Sacral fragility fractures represent an important but often underrecognized cause of pain, reduced mobility, and functional decline in elderly patients. These tend to be low-impact fractures or a repetitive physiological load in a person with compromised bone strength. Fractures of the

pelvis and sacrum are becoming a more relevant clinical issue with the current trend to more elderly people and the increased incidence of osteoporosis. Diagnosis can be difficult as symptoms are often non-specific and subtle or non-displaced fracture lines are often not apparent on plain radiographs (1, 2).

The sacrum plays a central role in transferring axial load from the spine to the pelvic ring. If osteoporosis or other factors associated with decreased bone strength exist, normal loading could exceed the structural strength of the sacral trabecular bone and lead to insufficiency fracture. The relatively low bone density of the sacral ala coupled with the high mechanical load is a key reason why it is more vulnerable. The fractures can be unilateral or bilateral, vertical, transverse or a combination of both. In some patients, there is a transverse fracture also, creating an "H-shaped" or "Honda sign" pattern of bilateral vertical fractures. More complex patterns often are associated with the presence of displacement, foraminal involvement, and/or other pelvic ring fractures (3, 4).

BMI is a key factor in the strength of bones and is used extensively for the diagnosis and evaluation of osteoporosis. Dual-energy X-ray absorptometry continues to be the preferred method to assess bone mineral density (BMD) at clinically relevant regions of the skeleton such as the total hip, femoral neck, and lumbar spine. The lower the T score, the more bone mass is lost, and the more prone one is to having fragility fractures. While BMD reduction is definitely linked to fracture risk, the correlation of the anatomical extent and complexity of sacral fragility fractures has been studied comparatively less (5, 6).

Disturbances of calcium and vitamin D metabolism also affect bone health in elderly people. The primary role of parathyroid hormone is to regulate calcium homeostasis, both by acting on bone and on the kidney and vitamin D metabolism. Chronic high levels of PTH can lead to the acceleration of bone turnover and bone resorption, especially in the presence of vitamin D deficiency, low calcium intake or impaired renal function. Secondary hyperparathyroidism is therefore commonly seen in older people and can be a factor in deteriorating bone quality in addition to the decrease in bone mineral density (7, 8).

The site of a sacral fragility fracture might be important for management of the patient. Bilateral fractures, H-shaped configurations, displacement, and associated pelvic ring injury may be associated with increased treatment needs and may be associated with greater ambulatory deficits and long-term pain. Biological markers associated with these larger patterns might be useful in risk stratification and promote early assessment of underlying osteoporosis and metabolic bone disease. Therefore, combining the assessment of BMD with serum PTH might give a more comprehensive picture of both structural and metabolic factors for sacral fragility fractures (9, 10).

Despite the clinical importance of sacral fragility fractures, limited information is available regarding the association of bone mineral density and serum parathyroid hormone concentrations with specific anatomical fracture characteristics in elderly patients. Therefore, the present study was conducted to evaluate the relationship of BMD and serum PTH levels with fracture laterality, orientation, H-shaped morphology, displacement, and associated pelvic injuries in elderly patients with sacral fragility fractures. The study also aimed to determine whether reduced BMD and elevated PTH independently predict complex sacral fracture morphology.

