HME can cause pain to people of all ages. To children, this can be especially painful. During exercise, it can cause a significant amount of pain. Exostoses may be visible to naked eye from outside. Multiple deformities, as mentioned above, can be present. The Exotoses appear to slow their rate of growth when they reach a certain, variable mass.

"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

It is characterized by the growth of cartilage-capped benign bone tumours around areas of active bone growth, particularly the metaphysis of the long bones. Typically five or six exostoses are found in upper and lower limbs. Most common locations are:

- Distal femur (70%)

- Proximal tibia (70%)

- Humerus (50%)

- Proximal fibula (30%)

HME can lead to the shortening and bowing of bones; affected individuals often have a short stature. Depending on their location the exostoses can cause the following problems: pain or numbness from nerve compression, vascular compromise, inequality of limb length, irritation of tendon and muscle, Madelung's deformity as well as a limited range of motion at the joints upon which they encroach. A person with HME has an increased risk of developing a rare form of bone cancer called chondrosarcoma as an adult. Problems may be had in later life and these could include weak bones and nerve damage. The reported rate of transformation ranges from as low as 0.57% to as high as 8.3% of people with HME.

An exostosis (plural: exostoses) is the formation of new bone on the surface of a bone. Exostoses can cause chronic pain ranging from mild to debilitatingly severe, depending on the shape, size, and location of the lesion. It is most commonly found in places like the ribs, where small bone growths form, but sometimes larger growths can grow on places like the ankles, knees, shoulders, elbows and hips. Very rarely are they on the skull.

They normally form on the bones of joints, and can grow upwards. For example, if an extra bone formed on the ankle, it might grow up to the shin.

Osteophytes are bone spurs that develop on the margins of joints secondary to external stimuli such as osteoarthritis. However, these are not always distinguished from exostoses in any definite way.

When used in the phrases "cartilaginous exostosis" or "osteocartilaginous exostosis", the term is considered synonymous with osteochondroma. Some sources consider the two terms to mean the same thing even without qualifiers, but this interpretation is not universal.

Osteochondromatosis is a condition involving a proliferation of osteochondromas.

Types include:

- Hereditary multiple exostoses

- Synovial osteochondromatosis

Osteochondromas or osteocartilaginous exostoses are the most common benign tumors of the bones.

The tumors take the form of cartilage-capped bony projections or outgrowth on the surface of bones (exostoses). It is characterized as a type of overgrowth that can occur in any bone where cartilage forms bone. Tumors most commonly affect long bones in the leg, pelvis, or scapula (shoulder blade). Development of osteochondromas take place during skeletal growth between the ages of 13 and 15 and ceases when the growth plate fuses at puberty. They arise within the first three decades of life affecting children and adolescents.

Osteochondromas occur in 3% of the general population and represent 35% of all benign tumors and 8% of all bone tumors. Majority of these tumors are solitary non-hereditary lesions and approximately 15% of osteochondromas occur as hereditary multiple osteochondromas (HMOs). They can occur as a solitary lesion (solitary osteochondroma) or multiple lesions within the context of the same bone (Multiple Osteochondroma). Osteochondromas do not result from injury and the exact cause remains unknown. Recent research has indicated that multiple osteochondromas is an autosomal dominant inherited disease. Germ line Mutations in "EXT1" and "EXT2" genes located on chromosomes 8 and 11 have been associated with the cause of the disease.

The treatment choice for osteochondroma is surgical removal of solitary lesion or partial excision of the outgrowth, when symptoms cause motion limitations or nerve and blood vessel impingements.

Limited normal functions and movements are caused by osteochondromas growing slowly and inwardly. The majority of osteochondromas are symptomless and are found incidentally. Each individual with osteochondroma may experience symptoms differently and most of the time individuals will experience no symptoms at all. Some of the most common symptoms are a hard immobile painless palpable mass, adjacent muscle soreness, and pressure or irritation with heavy exercising.

Major symptoms arise when complications such as fractures, bone deformity or mechanical joint problems occur. If the occurrence of an osteochondroma is near a nerve or a blood vessel, the affected limb can experience numbness, weakness, loss of pulse or color change. Periodic changes in the blood flow can also take place. Approximately 20% of patients experiencing nerve compression commonly acknowledge vascular compression, arterial thrombosis, aneurysm, and pseudoaneurysm. Formation of pseudoaneurysm and venous thrombosis lead to claudication, pain, acute ischemia, and symptoms of phlebitis. If the tumor is found under a tendon, it can cause pain during movement causing restriction of joint motion. Pain can also occur due to bursal inflammation, swelling or fracture at the base of the tumor stalk. Some of the clinical signs and symptoms of malignant osteochondroma are pain, swelling, and mass enlargement.

