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.

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.

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.

An individual may feel or hear a "pop" in their knee during a twisting movement or rapid deceleration, followed by an inability to continue participation in the sport and early swelling from hemarthrosis. This combination is said to indicate a 90% probability of rupture of the anterior cruciate ligament.

An individual may experience instability in the knee once they resume walking and other activities, and they may feel their knee is "giving out". Loss of full range of motion, and discomfort along the joint line are also common symptoms of an ACL injury.

Follow-up studies by Levy et al. and Stannard at al. both examined failure rates for posterolateral corner repairs and reconstructions. Failure rates repairs were approximately 37 – 41% while reconstructions had a failure rate of 9%.

Other less common surgical complications include deep vein thrombosis (DVTs), infection, blood loss, and nerve/artery damage. The best way to avoid these complications is to preemptively treat them. DVTs are typically treated prophylactically with either aspirin or sequential compression devices (SCDs). In high risk patients there may be a need for prophylactic administration of low molecular weight heparin (LMWH). In addition, having a patient get out of bed and ambulate soon after surgery is a time honored way to prevent DVTs. Infection is typically controlled by administering 1 gram of the antibiotic cefazolin (Ancef) prior to surgery. Excessive blood loss and nerve/artery damage are rare occurrences in surgery and can usually be avoided with proper technique and diligence; however, the patient should be warned of these potential complications, especially in patients with severe injuries and scarring.

Anterior cruciate ligament injury is when the anterior cruciate ligament (ACL) is either stretched, partially torn, or completely torn. Injuries are most commonly complete tears. Symptoms include pain, a popping sound during injury, instability of the knee, and joint swelling. Swelling generally appears within a couple of hours. In approximately 50% of cases other structures of the knee such as ligaments, cartilage, or meniscus are damaged.

The underlying mechanism often involves a rapid change in direction, sudden stop, landing following jumping, or direct contact. It is more common in athletes, particularly those who participate in alpine skiing, soccer, football, or basketball. Diagnosis is typically by physical examination and maybe support by magnetic resonance imaging (MRI).

Prevention is by neuromuscular training and core strengthening. Treatment recommends depend on desired level of activity. If there will be low levels of future activity, bracing and physiotherapy may be sufficient. In those with high activity levels, arthroscopic repair via anterior cruciate ligament reconstruction is often recommended. Surgery, if recommended, is generally not carried out until the initial inflammation from the injury has resolved.

As of 2009, about 200,000 people are affected per year in the United States. In some sports, females have a higher risk while in others, both sexes are equally affected. Without surgery, in those with a complete tear, many are unable to play sports and develop osteoarthritis.

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.

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.

An unhappy triad (or terrible triad, "horrible triangle", O'Donoghue's triad or a "blown knee") is an injury to the anterior cruciate ligament, medial collateral ligament, and medial meniscus. Analysis during the 1990s indicated that this 'classic' O'Donoghue triad is actually an unusual clinical entity among athletes with knee injuries. Some authors mistakenly believe that in this type of injury, acute tears of the medial meniscus always present with a concomitant lateral meniscus injury. However, the 1990 analysis showed that lateral meniscus tears are more common than medial meniscus tears in conjunction with sprains of the ACL.

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 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.

As with other types of fractures, scapular fracture may be associated with pain localized to the area of the fracture, tenderness, swelling, and crepitus (the crunching sound of bone ends grinding together). Since scapular fractures impair the motion of the shoulder, a person with a scapular fracture has a reduced ability to move the shoulder joint. Signs and symptoms may be masked by other injuries that accompany the scapular fracture.

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.

Tibial plateau fractures typically presents with knee effusion, swelling of the knee soft tissues and inability to bear weight. The knee may be deformed due to displacement and/or fragmentation of the tibia which leads to loss of its normal structural appearance. Blood in the soft tissues and knee joint (hemarthrosis) may lead to bruising and a doughy feel of the knee joint. Due to the tibial plateau's proximity to important vascular (i.e. arteries, veins) and neurological (i.e. nerves such as peroneal and tibial) structures, injuries to these may occur upon fracture. A careful examination of the neurovascular systems is imperative. A serious complication of tibial plateau fractures is compartment syndrome in which swelling causes compression of the nerves and blood vessels inside the leg and may ultimately lead to necrosis or cell death of the leg tissues.

The function of the PCL is to prevent the femur from sliding off the anterior edge of the tibia and to prevent the tibia from displacing posterior to the femur. Common causes of PCL injuries are direct blows to the flexed knee, such as the knee hitting the dashboard in a car accident or falling hard on the knee, both instances displacing the tibia posterior to the femur.

The posterior drawer test is one of the tests used by doctors and physiotherapists to detect injury to the PCL.

Surgery to repair the posterior cruciate ligament is controversial due to its placement and technical difficulty.

An additional test of posterior cruciate ligament injury is the "posterior sag test", where, in contrast to the drawer test, no active force is applied. Rather, the person lies supine with the leg held by another person so that the hip is flexed to 90 degrees and the knee 90 degrees. The main parameter in this test is "step-off", which is the shortest distance from the femur to a hypothetical line that tangents the surface of the tibia from the tibial tuberosity and upwards. Normally, the "step-off" is approximately 1 cm, but is decreased (Grade I) or even absent (Grade II) or inverse (Grade III) in injuries to the posterior cruciate ligament.

Patients who are suspected to have a posterior cruciate ligament injury should always be evaluated for other knee injuries that often occur in combination with an PCL injuries. These include cartilage/meniscus injuries, bone bruises, ACL tears, fractures, posterolateral injuries and collateral ligament injuries.

