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.

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.

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.

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.

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.

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.

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.

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.

Patients often complain of pain and instability at the joint. With concurrent nerve injuries, patients may experience numbness, tingling and weakness of the ankle dorsiflexors and great toe extensors, or a footdrop.

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

Common deformities of the knee include:

- Genu varum

- Genu valgum

- Genu recurvatum (Knee hyperextension)

- Knee flexion deformity

- Bipartite patella

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.

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.

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.

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.

Jacobson previously described the common problems to medial knee surgery. It was stressed that adequate diagnosis is imperative and all possible injuries should be evaluated and addressed intraoperatively. Damage to the saphenous nerve and its infrapatellar branch is possible during medial knee surgery, potentially causing numbness or pain over the medial knee and leg. As with all surgeries, there is a risk of bleeding, wound problems, deep vein thrombosis, and infection that can complicate the outcome and rehabilitation process. The long term complication of arthrofibrosis and heterotopic ossification (Pellegrini-Stieda syndrome) are problems that are best addressed with early range of motion and following defined rehabilitation protocols. Failure of graft due to intrinsic mechanical forces should be prevented with preoperative alignment assessment (osteotomy treatment) and proper rehabilitation.

A tear of a meniscus is a rupturing of one or more of the fibrocartilage strips in the knee called menisci. When doctors and patients refer to "torn cartilage" in the knee, they actually may be referring to an injury to a meniscus at the top of one of the tibiae. Menisci can be torn during innocuous activities such as walking or squatting. They can also be torn by traumatic force encountered in sports or other forms of physical exertion. The traumatic action is most often a twisting movement at the knee while the leg is bent. In older adults, the meniscus can be damaged following prolonged 'wear and tear' called a degenerative tear.

Tears can lead to pain and/or swelling of the knee joint. Especially acute injuries (typically in younger, more active patients) can lead to displaced tears which can cause mechanical symptoms such as clicking, catching, or locking during motion of the knee joint. The joint will be in pain when in use, but when there is no load, the pain goes away.

A tear of the medial meniscus can occur as part of the unhappy triad, together with a tear of the anterior cruciate ligament and medial collateral ligament.

Genu recurvatum is a deformity in the knee joint, so that the knee bends backwards. In this deformity, excessive extension occurs in the tibiofemoral joint. Genu recurvatum is also called knee hyperextension and back knee. This deformity is more common in women and people with familial ligamentous laxity. Hyperextension of the knee may be mild, moderate or severe.

The normal range of motion (ROM) of the knee joint is from 0 to 135 degrees in an adult. Full knee extension should be no more than 10 degrees. In genu recurvatum (back knee), normal extension is increased. The development of genu recurvatum may lead to knee pain and knee osteoarthritis.

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

A predisposing factor is tightness in the tensor fasciae latae muscle and iliotibial tract in combination with a quadriceps imbalance between the vastus lateralis and vastus medialis muscles can play a large role. However individuals with larger Q angles are genetically more predisposed to this type of injury due to the increased lateral angle at which the femur and tibia meet.

Another cause of patellar symptoms is "lateral patellar compression syndrome", which can be caused from lack of balance or inflammation in the joints. The pathophysiology of the kneecap is complex, and deals with the osseous soft tissue or abnormalities within the patellofemoral groove. The patellar symptoms cause knee extensor dysplasia, and sensitive small variations affect the muscular mechanism that controls the joint movements.

24% of people whose patellas have dislocated have relatives who have experienced patellar dislocations.

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.

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.

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.

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.