This observational cross-sectional study was conducted at Rawal Institute of Health Sciences, Islamabad, from April 2025 to October 2025. The study included 85 elderly patients diagnosed with sacral fragility fractures who presented to the orthopedic and radiology services during the study period. Patients were enrolled through a non-probability consecutive sampling technique after assessment for eligibility. Elderly patients with radiologically confirmed sacral fragility fractures were considered for inclusion. Patients with fractures caused by high-energy trauma, known primary or metastatic bone tumors, active bone infection, previous sacral surgery, or incomplete clinical, laboratory, or imaging records were excluded. Written informed consent was obtained from each participant or an authorized attendant before enrollment, and confidentiality of all patient information was maintained throughout the study. A structured data collection proforma was used to record the demographic and clinical data. The variables included were: age, sex, BMI, osteoporosis history, history of fragility fracture, recent history of fall, current osteoporosis treatment, and calcium or vitamin D supplementation. Medications and other conditions that might affect bone metabolism were also noted if available. BMI was obtained from the weight and height measured, and expressed in kg/m². Medical charts were checked for previous diagnosis of osteoporosis and previous low energy fractures. Dual-energy X-ray absorptiometry was used to measure bone mineral density. BMD values and T-scores were recorded at the lumbar spine, femoral neck and total hip. Bone mineral status was classified as normal, osteopenic or osteoporotic based on the T score at the sites analysed. Given that the femoral neck T Score was one of the major skeletal fragility markers used in the association analysis, particular emphasis was placed on this score. If several skeletal sites were available, the T-score from the lowest site with clinical relevance was used when determining the overall bone mineral status. Aseptic samples of venous blood were taken for biochemical evaluation. Measurements of the serum parathyroid hormone level were obtained by the immunoassay procedure available in the institutional laboratory. Calcium, phosphate, alkaline phosphatase, creatinine, and 25-hydroxyvitamin D levels were also measured for evaluation of bone and mineral metabolism. Serum PTH was measured as a continuous variable as well as, if applicable, normal or elevated using the laboratory reference range for PTH. Vitamin D status was also defined using the laboratory derived threshold. Routine institutional quality-control procedures were used to conduct all laboratory measurements. Diagnosis and anatomical characterization of sacral fragility fractures were made by available radiological imaging (computed tomography and other imaging modalities when necessary). Fracture characteristics documented included unilateral or bilateral fractures, sacral ala or body involvement, vertical or transverse orientation, combined fracture patterns, H-shaped or Honda-sign configuration, involvement of the sacral foramina, and fractures of the pelvic ring or pubic rami. When possible, fractures were classified based on the Denis anatomic zones. Fracture morphology was also determined to be simple or complex depending on the presence of bilateral involvement, combined vertical and transverse components, displacement of the fracture or the presence of associated pelvic ring injury. The data were analysed in SPSS version 25.0. Continuous variables were presented as a mean and standard deviation when they were found to be approximately normally distributed or presented as frequencies and percentages if not approximately normally distributed. When parametric assumptions were met, the independent-samples t-test was used to compare mean BMD T-scores and serum PTH levels among fracture morphology groups. Categorical variables (such as osteoporosis status, elevated PTH, and various anatomical fracture patterns) were analysed using the chi-square test or Fisher's exact test for association. Relationships between serum PTH, vitamin D and BMD parameters were assessed using Pearson or Spearman correlation analysis as appropriate. Multivariable logistic regression analysis was used to determine factors independently associated with complex sacral fracture morphology after adjusting for other potential confounding variables including age, sex, BMI, vitamin D status, serum calcium, femoral neck T score and elevated serum PTH. A p-value of < 0.05 was deemed as statistically significant. throughout.

In total 85 elderly patients with sacral fragility fracture were included in the study. The mean age of the subjects was 72.8 ± 6.7 years, ranging from 61 to 88 years. The majority of the study population was females (58, 68.2%) with males (27, 31.8%). The mean body mass index was 25.6 ± 3.8 kg/m². Nineteen (21.7%) patients had a history of osteoporosis and 24 (28.2%) had a history of previous fragility fracture.

Table 1. Demographic and clinical characteristics of the study participants (n = 85)

The bone mineral density study showed general decrease in skeletal mass of the study subjects. The mean lumbar spine T-score was −2.34 ± 0.78, while the mean femoral neck T-score was −2.61 ± 0.72 and the total hip T-score was −2.48 ± 0.75. According to the lowest measured T score, 57.6% (49 patients) met the criteria for osteoporosis, 34.1% (29 patients) had an osteopenic score and just 8.2% (7 patients) had a score higher than the osteopenic or osteoporotic range. The mean concentration of serum PTH was 71.6 ± 27.8 pg/mL. Thirty-three (38.8%) patients had elevated PTH levels. The mean serum 25-hydroxyvitamin D was 21.9 ± 8.6 ng/mL and 40 (47.1%) participants were vitamin D deficient. Among the patients, those with high PTH had lower levels of vitamin D and femoral neck BMD.

Table 2. Bone mineral density and biochemical characteristics of the patients

Of the 50 patients with bilateral sacral lesions, 35 (41.2%) had unilateral sacral fractures. The sacral ala was the most common site involved, 64 (75.3%) cases. Vertical fractures were found in 37 (43.5%) patients, combined vertical and transverse fractures in 34 (40.0%) patients and predominantly transverse fractures in 14 (16.5%) patients. Twenty-eight (32.9%) fractures were found to be of H-shaped or Honda-sign type. 24 (28.2%) patients had sacral foraminal involvement and 30 (35.3%) patients had associated pubic ramus fractures.

