Blount's disease occurs in young children and adolescents. The cause is unknown but is thought to be due to the effects of weight on the growth plate. The inner part of the tibia, just below the knee, fails to develop normally, causing angulation of the bone.

Unlike bowlegs, which tend to straighten as the child develops, Blount's disease is progressive and the condition worsens. It can cause severe bowing of the legs and can affect one or both legs.

This condition is more common among children of African ancestry. It is also associated with obesity, short stature, and early walking. There does not appear to be an obvious genetic factor.

The cause of PFFD is uncertain. Two hypotheses have been advanced. The theory of sclerotome subtraction posits injury to neural crest cells that are the precursors to sensory nerves at the level of L4 and L5. Histologic studies of a fetus with unilateral PFFD have prompted an alternative hypothesis that PFFD is caused by a defect in maturation of chondrocytes (cartilage cells) at the growth plate. In either hypothesis, the agent causing the injury is usually not known. Thalidomide is known to cause PFFD when the mother is exposed to it in the fifth or sixth week of pregnancy, and it is speculated that exposure to other toxins during pregnancy may also be a cause. Other etiologies that have been suggested, but not proven, include anoxia, ischemia, radiation, infection, hormones, and mechanical force. PFFD occurs sporadically, and does not appear to be hereditary.

Tibia shaft fractures are the most common long bone fractures. They account for approximately 4% of the fractures seen in the Medicare population.

Failure to treat Blount's disease may lead to progressive deformity.Blount's disease may come back after surgery, especially in younger children. Because of the bowing, a leg-length discrepancy may result. This may result in disability if the discrepancy is significant (greater than 1 inch) and is not treated.

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

In most cases persisting after childhood, there is little or no effect on the ability to walk. Due to uneven stress and wear on the knees, however, even milder manifestations can see an accelerated onset of arthritis.

The proposed mechanism involves shear stress and lack of displacement due to the periosteum that is relatively strong compared to the elastic bone in young children.

The following factors may be involved in causing this deformity:

- Inherent laxity of the knee ligaments

- Weakness of biceps femoris muscle

- Instability of the knee joint due to ligaments and joint capsule injuries

- Inappropriate alignment of the tibia and femur

- Malunion of the bones around the knee

- Weakness in the hip extensor muscles

- Gastrocnemius muscle weakness (in standing position)

- Upper motor neuron lesion (for example, hemiplegia as the result of a cerebrovascular accident)

- Lower motor neuron lesion (for example, in post-polio syndrome)

- Deficit in joint proprioception

- Lower limb length discrepancy

- Congenital genu recurvatum

- Cerebral palsy

- Multiple sclerosis

- Muscular dystrophy

- Limited dorsiflexion (plantar flexion contracture)

- Popliteus muscle weakness

- Connective tissue disorders. In these disorders, there are excessive joint mobility (joint hypermobility) problems. These disorders include:

- Marfan syndrome

- Ehlers-Danlos syndrome

- Benign hypermobile joint syndrome

- Osteogenesis imperfecta disease

Rate in the United States have been estimated to occur among an at-risk population of 1,774,210,081 people each year. Incidence rates published in the American Journal of Sports Medicine for ages 10–17 were found to be about 29 per 100,000 persons per year, while the adult population average for this type of injury ranged between 5.8 and 7.0 per 100,000 persons per year. The highest rates of patellar dislocation were found in the youngest age groups, while the rates declined with increasing ages. Females are more susceptible to patellar dislocation. Race is a significant factor for this injury, where Hispanics, African-Americans and Caucasians had slightly higher rates of patellar dislocation due to the types of athletic activity involved in: basketball (18.2%), soccer (6.9%), and football (6.9%), according to Brian Waterman.

Lateral Patellar dislocation is common among the child population. Some studies suggest that the annual patellar dislocation rate in children is 43/100,000. The treatment of the skeletally immature is controversial due to the fact that they are so young and are still growing. Surgery is recommended by some experts in order to repair the medial structures early, while others recommend treating it non operatively with physical therapy. If re-dislocation occurs then reconstruction of the medial patellofemoral ligament (MPFL) is the recommended surgical option.

There are typically four classes (or "types") of PFFD, ranging from class A to class D, as detailed by Aitken.

