Women report more pain than men after knee replacement surgery

Researchers find gender, age of patient, type of anesthesia and surgical technique play a role in postoperative pain

Middle-aged women with rheumatoid arthritis or arthritis resulting from an injury are among the patients most likely to experience serious pain following a knee replacement, researchers from Hospital for Special Surgery (HSS) in New York have found.

One of the biggest concerns patients have is the amount of pain they will have after knee replacement surgery. Although it is a very successful operation overall to relieve arthritis pain and restore function, persistent postoperative pain can be a problem for some patients. Researchers at HSS set out to determine which groups were at highest risk for increased postoperative pain based on demographic and surgical variables.

"There is no question that pain after total knee replacement is greater than that after total hip replacement," says senior study author Thomas P. Sculco, M.D., the hospital's surgeon-in-chief. "Many factors play a role, and our studies found that younger female patients, particularly those with post-traumatic or rheumatoid arthritis, had the highest pain scores."

In two companion studies to be presented at the annual meeting of the American Academy of Orthopaedic Surgeons in New Orleans on March 11, Dr. Sculco and colleagues also found that surgical factors like having general anesthesia or a longer tourniquet time during knee replacement also can contribute to pain following surgery.

For the studies, the researchers reviewed hospital records for 273 patients who underwent total knee replacement from October 2007 to March 2010. For the first study, investigators looked at demographic data such as gender, ethnicity, age, height, weight, type of knee arthritis and co-existing medical conditions. They also looked at the knee's preoperative range of motion, how well the patients could walk and the amount of pain they had before surgery.

The strongest predictors for severe postoperative pain during rest included being female; being between the ages of 45 and 65; having post-traumatic arthritis spurred by an injury, rheumatoid arthritis, or osteoarthritis; being obese; and having a higher level of pain at the time of hospital admission. Patients with avascular necrosis, a disease that causes cell death of bone components due to a decreased blood supply, had significantly lower postoperative pain.

During periods of activity, obesity, a higher pain level during hospital admission and being between the ages of 45 and 65 were the strongest predictors of postoperative pain. Patients who were Asian or Caucasian, and those with either underlying osteoarthritis or avascular necrosis, or both, had lower postoperative pain during periods of activity.

"Before patients come in to the hospital, surgeons should have a thorough discussion with them regarding postoperative pain, particularly in the groups that we found tended to have more pain," Dr. Sculco says. "More aggressive pain management techniques may be necessary for these patients."

For the second study, the researchers used the same medical records to gather information about surgical variables including the length of the incision, type of anesthesia, tourniquet time and pressure, how long the procedure took, estimated blood loss, and radiographic assessment including the amount of knee deformity and implant positioning and alignment.

Risk factors for severe postoperative pain at rest included having general anesthesia as opposed to an epidural or spinal block, longer tourniquet time , more blood loss, and having a large kneecap. Predictors for postoperative pain during activity included having a large kneecap, and techniques such as overstuffing of the patellofemoral joint (where the kneecap meets the thigh bone).

Surgical technique can play a role in reducing pain, Dr. Sculco says. "The surgeon must be aware not to use an implant that is too large for the knee, or a kneecap component that is excessive in size. In addition, the location of the joint line must be accurately positioned after the knee replacement, for if it is too high it may lead to increased pain." Patients with epidural anesthesia also tended to have less pain than those who had general anesthesia, he says.

"Technical accuracy is important, particularly the alignment, patella sizing and joint line level," Dr. Sculco says. "Patients with more complex preoperative deformities often required increased operating time and surgical dissection, which in turn led to increased pain, especially in the younger female patients."

Glucosamine fails to prevent deterioration of knee cartilage, decrease pain

A short-term study found that oral glucosamine supplementation is not associated with a lessening of knee cartilage deterioration among individuals with chronic knee pain. Findings published in Arthritis & Rheumatology, a journal of the American College of Rheumatology (ACR) journal, indicate that glucosamine does not decrease pain or improve knee bone marrow lesions—more commonly known as bone bruises and thought to be a source of pain in those with osteoarthritis (OA).

