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.

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.

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.

Laximetry is a reliable technique for diagnosing a torn anterior cruciate ligament.

Osteoarthritis between the radius bone and the carpals is indicated by a "radiocarpal joint space" of less than 2mm.

X-rays can be very helpful in diagnosing and differentiating between SNAC and SLAC wrists. On the other hand, X-rays are not always sufficient to distinguish between different stages. It is important to note that both hands need to be compared. Therefore, two X-rays are needed: one from the left and one from the right hand. When the X-ray is inconclusive, wrist arthroscopy can be performed.

SLAC

Because the scapholunate ligament is ruptured, the scaphoid and lunate are not longer connected. This results in a larger space between the two bones, also known as the Terry Thomas sign. A space larger than 3 mm is suspicious and a space larger than 5 mm is a proven SLAC pathology. Scaphoid instability due to the ligament rupture can be stactic or dynamic. When the X-ray is diagnostic and there is a convincing Terry Thomas sign it is a static scaphoid instability. When the scaphoid is made unstable by either the patient or by manipulation by the examining physician it is a dynamic instability.

In order to diagnose a SLAC wrist you need a posterior anterior (PA) view X-ray, a lateral view X-ray and a fist view X-ray. The fist X-ray is often made if there is no convincing Terry Thomas sign. A fist X-ray of a scapholunate ligament rupture will show a descending capitate. Making a fist will give pressure at the capitate, which will descend if there is a rupture in the scapholunate ligament.

SNAC

In order to diagnose a SNAC wrist you need a PA view X-ray and a lateral view X-ray. As in SLAC, the lateral view X-ray is performed to see if there is a DISI.

Computed tomography (CT) or Magnetic Resonance Imaging (MRI) are rarely used to diagnose SNAC or SLAC wrist osteoarthritis because there is no additional value. Also, these techniques are much more expensive than a standard X-ray. CT or MRI may be used if there is a strong suspicion for another underlying pathology or disease.

Magnetic resonance imaging (MRI) can be helpful in assessing for a ligamentous injury to the medial side of the knee. Milewski et al. has found that grade I to III classification can be seen on MRI. With a high-quality image (1.5 tesla or 3 tesla magnet) and no previous knowledge of the patient’s history, musculoskeletal radiologists were able to accurately diagnose medial knee injury 87% of the time. MRI can also show associated bone bruises on the lateral side of the knee, which one study shows, happen in almost half of medial knee injuries.

Knee MRIs should be avoided for knee pain without mechanical symptoms or effusion, and upon non-successful results from a functional rehabilitation program.

Anterior-posterior (AP) radiographs are useful for reliably assessing normal anatomical landmarks. Bilateral valgus stress AP images can show a difference in medial joint space gapping. It has been reported that an isolated grade III sMCL tear will show an increase in medial compartment gapping of 1.7 mm at 0° of knee flexion and 3.2 mm at 20° of knee flexion, compared to the contralateral knee. Additionally, a complete medial ligamentous disruption (sMCL, dMCL, and POL) will show increased gapping by 6.5 mm at 0° and 9.8 mm at 20° during valgus stress testing. Pellegrini-Stieda syndrome can also be seen on AP radiographs. This finding is due to calcification of the sMCL (heterotopic ossification) caused by the chronic tear of the ligament.

The MRI is perhaps the most used technique for diagnosing the state of the Anterior Cruciate Ligament but it not always the most reliable. In some cases the Anterior Cruciate Ligament can indeed not be seen because of the blood surrounding it.

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.

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

Examination will often show tenderness at the radioscaphoid joint (when palpated or while moving the radioscaphoid joint), dorsal radial swelling and instability of the wrist joint. Notice that people may say they have trouble with rising from a chair when pressure is exerted on the hands by pushing against the handrail. Younger people may complain about not being able to do push-ups anymore because of a painful hand.

There are a number of tests and actions that can be performed when a patient is suspected of having osteoarthritis caused by SLAC or SNAC.

SLAC:

- Tenderness 1 cm above Lister’s Tubercle

Tests:

- Watson's test

- Finger extension test

SNAC:

- Tenderness at the anatomical snuff box

- Painful pronation and supination when performed against resistance

- Pain during axial pressure

Diagnosis is simple; usually a doctor can diagnose shoulder arthritis by symptoms, but they may ask for an x-ray or MRI for confirmation.

