Deleterious Musculoskeletal Conditions Secondary to Lower Limb Loss: Considerations for Prosthesis-Related Factors

Abstract

Significance: The intent of this work was to summarize the existing evidence of, and highlight knowledge gaps specific to, prosthetic devices/componentry and training regimes, particularly in the context of the human–device interaction and deleterious musculoskeletal conditions secondary to lower limb loss.

Recent Advances: With the recent and evolving technological advancements in prostheses, there are numerous devices available to individuals with lower limb loss. Current literature demonstrates the importance of expanding the knowledge of all prosthetic device-specific factors and the significance of proper prescription, fit, and alignment, along with adequate device-/activity-specific training, to enhance human–device interaction, reduce gait abnormalities and compensatory motions, and as a result, mitigate risk for secondary musculoskeletal conditions.

Critical Issues: Inadequate device prescription, fit, alignment, and training are evident owing to the lack of knowledge or awareness of the many device-specific properties and factors, leading to suboptimal use, as well as, biomechanical compensations, which collectively and adversely affect the function, activity level, and overall health of the prosthesis user.

Future Directions: To maximize optimal outcomes after lower limb loss, it is essential to better appreciate the factors that affect both prosthesis use and satisfaction, particularly any modifiable factors that might be targeted in rehabilitation interventions such as device prescription, fit/alignment, and training regimes. A better understanding of such device-specific factors will help enhance the human–device interaction and resulting functional performance, thereby reducing secondary musculoskeletal conditions, allowing for the readiness of the fighting force (return-to-duty/redeployment) and/or improved reintegration into civilian society/work, and overall enhancing quality of life after lower limb loss.

Brad D. Hendershot, PhD

Scope and Significance

With the recent and ever-changing technological advancements in prostheses, there are numerous components/devices available to individuals with lower limb loss. The various options all have unique properties and offer distinct benefits to the user, and although numerous factors can influence the development of compensatory motions after amputation, the initial prescription and fit of prosthetic devices, along with the associated training/rehabilitation regimes, are thought to play a substantial role, thus highlighting the importance for the clinical team/prosthetist to fully understand all device-specific factors to assist in mitigating the development of secondary musculoskeletal conditions. The purpose of this study was to summarize existing evidence and highlight knowledge gaps specific to prosthetic devices and training regimes in the context of the human–device interaction and resultant secondary musculoskeletal conditions after lower limb loss.

Translational Relevance

To reach optimal functional performance and reduce the risk for secondary musculoskeletal conditions, it is essential for prosthetic devices to be properly prescribed for the patient and desired activity/function, and properly fit/aligned to the individual with adequate device- and activity-specific training. Achieving optimal functional performance after lower limb loss enhances human health and well-being for prosthesis users, encourages the reintegration into society and readiness to redeploy/return-to-duty (RTD), and overall enables positive health outcomes.

Clinical Relevance

Expanding scientific and clinical knowledge of the various prosthetic device properties and technological advancements, while enforcing a more targeted/individualized training intervention, is likely to yield optimal prosthesis use. Access to accurate prosthetic prescription, fit, and alignment, with effective rehabilitation and training, and a sustainable system of care (at-home monitoring/training regime), is thought to reduce subsequent injuries, enhance functional performance, and overall improve long-term quality of life (QoL) for prosthesis users.

Background

There are ∼2 million people with limb loss in the United States, and ∼185,000 new amputations occurring each year owing primarily to vascular disease (54%) and trauma (45%).^1,2 Regardless of etiology or patient population, individuals with limb loss suffer with reduced function, increased mortality and morbidity rates, and lessened QoL.³ Individuals with limb loss are also at greater risk for developing deleterious musculoskeletal conditions secondary to amputation,^4,5 which can become apparent at any point after lower limb loss (Fig. 1). Specifically, low back pain (LBP) affects 52–90% of persons with limb loss, 38% of whom report the back pain significantly interferes with their daily life.^5–8 The prevalence of LBP is such that it is the most commonly reported secondary health condition after lower limb loss, with the greatest implications on functional ability and overall QoL.^9–11 Lower limb prosthesis users are reported to be twice as likely to develop a lumbar-spine injury or lower limb overuse injury, and four times as likely to develop upper body/limb overuse injuries, compared with those with mild injuries, with 59–68% of these occurring within 1 year of amputation.¹² On the contrary, those who required (and received) a revision amputation/surgery demonstrated near-term improvements in functional performance, health status, and QoL measures,^13–15 and likely mitigated longer term risk for secondary issues had they not received a revision when needed. Furthermore, lower extremity joint pain and degeneration (e.g., osteoarthritis) are also more prevalent after (unilateral) amputation; 41–75% at the contralateral knee, and 55–61% at the contralateral hip, compared with 17.9–22% and 18–23%, respectively, among uninjured individuals.^6,16 Although the specific causes remain unclear, altered gait and compensatory motions resulting from poor human–device interaction play a substantial role in the onset and/or recurrence of these deleterious musculoskeletal conditions secondary to lower limb loss.

