Post-THA internal rotation test proves invaluable for assessing capsular healing

Patients with positive test results at 6 weeks could safely reduce their hip precautions , return to full activity and sports by 10 to 12 postoperative weeks.

A clinical test performed 6 weeks after total hip arthroplasty performed with posterior exposure turned out to be a good predictor of posterior capsular tendon healing, according to an orthopedist from New York who regularly uses the technique.

At the 2010 Winter Current Concepts in Joint Replacement Meeting, Chitranjan S. Ranawat, MD, of Hospital for Special Surgery in New York, presented results in 168 consecutive patients in whom he used the internal rotation (IR) test at 6 weeks after posterior total hip arthroplasty (THA) to assess the integrity of their operated hip capsules.

“A positive IR test is a reliable predictor of posterior capsular tendon healing and almost eliminates the risk for posterior dislocation,” Ranawat said, explaining that after performing the test he and his colleagues prospectively followed the patients between 6 months and 1 year to see who dislocated or had problems returning to full activities.

Indicates dislocation risk

Surgeons need to take precautions to avoid a hip dislocation following posterior THA, including using large femoral heads, repairing the capsule appropriately and instructing the patient to use proper hip precautions. But despite these attempts to mitigate problems, a certain incidence of THA dislocation persists, Ranawat said.

This is an MRI of a patient with negative internal rotation (IR) test demonstrating retraction of the short external rotator tendons, severe atrophy and of the obturator internus muscle and dehiscence of the posterior capsule.

This image demonstrates the IR test, performed with hip and knee flexed at 90° while patient is supine. Images: Ranawat CS

The IR test he recommended involves positioning the patient supine and flexing the hip 90° and the knee 90° on the operated side, trying to feel an “endpoint” of IR of 15° or less.

“If you have this, [it] is an indicator that the posterior capsule structure has healed well,” said Ranawat, who included patients treated with non-cemented THAs from January 2009 to January 2010 in his study to determine whether the IR test was a good predictor.

“Sensitivity and specificity for this test were high,” he noted.

MRIs analyzed

Ranawat and colleagues also studied in a separate group of 23 THA patients how well capsule and tendon healing correlated with IR test results. They found three-fourths of the patients had a positive test and 24% had a negative test.

“Those who had a positive test all had an intact posterior capsule and tendon and there was no muscle atrophy,” but among those with a negative test, 10 patients showed signs of capsular healing on MRI and none demonstrated tendon healing, Ranawat said. In the four patients who did not heal at all “you see atrophy in the muscle and gap in posterior capsule scar tissue.”

Using this test, “incidence of posterior dislocation during the first year after a total hip has been reduced.” he said.

A study limitation he mentioned was that the MRI evaluations were not done for the same set of patients that they followed prospectively. – by Susan M. Rapp

Reference:

• Ranawat CS. The posterior THA: Assuring capsular stability. Paper #46. Presented at the Current Concepts in Joint Replacement 2010 Winter Meeting. December 8-11, 2010. Orlando, Fla.

• Chitranjan S. Ranawat, MD, can be reached at 535 E. 70th St., New York, NY 10021; 646-797-8770.
• Disclosure: Ranawat receives consulting fees from Comformis and Mako and research support from DePuy, a Johnson and Johnson company, and Stryker.

The IR test proposed by Ranawat and colleagues provides the orthopedic practitioner with a reproducible, quantitative test of capsular healing and function. Su and colleagues and Pellicci and colleagues have shown that posterior capsule repair during the posterior approach to total hip replacement greatly reduces the risk of dislocation, however, it may be difficult to ascertain capsular healing and function without the use of costly imaging tests such as MRI.

To its benefit, the IR test is simple and easy to perform in a clinical setting requiring no special imaging or costly equipment. It provides a reproducible and validated endpoint at which dislocation restrictions may be lifted, thus allowing patients to return to normal activity.

— Joseph T. Moskal, MD, FACS
Chief of Orthopaedic Surgery
Carilion Clinic Medical Center, Roanoke, Va.
Disclosure: He is a consultant to DePuy, a Johnson and Johnson Company.

References:

• Su EP, et al. Integrity of repaired posterior structures after THA. Clin Orthop Relat Res. 2006;447:43-47.
• Pellicci PM, et al. Posterior approach to total hip replacement using enhanced posterior soft tissue repair. Clin Orthop Relat Res. 1998;355:224-228.