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Surgeon reveals keys to long term fixation using cementless sockets for THA

Issue: April 2012

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According to a presenter at Orthopedics Today Hawaii 2012, the use of cementless sockets in total hip arthroplasty has shown excellent long-term fixation, especially with designs featuring three-dimensional ingrowth surfaces. However, concerns have mounted in the literature regarding osteolysis of polyethylene and late loosening.

“The problem related to wear has been in higher activity patients with conventional polyethylene,” William J. Maloney, MD, said. “You can see the wear rates of patients in the third or fourth decade of life exceed the lysis threshold by a considerable amount. The problem then, radiographically and clinically, is bone resorption around these implants.”

Implants with three-dimensional ingrowth surfaces perform better than those with ongrowth surfaces, Maloney said. The most common reason for failure is aseptic loosening. Maloney highlighted a study by Charles A. Engh Jr., MD, and colleagues in which surgeons revised four of 174 hips implanted with anatomic medullary locking prostheses constructed with cobalt chromium beads at 10 years.

Hydroxyapatite (HA)-coated press-fit cups on a microtextured surface showed poor outcomes as well, Maloney said. He cited a study by Manley and colleagues in which 21 of 188 hips required revision. The investigators of the study also found a mechanical failure rate of 22% at 5 years to 9 years.

“The HA absorbed, and the underlying surface was not adequate to provide long-term stability,” Maloney said.

In their study, Manley and colleagues concluded, “Physical interlock between the cup and the supporting bone beneath it may be a prerequisite for long-term stability.”

Although it is difficult to quantity in vivo stability, Maloney said that press-fit constructs used alone are less stable than press-fit constructs affixed with screws. He uses a cluster cup with one to two screws to ensure implant stability and bone ingrowth and to minimize access channels.

Besides using screws, Maloney also under reams by 1 mm to 2 mm to maximize the contact area at the mouth of the socket, seal the interface and enhance initial stability. – by Renee Blisard

References:

• Maloney WJ. Cementless socket fixation. Presented at Orthopedics Today Hawaii 2012. Jan. 15-18. Wailea, Hawaii.
• Engh CA, Jr., Culpepper WJ II, Engh CA. Long-term results of use of the anatomic medullary locking prosthesis in total hip arthroplasty. J Bone Joint Surg Am. 1997; 79(2); 177-184.
• Manley MT, Capella WN, D’Antonio JA, et al. Fixation of acetabular cups without cement in total hip arthroplasty. A comparison of three different implant surfaces at a minimum duration follow-up of five years. J Bone Joint Surg Am. 1998; 80(8):1175-1185.

For more information:

• William J. Maloney, MD, can be reached at Stanford University School of Medicine, 450 Broadway St., Pavilion A, Redwood City, CA 94063; 650-498-7555; email: wmaloney@stanford.edu.
• Disclosure: Maloney receives royalties for total knee replacement from Wright Medical.