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.

The common signs and symptoms of a torn meniscus are knee pain, particularly along the joint line, and swelling. These are worse when the knee bears more weight (for example, when running). Another typical complaint is joint locking, when the affected person is unable to straighten the leg fully. This can be accompanied by a clicking feeling. Sometimes, a meniscal tear also causes a sensation that the knee gives way.

A person with a torn meniscus can sometimes remember a specific activity during which the injury was sustained. A tear of the meniscus commonly follows a trauma which involves rotation of the knee while it was slightly bent. These maneuvers also exacerbate the pain after the injury; for example, getting out of a car is often reported as painful.

Injuries in rock climbing may occur due to falls, or due to overuse (see Sports injury). Injuries due to falls are relatively uncommon; the vast majority of injuries result from overuse, most often occurring in the fingers, elbows, and shoulders. Such injuries are often no worse than torn calluses, cuts, burns and bruises. However, overuse symptoms, if ignored, may lead to permanent damage (esp. to tendons, tendon sheaths, ligaments, and joint capsules).

The climbers most prone to injuries are intermediate to expert within lead climbing or bouldering.

The most common symptom is pain over the heel area, especially when the heel is palpated or squeezed. Patients usually have a history of recent trauma to the area or fall from a height. Other symptoms include: inability to bear weight over the involved foot, limited mobility of the foot, and limping. Upon inspection, the examiner may notice swelling, redness, and hematomas. A hematoma extending to the sole of the foot is called "Mondor Sign", and is pathognomonic for calcaneal fracture. The heel may also become widened with associated edema due to displacement of lateral calcaneal border. Involvement of soft tissue (tendons, skin, etc.,) should be evaluated because soft tissue injury has been associated to serious complications (see below).

Shin splints, also known as medial tibial stress syndrome (MTSS), is defined by the American Academy of Orthopaedic Surgeons as "pain along the inner edge of the shinbone (tibia)." Shin splints are usually caused by repeated trauma to the connective muscle tissue surrounding the tibia. They are a common injury affecting athletes who engage in running sports or other forms of physical activity, including running and jumping. They are characterized by general pain in the lower region of the leg between the knee and the ankle. Shin splints injuries are specifically located in the middle to lower thirds of the anterior or lateral part of the tibia, which is the larger of two bones comprising the lower leg.

Shin splints are the most prevalent lower leg injury and affect a broad range of individuals. It affects mostly runners and accounts for approximately 13% to 17% of all running-related injuries. High school age runners see shin splints injury rates of approximately 13%. Aerobic dancers have also been known to suffer from shin splints, with injury rates as high as 22%. Military personnel undergoing basic training experience shin splints injury rates between 4–8%.

A tibial plateau fracture is a break of the upper part of the tibia (shinbone) that involves the knee joint. Symptoms include pain, swelling, and a decreased ability to move the knee. People are generally unable to walk. Complication may include injury to the artery or nerve, arthritis, and compartment syndrome.

The cause is typically trauma such as a fall or motor vehicle collision. Risk factors include osteoporosis and certain sports such as skiing. Diagnosis is typically suspected based on symptoms and confirmed with X-rays and a CT scan. Some fractures may not be seen on plain X-rays.

Pain may be managed with NSAIDs, opioids, and splinting. In those who are otherwise healthy, treatment is generally by surgery. Occasionally, if the bones are well aligned and the ligaments of the knee are intact, people may be treated without surgery.

They represent about 1% of broken bones. They occur most commonly in middle aged males and older females. In the 1920s they were called a "fender fracture" due to their association with people being hit by a motor vehicle while walking.

A scapular fracture is a fracture of the scapula, the shoulder blade. The scapula is sturdy and located in a protected place, so it rarely breaks. When it does, it is an indication that the individual was subjected to a considerable amount of force and that severe chest trauma may be present. High-speed vehicle accidents are the most common cause. This could be anywhere from a car accident, motorcycle crash, or high speed bicycle crash but falls and blows to the area can also be responsible for the injury. Signs and symptoms are similar to those of other fractures: they include pain, tenderness, and reduced motion of the affected area although symptoms can take a couple of days to appear. Imaging techniques such as X-ray are used to diagnose scapular fracture, but the injury may not be noticed in part because it is so frequently accompanied by other, severe injuries that demand attention. The injuries that usually accompany scapular fracture generally have the greatest impact on the patient's outcome. However, the injury can also occur by itself; when it does, it does not present a significant threat to life. Treatment involves pain control and immobilizing the affected area, and, later, physical therapy.

Shin splint pain is described as a recurring dull ache along the inner part of the lower two-thirds of the tibia. In contrast, stress fracture pain is localized to the fracture site.

Biomechanically, over-pronation is a common factor in shin splints and action should be taken to improve the biomechanics of the gait. Pronation occurs when the medial arch moves downward and towards the body's midline to create a more stable point of contact with the ground. In other words, the ankle rolls inwards so that more of the arch has contact with the ground. This abnormal movement causes muscles to fatigue more quickly and to be unable to absorb any shock from the foot hitting the ground.

Stress fractures are typically discovered after a rapid increase in exercise. They most commonly present as pain with weight bearing that increases with activity. The pain usually subsides with rest but may be constantly present with a more serious bone injury. There is usually an area of localized tenderness on or near the bone and generalized swelling to the area. Percussion or palpation to the bone may reproduce symptoms. Anterior tibial stress fractures elicit focal tenderness on the anterior tibial crest, while posterior medial stress fractures can be tender at the posterior tibial border.