Figure 1.

Schematic diagram to outline the process and overall timeline after lower limb loss.

Biomechanical compensations and asymmetries are commonly evident in prosthesis users,¹⁷ which can adversely affect the function, activity level, and overall health of the prosthesis user. For example, lower limb prosthesis users often perform activities of daily living (ADLs) with uneven weight distribution, increased external rotation of the lower limb, increased swing phase knee flexion, and decreased prosthetic stance phase knee flexion,^5,18 among others. Repeated performance of ADLs with these adaptations or compensations can lead to elevated mechanical demands on musculoskeletal tissues, directly linked to a heightened risk for deleterious secondary musculoskeletal health conditions.⁴ Moreover, these subsequent conditions often become chronic issues, negatively and substantially impacting longer term function and QoL.^3,5,19 Although numerous factors can adversely influence the human–device interaction after limb loss, resulting in various compensatory motions, the initial prescription and fit of prosthetic devices, along with the associated (or lack of) training/rehabilitation regimes likely play a substantial role^5,20,21; persons with limb loss who are not properly trained in the use of a given prosthetic device often perform tasks with suboptimal motions.^22,23

Studies have described the importance of proper device prescription, fit, and alignment, along with adequate device- and activity-specific training, to reduce gait abnormalities and compensatory motions which, in turn, reduce the prevalence of and risk for, secondary health issues.^3,5 With the ever-changing and advancing technology, there are numerous prosthetic devices available to individuals with lower limb loss. With every device, there are several individual components that work together and are crucial to the success of prosthesis. Each component has various options and alternatives available, dependent on the individual and the function needed/desired. It is important for the clinical team/prosthetist to fully understand the individual, his/her lifestyle, desired activities, and functional level. Patient-specific characteristics such as the sex/gender of the individual can play a critical role in the prosthetic prescription, fit, and training regimes. Because of differences in preferences, needs, desires, goals, and so on, associated with gender, men are more likely to be fitted to a prosthesis successfully, and are more likely to incur a shorter rehabilitation period.^24,25 For optimal device function, it is essential for each individual prosthesis component to be judiciously prescribed based on the individual patient-specific characteristics and the desired activity/function, and the inclusion of appropriate device and RTD/activity-specific training. The purpose of this narrative review was to summarize existing evidence and highlight knowledge gaps specific to prosthetic devices and training regimes in the context of compensatory motions and resultant secondary musculoskeletal conditions after lower limb loss. A better understanding of these important aspects can help enhance the human–device interaction, thereby optimizing functional performance and mitigating the risk for secondary musculoskeletal conditions, allowing for the reintegration into society and readiness to redeploy/RTD, and overall maximizing QoL after lower limb loss.

Discussion of Findings and Relevant Literature

Prosthetic components

Prosthetic socket

Achieving a comfortable and effective connection between the residual limb and prosthesis is crucial for optimal outcomes and successful prosthesis use. Along with the use of gel or silicone liners, the type of socket material (e.g., thermoplastic, bioelastic, and carbon fiber) and suspension system (e.g., pin locking, suction, or elevated vacuum) are all critical factors to consider when prescribing a prosthetic socket. Inadequate prescription, fit, or alignment to an individual's residual limb can directly affect comfort, function, activity level, and residual limb volume, physiology, and wound healing,^26–30 proving the socket system to be the most significant component for overall success when fitting a prosthetic device.^31,32 Moreover, socket fit/comfort directly affects the time to prosthetic fitting and first steps,³³ and an optimal residual limb-to-socket interface can minimize asymmetric loading during gait,³⁴ thereby reducing risk for secondary musculoskeletal conditions. A prosthetic socket can cause deleterious health effects (e.g., soft tissue injury, bleeding, bruising, pressure sores, and pain) if the residual limb physiology and residuum–socket interface (RSI) is not considered (i.e., appropriate load transmission and efficient movement control) when prescribing and fitting/aligning a socket, and thereby reduces the functional ability of the individual.³⁵ If the RSI is compromised, even the slightest, users ambulate with imbalance and instability, forcing compensatory movements to occur and resultant secondary musculoskeletal conditions.¹⁹

