Malnutrition can increase the risk of surgical site infections in elective spine surgery and joint replacements. Obesity and diabetes are two of the most prevalent comorbidities in malnourished patients. Although the prevalence of malnutrition disorders in patients undergoing elective orthopedic surgery remains at a high level, there are still some misconceptions about the awareness and management of the disorders among orthopedic surgeons. Serological tests such as total lymphocyte count, albumin, prealbumin, and serum transferrin levels can be used as markers of a patient’s nutritional status. Ren Zheng, Department of Traumatology and Orthopedics, Sixth Affiliated Hospital of Xinjiang Medical University
In addition, anthropometric markers such as calf abdomen, arm muscle circumference, triceps skin fold; other standard scoring systems such as Rainey-MacDonald nutritional index, Mini nutritional assessment, and institution-specific nutritional scoring tools are also helpful in diagnosing nutritional status. Preoperative assessment of nutritional status and adjustment of nutritional status, such as strict glycemic control, normalization of serum albumin, and appropriate weight loss, are measures that can reduce the occurrence of perioperative complications.
In daily life, malnutrition usually refers to nutritional deficiency. However, according to the definition of the World Health Organization, malnutrition includes deficiency or excess of nutrition. In fact, malnutrition is more common in obese people, and these patients are prone to develop diabetes in the later stages.
Definition of malnutrition
In the orthopedic literature, there are more methods to define malnutrition, including serum laboratory tests, human body surface marker point measurements, and standard nutrition scoring tools (Table 1).
Malnutrition is defined in the diagnosis of SSI or poor trauma healing as total blood lymphocytes <1500/mm3 and serum albumin concentration <3.5 g/dl. Total blood lymphocyte count is the total number obtained by summing all lymphocyte categories in the blood. Decreased serum prealbumin or serum transferrin level <200 mg/dl is one of the signs of malnutrition. Although serum zinc ion levels are not currently used as a uniform standard, reduced serum zinc ion levels (<95ug/dl) are associated with impairment of postoperative trauma healing capacity in orthopedics.
Serum albumin, prealbumin, and transferrin are proteins in the body that have a good sensitivity to potential nutritional deficiencies. Because of the short half-life of these indicators, they can detect recent acute changes in nutritional status. Prealbumin is not currently used as an indicator to assess perioperative nutritional status in clinical practice, probably because it is too sensitive to accurately reflect changes in protein-calorie nutritional status.
There are no clinical studies on the use of prealbumin for assessing nutritional status. Similarly, the usefulness of total lymphocytes in the diagnosis of malnutrition is still controversial, but even so, its use in clinical practice is common. Albumin is currently the most widely used and simplest indicator to assess the nutritional status of patients.
Table 1
Business assessment methods
Method
Strengths
Reference range
Serum laboratory tests
More sensitive to acute or junctional malnutrition One of the most used measurements in the clinical literature today
Total lymphocyte count <1500/mm3
Serum albumin <3.5g/dl
Serum transferrin <200mg/dl
Body marker point measurement
Indirectly reflect the nutritional status of patients by measuring body marker points, easy to apply and less expensive. It does not reflect acute or borderline malnutrition, but may better reflect long-term nutritional status than serological tests.
Calf gastrocnemius muscle circumference <31 cm< p="">
Upper arm muscle circumference <22 mm< p="">
Triceps skin folds, no exact reference value, but lower values suggest poorer nutritional status
Standardized scores
Standardized scoring of nutritional status is easier to grasp. The combination of different measurements allows for an accurate assessment of nutritional status. To ensure the accuracy and reliability of scoring tools, each tool should be tested for validity before application.
Rainey-MacDonald Nutritional Status Index
Mini Nutrition Assessment
Schwarzkopf Nutritional Assessment Index
The presence of malnutrition in patients can also be determined clinically by measuring specific body marker points, such as calf and upper arm circumference, and triceps skin folds. Adults with a calf circumference of less than 31 cm or an upper arm circumference of less than 22 cm should be alerted to the possibility of malnutrition. A standard upper arm muscle circumference of between 60-90% suggests moderate malnutrition, and a circumference of less than 60% suggests moderate malnutrition. Although triceps skinfold measurements are currently considered less practical for assessing the nutritional status of patients, they are still reported in the orthopedic literature.
The timeliness of human body surface marker point measurements to assess nutritional status is poor. The body fat and muscle systems do not change significantly in the early stages of malnutrition and become depleted in the later stages, thus body surface marker point measurements do not provide a timely response to the patient’s nutritional status at that time. However, these measurements can reliably document changes in a patient’s nutritional status over a long period of time.
There are also some nutritional status assessment tools to evaluate the nutritional status of patients, among which the Rainey-MacDonald Nutritional Status Index is more commonly used. The RMNI is calculated as RMNI = (1.2x serum albumin) + (0.013x serum transferrin) – 6.43, and a value of 0 or a negative number is indicative of nutritional depletion. the validity of the RMNI has not been conclusively proven.
The MNA (Multi-Question Mini Nutrition Assessment) is more reliable in assessing malnutrition in elderly patients (Figure 1). the MNA includes a series of questions with varying themes, such as circumference determination of body marker points, dietary habits, etc.
