Surgeon finds porous-coated TKA revision stems provide good fixation and build bone

Optimal results require retaining the soft tissue sleeve and fixing implants to the patient’s bone.

Leo A. Whiteside

Today’s uncemented porous-coated knee arthroplasty prostheses effectively meet the challenges that are inherent to revising a primary knee arthroplasty, including managing bone loss, bridging massive defects and avoiding implant instability, according to an orthopedic investigator.

Leo A. Whiteside, MD, said at the 2009 Current Concepts in Joint Replacement Spring Meeting that he finds among the options available for revising a total knee arthroplasty (TKA), uncemented porous-coated stems now provide the most adequate fixation. Also, the results with these implants surpass those that involve bone graft and cement.

“You have many choices of augments, reinforced components and porous stems. I am using a lot more porous stems than before and bone grafting a whole lot less than I used to,” he said.

Bone contact

During his presentation, Whiteside made a case for using fully and partially porous-coated tibial stems for TKA revisions, noting that cement and bone grafting now play a lesser role in his cases where he uses these implants. He presented some cases to illustrate the various indications for porous-coated revision TKA prostheses.

The medial condyle shown received an allograft during total knee arthroplasty (TKA) revision at 12-years postoperative. The graft failed, leaving the medial femoral condyle unsupported.

Bone destruction is apparent in a lateral radiograph of the same TKA. Both posterior femoral condylar bone structures were destroyed and the distal femoral surface severely damaged. Images: Whiteside LA

This AP radiograph of the same knee shows the porous titanium stem engaging the medullary canal and re-establishment of correct alignment and position of the joint surface.

Most importantly, he has found when these implants are in contact with a good bone rim and are well-fixed, they tend to remain stable in flexion and extension and the patients usually have excellent postoperative quadriceps function.

“If you preserve the soft tissue sleeve, as I do, by using a tubercle osteotomy to enter, these joint surfaces are going to be fairly close in flexion and you will have implants that will tension them in flexion,” Whiteside explained.

He told Orthopedics Today that the practice of using porous stems is highly dependent on the new porous coating technology, so that the implants maintain their strength and fatigue resistance. “The highly porous arc-deposited titanium porous coating makes this work,” he said.

Intraoperatively, the medial femoral condyle of the same knee indicates severe damage to the distal femur caused by loosened implants.

Whiteside positioned an L-shaped porous buildup against the deficient bone surface during revision surgery.

He seated a femoral component with porous stem on the lateral bone stock using a standard porous augment on the lateral condyle. Then held a porous augment against the deficient medial condylar surface and filled the gap between it and the femoral component with acrylic cement for a custom augment.

Loosening

The medial augment is seen contacting the deficient bone stock with its porous surface in a lateral radiograph. It is cemented to the main femoral component with acrylic bone cement.

Whiteside said he has encountered few stem fractures and one loosening.

“That is why I now advocate porous stems, porous build-ups and, of course I do not, in any regard, think you need to cement any of these in or cement any defects,” he said.

Postoperatively, the knee joint space returned to near normal with a difference from its preoperative measurement of up to 0.8 cm, even when he used massive porous implants to span large defects, he said.

Occasionally he has augmented the stability of these constructs by adding screw and peg fixation or morsellized bone graft to rebuild bone stock, but he tries to avoid using cemented stems, as they can lead to greater bone loss.

Responding to a question from the audience, Whiteside said he allows full weight-bearing without protection during postoperative rehabilitation if the quality of the tibial tubercle osteotomy repair warrants it.

For more information:

• Leo A. Whiteside, MD, can be reached at Missouri Bone & Joint Center, 1000 Des Peres Road, Suite 120, Saint Louis, MO 63131-2062; 314-205-2223; e-mail: Lwhite8283@aol.com. He has ownership interest in, teaching/speaking arrangements and intellectual property rights with Smith & Nephew Orthopaedics and Signal Medical Corp.

References:

• Whiteside LA. Cementless fixation in revision total knee arthroplasty. Clin Orthop Relat Res. 2006;446:140-148.
• Whiteside LA. Management of bone loss: It’s a changing world. #55. Presented at the 10th Annual Current Concepts in Joint Replacement Spring Meeting. May 17-20, 2009. Las Vegas.