Malnutrition in Orthopaedic Sports Medicine: A Review of the Current Literature

Abstract

Context:

Malnutrition is well-studied in various aspects of the orthopaedic literature, most commonly in relation to arthroplasty, spine surgery, and trauma. However, the management of nutritional deficiencies is commonly overlooked among orthopaedic sports medicine providers. The purpose of this article is to analyze the available sports medicine literature to review the associations between malnutrition and the management of orthopaedic sports medicine patients from a treatment and performance standpoint.

Evidence Acquisition:

PubMed was searched for relevant articles published from 1979 to 2019.

Study Design:

Clinical review.

Level of Evidence:

Level 4.

Results:

Few studies exist on the implications of macronutrient deficiencies specific to orthopaedic sports medicine procedures. Interestingly, micronutrient disorders—namely, hypovitaminosis D and iron deficiency—have been well studied and may lead to worse postoperative outcomes, injury rates, and athletic performance. Nutritional supplementation to correct such deficiencies has been shown to mitigate these effects, though further study is required.

Conclusion:

Nutritional deficiencies are highly prevalent in orthopaedic sports medicine patients, and practitioners should be aware of their potential effects on treatment and performance outcomes. Management of such deficiencies and their effect on surgical patients remain an area of potential future research. Future studies are warranted in order to explore the potential therapeutic role of nutritional supplementation to prevent complications after common orthopaedic sports medicine procedures, improve athletic performance, and reduce injury rates.

Malnutrition is an important medical comorbidity to consider in the treatment and prevention of musculoskeletal pathology. Often referring to macronutrient (protein, fat, carbohydrates) and/or micronutrient (minerals and vitamins) deficiencies, studies demonstrate that as high as 39% of patients undergoing elective orthopaedic procedures may be malnourished.⁶² The role of malnutrition in musculoskeletal health has been commonly studied in the orthopaedic literature, as dietary modifications can improve postoperative outcomes.

Malnutrition has been assessed and described by various methods. These include serologic laboratory values and standardized scoring methods, as well as anthropometric measurements that describe nutritional status on a macronutrient scale.^19,49,57,65 Frequently used standards for serologic laboratory values include total lymphocyte count <1500 cells/mm³, serum albumin <3.5 g/dL, and serum transferrin <200 mg/dL.^57,65

Using these measurements, malnutrition was first described as a risk for poor postoperative outcomes in hip fracture patients, where it was demonstrated that malnourished patients suffered increased complications and longer rehabilitation times.⁵⁷ These findings were recapitulated in the elective setting, as malnutrition was shown to independently increase hospital costs, morbidity, and mortality in the spine^2,13 and total joint arthroplasty^12,43,65 literature. Similarly, micronutrient deficiencies, including low serum levels of vitamin D, iron, and other minerals (zinc, magnesium, folate, and copper, among others) have been linked to poor outcomes after these elective orthopaedic procedures^27,41,55,83

In orthopaedic sports medicine, patients tend to be relatively healthy, and in sports medicine procedures, specifically arthroscopic procedures, complication rates are significantly lower than with other orthopaedic subspecialties.^14,50 As such, the role of correctable factors, including malnutrition, which is important for musculoskeletal health and surgical outcomes in this population, is often overlooked. Interestingly, sports medicine research has focused more on a micronutrient scale, namely vitamin D and iron deficiency.

Thus, the purpose of this article is to analyze the available sports medicine literature to review the associations between malnutrition and the management of orthopaedic sports medicine patients from a treatment and performance standpoint. Classified here into macronutrient and micronutrient deficiencies, we aim to highlight the critical findings as well as the deficient areas of the literature to improve awareness and understanding of the potential effects of malnutrition on patient outcomes.

Macronutrient Deficiencies in Orthopaedic Sports Medicine

Macronutrients, including proteins, fats, and carbohydrates, play an essential role in regulating metabolic pathways and immune system functions. Adequate macronutrient stores are necessary to repair damaged tissue and meet the increased energy requirements associated with surgery, postoperative recovery, and high-intensity exercise. Of particular interest in the orthopaedic surgery literature, protein deficiencies have been shown to worsen postoperative outcomes by negatively affecting immune system function,³⁶ increasing postoperative infection risks,^16,17,59 and impairing wound healing,⁶³ among others.