In the United States, more than US $3 billion is spent each year on arthroscopic knee surgeries that are known to be ineffective in people with degenerative knee pain.

Attenuated patella alta is an extremely rare condition affecting mobility and leg strength. It is characterized by an unusually small knee cap (patella) that develops out of and above the joint. Normally, as the knee cap sits in the joint, it is stimulated to growth by abrasion from the opposing bones. When not situated properly in the joint, the knee cap does not experience such stimulation and remains small and undeveloped. Note that the cartilage under and around the kneecap is eight times smoother than ice, so "abrasion" may not be the best term.

A similar condition, patella alta, can occur as the result of a sports injury, though the large majority of the time it is a congenital/developmental condition that is unrelated to trauma. A kneecap in an "alta" position sits above the "trochlear groove" and therefore is less stable. The "patellar tendon" that connects the kneecap to the tibia (shinbone)is elongated (longer than normal). This cannot happen by way of trauma, unless there has been a rupture of the tendon and a less-than-optimal surgical repair.

There has been only one documented case of the disorder noted from birth. In 1988, three-year-old Eric Rogstad of Minneapolis, Minnesota was discovered to suffer from the condition in both knees after several attempts by his parents and family physician to discover the cause of his abnormal difficulties with walking and running. After surgery and physical therapy, Eric gained the ability to walk and run without significant difficulty.

Insall Ratio: This ratio is calculated with the knee flexed to 30 degrees. It is the ratio of the length of the patella to the length of the patellar tendon. Normally this ratio is 1:1 but 20% variation represents patella alta or patella infera. Actually, the Insall-Salvati ratio can be measured at any degree of flexion, which is one reason for its popularity.

Women in sports such as association football, basketball, and tennis are significantly more prone to ACL injuries than men. The discrepancy has been attributed to gender differences in anatomy, general muscular strength, reaction time of muscle contraction and coordination, and training techniques.

Gender differences in ACL injury rates become evident when specific sports are compared. A review of NCAA data has found relative rates of injury per 1000 athlete exposures as follows:

- Men's basketball 0.07, women's basketball 0.23

- Men's lacrosse 0.12, women's lacrosse 0.17

- Men's football 0.09, women's football 0.28

The highest rate of ACL injury in women occurred in gymnastics, with a rate of injury per 1000 athlete exposures of 0.33

Of the four sports with the highest ACL injury rates, three were women's – gymnastics, basketball and soccer.

According to recent studies, female athletes are two to eight times more likely to strain their anterior cruciate ligament (ACL) in sports that involve cutting and jumping as compared to men who play the same particular sports (soccer, basketball, and volleyball). Differences between males and females identified as potential causes are the active muscular protection of the knee joint, the greater Q angle putting more medial torque on the knee joint, relative ligament laxity caused by differences in hormonal activity from estrogen and relaxin, intercondylar notch dimensions, and muscular strength.

Triplane fracture is a fracture at the epiphyseal plate of the tibia in early adolescence with involvement of the epiphysis and metaphysis of the tibia. The link presents two types of imaging. The first four images (figures 1-4) are radiographic images while the last 3 are CT scans of the left distal tibia and fibula. The first radiographic image is an anterior-posterior view of the distal third of the left tibia and fibula. The image presents a fracture of the distal epiphyseal plate of the tibia and fibula. The primary imaging (radiograph) identifies the abnormality in the anatomy of subject’s left distal tibia and fibula. However, it is difficult to view the extent of the fracture and classify the fracture based on radiographic image. Figure four is a CT scan of the posterior aspect of the left distal tibia and fibula. Note that in this image the extent of the fracture is more visible extending to the epiphysis and metaphysis. The type of fracture is a Salter-Harris type IV. The CT scan was an appropriate choice of advance imaging which helps clinicians determine the extent of the fracture and enable us to address the problem appropriately.

If a child is sickly, either with rickets or any other ailment that prevents ossification of the bones, or is improperly fed, the bowed condition may persist. Thus the chief cause of this deformity is rickets. Skeletal problems, infection, and tumors can also affect the growth of the leg, sometimes giving rise to a one-sided bow-leggedness. The remaining causes are occupational, especially among jockeys, and from physical trauma, the condition being very likely to supervene after accidents involving the condyles of the femur.