Table 3. Anatomical and radiological characteristics of sacral fragility fractures

Bone mineral density was found to be significantly related to fracture morphology. The mean femoral neck T-scores were lower for patients with bilateral sacral fractures than for those with unilateral fractures: −2.82 ± 0.61 versus −2.31 ± 0.75, respectively (p = 0.001). Patient with an "H" fracture pattern also had significantly lower femoral neck T-scores than patients without such a fracture pattern (−2.89 ± 0.58 versus −2.47 ± 0.75, p = 0.011). Patients who had bilateral fractures were also more likely to have osteoporosis than patients with unilateral fractures (68.0% vs. 42.9%, p = 0.020).

Table 4. Association of femoral neck bone mineral density with anatomical fracture characteristics

As well, serum PTH level was significantly different across fracture anatomy. The mean serum PTH level was higher in patients with bilateral sacral fracture than in patients with unilateral fracture (79.8 ± 29.0 pg/mL vs 59.9 ± 21.4 pg/mL; p = 0.001). Similarly, patients with an H-shaped fracture pattern had higher PTH levels (84.7 ± 29.6 pg/mL) than patients without such pattern (65.2 ± 24.6 pg/mL, p = 0.002). However, serum PTH levels were higher in patients with displaced fractures compared with non-displaced fractures (88.3 ± 30.4 versus 67.1 ± 25.5 pg/mL, p = 0.004).

Table 5. Association of serum PTH levels with anatomical characteristics of sacral fragility fractures

The correlation analysis showed that serum PTH was significantly negatively associated with femoral neck T score (r = −0.39, p < 0.001), suggesting that the higher the PTH, the lower the bone mineral density. The serum PTH level was also negatively associated with vitamin D (r = −0.36, p = 0.001). There was a positive correlation between the T score at the femoral neck and the vitamin D level (r = 0.31, p = 0.004).

Table 6. Correlation between PTH, vitamin D and bone mineral density

A complex fracture pattern was classified for multivariable analysis as involvement on both sides, H-shaped pattern, displacement, or a pelvic ring fracture. The association between lower femoral neck T-score and higher serum PTH levels was independent of age, sex, BMI, serum vitamin D and calcium levels. For every -1 unit decrease in the femoral neck T score, the risk of complex fracture anatomy was increased by ~2-fold (adjusted OR = 2.14, 95% CI: 1.24–3.69, p = 0.006). A higher serum PTH was also independently associated with complex fracture morphology (adjusted OR = 2.63, 95% CI: 1.08–6.40, p = 0.033).

Table 7. Multivariable logistic regression for factors associated with complex sacral fracture morphology

Overall, the findings demonstrated that reduced bone mineral density and elevated serum PTH levels were significantly associated with more extensive and complex anatomical patterns of sacral fragility fractures. Bilateral involvement, H-shaped fracture configuration, displacement and associated pelvic ring fractures occurred more frequently among patients with poorer femoral neck bone mineral density and higher serum PTH concentrations.

Figure 1. Comparison of mean femoral neck T-scores between patients with unilateral and bilateral sacral fragility fractures. Error bars represent standard deviations.