A large number of individuals with limb loss are dissatisfied with the comfort of their socket, thereby rejecting prosthesis use or reporting a low satisfaction level because of a suboptimal interaction between the socket and residual limb.^34,36 In addition, prosthesis fitting can be delayed because of postoperative complications and/or pre-prosthetic conditions, such as joint contractures or residual limb health issues. Postoperative joint contractures are a common complication in the residual limb after lower limb loss, causing a significant mobility impairment, pain, and tissue breakdown, where prosthesis use is limited or even forbidden.²¹ If residual limb health is not maintained (e.g., infection and wounds), volume fluctuations are not controlled, and/or an individual rejects prosthetic use for other reasons (e.g., fit, comfort, and suboptimal device prescription), this could lead to immobility (wheelchair/bed bound), reducing range of motion (ROM) and strength, causing deleterious musculoskeletal issues in the long term, proving the importance of socket/prosthetic fit/use to be significantly important. In an effort to maximize socket performance and comfort without adversely affecting residual limb health, prosthetists aim to minimize suspension-dependent movement between the socket and residual limb, but current approaches are limited as they rely on anecdotal visual cues along with subjective verbal feedback from the patient. Nevertheless, prosthetists use this information to revise socket parameters such as volume, geometry, and type of suspension to provide current ‘best’ fit for a patient. Various shape capture/fabrication techniques can be used to develop a well-fitting socket. These differing techniques include traditional hands-on approaches (varies per clinician) and hands-off approaches (e.g., electrical/digital scans, sensors, and three-dimensional [3D] printing).^37–39 Although hands-off/digital approaches allow for more rapid production of customized designs (infinite design options, material choices, and print settings) and more consistent results, the traditional fabrication techniques (hands-on; casting/mold by hand) is a more personal, patient-centric approach.³⁷ Regardless of prosthetic fitting, the volume of mature residual limbs are subject to both acute/daily^40,41 and chronic⁴² changes in volume; as such, interactions between the residual limb and socket represents a critical barrier to reach superior comfort, optimize prosthesis fit, and defend residual limb health.

Relatedly, several studies have explored the clinical benefits associated with vacuum suspension that includes retention of residual limb volume,^28–30 increased proprioception, improvements in skin health and wound healing,^43–45 and reduced movement between the socket and residual limb.^46–48 Additional studies have shown a positive effect on residual limb physiology, wound healing, and function, and ultimately superior control of the socket and prosthesis when using vacuum or suction suspensions.^26,36 Vacuum suspension systems have shown to lessen ROM restrictions of the lower extremities, increase comfort, improve hygiene, decrease perspiration, lessen skin pressure contact,⁴⁹ reduce fitting complications, and lessen skin surface area contained in the socket.^46,50,51 In contrast, other studies determined that pin-locking suspension systems allow for less heat/moisture to accumulate, an increased activity level, and greater comfort to certain individuals.^52–54 Regardless, suction suspension is still widely used and the preferred method for individuals with lower limb loss, and has shown to allow a better fit in comparison with distal suspension mechanisms (e.g., pin locking), maximum stability, and user proprioception.³⁶ Each suspension system encompasses unique benefits, making it important for clinicians to make an informed decision based on the individual's personal characteristics, goals, activity level, and residual limb anatomy and physiology.

In addition, alignment is an important factor that directly affects the fit/comfort of a socket. Malalignment of a socket has a direct and systematic effect on socket reaction moments, creating greater forces and in-socket pressures to the residual limb.^55,56 These larger forces and in-socket pressures not only cause discomfort and suboptimal function/performance, but also greater tissue damage⁵⁷ and stresses on the bone⁵⁸ that, over time, could further exacerbate secondary musculoskeletal conditions. Relatedly, the magnitude and duration of the coronal (valgus/varus) and sagittal (extension/flexion) socket reaction moments directly affect the load transfer of the prosthesis to the residual limb through the socket,⁵⁹ that when misaligned can cause contractures to subsequent joints, and therefore is another critical factor affecting the comfort and function of the prosthesis.