Autosomal recessive multiple epiphyseal dysplasia (ARMED), also called epiphyseal dysplasia, multiple, 4 (EDM4), multiple epiphyseal dysplasia with clubfoot or –with bilayered patellae, is an autosomal recessive congenital disorder affecting cartilage and bone development. The disorder has relatively mild signs and symptoms, including joint pain, scoliosis, and malformations of the hands, feet, and knees.

Some affected individuals are born with an inward- and downward-turning foot (a clubfoot). An abnormality of the kneecap called a double-layered patella is also relatively common. Although some people with recessive multiple epiphyseal dysplasia have short stature as adults, most are of normal height. The incidence is unknown as many cases are not diagnosed due to mild symptoms.

Formation on the lower jaw occurs much less commonly than on the upper jaw. They are painless and have no risk of turning into cancer, although they may slowly expand over years, or sometimes more rapidly.

Evidence for exostosis found in the fossil record is studied by paleopathologists, specialists in ancient disease and injury. Exostosis has been reported in dinosaur fossils from several species, including "Acrocanthosaurus atokensis", "Albertosaurus sarcophagus", "Allosaurus fragilis", "Gorgosaurus libratus", and "Poekilopleuron bucklandii".

Buccal exostoses are considered different entities to osteomas (e.g. seen in Gardner syndrome), even though the two lesions are histopathologically identical.

Maffucci syndrome is a sporadic disease characterized by the presence of multiple enchondromas associated with multiple hemangiomas. Also lymphangiomas may be apparent.

An osteolytic lesion (from the Greek words for "bone" (ὀστέον), and "to unbind" (λύειν)) is a softened section of a patient's bone formed as a symptom of specific diseases, including breast cancer and multiple myeloma. This softened area appears as a hole on X-ray scans due to decreased bone density. Osteolytic lesions can cause pain, increased risk of bone fracture, and spinal chord compression. These lesions can be treated using biophosphonates or radiation, though new solutions are being tested in clinical trials.

Synostosis (plural: synostoses) is fusion of two bones. It can be normal in puberty, fusion of the epiphysis, or abnormal. When synostosis is abnormal it is a type of dysostosis.

Examples of synostoses include:

- craniosynostosis – an abnormal fusion of two or more cranial bones;

- radioulnar synostosis – the abnormal fusion of the radius and ulna bones of the forearm;

- tarsal coalition – a failure to separately form all seven bones of the tarsus (the hind part of the foot) resulting in an amalgamation of two bones; and

- syndactyly – the abnormal fusion of neighboring digits.

Synostosis within joints can cause ankylosis.

Patients are normal at birth and the syndrome manifests during childhood and puberty. The enchondromas affect the extremities and their distribution is asymmetrical. The most common sites of enchondromas are the metacarpal bones and phalanges of the hands. The feet are less commonly afflicted.

Disfigurations of the extremities are a result. Pathological fractures can arise in affected metaphyses and diaphyses of the long bones and are common (26%).

The risk for sarcomatous degeneration of enchondromas, hemangiomas, or lymphangiomas is 15-30% in the setting of Maffucci syndrome. Maffucci syndrome is associated with a higher risk of CNS, pancreatic, and ovarian malignancies. Multiple enchondromas may present in 3 disorders: Ollier disease, Maffucci syndrome, and metachondromatosis. It is important to make the distinction between these diseases, particularly Ollier disease and Maffucci syndrome. Ollier disease is more common than Maffucci syndrome, and presents with multiple enchondromas often in a unilateral distribution. However, hemangiomas and lymphangiomas are not seen in Ollier disease. Metachondromatosis demonstrates autosomal-dominant transmission and presents with both multiple osteochondromas and enchondromas.

Multiple familial trichoepithelioma (also known as Brooke–Spiegler syndrome and epithelioma adenoides cysticum) is a cutaneous condition characterized by multiple cystic and solid nodules appearing on the face.

Osteophytes form because of the increase in a damaged joint's surface area. This is most common from the onset of arthritis. Osteophytes usually limit joint movement and typically cause pain.

Osteophytes form naturally on the back of the spine as a person ages and are a sign of degeneration in the spine. In this case, the spurs are not the source of back pains, but instead are the common symptom of a deeper problem. However, bone spurs on the spine can impinge on nerves that leave the spine for other parts of the body. This impingement can cause pain in both upper and lower limbs and a numbness or tingling sensations in the hands and feet because the nerves are supplying sensation to their dermatomes.

Spurs can also appear on the feet, either along toes or the heel, as well as on the hands. In extreme cases, bone spurs have grown along a person's entire skeletal structure: along the knees, hips, shoulders, ribs, arms and ankles. Such cases are only exhibited with multiple exostoses.

Osteophytes on the fingers or toes are known as Heberden's nodes (if on the distal interphalangeal joint) or Bouchard's nodes (if on the proximal interphalangeal joints).

