During World War II, the perception of amputation changed from ablative failure surgery to the modern paradigm of amputation as the first step in rehabilitation. The effect that the destructive component of the injury or disease process has on the affected individual and the steps that can be taken to return them to, as close as possible, their preinjury or disease state need to be addressed using a modern evidencebased model for health care. It is important to discuss the components of limb loss that universally affect the amputee population and the unique characteristics of upper versus lower extremity amputation, amputation in the adult compared with the child, and some of the nuances associated with amputation for injury compared with infection or disease.

The psychological effect of amputation on health-related quality of life has been best studied in trauma patients. The Lower Extremity Assessment Project was an observational study of more than 600 civilian patients who sustained mutilating lower extremity injuries, of whom more than 150 underwent amputation. Validated outcomes tools were used to achieve longitudinal observation of the effect of the injury on their quality of life. One of the most enlightening insights gained from this pivotal investigation was the appreciation that one of the most important factors for successful rehabilitation following traumatic amputation was family support structure.¹ Using insight gained from this observational study, the core investigators used similar tactics to evaluate amputees from Operation Enduring Freedom. The Military Extremity Trauma/Amputation Limb Salvage Study investigation provided further insight into these affected individuals, demonstrating that individuals with traumatic amputations had a high probability to exhibit severe symptoms of depression or posttraumatic stress disorder.²

This information provides modern evidence-based support that helps orthopaedic surgeons to objectively appreciate the obvious psychological effect that amputation has on the affected individual, both during the acute phase of injury and recovery, and the prolonged period of rehabilitation. The roles that depression and posttraumatic stress disorder play in each of the groups, whether it be the body image stresses affecting a child with a congenital amputation or a patient facing amputation for tumor, infection, or gangrene, can easily be extrapolated.³

The hand is a unique organ of prehension and sensation that helps differentiate humans from much of the rest of the animal kingdom. It is the special relationship between sensory input and functional prehension that makes amputation of the upper extremity far more disabling than amputation of the lower extremity. When planning reconstruction of the upper extremity following trauma, the orthopaedic surgeon must consider the negative effect that a prosthesis or orthosis has on the residual limb by both shielding the terminal
residual limb from its important role as a sensory probe with the world, and blocking the sight lines that are necessary to manipulate objects with a prosthetic terminal device.

Experience has demonstrated that a high percentage of patients reject even high-tech electronic-powered prostheses. They find that even the very sophisticated devices are perceived as being cumbersome and slow to respond to initiation of a task. Many patients will become proficient with a prosthesis and then use it only as a tool for performing necessary tasks. The fact that the prosthesis renders the upper extremity insensate shields the patient from proprioceptive feedback and demands continual visual monitoring to operate. Often, retention of a rudimentary post and palm that allows simple prehension is functionally superior to the most sophisticated prostheses.

The normal human foot is composed of more than 20 bones that allow the dual functions of a shock absorber at heel strike and a stable platform to allow propulsion at push-off. The ligaments that connect the bones of the foot are relaxed when the foot is loaded at heel strike. This unlocked position of the joints, combined with the unique durable cushioned plantar skin and subcutaneous fibrous connective tissue, allows the foot to dampen the effect of weight bearing. As the foot transitions from the unlocked load acceptance position of ankle dorsiflexion and foot supination at heel strike to the locked position of ankle plantar flexion and foot pronation at push-off, the foot is able to transition from an organ of dampening weight acceptance to a stable platform for propulsion at push-off.

Unlike the adaptable weight-bearing organ of the normal foot, an amputation residual limb is generally composed of one or two bones and a soft-tissue envelope that must interface with a prosthesis to mimic the organ functions of the normal foot. When surgically creating an amputation residual limb, surgeons need to be cognizant of these dual functions to create a terminal organ that will interface with a prosthesis to provide pressure-dissipating cushioning at loading and stability for push-off.

The self-selected walking speed of a person is determined by multiple factors that allow them to optimize energy consumption during walking. People are most efficient when healthy and well rested, and least efficient when affected by illness or injury. Engineering professionals view the joints of the lower extremity as energy couples. Illness or injury to the limb makes the mechanical construct both less energy efficient and more prone to activity-related discomfort. Prosthetic joints are not as efficient as the original equipment. Figure 1 depicts the metabolic/energy cost of walking with a prosthesis. The more proximal the level of amputation, the greater is the negative effect on function. Note that the transfemoral amputee uses very similar energy consumption during normal walking and maximum walking speed. Because these studies are performed in the laboratory, this is akin to having to run at all times.^4,5,6,7 It is further established that amputees tend to take a similar number of steps every day. This metabolic cost affects their daily lives, making amputees ration the number of steps they will take.⁸

Several important questions should be addressed by the surgeon before making the decision to proceed with limb salvage versus amputation, regardless of the disease or injury indication. Experience in trauma has taught the surgeon that the best time to make that decision is at the time of injury. It becomes very difficult to convince a patient to remove a nonfunctional limb after a substantial effort has been made to take the path of functional limb salvage. Patients with poorly conceived reconstruction plans are often doomed to a life of poor function and chronic neurogenic regional pain.