Historically, a significant limitation to traditional socket and liner materials is the thermal insulating function, thereby trapping heat/moisture inside the system, which can lead to numerous deleterious issues, including loss of suspension and significant problems with the residual limb. To mitigate these issues, new approaches are therefore needed to enhance breathability,⁶⁰ allowing the release of heat and drainage of moisture.⁶¹ Alternative options have shown improvements in balance,⁶² gait mechanics,^63,64 and overall an enhanced QoL.⁶³

Osseointegration

A viable alternative to socket use is osseointegration, a bone-anchored implant for direct attachment of a terminal prosthesis, can enhance function/mobility and improve QoL, especially for individuals with reduced prosthesis use from socket-related problems.^65,66 Individuals with lower limb loss have benefited from osseointegrated prostheses, specifically with improvements in device use, mobility, function, and overall QoL.^67–69 Although osseointegration implants for prosthetic systems in individuals with lower limb loss provide improved performance and eliminated socket issues/complications, the long-term durability of these implants is still unknown and the risk of infection is significantly higher compared with nonosseointegrated prostheses.^70,71 To this end, in a 5-year follow-up with individuals with osseointegrated prostheses, although patient-reported outcomes were significantly improved (increased use of prosthesis, improved mobility, and improved physical health-related QoL measures), 67% had superficial infections and 22% had deep infections requiring additional surgeries.^59,72 Further work is needed to investigate the longer term incidence rate of infections, and associated changes in mobility and functional performance, ideally with less compensatory movements to reduce secondary musculoskeletal conditions. Whether the prosthesis is osseointegrated or attached with a traditional socket, the residual limb interface is critical to the success of the adjoining distal components and overall function of the prosthesis.

Knee prostheses

The prosthetic knee type utilized largely depends on the individual's ability and lifestyle/function needed. There are various types of knee (e.g., single axis, manual locking, stance control, polycentric, fluid controlled; hydraulic/pneumatic, microprocessor, and powered), all with diverse properties, purposes, and functions. As with other prosthetic components, each knee type offers unique benefits dependent on the individual and activities performed, from having complete stance stability/locking mechanism, to having multi-axial rotation, similar to an anatomical knee, allowing the joint to actively swing and flex during the gait cycle.

The design and function of the prosthetic knee is of particular importance because it is the most proximal artificial joint that the person with limb loss must stabilize and control to effectively ambulate. Historically, new or elderly, less active lower limb prosthesis users will use a manual locking or stance control prosthesis. These devices have limited articulation and capabilities, but allow the individual to gain strength and confidence in using a prosthetic knee, where the knee is locked when weight is placed in the prosthesis, and bends when manually unlocked or weight is displaced.⁷³ However, suboptimal prescription and/or excessive use of a manual-locking device can lead to undesirable compensatory strategies, causing loss of joint motion over time, chronic pain, and/or secondary musculoskeletal conditions as a result of forcing the user to ambulate with stiff-knee gait.⁷⁴ Lower limb prosthesis users who are more ambulatory and qualify (e.g., based on Medicare Functional Classification Level/K-level) for an advanced, functional device, often will use a passive, mechanical (i.e., free swing, manual lock, constant friction, weight-activated friction, or fixed-aperture fluid) mechanism in the knee joint to control the swing and stance phases of gait to allow for more anatomically natural movements. More recently, these prostheses have adopted active, microprocessor-controlled systems. Although mechanical and microprocessor control knees are functionally similar, microprocessor control allows dynamic management of the flexion and extension behavior of the knee joint throughout the gait cycle.⁷³ Microprocessor knees have provided improved performance and reduction in falls/stumbles when compared with mechanical knees,⁷³ allowing for a significant reduction in oxygen/energy consumption,⁷⁵ improved swing-phase characteristics, and greater stability during stance phase,⁷⁶ overall enhancing functional gait performance.

Another option is a powered prosthesis in which a hydraulically actuated knee joint works together with a hydraulic power source and off-board electronics.⁷⁷ A powered knee prosthesis reportedly produces sufficient torque and mimics concentric quadriceps function in a body weight loaded condition⁷⁸ while reproducing several kinematic characteristics of healthy upslope walking that a passive prosthesis is unable to accomplish (i.e., knee flexion after heel strike).⁷⁹ The use of a powered knee prosthesis in comparison with a passive device, resulted in function more closely resembling an anatomical knee, with enhanced hip moment symmetry while sitting, and a more symmetric knee moment while standing.⁷⁸

To minimize compensatory motions and subsequent issues or injuries, a prosthetic knee must provide stability during stance, and freely flex/shorten the prosthesis during swing to enable the user to advance the limb.⁷⁶ The knee joint therefore directly influences the entire leg during both swing and stance, and thus a device that limits full ROM of the knee/subsequent joints or causes the user to perform ADLs with compensatory motions, can elevate the risk for secondary musculoskeletal conditions. Overall, the knee joint type, features (i.e., function/purpose/activity specific), and alignment directly affects the use and overall performance, and risk of developing secondary musculoskeletal conditions. It is important to consider all factors of the various prosthetic knees to determine the most suitable device for an individual to allow for optimal performance and function.

