The onset of the condition is usually gradual, although some cases may appear suddenly following trauma.

- Knee pain - the most common symptom is diffuse peripatellar pain (vague pain around the kneecap) and localized retropatellar pain (pain focused behind the kneecap). Affected individuals typically have difficulty describing the location of the pain, and may place their hands over the anterior patella or describe a circle around the patella (the "circle sign"). Pain is usually initiated when load is put on the knee extensor mechanism, e.g. ascending or descending stairs or slopes, squatting, kneeling, cycling, running or prolonged sitting with flexed (bent) knees. The latter feature is sometimes termed the "movie sign" or "theatre sign" because individuals might experience pain while sitting to watch a film or similar activity. The pain is typically aching with occasional sharp pains.

- Crepitus (joint noises) may be present

- Giving-way of the knee may be reported

Chondromalacia patellae is a term sometimes treated synonymously with PFPS. However, there is general consensus that PFPS applies only to individuals without cartilage damage, thereby distinguishing it from chondromalacia patellae, a condition characterized by softening of the patellar articular cartilage. Despite this academic distinction, the diagnosis of PFPS is typically made clinically, based only on the history and physical examination rather than on the results of any medical imaging. Therefore, it is unknown whether most persons with a diagnosis of PFPS have cartilage damage or not, making the difference between PFPS and chondromalacia theoretical rather than practical. It is thought that only some individuals with anterior knee pain will have true chondromalacia patellae.

The primary symptom of prepatellar bursitis is the swelling of the area around the kneecap. It generally does not produce a significant amount of pain unless pressure is applied directly to the swelling. The area of swelling may be red (erythema), warm to the touch, or surrounded by cellulitis, particularly if the area has become infected. In such cases, the bursitis is often accompanied by fever. Unlike arthritis, prepatellar bursitis generally does not affect the range of motion of the knee, though it may cause some discomfort when the knee is completely flexed. Flexion and extension of the knee may cause crepitus.

When the knee joint contains excess fluid, it may become difficult or painful to bend or straighten. Fluid may also show under the knee when straightened. Icing may help to decrease swelling. Heat may help relax the muscles of the knee.

One knee may appear larger than the other. Puffiness around the bony parts of the knee appear prominent when compared with the other knee.

Juvenile rheumatoid arthritis presents gradually with early morning stiffness, fatigue, and weight loss.

Osgood–Schlatter disease causes pain in the front lower part of the knee. This is usually at the ligament-bone junction of the patellar ligament and the tibial tuberosity. The tibial tuberosity is a slight elevation of bone on the anterior and proximal portion of the tibia. The patellar tendon attaches the anterior quadriceps muscles to the tibia via the knee cap.

Intense knee pain is usually the presenting symptom that occurs during activities such as running, jumping, squatting, and especially ascending or descending stairs and during kneeling. The pain is worse with acute knee impact. The pain can be reproduced by extending the knee against resistance, stressing the quadriceps, or striking the knee. Pain is initially mild and intermittent. In the acute phase, the pain is severe and continuous in nature. Impact of the affected area can be very painful. Bilateral symptoms are observed in 20–30% of people.

Knee pain is pain in or around the knee.

The knee joint consists of an articulation between four bones: the femur, tibia, fibula and patella. There are four compartments to the knee. These are the medial and lateral tibiofemoral compartments, the patellofemoral compartment and the superior tibiofibular joint. The components of each of these compartments can suffer from repetitive strain, injury or disease.

Running long distance can cause pain to the knee joint, as it is high-impact exercise.

Jumper's knee (patellar tendinopathy, patellar tendinosis, patellar tendinitis) commonly occurs in athletes who are involved in jumping sports such as basketball and volleyball. Patients report anterior knee pain, often with an aching quality. The symptom onset is insidious. Rarely is a discrete injury described. Usually, involvement is infrapatellar at or near the infrapatellar pole, but it may also be suprapatellar.

Depending on the duration of symptoms, jumper's knee can be classified into 1 of 4 stages, as follows:

Stage 1 – Pain only after activity, without functional impairment

Stage 2 – Pain during and after activity, although the patient is still able to perform satisfactorily in his or her sport

Stage 3 – Prolonged pain during and after activity, with increasing difficulty in performing at a satisfactory level

Stage 4 – Complete tendon tear requiring surgical repair

It begins as inflammation in the patellar tendon where it attaches to the patella and may progress by tearing or degenerating the tendon. Patients present with an ache over the patella tendon. Most patients are between 10 and 16 years old. Magnetic resonance imaging can reveal edema (increased T2 signal intensity) in the proximal aspect of the patellar tendon.

