Despite much research, the causes remain unclear but include repetitive physical trauma, ischemia (restriction of blood flow), hereditary and endocrine factors, avascular necrosis (loss of blood flow), rapid growth, deficiencies and imbalances in the ratio of calcium to phosphorus, and problems of bone formation. Although the name "osteochondritis" implies inflammation, the lack of inflammatory cells in histological examination suggests a non-inflammatory cause. It is thought that repetitive microtrauma, which leads to microfractures and sometimes an interruption of blood supply to the subchondral bone, may cause subsequent localized loss of blood supply or alteration of growth.

Trauma, rather than avascular necrosis, is thought to cause osteochondritis dissecans in juveniles. In adults, trauma is thought to be the main or perhaps the sole cause, and may be endogenous, exogenous or both. The incidence of repetitive strain injury in young athletes is on the rise and accounts for a significant number of visits to primary care; this reinforces the theory that OCD may be associated with increased participation in sports and subsequent trauma. High-impact sports such as gymnastics, soccer, basketball, lacrosse, football, tennis, squash, baseball and weight lifting may put participants at a higher risk of OCD in stressed joints (knees, ankles and elbows).

Recent case reports suggest that some people may be genetically predisposed to OCD. Families with OCD may have mutations in the aggrecan gene. Studies in horses have implicated specific genetic defects.

OCD is a relatively rare disorder, with an estimated incidence of 15 to 30 cases per 100,000 persons per year. Widuchowski W "et al." found OCD to be the cause of articular cartilage defects in 2% of cases in a study of 25,124 knee arthroscopies. Although rare, OCD is noted as an important cause of joint pain in active adolescents. The juvenile form of the disease occurs in children with open growth plates, usually between the ages 5 and 15 years and occurs more commonly in males than females, with a ratio between 2:1 and 3:1. However, OCD has become more common among adolescent females as they become more active in sports. The adult form, which occurs in those who have reached skeletal maturity, is most commonly found in people 16 to 50 years old.

While OCD may affect any joint, the knee—specifically the medial femoral condyle in 75–85% of knee cases—tends to be the most commonly affected, and constitutes 75% of all cases. The elbow (specifically the capitulum of the humerus) is the second most affected joint with 6% of cases; the talar dome of the ankle represents 4% of cases. Less frequent locations include the patella, vertebrae, the femoral head, and the glenoid of the scapula.

Hip dysplasia may be caused by a femur that does not fit correctly into the pelvic socket, or poorly developed muscles in the pelvic area. Large and giant breeds are most susceptible to hip dysplasia (possibly due to the body mass index (BMI) of the individual animal, though, many other breeds can suffer from it. The Orthopedic Foundation for Animals maintains a list of top 100 breeds affected.

To reduce pain, the animal will typically reduce its movement of that hip. This may be visible as "bunny hopping", where both legs move together, or less dynamic movement (running, jumping), or stiffness. Since the hip cannot move fully, the body compensates by adapting its use of the spine, often causing spinal, stifle (a dog's knee joint), or soft tissue problems to arise.

The causes of hip dysplasia are considered heritable, but new research conclusively suggests that environment also plays a role. To what degree the causality is genetic and what portion environmental is a topic of current debate. Neutering a dog, especially before the dog has reached an age of full developmental maturity, has been proven to almost double the chance he or she will develop hip dysplasia versus intact dogs or dogs that were neutered after reaching adulthood Other environmental influences include overweight condition, injury at a young age, overexertion on the hip joint at a young age, ligament tear at a young age, repetitive motion on forming joint (i.e. jogging with puppy under the age of 1 year). As current studies progress, greater information may help provide procedures to effectively reduce the occurrence of this condition.

The problem almost always appears by the time the dog is 18 months old. The defect can be anywhere from mild to severely crippling, and can eventually cause severe osteoarthritis.

It is most common in medium-large pure bred dogs, such as Newfoundlands, German Shepherd Dogs, retrievers (such as Labradors, Tollers, or Goldens), rottweilers and Mastiff, but also occurs in some smaller breeds such as spaniels and pugs.

