Osteosclerosis is a disorder that is characterized by abnormal hardening of bone and an elevation in bone density. It may predominantly affect the medullary portion and/or cortex of bone. Plain radiographs are a valuable tool for detecting and classifying osteosclerotic disorders. It can manifest in localized or generalized osteosclerosis. Localized osteosclerosis can be caused by Legg–Calvé–Perthes disease, sickle-cell disease and osteoarthritis among others. Osteosclerosis can be classified in accordance with the causative factor into acquired and hereditary.

In the animal kingdom there also exists a non-pathological form of osteosclerosis, resulting in unusually solid bone structure with little to no marrow. It is often seen in aquatic vertebrates, especially those living in shallow waters, providing ballast as an adaptation for an aquatic lifestyle. It makes bones heavier, but also more fragile. In those animal groups osteosclerosis often occurs together with bone thickening (pachyostosis). This joint occurrence is called pachyosteosclerosis.

"Fibrous dysplasia" causes bone thinning and growths or lesions in one or more bones of the human body.

These lesions are tumor-like growths that consist of replacement of the medullary bone with fibrous tissue, causing the expansion and weakening of the areas of bone involved. Especially when involving the skull or facial bones, the lesions can cause externally visible deformities. The skull is often, but not necessarily, affected, and any other bone(s) can be involved.

"Cleidocranial dysostosis" is a general skeletal condition named for the collarbone (cleido-) and cranium deformities which people with it often have. Common features include:

- Partly or completely missing collarbones.

- A soft spot or larger soft area in the top of the head where the fontanelle failed to close.

- Bones and joints are underdeveloped.

- The permanent teeth include supernumerary teeth.

- Permanent teeth not erupting

- Bossing (bulging) of the forehead.

- Hypertelorism

Hematologic manifestations related to bone marrow suppression and subsequent pancytopenia are a major source of morbidity and mortality. Additionally extramedullary hematopoiesis can result in liver and spleen dysfunction. Cranial nerve dysfunction and neurologic complications are usually associated with infantile osteopetrosis. Expansion of the skull bone leads to macrocephaly. Additionally, linear growth retardation that is not apparent at birth, delayed motor milestones and poor dentition can occur.

Axial osteomalacia is a rare osteosclerotic disorder characterized by axial skeleton pain, coarsening of the trabecular bone pattern on radiographs of the axial but not appendicular skeleton.

Despite this excess bone formation, people with osteopetrosis tend to have bones that are more brittle than normal. Mild osteopetrosis may cause no symptoms, and present no problems.

However, serious forms can result in...

- Stunted growth, deformity, and increased likelihood of fractures

- Patients suffer anemia, recurrent infections, and hepatosplenomegaly due to bone expansion leading to bone marrow narrowing and extramedullary hematopoiesis

- It can also result in blindness, facial paralysis, and deafness, due to the increased pressure put on the nerves by the extra bone

- Abnormal cortical bone morphology

- Abnormal form of the vertebral bodies

- Abnormality of temperature regulation

- Abnormality of the ribs

- Abnormality of vertebral epiphysis morphology

- Bone pain

- Cranial nerve paralysis

- Craniosynostosis

- Hearing impairment

- Hypocalcemia

The generalized increase in bone density of the medullary portion predominates with relative sparing of the cortices. The axial and appendicular skeleton are uniformly involved. Malignant infantile osteopetrosis is known for exhibiting specific plain radiographic abnormalities:

- Loss of differentiation between the medullary and cortical portions of bone is a radiographic hallmark of infantile osteopetrosis

- Characteristic endobone or “bone-within-bone” appearance in the spine, or “sandwich vertebra” appearance, characterized by dense endplate sclerosis with sharp margins

- Characteristic endobone or “bone-within-bone” appearance in the pelvis and long bones of extremities where areas of osteosclerosis intermingle with areas of relatively hypodense bone.