Serum albumin levels are widely accepted in the orthopaedic literature as an important indicator of overall macronutrient status, and hypoalbuminemia is regularly used to identify malnutrition and investigate its association with postoperative outcomes. Using a definition of serum albumin <3.5 g/dL, malnutrition has consistently been described in studies as a risk factor associated with postoperative complications in various areas of orthopaedics, such as total joint arthroplasty^12,63,65 and spine surgery.^2,13 Though well-described in these orthopaedic subspecialties, little data exist on the clinical implications of macronutrient deficiencies in orthopaedic sports medicine outcomes, such as bone-tendon interface healing; muscle, tendon, and ligament healing; and outcomes after orthopaedic sports medicine procedures (O. Jalali, BS, et al, unpublished data, 2019).^6,21,35,81

In 1 study of 4655 patients who underwent open shoulder replacement surgery, Garcia et al³⁵ demonstrated a 7.6% rate of malnourishment. Compared with healthy controls, malnourished patients in their study demonstrated a 2.5-times greater odds of requiring postoperative transfusions, 1.7-times greater odds of extended hospital length of stay, and an 18.1-times greater odds of mortality.³⁵ Cancienne et al²³ investigated risk factors for infection after shoulder arthroscopy procedures in a Medicare population. Independent of all other variables analyzed, patients with malnutrition demonstrated a 1.4-times greater odds of suffering a postoperative infection within 90 days.²³

Most recently, O. Jalali, BS, et al (unpublished data, 2019) analyzed complications and readmission data from 10,966 patients who underwent knee arthroscopy. In their study, there was a 4.0% rate of malnutrition (defined as albumin <3.5 g/dL), and patients with malnutrition were at 3.0-times greater odds of suffering any complication, a 2.8-times greater odds of requiring a return to the operating room, and a 2.6-times greater odds of requiring readmission within 30 days. Among all complications analyzed, malnourished patients were at a significantly increased risk of suffering infectious complications, including superficial surgical site infection (odds ratio [OR], 4.0), urinary tract infection (OR, 5.5), and deep infection (OR, 5.5) (O. Jalali, BS, et al, unpublished data, 2019).

Though perioperative protein supplementation has been shown to reduce complications in an elderly population after hip fracture surgery,¹⁵ no study has explored its application in elective orthopaedic procedures. Nonetheless, early evidence suggests hypoalbuminemia is associated with significantly worse outcomes after orthopaedic sports medicine procedures, including shoulder and knee arthroscopy. However, data are limited, and further studies are warranted exploring the role of macronutrient deficiencies in these common sports medicine procedures. Nutritional deficiencies at the micronutrient level have been found to be the main focus in orthopaedic sports medicine and will be discussed.

Hypovitaminosis D

Vitamin D deficiency is the most commonly studied nutritional disorder in orthopaedic sports medicine. The vitamin D receptor has been identified in almost every cell in the human body, and its active form, 1,25-dihydroxyvitamin D3, is known to regulate over 50 genes, many of which are related to musculoskeletal health.⁷³ Vitamin D deficiency and insufficiency, defined as <20 ng/mL and <30 to 32 ng/mL, respectively, are highly prevalent in patients undergoing orthopaedic procedures.^11,60 Second only to trauma patients, Bogunovic et al¹¹ demonstrated a 52.3% rate of vitamin D insufficiency in orthopaedic sports medicine patients.

Though several studies have emphasized the importance of avoiding vitamin D deficiencies in patients with orthopaedic disorders, the data on hypovitaminosis D and its effect on sports medicine surgical outcomes are sparse and inconclusive. In rotator cuff repair (RCR) procedures, Ryu et al⁶⁶ found that 88% of patients undergoing arthroscopic repair of a full-thickness rotator cuff tear had hypovitaminosis D. No correlation was found between preoperative vitamin D levels and preoperative tear size, extent of retraction, degree of fatty degeneration, postoperative repair integrity, or functional outcome scores.⁶⁶ In contrast to this, Harada et al³⁹ demonstrated an increased risk of requiring revision surgery and developing stiffness (requiring manipulation under anesthesia) in vitamin D–deficient patients undergoing arthroscopic RCR. Similarly, Cancienne et al²² found revision rates in vitamin D–deficient patients undergoing arthroscopic RCR of 5.9%, which was significantly increased compared with the rate of 3.7% in the normal vitamin D control group.

Notably, vitamin D deficiency has been shown to cause a myopathy of varying severity, and previous clinical studies indicate that vitamin D status is positively associated with muscle strength and physical performance^7,34,80 and inversely associated with risk of falling and early postoperative outcomes after total joint arthroplasty.^41,55,70 Moreover, interventional studies have cited increased strength and endurance with vitamin D supplementation.^5,9,80 The mechanism is hypothesized to be due to an increase in size, number, and strength of type II muscle fibers when vitamin D levels are sufficient or increased with supplementation.^4,24,32 Furthermore, vitamin D receptors have been found on myocytes, which may act as a modulator of cell growth, neuromuscular function, and immunomodulation.⁶⁰