High quality MRI images (1.5 T magnet or higher ) of the knee can be extremely useful to diagnose injuries to the posterolateral corner and other major structures of the knee. While the standard coronal, sagittal and axial films are useful, thin slice (2 mm ) coronal oblique images should also be obtained when looking for PLC injuries. Coronal oblique images should include the fibular head and styloid to allow for evaluation of the FCL and popliteus tendon.

A meniscal tear can be classified in various ways: by anatomic location, by proximity to blood supply, etc. Various tear patterns and configurations have been described. These include:

- Radial tears;

- Flap or parrot-beak tears;

- Peripheral, longitudinal tears;

- Bucket-handle tears;

- Horizontal cleavage tears; and

- Complex, degenerative tears.

These tears can then be further classified by their proximity to the meniscus blood supply, namely whether they are located in the “red-red,” “red-white,” or “white-white” zones.

The functional importance of these classifications, however, is to ultimately determine whether a meniscus is repairable. The repairability of a meniscus depends on a number of factors. These include:

- Age/strength

- Activity level

- Tear pattern

- Chronicity of the tear

- Associated injuries (anterior cruciate ligament injury)

- Healing potential

This test can see various warning signs that predict if OSD might occur. Ultrasonography can detect if there is any swelling within the tissue as well as cartilage swelling. Ultrasonography's main goal is to identify OSD in the early stage rather than later on. It has unique features such as detection of an increase of swelling within the tibia or the cartilage surrounding the area and can also see if there is any new bone starting to build up around the tibial tuberosity.

OSD may result in an avulsion fracture, with the tibial tuberosity separating from the tibia (usually remaining connected to a tendon or ligament). This injury is uncommon because there are mechanisms that prevent strong muscles from doing damage. The fracture on the tibial tuberosity can be a complete or incomplete break.

Type I: A small fragment is displaced proximally and does not require surgery.

Type II: The articular surface of the tibia remains intact and the fracture occurs at the junction where the secondary center of ossification and the proximal tibial epiphysis come together (may or may not require surgery).

Type III: Complete fracture (through articular surface) including high chance of meniscal damage. This type of fracture usually requires surgery.

According to the posterior cruciate ligament injuries only account for 1.5 percent of all knee injuries (figure 2). If it is a single injury to the posterior cruciate ligament that requires surgery only accounted for 1.1 percent compared to all other cruciate surgeries but when there was multiple injuries to the knee the posterior cruciate ligament accounted for 1.2 percent of injuries.

Diagnosis is based on symptom and confirmed with X-rays. In children an MRI may be required.

A grade III PCL injury with more than 10mm posterior translation when the posterior drawer examination is performed may be treated surgically. Patients that do not improve stability during physical therapy or develop an increase in pain will be recommended for surgery.

Isolated and combined posterolateral knee injuries are difficult to accurately diagnose in patients presenting with acute knee injuries. The incidence of isolated posterolateral corner injuries has been reported to be between 13% and 28%. Most PLC injuries accompany an ACL or PCL tear, and can contribute to ACL or PCL reconstruction graft failure if not recognized and treated. A study by LaPrade "et al." in 2007 showed the incidence of posterolateral knee injuries in patients presenting with acute knee injuries and hemarthrosis (blood in the knee joint) was 9.1%.

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

In all injuries to the tibial plateau radiographs (commonly called x-rays) are imperative. Computed tomography scans are not always necessary but are sometimes critical for evaluating degree of fracture and determining a treatment plan that would not be possible with plain radiographs. Magnetic Resonance images are the diagnositic modality of choice when meniscal, ligamentous and soft tissue injuries are suspected. CT angiography should be considered if there is alteration of the distal pulses or concern about arterial injury.

An effective rehabilitation program reduces the chances of reinjury and of other knee-related problems such as patellofemoral pain syndrome and osteoarthritis. Rehabilitation focuses on maintaining strength and range of motion to reduce pain and maintain the health of the muscles and tissues around the knee joint.

Segond and reverse Segond fractures are characterized by a small avulsion, or "chip", fragment of characteristic size that is best seen on plain radiography in the anterior-posterior plane. The chip of bone may be very difficult to see on the plain x-ray exam, and may be better seen on computed tomography. MRI may be useful for visualization of the associated bone marrow edema of the underlying tibial plateau on fat- saturated T2W and STIR images, as well as the associated findings of ligamentous and/or meniscal injury.

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.