Does Preoperative Opioid Use Increase the Risk of Early Revision Total Hip Arthroplasty?

BACKGROUND: The purpose of this study is to evaluate the impact of preoperative opioid use on the risk of subsequent revison after primary total hip arthroplasty (THA). METHODS: The Humana database was queried for unilateral THA between 2007-2015. Patients were tracked for the occurrence of an ipsilateral revision THA for 2 years. Factors analyzed included preoperative opioid use (defined as a history of opioid prescription filled within 3 months preceding primary THA), age, sex, diabetes, anxiety/depression, chronic kidney disease, and obesity (body mass index > 30 kg/m2). Multivariate logistic regression analysis was used to determine odds ratios. RESULTS: A total of 17,695 primary THA patients were analyzed and 0.88% (n = 155) underwent revision THA within 2 years. Preoperative opioid use occurred in 36.7% of all. Females comprised 58.7% of the total cohort and 80% were >50 years. Preoperative opioid users were significantly more likely to undergo early THA revision (1.2% vs 0.7%, P < .001). Other patient factors that significantly increased the risk of early THA revision included obesity (1.3% vs 0.8%, P = .03) and a preoperative diagnosis of anxiety/depression (1.9% vs 0.8%, P = .006). CONCLUSION: Opioid use within 3 months preceding THA independently predicts an increased risk of early revision. Additionally, independent predictors of early revision include obesity and a diagnosis of anxiety/depression. Factors such as these will need to be considered in risk adjustment models when assessing quality of care or implementing bundled payment initiatives. Further research is needed to evaluate whether discontinuing opioids before surgery mitigates this risk.

Preoperative Opioid Use and Its Association With Early Revision of Total Knee Arthroplasty.

BACKGROUND: Few studies have evaluated the impact of preoperative opioid use on risk of subsequent revision following primary total knee arthroplasty (TKA). The purpose of this study was to determine whether preoperative opioid use is associated with an increased risk of early revision TKA. METHODS: The Humana administrative claims database was queried to identify patients who underwent unilateral TKA during the years 2007-2015. Patients were tracked for the occurrence of an ipsilateral revision procedure within 2 years. Preoperative opioid use was defined as having an opioid prescription filled within the 3 months before TKA. Age, sex, diabetes, obesity, chronic kidney disease, and anxiety/depression were also analyzed. Univariate and multivariate analyses were performed. RESULTS: A total of 35,894 primary TKA patients were identified and 1.2% (n = 413) had a revision TKA procedure within 2 years. 29.2% of patients filled an opioid prescription within the 3 months before TKA. Preoperative opioid users were significantly more likely to undergo early TKA revision (1.6% vs 1.0%, P < .001). Preoperative opioid use (odds ratio [OR], 1.53; 95% confidence interval [CI], 1.25-1.88; P < .001), younger age (OR, 2.46; 95% CI, 1.43-3.95; P < .001), obesity (OR, 1.25; 95% CI, 1.01-1.56; P = .04), and smoking (OR, 1.66; 95% CI, 1.22-2.22; P < .001) were associated with early revision TKA. CONCLUSION: This study identified preoperative opioid use as being independently associated with a greater risk for an early revision TKA. Younger age, obesity, and smoking were also associated with elevated risk. These findings support efforts to reduce inappropriate opioid prescribing.

Topography of microglial activation in sensory- and affect-related brain regions in chronic pain.

Microglial activation in the spinal cord plays a central role in the development and maintenance of chronic pain after a peripheral nerve injury (PNI). There has not yet been a thorough assessment of microglial activation in brain regions associated with pain and reward. To this end, this study uses a mouse model of neuropathic pain in which the left sciatic nerve of male C57Bl/6J mice is loosely constricted (chronic constriction injury) to assess microglial activation in several brain regions 2 weeks after injury, a time point at which pain hypersensitivity is well established. We found significant microglial activation in brain regions associated with sensory pain transmission and affect, including the thalamus, sensory cortex, and amygdala. Activation was consistently most robust in brain regions contralateral to the side of injury. Brain regions not directly involved in either sensory or affective dimensions of pain, such as the motor cortex, did not display microglial activation. This study confirms that PNI induces microglial activation in regions involved with both sensory and affective components of pain. © 2016 Wiley Periodicals, Inc.

Two- to 4-Year Followup of a Short Stem THA Construct: Excellent Fixation, Thigh Pain a Concern.