The present study evaluated the association of bone mineral density and serum parathyroid hormone levels with the anatomical characteristics of sacral fragility fractures in elderly patients. The findings showed that reduced bone mineral density was common in this population, with more than half of the patients meeting criteria for osteoporosis. Bilateral sacral involvement and complex fracture configurations were also frequent. Importantly, patients with bilateral fractures, H-shaped fracture patterns, displacement, and associated pelvic ring injury had lower femoral neck T-scores than those with less extensive fracture patterns. These findings suggest that poorer skeletal strength may be associated not only with the occurrence of sacral fragility fractures but also with greater anatomical complexity (11, 12). The strong relationship between low T score of the femoral neck and bilateral sacral fractures is clinically meaningful because there is often a greater extent of structural weakness throughout the sacrum when both fractures are present. The mean femoral neck T score in the present study was −2.82 in patients with bilateral fractures and −2.31 in patients with unilateral fractures. The same trend was seen in both patients suffering from H-shaped fractures and displaced fractures. This can mean that the advanced bone loss stems from the reduction of the physiological loading the sacrum can handle and fracture lines can pass through more than one area of the sacrum. Thus, the fracture morphology may be more extensive in elderly people due to age-related cortical thinning, trabecular loss and osteoporosis (13, 14). A significant association with important anatomical fracture characteristics was also observed with serum PTH. Patients with bilateral fractures, H-shaped fracture and fracture displacement had higher mean PTH levels in comparison to patients who did not have these features. Moreover, an inverse correlation was identified between serum PTH and femoral neck T score, indicating that higher levels of PTH activity may be associated with lower levels of bone mineralization. In older people, elevated PTH can be caused by vitamin D deficiency, decreased calcium absorption, renal failure or other abnormalities of mineral metabolism. High levels of PTH over time can lead to increased bone turnover and may help to lead to a decline in bone microarchitecture that may make them more susceptible to complex insufficiency fractures (15, 16). Serum PTH also had an inverse association with the serum vitamin D level and vitamin D deficiency was common in the study population. The close physiological relationship of vitamin D status, calcium regulation and parathyroid activity, is supported by this finding. Vitamin D deficiency in elderly people could be caused by decreased exposure to sunlight, dietary intake or absorption of vitamin D, and aging-related changes in vitamin D metabolism. This can then lead to secondary hyperparathyroidism which can further increase bone resorption. Vitamin D was not an independent predictor of complex fracture morphology in the multivariable model, but may act indirectly through the effect on PTH and bone mineral density (17, 18). Another notable finding from this study was the radiological characteristics described, which further underscores the need for careful imaging evaluation of elderly patients with suspected sacral fragility fractures. The most common was the sacral ala, and a substantial number of patients had bilateral involvement or H-shaped morphology or pelvic ring fractures. Usually these injuries are hard to detect on standard radiographs, especially in cases without a fracture line. Therefore, cross-sectional imaging, particularly computed tomography is helpful to determine fracture extension, foraminal involvement, and displacement, as well as to determine associated pelvic injuries. These anatomical characteristics have to be recognised as more complex fracture morphology may lead to more pain and reduced mobility and require more intensive treatment (19). Both lower femoral neck T score and increased serum PTH remained independently associated with complex sacral fracture morphology after adjustment for age, sex, BMI, serum calcium and vitamin D status. This means that the two markers of skeletal density and disturbances in bone-mineral metabolism could complement each other in assessing elderly patients with fragility fractures. BMD provides information about structural weakness of the skeleton, while PTH can give information on active metabolic factors affecting bone turnover. The overall evaluation of these parameters may thus be useful to help identify those patients more likely to have extensive or unstable sacral fracture patterns (20). These results have implications for the treatment of elderly patients with sacral fragility fractures. The fracture assessment should not only cover the fracture itself, but also the underlying bone health status. Those with decreased BMD or elevated PTH might need to be evaluated further for osteoporosis, vitamin D deficiency, calcium imbalance and secondary causes of increase bone turnover. Early detection and treatment of these abnormalities may help to prevent a second fracture and minimize the likelihood of future fragility fractures. Therefore, multidisciplinary care (with orthopedic subspecialists, radiology, medicine and osteoporosis services) may be warranted for high-risk patients (21). Several limitations should be considered when interpreting the findings. The study took place in one institution and involved a relatively small number of patients (85), which may restrict applicability of the findings. A cross sectional study design also does not allow for the establishment of a temporal or causal relationship between high PTH, low BMD and complex fracture anatomy. Bone mineral density measurements may underestimate the strength of sacral bones, and the local bone quality has not been directly assessed. Besides, other risk factors for fragility, such as nutrition status, physical activity, renal function and chronic drug use, may not have been fully assessed. Larger multicenter prospective studies with longitudinal follow-up are suggested to validate these results and to assess if correction of metabolic abnormalities can prevent fracture progression, delayed healing or subsequent fragility fractures.

Reduced bone mineral density and elevated serum parathyroid hormone levels were significantly associated with more complex anatomical patterns of sacral fragility fractures in elderly patients. Lower femoral neck T-scores were particularly associated with bilateral fractures, H-shaped configurations, displacement, and associated pelvic ring injuries, while higher PTH levels showed similar relationships with fracture complexity. An inverse association between PTH and bone mineral density further suggests an important interaction between skeletal weakness and disturbed mineral metabolism. Assessment of BMD, PTH, vitamin D, and related biochemical parameters may therefore provide useful additional information when evaluating elderly patients with sacral fragility fractures and may help identify individuals requiring comprehensive osteoporosis and metabolic bone management.

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