After anterior cruciate ligament reconstruction (ACLR), muscle (quadriceps) weakness is an immediate and persistent impairment that can predispose patients to developing degenerative joint disease and requiring subsequent surgeries later in life. To explore the potential clinical therapeutic benefit of vitamin D to combat these changes in the postoperative setting, Barker et al⁸ measured changes in peak isometric forces in the injured limb of patients undergoing ACLR in vitamin D–insufficient (<30 ng/mL) and sufficient (≥30 ng/mL) patients. From 2 weeks before surgery to 3 months after surgery, participants with normal serum vitamin D levels experienced a 6-fold increase in peak isometric force compared with participants with insufficient vitamin D levels.⁸ Vitamin D–insufficient patients did not have a significant increase in single-leg peak isometric force at 3 months postsurgery compared with 2 weeks presurgery. Despite these findings, no study to our knowledge has analyzed the effect of vitamin D status on revision rates or functional outcomes after ACLR or other knee arthroscopy procedures.

Both a history of ACLR and hypovitaminosis D have independently been associated with an increased risk for the development of osteoarthritis (OA). Longitudinal studies have demonstrated that vitamin D deficiency increases the risk of patients developing OA,⁸² and cross-sectional studies have identified associations between low vitamin D levels and degenerative changes, including medial meniscal deterioration¹⁰ and the development of hip and knee OA.¹⁰ A recent analysis of data from the Osteoarthritis Initiative demonstrated a dose-dependent association between weekly vitamin D supplementation over 4 years and significantly less worsening of cartilage, meniscal, and bone marrow abnormalities on magnetic resonance imaging compared with no supplementation.⁴² Together, these studies highlight the potential role of vitamin D status on postoperative muscle strength and recovery and in the development of degenerative joint changes associated with arthroscopic knee surgeries in the long term, as well as identify vitamin D supplementation as a potential therapeutic option to improve outcomes after these procedures.

Additionally, vitamin D deficiency is associated with decreased athletic performance, and there exists a well-described relationship with vitamin D levels and muscle power, force, and endurance in this population.^28,29 Among elite athletes in the National Collegiate Athletic Association, National Football League (NFL), and National Basketball Association, 32.3% to 59% of athletes were vitamin D deficient.^33,64,77 Given its high prevalence, hypovitaminosis D has shown a correlation between injury rates, such as fractures and soft tissue injury, and decreased athletic performance.

A study of NFL Combine athletes with a history of lower extremity or core muscle injuries showed a significant association with lower vitamin D levels.⁶ Similarly, elite female gymnasts with muscle injuries had significantly lower vitamin D levels relative to their uninjured counterparts.⁴⁵ In addition to skeletal muscle injury, vitamin D deficiency has been associated with increased risk of fracture.^1,29,78 There was a 60% greater incidence of stress fractures in a vitamin D–deficient cohort of age-matched marines.¹ Noticeably, vitamin D supplementation has been shown to mitigate these risk factors.^44,71

Overall, vitamin D insufficiency is highly prevalent in orthopaedic patients, and methods to evaluate vitamin D, although readily available, are underutilized by orthopaedic surgeons. Management of vitamin D insufficiency and its effects on surgical patients remain an area of potential future research. Future studies are warranted exploring the potential therapeutic role of vitamin D supplementation to improve outcomes and prevent complications after common orthopaedic sports medicine procedures, including shoulder and knee arthroscopy.

Iron Deficiency and Preoperative Anemia

Iron deficiency (ID) is also a common micronutrient deficiency. Up to 40% of patients evaluated prior to elective orthopaedic surgeries are found to be anemic, and ID is the most common cause of this anemia.^67,68 Studies of interest to orthopaedic sports medicine providers demonstrate that ID is more common among athletes, particularly female athletes.²⁶ ID generally presents with poor energy, impaired bone health, and compromised reproductive function.⁵⁶

Preoperative anemia is an independent risk factor for increased morbidity and mortality after orthopaedic surgery.³⁷ In addition, preoperative hemoglobin levels are a major predictor of perioperative transfusion rates, which independently increase hospital length of stay, infection rates, and perioperative mortality.³⁷

As a result, addressing this correctable risk factor has been an area of recent focus in the orthopaedic literature.^37,67,68 In a systematic review and meta-analysis of 12 clinical trials comparing perioperative intravenous iron therapy (IVIT) to no iron therapy in patients undergoing orthopaedic surgery, IVIT significantly reduced the proportion of patients requiring transfusion and reduced the units of red blood cells per person transfused during the perioperative period.⁶⁹ Further, patients who received IVIT had a mean reduction of 1.6 days for hospital length of stay and a 33% reduction in postoperative infection rates, though no difference was observed in mortality rates.⁶⁹ Oral iron supplementation prior to elective orthopaedic surgery, often used with erythropoietic stimulating agents, has similarly shown benefits in reductions in transfusions and hospital lengths of stay.³