The questions to be addressed in the trauma bay, the diabetic foot clinic, or the oncology clinic are:

In the modern outcomes-oriented environment, it is clear that retention of limb length is closely correlated with optimal functional outcomes. When planning amputation surgery, the surgeon should strive to retain as many functional joints and residual limb length compatible with available tissue and prosthetic limb fitting. The most difficult decisions arise when the surgeon is required to choose between a longer residual limb length with a poor soft-tissue envelope and a more proximal amputation level with a more optimal residual limb. Results of the Lower Extremity Assessment Project study would suggest that the poor functional outcomes of the 17 knee disarticulations were due to suboptimal amputation residual limbs as opposed to poor ability to use a prosthesis. When the data were closely scrutinized, it was determined that most of the knee disarticulations performed in the Lower Extremity Assessment Project study were performed within the zone of injury and had poor soft-tissue envelopes. Those patients would likely have fared better with an optimally performed transfemoral amputation.¹

Bioengineering professionals view weight bearing as the transfer of load between the amputation residual limb and the prosthetic socket. The ground reaction force vector is applied to the amputation residual limb directly in disarticulations at the knee or ankle levels and thorough total surface bearing in the transosseous transfemoral or transtibial amputation levels. Orthopaedic surgeons use the terms direct load transfer, or end-bearing in disarticulations, and indirect load transfer, or total surface bearing in transosseous amputation levels (Figure 2).

End-bearing disarticulations behave much like normal weight transfer in a sound limb. Long bones are expanded at the level of the metaphysis to create a larger surface area for distribution of the weight-bearing load, and composed of low-elastic modulus cancellous bone to dissipate the impact of loading. A cushioned end pad acts to substitute for the dampening and cushioning function of the durable plantar tissue of the foot. Because the actual bony loading is similar to normal, prosthetic socket fit is not crucial. This is a valuable feature in patients with significant volume fluctuations, for example, renal failure, where the socket can be adjustable to compensate for volume changes^9,10 (Figure 2, A and Figure 3).

The bioengineering concept of indirect load transfer is better known in the prosthetic world as total surface bearing. This method of prosthetic socket construction is used in transosseous amputation levels where the surface area of the terminal bone is small and the bone is composed of higher stiffness cortical bone (Figure 2, B). The theoretic concept is to unload the small surface area of the stiff cortical bone of the terminal tibia in the transtibial amputation level and terminal femur in the transfemoral level. By flexing the knee 7° to 10° in the transtibial prosthesis and adducting the femur in the transfemoral prosthesis, pressure can be taken away from the distal end of the bone and distributed over the entire surface area of the residual limb.^11,12 To accomplish this task, prosthetic socket fit becomes crucial. If the patient loses as few as 5 lb, pain or ulceration overlying the prominent terminal cortical bone can develop. If the patient gains weight, they will not be able to fit the prosthetic socket.^9,10 The residual bone of transosseous amputees normally pistons during weight bearing. When the soft-tissue envelope of the residual tibia or femur is composed of mobile muscle and full-thickness normal skin, the bone will piston within the soft-tissue envelope. When the soft-tissue envelope is adherent to the bone, the pistoning occurs between the skin and the prosthetic socket, creating shear forces that lead to blisters and skin breakdown. This is best addressed surgically by creating an optimal soft-tissue envelope. When the skin of the amputation residual limb is adherent to the bone, the prosthetist will attempt to compensate by using some form of a silicone liner as an interface between adherent skin and the prosthetic socket (Figure 4).

The residual bone of an amputation residual limb serves as a platform for load transfer in lower extremity amputation and a lever arm to drive an upper
extremity prosthesis. The soft-tissue envelope serves as a cushion to dampen the effect of weight bearing and prevent tissue breakdown over bony prominences during prosthetic use. The optimal soft-tissue envelope is composed of mobile muscle and full-thickness skin (Figure 4).