Leg amputation causes serious functional impairment and prosthesis is used to restore function and encourage participation to achieve maximal functional potential. Functional abilities of the amputee patients are determined by K-level classification ranging from K0∼K4 as described by Gailey et al (Table 1).¹

Table 1 . K-level Classification Describing Functional Abilities of Persons Who Had Undergone Lower-limb Amputation¹.

Functional classification system
K0	Does not have the ability or potential to ambulate or transfer safely with or without assistance, and a prosthesis does not enhance quality of life or mobility.
K1	Has the ability or potential to use a prosthesis for transfers or ambulation in level surfaces at a fixed cadence. Typical of the limited and unlimited household ambulator.
K2	Has the ability or potential for ambulation with the ability to transverse low-level environmental barriers such as curbs, stairs, or uneven surfaces. Typical of the limited community ambulator.
K3	Has the ability or potential for ambulation with variable cadence. Typical of the community ambulator who has the ability to transverse most environmental barriers and may have vocational, therapeutic, or exercise activity that demands prosthetic use beyond simple locomotion.
K4	Has the ability or potential for prosthetic ambulation that exceeds basic ambulation skills, exhibiting high impact, stress, or energy levels. Typical of the prosthetic demands of the child, active adult, or athlete.

For amputees, preservation of the dominant leg during gait training is associated with functional prognosis. The dominant leg refers to the leg that is used to perform tasks.² During prosthetic gait training the non-amputated side is commonly determined as the dominant leg.³ In these cases, for transfemoral and knee disarticulation patients, initially the prosthesis length is set to be 1/2 inch shorter than the non-amputated, dominant side to enhance foot clearance of the prosthetic limb during swing phase.^4,5

However, if the non-amputated side is affected by a pathological condition such as fractures, nerve injury, or pain, the amputated side may be considered as the dominant leg. The functional goal is estimated to be lower compared to a case of sound conditions on the non-amputated side due to difficulty of supporting weight sufficiently on the non-amputated side, decreased safety of walking, proprioception, and strength. Previous studies have not reported whether a better outcome could be achieved if the dominant leg was the amputation site.

Here in this case series, we shed light on individualized rehabilitation strategies for four complicated amputee cases who had accompanying injuries and pain on the non-amputated legs.

Among patients who visited our institution between January 2011 and March 2023, four patients with amputation and pathological conditions on the non-amputation side were enrolled (Table 2 and Fig. 1). We classified the suitable functional goal using K-level classification for each patient.¹ We prescribed prostheses in accordance with the functional goal, psychologic and socioeconomic status. Certificated prosthetists affiliated with our center fabricated the prostheses and adjusted the alignment. For whom requiring orthoses, certificated orthotists in our center also fabricated them.

Figure 1. Prosthetic fitting. Case #1 (A), #2 (B), #3 (C) and #4 (D).

Table 2 . Clinical Characteristics and Prosthetic Components of Each Subject.

Subject	Sex (M/F)	Age	Diagnosis (stump bone length cm, % of non-amputated limb)	Etiology/K-level	Concurrent pathologic conditions	Orthosis	Prosthetic components
1	Male	33	Right transfemoral amputation (32.4 cm, 76.0%)	Trauma/K3	Left. femur shaft fracture Left 1st to 4th metatarsal fracture	(-)	Quadrilateral socket Pelvic belt Polycentric pneumatic control knee Dynamic response foot
2	Male	20	Left transfemoral amputation (25.50 cm, 52.0%)	Trauma/K3	Right fibular fracture Right sciatic nerve injury	PTB-AFO > PLS-AFO with metatarsal cutting	Quadrilateral socket Pelvic belt Polycentric hydraulic control knee Dynamic response foot
3	Male	64	Right transfemoral amputation (28.1 cm, 67.1%)	Trauma/K3	Left tibio-fibular fracture Left femur neck fracture Left common peroneal nerve injury Left knee osteoarthritis	(-)	Quadrilateral socket Pelvic belt Polycentric pneumatic control knee Dynamic response foot
4	Male	72	Right transtibial amputation (17.1 cm, 39.4%)	Trauma/K2	Left tibio-fibular fracture Left femur medial condyle fracture Left radio-ulnar fracture	KAFO with ischial seating	PTB socket Silicone liner Dynamic SACH foot (flexible keel)

For each patient, upper or lower ergometry was performed as an aerobic exercise. Manual stretching, joint mobility, strengthening exercises and back extensor strengthening exercise was performed. For patients with peripheral nerve injuries, electrical stimulation therapy was also performed. Following fabrication of the prosthesis, standing training was initiated using either parallel bars or a tilt table. Tilt-table standing was initiated to promote safe bone union in case the lower limb fractures. Upon radiological confirmation of gradual bone union, parallel bars were used for standing training. When the gait pattern was sufficiently maintained on the parallel bars and endurance was obtained, gait training using an assistive device was initiated. Subsequently, advanced gait training, including ramp and stairs, outdoor gait, multi-directional turn, falling control, and floor to standing, was conducted based on the functional goals (Fig. 2).

