Patient selection and optimization is critical for maximizing outcomes. We will discuss some of the important modifiable patient risk factors.
BMI has been increasing almost linearly for decades in the United States. In 1960, only 14% of men, 6% of women nationwide were obese (BMI > 30). In 2013, the rate of obesity in every state is over 20%, the vast majority of states are over 30%, and West Virginia and Alabama have rates over 35% . There is no sign of a plateau.
The trend toward obesity is similarly impressive in TJA patients. Obesity (BMI >30) and Morbid Obesity (BMI>40) in the TJA population is climbing more steeply than in the general population  . This is particularly notable in TKA patients, where weight and knee arthritis shows a closer correlation.
Recognizing that obesity is becoming more prevalent, it is important to understand its impact on TJA outcomes. While obesity appears to be an independent risk factor for adverse events, the correlation is complicated by its close association with many comorbidities.
Obesity has been studied widely and yet there is no consensus about what BMI cut off confers increased risk for adverse events. Its exceedingly rare in medicine for complications to neatly abide by a single numerical cut off (“You will have increased wound complications only at BMI >40”), while more commonly, complication risk occurs within a spectrum, where increasing risk follows increasing deviation from “normal”.
The summation of studies were used to formulate guidelines for managing obese patients by AAHKS . It stated that BMI > 40 showed a high correlation with increased complications, particularly surgical site infections, while all obese patients (BMI> 30) likely have some increased risk and should be counseled preoperatively about this increased risk. A study has proposed thinking of BMI as a continuous variable for complication risk (ie dose response) rather than a threshold model (risk only occurs over 30 or 35 or 40) which appears more in line with the general consensus that BMI is correlated to increased complication risk .
▪ Wound Complications. Significant increase from <1% in non-obese to over 4% in morbid obese.
-THA: [9, 10] 2x increased risk at BMI of 35 .
▪ Length of stay. Increased in both TKA and THA in obese. 
▪ Cardiopulmonary, GI, and dermatologic, and renal complications may only be statistically significantly higher in BMI > 40.  BMI > 35 confers risk for unplanned ICU admission.  
-THA: Some found increased loosening.   but appears less significant than TKA, and recent studies have found no strong correlation at any BMI .
▪ Patient satisfaction.
-THA: Despite increased risk for complications, obesity does not affect satisfaction and obese patients show similar improvements in WOMAC, HHS, SF-36 and this must be remembered. [18, 19]. Others however, report worse outcomes at 1 and 5 years .
What can be done?
The biggest challenge, once identifying the independent risk of obesity, lies in modifying this risk. It remains a question whether obesity is truly a modifiable risk factor. Obesity peaks in the 7th decade, when people have become ingrained in a certain lifestyle, activity has slowed down, and the ability to make dramatic changes is incredibly difficult. There isn’t great evidence in TJA to suggest that patients can lose significant weight through dieting. One study suggests that only 12% of patients lost at least 5% weight (that would be 10 lbs in a 200 lbs person) within a year before TJA surgery (while 80% remained unchanged, and 8% gained weight) . The risk for surgical site infections unfortunately did not decrease in the patients that were able to lose weight, which reflects that modest weight loss (5%) is insufficient to modify surgical risk. A study of weight loss not specific to TJA patients showed that exercise produced 2.4% weight loss, diet produced 8.5% weight loss, and a combined routine produced 10.8% .
Patients may argue that inability to lose weight is related to knee or hip pain preventing exercise. However, Kahn et al showed that improved pain and quality of life after TKA did not translate into postop weight loss, nor substantial increased activity .
Bariatric Surgery. Because weight loss programs appear to have marginal benefit at best before TJA procedures, surgeons have examined more dramatic techniques, such as bariatric surgery, to achieve lower BMI at the date of surgery. Bariatric surgery is shown to effectively promote weight loss and improve glucose control .
However, the clinical effect on complication risk after TKA is unclear. While early studies  showed that bariatric surgery helped improve outcome measures, and reduce complications, other studies suggest less promising results, with increased complications despite weight loss . The time interval between bariatric surgery and TKA is important because its been suggested that patients enter a catabolic state for 2 years following bariatric surgery, which possibly introduces the risk of poor nutrition status, poor tissue quality and thus increased wound healing complications.
