This feature highlights some of the studies that emerged from the 2011 AAOS annual meeting, including data supporting the long-term function of total knee replacement (TKR), imaging costs linked to defensive medicine, PE risks after knee arthroplasty, and the effect of stretching before running.

» TKR Improves Function for the Long-Term
» PE Risks After Knee Arthroplasty
» Are Two TKRs Better Than One?
» The Effects of Stretching Before Running
» Imaging Costs Linked to Defensive Medicine

TKR Improves Function for the Long Term

The Particulars: Most patients who undergo total knee replacement (TKR) are between the ages of 60 and 80. More than 90% of these individuals experience a dramatic reduction in knee pain and a significant improvement in their ability to perform common activities. However, questions have been raised about the decline in physical function over the long term despite the absence of implant-related problems.

Data Breakdown: Between 1975 and 1989, a study looked at TKRs performed in 128 patients who were living at 20 years follow-up. The average age at operation was 63.8. Of the study participants, 95 could walk at least five blocks when assessed at 20 years follow-up, and 48% reported unlimited walking ability. All but two patients could negotiate up and down stairs without a banister. Only three patients were considered housebound, and no implant failures were observed after 20 years.

Take Home Pearls: Elderly recipients of TKR appear to be using their surgically replaced knees for fairly active lifestyles many years after surgery. This study refutes the perception that well-functioning TKRs diminish over time because of an overall declining functional status.

PE Risks After Knee Arthroscopy [back to top]

The Particulars: More than 4 million knee arthroscopies are performed each year. Pulmonary embolism (PE) can lead to difficulty breathing, chest pain, and palpitations, and severe cases can lead to death. The risk of PE after knee arthroscopy has not been accurately defined. In previous research, risk factors have been suggested but not proven.

Data Breakdown: Researchers examined data on 374,033 patients undergoing 418,323 outpatient arthroscopic knee procedures between 1997 and 2006. There were 117 PE cases (.028%) and one reported death. Patients aged 30 and older were six times more likely than patients younger than 20 to develop PE. Operating room times longer than 90 minutes were associated with a three-fold higher risk when compared with procedures shorter than 30 minutes. Females were 1.5 times at greater risk than males. A history of cancer was associated with a three-fold greater risk for PE.

Take Home Pearls: The incidence of symptomatic PE after outpatient knee arthroscopy appears to be low. Age, increased operating time, female gender, and a history of cancer appear to be risk factors for PE after knee arthroscopy.

Are Two TKRs Better Than One? [back to top]

The Particulars: Previous investigations have suggested that the risk of adverse cardiovascular events may be higher after patients undergo simultaneous total knee replacement (TKR) when compared with having two separate surgeries.
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Data Breakdown: A study assessed 11,445 patients who underwent simultaneous TKR and 23,715 patients who had both knees replaced in two stages several months apart. Patients who underwent simultaneous TKR had a higher risk of heart attack and pulmonary embolism, similar risks of death and stroke, and a lower risk of major joint infection or major mechanical malfunction. The risk of developing a serious joint infection that required additional knee revision surgery was two times higher for patients who had staged knee replacements. Simultaneous TKR was associated with a moderately higher risk of adverse cardiovascular outcomes within 30 days when compared with staged TKR.

Take Home Pearls: When compared with TKR performed in two separate procedures, simultaneous TKR appears to be associated with significantly fewer prosthetic joint infections and other revision knee operations within 1 year after surgery. Simultaneous TKR should only be performed, however, in select patients because of cardiovascular risks.

The Effects of Stretching Before Running [back to top]

The Particulars: More than 70 million people throughout the world run recreationally or competitively. Recently, there has been controversy about whether or not frequent runners should stretch before running or not at all.

Data Breakdown: Of 2,729 runners who run 10 or more miles per week and participated in a study, 1,366 were randomized to a stretch group, while 1,363 were randomized to a non-stretch group prior to running. Runners in the stretch group stretched their quadriceps, hamstrings, and gastrocnemius/soleus muscle groups. Stretching before running neither prevented nor caused injury. The most significant risk factors for injury included a history of chronic injury or having suffered an injury in the past 4 months, higher BMI, and switching pre-run stretching routines. The risk for injury was the same for men and women, regardless of whether or not they were high- or low-mileage runners, and across all age groups.

Take Home Pearl: Stretching before running does not appear to prevent or cause injury in people who run 10 or more miles per week.

Imaging Costs Linked to Defensive Medicine [back to top]

The Particulars: For years, some physicians have ordered specific diagnostic procedures that have been shown to be of little or no benefit to patients in order to protect themselves from lawsuits. Efforts to measure defensive medicine practices have been limited, primarily because surveys that are sent to physicians ask only about whether or not the individual physician practiced defensive medicine.

Data Breakdown: A study involving 72 orthopedic surgeons who were members of the Pennsylvania Orthopaedic Society found that 19% of the imaging tests ordered in orthopedic patient encounters were for defensive purposes. Defensive imaging was responsible for $113,369 of $325,309 (34.8%) of total imaging charges for this patient cohort, based on Medicare dollars. The overall cost of these tests was 35% of all imaging ordered. Surgeons were more likely to practice defensive medicine if they had been in practice for more than 15 years.

Take Home Pearls: More than a third of imaging costs ordered for orthopedic patient encounters appears to be ordered for defensive purposes. Future research should attempt to ascertain a broader national picture of defensive medicine practices to improve understanding of the true costs of defensive imaging in orthopedics.