Continuing Education Activity

Obesity affects one-third of the North American population and increases the risk of multiple co-morbidities. In addition, obesity has been linked to exacerbate many orthopedic problems. This article describes and explains the process by which obesity can affect orthopedic-related diseases.

Objectives:

• Describe the biomechanical impact of obesity on arthritis.
• Describe the metabolic impact of obesity on arthritis.
• Explain how joint loading in the knee of obese patients leads to osteoarthritis.
• Identify common co-morbidities which obesity exposes patients to and their clinical significance in management by an interprofessional team.

Introduction

Obesity is defined by calculating the Body Mass Index (BMI) of an individual. A BMI of >30 kg/m2 is considered clinically obese.[1] Around one-third of adults in the United States are obese.[2] It has been suggested that by 2030, 1 in 2 people across the United States will be classed as obese.[3] Obesity increases the risk of multiple co-morbidities, including but not limited to: hypertension, type 2 diabetes, coronary artery disease, stroke, sleep apnea, and osteoarthritis.[4] 

Physical inactivity and high calorific consumption have been directly correlated with an increasing BMI. Socioeconomic status indirectly correlates to an increasing BMI. Despite these links being clear for many years, the causation between these factors is not fully understood.[5]

An increasing number of patients with obesity are presenting to orthopedic departments. An elevated BMI can impact orthopedic issues through two broad mechanisms: biomechanically and metabolically. These two concepts cause issues to both the bone itself and/or the surrounding soft tissue and its structures.

Issues of Concern

Pathophysiology

Biomechanical Effects

It is widely accepted that the additional load to the skeletal system, as seen in obesity, produces altered body mechanics that unfavorably affect the function of joints. Obesity has been identified as a top risk factor for the initiation and progression of osteoarthritis in load-bearing joints, primarily the knee, but also the hip and ankle.[6] The main biomechanical effects of obesity on joints are assumed to be altered gait and increased joint stress. This, in turn, causes increased stress on the articular cartilage and can also cause increased stress in other joint tissue such as synovial fluid, subchondral bone, and capsular and ligamentous structures.

Studies have shown that reduced muscle strength and unfavorable skeletal alignment predispose the knee to osteoarthritis regarding osteoarthritis of the knee. It has been demonstrated that the volume of articular cartilage in the knee positively correlates with local muscle mass around the knee. Furthermore, a lower muscle mass in the quadriceps is associated with a greater loss of articular cartilage over a given time period.[7] This suggests that with obesity, loss of muscle mass is more important in the development of osteoarthritis than adiposity itself. To support this theory, it has been shown that quadriceps weakness correlates with the development of knee osteoarthritis.[8] Exercises directed towards increasing muscle strength have been shown to reduce pain from arthritis.  

In addition to altered joint loading, skeletal alignment has also been shown to influence the onset and progression of osteoarthritis, particularly in the knee. Obesity influences the skeletal alignment of the knee by increasing load in the medial compartment of the knee through varus deformity. A study has shown that increasing BMI correlates with a decreasing medial joint space, narrowing in the medial compartment of the knee, and resulting in an increasing varus deformity.[9] This progressively increasing medial joint loading has been commonly documented in osteoarthritis.[10]

Metabolic Effects

Obesity is thought to cause a chronic, low-grade, proinflammatory state.[11] Overweight and obese adults have elevated serum markers of inflammation; these include C-reactive protein, interleukin-6, and leptin. These cytokines are derived from adipose tissue, hence 'adipokines.’ Clinical studies have shown a correlation between adipokine levels and cartilage volume loss. Additionally, leptin – one of the adipokines – is responsible for triggering an intra-articular pro-inflammatory cycle which contributes to the breakdown of collagen, thus leading to worsening osteoarthritis.[12] This may explain why osteoarthritis is also more prominent in non-weight bearing joints of the obese population, such as the shoulder and hand.