About 25% of people over the age of 50 experience knee pain from degenerative knee diseases.

Osteochondritis is a painful type of osteochondrosis where the cartilage or bone in a joint is inflamed.

It often refers to osteochondritis dissecans (sometimes spelt "dessecans", and abbreviated OCD). The term "dissecans" refers to the "creation of a flap of cartilage that further dissects away from its underlying subchondral attachments (dissecans)".

The other recognized types of osteochondritis are osteochondritis deformans juvenilis (osteochondritis of the capitular head of the epiphysis of the femur) and osteochondritis deformans juvenilis dorsi (osteochondrosis of the spinal vertebrae, also known as Scheuermann's disease).

Osteochondritis, and especially osteochondritis dissecans, can manifest in animals as a primary cause of elbow dysplasia, a chronic condition in some species and breeds.

In the United States, more than US $3 billion is spent each year on arthroscopic knee surgeries that are known to be ineffective in people with degenerative knee pain.

Elbow Dysplasia is a significant genetically determined problem in many breeds of dog, often manifesting from puppyhood and continuing for life. In elbow dysplasia, the complex elbow joint suffers from a structural defect, often related to its cartilage. This initial condition, known as a "primary lesion", causes an abnormal level of wear and tear and gradual degradation of the joint, at times disabling or with chronic pain. Secondary processes such as inflammation and osteoarthritis can arise from this damage which increase the problem and add further problems of their own.

The ultimate cause for these conditions is unknown, but the most commonly cited cause factors are rapid growth, heredity, trauma (or overuse), anatomic conformation, and dietary imbalances; however, only anatomic conformation and heredity are well supported by scientific literature. The way that the disease is initiated has been debated. Although failure of chondrocyte differentiation, formation of a fragile cartilage, failure of blood supply to the growth cartilage, and bone necrosis all have been proposed as the starting point in the pathogenesis, recent literature strongly supports failure of blood supply to growth cartilage as most likely.

Children younger than 6 have the best prognosis, since they have time for the dead bone to revascularize and remodel, with a good chance that the femoral head will recover and remain spherical after resolution of the disease. Children who have been diagnosed with Perthes' disease after the age of 10 are at a very high risk of developing osteoarthritis and coxa magna. When an LCP disease diagnosis occurs after age 8, a better outcome results with surgery rather than nonoperative treatments. Shape of femoral head at the time when Legg-Calve Perthes disease heals is the most important determinant of risk for degenerative arthritis; hence, the shape of femoral head and congruence of hip are most useful outcome measures.

The most common cause is osteochondrosis, which is a disease of the joint cartilage, and specifically Osteochondritis dissecans (OCD or OD), the separation of a flap of cartilage from the joint surface as a result of avascular necrosis, which in turn arises from failed blood flow in the subchondral bone. Other common causes of elbow dysplasia included ununited anconeal process (UAP) and fractured or ununited medial coronoid process (FCP or FMCP).

In OCD, the normal change of cartilage to bone in the development of the joint fails or is delayed. The cartilage continues to grow and may split or become necrotic. The cause is uncertain, but possibly includes genetics, trauma, and nutrition (including excessive calcium and decreased Vitamin C intake). OCD lesions are found in the elbow at the medial epicondyle of the humerus. Specific conditions related to OCD include fragmentation of the medial coronoid process of the ulna (FMCP) and an ununited anconeal process of the ulna (UAP). All types of OCD of the elbow are most typically found in large breed dogs, with symptoms starting between the ages of 4 to 8 months. Males are affected twice as often as females. The disease often affects both elbows (30 to 70 percent of the time), and symptoms include intermittent lameness, joint swelling, and external rotation and abduction of the paw. Osteoarthritis will develop later in most cases.

UAP is caused by a separation from the ulna of the ossification center of the anconeal process. FMCP is caused by a failure of the coronoid process to unite with the ulna. OCD of the medial epicondyle of the humerus is caused by disturbed endochondral fusion of the epiphysis of the medial epicondyle with the distal end of the humerus, which may in turn be caused by avulsion of the epiphysis.

