Purpose: The purpose of our study is to compare hips to knees in regards to the cost per increase in function, to determine the relationship of economic investment to improved quality of life.

Method: During the year 2005, a total of 23 TKA and 41 THA revisions were performed for aseptic mechanical failure. Patients were enrolled prospectively and quality of life questionnaires including the SF-36, WOMAC, Harris Hip Score (HHS), and Knee Society Score (KSS) were collected prior to and following their procedure at two year follow-up. The total cost of the procedure including the hospital, implant, and surgeon fee were implemented in a cost effectiveness model to calculate the mean cost per SF-36, WOMAC, and HHS or KSS point gained. Demographical variables and co-morbidities were collected to determine risk factors for low cost-effectiveness.

Results: The majority of patients had significant improvement in SF-36, WOMAC, HHS and KSS scales. Patients with THA revisions experience a cost per point increase for HHS of $3,000, and $500 per point SF-36 compared to knee patients who experienced a cost per point increase for KSS of $2,000, and $2,800 per point SF-36. The WOMAC exhibited similar cost effectiveness in the subscales of pain, stiffness and functioning.

Conclusion: There are few studies that have compared the cost effectiveness of total joint arthroplasty revision procedures. Given the increasing cost of health care expenditures, prioritization of funding for the different health practices will become necessary. This study demonstrates that revision THA and TKA are relatively cost effective procedures compared to other non-orthopaedic interventions.

Persistent wound drainage after total joint arthroplasty (TJA) has been associated with a higher incidence of superficial and deep periprosthetic infection but the predictors for prolonged drainage and its outcome have not been thoroughly studied.

A consecutive series of 7,153 TJA cases performed between 2000 and 2006 at our institute, were recruited into this study. There were 301 cases (4.2%) of persistent wound drainage, defined as discharge from the wound for > 48 hours. The cases were matched in a 2:1 ratio for type of surgery, joint replaced, and date of surgery.

This study identified higher BMI (p< 0.005), malnutrition as defined by serum albumin< 3.4g/dl (p< 0.04), longer operative time (p< 0.01), and higher medical comorbidities, in particular diabetes (p< 0.001) as important risk factors for persistent wound drainage. In addition, patients in the drainage group were more likely to have a peak INR of > 1.5 (p< 0.001) during their hospital stay. Patients with wound drainage had a significantly lower hemoglobin postoperatively (p< 0.01) that necessitated greater number of postoperative allogenic transfusions (p=0.004). The hospital length of stay for the drainage group was also significantly higher (p< 0.005). One of the major risk factors for development of deep infection was prolonged drainage (> 7 days). In the deep hematoma and periprosthetic subgroups, the mean of delay in treatment was 6 days in those with retention of the prosthesis and successful outcome, and 9.5 days for those with failure of incision and drainage leading to resection arthroplasty (p= 0.03).

72% of the patient were successfully treated by oral or intravenous antibiotics. 27% required at least one re-operation for deep hematoma and 13% developed deep periprosthetic infection, resulting in 6% rate of resection arthroplasty. 1.5% of those with drainage remained in girdlestone status.

This study suggests early surgery for persistent drainage and avoidance of aggressive anticoagulation.

Serological tests including erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) are frequently used in the preoperative workup to screen for periprosthetic infection (PPI) in total hip arthroplasty (THA). The cut-off points reported in the literature are arbitrarily chosen by investigators. Similarly, the values used in laboratories to distinguish elevated results vary from one institute to another. Therefore, we intended to define the appropriate cut-off points of ESR and CRP that can be used to differentiate infection from aseptic failure of THA.