Figure 1: MNA score entries
There are some differences between the screening tool and the assessment tool for nutrition. However, the study by Ozkalkanli et al. found a high correlation between malnutrition (assessment tool) or risk of malnutrition (screening tool) and orthopedic surgical mortality, with ORs of 3.5 and 4.1, respectively, so both tools can be used as a predictor of postoperative orthopedic mortality.
The World Health Organization defines obesity as Class I, BMI 30.0-34.9, Class II, 35-39.9, and Class III, over 40. and the criteria for diagnosing DM are shown in Table 2.
Table 2
Four diagnostic criteria for diabetes mellitus of the American Diabetes Association
HbA1c ≥6.5%
Fasting (≥8h) glucose ≥126mg/dL (7mmol/L)
Blood glucose ≥200 mg/dL (11.1 mol/L) 2 hours after oral glucose tolerance test
With typical symptoms of hyperglycemia (polydipsia, polyuria) or hyperglycemic crisis and random blood glucose ≥ 200mg/dL (11.1mmol/L)
Mechanisms by which malnutrition increases the risk of infection
Malnourished patients are more likely to develop SSI due to impaired wound healing and prolonged inflammatory response period. reduced lymphocytes in malnourished patients can lead to a decreased ability of the immune system to clear or prevent infection.
Obesity causes SSI because obese patients have more difficulty in closing the wound and are prone to fat necrosis within the wound, creating a dead space and making local wound healing difficult. Obesity is also associated with prolonged operative time.
Diabetic patients are susceptible to SSI because they are unable to adequately oxidize blood glucose due to glycosylation of hemoglobin, which leads to local tissue ischemia and hypoxia due to large and microangiopathy, resulting in decreased resistance to infection in the trauma.
Malnutrition and SSI in spinal surgery
Superficial and deep SSIs after orthopedic surgery are associated with more markers of malnutrition, including serum laboratory tests, hyperglycemia, obesity, and diabetes mellitus. Patients with neuromuscular disease are at risk of developing deep tissue infections, so current spine surgery researchers are working to identify risk factors associated with spinal surgical incision infections.
Whether preoperative malnutrition, as determined by serologic testing, is associated with an increased risk of postoperative deep tissue infection after spine surgery has been the focus of current literature. came to a similar conclusion.
Although most current literature reports suggest a significant correlation between serum laboratory test results and infection, a multicenter retrospective study found no significant correlation between poor nutritional status and increased incisional infection rates in patients.
A 2007 study by Friedman et al. found that DM and BMI >35 were risk factors for SSI, with ORs of 4.2 and 7.1, respectively. a 2008 study came to similar conclusions and found that preoperative glucose >125 mg/dl and postoperative glucose >200 mg/dl were also associated with the development of SSI. Even when patients were not diagnosed with diabetes, high blood glucose levels were associated with trauma infection, suggesting that hyperglycemia or impaired glucose regulation is a risk factor for SSI.
Malnutrition and arthroplasty
A retrospective analysis of 6489 total knee arthroplasty patients by Peersman et al. found that 97 patients developed periprosthetic infections during the 7-year postoperative follow-up period. Comparison with matched controls revealed a significant association between malnutrition, obesity, DM and increased PJI.
Malnutrition and persistent intratracheal drainage were associated with PJI. A study of 11,785 lower extremity joint replacement patients found a significant correlation between nutritional status and trauma drainage and subsequent deep PJI in patients, with 83 patients having persistent postoperative intra-trauma drainage that required irrigation and debridement. Thirty-five percent of patients who had failed second-stage surgery with secondary deep infection had malnutrition (serum albumin <3.5 g/dl, total lymphocytes <1500/mm3, and transferrin <200 mg/dl). The probability of successful second-stage surgical debridement in malnourished patients was only 5%.
The relationship between obesity and PJI has been reported in a larger number of studies. In a study of 1509 patients undergoing TKA, it was found that although morbid obesity increased the risk of deep infection, the two did not reach a significant level of difference. However, Peersman et al. found a significant association between obesity and increased risk of PJI, and other more studies have correlated malnutrition status with PJI infection.
Summary and clinical recommendations
Considering the incidence of malnutrition and its impact on postoperative orthopedic function and complications, patients with preoperative serum albumin levels, total lymphocyte counts, and transferrin levels less than normal targets require nutritional assessment by a nutrition specialist. Diabetic patients should have good glycemic control prior to elective surgery and close postoperative monitoring of blood glucose. In clinical practice, blood HbA1c should be used as a routine screening measure, and if this value is greater than 7%, surgical postponement needs to be considered.
Similarly, obese patients need to undergo weight reduction through appropriate methods prior to surgery, including diet control, exercise, and medication, which unfortunately may not be covered by health insurance.
Although body marker point measurement can be used as a method for malnutrition assessment, it is not currently recommended for clinical use because of its inconsistent threshold criteria, large measurement error, and lack of timely feedback on changes in patients’ clinical nutritional status. The nutritional status scoring system can be used as an alternative to serum testing.
If a patient is diagnosed with malnutrition, it is recommended that such patients correct their own malnutrition status before undergoing elective surgery. According to the available literature, there is no definitive conclusion on whether correcting the patient’s preoperative nutritional status has a significant impact on the patient’s final clinical functional prognosis; however, given the available studies suggesting a significant correlation between malnutrition and increased postoperative mortality, preoperative correction of the patient’s malnutrition status is recommended. In the long term, more studies are needed to confirm whether there is a significant correlation between improvement in preoperative nutritional status and postoperative clinical prognosis.