Osgood–Schlatter disease (OSD), also known as apophysitis of the tibial tubercle, is inflammation of the patellar ligament at the tibial tuberosity. It is characterized by a painful bump just below the knee that is worse with activity and better with rest. Episodes of pain typically last a few months. One or both knees may be affected and flares may recur.

Risk factors include overuse, especially sports which involve running or jumping. The underlying mechanism is repeated tension on the growth plate of the upper tibia. Diagnosis is typically based on the symptoms. A plain X-ray may be either normal or show fragmentation in the attachment area.

Pain typically resolves with time. Applying cold to the affected area, stretching, and strengthening exercises may help. NSAIDs such as ibuprofen may be used. Slightly less stressful activity may be recommended.

About 4% of people are affected at some point in time. Males between the ages of 10 and 15 are most often affected. After growth slows, typically age 16 in boys and 14 in girls, the pain will no longer occur despite a bump potentially remaining. The condition is named after Robert Bayley Osgood (1873–1956), an American orthopedic surgeon and Carl B. Schlatter, (1864–1934), a Swiss surgeon who described the condition independently in 1903.

In some cases, an audible snapping or popping noise as the tendon at the hip flexor crease moves from flexion (knee toward waist) to extension (knee down and hip joint straightened). After extended exercise pain or discomfort may be present caused by inflammation of the iliopsoas bursae. Pain often decreases with rest and diminished activity. Symptoms usually last months or years without treatment and can be very painful.

Common deformities of the knee include:

- Genu varum

- Genu valgum

- Genu recurvatum (Knee hyperextension)

- Knee flexion deformity

- Bipartite patella

Transient synovitis is a reactive arthritis of the hip of unknown cause. People are usually able to walk and may have a low grade fever. They usually look clinically nontoxic or otherwise healthy. It may only be diagnosed once all other potential serious causes are excluded. With symptomatic care it usually resolves over one week.

Patients often complain of pain and swelling over the medial aspect of the knee joint. They may also report instability with side-to-side movement and during athletic performance that involves cutting or pivoting.

Prepatellar bursitis is an inflammation of the prepatellar bursa at the front of the knee. It is marked by swelling at the knee, which can be tender to the touch but which does not restrict the knee's range of motion. It is most commonly caused by trauma to the knee, either by a single acute instance or by chronic trauma over time. As such, prepatellar bursitis commonly occurs among individuals whose professions require frequent kneeling.

A definitive diagnosis of the condition can usually be made once a clinical history and physical examination have been obtained, though determining whether or not the bursitis is septic is not as straightforward. Treatment of prepatellar bursitis depends on the severity of the symptoms. Mild cases may only require rest and icing of the knee. A number of different treatment options have been used for severe septic cases, including intravenous antibiotics, surgical irrigation of the bursa, and bursectomy.

Chondromalacia patellae (also known as CMP) is inflammation of the underside of the patella and softening of the cartilage.

The cartilage under the kneecap is a natural shock absorber, and overuse, injury, and many other factors can cause increased deterioration and breakdown of the cartilage. The cartilage is no longer smooth and therefore movement and use is painful. While it often affects young individuals engaged in active sports, it also afflicts older adults who overwork their knees.

"Chondromalacia patellae" is sometimes used synonymously with patellofemoral pain syndrome. However, there is general consensus that "patellofemoral pain syndrome" applies only to individuals without cartilage damage.

People with Joint Hypermobility Syndrome may develop other conditions caused by their unstable joints. These conditions include:

- Joint instability causing frequent sprains, tendinitis, or bursitis when doing activities that would not affect others

- Joint pain

- Early-onset osteoarthritis (as early as during teen years)

- Subluxations or dislocations, especially in the shoulder (severe limits to ability to push, pull, grasp, finger, reach, etc., is considered a disability by the US Social Security Administration)

- Knee pain

- Fatigue, even after short periods of exercise

- Back pain, prolapsed discs or spondylolisthesis

- Joints that make clicking noises (also a symptom of osteoarthritis)

- Susceptibility to whiplash

- Temporomandibular Joint Syndrome also known as TMJ

- Increased nerve compression disorders (such as carpal tunnel syndrome)

- The ability of finger locking

- Poor response to anaesthetic or pain medication

- "Growing pains" as described in children in late afternoon or night

Those with hypermobile joints are more likely to have fibromyalgia, mitral valve prolapse, and anxiety disorders such as panic disorder.

