OVERUSE INJURIES

LONG DISTANCE RUNNING AND OSTEOARTHRITIS

By Erik Hohmann, FRCS, MD and Adam Bryant, BHMSc (Hon), PhD

INTRODUCTION Since the days we roamed the planet as hunters and gatherers, human beings have become more and more sedentary. These days more time is spent in the office than being physically active. As a consequence, obesity, diabetes mellitus, coronary artery disease and other so called ‘diseases of civilisation’ have become increas- ingly prevalent. The annual cost of physical inactivity to the Australian health system is approximately $400 million and is responsible for up to 8,000 deaths per year (1). It is therefore a positive trend that more people are engaging in jogging and long distance running. In fact, the desire to complete a marathon race has resulted in an exponential increase in participation in long- distance running. While distance running has positive effects on cardiovascular fitness, diabetes and mental health, the effects of impact loading on the integrity of the articular cartilage of the hip, knee and ankle joints is unclear.

While completing a marathon distance of 42.2 km, it is estimated that a runner takes an average of 38,000 steps. Each step loads the lower extremity with 4 to 8 times body weight. If we use these figures to extrapolate loading over the marathon distance, the lower extremity joints absorb forces in excess of 5,000 tons. In addition, preparation for a marathon requires approximately 40 kilometers of running weekly. So is running these distances healthy for our joints? This is an important question given that long-distance running is currently one of the most popular fitness activities, involving an estimated 30 million people in the United States alone.

Undoubtedly there has been an increase in marathon runners over the last five years (2). Many organisers worldwide have had to limit the numbers of runners registering for their events. With increasing numbers, a substantial increase in overuse and running

injuries have been reported (3). Whether these findings indicate that overuse injuries are the precursor of articular cartilage over- load and subsequently can result in early osteoarthritis or accel- erate pre-existing damage, is currently unknown (4).

CONCEPT OF OVERUSE AND REPAIR MECHANISMS Let us look at the possible physiologic mechanisms that could compensate for the enormous impact loading associated with long distance running. Burr (5) developed the concept of overuse injuries and repair mechanisms for stress fractures. This concept could potentially be transferred to hyaline articular cartilage. Even though chondrocytes have a slower metabolic rate than osteocytes, they function as a ‘slow basic mitosis unit’ producing extracellular matrix and constantly repairing defects. As long as this remodeling process is above the threshold of nonreversible microdamages of the cartilage, the joint surfaces will remain intact. As a consequence, osteoarthritis does not occur. However, several variables can influence the repair process negatively such as drugs, skeletal malalignment, obesity, pre-existing damage, lig- amentous instability or metabolic pathology such as diabetes, gout, rheumatoid arthritis and other autoimmune diseases. We will revisit this concept later. Presumably long distance running subjects the articular cartilage and subchondral bone to increased stress by repetitive external impact loading above the physiolog- ical threshold. To be at an increased risk of developing early onset or to have an increased incidence of osteoarthritis, the stresses on bone and cartilage must exceed a critical level that results in chronic changes in the cartilaginous matrix (6). A number of stud- ies have attempted to answer this question.

RADIOLOGICAL EVIDENCE Our group (4,6) investigated hips and knees of runners prior to and following running a marathon using MRI. The pre-MRI served not only as a screening tool for possible pathology but also sum-

10

www.sportex.net