To raise awareness of this emerging body of evidence, the Network for Advancement of Transfusion Alternatives developed practice guidelines for the detection, evaluation, and management of preoperative anemia in elective orthopaedic surgery.³⁷ Based on the evidence of improved outcomes and adequate cost-efficiency, they recommend all elective orthopaedic surgical patients be enrolled in standardized preoperative blood management protocols, which include measurement of hemoglobin levels 28 days before surgery with appropriate work-up and supplementation to correct the anemia prior to surgery.³⁷

Decreased athletic performance is also well documented with ID, and it has been correlated with decreased work capacity and endurance performance.^30,31 In a study of iron-insufficient rowers, those with ID had decreased training capacity and a lower oxygen capacity compared with their nondeficient counterparts.³¹ In a similar study, iron-depleted female rowers had slower race times.³¹

However, it is important to note that athletes can present with pseudoanemia at screening since athletes’ plasma levels can increase by up to 20% as a result of increased physical activity.²⁰ In these cases, red blood cell morphology, mean corpuscular volume, and/or other parameters of iron depletion must also be abnormal to determine true ID.⁵⁴ Iron supplementation in those with deficiencies improves aerobic fitness measures,⁶¹ endurance capacity,⁷⁴ energy efficiency,⁷⁴ and skeletal muscle strength.²⁶

Other Micronutrient Deficiencies

Other micronutrient deficiencies, such as low zinc, copper, vitamin C, magnesium, and folate, are also often overlooked and affect between 31% and 74% of Americans.⁷⁹ While the majority of Americans exceed their recommended daily caloric needs, it is not uncommon for these same Americans to miss their daily micronutrient requirements. A recent study found that male participants averaged deficiencies in 40% of the required vitamins and 54.2% of the required minerals; likewise, female participants averaged deficiencies in 29% and 44.2% of the required vitamins and minerals, respectively.⁵³ This is concerning because water-soluble vitamins are key cofactors in mitochondrial energy metabolism, and numerous minerals such as magnesium and zinc play significant roles in promoting wound healing and muscle strength and maintaining healthy immune system and cardiorespiratory system functions.^40,46,51

In particular, zinc deficiency has been shown to lead to an increase in the production of proinflammatory cytokines, predisposing the body to inflammatory states.³⁶ In a prospective study, Zorrilla et al⁸³ demonstrated that zinc deficiency (<95 µg/dL) correlates with delayed wound healing in elective total hip arthroplasty. Similarly, vitamin C is an essential cofactor in collagen cross-linking for normal wound healing and has antioxidant, immunostimulant, antibacterial, and antiviral properties.^58,72 As such, studies have been performed exploring its application in mitigating the systemic inflammatory response after elective orthopaedic surgery,²⁷ reducing regional pain syndrome,⁷² and promoting healthy wound healing.⁵⁸ Overall, however, limited data exist regarding the clinical implications of these micronutrient deficiencies in elective orthopaedic procedures, precluding guidelines for the screening and management of such deficiencies in clinical practice.

Micronutrients, including vitamins B₁, B₂, and C and the minerals potassium, calcium, iron, copper, zinc, and especially magnesium, are known to be lost in sweat or urine.^18,51,52,75 Further, studies on athletes’ dietary intake demonstrate that they regularly do not meet the recommended minimum intake in several micronutrients such as vitamin E, magnesium, folate, and copper, among others.²⁵ As such, it may be important to monitor micronutrient deficiencies in the elite athlete population as it can affect physical performance.

In a recent study, aerobic endurance and anaerobic strength exercises significantly correlated with serum zinc and copper levels and inversely with urine concentrations.³⁸ Magnesium deficiency led to reduced endurance performance and increased oxygen requirements to complete submaximal exercise.⁴⁷ Similarly, zinc-deficient individuals have decreased muscle function, aerobic endurance, and poorer recovery after physical activity.^28,48,76 Such findings are also supported by other similar studies.^53,79

However, questions remain with regard to supplementation of vitamins and minerals in athletes. For example, 1 study examined the total work capacity of knee and shoulder muscles in zinc-deficient and normal cohorts.⁷⁶ As expected, zinc-deficient individuals had worse performance, but interestingly, once zinc was replenished, they did not recover to normal levels of function. Unfortunately, few clinical studies exist with regard to vitamin and mineral supplementation and repletion and its potential consequences. This may be an area of future interest in optimizing performance in the elite athlete.

Conclusion

Malnutrition is highly prevalent in orthopaedic sports medicine patients, and practitioners should be aware of their potential effects on treatment and performance outcomes. There is a need for further study with potential areas of interest, including the role of these nutritional deficiencies on key areas such as ligament reconstruction, bone-tendon interface healing, and other surgical outcomes. Further, future studies are warranted to explore the potential therapeutic role of nutritional supplementation to prevent complications after common orthopaedic sports medicine procedures, improve athletic performance, and reduce injury rates.