BACKGROUND: Short stem cementless femoral components were developed to aid insertion through smaller incisions, preserve metaphyseal bone, and potentially decrease or limit the incidence of thigh pain. Despite some clinical success, the senior author (DDG) believed a higher percentage of his patients who had received a cementless short stem design were experiencing thigh pain, which, coupled with concerns about bone ingrowth fixation, motivated the review of this case series. QUESTIONS/PURPOSES: (1) What is the proportion of patients treated with a short stem cementless THA femoral component that develop thigh pain and what are the hip scores of this population? (2) What are the radiographic results, specifically with respect to bone ingrowth fixation and stress shielding, of this design? (3) Are there particular patient or procedural factors that are associated with thigh pain with this short stem design? METHODS: Two hundred sixty-one primary THAs were performed in 238 patients by one surgeon between November 2010 and August 2012. During this time period, all patients undergoing primary THA by this surgeon received the same cementless short titanium taper stem. Seven patients (eight hips) died and five patients (five hips) were lost to followup, leaving 226 patients (248 hips) with a mean followup of 3 years (range, 2-5 years). Patients rated their thigh pain during activity or rest at final followup on a 10-point visual analog scale. Harris hip scores (HHS) were obtained at every clinic appointment. Thigh pain was evaluated at the final followup or by contacting the patient by phone. Radiographs were evaluated for bone-implant fixation, bone remodeling, and osteolysis. An attempt was made to correlate thigh pain with patient demographics, implant specifications, or radiographic findings. RESULTS: Seventy-six percent of hips (180 of 238) had no thigh pain, 16% of hips (37 of 238) had mild thigh pain, and 9% (21 of 238) had moderate or severe thigh pain. Preoperatively, mean HHS was 47 (SD, 16) and at last followup, mean HHS was 88 (SD, 13). There were two femoral revisions, one for severe thigh pain and the other for infection. All but two components demonstrated bone ingrowth fixation (99%). Femoral stress shielding was mild in 64% of hips (135 of 212), moderate in 0.5% (one of 212), and severe in no hips. There is an inverse linear relationship between age and severity of thigh pain (r = -0.196; p < 0.0024). CONCLUSIONS: Although reliable fixation was achieved and good HHS were attained, the frequency and severity of thigh pain with this short cementless stem were concerning. The surgeon has subsequently abandoned this short stem design and returned to a conventional length stem. Future study direction might investigate the biomechanical grounds for the thigh pain associated with this stem design. LEVEL OF EVIDENCE: Level IV, therapeutic study.

The John N. Insall Award: Do Intraarticular Injections Increase the Risk of Infection After TKA?

BACKGROUND: Infection after total knee arthroplasty (TKA) can result in disastrous consequences. Previous research regarding injections and risk of TKA infection have produced conflicting results and in general have been limited by small cohort size. QUESTIONS/PURPOSES: The purpose of this study was to evaluate if intraarticular injection before TKA increases the risk of postoperative infection and to identify if time between injection and TKA affect the risk of TKA infection. METHODS: The Humana data set was reviewed from 2007 to 2014 for all patients who received a knee injection before TKA. Current Procedural Terminology (CPT) codes and laterality modifiers were used to identify patients who underwent knee injection followed by ipsilateral TKA. Postoperative infection within 6 months of TKA was identified using International Classification of Diseases, 9th Revision/CPT codes that represent two infectious endpoints: any postoperative surgical site infection (encompasses all severities of infection) and operative intervention for TKA infection (surrogate for deep TKA infection). The injection cohort was stratified into 12 subgroups by monthly intervals out to 12 months corresponding to the number of months that had elapsed between injection and TKA. Risk of postoperative infection was compared between the injection and no injection cohorts. In total, 29,603 TKAs (35%) had an injection in the ipsilateral knee before the TKA procedure and 54,081 TKA cases (65%) did not. The PearlDiver database does not currently support line-by-line output of patient data, and so we were unable to perform a multivariate analysis to determine whether other important factors may have varied between the study groups that might have had a differential influence on the risk of infection between those groups. However, the Charlson Comorbidity index was no different between the injection and no injection cohorts (2.9 for both) suggesting similar comorbidity profiles between the groups. RESULTS: The proportion of TKAs developing any postoperative infection was higher among TKAs that received an injection before TKA than in those that did not (4.4% versus 3.6%; odds ratio [OR], 1.23; 95% confidence interval [CI], 1.15-1.33; p < 0.001). Likewise, the proportion of TKAs developing infection resulting in return to the operating room after TKA was also higher among TKAs that received an injection before TKA than those that did not (1.49% versus 1.04%; OR, 1.4; 95% CI, 1.3-1.63; p < 0.001). Month-by-month analysis of time between injection and TKA revealed the odds of any postoperative infection remained higher for the injection cohort out to a duration of 6 months between injection and TKA (ORs ranged 1.23 to 1.46 when 1-6 months between injection and TKA; p < 0.05 for all) as did the odds of operative intervention for TKA infection when injection occurred within 7 months of TKA (OR ranged from 1.38 to 1.88 when 1-7 months between injection and TKA; p < 0.05 for all). When the duration between injection and TKA was longer than 6 or 7 months, the ORs were no longer elevated at these endpoints, respectively. CONCLUSIONS: Injection before TKA was associated with a higher risk of postoperative infection and appears to be time-dependent with closer proximity between injection and TKA having increased odds of infection. Further research is needed to better evaluate the risk injection before TKA poses for TKA infection; a more definitive relationship could be established with a multivariate analysis to control for other known risk factors for TKA infection. LEVEL OF EVIDENCE: Level III, therapeutic study.

