Relationship Between Bone Mineral Density and Functional Parameters of Paraplegic Patients in Short-Term After Spinal Cord Injury-Original Investigation

  • Güliz Gönül
  • Binkan Sonel Tur
  • Yesim Kurtais
  • Özlem Küçük
  • Duygu Geler Külcü
  • Duygu Geler Külcü

Turk J Osteoporos 2008;14(3):-

SummaryAim: To determine the relationship between bone mineralization and functional activity level of paraplegic patients in short-term after spinal cord injury (SCI). Material and Methods: Thirty paraplegic patients and twentynine healthy controls were admitted to this study. Bone mineral density (BMD) and Z-scores, together with serum calcium, phosphorus, alkaline phosphatase, parathyroid hormone and 25-hydroxyvitamin-D levels, urinary calcium and deoxypyridinoline excretion were measured. All patients underwent a rehabilitation program including range of motion and progressive resistance exercises, upper body ergometry exercises, standing training with long leg orthosis, wheelchair ambulation or walking either by orthosis or walking aids five times/week during hospitalization.Results: There was no difference between the groups regarding BMD values and Z-scores. Mean serum calcium and parathyroid hormone levels were lower (p=0.016 and pConclusion: Early rehabilitation interventions may prevent bone demineralization. Paraplegic patients should be followed and evaluated also in long term for the increased risk of osteoporosis. (From the World of Osteoporosis 2008;14: 57-61)Key words: Spinal cord injury, bone mineral density, bone turn over markers, osteoporosisÖzetAmaç: Paraplejik hastalarda fonksiyonel aktivite düzeyi ile kemik mineralizasyonu arasindaki iliskiyi omurilik yaralanmasi sonrasi kisa dönem içinde arastirmaktir.Gereç ve Yöntem: Çalismaya otuz paraplejik hasta ve yirmidokuz saglikli kontrol alindi. Kemik mineral yogunlugu (KMY) ve Z-skorlari ölçüldü. Serum kalsiyum, fosfor, alkalen fosfataz, paratiroid hormon ve 25-hydroksivitamin-D düzeyleri, idrar kalsiyum ve deoksipridinolin düzeyleri çalisildi. Tüm hastalar yatislari süresince haftada bes kez eklem hareket açikligi egzersizleri, progresif dirençli egzersizler, üst ekstremite ergometri egzersizleri, uzun bacak yürüme cihaziyla ayakta durma egzersizleri, tekerlekli sandalye ile ambulasyon egitimi ve ortez veya yardimci cihazla yürüme egitimine alindi. Bulgular: Kemik mineral yogunlugu degerleri ve Z skorlari açisindan gruplar arasinda fark yoktu. Paraplejik grupta kontrol grubuna göre ortalama serum kalsiyum ve paratiroid hormon düzeyleri düsük, (sirasiyla p=0.016 ve pSonuç: Erken rehabilitasyon uygulamalari kemik deminerlizasyonunu önleyebilir. Paraplejik hastalar, artmis osteoporoz riski açisindan uzun dönemde de takip edilmeli ve degerlendirilmelidirler. (Osteoporoz Dünyasindan 2008;14: 57-61)Anahtar kelimeler: Omurilik yaralanmasi, kemik mineral yogunlugu, kemik döngüsü belirteçleri, osteoporoz


It is known that bone demineralization and osteoporosis occur in patients with spinal cord injury (SCI), which may lead to pathological fractures (1).The acute treatment of patients with SCI has always focused on the injury itself, but there are complications which arise immediately after the injury. Bone loss as a consequence of SCI should not be of secondary concern. Bone demineralization occurs rapidly during the first months after injury and slowly continues up to two years before equilibrium between bone resorption and formation is restored (2,3). Many factors may affect bone mineral density (BMD) in spinal cord-injured patients such as age, sex, level of injury, time since injury, ambulatory status, and rehabilitative interventions (1).Early intervention may be critical to prevent osteoporosis. In order to design the neccessary interventions, it may be useful to understand the relationship between bone demineralization and the patient’s functional status in the early stages of SCI. The aim of this study has been to determine this possible short-term relationship by investigating BMD and bone turnover in paraplegic patients.


