Paget’s disease of bone most commonly affects the pelvis, skull, spine, and the long bones of the legs (the femur and tibia). It can technically occur in any bone, but these four sites account for the vast majority of cases. Most people with Paget’s disease have it in more than one bone: roughly 65 to 90 percent of patients have multiple bones involved, while only 10 to 35 percent have disease limited to a single bone.
How the Disease Changes Bone
Paget’s disease is a disorder of bone turnover. It starts when bone-breaking cells become overactive and begin dissolving bone faster than normal. The body responds by ramping up bone-building cells to fill in the gaps, but because the process is so accelerated, the new bone gets laid down in a disorganized, haphazard pattern rather than the neat, layered structure of healthy bone. The result is a mosaic of poorly organized bone tissue that is thicker and larger than normal but structurally weaker. This bone is more prone to fractures, bowing, and deformity despite appearing denser on imaging.
The disease progresses through phases. Early on, bone loss dominates. Then a mixed phase takes over where both breakdown and rebuilding happen simultaneously. In the final stage, dense but poorly organized bone fills the affected area. A blood marker called alkaline phosphatase, which reflects bone turnover, is often significantly elevated. Normal levels run between 30 and 120 U/L; in Paget’s disease, levels can climb well above 300 U/L.
Pelvis
The pelvis is the single most commonly affected bone in Paget’s disease. When pagetic bone forms in the pelvis, it can change the shape of the hip socket and alter the way the joint fits together. This is a major reason Paget’s disease accelerates osteoarthritis in the hip. In one study examining 100 joints adjacent to pagetic bone, 86 were hips, and those joints showed more severe arthritis compared to the unaffected side. Some patients eventually need hip replacement surgery because of this secondary joint damage. Pelvic involvement can also cause deep, aching pain in the groin or buttock that worsens with walking or standing.
Skull
When the skull is involved, the outer layer of bone thickens and expands. Some people notice that hats no longer fit or that their forehead appears more prominent. Beyond cosmetic changes, skull involvement carries a distinct risk: hearing loss.
Hearing loss in Paget’s disease typically involves both a high-frequency nerve-related component and a low-frequency conductive component. For years, researchers suspected this was caused by the expanding bone compressing the auditory nerve. But more recent evidence points to a different mechanism. Studies using brain-stem response testing found that auditory nerve function remains intact in most patients. The real problem appears to be changes in the cochlea itself, the small spiral structure of the inner ear. Loss of bone mineral density in the cochlear capsule disrupts how sound vibrations are transmitted, leading to gradual hearing impairment.
Spine
Spinal involvement can affect one or several vertebrae. The pagetic bone becomes enlarged and structurally weak, which can lead to compression fractures where a vertebra partially collapses under the body’s weight. These fractures cause back pain and can reduce height over time.
A more serious complication is spinal stenosis, where the enlarged bone narrows the spinal canal and presses on the spinal cord or nerve roots. This can produce pain that radiates into the legs, numbness, tingling, or in rare cases, weakness and difficulty walking. Because these symptoms can mimic other spinal conditions, imaging is important for distinguishing Paget’s-related compression from other causes like disc herniation or tumors.
Femur and Tibia
The femur (thighbone) and tibia (shinbone) are the most commonly affected long bones. Because these bones bear the full weight of the body, the structurally weak pagetic bone is especially vulnerable to bowing deformities. The femur typically bows forward and outward, while the tibia tends to bow forward. This bowing develops gradually and can alter your gait, put extra stress on the knees and hips, and cause chronic pain in the legs.
Stress fractures and complete fractures are more common in pagetic long bones. The bone may also develop small cracks called Looser zones, which are visible on X-rays and indicate areas of incomplete fracture. Surgical correction, including the use of internal rods, sometimes needs to accommodate the abnormal curvature of the bone.
Less Common Sites
While the pelvis, skull, spine, femur, and tibia dominate, Paget’s disease can appear in other bones. The humerus (upper arm bone) is one example. Case reports describe intense disease activity in the humeral head and shaft. The collarbone, shoulder blade, and bones of the forearm are occasionally involved but rare. Jaw involvement has also been documented and can lead to complications like osteomyelitis (bone infection) and dental problems.
How Affected Bones Are Identified
Many people with Paget’s disease have no symptoms at all, and the condition is discovered incidentally through a blood test showing elevated alkaline phosphatase or an imaging study done for another reason. A radionuclide bone scan is the most sensitive tool for mapping which bones are involved. The scan lights up areas of high bone activity, and pagetic lesions produce an intensely “hot” signal with a characteristic pattern: the tracer accumulates uniformly throughout the affected bone rather than in scattered spots.
In long bones, the disease typically starts at one end near a joint and advances along the shaft, producing a sharp V-shaped front that looks like a flame on imaging. X-rays are less sensitive and may miss early disease entirely, since pagetic changes only become visible on plain film after 30 to 50 percent of the bone has already been resorbed. For this reason, bone scans are preferred for determining the full extent of skeletal involvement.
Joint Damage Near Affected Bones
Paget’s disease doesn’t directly attack joints, but it frequently damages them indirectly. When pagetic bone sits next to a joint surface, the altered shape and mechanics accelerate cartilage breakdown. The hip is the most vulnerable joint by a wide margin, followed by the knee. Osteoarthritis on the side with pagetic bone tends to be measurably worse than on the opposite, unaffected side. This secondary arthritis is one of the most common reasons patients with Paget’s disease experience daily pain and reduced mobility.