A review of our joint registry database revealed that 515 THA revisions (131 infected cases) were performed during 2000–2005. Intraoperative samples for culture were taken in all cases. The criteria used for diagnosis of infection were a positive intraoperative culture on solid media, presence of an abscess or sinus tract that communicated with the joint, positive preoperative aspiration culture, and/or elevated fluid cell count and neutrophil differential of the aspirated fluid. Non-infected patients with confounding factors that can elevate ESR and CRP including collagen vascular disease, inflammatory arthropathy, malignancy, and urinary tract infection were excluded. Receiver operator curves were used to determine the ideal cut-off point for both ESR and CRP.

The mean value of ESR in the infected group (77mm/ hr) was significantly higher compared to that of the non-infected cohort (29mm/hr) (p=0.0001). Similarly, infected patients presented with a greater mean CRP (9.8 mg/dl) than their non-infected cohort (1.48 mg/ dl) (p=0.0001). The infection threshold for ESR was 45mm/hr with a sensitivity of 85% and specificity of 79%, while the optimal cut-off value for CRP was defined as 1.6 mg/dl which yielded a sensitivity of 86% and specificity of 83%.

The optimal threshold values we determined are higher than the arbitrarily chosen values cited in the literature for ESR (30mm/hr) and CRP (1mg/dl). Although it has been previously reported that the sensitivity and specificity of CRP are far greater than that of ESR, we found that the two tests have comparable diagnostic value.

The accurate differentiation of aseptic loosening from periprosthetic infection in the painful hip prosthesis is a major clinical challenge. FDG-PET imaging has shown great promise in various clinical settings for detection of infection. This prospective study was designed to determine the efficacy of FDG-PET imaging in the assessment of patients with painful hip prosthesis.

One hundred and thirteen patients with 127 painful hip prostheses were evaluated by FDG-PET. Approximately 60 minutes after the intravenous administration of FDG images of the lower extremities were acquired using a dedicated PET machine. FDG-PET images were interpreted by experienced nuclear medicine physicians. Images were considered positive for infection if PET demonstrated increased FDG activity at the bone-prosthesis interface of the femoral component of the prosthesis. Surgical findings, histopathology, and clinical follow-up served as the “gold standard”.

FDG-PET was positive for infection in 35 hips and negative in 92 hips. Among 35 positive PET studies, 28 were proven to be infected by surgical and histopathology findings as well as follow-up tests. Of 92 hip prostheses with negative FDG-PET findings, 87 were proven to be aseptic. The sensitivity, specificity, positive and negative predictive values for FDG-PET were 0.85 (28/33), 0.93 (87/94), 0.80 (28/35), and 0.95 (87/92), respectively. The overall accuracy of FDG-PET in this clinical setting was 90.5% (115/127).

The results demonstrate that FDG-PET is a highly accurate diagnostic test for differentiating infected from non-infected painful hip prosthesis. Therefore, FDG-PET imaging is considered the study of choice in the evaluation of patients with suspected hip prosthesis infection.

The accurate diagnosis of periprosthetic infection poses a challenge to the clinician and the imaging specialist alike. In recent years, FDG-PET imaging has shown great promise in the evaluation of occult infection at various anatomic sites. The purpose of this investigation was to determine the accuracy of FDG-PET imaging in diagnosing periprosthetic infection associated with total knee arthroplasty.

Sixty eight painful knee prostheses were referred for further evaluation with FDG-PET imaging. Approximately 60 minutes after the intravenous administration of FDG, PET images of both knees were acquired and interpreted by experienced nuclear medicine physicians. PET images demonstrating increased FDG activity at the bone-prosthesis interface were considered infected. Final diagnosis was made on the basis of surgical findings, histopathology, and clinical follow-up.

FDG-PET correctly diagnosed 19 of the 22 infected cases for a calculated sensitivity of 86.4% (19/22). FDG-PET correctly predicted the absence of infection in 38 of 46 aseptic knee prostheses for a calculated specificity of 82.6% (38/46). The negative and positive predictive values for FDG-PET imaging in this setting were 92.7% (38/41) and 70.4% (19/27), respectively. The overall accuracy of FDG-PET imaging was 83.8% (57/68). FDG-PET was indeterminate in three cases which were not included in this analysis.