Ankle–foot prostheses

There are numerous commercially available ankle–foot prostheses for individuals with lower limb loss. The various prosthetic ankle–foot options from rigid, passive, articulating, or powered (i.e., solid ankle cushion heel, single axis, multi-axis, dynamic response, with either hydraulic, microprocessor, or powered control) offer unique functional properties/features and benefits. In most cases, a patient needs/is prescribed more than one ankle–foot prosthesis (i.e., an everyday walking foot along with activity-specific feet), largely dependent on the tasks/activities to be performed. When prescribing an ankle–foot prosthesis, it is important to fully understand the features/benefits of all device options compatible for the patient, and possible congruency or interactions with the chosen prosthetic knee (if transfemoral amputation). The prosthetic ankle–foot used directly affects the user's gait activity, performance, and functional ability,³⁵ thereby emphasizing the importance of selecting the appropriate device.

Rigid prosthetic devices do not completely restore the biomechanical functionality provided by the ankle muscles, leading to gait asymmetries and increased reliance on the intact limb.⁸⁰ Although compliant prosthetic ankles provide increased energy storage and return (ESR), they also increase hip joint power and vertical ground reaction force on the intact limb.⁵³ Using a mechanically passive (noncomputerized) device is thought to be limiting compared with an active articulating device, because of its nonadaptive capabilities, resulting in significant gait alterations.¹⁸ On the contrary, an articulating device that allows prosthetic ankle dorsiflexion and ESR has been shown to reduce compensations and improve whole-body mechanics.⁸¹ Of note, various alterations of hindfoot and forefoot stiffness offer different biomechanical benefits,⁸² where optimal foot stiffness ultimately reduces metabolic cost and intact knee joint loading, improving the overall human–device interaction.⁸³

New technology has also introduced powered articulation, capable of providing real-time adaptations to activity and terrain through electromyogram sensors/pattern recognition control algorithms, thus improving metabolic energy, ambulation/mobility, and overall function.^79,84 In addition, it is valuable to consider ankle–foot dynamics and power when evaluating an individual's gait to best prescribe a prosthetic ankle–foot.⁸⁵ Compared with passive devices, the use of a powered ankle reduced metabolic demand, improved step-to-step transition work, and improved ankle power while walking on level ground.⁸⁶ The use of a powered ankle–foot prosthesis also reduces the biomechanical risk factors for osteoarthritis development by decreasing the peak vertical force and loading rate on the affected limb,⁸⁷ and mitigates the forces and knee adduction moment applied to the unaffected limb⁸⁸ of a person with unilateral lower limb loss, although the added weight and bulk often leaves this option to be less desirable. Of note, a combined powered knee–ankle device, in which both joints are controlled together in a coordinated manner, much as the human neuromuscular system controls those joints in an intact limb, may further improve walking performance and core muscle activity.⁸⁹

Other/miscellaneous componentry

The selection of the distal components and the abutments/connecters are equally important. Typically, a shock absorbing or rigid pylon⁹⁰ is used to attach or connect prosthetic components to one another and/or to the socket pyramid. Ensuring proper alignment among all components is critical. Predominantly, when an ankle–foot is misaligned (angular and/or translational), greater loads are forced on the ipsilateral knee joints⁹¹ and the subpatellar area⁹² during gait of individuals with lower limb loss. The external knee moments applied to the knee ligaments and knee muscles on the amputated side change systematically in response to different plantar flexion or dorsiflexion angles of the prosthetic ankle–foot. These angular and translational malalignments significantly increase the stresses on knee ligaments and the posterior knee capsule.⁹³ Proper prescription, along with optimal fit and alignment would permit comfort, balance, energy efficiency, proper gait biomechanics, and minimize mechanical load/force on subsequent joints.

Prosthetic prescription

The initial prescription of a device that is unsuitable/suboptimal to the patient can lead to increased metabolic cost/energetic burden,⁹⁴ device abandonment,⁹⁵ decreased balance that increases the likelihood of falls/injuries, decreased activity levels, and ultimately a lesser QoL.^96,97 Burger and Vidmar reported 23–45% of prosthesis users suffer from various overuse syndromes/injuries from improper prosthetic device prescription.⁹⁸ Ultimately, these complications and limitations lead to inefficient/inadequate performance, compensatory motions, and pain/injuries to subsequent joints (secondary issues). Individual needs, priorities, and characteristics vary greatly across patients; therefore, optimal prescription likely requires a more individualized, customizable regime. Although there have been studies looking to address these shortcomings through mobile monitoring,⁸⁹ haptic feedback,⁹⁹ and K-level functional-specific prescription,¹⁰⁰ there has been no longstanding solution to optimize prosthesis prescription for those with lower limb loss. Because no two patients are alike (i.e., demographics, risk factors, needs, goals, preferences, medical health status, function, mobility, and abilities), to achieve optimal performance in ADLs and other occupational or recreational activities/tasks, it is important to determine what patient characteristics, goals, and outcome measures/specific criteria are most indicative of the appropriate device(s) to be prescribed. In most cases, this may involve prescribing more than one device (e.g., an everyday walking leg and a running/activity-specific leg) to obtain optimal performance in all activities. Of note, 3D printing can be used to develop custom prostheses (e.g., shorty feet for individuals beginning to walk after bilateral lower limb loss), or adaptive activity-specific attachments (e.g., ice skates, climbing feet, mechanic's feet, etc.) to enhance functional capabilities and outcomes individualized to the patient.¹⁰¹