Osteophytes may also be the end result of certain disease processes. Osteomyelitis, a bone infection, may leave the adjacent bone with a spur formation. Charcot foot, the neuropathic breakdown of the feet seen primarily in diabetics, can also leave bone spurs that may then become symptomatic.

Some or all of the following may be seen in someone with Gorlin syndrome:

1. Multiple basal-cell carcinomas of the skin

2. Keratocystic odontogenic tumor: Seen in 75% of patients and is the most common finding. There are usually multiple lesions found in the mandible. They occur at a young age (19 yrs average).

3. Rib and vertebrae anomalies

4. Intracranial calcification

5. Skeletal abnormalities: bifid ribs, kyphoscoliosis, early calcification of falx cerebri (diagnosed with AP radiograph)

6. Distinct faces: frontal and temporoparietal bossing, hypertelorism, and mandibular prognathism

7. Bilateral ovarian fibromas

8. 10% develop cardiac fibromas

The skeletal structures of individuals who have this disorder may have pronounced deformities. As reported by several medical doctors, the following features are commonly found in people who suffer from nail–patella syndrome:

Bones and joints

- Patellar involvement is present in approximately 90% of patients; however, patellar aplasia occurs in only 20%.

- In instances in which the patellae are smaller or luxated, the knees may be unstable.

- The elbows may have limited motion (e.g., limited pronation, supination, extension).

- Subluxation of the radial head may occur.

- Arthrodysplasia of the elbows is reported in approximately 90% of patients.

- General hyperextension of the joints can be present.

- Exostoses arising from the posterior aspect of the iliac bones ("iliac horns") are present in as many as 80% of patients; this finding is considered pathognomonic for the syndrome.

- Other reported bone changes include scoliosis, scapular hypoplasia, and the presence of cervical ribs.

Kidney issues may arise such as proteinuria and nephritis. Proteinuria is usually the first sign of renal involvement and either rapidly or years after suffering from asymptomatic proteinuria, renal failure occurs in around 5% of NPS patients. Hypothyroidism, irritable bowel syndrome, attention deficit hyperactivity disorder (ADHD), and thin tooth enamel are associated with NPS, but whether these are related or simply coincidences are unclear.

Osteophytes, commonly referred to as bone spurs are bony projections that form along joint margins. They should not be confused with enthesophytes, which are bony projections that form at the attachment of a tendon or ligament. Osteophytes are not always distinguished from exostoses in any definite way, although in many cases there are a number of differences. Osteophytes are typically intra-articular (within the joint capsule).

When a patient has multiple abnormalities (multiple anomaly, multiple deformity), they have a congenital abnormality that can not be primarily identified with a single system of the body or single disease process. Most medical conditions can have systemic sequelae, but multiple abnormalities occur when the effects on multiple systems is immediately obvious.

Radioulnar synostosis is one of the more common failures of separation of parts of the upper limb. There are two general types: one is characterized by fusion of the radius and ulna at their proximal borders and the other is fused distal to the proximal radial epiphysis. Most cases are sporadic, congenital (due to a defect in longitudinal segmentation at the 7th week of development) and less often post-traumatic, bilateral in 60%, and more common in males. Familial cases in association with autosomal dominant transmission appear to be concentrated in certain geographic regions, such as Sicily.

The condition frequently is not noted until late childhood, as function may be normal, especially in unilateral cases. Increased wrist motion may compensate for the absent forearm motion. It has been suggested that individuals whose forearms are fixed in greater amounts of pronation (over 60 degrees) face more problems with function than those with around 20 degrees of fixation. Pain is generally not a problem, unless radial head dislocation should occur.

Most examples of radioulnar synostosis are isolated (non-syndromic). Syndromes that may be accompanied by radioulnar synostosis include X chromosome polyploidy (e.g., XXXY) and other chromosome disorders (e.g., 4p- syndrome, Williams syndrome), acrofacial dysostosis, Antley–Bixler syndrome, genitopatellar syndrome, Greig cephalopolysyndactyly syndrome, hereditary multiple osteochondromas (hereditary multiple exostoses), limb-body wall complex, and Nievergelt syndrome.

Craniosynostosis (from cranio, cranium; + syn, together; + ostosis relating to bone) is a condition in which one or more of the fibrous sutures in an infant skull prematurely fuses by turning into bone (ossification). Craniosynostosis has following kinds: scaphocephaly, trigonocephaly, plagiocephaly, anterior plagiocephaly, posterior plagiocephaly, brachycephaly, oxycephaly, pansynostosis.

Subungual exostoses are bony projections which arise from the dorsal surface of the distal phalanx, most commonly of the hallux.

The classification of this syndrome is difficult. Three conditions are known to be caused by mutations in the" CYLD" gene: Brooke-Spiegler syndrome, multiple familial trichoepithelioma, and familial cylindromatosis. Clinically, these are distinct, but appear to arise from mutations in the same gene.

Types include: