Fibula is a slender and long bone located on the outside of the lower leg, from outside and underneath the knee and extends down to form the outside of the ankle joint. Next to the fibula bone is the tibia, which is thicker. It forms the base of the knee called the tibial plateau and extends down to form the inside of the ankle joint. The two bones, tibia and fibula, are connected by ligaments underneath the knee and at the ankle. There is also a soft tissue in between the two bones, called the interosseous  membrane, which runs the length of the two bones. The interosseous membrane binds the two bones together to keep them stable. The ligaments and the interosseous membrane have a little flexibility in them, to allow the ankle joint and the two bones to move during walking and motion of the ankle. The fibula can bend slightly and it can also rotate within its ligament. It can also slides up and down during ankle motion; inward and outward.

Fibula bone plays a minor role in bearing the weight of the body as we walk. The tibia bears approximately 80% of the body weight. The fibula bone bears only 15 to 20% of the body weight. Moreover, it transfers forces as the ankle hits the ground during walking. The mechanism of transferring ground reaction forces occurs due to muscles attachments on the upper part of the fibula bone underneath the knee. The interosseous membrane also helps in transferring rotational forces from the ankle to the knee. There are nerves tissues, veins and arteries which pass behind the fibula, near the knee. The fibula is a site of five muscles attachment.

Fibula bone fracture is a common injury seen in the emergency room. The fracture occurs from a direct blow to the outside of the leg, from twisting  the lower leg awkwardly and, most common, from a severe ankle sprain. The injury is common in athlete who is engaged in collision or contact sport  such as soccer, football, basketball, rugby and Lacrosse. Downhill skier, snowboarding, and skiers  have a high rates of fibula bone fractures as well. In the elderly population, slipped and fall is the cause of fibula bone fracture.  It could also occur from reduce bone mass in the elderly. Moreover, surprisingly, smoking is an important risk factor for fibula bone fracture.

A short lesson on the principle of bone healing is needed to understand why non weight-bearing on the fractured leg is necessary. When a bone fractures, the body starts to heal it. There are 3 phases of bone healing; inflammation phase, repair phase, and remodeling phase. As the bone fractures, it bleeds causing inflammation. The blood or hematoma (blood clot) enters in the space between the two fractured fragments to initiate healing or the repair process.  The inflammatory phase takes 5 days and the repair phase takes 40 days. During the repair process or phase, a soft callus is formed across the fractured site. The soft callus fills the bone and develops into a hard rigid callus. After the hard rigid callus is formed, the remodeling phase starts.  In this phase, the bone remodels itself into its original size and regain its strength properties. This phase takes 100 days. Furthermore, an average time for bone healing is 8 to 10 weeks, and complete healing time is 12 to 16 weeks, following the natural healing time as explained above. The natural healing time should be allowed to take its usual course. Interference with the natural healing time, such as not following the weight bearing status from the physician, can displaced the hematoma and the bone cannot heal. Too much motion early at the fractured site, prevent the hard rigid callus to form resulting in non-union of the fracture fragments. The fractured site becomes unstable.  Poor blood supply to the fractured site also prevents the formation of the hard rigid callus. That is why smokers have a hard time healing. Smoking decreases blood supply to the fractured site.

There are different  locations where fibula bone fractures occur. For example, the fracture can occur at the knee joint, above the ankle, in the shaft of the fibula bone and at the ankle joint. The tip of the fibula bone at the ankle joint can also separate, which is called an avulsion fracture. This happens from a severe ankle sprain. The location of the fracture dictates restrictions placed on patients, and immobilization. For example, an isolated fracture, such as a fracture in the shaft of the fibula bone is uncomplicated and complete healing is high. However, fracture at the knee and ankle takes longer time to heal and restriction and immobilization are paramount. Fracture at the knee is associated with complication due to the muscles, ligaments and interosseous membrane attachments in that location. But, what concern the physician the most at this location are the surrounding nerves, veins and arteries. The concern mounts higher when the fracture is above the ankle and at the ankle joint. The concern here is the tearing of the ligaments that connect the tibia bone and the fibula bone that form the ankle joint. The restriction and immobilization are severe due to instability concern. What one has to take into account here is the time it takes for bone and ligaments to heal, before putting weight on it, as both tissues heal at different time.