Prosthetic fit and alignment

After device prescription, the primary factors influencing successful and functional use of a lower limb prosthesis is ensuring proper fit and alignment of the device(s). Optimal device use and performance, and greater functional mobility and independence, have been associated with the successful fitting of a prosthetic device.¹⁰² Specifically, improper fit or alignment (i.e., relative orientation of prosthetic components, such as the prosthetic socket to the foot) to a given individual can adversely affect comfort, and thus result in gait adaptations and compensations while performing tasks/activities. Prosthetic device components can have angular (flexion, extension, abduction, and adduction) and translational (anterior, posterior, lateral, and medial) malalignment referenced from nominal/optimal alignment (as defined by conventional clinical methods).⁵⁵ Such malalignment can lead to pelvic tilt/obliquity, leg length inequality, unbalanced postures, as well as greater energy consumption, socket moment reactions, and force on subsequent joints during ADLs or specific tasks.

Individuals with lower limb loss use their prosthesis significantly less, with suboptimal performance, if improperly fitted and uncomfortable to them.¹⁰³ Proper device fit and alignment greatly influences the comfort, rehabilitation, community integration, employment, activity level, readiness to RTD, and overall QoL.¹⁰² Although most individuals achieve successful prosthetic fitting within 1 year after a lower limb amputation, a number of medical variables and psychosocial factors are associated with prosthetic fitting, utilization, and function.¹⁰⁴ With the numerous variations in device type and function, it is critical for clinicians to understand the proper device to be prescribed along with the proper alignment and fitting for the patient, customized to the specific parameters of the individual and activities/tasks to be performed.

Prosthetic device/activity-specific training

After successfully prescribed and fitted to a prosthesis, the patient must undergo extensive training to reach optimal performance. To maximize the functional potential of a prosthesis and allow for all control motions, it is essential for the patient to maintain appropriate joint mechanics and ROM.¹⁰⁵ Continual maintenance of joint ROM, increased muscle strength, and attainment of maximal functional independence, are all crucial elements to ensure patient success with the prosthesis, making the training and rehabilitation phase of critical importance. Effective training and rehabilitation facilitates the highest level of function possible, enabling the return to daily life duties at the most functional independence. Individuals with limb loss who received proper training, such as minimizing abnormal loading of the intact limb and performing tasks with optimal body mechanics, have been shown to perform tasks with their prosthesis in a skillful, efficient manner, exceeding the performance of untrained amputees.^21,34 Current methods include patient education, evaluation, ROM assessment, strength testing, ADL assessment, followed by specific ROM, ADL, and strengthening exercises.⁹³ The exercise program and specific tasks performed are designed according to the abilities and needs of the patient. The strengthening exercises focus on areas of weakness and primary muscle groups important to prosthetic harnessing and operation. Specific muscles deemed as potential myocytes for myoelectric prosthetic operation are also important to incorporate into strengthening exercises.¹⁰⁶ Current methods primarily focus on the initial evaluation and assessment with a brief demonstration of proper movement, although, often times, users never receive any specialized physical therapy, where training of proper device use is often overlooked.^21,107,108 In some cases, patients are even trained over the phone and learn how to use the device on their own with no real practice of proper movements and exercises. Recent literature found that military service members with limb loss utilize training/physical therapy services significantly more than civilians with limb loss.¹⁰⁹ Active interventions (i.e., therapeutic exercise and gait training) to assist with functional recovery were reported as the major focus with service members in the first year after lower limb loss, with manual therapies and education being less utilized.¹⁰⁹ Active interventions (i.e., walking/gait training, muscle strengthening, balance exercises, and functional training programs) after lower limb loss, directly improves gait performance and functional abilities.¹¹⁰

In addition to the proper exercises and initial training interventions, it is important to have a maintenance plan and long-term system of care, whereby the user can continually practice and improve movement patterns,¹⁰⁶ and accommodate for numerous changes per individual (i.e., residual limb size/strength, device, function, performance, and activity). Unfortunately, this crucial phase is often left to the patient to perform on their own with no real direction or motivation to continue after the initial evaluation, and therefore exclusive of any device or RTD/activity-specific training. Although support of the specific connection is limited/remains unclear, thus further investigation is needed to identity the direct correlation and long-term effects that training has on resultant secondary musculoskeletal conditions.

