This study compared three groups of fracture patients: those with spinal fractures and no hip fractures, those with both spinal and hip fractures and those with hip fractures and no spinal fractures. Our analysis has attempted to sort out the relative contributions of trabecular and cortical bone deficiency to the different fractures and we were particularly interested to see if the presence of vertebral fractures in the ihip fracture population might identify a group with deficient trabecular bone and so be a group who could be responsive to treatment, as opposed to being a group in whom the presence of vertebral fractures was simply another reflection of their falling and hence more traumatic in nature. Patients presenting to the osteoporosis clinic with spinal fractures have generally more deficient bones than those of similar age presenting with hip fractures, including a tendency to a lower hip density. In most measurements the spinal fracture only patients have the lowest bones mass and the hip fracture patients without spinal fractures the highest and those with both spinal and hip fracture in between. This is clear for the spinal density but a similar, though less marked, trend is seen for the hip density measurements that reflect trabecular bone, and less again for the cortical site of the neck of femur. Additionally, patients presenting with spinal fractures only, tend to have both a higher number of spinal fractures than those presenting with a hip fracture and spinal fractures, although the severity of the individual fractures and the distribution of the fractures in the spine is similar. The bimodal trend of fracture location with an increased frequency around T7-T8 and another peak around T12-L1 is consistent with previous findings . This pattern was not affected by the presence of hip fractures. We had hypothesised that if the vertebral fractures had been more related to trauma (falling) in the hip fracture population, there might have been a trend towards more fractures in the lower spine, the site most vulnerable to traumatic damage . This appears not to be the case. These patients appear to have trabecular osteoporosis though perhaps of a milder degree than the spinal fracture only patients.
Most studies evaluating the effectiveness of osteoporosis medications have focused on patients with poor trabecular bone, as reflected in low spinal density, with or without spinal fractures, and treated them with antiresorptives which are known to mostly act on trabecular bone. In general the effect on the prevention of further vertebral fractures has been impressive while the effect on non-vertebral fractures has been less so. Few studies have focused directly on the prevention of non-vertebral fractures in less selected patients and those that have, have not been very successful. Black and colleagues showed the presence of prevalent vertebral fractures indicated a high risk for future hip fracture whereas in the study conducted by McClung, the younger 70–79 year old group showed no benefit of treatment if the patients had no prevalent vertebral fractures [17, 18]. Likewise, recruiting older (>80 year old) patients on the basis of falling risk, with, in most cases, no reference to bone density, and treating with risedronate, had little effect on subsequent hip fracture rate . Although some of these patients had reduced bone density this was femoral neck bone density, a measure of cortical bone, and there was no significant reduction in femoral fracture with treatment.
It also appears that recruiting patients on the basis of a prior hip fracture without regard to trabecular bone status has limited benefit in the prevention of further hip fractures. For example, the zoledronic acid study of fracture prevention in hip fracture patients showed greater ability to prevent further (clinical) spine fractures and a more modest and non-significant benefit in the prevention of further hip fractures . Unfortunately the spinal state of these patients at the start of the study is unknown. In the other study with zoledronic acid, the fracture prevention study, although the bone density qualification for the study was on the basis of the femoral neck measurement, 63% had baseline vertebral fractures suggesting significant prevalence of trabecular bone deficiency, and a reduction in hip fractures was seen .
