Bone loss and fractures in limbs paralyzed by spinal cord injury: Prevention, diagnosis, and treatment

It is now well known that spinal cord injury (SCI) leads to immediate bone loss in the paralyzed limbs and is associated with hypercalciuria. This bone loss may continue for as long as 2 years, when it seems to stabilize. By that time, the bones in the paralyzed limbs have lost more than half their mass and thus have become osteoporotic and are at increased risk for fractures. The osteoporosis often can be seen on X-rays, but is more accurately assessed by dual-energy X-ray absorptiometry (DXA), which provides values of bone mineral density (BMD) measured in grams per meter square (g/m²). Studies using DXA have shown in all SCI subjects a reduction of BMD values, although the range of such values is variable, which in turn may indicate individually variable fracture risk.¹ Osteoporosis associated with SCI was unknown to clinicians when life expectancy of people with SCI was short. In 1948, the first paper was published which described bone disturbances in persons with paraplegia.² It was authored by Arthur S. Abramson, MD, the founding Chairman of the Department of Rehabilitation Medicine at Albert Einstein College of Medicine in New York City. He himself had been rendered paraplegic by a snipers’ bullet during the Battle of the Bulge during World War II. Dr Abramson concluded that the osteoporosis was due to disuse, although many investigators have later suggested that the etiology may be multifactorial.

Fundamentally, bone loss after SCI is caused by an increase in the number of osteoclasts and their activity, which facilitate bone absorption. The increased osteoclastic activity is often felt to be related to low levels of physical activity, but the development of osteoporosis may also be influenced by vitamin D deficiency, altered calcium metabolism, smoking, poor nutrition, low levels of testosterone, estrogen and use of glucocorticoids hormones, genetics, certain medications, infections, severe pressure ulcers, etc.³

As is the case with most other people with osteoporosis, in those with SCI the condition is asymptomatic until a fracture occurs. The absence of pain and a history of minor or no trauma will make the diagnosis of fracture somewhat difficult. In the asensate limb, a fracture may be suspected on the basis of the presence of a localized swelling, deformity, autonomic symptoms, etc., but the diagnosis is confirmed by radiological studies. Fortunately, fractures in the paralyzed limbs are relatively rare.⁴ During follow-up evaluations, the cumulative incidence of lower limb fractures in persons, who had lived with SCI for 20 years, was <5%. Subclinical fractures in anesthetic limbs are probably more common. Since osteoporosis is always present in the paralyzed limbs after SCI, is asymptomatic and has no proven effective treatment, it may be questioned if regularly performed DXA is required to diagnose and monitor the condition.

Obviously, prevention of factures in osteoporotic bones is of utmost importance. Regular weight-bearing exercises⁵ and functional electrical stimulation (FES) ergometry for the paralyzed limbs^6,7 have been recommended to increase bone strength, but their efficacy is largely unproven. Medications such as bisphosphonates and dietary supplements, such as vitamin D and calcium, have been considered for osteoporosis prevention and treatment.³ Vitamin D and calcium supplements seem prudent and relatively risk-free for persons with SCI to take, but long-term use of bisphosphonates in the general population has been associated with potential adverse events, including increased risk of atypical femoral subtrochanteric fractures and osteonecrosis of the jaw.^8,9 Regular lower limb resistance and high-impact exercises have also been recommended for prevention of osteoporosis, but these are difficult or impossible to perform for most persons with SCI.

In this issue of The Journal of Spinal Cord Medicine, Akhigbe et al.¹⁰ report on their retrospective review of lower extremity fracture care in patients with SCI in the U.S. Veterans Administration system. They confirm what was previously known, that in this population tibia/fibula and femur fractures are most common. They also noted that almost one-third of all fractures in their sample occurred during transfers, either to or from wheelchair or not involving the wheelchair, while other fractures were attributed to environmental hazards, collisions with objects, equipment failures, and performance of various self-care activities. For other populations with osteoporosis, detailed lists of recommendations have been developed in an effort to reduce the risks of falling and thus sustaining fractures,^11,12 but no such lists exist for persons with SCI. The authors wisely advise that regular wheelchair skills assessment and retraining should be included as continuing care for people with SCI. They also note that wheelchair malfunction was a contributing factor for many factures, and that after sustaining the fracture 83% of patients either received a new wheelchair or had their existing wheelchair modified. This observation points to the importance of having high-quality and long-lasting wheelchairs in good working condition in order to prevent injuries to their users.

Even with optimal prevention efforts and management of the osteoporosis, fractures of osteoporotic bones will occur. In such an event, it is important to recognize that fractured osteoporotic bones in persons with SCI generally show an excellent healing response, often with exuberant callus formation. For decades, most fractures in the paralyzed lower limbs were treated non-operatively as it was felt that the inferior quality of the osteoporotic bones would not make them ideal for internal fixation with plates and screws and because of the risk of complications. Today, open reduction with internal fixation (ORIF) is commonly done, especially for femoral and tibial shaft fractures sustained during the acute phase of SCI.^13,14 Many fractures of osteoporotic bones can be treated with well-padded plaster of Paris splints or bivalved circular casts for easy removal and frequent inspection of the skin in the sensory impaired limb. While good anatomical alignment is desirable, slight shortening and angulation is usually acceptable. Significant rotational deformity of the paralyzed limb should be avoided by all means, since it may affect proper placement of the foot on the wheelchair's footrest. In addition to fractures of the tibia and femoral shafts, ORIF is usually indicated for fractures of the femoral neck and the intertrochanteric region of the femur. These types of hip fractures are usually associated with external rotation of the limb and additionally they may affect proper sitting position in the wheelchair, if not fixed in an anatomical alignment. Fractures of the femoral or tibial shafts, which require ORIF, can be done with intramedullary pins or, less desirably, with plates and screws. Regardless of the fracture treatment, careful early passive range of motion exercises of the adjacent joints are important to prevent the development of joint contractures, which could interfere with mobility and self-care functions as well as with proper sitting posture. The ultimate goal of fracture treatment should be a solid healing of the bone without contracture of adjacent joints that permits the person with SCI to be as self-sufficient and mobile as prior to the fracture.

The article by Akhigbe et al. is another reminder that practice guidelines are needed for the prevention, diagnosis, monitoring, and management of osteoporosis in persons with SCI. Unfortunately, for this population there are limited data available regarding the efficacy of medications, dietary supplements, passive standing, ambulation, and other treatments often recommended to slow bone loss.¹ The risk factors for fractures in the SCI population have not been clearly identified and consequently no specific list of recommendations exists aimed to reduce the risk. Similarly, guidelines have not been written for managing fractures of the osteoporotic bones in persons with SCI. In the absence of clear guidelines, both over- and under-treatment of osteoporosis and fractures in this population are likely to continue.