Lower limb injuries among motor vehicle occupants are relatively common and are one of the principle causes of permanent disability. The author has reviewed the current literature and his own experience as an orthopaedic surgeon and research accident investigator concerning lower limb injuries among motor vehicle occupants. An unreported series of knee, thigh, hip, pelvis injuries with indepth accident investigation is reported.

Incidence rates for specific injury diagnoses are not available. Gross tabulations reveal that lower limb injury is second only to head injury in frequency among injured motor vehicle occupants. Lower limb injuries are possibly the commonest cause of permanent disability and impairment resulting from motor vehicle accidents.

Accident investigation studies have identified the mechanisms of the more common lower limb injuries which are as follows:​

1. Intrapelvic fracture-dislocations of the hip are caused by lateral impacts selectively loading the greater trochanter of the proximal femur.
2. Pelvic rami fractures occur with lateral impacts in which the load is distributed to the iliac wing and pelvis as well as the greater trochanter by a padded or yielding surface.
3. Posterior hip dislocations are caused by axial loading of the femur through the knee with the hip in acute flexion. Similar loading and less flexion causes fractures of the posterior wall of the acetabulum (hip socket) followed by dislocation.
4. Femoral shaft fractures are caused by axial loading of the femur through the knee and the application of a bending moment to the thigh. Penetration of the knee into the clash, slipping below the lower dash, or impaction of the thigh against the steering wheel or steering column are the usual causes of the bending moment.
5. Supracondylar and comminuted shaft fractures occur in more severe accidents with increased energy transfer to the femur through the knee and without bending moment.
6. Patellar fractures occur because of load concentration on the patella. Knee contact with dash support structures or dash mounted accessories may provide such concentration, resulting in patellar fractures.
7. Knee ligament and other soft tissue and joint surface injuries are caused by knee impact with the lower dash and/or interaction between the knee, dash and foot, toepan and/or pedals.
8. Posterior cruciate ligament injury is caused by loading of the proximal tibia through the lower dash displacing the tibia posteriorly beneath the femoral condyles.
9. Tibial shaft fracture are caused by axial loading because of knee-dash fixation and upward and rearward movement of the toepan coupled with torsion and/or a bending moment.
10. Foot and ankle injuries are caused by upward and rearward displacement of the toepan after the knee has impacted and become fixed in the lower dash or by rolling off the brake pedal.

Treatment of lower limb fractures is necessarily prolonged because of the necessity for bone healing and rehabilitation of injured joints. Cast immobilization of 6 weeks to as much as a year may be necessary. Certain fractures are best treated by open reduction and internal fixation with plates and screws, intramedullary nails, circumferential wires and bands. Occasionally, immobilization in traction or external fixation with the use of trans-fixation pins extending trhough the skin into the bone, is necessary. Soft tissue damage and loss must be repaired or replaced by graft or substitution with an artificial implant. Minimum healing time is seldom less than 3 months, typically requires 6-12 months, and may extend as long as several years.

Permanent disability frequently results from lower extremity injuries. Fractures extending into major joints,' the hip, knee and ankle frequently cause traumatic (degenerative) arthritis. Total joint replacement of the hip and knee, and fusion of the ankle are ultimately often necessary to provide even partial relief from such disability. Ligamentous injuries of the knee may lead to long term instability and traumatic arthritis. Deformities due to bone loss, malunion and infection are also common sequelae of more severe fractures of the lower limb.