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Correlation between nutritional status and staphylococcus colonization in hip and knee replacement patients.

Nutritional status is a significant factor that may influence operative outcomes in orthopaedic patients. Nutritional status can be evaluated using a variety of methods, including laboratory data, patient demographics, and exam findings. (1-6) Nutritional screening tools are meant to identify patients with poor nutrition that are at a higher than normal nutritional risk. Delayed wound healing and surgical site infection after orthopaedic surgery have been correlated with different patient biochemical and immunological parameters indicative of poor nutrition, such as low serum albumin, transferin and zinc levels, and total lymphocyte count. (7-10)

Patients undergoing orthopaedic surgery are often older and are at higher risk of impaired nutrition status. (11,12) Nasal colonization with Staphylococcus aureus, and especially with methicillin-resistant Staphylococcus aureus (MRSA), has also been shown to be a risk factor for surgical site infections. (13-16) Staphylococcus nasal colonization among high-risk orthopaedic patients was shown to be 18% for MSSA and 2.17% for MRSA. (17) Institutionalized and nursing home patients are at an increased risk for positive nasal colonization by Staphylococcus aureus. (18) Among other risk factors for positive colonization are hemodialysis, immunodeficiency, and increased age. (19) We hypothesized that poor nutritional status may correlate with the incidence of patient Staphylococcus colonization. At our institution both nutritional screening tools and a nasal screening and decolonization protocol have been incorporated in the pre-admission testing protocol for all hip and knee replacement patients. The nutritional screening tools are based on the MUST (Malnutrition Universal Screening Tool) system. (20) The MUST tool was developed and validated as an evidence based tool designed to identify patients who are malnourished. (21,22) Nasal colonization screening for patients undergoing total joint replacement surgery is conducted by an anterior nasal swab cultured for Methicillin-resistant Staphylococcus aureus (MRSA), and Methicillin-sensitive Staphylococcus aureus (MSSA).

The purpose of this study was to determine the incidence of preoperative malnutrition in our hip and knee replacement population and to examine the correlation between the patients' nutritional grading scores and the prevalence of a positive nasal Staphylococcus cultures.

Methods and Materials

Study Design

We conducted a retrospective chart review of prospectively collected data of the total joint arthroplasty patient population in our institution. The study was IRB approved by our institutional board.

Patient Screening

Retrospective chart review was completed on patients who underwent total hip or knee replacements between January and June 2009 and had undergone a nutritional assessment prior to surgery. Patient demographics, preoperative nasal culture results, nutritional screening evaluation score, and postoperative infection rates were collected for all patients who had a positive nasal culture on preoperative testing, as well as a random sample of patients from the same cohort. Our hospital has instituted a policy of MRSA and MSSA nasal screening and decolonization protocol for all patients undergoing total hip and total knee replacement surgery. Over the study period of 6 months, all patients that were seen at pre-admission testing (PAT) had their anterior nasal nares cultured for MRSA and MSSA colonization and had their nutritional status assessed were included in the study. A registered dietitian conducted the nutritional status screening. The screening evaluation included the patient's intake and appetite, medical diagnoses and feeding modality, body mass index (BMI), recent weight loss, and the existence of pressure ulcers were incorporated in the evaluation (Table 1). A cumulative raw score was developed based on these criteria, ranging from 0-5. This score was also associated with a risk level ranging from 1-3: Risk Level 1 (No-Low Risk), score 0-1; Risk Level 2 (Moderate Risk), score 2-4; Risk Level 3 (High Risk), score [greater than or equal to] 5, which gives a second assessment value. The associations between nutritional risk level and clinical data points were evaluated by chi-square analysis and independent samples t-tests utilizing nutritional score and nutritional risk.

Statistical Analysis

For this study, all patients who had a positive nasal culture on preoperative testing were included, as well as a random sample of patients from the same cohort accounting for 55% of eligible and complete cases. Pearson's chi-square test and Fischer's exact test were used to evaluate the association between the patient's nutritional risk rating level and the rates of colonization among the population, as well as with the incidence of surgical site infections. Additionally, independent sample t-tests were utilized in order to determine if the mean nutritional score differed between patients with and without colonization as well as with and without surgical site infections. Odds ratios for nutritional total score were calculated by logistic regression.