These results demonstrate that FDG-PET is a useful diagnostic tool for the evaluation of possible infection associated with knee arthroplasty. Considering the large number of subjects who undergo total knee arthroplasty and the sizable fraction who develop complications following surgery, the impact of FDG-PET imaging could be substantial. Examination of a larger number of patients with painful knee prostheses will further clarify the merit of this powerful technique in this clinical setting.

Currently two-stage resection arthroplasty is the preferred method for surgical treatment of periprosthetic infection in North America. However, the success of this treatment strategy has varied from 54% to 98% based on previous reports. The exact reason for this variation in outcome is not known. The purpose of this study was to determine the efficacy of this treatment modality and delineate patient risk factors that result in recurrent infection and failure.

During the period of this study (2000–2005) 77 patients with an infected THA were treated at our institution. Fifty-four patients underwent two-stage exchange arthroplasty while the remaining 22 failed to have the second stage reimplantation due to ill health. The latter 22 were excluded from the analysis. All patients were followed up prospectively for at least two years after reimplantation. Detailed data including demographics, comorbidities, surgical history, and medication intake was collected. Intraoperative data, organism profile, and complications were also documented. Failure was defined as patient requiring additional surgical procedure for control of infection or loosening.

Two-stage exchange arthroplasty successfully eradicated infection in 36 patients (67%) without need for further treatment. Seven patients (13%) had recurrent infection that necessitated resection arthroplasty. Eleven (20%) patients required irrigation and debridement for postoperative purulent drainage which successfully treated infection in 8 of the cases. The remaining 3 patients failed and required resection arthroplasty. Three additional patients had early loosening of components and required revision arthroplasty. The exact cause of loosening in these patients could not be determined and despite lack of isolation of organisms infection was suspected. Multivariate analysis identified previous medical comorbidity and postoperative allogenic transfusion as risk factors for failure.

Current strategies to treat periprosthetic infection remain imperfect. Two-stage exchange arthroplasty with all its inherent problems and inconveniences imparted a modest success in treatment of PPI at our high volume specialized center. With the increase in the number of virulent and resistant organisms, and the rise in arthroplasties being performed in infirm patients with medical comorbidities the success of this procedure is likely to be jeopardized. Novel treatment modalities to combat this dreaded condition is needed.

Debridement of an infected total joint arthroplasty with retention of mechanically stable components is often performed for acute cases of periprosthetic infection (PPI). However, the reported success of such a procedure to fully eradicate infection has varied widely. The objective of this study was to elucidate the efficacy of debridement in both infected THA and TKA and attempt to identify risk factors responsible for failure.

During the years 2000–2005, 71 TKA and 69 THA underwent irrigation and debridement for acute PPI (< 4 weeks). All patients were followed up prospectively for at least two years. Detailed data including demographics, comorbidities, surgical history, and medication intake was collected. Intraoperative data, organism profile, and complications were also documented. Failure was defined as patient requiring additional surgical procedure for control of infection or loosening.

Of the 140 patients, 24% required repeat irrigation and debridement for postoperative drainage, hema-toma formation, or systemic symptoms. One third of these revision debridement patients underwent multiple consecutive debridements. Two-stage resection arthroplasty was required in 65 patients (46%) of the entire cohort. Fifty-eight percent of the patients with resection required revision of their cement spacer block due to continuous drainage and systemic symptoms indicative of persistent infection. We noted a total of 86 failures (61%) that required either an additional debridement or resection arthroplasty after the first debridement procedure. The failure rates of THA (62%) and TKA (55%) individually were similar (p=0.253).

Although the concept of conservative management of PPI with debridement and retention of components is an attractive alternative to resection arthroplasty, we have found that 60% of patients undergoing this procedure will inevitably undergo two-stage arthroplasty. Furthermore, more than half of the patients that required resection arthroplasty developed infection of their spacer that entailed revision of the cement block. Therefore, we can conclude that this procedure has a high failure rate and should be implemented in only a select group of patients.