Infrapatellar bursitis is the inflammation of one or both of the infrapatellar bursa, which are located just below the kneecap. Symptoms of bursitis commonly include swelling and knee pain. Bursitis often develops gradually over a period of days to even months but may develop more rapidly, especially in the event of trauma or infection.

Bursitis affecting the superficial infrapatellar bursa is an occupational hazard of persons whose work involves kneeling on hard surfaces. Depending on the occupation affected it is known by a variety of nicknames, most commonly floor layers' knee, but also plumbers' knee, clergyman's knee, or housewife's knee (prepatellar bursitis).

The deep infrapatellar bursa occasionally also become inflamed, swollen, and painful. Bursitis in the deep infrapatellar bursa usually develops from chronic overuse of the knee extensor tendon (patellar tendon) as can occur with repetitive flexing of the knee under pressure in work duties or exercise. Examples might include climbing stairs, jumping, or deep knee bends.

Patellar tendinitis (patellar tendinopathy, also known as jumper's knee), is a relatively common cause of pain in the inferior patellar region in athletes. It is common with frequent jumping and studies have shown it may be associated with stiff ankle movement and ankle sprains.

A sprain is a type of acute injury which results from the stretching or tearing of a ligament. Depending on the severity of the sprain, the movement on the joint can be compromised since ligaments aid in the stability and support of joints. Sprains are commonly seen in vulnerable areas such as the wrists, knees, and ankles. They can occur from movements such as falling on an outstretched hand, or a twisting of the ankle or foot.

The severity of a sprain can also be classified:

Grade 1: Only some of the fibers in the ligament are torn, and the injured site is moderately painful and swollen. Function in the joint will be unaffected for the most part.

Grade 2: Many of the ligament fibers are torn, and pain and swelling is moderate. The functionality of the joint is compromised.

Grade 3: The soft tissue is completely torn, and functionality and strength on the joint is completely compromised. In most cases, surgery is needed to repair the damage.

People often describe pain as being “inside the knee cap.” The leg tends to flex even when relaxed. In some cases, the injured ligaments involved in patellar dislocation do not allow the leg to flex almost at all.

Bursitis commonly affects superficial bursae. These include the subacromial, prepatellar, retrocalcaneal, and pes anserinus bursae of the shoulder, knee, heel and shin, etc. (see below). Symptoms vary from localized warmth and erythema to joint pain and stiffness, to stinging pain that surrounds the joint around the inflamed bursa. In this condition, the pain usually is worse during and after activity, and then the bursa and the surrounding joint becomes stiff the next morning.

Snapping hip syndrome (also referred to as coxa saltans, iliopsoas tendinitis, or dancer's hip) is a medical condition characterized by a snapping sensation felt when the hip is flexed and extended. This may be accompanied by an audible snapping or popping noise and pain or discomfort. Pain often decreases with rest and diminished activity. Snapping hip syndrome is classified by location of the snapping, either or articular.

The condition may result from acute injury to the patella or chronic friction between the patella and a groove in the femur through which it passes during knee flexion. Possible causes include a tight iliotibial band, neuromas, bursitis, overuse, malalignment, core instability, and patellar maltracking.

Pain at the front or inner side of the knee is common in both young adults and those of more advanced years, especially when engaging in soccer, gymnastics, cycling, rowing, tennis, ballet, basketball, horseback riding, volleyball, running, combat sports, figure skating, snowboarding, skateboarding and even swimming. The pain is typically felt after prolonged sitting. Skateboarders most commonly experience this injury in their non-dominant foot due to the constant kicking and twisting required of it. Swimmers acquire it doing the breaststroke, which demands an unusual motion of the knee. People who are involved in an active life style with high impact on the knees are at greatest risk. Proper management of physical activity may help prevent worsening of the condition. Athletes are advised to talk to a physician for further medical diagnosis as symptoms may be similar to more serious problems within the knee. Tests are not necessarily needed for diagnosis, but in some situations it may confirm diagnosis or rule out other causes for pain. Commonly used tests are blood tests, MRI scans, and arthroscopy.

While the term "chondromalacia" sometimes refers to abnormal-appearing cartilage anywhere in the body, it most commonly denotes irritation of the underside of the kneecap (or "patella"). The patella's posterior surface is covered with a layer of smooth cartilage, which the base of the femur normally glides effortlessly against when the knee is bent. However, in some individuals the kneecap tends to rub against one side of the knee joint, irritating the cartilage and causing knee pain.