Concerning still is a recent study that showed patients with BMI >40 experienced fewer complications than patients that were previously morbidly obese but were corrected to a BMI < 40 after bariatric surgery .
Many orthopedic surgeons continue to recommend bariatric surgery because many studies have shown that patients become healthier overall after the procedure, with tighter glucose control, improved cholesterol and other health factors. Furthermore, weight loss alone addresses the reports of increased risk for aseptic loosening and malalignment secondary to the obesity. Surgeons believe that as long as bariatric surgery does not show convincing inferior outcomes, there is little harm and notable benefit to the surgery.
However, the effect of intensive weight loss therapy with nutritionist consultation is something that requires further study, and remains a great hope. This provides both the requisite weight loss (a specific numerical target is again not available) without the concerns of malnutrition or poor soft tissue.
Roughly 30 million people have diabetes in 2015, and that number is expected to increase to 50 million by 2050. This is a medical condition here to stay. Its important for TJA surgeons to think about in all patients because the CDC believes about 30% of cases are currently undiagnosed.
Diabetes is defined as: fasting blood glucose > 126 mg/dL, or random blood glucose > 200 mg/dL, or HgA1C > 6.5% (HgA1C is average blood glucose levels over preceding 8-12 weeks).
There are some initial studies that suggest diabetes is associated with DJD as diabetic patients undergo TKA at a younger age (although the association between diabetes and obesity, a known risk factor for premature arthritis, makes it less clear whether diabetes is an independent risk factor) .
Diabetes is a risk factors for Periprosthetic Joint Infection in patients undergoing TJA, with reports of 2x to 4x higher rates of infection compared to non-diabetics  . Additionally, insulin dependent diabetics have greater risk than noninsulin dependent diabetics. About 8.5% of patients undergoing TJA have diabetes. Additional risks associated with diabetes are widespread due to its systemic effects on the body, particularly in promoting renal and cardiopulmonary disease .
Is the target is a Hemoglobin A1C < 7.0?
Many say this is a good threshold to set because its associated with improved outcomes. 
Yet it is likely that glucose control exists along a spectrum of risk, similar to obesity, with a dose-dependent association to infection and wound complication. This concept was suggested in a study by Harris et al.  that looked at Veteran’s Health Database (over 20% of TJA patients had diabetes) and showed that lower HgbA1C correlated with lower complications along a continuum from 5 to 9, with almost linear correlation between HgbA1C and complication rates. Yet even diabetics with well-controlled HgbA1C appear to present with an elevated risk of complications. 
These findings suggest that all diabetics need to be counseled for increased risk of TJA, but also that Hgb A1C < 7 should not represent a hard-stop for performing surgery, and that HgbA1C should play a role as one variable in determining the risk/benefit balance of surgery. Giori et al have demonstrated the challenge that many patients have in obtaining HgbA1C < 7 and have recommended accepting a level of 8.0% in many cases .
Additional studies have found that perioperative glucose levels are more predictive of acute complications than the prior 2-3 months of glucose control, as represented by HgbAIC    . These studies suggest that even nondiabetic patients with postoperative glucose levels over 140 (which can result from steroid administration, excessive fluids containing glucose, postsurgical stress, or poorly controlled underlying diabetes) are at 3x increase risk for infection.
The key is to optimize patients toward a target HgbA1C around 7.0% (even if there is increasing evidence to suggest that this one value is not a hard stop for surgery), while providing tight pre-op and post-op glucose control .
Perioperative Glucose management for diabetics.
Hold the short-acting insulin and oral medications on the morning of surgery. Give half dose of long-acting insulin, and allow insulin pumps to continue during morning of surgery.
Postoperative Glucose management for diabetics.
Resume the patients optimized insulin protocol as a regular diet is begun. Start oral medications the following morning (postop day 1). Ensure proper hydration and kidney function the next morning before starting metformin. All patients, including non-diabetics, should have glucose checked postop day 1. Early wound complications (< 30 days) are associated with in-hospital blood glucose levels with an average over >200 mg/dL, or when levels spike over 260. A target between 140 – 180 mg/dL appears acceptable to avoid complications .
