Specific populations at high risk of primary PFPS include runners, bicyclists, basketball players, young athletes and females.

A rotator cuff tear can be caused by the weakening of the rotator cuff tendons. This weakening can be caused by age or how often the rotator cuff is used. Adults over the age of 60 are more susceptible to a rotator cuff tear. According to a study in the Journal of Orthopaedic Surgery and Traumatology the frequency of rotator cuff tears can increase with age. The study shows the participants that were the ages of 70–90 years old had a rate of rotator cuff tears that were 1 to 5. The participants who were 90+ years old the frequency of a rotator cuff tear jumped to 1 to 3. This study shows that with an increase in age there is also an increase in the probability of a rotator cuff tear.

The cause of snapping hip syndrome is not well understood, and confusion exists within the medical community regarding causation. Athletes appear to be at an enhanced risk for snapping hip syndrome due to repetitive and physically demanding movements.

In athletes such as ballet dancers, gymnasts, horse riders, track and field athletes and soccer players, military training, or any vigorous exerciser, repeated hip flexion leads to injury. In excessive weightlifting or running, the cause is usually attributed to extreme thickening of the tendons in the hip region. Snapping hip syndrome most often occurs in people who are 15 to 40 years old.

It is possible to prevent the onset of prepatellar bursitis, or prevent the symptoms from worsening, by avoiding trauma to the knee or frequent kneeling. Protective knee pads can also help prevent prepatellar bursitis for those whose professions require frequent kneeling and for athletes who play contact sports, such as American football, basketball, and wrestling.

Extra-articular snapping hip syndrome is commonly associated with leg length difference (usually the long side is symptomatic), tightness in the iliotibial band (ITB) on the involved side, weakness in hip abductors and external rotators, poor lumbopelvic stability and abnormal foot mechanics (overpronation). Popping occurs when the thickened posterior aspect of the ITB or the anterior gluteus maximus rubs over the greater trochanter as the hip is extended.

Identified risk factors for plantar fasciitis include excessive running, standing on hard surfaces for prolonged periods of time, high arches of the feet, the presence of a leg length inequality, and flat feet. The tendency of flat feet to excessively roll inward during walking or running makes them more susceptible to plantar fasciitis. Obesity is seen in 70% of individuals who present with plantar fasciitis and is an independent risk factor.

Studies have suggested a strong association exists between an increased body mass index and the development of plantar fasciitis in the non-athletic population; this association between weight and plantar fasciitis has not been observed in the athletic population. Achilles tendon tightness and inappropriate footwear have also been identified as significant risk factors.

While people with rotator cuff tears may not have any noticeable symptoms, studies have shown that over time 40% will have enlargement of the tear over a five-year period. Of those whose tears enlarge, 20% have no symptoms while 80% eventually develop symptoms.

There is no irrefutable evidence that rotator cuff surgery benefits patients more than non-surgical management and a percentage of patients never regain full range of motion after surgery.

Epidemiological studies strongly support a relationship between age and cuff tear prevalence. In a recent study the frequency of such tears increased from 13% in the youngest group (aged 50–59 y) to 20% (aged 60–69 y), 31% (aged 70–79 y), and 51% in the oldest group (aged 80–89 y). This high rate of tear prevalence in asymptomatic individuals suggests that rotator cuff tears could be considered a "normal" process of aging rather than a result of an apparent pathological process.

The prevalence of Achilles tendinitis fluctuates greatly among different ages and groups of people. However, Achilles tendinitis is most commonly found in individuals aged 30–40. A study was conducted in 1981 on recreational and competitive runners and what type of injury they were most likely to suffer from. Out of the 232 runners, 25 (11%) complained that their Achilles bothered them.

A study conducted in the city of Oulu found that a peak incidence of 18 injured Achilles occurred in 1994 and was highest in the male group aged 30–39. The study also found that 90% of the injuries occurred while playing a sport.

Risk factors include participating in a sport or activity that involves running, jumping, bounding, and change of speed. Although Achilles tendinitis is mainly diagnosed in runners, it does occur in basketball, volleyball, dancing, gymnastics and other athletic activities. Other risk factors include gender, age, improper stretching, overuse, and conditions which the individual may be born with. Congenital conditions occur when an individual’s legs rotate abnormally, which in turn causes the lower extremities to overstretch and contract; this puts stress on the Achilles tendon and will eventually cause Achilles tendinitis.

