If the knee is swollen and red and warm to the touch when compared to the other knee, a doctor may be concerned about inflammation due to rheumatoid arthritis or a crystalline arthritis, such as gout or pseudogout, or joint infection. Besides sending the joint fluid to a laboratory for analysis, blood tests may requested to determine a white blood cell count, erythrocyte sedimentation rate, and perhaps the level of C-reactive protein or uric acid. If blood tests reveal Lyme disease antibodies forming, the condition may be attributed to it.

An X-ray is useful to verify that there is no break or dislocation when there is a history of trauma. May show signs of osteoarthritis.

Diagnosis is made with reasonable certainty based on history and clinical examination. X-rays may confirm the diagnosis. The typical changes seen on X-ray include: joint space narrowing, subchondral sclerosis (increased bone formation around the joint), subchondral cyst formation, and osteophytes. Plain films may not correlate with the findings on physical examination or with the degree of pain. Usually other imaging techniques are not necessary to clinically diagnose osteoarthritis.

In 1990, the American College of Rheumatology, using data from a multi-center study, developed a set of criteria for the diagnosis of hand osteoarthritis based on hard tissue enlargement and swelling of certain joints. These criteria were found to be 92% sensitive and 98% specific for hand osteoarthritis versus other entities such as rheumatoid arthritis and spondyloarthropathies.

Related pathologies whose names may be confused with osteoarthritis include pseudo-arthrosis. This is derived from the Greek roots "pseudo-", meaning "false", and "arthr-", meaning "joint", together with the ending "-osis" used for disorders. Radiographic diagnosis results in diagnosis of a fracture within a joint, which is not to be confused with osteoarthritis which is a degenerative pathology affecting a high incidence of distal phalangeal joints of female patients. A polished ivory-like appearance may also develop on the bones of the affected joints, reflecting a change called eburnation.

There are no set standards for the diagnosis of suspected transient synovitis, so the amount of investigations will depend on the need to exclude other, more serious diseases.

Inflammatory parameters in the blood may be slightly raised (these include erythrocyte sedimentation rate, C-reactive protein and white blood cell count), but raised inflammatory markers are strong predictors of other more serious conditions such as septic arthritis.

X-ray imaging of the hip is most often unremarkable. Subtle radiographic signs include an accentuated pericapsular shadow, widening of the medial joint space, lateral displacement of the femoral epiphyses with surface flattening (Waldenström sign), prominent obturator shadow, diminution of soft tissue planes around the hip joint or slight demineralisation of the proximal femur. The main reason for radiographic examination is to exclude bony lesions such as occult fractures, slipped upper femoral epiphysis or bone tumours (such as osteoid osteoma). An anteroposterior and frog lateral (Lauenstein) view of the pelvis and both hips is advisable.

An ultrasound scan of the hip can easily demonstrate fluid inside the joint capsule (Fabella sign), although this is not always present in transient synovitis. However, it cannot reliably distinguish between septic arthritis and transient synovitis. If septic arthritis needs to be ruled out, needle aspiration of the fluid can be performed under ultrasound guidance. In transient synovitis, the joint fluid will be clear. In septic arthritis, there will be pus in the joint, which can be sent for bacterial culture and antibiotic sensitivity testing.

More advanced imaging techniques can be used if the clinical picture is unclear; the exact role of different imaging modalities remains uncertain. Some studies have demonstrated findings on magnetic resonance imaging (MRI scan) that can differentiate between septic arthritis and transient synovitis (for example, signal intensity of adjacent bone marrow). Skeletal scintigraphy can be entirely normal in transient synovitis, and scintigraphic findings do not distinguish transient synovitis from other joint conditions in children. CT scanning does not appear helpful.

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

Knee MRIs should be avoided for knee pain without symptoms or effusion, unless there are non-successful results from a functional rehabilitation program.

Depending on the level of pain and damage suffered by a patient, a physician will recommend a treatment regimen that will relieve symptoms. Some of the most common recommendations include avoiding activities that make the pain worse, ice the knee for 20 to 30 minutes throughout the day to reduce inflammation, use over the counter anti-inflammatory medications, paracetamol (acetaminophen) and physical therapy.