3. METABOLIC SYNDROME
Obesity is often the tip of this iceberg, the visible aspect of a medical unhealthiness that runs far deeper.
Metabolic syndrome is typically defined as the constellation of 3 out of 4 medical conditions frequently found in association: diabetes (HgbAIC >7.0), dyslipidemia (cholesterol >200), obesity (BMI > 30) and hypertension (SBP > 140, DBP >90). Metabolic syndrome has been increasing in TJA and is estimated in 14% of TKA, and 10% of THA.
In obese patients, a full work up of associated medical conditions, particularly those associated with metabolic syndrome. Interestingly, when a patient with metabolic syndrome has all of these comorbidities well controlled, the rate of complications approaches the control group (overall complication about 8%) while poorly controlled comorbidities (even just one uncontrolled aspect of metabolic syndrome) leads to dramatically higher complication rates (49%) .
There is a growing body of literature to suggest that nutritional status is as important as obesity and other variables as an independent risk factor for TJA complications. Nutritional deficiency prevents normal wound healing and is associated with impaired immune function.
Malnutrition status is defined as Total WBC (< 1500), and Albumin (< 3.5). Other markers include transferrin, or Prealbumin.
Hypoalubminemia (<3.5) is the parameter most commonly studied in the TJA literature, and it is associated with higher rates of prothetic joint infection (PJI), delayed wound healing   and prolonged wound drainage.
However, many of these studies obtain data from large registries, and its unclear whether albumin deficiency is simply a marker for really significant comorbidities (such as cancer) or if controlling for comorbidities, it independently identifies patients with generally poor health and disabled healing potential . A recent study however controlled for such comorbidities and found a correlation with risk for PJI, longer hospital stay, pneumonia, and readmission .
5. PSYCHIATRIC DISORDERS
TJA is ultimately an elective procedure, and improvement in pain is the primary outcome of TJA (even though functional outcome scores attempt to balance the emphasis on pain, pain remains an integral part of all these scoring systems). Pain has a psychological component, and is affected by psychology and pathology. As a result, the outcomes of TJA are also influenced by the psychologic disposition of patients. Psychiatric pathologies, like catastrophising, depression, poor motivation, and perceived disability all negatively impact the benefits of TJA. Preoperative pain management therapy sessions using cognitive behavioral therapy appear to reduce the perioperative pain experience and affect outcomes. CBT empowers patients to take control of their pain and teaches methods of diverting attention from pain.  
6. RECENT STEROID INJECTION
Does intervention prior to arthroplasty predispose patients to risk of infection? Most patients suffering from arthritis receive multiple steroid or hyaluronic acid injections before electing TJA. Can steroid injections introduce bacteria, which increases risk for PJI? In theory, injections certainly pose that risk. Charalambous et al. looked at antiseptic techniques used in the offices of general practitioners, rheumatologists and orthopedic surgeons within the UK when administering steroid injections. . Less than 50% of doctors used betadine or chlorhexadine to prep the injection site, and less than 1/3 routinely used sterile gloves, yet only 10% reported seeing septic arthritis secondary to injection. These findings certainly suggest that many offices perform injections under substandard protocols that probably increase the risk for bacterial infection, but it does not answer whether this risk is clinically relevant.
Other studies have looked specific at rates of PJI and the timing of steroid injection. Papavasiliou et al. looked at 144 TKA and found a higher rate of deep infection in those receiving steroid injection within the last year . Cancienne et al. looked at timing of steroid injection within 3 months or within 6 months of TKA, and found a significant increase in PJI if steroids were giving within 3 months of surgery but not within 6 months . Yet Charalambous et al. found no correlation with deep or superficial infection in their meta-analysis of reported PJI after TKA and its association with steroid injection . However, the meta-analysis is likely unable to distinguish between critical time periods for exposure, and thus many surgeons believe injections should be held within 3 months of surgery.
Injections are less commonly performed in patients with hip arthritis because the technique is more challenging and fewer physicians are comfortable performing an in-offices injection. However, steroid injections are still performed in the hip and studies have similarly examined the risk of PJI when this injection preceeds THA. Kaspar et al found increased PJI in hips that were previously injected, although timing of the injections were not discussed . Meermans examined 175 patients that received steroid injections under sterile conditions within 1 year of THA and found no added risk of PJI . McIntosh et al. similarly didn’t find increased risk of PJI in patients injected within 1 year of THA, however, the average time to injection for the 3 out 217 patients that developed PJI was only 40 days, which was not statistically significant but does highlight a concern about injecting steroids soon before surgery.