From January to June 2009, 731 patients underwent total hip or knee replacement and completed preoperative testing at our institution. Patients were excluded from the study if they failed to undergo the nasal cultures or the nutritional assessment, which left 652 patients. A total of 302 patients were selected for inclusion in this study based upon the sampling method indicated in the method section.

Among the entire eligible population (n = 652), nasal cultures were MSSA positive in 97 cases (14.9%) and MRSA positive in 15 cases (2.3%). Eleven patients (1.7%) presented with postoperative surgical site infections.

Within the study population (n = 302), patients' demographic characteristics can be found in Table 2. Mean patient age was 61.4 years (range: 27.7 to 82.4 years). The patient population was divided evenly between female (54.3%) and male (45.7%) and among total knee procedures (53.3%) and total hip procedures (46.7%).

Both the nutritional score and the nutritional risk level were evaluated for association with patient markers and demographic characteristics. The minimum nutritional score using the MUST system is zero, and the maximum score is 5. The nutritional evaluation scores in our population ranged from 0 to 4 with a mean of 0.4, and 25.5% of our patients had a measurable amount of nutritional depletion that was categorized by a score of 1 or above. None of the patients had a score of 5 or above (Table 2). Analysis of nutritional score indicated that nutritional score was not significantly associated with surgery types (p = 0.07, OR = 0.93, CI = 0.71 to 1.21), preoperative MSSA nasal culture status (p = 0.42, OR = 1.22, CI = 0.92 to 1.60), preoperative MRSA nasal culture status (p = 0.91, OR = 1.03, CI = 0.56 to 1.88), or surgical site infection (p = 0.73, OR = 1.26, CI = 0.69 to 2.32).

When we examined the correlation between the nutritional risk level score, which ranged from low risk = 1 to high risk = 3, no significantly association was found between nutritional risk level and surgery type (p = 1.0, OR = 0.96, CI = 0.52 to 1.78), preoperative MSSA nasal culture status (p = 0.13, OR = 0.61, CI = 0.32 to 1.15), preoperative MRSA nasal culture status (p = 0.72, OR = 0.74, CI = 0.20 to 2.74) or surgical site infection (p = 0.52, OR = 0.49, CI = 0.12 to 1.91).


Malnourishment among patients undergoing total joint arthroplasty is a modifiable risk factor for patient morbidity. Jensen and colleagues (11) found an average incidence of malnutrition of 42.4% when they analyzed a series of 129 consecutive patients admitted to an orthopaedic service. In this study, 28.6% of patients undergoing total hip arthroplasty were nutritionally depleted, which is similar to our finding of 25.5% among our total joint arthroplasty patients. Greene and associates (23) reported a five-time increase in postoperative major wound complications among patients with decreased nutritional status, which was assessed by a lymphocyte count of < 1,500 cells/mm, and a seven-time increase when preoperative albumin was < 3.5 g/dL. Similar conclusions were achieved by Koval and coworkers. (24) Their study presented poor outcomes in hip fracture patients with low preoperative albumin and total lymphocyte count. Smith and colleagues (12) reported that malnutrition in orthopaedic patients is a major risk factor in the development of postoperative complications, including surgical site infections. Marin and associates (9) reported that decreased nutritional parameters correlated with delayed wound healing. However, the incidence of postoperative complications may vary according to type of surgery and patient demographics.

Our study aimed to examine incidence of nutritional depletion and the correlation of preoperative nutritional status among total joint arthroplasty patients and the risk of nasal colonization with MRSA and MSSA, and to begin to examine any impact on the risk for postoperative surgical site infections. Our analysis found that the nutritional score was not significantly associated with surgery types, preoperative MSSA nasal culture, preoperative MRSA nasal culture, or surgical site infection (Table 2).

