By: 8 March 2013

O Uhiara, R Fawdington and K Kosygan report on an unexpected risk that may be posed by using a Wii Fit exercise board

Wii Fit is an exercise video game that utilises an electronic balance board. It has been marketed for recreational and family use since its release in 2008. We report a case of a long bone stress fracture caused by using a Wii Fit exercise board, a mechanism of injury which has not been reported in the medical literature until now.

Wii Fit consists of a Nintendo Wii games console and an electronic balance board1. The board is approximately 53cm x 33cm x 8cm in size. It contains pressure sensors that detect the user’s bodyweight which is relayed via infrared to the Wii console. Training activities include yoga, aerobics and balance training, which are to be performed barefoot. It was originally marketed for recreational and family use, and its popularity has extended it to be used in rehabilitation for physiotherapy2. However, there has been a rise in the incidence of Wii-related injuries, ranging from tendinitis3 to acute fracture4. We report a case of stress fracture occurring in the tibia of a patient after using a Wii Fit exercise board. In our case report we briefly discuss the pathophysiology of the condition, its presenting features and management.

Case presentation
A healthy 36-year-old female paramedic attended the Accident & Emergency (A&E) department in New Cross Hospital, Wolverhampton with a painful left leg. This symptom had started six weeks previously with an insidious onset and no obvious identifiable history of trauma. The pain had gradually worsened in severity, initially exacerbated by walking but then progressed to pain even at rest on occasion. She described it as a dull ache with no radiation up or down her leg. On examination, she was apyrexial and comfortable at rest. She was able to fully weight-bear, but this precipitated throbbing in the affected area. She walked with a mildly antalgic gait on the left side. A swelling could not be identified, but she stated a lump had been present above the ankle a few weeks before. There was localised tenderness over the anteromedial aspect of the distal tibia. Movements of the ankle were pain-free with full ranges of motion, and the limb was neurovascularly intact. A radiograph taken in A&E showed periosteal reaction in the distal tibia (Image 1), and an orthopaedic opinion was sought.

On further questioning, she stated that she had started using a Wii Fit balance board approximately six weeks before attending the A&E department. This coincided with the onset of her symptoms. Her activities included jogging and other aerobic activities requiring repetitive movements on the board. She had not fallen, twisted or received a direct blow to the leg. In the absence of a specific episode of an injury, an MRI scan was performed. This confirmed our diagnosis of a stress fracture and also helped to rule out any underlying bone pathology that would predispose it to fracture with a low energy mechanism, such as a bone cyst. She was subsequently managed conservatively with analgesia and a period of rest for three to four weeks, and her pain fully resolved.

The true incidence of stress fractures is unknown (as not all affected individuals seek medical attention, and there has been variability in reporting of such fractures), but studies involving athletes have demonstrated a rate of approximately 20%5. Predisposing factors include duration and intensity of physical activity, footwear used, and type of training surface. Osteopaenia, low body mass index/eating disorder and menstrual irregularities in combination in women (the female athlete triad) have also been shown to be risk factors for the development of such injuries6. Stress fractures can be classified as either insufficiency or fatigue fractures. In the former, physiological loads are applied to bone with reduced elasticity (e.g. weakened by osteoporosis, infection, and tumour).

Fatigue fractures on the other hand occur when stresses are applied repetitively to normal bone: the load in itself is not capable of causing a fracture, but over a period of time causes weakening and eventually bone failure.

The anatomical sites of stress fractures are activity dependent7. For instance, dancers sustain fractures of the metatarsals, jumping activities such as basketball predispose to calcaneal fractures, while running can cause tibial fractures. Over half of tibia fractures occur in the distal third of the bone. It is believed that co-ordinated muscular contraction helps to shield bone from abnormal loads. With repetitive or rigorous activity, muscle fatigue fails to dissipate these forces, and so more force is applied to bone. The resorption or osteoclastic phase of bone remodelling is enhanced at the expense of bone formation, increasing the risk of a stress fracture8. Also, when a new activity such as jogging is commenced (as demonstrated in our case report), conditioning of the musculotendinous units occurs at a pace quicker than that of bone. This creates an imbalance of forces as the muscle pull on the skeletal structure is greater, again creating abnormal loads and causing bone failure7.

Individuals usually present to medical attention with activity-related pain which tends to be fairly localised. This is alleviated with cessation of the activity, but recurs when it is resumed. With increasing severity rest pain develops. Usually the symptoms are noted to occur after an increase in training intensity or change to a more strenuous activity. Signs include localised bony tenderness, soft tissue discoloration and swelling.

Various imaging modalities can be employed to elucidate these lesions. Plain radiographs are usually the first-line investigation in the A&E setting, but are not sensitive, especially in the early phase. The characteristic features on the film are radiolucent lines in the cortex, and periosteal thickening as the bone starts to heal. MRI on the other hand is sensitive in detecting even early changes of fatigue fractures. On T1 weighted images the affected area appears as low signal (Image 2). On T2 images the signal is greater and appears white secondary to bone oedema. Over time these lesions become low signal on T2 due to callus formation9. Computed tomography is useful in delineating cortical detail, especially osteopaenia and resorption cavities, while bone scanning with radio-labelled Technetium has been shown to be the most sensitive investigation10.

The vast majority of stress fractures are treated conservatively, primarily by cessation of the sporting activity, as in our patient. This can last for a few weeks only, with gradual resumption once day-to-day activities are tolerated. Addressing risk factors such as footwear, training surface, weight and bone mass help prevent the development of stress fractures. Rarely, tibia fractures progress to non-union: reamed intramedullary nailing has been reported to provide good to excellent results in one case series11.

So far there have been no reported cases of stress fractures of long bones caused by a games console. Our case report demonstrates a unique injury attributed to use of the Wii Fit exercise board.


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