According to the ACR 27 million Americans over 25 years of age are diagnosed with OA—the most common form or arthritis and primary cause of disability in the elderly. Patients may seek alternative therapies to treat joint pain and arthritis, with prior research showing glucosamine as the second most commonly-used natural product. In fact, a 2007 Gallup poll reports that 10% of individuals in the U.S. over the age of 18 use glucosamine, with more than $2 billion in global sales of the supplement.

For this double-blind, placebo-controlled trial, Dr. C. Kent Kwoh from the University of Arizona in Tucson and colleagues, enrolled 201 participants with mild to moderate pain in one or both knees. Participants were randomized and treated daily with 1500 mg of a glucosamine hydrochloride in a 16-ounce bottle of diet lemonade or placebo for 24 weeks. Magnetic resonance imaging (MRI) was used to assess cartilage damage.

Trial results show no decrease in cartilage damage in participants in the glucosamine group compared to the placebo group. Researchers report no change in bone marrow lesions in 70% of knees, 18% of knees worsened and 10% improved. The control group had greater improvement in bone marrow lesions compared to treated participants, with neither group displaying a worsening of bone marrow lesions. Glucosamine was not found to decrease urinary excretion of C-telopeptides of type II collagen (CTX-II)—a predictor of cartilage destruction.

The joints on glucosamine (JOG) study is the first to investigate whether the supplement prevents the worsening of cartilage damage or bone marrow lesions. Dr. Kwoh concludes, "Our study found no evidence that drinking a glucosamine supplement reduced knee cartilage damage, relieved pain, or improved function in individuals with chronic knee pain."

Lower index to ring finger ration associated with higher risk of osteoarthritis in knee

A new study published online today in the journal Rheumatology has found that the lower the ratio between a person's index finger (2D) and their ring finger (4D), the higher their risk of developing severe osteoarthritis in their knees, requiring a total knee replacement.

Osteoarthritis (OA) is a major public health problem linked with significant disability in knees and hips. Hormonal factors are thought to play a role, which is thought to account for the well documented difference in prevalence of OA between men and women. Anthropological studies have suggested that there are consistent sex differences in the ratio of the lengths of the index and ring fingers (expressed as 2D:4D), with men showing a lower average 2D:4D than women. The aim of this new study was to determine whether 2D:4D was associated with the risk of severe knee or hip OA requiring total joint replacement in a large cohort study.

Dr Yuanyuan Wang and colleagues assessed the hands of 14,511 middle-aged and older participants in the Melbourne Collaborative Cohort Study from hand photocopies and noted the 2D:4D. The incidence of total knee replacement and total hip replacement between 2001 and 2011 was determined by linking the cohort records to the Australian Orthopaedic Association National Joint Replacement Registry.

Over an average 10.5 year follow up, 580 participants had total knee replacements and 499 had total hip replacements for OA. Lower 2D:4D was associated with a higher incidence of total knee replacement, while there was no significant evidence of a link between 2D:4D and total hip replacement. This was the case when the ratio was examined on either the right or left hand, or the average, although the risk was stronger with the right hand.

There were 830 participants whose fingers had features that might have affected the validity of the measurements, and so they were excluded in the additional sensitivity analysis. Among the remaining 13,681 participants, there were 524 total knee replacements and 454 total hip replacements. Again, a lower 2D:4D was associated with a higher incidence of total knee replacement. There was again no significant evidence of a link between 2D:4D and total hip replacement.

Dr Wang says, "Although there is some evidence from previous studies that sporting ability and achievement in sports and athletics are negatively related to 2D:4D, this might not reflect levels of regular physical activity in the general population. In our study, the measure of physical activity did not directly assess sporting activity, nor did the measure report past physical activity that may also be important in this regard."

"Although our study's results may in part be explained by joint injuries associated with high-level physical activity in those with a lower 2D:4D and the greater susceptibility of knee OA in response to injury than hip OA, they may also reflect hormonal influences on the growth of bone, cartilage, and soft tissue, which warrants further investigation."