Tibial plateau fractures constitute 1% of all fractures. Peak age is 30–40 years old in men and 60-70 in women. Approximately half of the people who sustain a tibial plateau fracture are aged over 50 years old.

The most important factors of knee stability include:

- Ligaments of the knee: The knee joint is stabilized by four main ligaments:

- Anterior cruciate ligament (ACL). The ACL has an important role in stabilization of knee extension movement by preventing the knee from hyperextending.

- Posterior cruciate ligament (PCL)

- Medial collateral ligament (MCL)

- Lateral collateral ligament (LCL)

- Joint capsule or articular capsule (especially posterior knee capsule)

- Quadriceps femoris muscle

- Appropriate alignment of the femur and tibia (especially in knee extension position )

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%.

Risk factors for developing shin splints include:

- Excessive pronation at subtalar joint

- Excessively tight calf muscles (which can cause excessive pronation)

- Engaging the medial shin muscle in excessive amounts of eccentric muscle activity

- Undertaking high-impact exercises on hard, noncompliant surfaces (ex: running on asphalt or concrete)

- Smoking and low fitness level

While medial tibial stress syndrome is the most common form of shin splints, compartment syndrome and stress fractures are also common forms of shin splints. Females are 1.5 to 3.5 times more likely to progress to stress fractures from shin splints. This is due in part to females having a higher incidence of diminished bone density and osteoporosis.

Smokers generally have lower bone density than non-smokers, so have a much higher risk of fractures. There also is evidence that smoking delays bone healing.

Since approximately one third of the tibia lies directly beneath the skin, open fractures are common compared to other long bones. These open fractures are most commonly caused by high velocity trauma (e.g. motor vehicle collisions), while closed fractures most commonly occur from sports injuries or falls. Osteoporosis can be a contributing factor. Skiing and football (soccer) injuries are also common culprits.

Dysbaric osteonecrosis is a significant occupational hazard, occurring in 50% of commercial Japanese divers, 65% of Hawaiian fishermen and 16% of commercial and caisson divers in the UK.

Its relationship to compressed air is strong in that it may follow a single exposure to compressed air, may occur with no history of DCS but is usually associated with significant compressed air exposure. The distribution of lesions differs with the type of exposure - the juxta-articular lesions being more common in caisson workers than in divers.

There is a definite relationship between length of time exposed to extreme depths and the percentage of divers with bone lesions. Evidence does not suggest that dysbaric osteonecrosis is a significant risk in recreational scuba diving.

Surgical repair using open reduction and internal fixation is generally required, and because there is no lateral restraint of the foot, the ankle cannot bear any weight while the bone knits. This typically takes six weeks in an otherwise healthy person, but can take as much as twelve weeks. Non-surgical treatment may sometimes be considered in cases where the patient has significant health problems or where the risk of surgery may be too great.

In children, whose bones are still developing, there are risks of either a growth plate injury or a greenstick fracture.

- A greenstick fracture occurs due to mechanical failure on the tension side. That is, since the bone is not so brittle as it would be in an adult, it does not completely fracture, but rather exhibits bowing without complete disruption of the bone's cortex in the surface opposite the applied force.

- Growth plate injuries, as in Salter-Harris fractures, require careful treatment and accurate reduction to make sure that the bone continues to grow normally.

- Plastic deformation of the bone, in which the bone permanently bends, but does not break, also is possible in children. These injuries may require an osteotomy (bone cut) to realign the bone if it is fixed and cannot be realigned by closed methods.

- Certain fractures mainly occur in children, including fracture of the clavicle and supracondylar fracture of the humerus.

High school athletes are at increased risk for ACL tears when compared to non-athletes. This risk increases with certain types of sports. Among high school girls, the sport with the highest risk of ACL tear is soccer, followed by basketball and lacrosse. The highest risk sport for boys was basketball, followed by lacrosse and soccer. Children and young athletes may benefit from early surgical reconstruction after ACL injury. Young athletes who have early surgical reconstruction of their torn ACL are more likely to return to their previous level of athletic ability when compared to those who underwent delayed surgery or nonoperative treatment. They are also less likely to experience instability in their knee if they undergo early surgery.