Topical creams and patches can also be used for pain treatment and they have been proven to reduce pain by 33 to 57%.

Exercises can help increase range of motion and flexibility as well as help strengthen the muscles in the leg. Physical therapy and exercise are often effective in reducing pain and improving function. Working with a physical therapist to find exercises that promote function without risking further injury is effective for most patients. Many of the exercises used can be performed while sitting in a chair or standing in place. They are performed so that additional stress or weight is not placed on the knee joint. Water exercises are highly recommended along with the use of elastic bands.

Supportive devices like knee braces can be used. In most cases, the arthritis is centered on a single side of the knee, so braces are effective in providing stability to one side. Two different forms of braces are available. A support brace provides the aid the entire knee requires, where an up-loader brace shifts the pressure away from the specific part of the knee that is experiencing the pain. Shoes or inserts that are considered to be energy absorbing are found useful for some patients as well as walking devices like a cane. Shoe insoles that are fitted to correct flat feet have provided relief to many patients.

The use of oral steroids and anti-inflammatory medicines help to reduce the amount of inflammation and pain felt in the knee. If over the counter medicines like ibuprofen or naproxen are not strong enough, prescription strength medicines are used. If oral medicine and physical therapy don't help your knee enough, doctors may consider giving patients injections with pain medicine. Hyaluronic acid is present in the knee, but injections of it can be used to protect the joint when the cartilage becomes thinner and can't do it alone. These injections can provide more pain relief than oral medications lasting from six months to a year.

Surgery is the final option but may be required to relieve symptoms. Arthroscopy is performed through tiny cuts where damaged parts of the knee can be removed. Osteotomy is performed to reshape the bones in the knee and is only performed if one side of the knee is damaged. Arthroplasty is a replacement surgery where an artificial joint is used.

Low level laser therapy can be considered for relief of pain and stiffness associated with osteoarthritis.

Pain in or around the hip and/or limp in children can be due to a large number of conditions. Septic arthritis (a bacterial infection of the joint) is the most important differential diagnosis, because it can quickly cause irreversible damage to the hip joint. Fever, raised inflammatory markers on blood tests and severe symptoms (inability to bear weight, pronounced muscle guarding) all point to septic arthritis, but a high index of suspicion remains necessary even if these are not present. Osteomyelitis (infection of the bone tissue) can also cause pain and limp.

Bone fractures, such as a toddler's fracture (spiral fracture of the shin bone), can also cause pain and limp, but are uncommon around the hip joint. Soft tissue injuries can be evident when bruises are present. Muscle or ligament injuries can be contracted during heavy physical activity —however, it is important not to miss a slipped upper femoral epiphysis. Avascular necrosis of the femoral head (Legg-Calvé-Perthes disease) typically occurs in children aged 4–8, and is also more common in boys. There may be an effusion on ultrasound, similar to transient synovitis.

Neurological conditions can also present with a limp. If developmental dysplasia of the hip is missed early in life, it can come to attention later in this way. Pain in the groin can also be caused by diseases of the organs in the abdomen (such as a psoas abscess) or by testicular disease. Rarely, there is an underlying rheumatic condition (juvenile idiopathic arthritis, Lyme arthritis, gonococcal arthritis, ...) or bone tumour.

A number of classification systems are used for gradation of osteoarthritis:

- WOMAC scale, taking into account pain, stiffness and functional limitation.

- Kellgren-Lawrence grading scale for osteoarthritis of the knee. It uses only projectional radiography features.

- Tönnis classification for osteoarthritis of the hip joint, also using only projectional radiography features.

Osteoarthritis can be classified into either primary or secondary depending on whether or not there is an identifiable underlying cause.

Both primary generalized nodal osteoarthritis and erosive osteoarthritis (EOA, also called inflammatory osteoarthritis) are sub-sets of primary osteoarthritis. EOA is a much less common, and more aggressive inflammatory form of osteoarthritis which often affects the distal interphalangeal joints of the hand and has characteristic articular erosive changes on x-ray.

