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.

Posterior dislocations are uncommon, and are typically due to the muscle contraction from electric shock or seizure. They may be caused by strength imbalance of the rotator cuff muscles. Patients typically present holding their arm internally rotated and adducted, and exhibiting flattening of the anterior shoulder with a prominent coracoid process.

Posterior dislocations may go unrecognized, especially in an elderly patient and in the unconscious trauma patient. An average interval of 1 year was noted between injury and diagnosis in a series of 40 patients.

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.

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.

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.

Ulnar collateral ligament injuries can occur during certain activities such as overhead baseball pitching. Acute or chronic disruption and/or attenuation of the ulnar collateral ligament often result in medial elbow pain, valgus instability, neurologic deficiency, and impaired throwing performance. There are both non-surgical and surgical treatment options.

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.

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.

In over 95% of shoulder dislocations, the humerus is displaced anteriorly. In most of those, the head of the humerus comes to rest under the coracoid process, referred to as sub-coracoid dislocation. Sub-glenoid, subclavicular, and, very rarely, intrathoracic or retroperitoneal dislocations may also occur.

Anterior dislocations are usually caused by a direct blow to, or fall on, an outstretched arm. The patient typically holds his/her arm externally rotated and slightly abducted.

A Hill-Sachs deformity is an impaction of the head of the humerus left by the glenoid rim during dislocation. Hill-Sachs deformities occur in 35%-40% of anterior dislocations. They can be seen on a front-facing X-ray when the arm is in internal rotation. Bankart lesions are disruptions of the glenoid labrum with or without an avulsion of bone fragment.

Damage to the axillary artery and axillary nerve (C5,C6) may result. The axillary nerve is injured in 37% making it the most commonly injured structure with this type of injury. Other common, associated, nerve injuries include injury to the suprascapular nerve (29%) and the radial nerve (22%). Axillary nerve damage results in a weakened or paralyzed deltoid muscle and as the deltoid atrophies unilaterally, the normal rounded contour of the shoulder is lost. A patient with injury to the axillary nerve will have difficulty in abducting the arm from approximately 15° away from the body. The supraspinatus muscle initiates abduction from a fully adducted position.

Signs and symptoms of a dislocation or rotator cuff tear such as:

- Significant pain, which can sometimes be felt past the shoulder, along the arm.

- Inability to move the arm from its current position, particularly in positions with the arm reaching away from the body and with the top of the arm twisted toward the back.

- Numbness of the arm.

- Visibly displaced shoulder. Some dislocations result in the shoulder appearing unusually square.

- No bone in the side of the shoulder showing shoulder has become dislocated.

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.

Pain along the inside of the elbow is the main symptom of this condition. Throwing athletes report it occurs most often during the acceleration phase of throwing. Closing the hand and clenching the fist has also been shown to reproduce the painful symptoms. The injury is often associated with an experience of a sharp “pop” in the elbow, followed by pain during a single throw. In addition, swelling and bruising of the elbow, loss of elbow range of motion, and a sudden decrease in throwing velocity are all common symptoms of a UCL injury. If the injury is less severe, pain can be minimal with complete rest.

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.

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.

Symptoms of an ankle fracture can be similar to those of ankle sprains (pain), though typically they are often more severe by comparison. It is exceedingly rare for the ankle joint to dislocate in the presence of ligamentous injury alone. However, in the setting of an ankle fracture the talus can become unstable and subluxate or dislocate. Patients may complain of ecchymosis (bruising), or there may be an abnormal position, abnormal motion, or lack of motion.

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.

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.

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.

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.

A strain is a type of acute injury that occurs to the muscle or tendon. Similar to sprains, it can vary in severity, from a stretching of the muscle or tendon to a complete tear of the tendon from the muscle. Some of the most common places that strains occur are in the foot, back of the leg (hamstring), or back.

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.

Individuals with Jefferson fractures usually experience pain in the upper neck but no neurological signs. The fracture may also cause damage to the arteries in the neck, resulting in lateral medullary syndrome, Horner's syndrome, ataxia, and the inability to sense pain or temperature.

In rare cases, congenital abnormality may cause the same symptoms as a Jefferson fracture.

A strain can occur as a result of improper body mechanics with any activity (e.g., contact sports, lifting heavy objects, overstretching) that can induce mechanical trauma or injury. Generally, the muscle or tendon overstretches and is placed under more physical stress than it can exert. Strains commonly result in a partial or complete tear of a tendon or muscle, or they can be severe in the form of a complete tendon rupture. The most common body location for strains to occur is in the foot, leg, or back.

- Acute strains are more closely associated with recent mechanical trauma or injury.

- Chronic strains typically result from repetitive movement of the muscles and tendons over a long period of time.

Degrees of Injury (as classified by the American College of Sports Medicine)

• First degree (mildest) – little tissue tearing; mild tenderness; pain with full range of motion.

• Second degree – torn muscle or tendon tissues; painful, limited motion; possibly some swelling or depression at the spot of the injury.

• Third degree (most severe) – limited or no movement; pain will be severe at first, but may be painless after the initial injury

Symptoms of gamekeeper's thumb are instability of the MCP joint of the thumb, accompanied by pain and weakness of the pinch grasp. The severity of the symptoms are related to the extent of the initial tear of the UCL (in the case of Skier's thumb), or how long the injury has been allowed to progress (in the case of gamekeeper's thumb).

Characteristic signs include pain, swelling, and ecchymosis around the thenar eminence, and especially over the MCP joint of the thumb. Physical examination demonstrates instability of the MCP joint of the thumb.

The patient will often manifest a weakened ability to grasp objects or perform such tasks as tying shoes and tearing a piece of paper. Other complaints include intense pain experienced upon catching the thumb on an object, such as when reaching into a pants pocket.