Plantar fasciitis is the most common type of plantar fascia injury and is the most common reason for heel pain, responsible for 80% of cases. The condition tends to occur more often in women, military recruits, older athletes, the obese, and young male athletes.

Plantar fasciitis is estimated to affect 1 in 10 people at some point during their lifetime and most commonly affects people between 40–60 years of age. In the United States alone, more than two million people receive treatment for plantar fasciitis. The cost of treating plantar fasciitis in the United States is estimated to be $284 million each year.

The various nicknames associated with prepatellar bursitis arise from the fact that it commonly occurs among those individuals whose professions require frequent kneeling, such as carpenters, carpet layers, gardeners, housemaids, mechanics, miners, plumbers, and roofers. The exact incidence of the condition is not known; it is difficult to estimate because only severe septic cases require hospital admission, and mild non-septic cases generally go unreported. Prepatellar bursitis is more common among males than females. It affects all age groups, but is more likely to be septic when it occurs in children.

The most common examples of this condition:

- Prepatellar bursitis, "housemaid's knee"

- Infrapatellar bursitis, "clergyman's knee"

- Trochanteric bursitis, giving pain over lateral aspect of hip

- Olecranon bursitis, "student's elbow", characterised by pain and swelling in the elbow

- Subacromial bursitis, giving shoulder pain, is the most common form of bursitis.

- Achilles bursitis

- Retrocalcaneal bursitis

- Ischial bursitis, "weaver's bottom"

- Iliopsoas bursitis

- Anserine bursitis

The incidence of adhesive capsulitis is approximately 3 percent in the general population. Occurrence is rare in children and people under 40 but peaks between 40 and 70 years of age. At least in its idiopathic form, the condition is much more common in women than in men (70% of patients are women aged 40–60). Frozen shoulder is more frequent in diabetic patients and is more severe and more protracted than in the non-diabetic population.

People with diabetes, stroke, lung disease, rheumatoid arthritis, or heart disease are at a higher risk for frozen shoulder. Injury or surgery to the shoulder or arm may cause blood flow damage or the capsule to tighten from reduced use during recovery. Adhesive capsulitis has been indicated as a possible adverse effect of some forms of highly active antiretroviral therapy (HAART). Cases have also been reported after breast and lung surgery.

The literature on the pathophysiology of bursitis describes inflammation as the primary cause of symptoms. Inflammatory bursitis is usually the result of repetitive injury to the bursa.

In the subacromial bursa, this generally occurs due to microtrauma to adjacent structures, particularly the supraspinatus tendon. The inflammatory process causes synovial cells to multiply, increasing collagen formation and fluid production within the bursa and reduction in the outside layer of lubrication (Ishii et al., 1997).

Less frequently observed causes of subacromial bursitis include hemorrhagic conditions, crystal deposition and infection.

Many causes have been proposed in the medical literature for subacromial impingement syndrome. The bursa facilitates the motion of the rotator cuff beneath the arch, any disturbance of the relationship of the subacromial structures can lead to impingement. These factors can be broadly classified as intrinsic such as tendon degeneration, rotator cuff muscle weakness and overuse. Extrinsic factors include bone spurs from the acromion or AC joint, shoulder instability and neurologic problems arising outside of the shoulder.

In most patients with PFPS an examination of their history will highlight a precipitating event that caused the injury. Changes in activity patterns such as excessive increases in running mileage, repetitions such as running up steps and the addition of strength exercises that affect the patellofemoral joint are commonly associated with symptom onset. Excessively worn or poorly fitted footwear may be a contributing factor. To prevent recurrence the causal behaviour should be identified and managed correctly.

The medical cause of PFPS is thought to be increased pressure on the patellofemoral joint. There are several theorized mechanisms relating to how this increased pressure occurs:

- Increased levels of physical activity

- Malalignment of the patella as it moves through the femoral groove

- Quadriceps muscle imbalance

- Tight anatomical structures, e.g. retinaculum or iliotibial band.

The cause of pain and dysfunction often results from either abnormal forces (e.g. increased pull of the lateral quadriceps retinaculum with acute or chronic lateral PF subluxation/dislocation) or prolonged repetitive compressive or shearing forces (running or jumping) on the PF joint. The result is synovial irritation and inflammation and subchondral bony changes in the distal femur or patella known as "bone bruises". Secondary causes of PF Syndrome are fractures, internal knee derangement, osteoarthritis of the knee and bony tumors in or around the knee.