Cigarette smoke contains roughly 70 known carcinogens among over 7,000 chemicals that have the combined effect of decreasing oxygen-carrying capacity of blood, inducing vasoconstriction of peripheral vessels, and leading to tissue hypoxia.
These effects lead to problems with wound healing (nutrients and oxygen isn’t delivered to the surgical site, and impaired collagen synthesis), impaired immunity (lymphocytes aren’t delivered to the site of surgery), and promotion of venous thrombosis.
Tobacco likely delays bony ingrowth, and is associated with higher rates of implant loosening. This leads to more complications and more revision surgery  .
Tobacco has a negative effect on multiple outcomes. It may increase complication risk up to 50%, and hospital costs were on average $5k higher.
Tobacco cessation programs, implemented 6-8 weeks prior to surgery appear to effectively reduce postoperative complications, particularly wound complications. Benefits of short-term cessation have been supported by multiple other studies in other fields of surgery. Yet current and former smokers retain an increased risk for complication compared to never-smokers .
Using a Cessation program encourages about 60% of patients to effectively stop smoking, while only 8% will stop if the extent of intervention is limited to a doctor telling the patient to stop. Overall, paying for a program is less expensive for a hospital than accepting the higher complication rates       .
Patients can be monitored for smoking through testing for a nicotine metabolite called Cotinine (<10 ng/mL is associated with not smoking).
8. STAPH COLONIZATION
Staphylococcus aureus is the most common bacteria associated with surgical site infection and 20-30% of people are carriers of nasal MSSA, and up to 5% carry MRSA. . Wertheim et al. screened 14,000 patients for nasal s.aureus and monitored for s.aureus bacteremia, and found a 3x higher risk in the nasal carriers , suggesting that nasal bacteria could theoretically lead to seeding of a prosthetic implant. In a study of all orthopedic patients, the infection rate among MRSA nasal carriers was significantly higher than noncarriers (0.97% vs. 0.14%) .
Preoperative S.Aureus Evaluation.
Patients are screened with a nasal swab culture for diagnosis approximately 3 months before surgery. If positive, patients perform chlorhexadine showers and apply 2% mupirocin nasal ointments twice daily for five days about a week before surgery. Additionally, all MRSA positive patients receive vancomycin instead of ancef before incision.
Implementation of this program has decreased the prevalence of MRSA at an orthopedic specialty hospital by 33% when strict adherence (95%) was maintained . S. aureus eradication was associated with a significant decrease in infection rates  . A meta-analysis similarly demonstrated at many hospitals, an eradication program decreased surgical site infections, wound complications, and reduced hospital costs. However, a follow up meta-analysis that only examined randomized prospective trials found a trend but not statistical significance to support the use of these screening and decolonizing protocols [65, 66].
Treatment of refractory pain is the primary reason for TJA, and thus many patients will be taking medication to mitigate their discomfort. However studies have shown that high levels of pain medication use preoperatively has a detrimental effect on outcome.
Preoperative long-acting opioids (re Oxycontin) are associated with increased risk for postop complications. 
Preoperative opioid use is a significant risk factor for prolonged postoperative (> 6 months) opioid use. A study found in a group of patients not taking narcotics preoperatively, about 8% of TKA and 4% of THA patients required opioids > 6 months after surgery. In contrast, patients using opioids preoperatively had a 53% and 35% risk of continuing opioids at 6 months, in TKA and THA respectively. Patients taking higher doses of opioids preoperative at over 80% risk of continuing opioids at 6 months. 
Pevic et al found that an opioid group compared to an opioid-naïve group required significant higher dosages of opioids during postop hospitalization, higher risk of continued opioid use after 6 weeks, and worse Harris Hip Score at final follow up . More encouraging however, was the finding that over 50% of patients taking preop opioids were completely off by 6 weeks, and 80% were weaned off by final follow up (average 54 months)
All patients experience postoperative pain despite our best efforts. Current multimodal medications attack pain pathways through multiple approaches. These efforts are complicated when patients are taking significant pain medication before surgery, thus developing a tolerance to medication.
