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Aim The morbidity associated with osteoporosis and fractures in children and adolescents with spina bifida highlights the importance of osteoporosis prevention and treatment in these patients. The aim of this study was to examine the occurrence and pattern of bone fractures in paediatric patients with spina bifida.
Method We reviewed the data of all paediatric patients with spina bifida who were treated in our centre between 1999 and 2008.
Results One hundred and thirteen patients were included in the study (63 females, 50 males; mean age 10y 8mo, SD 4y 10mo, range 6mo–18y). The motor levels were thoracic in six, upper lumbar in 22, lower lumbar in 42, and sacral in 43 patients. Of the 113 patients, 58 (51.3%) had shunted hydrocephalus. Thirty-six (31.8%) were non-ambulatory (wheelchair–dependent [unable to self-propel wheelchair] n=3, wheelchair-independent [able to self-propel wheelchair] n=33), 13 were partial ambulators, 61 were full ambulators, and three were below the age of walking. Forty-five fractures were reported in 25 patients. The distal femur was the most common fracture site. Statistical analyses showed that patients with higher levels of involvement and in wheelchairs had a significantly increased risk of having a second fracture (p<0.001). Spontaneous fractures were the principal mechanism of injury, and an association was identified between fracture mechanism, type of ambulation, and lesion level: the fractures of patients with higher levels of motor functioning and those in wheelchairs were mainly pathological (p=0.01). We identified an association between risk of a second fracture, higher motor level lesion, and non-ambulation. There was an increased risk of having a second fracture after a previous spontaneous fracture (p=0.004).
Interpretation Data in this study indicate a high prevalence of fractures in patients with spina bifida.
In congenital paraplegia caused by myelomeningocele, the body lacks the usual axial burden on the legs, muscular activity, and sensation.1 There is a direct influence of working muscles on the remodelling process of the growing tibia. Post-mortem studies of patients with spina bifida reveal a thin and atrophic cortex of the tibia with a diminished number of Haversian systems and large remodelling cavities.2 In fact, patients with spina bifida have lower bone mineral density and are at risk of pathological bone fractures.3 The clinical status of children with spina bifida can be significantly worsened by the effects of secondary osteoporosis, including fractures and subsequent further immobilization, and the leg bones of patients with spina bifida have an additional risk of fractures after inactivity (e.g. postoperatively).1,4–6
Our primary aim in this study was to examine the frequency and characteristics of fractures in paediatric patients with spina bifida. A secondary aim was to identify other variables that may contribute to the presence of fractures, such as neurological level, shunted hydrocephalus, syringomyelia, type of ambulation, mechanism of injury, and prolonged immobilization. We hypothesized that patients who use wheelchairs would have a higher fracture frequency.
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The study, conducted at Dona Estefânia Hospital, Lisbon, Portugal, was a retrospective evaluation of the hospital records of all patients with a diagnosis of spina bifida who were followed at our unit between 1999 and 2008. Our centre is a state tertiary-care paediatric hospital located in an urban setting, which serves patients from the entire country. The study was approved by the hospital’s ethics committee.
Patients were included if they had spina bifida confirmed by in-patient documentation, were aged 0 to 18 years, and were still living. Patients were excluded from the study if they had had no clinic visit in the past 2 years, if their medical records were unavailable, if they had been transferred to another care centre, or if they had spina bifida occulta or isolated caudal regression syndrome. Once the eligible population of patients with spina bifida had been assembled, charts were reviewed to evaluate data from their health records. In addition, we also interviewed at least one parent of each patient, either face to face or by telephone, to identify all occurrences of fractures, surgical interventions, and hospitalizations in other centres.
The neurological level and ambulatory status of each participant were determined by two graduate assistants, from the departments of Physical Medicine and Rehabilitation and Paediatric Neurology. The neurological level in the patients was categorized as thoracic, upper lumbar (L1–L2), lower lumbar (L3–L5), or sacral. The International Myelodysplasia Study Group criteria for assigning motor levels was used to evaluate the level of neurological involvement.7
Ambulatory status was recorded, using a modified version of the International Myelodysplasia Study Criteria Manual,8 as non-ambulatory, partially ambulatory, or fully ambulatory. Non-ambulatory wheelchair users were subdivided into those who were totally dependent on their wheelchair and could not move it themselves (i.e. they needed to be driven by caregivers; termed ‘wheelchair-dependent’) and those who were able to propel the wheelchair without physical assistance (‘wheelchair-independent’). Partially ambulatory patients could move around their own home; fully ambulatory patients could move further afield. Because our study included patients younger than 15 months, we added the category of ‘below the age of walking’.9
The mechanism of injury was divided into spontaneous fracture (without known trauma), minor trauma (trivial injury), and major stress. Spontaneous fractures and those due to minor trauma were defined as pathological. For each participant, we recorded date of birth, sex, neurological level, ambulation status, presence of shunted hydrocephalus, shunt revision, or syringomyelia, number and location of fractures, age at occurrence of each fracture, and mechanism of injury.
We also reviewed each patient’s history of neurosurgical, orthopaedic, and other surgical interventions and medical conditions for evidence of prolonged immobilization, focusing on the length of time spent immobilized after each procedure and the interval between removal of the cast and the occurrence of fractures.