At present, only a few studies have investigated the use of technology to assist with prosthetic training, showing real-time feedback to be effective in improving design/fit¹¹¹ and performance with neural or myoelectric devices,¹¹² and in gait biomechanics.¹¹³ Providing mobile and real-time feedback, with therapist-driven intervention, has shown to be feasible, demonstrating the importance of further advancing the effectiveness of rehabilitation and training for prosthesis users.¹¹⁴ Thus, incorporating real-time feedback technologies into traditional clinical care (i.e., device fit/alignment and acute/long-term optimal training) would reduce adaptations and enhance functional performance in prosthesis users. Improvements in training and rehabilitation would significantly enhance prosthesis use and expand the ability to optimally participate in various activities, sports, or RTD. Improvement in functional outcomes and gait are evident in those with greater daily activity.¹¹⁵ Individuals with limb loss have been shown to improve in performance, function, overall health, well-being, and QoL when participating in adaptive sports or recreational activities. Whether the activity is a musical performance, a friendly round of golf, or a high-level track-and-field competition, the benefits of participation in sports and recreation are numerous both at the individual and at the societal level.¹¹⁶ Properly prescribed prosthetic components that are appropriately fit/aligned to the individual, along with adequate rehabilitation/training procedures, allows for the prosthesis user to participate in desired activities/sports with optimal performance and reduced risk of secondary musculoskeletal conditions.

Future Directions

Literature has begun to demonstrate the importance of proper device prescription, fit, and alignment, along with adequate device- and activity-specific training, to reduce gait abnormalities and compensatory motions, and as a result, reduce secondary musculoskeletal conditions. Long-term practice of performing ADLs or activities with alterations or compensations increases the risk of secondary health issues. It is likely that proper device prescription, fit, and alignment, along with ongoing device- and activity-specific training could optimize performance and reduce secondary health effects, allowing for the readiness of fighting forces and greater RTD rates.

Summary

Despite technological advancements in prostheses, the vast majority of those living with the loss or deficiency of a limb ultimately abandon/reject prosthesis use.^1,117 Overall, 60% of prosthesis users have been reported to suffer from pain when using their device, with a 40% overall device rejection/abandonment rate.⁹⁰ Regardless, the majority of prosthesis users perform ADLs with compensations¹¹⁸ and gait abnormalities or deviations,^88,119,120 many of which are commonly associated with an elevated risk for secondary musculoskeletal conditions (e.g., joint degeneration and pain).⁵ Lower limb loss is directly associated with suboptimal spinal kinematics and kinetics, causing LBP to be the most prevalent secondary health condition, adversely affecting functional ability and overall QoL.^7,121 Although there exists a number of outcome measures specific to prosthetic devices, mobility/function, QoL, and residual limb/socket comfort/health,^122–129 appropriate outcome measures designed specifically for secondary musculoskeletal issues after lower limb loss are at present limited/nonexistent. Evidence of compensatory motions and secondary musculoskeletal conditions can likely be reduced by enhancing the human–device interaction through proper prosthetic device prescription, suitable fit/alignment, and adequate training.

Prosthetic prescription and fitting are typically subjective to the clinician. Moreover, device-specific rehabilitation and training are limited, traditionally only provided during acute care for initial prosthetic device fitting and ambulation, with no long-term system of care to accommodate or adapt over time (e.g., to changes in residual limb health/volume, desired activity level) or for device- or activity/adaptive sport-specific training. Knowing a patient's individual characteristics, needs, requirements, and priorities, along with an appropriate understanding of all available device parameters and functions, would result in optimal prosthesis prescription. Literature suggests that considering patient-specific variables when prescribing a prosthesis and individualizing the physical therapy intervention would better predict the rehabilitation outcomes and yield greater optimal functional performance.¹³⁰ Because prosthetic technology and medicine are ever-changing,¹³¹ there is a need for a mechanism by which clinicians and prosthetists can stay abreast of all devices and technological advancements, along with optimal device training for the patients while demonstrating how guidelines and standards improve the outcomes of those whom require prostheses.¹³² This would ensure that most optimal device is prescribed with adequate device-/activity-specific training to reduce compensatory motions and enhance functional performance.