- Failure of remodeling of the distal femoral and proximal humeral metaphyses giving the affected bones a funnel shaped appearance known as (Erlenmeyer flask deformity)

- Alternating radiolucent femoral metaphyseal bands

- Pathologic fractures

Melorheostosis is a mesenchymal dysplasia manifesting as regions of dripping wax appearance or flowing candle wax appearance. It is thought to be caused by a mutation of the LEMD3 gene. The disorder can be detected by radiograph due to thickening of bony cortex resembling "dripping candle wax". It is included on the spectrum of developmental bone dysplasias including pycnodysostosis and osteopoikilosis. The disorder tends to be unilateral and monostotic (i.e. affecting a single bone), with only one limb typically involved. Cases with involvement of multiple limbs, ribs, and bones in the spine have also been reported. There are no reported cases of involvement of skull or facial bones. Melorheostosis can be associated with pain, physical deformity, skin and circulation problems, contractures, and functional limitation. It is also associated with a benign inner ear dysplasia known as osteosclerosis.

It is not known if LEMD3 mutations can cause isolated melorheostosis in the absence of Buschke-Ollendorff syndrome.

Melorheostosis is a medical developmental disorder and mesenchymal dysplasia in which the bony cortex widens and becomes hyperdense in a sclerotomal distribution. The condition begins in childhood and is characterized by thickening of the bones. Pain is a frequent symptom and the bone can have the appearance of dripping candle wax.

Autosomal Dominant Osteopetrosis(ADO), also known as Albers-Schonberg disease. Most do not know they have this disorder because most individuals do not show any symptoms. However, the ones that do show symptoms, they will typically have a curvature of the spin(scoliosis), and multiple bone fractures. There are two types of adult osteopetrosis based on the basis of radiographic, biochemical, and clinical features.

Many patients will have bone pains. The defects are very common and include neuropathies due to the cranial nerve entrapment, osteoarthritis, carpal tunnel syndrome. About 40% of patients will experience recurrent fractures of their bones. 10% of patients will have osteomyelitis of the mandible.

Pachyosteosclerosis is a combination of thickening (pachyostosis) and densification (osteosclerosis) of bones. It makes bones more heavy, but also more fragile. The condition often occurs in aquatic vertebrates, especially those living in shallow waters, creating ballast as an adaptation for maintaining neutral buoyancy and horizontal trim. It is in no way pathological. To resist roll, it frequently is found especially in ventral bones, whereas concentration near the lungs helps in maintaining trim.

Examples of animals showing pachyosteosclerosis are seacows (dugongs and manatees), the extinct Plesiosauria and Mesosauria and extinct aquatic sloths.

In contrast to STD, the subtype spondylocostal dysostosis, or SCD features intrinsic rib anomalies, in addition to vertebral anomalies. Intrinsic rib anomalies include defects such as birfurcation, broadening and fusion that are not directly related to the vertebral anomalies (such as in STD, where extensive posterior rib fusion occurs due to segmentation defects and extreme shortening of the thoracic vertebral column). In both subtypes, the pulmonary restriction may result in pulmonary hypertension, and have other potential cardiac implications.

Spondylothoracic dysplasia, or STD, has been repeatedly described as an autosomal recessively inherited condition that results in a characteristic fan-like configuration of the ribs with minimal intrinsic rib anomalies. Infants born with this condition typically died early in life due to recurrent respiratory infections and pneumonia due to their restricted thorax. Recently, a report has documented that actual mortality associated with STD is only about 50%, with many survivors leading healthy, independent lives.

A unicameral bone cyst, also known as a simple bone cyst, is a cavity filled with a yellow-colored fluid. It is considered to be benign since it does not spread beyond the bone. Unicameral bone cysts can be classified into two categories: active and latent. An active cyst is adjacent to the epiphyseal plate and tends to grow until it fills the entire diaphysis, the shaft, of the bone; depending on the invasiveness of the cyst, it can cause a pathological fracture or even destroy the epiphyseal plate leading to the permanent shortening of the bone. A latent cyst is located away from the epiphyseal plate and is more likely to heal with treatment. It is typically diagnosed in children from the aged 5 to 15. Although unicameral bone cysts can form in any bone structure, it is predominantly found in the proximal humerus and proximal femur; additionally, it affects males twice as often as females.

Idiopathic osteosclerosis is a condition which may be found around the roots of a tooth. It is usually painless and found during routine radiographs. It appears as a radiopaque (light area) around a tooth, usually a premolar or molar. There is no sign of inflammation of the tooth.

Focal radiodensity of the jaw which is NOT inflammatory, dysplastic, neoplastic or a manifestation of a systemic disease.

This is common and affects 5% of the population, usually seen in teens and those in their 20's. Typically asymptomatic and is an incidental finding on a radiograph. found anywhere in the jaw, most commonly in the mandibular premolar-molar region. The shape ranges from round to linear streaks to occasional angular forms.

