Simple liner exchange is often insufficient to prevent further dislocations

Dislocation after total hip arthroplasty (THA) is a relatively common complication, noted James J. Purtill, MD, of the Rothman Institute of Orthopaedics at Thomas Jefferson University.

“Most dislocations are single episodes that respond well to closed reduction and do not recur,” he said, “but some patients do have recurrent dislocations and require surgical treatment.”

Surgeons have the following options to treat recurrent dislocations:

• replacing worn or loose components
• revising the acetabulum
• changing and/or correcting the position of the implant
• increasing the size of the head and liner
• using constrained or elevated liners

With so many possible treatment modalities available, some uncertainty exists regarding the best surgical strategies for correcting instability in an individual patient (Fig. 1). Surgeons may reduce the risk of recurrent dislocation by optimizing certain factors during surgery, according to the results of a study Dr. Purtill presented at the 2010 annual meeting of the American Association of Hip and Knee Surgeons.

Analyzing the data
Dr. Purtill and his fellow researchers obtained information from their institution’s prospective joint registry database on 154 patients (57 males, 97 females; 156 hips) who underwent revision THA for recurrent dislocations between 2000 and 2007. The average patient age at time of revision was 67 years, and the average follow-up was 67 months (range, 24 months to 119 months).

“We reviewed the medical record and radiographs, and we gathered data prospectively on both the nature of the problem and the treatment that was employed,” stated Dr. Purtill. Surgical options included the following:

• isolated liner exchange
• acetabular component revision
• femoral stem revision with liner exchange
• revision of both components

No patient was lost to follow-up, although 24 patients died within the follow-up period. No dislocations occurred in any of the patients who died.

The investigators analyzed the data using Fisher’s Exact Test, two-tailed unpaired t-test, and multivariate logistic regression.

Acetabular component revision most often required
Acetabular component revision was performed in 100 hips, and liner exchange was performed in 56 hips. The revision procedure was unsuccessful in preventing a subsequent dislocation in 33 patients (21.3 percent).

Patients who had acetabular component revision had a significantly lower dislocation rate (14 percent) than those who received a liner exchange (34 percent, p = 0.004). Among patients undergoing a second revision surgery, the dislocation rate was 29.3 percent, compared to a rate of 16.3 percent in patients undergoing their first revision surgery (p = 0.05).

Researchers also found that femoral head size made a significant difference in the dislocation rate in patients who received unconstrained liners. The dislocation rate was 9.4 percent in patients with 36 mm heads; among patients with a smaller head size, the dislocation rate was 27 percent (p = .05).

According to Dr. Purtill, 28 mm heads with unconstrained liners had the highest dislocation rate (44 percent). Multivariate logistic regression analysis showed a fourfold increase in failure rate if a 28 mm head was used with an unconstrained liner.

Complications
“Complications were common,” said Dr. Purtill, noting that 13.4 percent of patients had complications (Fig. 2). “Ten patients had infections, and seven required acetabular revision for loosening at a later time.”

“It’s important to note that patients who had a revision from a primary THA were more likely to have a successful result than those who were having a second revision THA,” said Dr. Purtill.

“In addition,” he added, “revising the entire acetabular component was more likely to be successful than simply revising the liner.”

Lessons learned
That fact, noted Dr. Purtill, “likely points to our failure as surgeons to recognize and correct malpositioned acetabular components.”

Dr. Purtill noted that his institution’s treatment algorithm for patients with recurrent instability requires revision of the cup if the component is not well-positioned.

“If the component is well-positioned and well-fixed, and the abductor is sufficient, we will consider liner exchange,” he explained, “as long as the head can be up-sized and the patient is stable intraoperatively; otherwise, the use of a constrained liner is suggested.”

Coauthors of “Revision for Instability: What are the Predictors of Failure?” included Aaron Carter, Eoin C. Sheehan; S.M. Javad Mortazavi, MD; Peter F. Sharkey, MD; and Javad Parvizi, MD, FRCS.

Disclosure information: Drs. Purtill and Mortazavi—no conflicts; Mr. Carter and Mr. Sheehan—no conflicts; Dr. Sharkey—Physician Recommended Nutriceuticals, Inc., Stryker Stelkast, Inc.; Dr. Parvizi—SmarTech, Stryker, 3M, Musculoskeletal Transplant Foundation, Stryker Saunders/Mosby-Elsevier, SLACK Inc., Wolters Kluwer Health-Lippincott Williams & Wilkins.

Jennie McKee is a staff writer for AAOS Now. She can be reached at mckee@aaos.org

Bottom Line

• Dislocation is a relatively common complication of THA.
• Simple liner exchange may have a stronger correlation with subsequent dislocation than cup revision, femoral head size, or previous revision surgery.
• According to the treatment algorithm used at Dr. Purtilll’s institution for patients with recurrent instability, the cup is revised if the component is not well-positioned. If the component is well-positioned and well-fixed, and the abductor is sufficient, noted Dr. Purtill, liner exchange is considered, as long as the head can be up-sized and the patient is stable intra- operatively; otherwise a constrained liner may be used.