intramedullary cavity of the middle phalanx. Both implant parts are CoCr alloy with a coating of plasma sprayed porous titanium. Studies have shown that bone grows well into the titanium surface of experimental implants, but it is also fixed into bone using cement.

With the new type of PIP prostheses there is often excellent if not total long-term pain relief and little or no loss of movement. The stability becomes considerably better compared with older types of prostheses. The outcome is however dependant on the skill and experience of the surgeon.

The purpose of this study is to compare the early migration and the periprosthetic bone changes of cemented versus non-cemented interphalangeal implants. Furthermore a thorough occupational therapist evaluation on the functional progress prior to and after surgery will be assessed.

To evaluate both the implant-bone micromotions, metal markers have been placed on the implant preoperatively and other markers will be fixed in the phalangeal bone intra-operatively. This allows us to evaluate the implant micromotion with stereo x-rays by photogrammetric computer analyses called RSA at the Orthopaedic Center, Aarhus University Hospital. Follow-up stereo x-rays will be scheduled for 1 week, 6 weeks, 12 weeks, 6 months, 1 year and 2 years post-surgery. Periprosthetic bone density will be evaluated at 1 week, 1 year and 2 years upon inclusion at the Orthopaedic Center, Aarhus University Hospital. An occupational therapist will evaluate the joint range of motion, pain, edema and grip strength prior to surgery and throughout the 2 year follow up.