Although technological advancements are allowing the opportunity for individuals after limb loss to participate in any and all activities, and permitting the resumption of all activities/duties they once performed, optimal device use and training procedures are still lacking. To reintegrate into the work force and community, it is especially important to incorporate biomechanical methodologies to ensure optimal movements and performance with minimal compensatory motions, to reduce the risk of developing secondary musculoskeletal conditions. Because a successful training and rehabilitation program is essential, the demand for advanced rehabilitation techniques is substantially high, with a need for advanced rehabilitative interventions to optimize prosthetic training for individuals with limb loss.¹³³ There is a significant need for innovative training and therapeutic approaches to advance rehabilitation techniques, especially for higher functioning persons with limb loss with the goal of RTD in the military or returning to specific tasks or sports/activities in the civilian community.^134,135 Access to accurate prosthesis prescription, fit, and alignment, with effective rehabilitation and training, and long-term sustainable system of care (at-home monitoring/training regime), can enhance functional performance, reduce compensatory motions and the risk for subsequent issues/injuries or secondary musculoskeletal conditions, and overall improve QoL for prosthetic users.

Take-Home Messages

• With ongoing technological advancements, there are growing numbers and varieties of prosthetic components/devices available to individuals with lower limb loss, all with unique properties and benefits, making it important for the clinical team/prosthetist to stay abreast and appreciate all influential device-specific factors.

• Individual needs, priorities, and characteristics also vary greatly across patients, highlighting the need for a more individualized, customizable regime to allow for optimal prosthesis prescription, fit, and alignment.

• Improvements in training and rehabilitation would significantly enhance prosthesis use and expand the ability to participate in various activities, sports, or RTD with minimal compensatory motions and optimal performance.

• Overall, access to accurate prosthesis prescription, fit, and alignment, with effective rehabilitation and training, and a long-term sustainable system of care (long-term monitoring/training regime), can enhance the human–device interaction and resulting functional performance, thereby reducing secondary musculoskeletal conditions, allowing for the readiness of the fighting forces (RTD/redeployment), and/or improved reintegration into society/work, and overall enhancing QoL after lower limb loss.

Abbreviations and Acronyms

3D

three-dimensional

ADLs

activities of daily living

EACE

Extremity Trauma and Amputation Center of Excellence

EMG

electromyogram

ESR

energy storage and return

LBP

low back pain

QoL

quality of life

ROM

range of motion

RSI

residuum–socket interface

RTD

return-to-duty

USUHS

Uniformed Services University of the Health Sciences

WRNMMC

Walter Reed National Military Medical Center

Acknowledgements and Funding Sources

This work was supported by the DoD-VA Extremity Trauma & Amputation Center of Excellence (EACE; Public Law 110–417, National Defense Authorization Act 2009, Section 723), and several DoD Awards (65826, 65915, 65529, 65732, 65621). The authors also thank the patients, and the clinical and research teams at Walter Reed National Military Medical Center (WRNMMC) and across the Military Health System.

Author Disclosure and Ghostwriting

No competing financial interests exist. The content of this article was expressly written by the authors listed. No ghostwriters were used to write this article. The views expressed in this article are those of the authors, and do not necessarily reflect the official policy of the Uniformed Services University of the Health Sciences (USUHS), Departments of the Army, Navy, Defense, Veterans Affairs, nor the United States Government.

About the Authors

Ashley D. Knight, PhD, is a Biomedical Engineer and the Orthotics & Prosthetics Research Lead within the EACE at WRNMMC. Dr. Knight's research interest is primarily focused on improving human-device interaction and enhancing optimal functional performance of those following extremity trauma/limb loss, thereby reducing compensatory musculoskeletal conditions and encouraging physical activity/real-world mobility to ultimately improve long-term QoL. Christopher L. Dearth, PhD, serves as Chief of the Research and Surveillance Division for the EACE, and as an Associate Professor within the Department of Surgery at the USUHS, where he is the Director of the Regenerative Biosciences Laboratory. In these roles, Dr. Dearth leads a multidisciplinary team of clinicians and researchers whose collective focus is on the mitigation, treatment, and rehabilitation of traumatic extremity injuries and amputations. Brad D. Hendershot, PhD, is the EACE Facility Research Director at WRNMMC. In this role, he directs the Biomechanics and Virtual Reality Laboratories within the Department of Rehabilitation. Dr. Hendershot's research aims to characterize factors underlying the high prevalence of musculoskeletal complications secondary to extremity trauma, to mitigate development/ recurrence over the longer term, and ultimately improve QoL for service members and veterans with extremity trauma/limb loss.