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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Lisfranc injury, also known as Lisfranc fracture, is an injury of the foot in which one or more of the metatarsal bones are displaced from the tarsus. The injury is named after Jacques Lisfranc de St. Martin (2 April 179013 May 1847), a French surgeon and gynecologist who described an amputation of the foot through the tarsometatarsal articulation, in 1815, after the War of the Sixth Coalition.

The Hume fracture is an injury of the elbow comprising a fracture of the olecranon with an associated anterior dislocation of the radial head which occurs in children. It was originally described as an undisplaced olecranon fracture, but more recently includes displaced fractures and can be considered a variant of the Monteggia fracture.

The injury was described in 1957 by A.C. Hume of the orthopaedic surgery department of St. Bartholomew's Hospital, Rochester.

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

The injury can be difficult to diagnose initially as the attention is focused on the injury to the radial head, leading to the distal radio-ulnar injury being overlooked. The examination finding of tenderness of the distal radio-ulnar joint suggests an Essex-Lopresti injury in patients who have sustained high energy forearm trauma. Plain radiography shows the radial head fracture, with dorsal subluxation of the ulna often seen on lateral view of the pronated wrist.

Injury

Because the medial collateral ligament resists widening of the inside of the knee joint, the ligament is usually injured when the outside of the knee joint is struck. This force causes the outside of the knee to buckle, and the inside to widen. When the MCL is stretched too far, it is susceptible to tearing and injury. This is the injury seen by the action of "clipping" in a football game.

An injury to the MCL may occur as an isolated injury, or it may be part of a complex injury to the knee. Other ligaments ACL, or meniscus, may be torn along with a MCL injury.

Symptoms

The most common symptom following an MCL injury is pain directly over the ligament. Swelling over the torn ligament may appear, and bruising and generalized joint swelling are common 1 to 2 days after the injury. In more severe injuries, patients may complain that the knee feels unstable.

Treatment

Treatment of an MCL tear depends on the severity of the injury. Treatment always begins with allowing the pain to subside, beginning work on mobility, followed by strengthening the knee to return to sports and activities. Bracing can often be useful for treatment of MCL injuries. Fortunately, most often surgery is not necessary for the treatment of an MCL tear.

Ideal x-ray visualization of an elementary fracture will depend on the fracture type:

- Posterior wall fracture: Iliac oblique and obturator oblique views

- Posterior column fracture: Iliac oblique and obturator oblique views

- Anterior wall fracture: Iliac oblique view

- Anterior column fracture: Obturator oblique view

In all cases, CT scan can assist in identifying impacted bone pieces, which may be found within the joint, and MRI may be done to identify the extent of potential injury to the sciatic nerve.

In humans, the midfoot consists of five bones that form the arches of the foot (the cuboid, navicular, and three cuneiform bones) and their articulations with the bases of the five metatarsal bones. Lisfranc injuries are caused when excessive kinetic energy is applied either directly or indirectly to the midfoot and are often seen in traffic collisions or industrial accidents.

Direct Lisfranc injuries are usually caused by a crush injury, such as a heavy object falling onto the midfoot, or the foot being run over by a car or truck, or someone landing on the foot after a fall from a significant height. Indirect Lisfranc injuries are caused by a sudden rotational force on a plantar flexed (downward pointing) forefoot. Examples of this type of trauma include a rider falling from a horse but the foot remaining trapped in the stirrup, or a person falling forward after stepping into a storm drain.

In athletic trauma, Lisfranc injuries occur commonly in activities such as windsurfing, kitesurfing, wakeboarding, or snowboarding (where appliance bindings pass directly over the metatarsals). American football players occasionally acquire this injury, and it most often occurs when the athlete's foot is plantar flexed and another player lands on the heel. This can also be seen in pivoting athletic positions such as a baseball catcher or a ballerina spinning.

The Essex-Lopresti fracture is a fracture of the radial head with concomitant dislocation of the distal radio-ulnar joint and disruption of the interosseous membrane. The injury is named after Peter Essex-Lopresti who described it in 1951.

The Segond fracture is a type of avulsion fracture (soft tissue structures tearing off bits of their bony attachment) of the lateral tibial condyle of the knee, immediately beyond the surface which articulates with the femur.

Symptoms reported by sufferers include: pain and aching to the neck and back, referred pain to the shoulders, sensory disturbance (such as pins and needles) to the arms and legs, and headaches. Symptoms can appear directly after the injury, but often are not felt until days afterwards. Whiplash is usually confined to the spine. The most common areas of the spine affected by whiplash are the neck and middle of the spine. "Neck" pain is very common between the shoulder and the neck. The "missing link" of whiplash may be towards or inside the shoulder and this would explain why neck therapy alone frequently does not give lasting relief.

Cognitive symptoms following whiplash trauma, such as being easily distracted or irritated, seems to be common and possibly linked to a poorer prognosis.

The Jersey Finger is a finger-related tendon injury that is common in athletics and can result in permanent loss of flexion of the end of the finger if not surgically repaired.

This injury often occurs in American football when a player grabs another player's jersey with the tips of one or more fingers while that player is pulling or running away.

A "Jersey finger" is an injury to an FDP tendon at its point of attachment to the distal phalanx. This injury often occurs in American football when a player grabs another player's jersey with the tips of one or more fingers while that player is pulling or running away. The force of this action hyperextends the tip of the finger at the DIP joint while the proximal portion of the finger is flexed. This action can partially or completely rupture the FDP tendon at or near its attachment point on the distal phalanx. Sometimes, the force is great enough to pull off or avulse a piece of phalangeal bone to which the tendon can remain attached. Although it is a common football injury, this injury can occur during other sports or activities as well.

After the injury occurs, the torn FDP tendon may retract slightly, remaining in the finger near the PIP joint, or can retract more fully into the palm of the hand. A person who suffers a jersey finger injury in which the FDP tendon is completely ruptured cannot flex the affected digit at the DIP joint without assistance.

Signs and Symptoms include:

- A pop or rip felt in the finger at the time of the injury

- Pain when moving the injured finger and the inability to bend the DIPjoint

- Tenderness, swelling. and warmth of the injured finger

- Bruising after 48 hours

- Occasionally a lump felt in the palm of the finger

- Mallet finger deformity

Typical signs and symptoms of a strain include pain, functional loss of the involved structure, muscle weakness, contusion, and localized inflammation. A strain can range from mild annoyance to very painful, depending on the extent of injury.