The loss of part of a limb is a difficult event for anyone. However, there are times either after an acute injury or following a complex chronic problem (ex. Diabetic foot infection) where a below-the-knee amputation is not only warranted, but offers the patient the best chance for a more functional, and often less painful extremity. Patients with a well-fitted below-the-knee prostheses may be able to function at high level often without a noticeable limp. However, mobility and function following successful surgery and rehabilitation is often limited by the patients pre-surgery level of function. Those that had limited function prior to surgery may also be limited post-surgery. Recovery from a below knee amputation involves wound healing, rehabilitation, and emotional support.
There are a variety of indications for a below knee amputation including:
- An uncontrolled infection of the foot (ex. a severe diabetic foot infection)
- A traumatic injury to the foot or lower leg that can not be salvaged
- Loss of blood supply to the foot either from trauma or vascular disease
- A chronic foot or ankle injury that can not be salvaged or reconstructed and where the patient has a high likelihood of having significantly improved pain-control and/or function following an amputation
The procedure is performed so as to preserve function of the knee joint, leave a long enough amputation stump to fit a prosthesis, and provide adequate soft-tissue padding over what would otherwise be a prominent stump of bone. The amputation is typically performed in the middle of the lower leg. The skin incision and dissection is typically made significantly longer in the back (posteriorly) than in the front (anteriorly). This allows the calf muscle to be brought forward to provide padding over the bony stump. The major veins and arteries are identified, tied off and then cut. Nerves are cut short to minimize the risk of painful neuroma. The major nerves are identified and both the big bone (tibia) and smaller bone (fibula) of the lower leg are cut with a saw and smoothed. The smaller bone (fibula) is usually cut shorter than the big bone (tibia). The front of the cut tibia is beveled to avoid a sharp beak of bone at the front of the leg. The amputation is then closed by suturing layers of tissues together including often suturing a remnant of what was part of the Achilles tendon to the front of the tibia to improve stability of the stump.
Healing Phase (0 thru 6-12 weeks)
During the healing phase the wound of the amputation stump is healing. Sutures are usually removed at 2-3 weeks post-surgery although this may be much longer in patients with diabetes. Often a stump shrinker (a sock that provides even pressure to the healing stump) is applied once the sutures have been removed. It is important to keep the knee functioning as normally as possible (including the ability to fully straighten) during the healing phase. It is not uncommon for patients to fall during this phase as they may momentarily “forget” that they have had their leg amputated.
Prosthetic Fitting (8+ weeks)
Prosthetic fitting is started once the wound and soft-tissues have healed adequately. A prosthetist is a trained expert who coordinates the prosthetic fitting. This individual needs to work closely with the patient over a number of months to ensure that the prosthesis fits optimally. Initially a preparatory prosthesis is molded and fit. Patients are encouraged to slowly start walking with support and often begin physical therapy at this time. Initially patients can only wear the prosthesis for short periods of time, but gradually this time period increases. Over time the amputation stump shrinks from a combination of less swelling and atrophy of the muscles. As this occurs more and more stump shrinkers need to be added and the socket of the prosthesis needs to be adjusted. When the stump has reached a stable size usually 6-9 months following the amputation a “permanent” prosthesis is made including a new lighter molded socket.
Learning to walk with the prosthesis and rehabilitating muscles and joints that often have not been used normally for many months is critical for a successful result following a below knee amputation. Regular physical therapy is essential. Starting with a lot of support (ex a walker) and gradually progressing to improve strength, balance, and endurance will help optimize the results. There are often setbacks and patients need to try not to become discouraged when these occur. Often the amputation stump will become irritated in localized areas requiring the patient to decrease their activities for a period of time. Alterations in the liner and socket of the prosthesis are usually required so regular visits to the prosthetist are common.
There are a variety of potential complications that can occur following a below knee amputation. These include general postsurgical complications as well as more specific complications such as:
Wound healing problems
Phantom limb pain
Difficult with prosthetic fitting
Decreased function (increased energy expenditure)