If it is true that the presence or absence of trabecular bone mass reduction has an influence on the likelihood of response to treatment, it does not mean that trabecular bone loss is required for a hip fracture to occur, it simply increases the risk and may influence the type of fracture that occurs. Although the definition of osteoporosis has evolved to a risk paradigm, the notion of a t-score of −2.5 representing a significantly low BMD has to some extent survived, particularly at the spine site . Only a minority of our patients with a hip fracture had a spinal BMD t-score below this osteoporotic threshold, even fewer if there were no spinal fractures. Our sample is not random, and is in fact biased toward the spinal fracture subjects, as the presence of spinal fractures in the hip fracture population is likely less than the 50% we selected here. Nonetheless, using spinal BMD and a cut point of t-score of −2.5 only 30% of those with hip and spinal fractures and 18% of those with hip fracture without spinal fractures fell below that point, while 50% of those with spinal fractures alone did so. In addition we find that most women and all men in our study would not have been in the high risk category using the CAROC paradigm on the basis of femoral neck BMD alone although the CAROC graph for men is unusual in showing no age-related rise in fracture risk. We were not able to calculate prior risk on the FRAX model as we had not gathered the extra information required by that model. These observations are similar to those reported by others, and the observations of Stone and colleagues who found low bone density to explain only a modest number of fractures [21–23]. These observations speak against the automatic labelling of hip fracture patients as osteoporotic and presumably reflect the large number of outcomes (hip fractures) that originate in the larger population of people at relatively low or moderate risk, have fairly good bones, but fall in such a way as to endanger the integrity of the hip bone. Although the absolute risk in such patients is low, their greater numbers likely ensure they contribute substantially to the overall hip fracture numbers but treatment of such low risk subjects may not be of value as far as the hip fracture prevention is concerned. Certainly treating those with relatively good femoral neck bone density was of no benefit . If preventing a hip fracture in such patients with bisphosphonates is relatively unsuccessful then preventing a second hip fracture in such patients is also likely to be unsuccessful.
A prior “fragility fracture” is certainly associated with an increased risk of a further one, but this may be on the basis of a risk of recurrent falling. If there is no second fall, there will be no second fracture. Of note is the finding that the increased risk of a second fracture in those who have experienced a first fragility fracture, is largely independent of bone density, and even more so in older age, pointing to falling as the predominant risk factor . Likewise in their study of the time for people with a certain bone density at the hip to cross the osteoporosis threshold, Gourley found that the presence of a prior fracture had no effect .
It is notable that in our study the z-scores in the hip fracture patients without spinal fracture are normal (that is, above or close to zero) indicating no greater deficiency in skeletal mass in these patients than in the age and gender matched normative databases of the particular densitometers (Table 1). Given the dynamics of falling in old age, with a greater tendency to fall from a static position backwards on to the greater trochanter, it may be that all older people are at risk of a hip fracture should they fall in this manner. However those with trabecular bone deficiency will be at higher risk as the trabecular bone contributes 50% of the hip mass. The relative degree of loss of trabecular versus cortical bone loss may be important in determining the nature of the hip fracture. Thus the intertrochanteric site has more trabecular bone than the subcapital site and patients with IT fractures have lower spinal density . It has been suggested that lower trabecular bone mass places the intertrochanteric site at risk, and, as it collapses more readily, this protects the subcapital site from the transmitted force . Other studies have found that femoral neck length was greater in those who suffered a subcapital fracture [29–32]. Our data suggests this may be related simply to greater person height as neck length, neck width and summed vertebral body heights are related. Taller people may be at more risk of a hip fracture in a fall with trauma, rather than bone deficiency, being the predominant cause and leading to a greater tendency to subcapital fractures . Our study suggests that these architectural considerations are independent of the presence or otherwise of trabecular bone status.
A potential weakness of the study is that the patients with hip fracture are a selected group of convenience. Patients missed, as noted above, are those who are younger and go directly home and those who go directly to LTC, who tend to be older. However as our comparison is with elderly ambulatory osteoporotic patients attending the osteoporosis clinic, the exclusion of a younger group, and an older, particularly frail group, is not inappropriate. Our study includes both genders on the assumption that hip fractures in either sex will show similar deficiencies regardless of gender. Although there are more women in the group with hip fracture and no spinal fracture, the analysis shows this to be group with the best bones, a finding which would be biased against by a predominance of women. On the other hand the spinal fracture alone group were slightly younger, but they turned out to have the most deficient bones. The analysis was re-run on the women alone. The smaller numbers made some comparisons fall below the significance level but overall the trends were unchanged.