Figure 2. Progress of prosthetic gait training of each subject.

1. Case 1

Following a traffic accident in 2013, the 33-year-old male patient underwent a right transfemoral amputation. Furthermore, fracture of the left metatarsal bones and the femur was also present. At the time of admission in October 2013, radiography revealed bone union of the left femur with heterotrophic ossification and post operative status of left metatarsal bones (Fig. 3-A and 3-B). Upon weight bearing on the left leg, the patient expressed fracture site pain of visual analogue scale (VAS) 9 despite being on pain medications. Also the patient had hip extension contracture of -5, knee flexion and extension contracture of -70, -5 degrees respectively and ankle dorsiflexion and plantar flexion contracture of -10 and -20 degrees respectively. Therefore, due to pain and contractures of the hip and ankle of the non-amputated leg, the amputated side was considered as the dominant leg. The K-level was determined as K3 and the height of the prosthesis was adjusted such that the length of both legs was equal. After 8 weeks of gait training, the patient had increase in pain free gait endurance and successfully discharged home.

Figure 3. (A) Case 1. The plain film image of left femur internal fixation and heterotrophic ossification; (B) Case 1. The plain film image of left metatarsal bones and internal fixation. (C) Case 4. The plain film image of left tibio-fibu-lar fracture and medial condylar fracture after surgery; (D) Bone union is noted on the follow-up plain film image.

2. Case 2

The 20-year-old male patient underwent a left transfemoral amputation following a crush injury in January 2016. The non-amputated side had concomitant fracture of right fibula and right sciatic nerve injury. The non-amputated limb had motor impairment where the manual muscle grade of right leg upon admission was knee flexor poor, knee extensor good, ankle dorsiflexion zero and ankle plantar flexor zero. The patient also had accompanying sensory impairment below the right knee and neuropathic pain of VAS 4 on the right foot was noted. Here we applied a patellar tendon bearing ankle foot orthosis (PTB-AFO) as a weight-reduction orthosis on the non-amputated right side to compensate motor and sensory impairment. Then we applied a Left lower extremity prosthesis initially for standing purpose. Strengthening exercise and electrical stimulation therapy for right side were also applied. In August 2016, after confirmation of bone union of the fibular fracture on a plain film, gait training commenced. The K-level was determined as K3, and the non-amputated side was considered as the dominant leg. The height of the prosthesis was adjusted such that both legs were of the same length. After 8 weeks of gait training, the patient could attempt ramping, stair up and down without pain medication and was discharged. During the outpatient clinic follow up, the patients motor function recovered where the right knee flexor improved from poor to fair and ankle plantar flexor from zero to fair. Therefore, the PTB-AFO was modified to posterior leaf spring AFO (PLS-AFO) with metatarsal cutting. However, despite some motor recovery, the patient could not perform efficient gait without the orthosis of the non-amputated limb therefore kept using both the orthosis and prosthesis.

3. Case 3

The 64-year-old male patient underwent a right transfemoral amputation due to a car accident in April 2021. Due to Left lower extremities fractures, left total hip arthroplasty and left tibial internal fixation were performed. Upon admission, minimal callus was observed on the left tibia and fibular fractures. Also Left common peroneal nerve injury was diagnosed using an electrodiagnostic study. Upon manual muscle testing, ankle dorsiflexion and plantarflexion were graded as both fair which was assumed to be due to both common peroneal nerve injury and pain. Initially, to promote bone union, a prosthesis for standing was fabricated where the prosthetic side was 1/2 inch shorter to promote weight bearing of the fractured limb. After 3 months of pre-gait training, we could see bony bridge formation of tibia without displacement on the plain films. Then gait training was initiated. Due to poor weight bearing of the non-amputated limb, the amputated leg was considered as the dominant leg. There were some motor recoveries and all muscles in the left leg were graded as motor level good. Despite extensive injuries, we set the K-level as K3 as the patient had no previous medical conditions and also had good pre-functional fitness level due to regular tennis and fitness center visits. The length of the prosthesis was adjusted such that the height of both legs were equal. After 8 weeks of gait training, he was discharged.