Periprosthetic infection (PPI) is one of the most devastating complications of total knee arthroplasty (TKA). It is widely accepted that resection arthroplasty supplemented with intravenous antibiotics and delayed exchange arthroplasty is the treatment modality of choice for infected TKA. However, the outcome after reimplantation has varied and unpredictable results have been reported. This study evaluates the outcome of this treatment strategy in a single high volume specialised center. Furthermore, our study aims to identify the factors that lead to failure of this treatment.

A thorough review of our joint registry database revealed that 80 patients with an infected TKA underwent resection arthroplasty at our institution during 2000–2005. Sixty-five patients underwent two-stage exchange arthroplasty while the remaining 15 failed to have the second stage reimplantation due to ill health or underwent arthrodesis or amputation. The latter 15 were excluded from the analysis. All patients were followed up prospectively for at least two years. Detailed data including demographics, comorbidities, surgical history, and medication intake was collected. Intraoperative data, organism profile, and complications were also documented. Failure was defined as patient requiring additional surgical procedure for control of infection or loosening.

Two-stage exchange arthroplasty successfully eradicated infection in 45 patients (31%) without need for further treatment. Twelve patients (18%) had recurrent infection that necessitated another resection arthroplasty. Eleven (17%) patients required irrigation and debridement for postoperative purulent drainage which successfully treated infection in 5 cases (46%). The remaining 6 patients failed and required resection arthroplasty. Three additional patients had early loosening of components and required revision arthroplasty. The exact cause of loosening in these patients could not be determined, and despite lack of isolation of organisms infection was suspected. Our analysis identified that irrigation and debridement prior to resection arthroplasty are major risk factors for failure.

Current strategies to treat periprosthetic infection remain imperfect. Two-stage exchange arthroplasty with all its inherent problems and inconveniences imparted a modest success in treatment of PPI at our high volume specialised center. The rise in the number of resistant and virulent organisms, increase in the number of patients with severe medical comorbidities who develop infection may account for the decline in the success of two-stage resection arthroplasty. Novel strategies for treatment of PPI are desperately needed.

One of the routinely used intraoperative tests for diagnosis of periprosthetic infection (PPI) is Gram stain that is reported to carry a very high specificity and a poor sensitivity. However, it is not known if the result of this test can vary according to the type of joint affected or the number of specimen samples collected. This study intended to examine the role of this diagnostic test in a large cohort of patients from single institution.

A review of our joint registry database revealed that 453 total knee arthroplasty (TKA) and 551 total hip arthroplasty (THA) of which 171 and 150 cases were respectively infected underwent revision surgery during 2000–2005 and had intraoperative cultures available for interpretation. A positive gram stain was defined as the visualisation of bacterial cells or ‘many leukocytes’ (> 5 per high power field) under the smear. The sensitivity, specificity, and predictive values of each individual diagnostic arm of Gram stain were determined. Combinations were performed in series that require both tests to be positive to confirm infection and in parallel that necessitate both tests to be negative to rule out infection. This analysis was performed for THA and TKA separately and later compared for each joint type.

The presence of organism cells and ‘many’ neutrophils on a Gram smear had high specificity (98%–100%) and positive predictive value (89%–100%) in both THA and TKA. The sensitivities (30%–50%) and negative predictive values (70%–79%) of the two tests were low as expected among both joint types. When the two tests were combined in series the specificity and positive predictive value were absolute (100%). The sensitivity (43%–64%) and the negative predictive value (82%) improved among both THA and TKA.

The presence of organisms or ‘many’ leukocytes on the Gram smear can confirm PPI in TJA. As expected, the sensitivity and negative predictive value of the two tests were low, and therefore infection could not be safely ruled out. Although the two diagnostic arms of Gram stain can be combined to achieve improved negative predictive value (82%), Gram stain continues to have poor value in ruling out PPI. With the advances in the field of molecular biology, novel diagnostic modalities need to be designed that can replace these traditional and poor tests.

