What are the recommended residual limb lengths for above‑knee and below‑knee amputations to optimize prosthetic fitting?

Optimal Residual Limb Lengths for Above-Knee and Below-Knee Amputations

For below-knee (transtibial) amputations, aim for a residual limb length of approximately 16 cm (measured from the tibial plateau to the bone end), and for above-knee (transfemoral) amputations, target approximately 28 cm (measured from the greater trochanter to the bone end). 1

Below-Knee (Transtibial) Amputation Length

Target Length

• The optimal transtibial stump length is 16.0 cm (mean length from clinical evaluation of 93 consecutive amputees). 1
• This measurement represents the distance from the tibial plateau to the distal end of the bone. 1

Critical Length Threshold

• Stumps shorter than 15.1 cm demonstrate significantly weaker muscle strength and compromised prosthetic control. 2
• Short stumps (under 15.1 cm) show significantly reduced peak torque in isokinetic contraction and maximal average torque in isometric contraction compared to longer stumps (p < 0.05). 2
• The short lever arm provided by stumps under 15.1 cm interferes with the thigh muscles' ability to control the prosthesis efficiently during standing and walking. 2

Functional Implications

• Adequate length is essential for proper prosthetic application and control. 3
• Longer stumps within the transtibial range provide better leverage for muscle control and more effective prosthetic function. 2

Above-Knee (Transfemoral) Amputation Length

Target Length

• The optimal transfemoral stump length is 28.0 cm (mean length from clinical evaluation of 62 consecutive amputees). 1
• This measurement represents the distance from the greater trochanter to the distal end of the femur. 1

Functional Considerations

• Adequate femoral length is critical for prosthetic socket suspension and control. 1
• The longer the residual femur, the better the leverage and control over the prosthetic knee unit. 1

Common Pitfalls to Avoid

Surgical Planning Errors

• Do not sacrifice length for the sake of easier wound closure—every centimeter of bone length preserved improves prosthetic function and muscle leverage. 2
• Avoid creating stumps shorter than 15.1 cm for transtibial amputations whenever anatomically possible, as this significantly compromises functional outcomes. 2

Scar Placement Issues

• Position the surgical scar to avoid adherence to underlying bone—adherent scars occurred in 13% of transtibial and 2% of transfemoral stumps and compromise prosthetic fitting. 1
• Deeply wrinkled scars (occurring in 7% of transtibial and 10% of transfemoral stumps) are most common in trauma patients (33%) and should be prevented through proper surgical technique. 1

Postoperative Management Impact on Outcomes

Rigid Dressing Systems

• Apply removable rigid dressings (RRDs) immediately postoperatively to optimize stump maturation and shaping for prosthetic fitting. 4
• RRDs reduce time to prosthetic fitting by 55% compared to soft dressings and provide superior limb protection. 5
• Time to first prosthetic casting averages 27-37 days with rigid or removable rigid dressings. 5

Protection from Trauma

• RRDs reduce fall-related trauma to the residual limb from 17-22% to zero. 4
• Falls can result in lacerations, fractures, and wound dehiscence requiring revision surgery, which would further compromise stump length. 4

When Stump Length is Inadequate

Lengthening Procedures

• For stumps that are too short for functional prosthetic use, surgical lengthening using the Ilizarov technique can achieve 40-60% length increase. 3
• Lengthening procedures are viable but controversial, with common complications and additional procedures required. 6
• Patients can typically use their prosthesis 6 months after lengthening surgery. 3