In this study, relationships between BMD and functional parameters have been investigated in the short-term after SCI in paraplegic patients. The results of this study have shown that the radius and the femur BMD levels are significantly correlated with the functional activity level in paraplegic patients. No BMD difference was found between the two groups in this study. Recent studies, which evaluated BMD of the forearm, femur neck and the lumbar spine have presented conflicting results (5-7). Maimoun et al (8), observed no differences in the BMD of these three regions three months after injury and Roberts et al (9) reported no BMD variation in the femoral neck between 8 and 24 weeks after injury.The results of these studies were similar to the results of our study. These results suggest that the dual X-ray absorptiometry (DEXA) technique for BMD estimation may not show evidence of demineralization in the early stages of SCI. However, in some studies osteoporosis in sublesional areas has been shown shortly after SCI by using the DEXA technique (6,7). Several reasons may explain our findings. We did not know the basal BMD values of the patients just after injury. These data were estimated from measurements in our control subjects. This might cause bias in estimating the real bone loss. Furthermore, we did not survey and consider the physical activity level before SCI which might affect premorbid BMD level as well as the post-injury BMD level. An inverse relationship between the femur BMD values and the total duration of immobilization and a positive relationship between the femur BMD and the total duration of therapeutic standing have been found in this study. These results show the importance of early mobilization on bone mineralization in the early stages of SCI. Early passive verticalization of the patient, such as therapeutic standing, decreases the magnitude of demineralization (2,3,4,5,6,7,8,9,10). Gravity associated with vertical positioning of the bones, e.g. standing, provides a stimulus for bone mineralization by increasing the intramedullary fluid pressure (11,12).The increased intramedullary blood pressure has a positive effect on bone mineralization (12). The loss of physical function after SCI leads to the degradation of trabecular bone micro architecture. It is hypothesized that the magnitude of the loads imposed on bone dictates its mineralization and structural design (13). High frequency, low-magnitude stimulation, such as exerted by skeletal muscle contractions during standing or low level functional activity, may be the primary determinant of trabecular bone structure (14,15).Furthermore, weight loading stimulates the osteoblastic activity in the spine (16,17). Modlesky C et al (18) investigated trabecular bone micro architecture of the proximal tibia and the distal femur in men with SCI by using magnetic resonance imaging and found that they were markedly deteriorated. Although, loading associated with ambulation and normal physical function is suggested to be critical to maintain both the trabecular connectivity and bone mineral mass by several studies (16-18), there are some opposing results reporting that standing or walking by themselves do not improve BMD and do not prevent osteoporosis (3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20). Our results are also somewhat contradictory to each other, since there was a positive correlation between the femur BMD values and the total duration of therapeutic standing but not with the total duration of walking. The reason for this observation may be due to limited number of walking patients. Positive correlations between the radius BMD values and the duration of wheelchair use and upper body ergometry exercise were found in the present study. This result shows the importance of muscle strengthening exercises on bone mineralization. Goemaere et al (21). reported that using wheelchair increases the forearm BMD in SCI patients. In healthy tennis players BMD of dominant extremities was found to be higher than those of normal population which is possibly related to the mechanical stress exerted to the upper extremity used in the sportive activity (22). Although radius BMD values were 13% higher than those of the controls, no significant difference was observed between the two groups in this study. This result was considered to be due to evaluation in the short-term and suggested that radius BMD values might increase in the long-term due to the influence of exercises as reported previously (21,22). In the present study, calcium homeostasis was found to have deteriorated, but bone formation and bone resorption markers of the patients were not found to be different than those of the controls except for the elevated tALP levels. However, recent studies have demonstrated elevated resorption markers in the early stages of injury by assessing “modern” markers such as N-terminal cross-linked telopeptides of type I collagen (NTX), C-terminal cross-linked telopeptides of type I collagen (CTX), procollagen type I N propeptide (PINP) (9). Possible reasons for the differences with our results may be due to the smaller sample size and particularly less specific markers used in this study as compared to those of recent studies.Since bone mineralization in SCI is multifactorial, medication should be started soon after injury in addition to the rehabilitation interventions, to prevent bone demineralization. Bisphosphonates should be chosen for the treatment since these have been shown by several studies (27-29) to prevent bone loss in SCI. Bisphosphonates inhibit osteoclast recruitment and activity and reduce accelerated bone resorption in SCI (30). Pearson et al (29) have compared the effects of conventional rehabilitation programs with and without cyclic etidronate, and found that BMD loss was prevented in only those patients who had become ambulatory and had received etidronate.In conclusion, functional status of the paraplegic patients in the early stages of SCI was found to be closely related to bone mineralization. Early rehabilitation interventions should have positive effect on preventing bone demineralization. Patients with SCI should be followed and evaluated also in the long term for the increased risk of osteoporosis.