Osteoarthritis can be classified by the joint affected:

- Hand:

- Trapeziometacarpal osteoarthritis

- Wrist (wrist osteoarthritis)

- Vertebral column (spondylosis)

- Facet joint arthrosis

- Hip osteoarthritis

- Knee osteoarthritis

As of July 2000, hypermobility was diagnosed using the Brighton criteria. The Brighton criteria do not replace the Beighton score but instead use the previous score in conjunction with other symptoms and criteria. HMS is diagnosed in the presence of either two major criteria, one major and two minor criteria, or four minor criteria. The criteria are:

There is no specific test for this condition. Diagnosis is based on signs and symptoms, and exclusion of other conditions.

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.

The diagnosis of the cause of a limp is often made based on history, physical exam findings, laboratory tests, and radiological examination. If a limp is associated with pain it should be urgently investigated, while non-painful limps can be approached and investigated more gradually. Young children have difficulty determining the location of leg pain, thus in this population, "knee pain equals hip pain". SCFE can usually be excluded by an x-ray of the hips. A ultrasound or x-ray guided aspiration of the hip joint maybe required to rule out an infectious process within the hip.

The diagnosis of patellofemoral pain syndrome is made by ruling out patellar tendinitis, prepatellar bursitis, plica syndrome, Sinding-Larsen and Johansson syndrome, and Osgood–Schlatter disease.

The Schober's test is a useful clinical measure of flexion of the lumbar spine performed during the physical examination.

Patients can be observed standing and walking to determine patellar alignment. The Q-angle, lateral hypermobility, and J-sign are commonly used determined to determine patellar maltracking. The patellofemoral glide, tilt, and grind tests (Clarke's sign), when performed, can provide strong evidence for PFPS. Lastly, lateral instability can be assessed via the patellar apprehension test, which is deemed positive when there is pain or discomfort associated with lateral translation of the patella.

Once PVNS is confirmed by biopsy of the synovium of an affected joint, a synovectomy of the affected area is the most common treatment. Bone lesions caused by the disorder are removed and bone grafting is performed as needed. Because diffuse PVNS has a relatively high rate of recurrence, radiation therapy may be considered as a treatment option. In some cases, a total joint replacement is needed to relieve symptoms when PVNS causes significant joint destruction.

It is not always certain why arthritis of the knee develops. Most physicians believe that it is a combination of factors that can include muscle weakness, obesity, heredity, joint injury or stress, constant exposure to the cold, and aging. Cartilage in the knee begins to break down and leaves the bones of the knee rubbing against each other as you walk. Persons who work in a place that applies repetitive stress on the knees are at a high risk of developing this condition. Bone deformities increase the risk for osteoarthritis of the knee since the joints are already malformed and may contain defective cartilage. Having gout, rheumatoid arthritis, Paget's disease of bone or septic arthritis can increase your risk of developing osteoarthritis.

Some physicians and most podiatrist believe that Pes Planus (flat feet) cause increased rates and earlier incidence of knee osteoarthritis. In a study of army recruits with moderate to severe flat feet, the results showed that they had almost double the rate of knee arthritis when compared to recruits with normal arches.

The Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), developed in Bath (UK), is an index designed to detect the inflammatory burden of active disease. The BASDAI can help to establish a diagnosis of AS in the presence of other factors such as HLA-B27 positivity, persistent buttock pain which resolves with exercise, and X-ray or MRI-evident involvement of the sacroiliac joints. It can be easily calculated and accurately assesses the need for additional therapy; a person with AS with a score of four out of a possible 10 points while on adequate NSAID therapy is usually considered a good candidate for biologic therapy.

The Bath Ankylosing Spondylitis Functional Index (BASFI) is a functional index which can accurately assess functional impairment due to the disease, as well as improvements following therapy. The BASFI is not usually used as a diagnostic tool, but rather as a tool to establish a current baseline and subsequent response to therapy.

As stated earlier, musculoskeletal disorders can cost up to $15–$20 billion in direct costs or $45–$55 billion in indirect expenses. This is about $135 million a day Tests that confirm or correct TTS require expensive treatment options like x-rays, CT-scans, MRI and surgery. 3 former options for TTS detect and locate, while the latter is a form of treatment to decompress tibial nerve pressure Since surgery is the most common form of TTS treatment, high financial burden is placed upon those diagnosed with the rare syndrome.