4. Case 4

The 72-year-old male patient underwent a right transtibial amputation due to a crush injury in 2013. Internal fixations were performed for the left proximal tibiofibular, left femoral medial condyle fractures and left distal radio-ulnar open fracture. At the time of admission, fractures of the left femur and tibia were non-union status (Fig. 3-C). In December 2013, for the purpose of early standing and bone union facilitation through weight bearing, prosthesis was applied to right side and knee-ankle-foot-orthosis (KAFO) with ischial seat was applied to non-amputated left side. The height of the prosthesis was adjusted such that both legs were of the same length. After 4 months of tilt-table standing exercises, bone union was observed by radiography, and gait training was initiated (Fig. 3-D). Due to multiple fractures on the non-amputated leg and VAS 5 medial knee pain upon initiation of gait training, the amputated leg was considered as the dominant leg. The patient had underlying hypertension and also on a transthoracic echocardiogram, although the ejection fraction was preserved at 71%, cardiomegaly, LV concentric remodeling and diastolic dysfunction were observed. Therefore, due to patient’s accompanying Lt upper extremity fracture and medical conditions, the K-level was determined as K2. After 7 weeks of gait training, he was discharged. The patient carried out gait training and by November 2014, with successful bone reunion, he was able to removal left lower extremity orthosis and has reached K2 level of ambulation.

This is the first report focusing on strategic prosthetic rehabilitation for patients with pathologic conditions in the non-amputated leg. There is a tendency to underestimate the functional goal in cases of accompanying complications such as fracture, nerve injury, or pain in the non-amputated leg. However, in this study, we suggested how to tackle the concurrent problems and proceed to gait training to achieve better functional outcomes by four complicated cases.

According to Howard et al.,⁶ patients who underwent unilateral amputation showed an overall tendency to use the non-amputated leg as the active or preferred leg. In a study analyzing the gait of patients who underwent amputation, the stance phase was longer (9.2%) in the non-amputated leg compared to the amputated leg, for the following reasons: 1) a greater ability of the non-amputated leg to advance steps and maintain balance, and 2) patients experienced greater confidence when the sound limb was loaded since better control of the movement can be achieved and postural adjustments necessary for maintaining balance can be made.⁷ However, it is inappropriate to apply the same interpretation in cases where weight reduction of the load is necessary or when weight-bearing is difficult using the non-amputated leg. If it is impossible to overcome the performance limitations of the amputated limb using the non-amputated leg, the amputated leg can be considered as the dominant leg.

Abnormal gait patterns, such as circumduction or vaulting, are common in patients with leg amputation to compromise for ground clearance in the swing phase. These patterns occur when the prosthesis is too long.⁸ To improve ground clearance, the prosthesis height can be adjusted such that the amputated leg is shorter than the anatomic leg until the swing phase control ability is improved.⁴ At our institute, transfemoral or knee disarticulation patients will start off with prosthesis which is 1/2 inch shorter which can later be lengthened to match the non-amputated limb. However, for patients with accompanying pathologic conditions of the non-amputated leg, the dominant leg changes and the prosthesis length is adjusted so that it was equal to the non-amputated leg to improve stability and the ground clearance of the non-amputated leg.

Accompanying fractures may occur in cases of amputation due to trauma, and axial loading is essential to promote bone union. Shin et al.⁴ emphasized on the importance of early standing in such patients with an accompanying fracture. In this case series, patients 1, 2, 3, and 4 were monitored for bone union while performing weight-bearing on fractured bone. Especially, patients 2 and 4 carefully performed early standing with the aid of prostheses and weight-reduction orthoses.

In all the cases, a strategic rehabilitation approach was taken to address the concurrent medical problems and all patients achieved pre-determined functional level. Patients 1, 2 and 3 were classified with K-level K3 to proceed with advanced gait training. Although patient 3 had extensive injuries, he had good pre-functional level and also no medical history which allowed us to set the target as K3. However, patient 4 was determined as K2, due to his age, underlying cardiac conditions and concomitant upper extremity fracture which interfered with gait training process. Patient 3 and 4 underwent 3∼4 months of pre-gait training period, and this emphasizes the importance of rehabilitation during post-operative period for successful gait training.

Here, the importance of addressing pain of the non-amputated side in order to achieve better functional outcomes were highlighted. Disregarding the cause, majority of the patients in the case series had pain in the non-amputated side. Whether it is due to previous fracture, neuropathic pain due to nerve injury or aggravation of arthritis, proper management of pain was necessary. In cases for the need for weight reduction of the non-amputated side, weight reducing orthosis was applied and also adequate pain medication and injection techniques were used to prevent pain of the non-amputated side.

Unfortunately, since this report presents a series of cases, it is difficult to generalize the interpretation of the results. However, we intend to conduct a study comparing kinematics, energy consumption, and functional outcomes based on limb dominance in the future.

Through comprehensive and individualized assessment of the patient, appropriate dominant leg can be assigned and via step-wise gait training where treatment goals and rehabilitation strategies are adjusted throughout the treatment period, pain free functional outcomes could be achieved in individuals with leg amputation with concurrent pathologic conditions of the non-amputated side.