Complications

Soft Tissue

Multiple studies have shown the correlation of obesity as a risk factor in multiple soft tissue injuries, which the orthopedic surgeon must consider. A systematic review broadly looking into the incidence of tendinopathies concluded that obesity was a significant risk factor.[13]

Within the upper limb, rotator cuff tendonitis and shoulder impingement are more common in the obese population.[14] Further to this, surgical management of these conditions in the obese population has shown inferior surgical outcomes compared with non-obese individuals undergoing identical surgical procedures.[15]

The incidence of carpal tunnel syndrome correlates with obesity, yet weight loss does not improve symptoms.[16] This alludes to the potential impact of the metabolic effects previously mentioned and their role in carpal tunnel syndrome in the obese.

Plantar fasciitis, Achilles tendonitis, and posterior tibial tendon dysfunction are more common in the obese population within the lower limb.[17][18] Studies have also demonstrated the significance between meniscal tears within the knee and an increased BMI. A larger proportion of the obese population requires surgical intervention for these conditions when compared to those with a normal BMI.[19]

Bone

The association between fracture risk and obesity is less well documented. It was previously thought that obesity was a protective measure against fractures. However, reports over the last decade have suggested a higher incidence of fractures in those with obesity, especially in the elderly population. It must be noted that to date, obesity is a proven risk factor for ankle, leg, and humeral fracture but a protective factor for wrist, hip, and pelvic fractures.[20][21] The science behind this correlation is not fully understood but thought to be due to falls risk, co-morbidities in obesity, distribution of body fat, and fracture patterns observed.

Other Complications of Obesity

Studies have indicated that obesity leads to worsening outcome measures in the peri-operative period. Lack of anatomical landmarks may make the surgical intervention more difficult and prone to unfavorable outcomes. Obesity also increases the risk of post-operative infection, non-union, chronic pain, and failure of implants.  The reduced vascularization to adipose tissue and the higher incidence of protein malnutrition can adversely affect wound healing. Further to this, comorbidities associated with obesity, such as type II diabetes mellitus, hypertension, dyslipidemia, cardiovascular disease, stroke, sleep apnea, hyperuricemia, gout, and others, can adversely affect the perioperative period, anesthetic risk, and surgical outcome.[17]

Advanced imaging such as MRI and CT scans have weight limits that obese patients may occasionally exceed. Delay or lack of imaging in orthopedic patients may adversely affect management outcomes.

Clinical Significance

Obesity is a complex process that mainly impacts orthopedic issues through biomechanical and metabolic processes. The prevalence of obesity makes the issue very common for the orthopedic surgeon, the impact of obesity on osteoarthritis is well documented, but perhaps further research into the pathogenesis of soft tissue injuries and obesity will help aid prevention and management of these orthopedic issues.

Enhancing Healthcare Team Outcomes

Obesity in orthopedics requires a multidisciplinary approach. There are several team members that can positively improve a patient's outcome and help manage obesity. This team includes a nutritionist, an endocrinologist or internal medicine doctor to manage related disorders such as thyroid disease or diabetes, a personal trainer, and in severe cases, a nurse who specializes in weight loss, a psychologist or therapist, a general surgeon who specializes in bariatric surgery. 

Through interprofessional communication, these team members can maximize improved outcomes and enhance team performance. For example, a trainer may communicate that a patient is working out hours per day and the dietician also notes that the patient is eating a healthier diet. This communication to the endocrinologist may encourage them to do a further metabolic workup on the patient. Physical therapy may help the patient learn proper exercises to help recover from injuries that result from excessive weight-bearing. A systematic review has shown that the consultation of a dietician has been shown to improve dietary change, cholesterol, blood pressure, and triglycerides.[22]  [Level 2]

In summary, using interprofessional team strategies results in improved patient outcomes when addressing obesity-related orthopedic issues. [Level 5]

Nursing, Allied Health, and Interprofessional Team Interventions

General practice nurses and bariatric nurses, personal trainers, and dieticians are vital to interprofessional team interventions. While some medications may be helpful with managing some of the causes of obesity, non-medical modalities can be effectively utilized by this interprofessional team of practitioners.[22][23]

Nursing, Allied Health, and Interprofessional Team Monitoring

Monitoring by an interprofessional team is vital to success in weight loss. Nurses, personal trainers, and dieticians will utilize calorie counting, weight measurements, and estimated calorie burn via exercise. Additionally, newer technologies provide for active monitoring of activity.[24]