On one level, there is not much difference organically between a ligament and a tendon. Both are formed from chains of collagen cells produced by proteins stored in the body. This is where the similarity stops, however. A ligament acts much like a shock absorber and connects bone to bone. A tendon acts more like an anchoring point for a band of muscles and attaches muscle to bone. The large Achilles tendon, for example, attaches calf muscles to the ankle bone, while a ligament holds the calf and thigh bones together at the knee joint.
When a person suffers a traumatic injury such as a sprain, both ligaments and tendons could be torn or even separated completely. A significant loss of mobility is possible with both a ligament and a tendon injury, since the body's weight-bearing structure has been compromised. Treatment for ligament or tendon sprains often includes immobility of the affected joint or limb until the body can regenerate the collagen and heal itself.
One difference between a ligament and a tendon injury is the type of surgery which may be required. A torn tendon may cause the entire attached muscle group to fail. Surgical repair of a tendon often involves an actual reattachment of the tendon to the bone and possibly months of immobilization and rehabilitation as the tendon's attachment becomes stronger and the muscles become less atrophied through regular exercise. A severely torn tendon can take at least 6-8 weeks to heal before minimal mobility is restored.
Orthopedic surgery for a ligament involves a different approach. The damaged ligament can sometimes be reattached to the joint bones surgically, but other times a substitute material is injected to provide cushioning and protection as the body's natural collagen begins to replace the damaged ligament. Recovery from a ligament injury can take just as long as a tendon injury, but some people regain mobility sooner following treatment for a ligament injury. Doctors may also suggest a longer period of immobility for a ligament injury, in order to give the body enough time to repair the damaged collagen from within. Too much movement of the joint could cause the new ligament material to fail again.