Statistical differences were evaluated with a χ2 test and Fisher’s exact test using StatXact 8 (Cytel Studio, Cambridge, MA, USA) and MATLAB version 7.1 (Math Works, Cambridge, UK). A logistic regression model was used to adjust the data on lesion level and ambulatory status for patients who presented with a second fracture. Occurrence of a second fracture was the dependent variable, with lesion level and ambulatory status as the risk factors being tested. For a given patient, i, the probability of occurrence of a second fracture Zi is related to the level of lesion X=xi and type of ambulation Y=yi, by the following equation:
All calculations were performed using Statistica 6.0 (StatSoft, Tulsa, OK, USA). The parameters β0, β1, and β2 were estimated by the maximum likelihood method. The quasi-Newton method was used to maximize the maximum likelihood loss function. The relationship between these risk factors and second fracture occurrence was estimated using odds ratios and 95% confidence intervals (CI). Statistical significance was set at p<0.05.
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In 113 children and adolescents with spina bifida, 45 fractures were detected in 25 patients (22.1%). The frequency of fractures in our research is consistent with those reported in the literature (range 11–30%).11–16
As can be found in other analyses,1,11,14 our data show that the level of neurological involvement is directly related to the incidence of fractures.
Sex was not associated with the occurrence of fractures. The recent article of Dosa et al. 17 showed similar results.
Ambulatory status affected the incidence of fractures, with wheelchair-independent patients having a greater risk of fracture. This is likely to be related to the fact that non-ambulatory children with a chronic severe disability have low bone mineral density18 with subsequent morbidity.19
In our study, the most common site of fracture was the distal femur. An analysis of the literature shows that this is the most common site of fractures in children with immobility, independent of the primary disease.19,20 The sites of fractures in patients with spina bifida were similar to those encountered in patients with spinal-cord injury.20 We failed to find vertebral fractures, which suggests a possible protective effect on vertebral fractures among patients with spina bifida who use wheelchairs. This may be due to maintenance of load on the spine while sitting. These results are also analogous to the population with spinal-cord injury.17,22
Lock and Aronson suggested the possibility that fractures involving the lower extremities occur distal to the level of neurological involvement, with fracture of the femur being more frequent with higher motor levels (thoracic) and fracture of the tibia more frequent with lumbar motor levels.11 In our survey, there was no significant relationship between the motor lesion and the fracture location, but there was undoubtedly a trend suggestive of this relationship.
Fractures may occur without significant trauma and, due to the lack of sensation, may be imperceptible. Pathological fractures were the main cause of fracture and manifested with local warmth, redness, swelling, and an increase in temperature. Pathological fractures should, therefore, be suspected even in patients presenting with only swelling of the extremity.
We identified an association between the mechanism of the fracture and the type of ambulation and level of the lesion. In patients with higher levels of neurological involvement, who were in wheelchairs, fractures were mainly pathological. None of the patients with lesions at the sacral level experienced a spontaneous fracture. The hypothesis is that less torque is needed to produce failures in bone in people with higher motor level lesions than in individuals who have lesions at lower levels who largely sustain independent gait.
Most of the fractures (71.1%) occurred before 9 years of age, which is similar to the findings of Lock and Aronson. This could be because a higher number of surgical interventions are necessary in younger patients to attempt gait improvement.11
In our data, it was possible to detect an association between prolonged postoperative inactivity and fractures in several cases, and this has already been documented in previous studies.1,5,11
After orthopaedic procedures, fractures that occurred within 1 month of the plaster being removed were more common when the patient was immobilized in a spica cast following hip surgery and less common when the patient was in a short-leg cast after foot surgery. This risk factor should be taken into account when one considers operations in patients with spina bifida. Drummond et al. suggested immobilizing the hip for only 4 weeks after femoral osteotomy.5
The association between neurosurgical interventions and the occurrence of fractures was not statistically significant. When we looked for a temporal linkage, this relationship was clearly less evident than for orthopaedic interventions. This finding is consistent with the results of Parsch.1
The association identified between the risk of a second fracture and higher motor level lesion and non-ambulation could help physicians identify children at risk of experiencing multiple fractures.
The increased risk of having a second fracture after a spontaneous fracture could explain why most orthopaedic specialists make a diagnosis of osteoporosis in children and adolescents only in the presence of one fragility fracture (beyond the presence of low bone mineral density), i.e. only in the presence of what would be considered a complication of osteoporosis in adults.23
Our data support the hypothesis that fractures should be expected in patients with spina bifida after major reconstructive surgery. Whenever possible, the period of immobilization following surgery should be shortened,5,11,24 and weight bearing on the paralysed legs must be allowed as soon as possible.1 If several operations are necessary, many authors recommend undertaking them all at one stage, or at least within the period that the patient needs to be immobilized for one of the procedures.5,24 Whenever possible, a spica cast should be avoided, and when long-leg casts are used to prevent post-immobilization fractures, a major issue is to avoid crawling for the first 3 weeks. When some immobilization is needed, a bulky Webril dressing provides less rigid immobilization than a plaster cast.11 If a plaster cast is unavoidable, it should be constructed to allow the earliest opportunity to stand.1
Limitations of the study
As in any retrospective study design, the incidence of fracture and its relationship to prolonged inactivity may be underestimated owing to the varying quality of information in the medical records. Further, it was not possible in all cases to characterize the location of fractures in long bones.