Perthes' disease is one of the most common hip disorders in young children, occurring in roughly 5.5 of 100,000 children per year. The lifetime risk of a child developing the disease is about one per 1,200 individuals. Boys are affected about three to five times more often than girls. New cases of Perthes' disease rarely occur after age 14 years (if diagnosed after 14 years of age, then it is usually old disease from early in childhood or avascular necrosis from an alternative cause).

White northern Europeans appear to be affected more frequently than other races, though a paucity of reliable epidemiology exists in the Southern Hemisphere. Children of sufferers of the disease themselves may have a very slightly increased risk, though it is unclear if this is because of a genetic predisposition, or a shared environmental factor. It is most commonly seen in persons aged three to 12 years, with a median of six years of age. The UK incidence rates show an intriguing pattern with low incidence rates in London, and a progressive increase in disease in more northerly areas (maximal in Scotland). Some evidence suggests, at least in developed countries, more socioeconomically deprived communities have a greater risk of disease (a similar trend to diseases such as adult heart disease), though the reason for this remains unknown. One possible explanation that has been considered is tobacco smoke exposure, though this is significantly confounded by the strong socioeconomic gradient common to both smoking and Perthes' disease. Dietary factors of the child, and of the mother during pregnancy, are of interest to the research groups.

In dogs, hip dysplasia is an abnormal formation of the hip socket that, in its more severe form, can eventually cause crippling lameness and painful arthritis of the joints. It is a genetic (polygenic) trait that is affected by environmental factors. It is common in many dog breeds, particularly the larger breeds, and is the most common single cause of arthritis of the hips.

Being an extremely rare disease, it is unknown as to what exactly causes Panner Disease. It is believed that the disease may be brought on by continuous overuse of the elbow and that puts pressure on the elbow and also strains the elbow in children during the period of rapid bone growth. The overuse of the elbow can be due to the involvement in sports such as baseball, handball, and gymnastics where these sports involve throwing or putting a lot of pressure on the joints. These repeated activities cause microtraumas and results in the affected elbow being swollen, irritated, and in pain. Panner Disease results when the blood supply to the capitellum is disrupted and therefore the cells within the growth plate of the capitellum die and it becomes flat due to the softening and collapsing of the surrounding bone. To prevent future instances of Panner Disease the child is instructed to cease all physical and sports activities that involve the use of the affected elbow until the symptoms are relieved.

Panner Disease affects the elbow of the arm. At the elbow, the humerus meets the ulna and the radius. The humerus is the long bone that runs from the shoulder to the elbow, and the ulna and radius are the two bones that make up the forearm. The capitellum is the rounded knob on the end of the humerus and it is held by the radius due the radius’s cup-like shape. Panner Disease is part of a family of bone development diseases known as osteochondrosis. In osteochondrosis, the blood supply to an area of developing bone in the dominant elbow is temporarily disrupted by something that is not yet well understood. Therefore, the tissues in the bone are not getting enough blood and they begin to go through necrosis, and they begin to die. Normally, bones grow by the expansion and uniting of the growth plates, but osteochondrosis disrupts this process and the result is cell death and the loss of newly formed tissue. The death of the tissues eventually leads to deterioration of the bone’s growth plate. The bone’s growth plate is defined as the area at the end of a developing bone where cartilage cells change into bone cells. The bone tissue does regrow, but the necrosis can cause temporary problems in the affected area until the strenuous arm and elbow activity is significantly decreased or stopped for a period of time.

It is believed that Panner Disease is a precursor to a similar condition called osteochondritis dissecans of the capitellum (OCD). OCD is different from Panner disease because OCD occurs in older children and it does not involve the growth plate because by the time that OCD occurs the growth plates have already fused and the skeleton has finished growing.

Osteochondrosis is a family of orthopedic diseases of the joint that occur in children and adolescents and in rapidly growing animals, particularly pigs, horses, dogs, and broiler chickens. They are characterized by interruption of the blood supply of a bone, in particular to the epiphysis, followed by localized bony necrosis, and later, regrowth of the bone. This disorder is defined as a focal disturbance of endochondral ossification and is regarded as having a multifactorial cause, so no one thing accounts for all aspects of this disease.

