Bone density is not uniform across your skeleton. Different parts of your body are made up of different proportions of bone types, are affected differently by hormonal changes, and respond differently to the mechanical demands placed on them. This is why your T-score at the spine and your T-score at the hip can tell quite different stories.
Two types of bone
Your skeleton is made up of two types of bone tissue. Cortical bone is the dense, hard outer shell. It makes up about 80 percent of your skeleton and is found predominantly in the long bones of the arms and legs. Trabecular bone is the spongy, latticed inner tissue. It is more metabolically active, and more vulnerable to the hormonal changes of menopause. It makes up a higher proportion of the spine and hip.
Because trabecular bone turns over faster and responds more quickly to estrogen loss, it tends to show the effects of bone density decline earlier. This is why the spine is often the first site to show significant loss.
Why the spine score can be misleading
The lumbar spine is the most sensitive site for detecting early bone loss. It is also the most prone to interference. Osteoarthritis, calcified ligaments, previous fractures, and even aortic calcification can artificially inflate the BMD reading at the spine, making it appear denser than it actually is. This means a spine score can sometimes look better than it really is, particularly in older women.
Your doctor will take this into account when interpreting your results, which is one reason the hip score is often considered the more reliable measure in women over 65.
Why the hip score carries more weight
Hip fractures are the most serious consequence of osteoporosis. They frequently require surgery, carry significant risks of complications, and are associated with loss of independence and, in older women, increased mortality. Because of this, the hip T-score carries considerable clinical weight, particularly when making treatment decisions.
The hip measurement on your report may include several sub-regions including the femoral neck, the total hip, and sometimes the trochanter. Your doctor will typically focus on the femoral neck and total hip values.
Which score determines your diagnosis?
Your overall diagnosis is based on the lowest T-score across all sites measured. If your spine shows -2.6 and your hip shows -1.8, your diagnosis is osteoporosis based on the spine result. The full picture matters, but the most significant number sets the classification.
What this means in practice
Different medications have different evidence bases at different sites. Some are particularly effective at the spine, others at the hip. Understanding which of your sites is most affected helps frame the conversation with your doctor about which treatment approach is most appropriate for your specific pattern of bone loss.
If your scores vary significantly between sites, or if your spine score seems unexpectedly good relative to your age and symptoms, it is worth asking your doctor whether they are confident the spine reading is accurate, or whether anything might be affecting it.