There can be several concurrent causes. Trauma, auto-immune disorders, infection and iatrogenic (medicine-related) factors can all cause bursitis. Bursitis is commonly caused by repetitive movement and excessive pressure. Shoulders, elbows and knees are the most commonly affected. Inflammation of the bursae may also be caused by other inflammatory conditions such as rheumatoid arthritis, scleroderma, systemic lupus erythematosus and gout. Immune deficiencies, including HIV and diabetes, can also cause bursitis. Infrequently, scoliosis can cause bursitis of the shoulders; however, shoulder bursitis is more commonly caused by overuse of the shoulder joint and related muscles.

Traumatic injury is another cause of bursitis. The inflammation irritates because the bursa no longer fits in the original small area between the bone and the functionary muscle or tendon. When the bone increases pressure upon the bursa, bursitis results. Sometimes the cause is unknown. It can also be associated with various other chronic systemic diseases.

Training of the feet, utilizing foot gymnastics and going barefoot on varying terrain, can facilitate the formation of arches during childhood, with a developed arch occurring for most by the age of four to six years. Ligament laxity is also among the factors known to be associated with flat feet. One medical study in India with a large sample size of children who had grown up wearing shoes and others going barefoot found that the longitudinal arches of the bare-footers were generally strongest and highest as a group, and that flat feet were less common in children who had grown up wearing sandals or slippers than among those who had worn closed-toe shoes. Focusing on the influence of footwear on the prevalence of pes planus, the cross-sectional study performed on children noted that wearing shoes throughout early childhood can be detrimental to the development of a normal or a high medial longitudinal arch. The vulnerability for flat foot among shoe-wearing children increases if the child has an associated ligament laxity condition. The results of the study suggest that children be encouraged to play barefooted on various surfaces of terrain and that slippers and sandals are less harmful compared to closed-toe shoes. It appeared that closed-toe shoes greatly inhibited the development of the arch of the foot more so than slippers or sandals. This conclusion may be a result of the notion that intrinsic muscle activity of the arch is required to prevent slippers and sandals from falling off the child’s foot.

The exact cause is unclear. Proposed factors include wearing overly tight shoes, family history, and rheumatoid arthritis. Some state that footwear only worsens a problem caused by genetics.

In 1997 Morrison et al.

published a study that reviewed the cases of 616 patients (636 shoulders) with impingement syndrome (painful arc of motion) to assess the outcome of non-surgical care. An attempt was made to exclude patients who were suspected of having additional shoulder conditions such as, full-thickness tears of the rotator cuff, degenerative arthritis of the acromioclavicular joint, instability of the glenohumeral joint, or adhesive capsulitis. All patients were managed with anti-inflammatory medication and a specific, supervised physical-therapy regimen. The patients were followed up from six months to over six years. They found that 67% (413 patients) of the patients improved, while 28% did not improve and went to surgical treatment. 5% did not improve and declined further treatment.

Of the 413 patients who improved, 74 had a recurrence of symptoms during the observation period and their symptoms responded to rest or after resumption of the exercise program.

The Morrison study shows that the outcome of impingement symptoms varies with patient characteristics. Younger patients ( 20 years or less) and patients between 41 and 60 years of age, fared better than those who were in the 21 to 40 years age group. This may be related to the peak incidence of work, job requirements, sports and hobby related activities, that may place greater demands on the shoulder. However, patients who were older than sixty years of age had the "poorest results". It is known that the rotator cuff and adjacent structures undergo degenerative changes with ageing.

The authors were unable to posit an explanation for the observation of the bimodal distribution of satisfactory results with regard to age. They concluded that it was "unclear why (those) who were twenty-one to forty years old had less satisfactory results". The poorer outcome for patients over 60 years old was thought to be potentially related to "undiagnosed full-thickness tears of the rotator cuff".

Development of tendinitis depends on the type, frequency and severity of exercise or use; for example, rock climbers tend to develop tendinitis in their fingers, swimmers in their shoulders. Achilles tendinitis is a common injury, particularly in sports that involve lunging and jumping. It is also a known side effect of fluoroquinolone antibiotics such as ciprofloxacin, as are other types of tendinitis.

Swelling in a region of micro-damage or partial tear can be detected visually or by touch. Increased water content and disorganized collagen matrix in tendon lesions may be detected by ultrasonography or magnetic resonance imaging.