Recent Trends in Blood Utilization After Revision Hip and Knee Arthroplasty.

BACKGROUND: Blood transfusion guidelines in elective surgery have been implemented over the last decade to minimize risk and cost related to transfusion without sacrificing patient outcomes. Blood utilization in primary total hip (THA) and total knee arthroplasty (TKA) has been extensively studied but there is a paucity of studies evaluating utilization in revision THA and TKA. The purpose of this study is to evaluate current trends in transfusion following revision THA and TKA. METHODS: The Humana dataset was reviewed for transfusion trends from 2007 to 2015 for patients undergoing revision THA and TKA. Subgroup analysis was performed to evaluate the impact of age, gender, geographic location, and obesity. RESULTS: In total, 9176 and 12,493 revision THA and TKA patients were analyzed with transfusion rates of 19.2% and 11.9%, respectively. Allogeneic packed red blood cells were most commonly transfused (90% and 92%, respectively). Transfusion rates decreased significantly from 24.7% to 10.3% and 15.9% to 4.5%, respectively, over the years 2007-2015. Women had higher transfusion rates (odds ratio [OR] THA:TKA 1.24:1.23), while obesity was associated with lower transfusion rates after revision THA (OR 0.88). Transfusion rates were higher in 2-component revisions compared to primary (OR THA:TKA 1.24:1.24), while 1-component revisions had lower transfusion rates than primary procedures (OR THA:TKA 0.79:0.25). CONCLUSION: Transfusion rates after revision THA and TKA have fallen substantially since 2007. In 2016, only 10% and 4% of revision THA and TKA, respectively, required transfusion. The study should provide benchmark data for surgeons to use as comparison to the blood utilization following revision joint replacement at their institutions.

Are Trends in Total Hip Arthroplasty Bearing Surface Continuing to Change? 2007-2015 Usage in a Large Database Cohort.

BACKGROUND: Bearing surface issues related to trunnionosis or metal-on-metal (MoM) articulations have likely impacted recent trends in bearing surface choice. The purpose of this study is to evaluate trends in total hip arthroplasty (THA) bearing surface use, including 2015 data, with respect to the date of operation and patient demographics. METHODS: The Humana dataset was reviewed from 2007 through 2015 to analyze bearing surface usage in primary THA. Four bearing surface types were identified by International Classification of Disease, 10th Revision codes and trended throughout the years: metal-on-polyethylene (MoP), ceramic-on-ceramic (CoC), ceramic-on-polyethylene (CoP), and MoM. Prevalence was analyzed as a function of age and sex. RESULTS: Of the 28,504 primary THA procedures, the most commonly used bearing was MoP (46.1%), followed by CoP (33.2%), MoM (17.1%), and ceramic-on-ceramic (3.6%). The use of CoP bearings significantly increased from 6.4% in 2007 to 52.0% in 2015, while MoM bearings decreased during this period. MoP bearings decreased over 2012-2015 (P < .001). CoP usage decreased with age, while MoP bearings increased with a transition occurring at 65-69 years of age. Women were more likely to receive MoP bearings (odds ratio [OR] 1.2), while men were more likely to receive MoM and CoP bearings (OR 1.1). Multivariate logistic regression showed age to be an independent predictor of bearing surface choice with patients 65 and older more likely to receive MoP bearings (OR 3.2). CONCLUSION: Bearing surface choice in primary THA has changed tremendously from 2007 to 2015. MoM bearing use has decreased as a result of adverse effects. Age continues to remain a significant factor in bearing surface choice.

Recent Trends in Blood Utilization After Primary Hip and Knee Arthroplasty.

BACKGROUND: Blood conservation strategies have evolved greatly over the last 5 years. There is a paucity of large blood utilization studies of total hip arthroplasty (THA) and total knee arthroplasty (TKA) that include recently performed surgery. The purpose of this study was to use a large database to evaluate trends in blood transfusion after THA and TKA, including 2015 data. METHODS: The Humana data set was reviewed from 2007 to the third quarter of 2015 for all patients undergoing primary THA and TKA. Rates and type of postoperative blood transfusion were trended through the years of the data set. Further subgroup analysis was performed to evaluate the impact of patients' age, gender, geographic location, and obesity on the incidence of blood transfusion using standard statistical techniques. RESULTS: In total, 69,350 THA patients and 139,804 TKA patients were analyzed. Overall transfusion rate was 18.2% and 12.7% after TKA and THA, respectively. The most common type of blood transfused was allogeneic packed red blood cells (88% of all transfusions) followed by perioperative collected autologous blood (12% of all transfusions). There were no transfusions of preoperatively collected autologous blood. Transfusion rates decreased significantly from 21.3%-8.7% and 17.3%-4.4% for THA and TKA, respectively, over the years 2007-2015 (P < .001). CONCLUSION: Rates of blood transfusion after primary THA and TKA have fallen precipitously since 2010 and are now down to 9% and 4% for THA and TKA, respectively. Blood management strategies instituted over the last 5 years have had a large impact on transfusion rates after joint arthroplasty.

What Can We Learn From 20-year Followup Studies of Hip Replacement?

BACKGROUND: A patient who dies during the followup period of a study about total hip arthroplasty (THA) cannot subsequently undergo a revision. The presence of competing events (such as deaths, in a study on implant durability) violates an assumption of the commonly used Kaplan-Meier (KM) survivorship approach. In that setting, KM-based estimates of revision frequencies will be high relative to alternative approaches that account for competing events such as cumulative incidence methods. However, the degree to which this difference is clinically relevant, and the degree to which it affects different ages of patient cohorts, has been poorly characterized in orthopaedic clinical research. QUESTIONS/PURPOSES: The purpose of this study was to compare KM with cumulative incidence survivorship estimators to evaluate the degree to which the competing event of death influences the reporting of implant survivorship at long-term followup after THA in patients both younger than and older than 50 years of age. METHODS: We retrospectively reviewed 758 cemented THAs from a prospectively maintained single-surgeon registry, who were followed for a minimum of 20 years or until death. Revision rates were compared between those younger than or older than age 50 years using both KM and cumulative incidence methods. Patient survivorship was calculated using KM methods. A total of 21% (23 of 109) of the cohort who were younger than 50 years at the time of THA died during the 20-year followup period compared with 72% (467 of 649) who were older than 50 years at the time of surgery (p < 0.001). RESULTS: In the cumulative incidence analysis, 19% of the younger than age 50 years cohort underwent a revision for aseptic causes within 20 years as compared with 5% in the older than age 50 years cohort (p < 0.001). The KM method overestimated the risk of revision (23% versus 8.3%, p < 0.001), which represents a 21% and 66% relative increase for the younger than/older than age 50 years groups, respectively. CONCLUSIONS: The KM method overestimated the risk of revision compared with the cumulative incidence method, and the difference was particularly notable in the elderly cohort. Future long-term followup studies on elderly cohorts should report results using survivorship curves that take into account the competing risk of patient death. We observed a high attrition rate as a result of patient deaths, and this emphasizes a need for future studies to enroll younger patients to ensure adequate study numbers at final followup. LEVEL OF EVIDENCE: Level III, therapeutic study.

Risk of Acute Kidney Injury After Primary and Revision Total Hip Arthroplasty and Total Knee Arthroplasty Using a Multimodal Approach to Perioperative Pain Control Including Ketorolac and Celecoxib.

Safe and effective perioperative analgesia is instrumental to patient satisfaction and decreasing LOS after TJA. We evaluated rates of acute kidney injury (AKI) in primary and revision TJA using a multimodal pain control regimen including scheduled celecoxib and PRN ketorolac. Postoperative AKI was identified in 43/903 (4.8%) of 903 of patients with adequate preoperative renal function. Those who developed AKI had significantly increased LOS (P < .01), were older, more obese, and more likely to have diabetes (P < .05). With a protocol incorporating NSAIDs in patients without evidence of preoperative renal impairment, there is a 4.8% rate of AKI, which is 2.7 times higher than the reported literature. Acute postoperative kidney injury was significantly correlated with increased LOS and has important patient safety and healthcare-related cost implications.

Metal-on-Metal Total Hip Arthroplasty at Five to Twelve Years Follow-Up: A Concise Follow-Up of a Previous Report.

BACKGROUND: Concern has arisen regarding potential complications with modular metal-on-metal (MoM) acetabular components in total hip arthroplasty. The purpose of this study was to analyze longitudinally the longer term results of a previously reported cohort of patients utilizing a cementless modular acetabular component with a MoM bearing. METHODS: One hundred sixty-nine consecutive but selected total hip arthroplasties were performed in 148 patients at 2 institutions using a modular acetabular MoM component. One hundred thirty-nine patients (158 hips) were living at minimum 5 years, 1 patient (1 hip) was lost to follow-up and 8 patients (10 hips) were deceased. Patients were evaluated clinically in terms of revision as well as radiographically. Additional testing (metal ion levels, advanced imaging) was performed when concerns for adverse local tissue reaction (ALTR) arose. RESULTS: There were 6 (3.8%) additional hips revised since the prior report for a total of 7 hips (4.4%) revised at 5-12 year follow-up. All newly revised hips (3.8%) demonstrated ALTR. There were 7 (4.7%) additional cases of radiographically detected acetabular osteolysis and 7 (4.7%) cases of femoral osteolysis. CONCLUSION: Longitudinal evaluation of a modular MoM bearing surface acetabular component demonstrated increased rates of ALTR and osteolysis at longer duration follow-up. Although greater than 95% of hips in this study performed well at 5-12 years, when comparing the results to metal-on-polyethylene bearings using the same acetabular component, the results were inferior. Longitudinal surveillance is warranted with this design and this bearing surface couple as cases of ALTR and osteolysis increased with longer follow-up.

Minimum 10-Year Follow-Up of Cementless Total Hip Arthroplasty Using a Contemporary Triple-Tapered Titanium Stem.

BACKGROUND: There is extensive variation in design and insertion technique of cementless tapered femoral stems. The purpose of our study was to evaluate a consecutive series of contemporary tapered cementless femoral stems inserted with a ream-and-broach technique at a minimum 10-year follow-up in patients undergoing total hip arthroplasty (THA). METHODS: One hundred consecutive THAs (88 patients) performed by a single surgeon were followed for a minimum of 10 years. Hips were evaluated clinically for revision status, Western Ontario and McMaster Universities Osteoarthritis Index, 36-item Short Form Health Survey, Harris Hip Score, and University of California, Los Angeles, and Tegner Activity Scores. Radiographic evaluation included assessment for loosening, osteolysis, and stress shielding. Kaplan-Meier survivorship analysis included end points for revision and radiographic evidence of femoral component loosening. RESULTS: At minimum 10-year follow-up, 66 patients (74 hips) were living, 20 patients (24 hips) were deceased, and 2 patients (2 hips) were lost to follow-up. Four hips required reoperation, but no femoral components were revised for aseptic loosening. One femoral component (1%) was revised due to a postoperative periprosthetic fracture. Radiographic evaluation demonstrated bone ingrowth of all stems without evidence of component loosening and 1 case of severe stress shielding. Kaplan-Meier survivorship at 10 years was 100% for the end points of femoral revision for loosening or femoral radiographic loosening. CONCLUSION: This contemporary, cementless titanium-tapered femoral component inserted with ream-and-broach technique demonstrated excellent results in terms of outcomes and clinical durability as well as osteointegration on radiographs at minimum 10-year follow-up. This study corroborates, with level 2 and level 3 data, level 1 data reported in national registries.

Systematic review of literature of cemented femoral components: what is the durability at minimum 20 years followup?