A detailed history is the first step of a lameness exam.

1. Age: Foals are more likely to have infectious causes of lameness (septic arthritis). Horses just starting training may be lame due to a developmental orthopedic disease, such as osteochondrosis. Older animals are more likely to experience osteoarthritis.

2. Breed: Breed-specific diseases, such as HYPP, can be ruled out. Additionally, some breeds or types are more prone to certain types of lameness.

3. Discipline: Certain lamenesses are associated with certain uses. For example, racehorses are more likely to have fatigue-related injuries such as stress fractures and injury to the flexor tendons, while western show horses are more likely to suffer from navicular syndrome and English sport horses are more likely to have osteoarthritis or injury to the suspensory ligament.

4. Past history of lameness: An old injury may be re-injured. In the case of progressive disease, such as osteoarthritis, a horse will often experience recurrent lameness that must be managed. Shifting lameness may suggest a bilateral injury or infectious cause of lameness.

5. Duration and progression the lameness: Acute injury is more common with soft tissue injury. Chronic, progressive disease is more common in cases such as osteoarthritis and navicular disease.

6. Recent changes in management: such as turn-out, exercise level, diet, or shoeing.

7. Effect of exercise on degree of lameness.

8. Any treatment implemented, including rest.

Lameness is an abnormal gait or stance of an animal that is the result of dysfunction of the locomotor system. In the horse, it is most commonly caused by pain, but can be due to neurologic or mechanical dysfunction. Lameness is a common veterinary problem in racehorses, sport horses, and pleasure horses. It is one of the most costly health problems for the equine industry, both monetarily for the cost of diagnosis and treatment, and for the cost of time off resulting in loss-of-use.

Morton's neuroma (also known as Morton neuroma, Morton's metatarsalgia, Intermetatarsal neuroma and Intermetatarsal space neuroma.) is a benign neuroma of an intermetatarsal plantar nerve, most commonly of the second and third intermetatarsal spaces (between 2nd−3rd and 3rd−4th metatarsal heads), which results in the entrapment of the affected nerve. The main symptoms are pain and/or numbness, sometimes relieved by removing narrow or high-heeled footwear. Sometimes symptoms are relieved by wearing non-constricting footwear.

Some sources claim that entrapment of the plantar nerve because of compression between the metatarsal heads, as originally proposed by Morton, is highly unlikely, because the plantar nerve is on the plantar side of the transverse metatarsal ligament and thus does not come in contact with the metatarsal heads. It is more likely that the transverse metatarsal ligament is the cause of the entrapment.

Despite the name, the condition was first correctly described by a chiropodist named Durlacher, and although it is labeled a "neuroma", many sources do not consider it a true tumor, but rather a perineural fibroma (fibrous tissue formation around nerve tissue).

Chondritis is inflammation of cartilage.

It takes several forms, osteochondritis, costochondritis, Relapsing polychondritis among them. Costochondritis is notable for feeling like a heart attack.

Negative signs include no obvious deformities, erythema, signs of inflammation, or limitation of movement. Direct pressure between the metatarsal heads will replicate the symptoms, as will compression of the forefoot between the finger and thumb so as to compress the transverse arch of the foot. This is referred to as Mulder’s Sign.

There are other causes of pain in the forefoot. Too often all forefoot pain is categorized as neuroma. Other conditions to consider are capsulitis, which is an inflammation of ligaments that surrounds two bones, at the level of the joint. In this case, it would be the ligaments that attach the phalanx (bone of the toe) to the metatarsal bone. Inflammation from this condition will put pressure on an otherwise healthy nerve and give neuroma-type symptoms. Additionally, an intermetatarsal bursitis between the third and fourth metatarsal bones will also give neuroma-type symptoms because it too puts pressure on the nerve. Freiberg's disease, which is an osteochondritis of the metatarsal head, causes pain on weight bearing or compression.