Stiffness after knee replacement surgery, or total knee arthroplasty (TKA), is a rare but frustrating complication, affecting between 1% and 7% of patients who receive the artificial joints. “Why some people and not others experience limited range of motion after TKA is unknown,” said Ioannis Gkiatas, MD, PhD, an orthopedic surgeon at the University of Ioannina, in Greece, and the first author of the new study who also recently completed a research Complex Joint Reconstruction fellowship at HSS.

“The goal of the study was to see if we can help physicians predict how patients will do following the revision surgery, using information gathered before and after the procedure, to shape their postoperative treatment plans,” said Dr. Gkiatas. The work was conducted under the supervision of Peter K. Sculco, MD, hip and knee surgeon at HSS, who is leading a large, ongoing study of patient outcomes after revision TKA for reduced range of motion after index TKA.

For the study, Drs. Gkiatas, Sculco and their colleagues followed 19 men and women who underwent revision TKA at HSS to try to improve stiffness in patients with prior TKA. Patients underwent range of motion testing before the procedure and at six weeks, six months and one year after the operation.

A healthy knee has a wide range of motion — from full extension (0 degrees) through the sitting position (90 degrees) to kneeling (approximately 140 degrees). All patients gained some mobility after the revision surgery, with the average improvement being approximately 28 degrees of motion. Most of the benefit appeared to occur in the first six weeks after the operation, then gradually tapered off over time.

The researchers found that patients with the least restricted mobility experienced the greatest gains from the revision surgery. Patients who could bend their affected knee more than 82 degrees before TKA revision had an 80 percent chance of maintaining that level of mobility, or gaining flexibility in the joint, after the operation and throughout the follow-up period.

However, two-thirds of patients whose range of motion was less than 64 degrees before surgery experienced regression in that mobility across all time points of the study and never attained the 82-degree threshold.

“Although 82 degrees doesn’t seem much more than 64 degrees, for the patient it’s a significant difference. With 82 degrees you can perform the basic activities of everyday life,” Dr. Gkiatas said. “With these new data, if at six weeks a patient reaches 82 degrees of motion in their knee, we can say they have an 80 percent chance of at least maintaining this range of motion one year after surgery.” The results of this study provide surgeons with the information needed to educate patients with stiff TKA on expected range of motion outcomes after revision surgery. Less than 60 degrees being a poor prognostic finding. In addition, when patients return to the office for their six-week appointment after revision TKA, and have less than 82 degrees of motion, additional pharmacologic or manual knee manipulation treatments should be implemented as this patient is at a high risk for range of motion regression and inferior clinical outcome at one-year post-revision.

Now, researchers at Hospital for Special Surgery (HSS) have examined racial disparities separately for aseptic and septic revision total knee replacement using data from three large states. In their study published July 21 in JAMA Network Open, they found that Black patients had a 39% higher risk of aseptic revision and an 11% higher risk of septic revision than white patients.

“As we predicted, the risk factors were very different for patients needing aseptic versus septic revision,” says lead and corresponding study author Anne R. Bass, MD, rheumatologist at HSS. “But we were totally surprised to find Black race was one of the only risk factors associated with aseptic revision and that this disparity was so much higher for patients treated at high-volume hospitals.”

Dr. Bass and HSS colleagues analyzed data from statewide databases from California, Florida and New York for almost 725,000 patients who had total knee replacement between 2004 and 2014. The investigators looked at an extensive range of variables that have been linked to risk of revision total knee replacement in previous studies, including age; sex; insurance status; presence of other conditions such as diabetes, obesity, renal disease and chronic obstructive pulmonary disease (COPD); inflammatory arthritis; surgical site complications; infection on admission for knee replacement surgery; and hospital factors, including non-government, not-for-profit, teaching hospital, rural location, number of beds, and annual total knee replacement volume.

In addition to being Black, other factors associated with a higher risk of septic revision total knee replacement were diabetes, obesity, renal disease, COPD, inflammatory arthritis, surgical site complications, Medicaid insurance and low hospital total knee replacement volume. Similarly, for aseptic revision, additional risk factors were male sex, workers’ compensation insurance and low hospital total knee replacement volume.

When the researchers analyzed the data according to different categories of hospital volume, they discovered Black patients had a 20% higher risk of aseptic revision total knee replacement than white patients if they underwent replacement at low-volume hospitals, defined as 89 or fewer total knee replacements annually. However, the relative risk was 68% higher for those who had knee replacements at very high-volume hospitals, defined as 645 or more procedures per year.

“The question now is why do these disparities exist,” says Dr. Bass. “Our study did not reveal causes, but we can use this learning to develop theories for further investigation.”

“We know that Black patients tend to bypass larger, higher-volume hospitals and have surgery at lower-volume hospitals,” says study co-author Michael L. Parks, MD, a hip and knee surgeon at HSS. “One of the reasons why they may have higher revision rates at higher-volume hospitals is that they tend to present later with more advanced disease and require more complicated surgeries than white patients.”

“The other hypothesis is that care is not being delivered equally across patient groups at high-volume hospitals,” says Dr. Bass. “If that’s the case, hospitals should review and ensure care processes are accessed and applied equally across racial groups to improve surgical outcomes.”

Dr. Bass, Dr. Parks and colleagues are currently conducting further research to look for a relationship between revision total knee replacement risk, hospital volume and annual volume by surgeon to see if they can learn more about racial disparities.

The study was supported by funding provided by the Stavros Niarchos Complex Joint and Reconstruction Center at HSS.

Now, in a new study published in Arthritis Care & Research that looked at the risk of total knee replacement revision or failure, HSS investigators found very a different result. “There was a trend toward race being a risk factor, but it was not statistically significant, and poverty had no impact: There wasn’t even a trend,” said lead study author Anne R. Bass, MD, an attending physician and program director of the Rheumatology Fellowship Program at Hospital for Special Surgery, and a professor of clinical medicine at Weill Cornell Medicine. “We were definitely surprised by our results.”

For about 85 percent to 90 percent of people who have total knee replacements, the artificial joints last about 15 to 20 years. In elderly patients, that may mean the rest of their lives. But for younger patients, especially those who are very active, the implants may fail over time and require revision. Over the last five years or so, the team of HSS researchers have been collaborating to understand the factors placing some patients at higher risk of poor outcomes, including needing revisions.

This study was the first to link patient data to a statewide discharge database. The researchers linked the HSS Knee Replacement Registry with the Statewide Planning and Research Cooperative System (SPARCS) database and captured discharge information for patients who received revisions at other hospitals within the state of New York. Also new with this study, they explored whether race and poverty played a role in knee replacement failure, a broader outcome definition that includes patients who failed to improve at all after their initial procedures but who did not have revisions. Poverty information was collected from the U.S. census data.

Among a total of 4,062 patients who had a total knee replacement between January 2008 and February 2012 at HSS, only 122 or 3 percent required revisions during a median of five years of follow-up. Black patients had a 1.7 times higher risk of knee replacement revision than white patients, but when the researchers analyzed multiple variables, race and poverty were not driving factors. Race and poverty also did not explain differences among patients with knee replacement failure.

The factors that were associated with a higher risk for revision were younger age, being male, and the use of a constrained prosthesis—a knee implant with conforming components that provides more stability. The risk factors driving failure included being treated by a surgeon that performs a low number of knee replacement surgeries and patients’ low expectations for improvement after surgery.

“Younger people and males are typically more active, putting more strain on their implants. Constrained prostheses are only used in patients with bigger deformities and ligament imbalances, which tend to put more strain on the implant and loosen the bone-cement interface,” said study author Mark P. Figgie, MD, an attending orthopedic surgeon and Chief Emeritus of the Surgical Arthritis Service at HSS, and professor of clinical orthopedic surgery at Weill Cornell Medicine. “Our findings suggest that all patients should seek care from experienced surgeons at a high-volume hospital.”

To explore their findings on a larger scale, the research team is conducting a new study, linking data from about one million patients from California, New York, Florida, Arizona, and Arkansas with their respective statewide databases. “We are asking the same questions about race and poverty, and we will be able to look at the influence of hospital choice on the risk of revision by linking to the American Hospital Association database,” Dr. Bass said. “We are also looking at differences in revisions caused by infections versus mechanical issues.” The more extensive study is expected to be completed later this year.