BACKGROUND: Cemented femoral total hip arthroplasty may be one of the most successful surgical interventions of all time. However, although results are very encouraging over the early to mid-term followup, relatively few studies have analyzed the durability of these implants beyond 20 years followup. To evaluate the performance of contemporary implants, it is important to understand how previous implants perform at 20 or more years of followup; one way to do this is to aggregate the available data in the form of a systematic review. QUESTIONS/PURPOSES: (1) How durable is cemented femoral fixation in the long term (minimum 20-year followup) with respect to aseptic loosening? (2) Is the durability of cemented femoral fixation dependent on age of the patient? (3) Are the long-term results of the cemented femoral fixation dependent on any identifiable characteristics of the prosthesis such as surface finish? METHODS: A systematic review was performed to identify long-term studies of cemented femoral components. After application of inclusion and exclusion criteria to 1228 articles found with a search in PubMed and EMBASE, 17 studies with a minimum of 20-year followup on cemented femoral components were thoroughly analyzed in an attempt to answer the questions of this review. The quality of the studies reviewed was assessed with the Methodological Index for Nonrandomized Studies (MINORS) instrument. All studies were case series and cohort sizes ranged from 110 to 2000 hips for patients older than 50 years of age and 41 to 93 hips for patients younger than 50 years at the time of surgery. RESULTS: Among the six case series performed in patients older than 50 years of age, survivorship for aseptic loosening of the femoral component ranged from 86% to 98% at 20 years followup. There were no obvious differences for younger patients when analyzing the five studies in patients younger than age 50 years in which survivorship free from aseptic loosening for these studies ranged from 77% at 20 years in one study and 68% to 94% at 25 years in the other studies. Although data pooling could not be performed because of heterogeneity of the studies included here, it appeared that stems with a rougher surface finish did not perform as well as polished stems; survivorship of stems with rougher surface finishes varied between 86% and 87%, whereas those with smoother finishes ranged between 93.5% and 98% at 20 years. CONCLUSIONS: Excellent long-term fixation in both older and younger patients can be obtained with cemented, polished femoral stems. These results provide material for comparison with procedures performed with newer cementing techniques and newer designs, both cemented and cementless, at this extended duration of followup.

Correlation of knee and hindfoot deformities in advanced knee OA: compensatory hindfoot alignment and where it occurs.

BACKGROUND: Many patients undergoing TKA have both knee and ankle pathology, and it seems likely that some compensatory changes occur at each joint in response to deformity at the other. However, it is not fully understood how the foot and ankle compensate for a given varus or valgus deformity of the knee. QUESTIONS/PURPOSES: (1) What is the compensatory hindfoot alignment in patients with end-stage osteoarthritis who undergo total knee arthroplasty (TKA)? (2) Where in the hindfoot does the compensation occur? METHODS: Between January 1, 2005, and December 31, 2009, one surgeon (JJC) obtained full-length radiographs on all patients undergoing primary TKA (N=518) as part of routine practice; patients were analyzed for the current study and after meeting inclusion criteria, a total of 401 knees in 324 patients were reviewed for this analysis. Preoperative standing long-leg AP radiographs and Saltzman hindfoot views were analyzed for the following measurements: mechanical axis angle, Saltzman hindfoot alignment and angle, anatomic lateral distal tibial angle, and the ankle line convergence angle. Statistical analysis included two-tailed Pearson correlations and linear regression models. Intraobserver and interobserver intraclass coefficients for the measurements considered were evaluated and all were excellent (in excess of 0.8). RESULTS: As the mechanical axis angle becomes either more varus or valgus, the hindfoot will subsequently orient in more valgus or varus position, respectively. For every degree increase in the valgus mechanical axis angle, the hindfoot shifts into varus by -0.43° (95% confidence interval [CI], -0.76° to -0.1°; r=-0.302, p=0.0012). For every degree increase in the varus mechanical axis angle, the hindfoot shifts into valgus by -0.49° (95% CI, -0.67° to -0.31°; r=-0.347, p<0.0001). In addition, the subtalar joint had a strong positive correlation (r=0.848, r2=0.72, p<0.0001) with the Saltzman hindfoot angle, whereas the anatomic lateral distal tibial angle (r=0.450, r2=0.20, p<0.0001) and the ankle line convergence angle (r=0.319, r2=0.10, p<0.0001) had a moderate positive correlation. The coefficient of determination (r2) shows that 72% of the variance in the overall hindfoot angle can be explained by changes in the subtalar joint orientation. CONCLUSIONS: These findings have implications for treating patients with both knee and foot/ankle problems. For example, a patient with varus arthritis of the knee should be examined for fixed hindfoot valgus deformity. The concern is that patients undergoing TKA, who also present with a stiff subtalar joint, may have exacerbated, post-TKA foot/ankle pain or disability or malalignment of the lower extremity mechanical axis as a result of the inability of the subtalar joint to reorient itself after knee realignment. A prospective study is underway to confirm this speculation. LEVEL OF EVIDENCE: Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.