Immobilization, either with CAM walker boot or surgery with screws and plates, depends on the distance between the fractured fragments. The larger the distance between the fractured fragments, the more immobilization is required, because healing depends on the hematoma fitting the space between the fractured fragments. It is the hematoma that initiates the healing process, leading to the soft callus to the hard rigid callus to remodeling . The immobilization with boot and surgery bring the fractured segment closer so the blood clot can  fit the space to initiate healing. Keep in mind that early motion and early weight bearing can displace the blood clot and healing is interrupted. This is why physicians recommend non-weight bearing for the first 4 to 6 weeks. Remember, 4 to 6 weeks, the hard rigid callus is formed and remodeling is about to begin. At this time, weight-bearing becomes essential in term of helping the bone to remodel in its original size. Moreover, control or gradual weight bearing is paramount.

Weight bearing on the healing leg progresses from non-weight bearing to touch weight bearing to partial weight bearing to weight bearing as tolerated and finally to full weight bearing. Non-weight bearing is absolute no weight of the healing leg. This is accomplished by the use of a properly adjusted pair of crutches. A wheel walker can be used when coordination required for the use of crutches is difficult. A knee scooter can also be used. The knee scooter is designed with knee pad and wheels. The knee is placed on the pad and the whole lower leg is supported by the scooter. Most of the weight is on the knee. There is a handle bar which can be used to steer and for balance. There is a brake to keep the scooter stationary during hopping on and off the scooter.

Touch weight bearing  is when the foot and toes are touching the floor. It gives the muscles of the leg a break from holding the leg up. It also helps the leg to accustom to minimal weight bearing. Partial weight bearing is the gradual weight bearing of the healing leg  from light to up to 50% of the body weight. The weight of the body is equally distributed on the healing leg and the assistive device. Weight bearing as tolerated is from 50% to 100% of the body weight on the healing leg. Finally, full weight bearing is 100% of the body weight on the healing leg with no assistive device.

Immobilization is paramount in the process of healing. It keeps the distance between the fracture fragments close to allow healing to take place as explained earlier. It provides compression to the fractured fragments to give support and  keep it stable. Compression also takes stress off the surgical stitches. There are several types of immobilization used in the treatment of fibula fracture, such CAM walking boot which comes in non-inflatable, adjustable inflation, allows range of motion and rock bottom boot. The CAM walking boot wraps the foot, ankle and  the whole lower leg to below the knee. The non-inflated CAM walker provides basic support to the fractured fragments. The inflated CAM walking boot is where the bladder of the boot is inflated with air to increase stability and to accommodate swelling in the leg. The range of motion boot is adjusted to allow restricted range of motion. The rock bottom boot allows natural rocking motion on the foot during walking. As the fractured leg heals, the CAM boot is replaced by a plastic air stirrup type brace or an ankle laced up brace.

After surgery to immobilize the fractured fragment, RICE principle is used to manage swelling, and pain. RICE stands for Rest the injured/surgical leg, Ice the injured leg, Compression is applied to the injured leg using an ace wrap, and Elevation of the injured leg above the heart to drain the swelling. Ice every 2 to 3 hours. Compression applied all the times with an ace wrap. Elevate the injured leg as much as possible, during sitting and sleeping. One key to success after fibula bone fracture surgical procedure is to decrease swelling by compression and elevation. The faster  the swelling subsides, the faster is the recovery.

A word on fibula bone stress fracture. It is not a true fracture. It is called a hairline fracture due to repetitive stress on the fibula bone. The fracture fragments are not separated completely. One can think of it as a crack in the bone. During long distance running, hiking and so forth, the bone reacts to the excessive stress on it, resulting in the hairline fracture. Activity increase the pain and rest decreases the pain. Removing the stress on the bone is the only way to recovery.

Fibula bone fracture heals faster than other weight bearing bone such as the tibia. Complication arises from early weight bearing and early motion at the fracture site.

Call STARS at (208) 367-3315 if you have any questions regarding fibula fracture.

by Raj Issuree, MPT

References:

McKibbin B. The biology of fracture healing in long bones. J Bone Joint Surg 1978; 60-B (2): 150-162

Perren SM, Rahn BA. Biomechanics of fracture healing. Can J Surg 1980; 23(3): 228-32

Connolly JF, Maha H et al. Fracture healing in weight-bearing and non-weight bearing bones. J Trauma 1978; 18(11); 766-70