Purpose: Periprosthetic infection (PPI) is a devastating complication. Surgical intervention to treat PPI is often required. The objective of this prospective study is to determine if there is any difference in functional improvement following revision TKA in patients with infected and non-infected failures.

Methods: 123 consecutive patients undergoing revision TKA at our institution were prospectively recruited into this study. The indication for revision TKA was PPI in 37 cases and aseptic failure in 86 cases. Detailed patient demographics and functional outcome using SF-36, KSS, Womac, lower extremity functional outcome score were collected at base line and at various time points after revision TKA. The baseline and two year follow up functional scores were calculated and compared. The functional score at the time of diagnosis of PPI (prosthesis in place) were used for baseline comparisons

Results: All baseline functional scores, and their individual elements, for the infected cases were worse than the non-infected cases. The functional scores at the two-year follow-up were not different between the infected and non-infected cases. Hence, there was a more impressive improvement (Δ) in functional outcome for the infected cases following revision TKA compared to non-infected cases. However, the general health perception as determined by the patients themselves appeared to deteriorate after revision TKA in both groups.

Discussion: It appears that patients with PPI are markedly more disabled at base line than the non-infected cases. These patients, however, benefit the most from surgical intervention compared to the non-infected cases. It appears that the patients’ perception of improvement in functional scores is less optimistic than physician measured parameters.

Introduction: Intraoperative tissue culture remains the “gold standard” in diagnosing periprosthetic infection (PPI). However, an organism is not always cultured and this has been attributed to the fact that preoperative antibiotics were administered. This study intends to examine if preoperative antibiotics prevent isolation of intraoperative organisms.

Methods: 91 total joint arthroplasty patients diagnosed with PPI during (1999–2005) and who had positive aspiration culture were included in the study. All intravenous antibiotics that were given to the patient within seven days of surgery were documented. The total number of positive intraoperative fluid and tissue samples of patients who did and did not receive antibiotics was calculated. Susceptibility of the organism(s) to antibiotics was determined by antibiogram of the preoperative and intraoperative culture.

Results: 60 out of 91 patients received preoperative antibiotics within seven days of surgery. Antibiotics prevented isolation of an intraoperative organism in 6 out of the 60 (10%) cases. All of the 31 patients who did not receive any preoperative antibiotics had positive intraoperative cultures. Chi-square analysis revealed no significant difference between giving preoperative antibiotics within 7 days and isolating an intraoperative organism (p=0.068). Giving antibiotics that specifically targets the culprit organism did not significantly affect the fluid (p=0.585) or tissue culture yield (p=0.152) either.

Discussion: Although, giving preoperative antibiotics can prevent isolation of intraoperative organisms in 10% of cases, this is not statistically or clinically significant in patients with positive aspiration cultures because the organism is known beforehand. However, it is clinically and medicolegally relevant to withhold antibiotics in patients with negative aspiration cultures since the postoperative treatment antibiotic is tailored according to the organism cultured.

Introduction: Diabetes mellitus type 2 (DM II) affects 18.2 million Americans and can cause several chronic and morbid complications. Furthermore, 90% of Americans have radiographic evidence of osteoarthritis by age 40. Diabetes may be an important risk factor for symptomatic osteoarthritis later in life. The aim of our study is to determine if diabetic patients are predisposed to osteoarthritis.

Methods: We conducted a review of the all total knee arthroplasty (TKA) cases performed at our institute during the past two years for end stage osteoarthritis. We excluded TKAs performed for post-traumatic arthritis and patients with inflammatory diseases. Comorbidities and demographical information including age, gender, BMI, and family history were collected from our database. A cross sectional study was performed to analyze the prevalence of DM II in our population. This prevalence was compared to that of diabetics in the general population available from various sources including the National Center for Health Statistics.