Whats the best age for getting a TJA? Should patients endure the pain just a little bit longer until they reach the age of 70? Should patients hurry up and get their joint replaced before they get too old? Like everything in medicine, a pure numeric threshold is just artifice, and patient specific factors are most important for clinical decisions. Yet broader trends can help to inform decisions and thus we examine the impact of age (whether it is age itself, or whether age represents a constellation of important variables).
Older patients (>80 years old).
Patients > 80 years old achieve improved pain and improved function similar to patients in their 60s and 70s. One study looked at people in their 90s and found that they too improved significantly with pain and function after TKA, and therefore, age alone should not prevent people from getting a surgery that can improve quality of life [1, 2].
Yet it is seen that older patients are more likely to have other medical conditions (including atrial fibrillation, high blood pressure etc) that can complicate recovery. There are reports of higher complication rates after surgery due to these medical conditions. One study suggested that the risk of death after surgery was 3x higher, the risk of MI or other cardiac complication was 2.5x higher, and the risk of pneumonia was 3.5x higher.  Another study looking 1 year mortality risk saw 5% in 90 year olds, 3% in 80 year olds and 0.8% in younger patients (not all of this is attributed to the surgery because the overall mortality rate for all 90 year olds is 12% at 1 year...which is actually higher than those undergoing surgery probably because those cleared for surgery are healthier) [4, 5]. This significant increased risk is important to remember because a hip and knee replacement surgery is life-improving but not life-saving and therefore patients need to know that the surgery can be considerable more life-threatening in patients older than 80 [6, 7].
The length of hospitalization is also longer (3.4 days for 90s, 3.3 days for 80s, and 2.8 days for < 80).
Younger Patients (<55 years old)
The average age for a joint replacement is about 70 years old. But < 55 is the vastest growing group undergoing TJA. In 2007 only 6% of TKAs were performed in patients under 50 years old .
The etiology for TJA in young patients is significantly different than in the elderly. The incidence of primary osteoarthritis is less common, with over 50% presenting for other reasons such as AVN, post-traumatic arthritis (30% of cases in TKA), and inflammatory arthritis, which at baseline are all associated with higher complication rates.
In TKA, many studies suggest good mid-term (5-10 yr) survival of 95-99% . Yet other studies suggest the mid-term (7 year) revision rate is higher than average, about 8%, most commonly due to aspetic loosening and deep infection   . Survivorship appears lower than the overall TKA population, and the rate of early aspetic loosening may be 4x higher. The Australian registry reported 12% revision rate at 10 years for patients with TKA under 55 yo. The Kaiser registry showed 2x higher revision rate in younger patients .
In THA, mid-term (10 year) survivorship, for cementless implants using highly crosslinked poly, appears equivalent to older THA population [14, 15], with wear rates of 0.02 mm/yr. Long-term revision rate (18 year avg) in patients under 50 yo was about 80%, with 95% survival of the femoral component and 85% survival of the acetabular component   . These figures reflect survival using contemporary cementless implants, while survival rates of cemented/older designs appears notably inferior . Some studies report accelerated poly wear rates of 0.2 mm/yr (due to increased activity) , while other studies have looked at activity levels in THA under 50 yo and found activity level (1.2 millino gait cycles/yr) and wear rates (0.1mm/yr) comparable to older counterparts .
The higher revision rate may be predisposed due to the underlying cause for TJA, such as posttraumatic arthritis. Others argue that younger patients are more active and thus place greater demands on the implants, accelerating the wear. However, studies have shown that young patients are not uniformly more active, and that there is significant variability among young patients[21, 22]. In THA about 37% returned to recreational sports (impact activity), yet for TKA only 10% returned to such activities. Furthermore, in THA, the use of HXLPE has reduced wear to levels similar to average population age.
It appears that at 10 years after UKA in patients under 60 years old, 90% survival compared with 96% in people over 60 years old .
One issue is that younger patients have higher expectations than older patients , appear more sensitive to residual symptoms , and found that age is the most important preoperative characteristic that predicts postop patient-reported outcomes .
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