We did not find a statistical significant correlation in our study between a positive MSSA or MRSA nasal cultures preoperatively and surgical site infections in our patient group (p = 0.8 and 0.24, respectively). However our study is underpowered to find such a correlation due to the low number of surgical site infections. Other studies have demonstrated a correlation between Staphylococcus nasal colonization and bacteremia and surgical site infection, (13-16) although some studies have failed to show a correlation. (25)

This study was limited to elective total hip and knee patients that presented to preoperative testing prior to surgery, and cannot be generalized to the entire orthopaedic patient population. This study is also limited by the number and types of nutritional assessment parameters used to evaluate patients' nutritional status. Other commonly used nutritional parameters with short half-lives, such as retinol binding protein, transferin, and prealbumin were not assessed in our study due to the time gap between the patients' preoperative assessments and the date of their surgeries. It is possible that these parameters may demonstrate a higher correlation with Staphylococcus nasal colonization or surgical site infection, but at this time we can demonstrate no correlation between patients' preoperative nutritional status as determined by staff nutritionists and chronic Staphylococcus colonization.


In conclusion, a high percentage (25.5%) of our patients demonstrated some level of nutritional depletion prior to hip and knee replacement: a fact surgeons should consider when evaluating and counseling patients prior to surgery. Overall nutritional screening scores, using the nutritional risk ratings employed by our institution's nutrition service, were not significantly associated with surgery type, preoperative nasal culture status, or surgical site infection in our patient population. Therefore, the colonization of patients with Staphylococcus does not appear to be directly associated with nutritional status and other factors appear to be causative. Further studies are necessary to determine if preoperative assessment of nutritional status using laboratory values may be more useful in predicting patients who are at risk for chronic Staphylococcus colonization.

Disclosure Statement

None of the authors have a financial or proprietary interest in the subject matter or materials discussed, including, but not limited to, employment, consultancies, stock ownership, honoraria, and paid expert testimony.


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Ran Schwarzkopf, M.D., M.Sc., * Tara A. Russell, M.P.H,* Megan Shea, M.Sc., R.D., and James D. Slover, M.D., M.Sc.

* Ran Schwarzkopf, M.D., M.Sc., and Tara A. Russell, M.P.H., each contributed equally to this study.

Ran Schwarzkopf, M.D., M.Sc., Tara A. Russell, M.P.H, Megan Shea, M.Sc., R.D., and James D. Slover, M.D., M.Sc., are from the Adult Reconstruction Division, Department of Orthopaedic Surgery, NYU Hospital for Joint Diseases, New York, New York.

Correspondence: Ran Schwarzkopf, M.D., M.Sc., NYU Hospital for Joint Diseases, 301 East 17th Street, New York, New York 10003;
Table 1 Nutritional Screening Form Used by the Dietitian During the
Evaluation of Patients Prior to Surgery

Nutritional Screening Form Score

 Good Fair Poor < 51%
 75%-100% 51%-74%

Intake / Appetite 0 1 2

Diagnoses / 0 1 2
Feeding Modality

Unintended weight
loss > 10% in 1 NO Yes

 0 2

Pressure Ulcer Stage I-II Sage III-IV

 2 3

Score 0-1, patient Risk Level 1

Score 2-4, patient Risk level 2 Total

Score 5 or higher, patient risk Level 3

Table 2 Patient Demographic Data (n = 302), SSI and
Nasal Cultures (n = 652)

 n %

 Male 138 45.7
 Female 164 54.3
 Hip 141 46.7
 Knee 161 53.3
Nutritional Score
 0 225 74.5
 1 29 9.6
 2 41 13.6
 3 4 1.3
 4 3 1.0
 Surgical Site Infection--DIP 11 1.7
Preoperative Positive Nasal Culture
 MSSA 97 14.9
 MRSA 15 2.3
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Author:Schwarzkopf, Ran; Russell, Tara A.; Shea, Megan; Slover, James D.
Publication:Bulletin of the NYU Hospital for Joint Diseases
Date:Oct 1, 2011
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