Most unicameral bone cysts do not cause any symptoms and are discovered as accidental findings on radiographs or CT scans made for other reasons. Large lesions can cause nearby areas of bone to thin, which may result in a fracture and cause pain.

Hair abnormalities are very prominent in majority of the cases of TDO. Kinky/curly hair that is unusually dry and easily sheds is present at birth. In 80% of cases, the hair has a more relaxed appearance by adolescence. The presence of this hair texture type is a defining characteristic between a diagnosis of TDO verses amelogenesis imperfecta with hypomaturation. Additionally, in TDO the nails are usually abnormally thin, brittle, and split frequently. Cranial deficiencies are marked by the presence of having a long skull relative to its width, or protrusive foreheads due to increased thickness of the cranial bones and premature closing of the associated sutures in the skull. The long bones in the body (arms, legs) are also abnormally long and tend to fracture very easily. Osteosclerosis, commonly seen in TDO cases is characterized by an increase in bone density, affecting the skull and the mastoid process located behind the jawbone on the skull, as well as a shortened ramus seen in people with TDO. There are no known pathological problems associated with hair and bone changes in people with this disease. Changes in the long bones tend to appear later in development, but changes in the teeth appear once the teeth being to form, called primary dentition. The hair and bone abnormalities are evaluated radiographically during initial diagnosis, and visually during the course of the disease. Radiographic exams may be repeated if there is suspect of fracture.

Axial spondyloarthritis (also often referred to as axSpA) is a chronic, autoinflammatory disease predominantly affecting the axial skeleton (sacroiliac joints and spine). The most known member of the axial spondyloarthritis disease family is ankylosing spondylitis. Axial spondyloarthritis is an umbrella term that has been introduced in the year 2009 to characterize a diverse disease family that share clinical and genetic features, such as the involvement of the axial skeleton. The expression was introduced in order to unify (1) less severe forms of spondylitis, (2) the early phase of ankylosing spondylitis as well as (3) ankylosing spondylitis itself into one term.

For SPB the most common presenting symptom is that of pain in the affected bone. Back pain and other consequences of the bone lesion may occur such as spinal cord compression or pathological fracture. Around 85% of extramedullary plasmacytoma presents within the upper respiratory tract mucosa, causing possible symptoms such as epistaxis, rhinorrhoea and nasal obstruction. In some tissues it may be found as a palpable mass.

Individuals with Jefferson fractures usually experience pain in the upper neck but no neurological signs. The fracture may also cause damage to the arteries in the neck, resulting in lateral medullary syndrome, Horner's syndrome, ataxia, and the inability to sense pain or temperature.

In rare cases, congenital abnormality may cause the same symptoms as a Jefferson fracture.

Grisel’s syndrome is a non-traumatic subluxation of the atlanto-axial joint caused by inflammation of the adjacent tissues. This is a rare disease that usually affects children. Progressive throat and neck pain and neck stiffness can be followed by neurologic symptoms such as pain or numbness radiating to arms (radiculopathies). In extreme cases, the condition can lead to quadriplegia and even death from acute respiratory failure. The condition often follows soft tissue inflammation in the neck such as in cases of upper respiratory tract infections, peritonsillar or retropharyngeal abscesses. Post-operative inflammation after certain procedures such as adenoidectomy can also lead to this condition in susceptible individuals such as those with Down's syndrome.

Worth syndrome, also known as benign form of Worth hyperostosis corticalis generalisata with torus platinus, autosomal dominant osteosclerosis, autosomal dominant endosteal hyperostosis or Worth disease, is a rare autosomal dominant congenital disorder that is caused by a mutation in the LRP5 gene. It is characterized by increased bone density and benign bony structures on the palate.

The most common symptom is pain over the heel area, especially when the heel is palpated or squeezed. Patients usually have a history of recent trauma to the area or fall from a height. Other symptoms include: inability to bear weight over the involved foot, limited mobility of the foot, and limping. Upon inspection, the examiner may notice swelling, redness, and hematomas. A hematoma extending to the sole of the foot is called "Mondor Sign", and is pathognomonic for calcaneal fracture. The heel may also become widened with associated edema due to displacement of lateral calcaneal border. Involvement of soft tissue (tendons, skin, etc.,) should be evaluated because soft tissue injury has been associated to serious complications (see below).