Results: Our cohort included a total of 3421 patients (1972 females, 1449 males) who had undergone TKA for end stage osteoarthritis. The average age and BMI were 66 years (range: 39–92) and 32 (range: 21–65) respectively. The prevalence of diabetes mellitus type 2 in our cohort was 12%, while the prevalence of DM II in the general US population currently ranges from 6%–7%.

Discussion: Chronic diabetes causes multiorgan failure via microvascular and macrovascular damage and may possibly lead to degeneration of articular cartilage and eventual arthritis. Based on this study, diabetes appears to be a strong predisposing factor for arthritis. Our laboratory has launched an extensive series of experiments delinating the potential cellular mechanism for such association.

Introduction: Although there is no absolute diagnostic test for PPI, synovial leukocyte counts and neutrophil percentages have been reported to have high sensitivity and specificity making them valuable tests for diagnosis. However, no cut off value for the latter is agreed upon. This study intends to evaluate to define definite cut-off values for preoperative synovial fluid leukocyte count and PMN percentage that allow physicians to diagnose infection in a prosthetic joint.

Methods: We analyzed synovial fluid aspirated preoperatively from 593 total knee arthroplasties (161 infected; 432 aseptic) from three different institutions. Using ROC curves, we determined cut-off values with optimal accuracy in diagnosis of infection for fluid leukocyte count and PMN percentage. The sensitivity, specificity, and predictive values were calculated for the above cutoff values.

Results: The synovial fluid leukocyte count was higher in patients with PPI (median, 31 × 103 cell/μl) compared to aseptic joint arthroplasties (median, 0.219 × 103 cells/μl)(p< 0.0001). Similarly, the neutrophil percentage was higher in patients with PPI (median, 90%) than in those with noninfected joints (median, 26%)(p< 0.0001). The cut-off values for optimal accuracy in diagnosis of infection were 1760 cells/μl for fluid leukocyte count and 73% for PMN percentage. A fluid cell count > 1760 cells/μl had a PPV of 99% and NPV of 88%, while a neutrophil percentage > 73% yielded a PPV of 96% and NPV of 91%. Chi-square analysis revealed the fluid WBC count and the neutrophil percentage to be significantly associated with the diagnosis of infection (p< 0.0001).

Discussion: Synovial fluid leukocyte count and differential are useful adjuncts to ESR and CRP in the preoperative diagnosis for infection in TKA. This study has identified a cut-off value for leukocyte count and neutrophil percentage that can be used to diagnose infection in a prosthetic joint.

Introduction: Management of bone loss during revision total knee arthroplasty (TKA) can be challenging. The degree and location of bone loss often dictates the type of prosthesis that can be utilized during revision surgery. The aim of this prospective study was to determine if plain radiographs are adequate in assessing the degree of bone loss around TKA and identify the limitations of plain radiographs for this purpose, if any.

Methods: 205 patients undergoing revision TKA at our institution were included. The indication for revision was aseptic failure in 120 patients and septic failure in the remaining patients. The plain radiographs were evaluated by a research fellow and the attending surgeon. The degree and the location of bone loss around the TKA was determined using the UPenn Bone Loss chart. The degree of real bone loss was then determined intraoperatively.

Results: The predicted amount of bone loss for the tibia based on the AP (p=0.136) and lateral (p=0.702) radiographs correlated well with the intraoperative findings. However, plain radio-graphs underestimated the degree of bone loss around femur, particularly the condyles (p=0.005).

Discussion: Reconstructive surgeons performing revision TKA need to be aware of the limitations of routine radiographs in assessing the degree of bone loss around the femoral component. Hence, patients undergoing revision TKA with suspected bone loss may need to be evaluated by additional imaging techniques and/or alternative reconstructive options need to be available to deal with greater than expected degree of bone loss intraoperatively.