There are several types of inflammation that can cause knee pain, including sprains, bursitis, and injuries to the meniscus. A diagnosis of prepatellar bursitis can be made based on a physical examination and the presence of risk factors in the person's medical history; swelling and tenderness at the front of the knee, combined with a profession that requires frequent kneeling, suggest prepatellar bursitis. Swelling of multiple joints along with restricted range of motion may indicate arthritis instead.

A physical examination and medical history are generally not enough to distinguish between infectious and non-infectious bursitis; aspiration of the bursal fluid is often required for this, along with a cell culture and Gram stain of the aspirated fluid. Septic prepatellar bursitis may be diagnosed if the fluid is found to have a neutrophil count above 1500 per microliter, a threshold significantly lower than that of septic arthritis (50,000 cells per microliter). A tuberculosis infection can be confirmed using a roentgenogram and urinalysis.

X-ray images (normally during weightbearing) can be obtained to rule out other conditions or to see if the patient also has osteoarthritis. The menisci themselves cannot be visualised with plain radiographs. If the diagnosis is not clear from the history and examination, the menisci can be imaged with magnetic resonance imaging (an MRI scan). This technique has replaced previous arthrography, which involved injecting contrast medium into the joint space. In straightforward cases, knee arthroscopy allows quick diagnosis and simultaneous treatment. Recent clinical data shows that MRI and clinical testing are comparable in sensitivity and specificity when looking for a meniscal tear.

It is important to differentiate between infected and non-infected bursitis. People may have surrounding cellulitis and systemic symptoms include a fever. The bursa should be aspirated to rule out an infectious process.

Bursae that are not infected can be treated symptomatically with rest, ice, elevation, physiotherapy, anti-inflammatory drugs and pain medication. Since bursitis is caused by increased friction from the adjacent structures, a compression bandage is not suggested because compression would create more friction around the joint. Chronic bursitis can be amenable to bursectomy and aspiration.

Bursae that are infected require further investigation and antibiotic therapy. Steroid therapy may also be considered. In cases when all conservative treatment fails, surgical therapy may be necessary. In a bursectomy the bursa is cut out either endoscopically or with open surgery. The bursa grows back in place after a couple of weeks but without any inflammatory component.

Diagnosis is made by clinical examination from an appropriate health professional, and may be supported by other tests such as radiology and blood tests, depending on the type of suspected arthritis. All arthritides potentially feature pain. Pain patterns may differ depending on the arthritides and the location. Rheumatoid arthritis is generally worse in the morning and associated with stiffness; in the early stages, patients often have no symptoms after a morning shower. Osteoarthritis, on the other hand, tends to be worse after exercise. In the aged and children, pain might not be the main presenting feature; the aged patient simply moves less, the infantile patient refuses to use the affected limb.

Elements of the history of the disorder guide diagnosis. Important features are speed and time of onset, pattern of joint involvement, symmetry of symptoms, early morning stiffness, tenderness, gelling or locking with inactivity, aggravating and relieving factors, and other systemic symptoms. Physical examination may confirm the diagnosis, or may indicate systemic disease. Radiographs are often used to follow progression or help assess severity.

Blood tests and X-rays of the affected joints often are performed to make the diagnosis. Screening blood tests are indicated if certain arthritides are suspected. These might include: rheumatoid factor, antinuclear factor (ANF), extractable nuclear antigen, and specific antibodies.

X-rays of the hip may suggest and/or verify the diagnosis. X-rays usually demonstrate a flattened, and later fragmented, femoral head. A bone scan or MRI may be useful in making the diagnosis in those cases where X-rays are inconclusive. Usually, plain radiographic changes are delayed 6 weeks or more from clinical onset, so bone scintigraphy and MRI are done for early diagnosis. MRI results are more accurate, i.e. 97 to 99% against 88 to 93% in plain radiography. If MRI or bone scans are necessary, a positive diagnosis relies upon patchy areas of vascularity to the capital femoral epiphysis (the developing femoral head).