Achilles tendinitis is thought to have physiological, mechanical, or extrinsic (i.e. footwear or training) causes. Physiologically, the Achilles tendon is subject to poor blood supply through the synovial sheaths that surround it. This lack of blood supply can lead to the degradation of collagen fibers and inflammation. Tightness in the calf muscles has also been known to be involved in the onset of Achilles tendinitis.

During the loading phase of the running and walking cycle, the ankle and foot naturally pronate and supinate by approximately 5 degrees. Excessive pronation of the foot (over 5 degrees) in the subtalar joint is a type of mechanical mechanism that can lead to tendinitis.

An overuse injury refers to repeated stress and strain, which is likely the case in endurance runners. Overuse can simply mean an increase in running, jumping or plyometric exercise intensity too soon. Another consideration would be the use of improper or worn-down footwear, which lack the necessary support to maintain the foot in the natural/normal pronation.

Pes anserine bursitis is an inflammatory condition of the medial (inner) knee at the anserine bursa, a sub muscular bursa, just below the pes anserinus.

Flat feet can also develop as an adult ("adult acquired flatfoot") due to injury, illness, unusual or prolonged stress to the foot, faulty biomechanics, or as part of the normal aging process. This is most common in women over 40 years of age. Known risk factors include obesity, hypertension and diabetes. Flat feet can also occur in pregnant women as a result of temporary changes, due to increased elastin (elasticity) during pregnancy. However, if developed by adulthood, flat feet generally remain flat permanently.

If a youth or adult appears flatfooted while standing in a full weight bearing position, but an arch appears when the person plantarflexes, or pulls the toes back with the rest of the foot flat on the floor, this condition is called flexible flatfoot. This is not a true collapsed arch, as the medial longitudinal arch is still present and the windlass mechanism still operates; this presentation is actually due to excessive pronation of the foot (rolling inwards), although the term 'flat foot' is still applicable as it is a somewhat generic term. Muscular training of the feet is helpful and will often result in increased arch height regardless of age.

The pes anserinus is the insertion of the conjoined tendons sartorius, gracilis, and semitendinosus into the anteromedial proximal tibia. Theoretically, bursitis results from stress to this area (e.g. stress may result when an obese individual with anatomic deformity from arthritis ascends or descends stairs). An occurrence of pes anserine bursitis commonly is characterized by pain, especially when climbing stairs, tenderness, and local swelling.

Causes of the swelling can include arthritis, injury to the ligaments of the knee, or an accident after which the body's natural reaction is to surround the knee with a protective fluid. There could also be an underlying disease or condition. The type of fluid that accumulates around the knee depends on the underlying disease, condition or type of traumatic injury that caused the excess fluid. The swelling can, in most cases, be easily cured.

Underlying diseases may include

- Knee osteoarthritis

- Rheumatoid arthritis

- Infection

- Gout

- Pseudogout

- Prepatellar bursitis (kneecap bursitis)

- Cysts

- Tumours

- Repetitive strain injury

Having osteoarthritis or engaging in high-risk sports that involve rapid cut-and-run movements of the knee — football or tennis, for example — means an individual is more likely to develop water on the knee.

In overweight or obese individuals the body places more weight on the knee joint. This causes more wear in the joint. Over time, the body may produce excess joint fluid.

Bursitis normally develops as a result either of a single injury to the elbow (for example, a hard blow to the tip of the elbow), or perhaps more commonly due to repeated minor injuries, such as repeated leaning on the point of the elbow on a hard surface. The chance of developing bursitis is higher if one's job or hobby involves a repetitive movement (for example, tennis, golf, or even repetitive computer work involving leaning on one's elbow). The likelihood of developing the condition is increased as one gets older.

As a reaction to injury, the lining of the bursa becomes inflamed. It then secretes a much greater than normal amount of fluid into the closed cavity of the bursa, from where it has nowhere to go. The bursa therefore inflates, producing a swelling over the proximal end of the ulna which is usually inflamed and tender.

Another possible cause of inflammation of the bursa is infection, which can usually (but not always) be traced to a crack or other lesion in the skin which allowed for bacteria of the normal skin flora to invade deeper layers of tissue.

Because wear on the hip joint traces to the structures that support it (the posture of the legs, and ultimately, the feet), proper fitting shoes with adequate support are important to preventing GTPS. For someone who has flat feet, wearing proper orthotic inserts and replacing them as often as recommended are also important preventive measures.

Strength in the core and legs is also important to posture, so physical training also helps to prevent GTPS. But it is equally important to avoid exercises that damage the hip.