What artery should be checked before a below-knee amputation due to an ischemic limb?

Assessment of Popliteal Artery is Critical Before Below-Knee Amputation

Before performing a below-knee amputation for an ischemic limb, the popliteal artery (option C) should be evaluated as the most critical vessel to assess limb viability and determine appropriate amputation level.

Rationale for Popliteal Artery Assessment

The popliteal artery is the key vessel to evaluate before below-knee amputation for several important reasons:

1. Anatomical Significance: The popliteal artery is the direct continuation of the superficial femoral artery and provides the main blood supply to tissues at the below-knee amputation level 1.

2. Predictive Value for Healing:

   • According to guidelines, the most distal artery with continuous flow from above and without significant stenosis (>20%) should be used as the point of origin for distal bypass 1.
   • The popliteal artery's patency directly correlates with below-knee amputation success rates 1.

3. Revascularization Potential: If the popliteal artery has adequate flow, it may serve as the inflow vessel for potential bypass procedures to salvage the limb rather than proceeding with amputation 1.

Comprehensive Pre-Amputation Assessment

Vascular Assessment:

• Popliteal Artery Evaluation:

  • Doppler ultrasound assessment of popliteal artery signals and pressures
  • Presence of popliteal pulse indicates an 89% chance of healing at below-knee level 2
  • Absence of detectable popliteal artery signal strongly suggests need for above-knee amputation 3

• Perfusion Measurements:

  • Ankle pressure <50 mmHg or ABI <0.5 indicates high risk for amputation failure 1
  • Skin perfusion pressure (SPP) >30 mmHg at below-knee level predicts 97% healing success 2
  • Transcutaneous oxygen pressure (TcPO₂) ≥40 mmHg indicates good healing potential 4

Imaging:

• Comprehensive vascular imaging is mandatory to evaluate revascularization options 1
• Color duplex ultrasound, CT angiography, MR angiography, or intra-arterial digital subtraction angiography to visualize the entire lower extremity arterial circulation 1
• Detailed visualization of below-knee arteries in anteroposterior and lateral planes 1

Decision Algorithm for Amputation Level

1. If popliteal artery shows:

   • Good flow with pressure >70 mmHg: Proceed with below-knee amputation 3
   • Detectable signal but pressure <70 mmHg: Higher risk of failure; consider revascularization first 3
   • No detectable signal: Consider above-knee amputation 3

2. Additional perfusion criteria:

   • SPP >30 mmHg: Proceed with below-knee amputation (97% success rate) 2
   • SPP 20-30 mmHg: 54% failure rate for below-knee amputation 2
   • SPP <20 mmHg: 89% failure rate for below-knee amputation 2

3. Consider revascularization before amputation:

   • Guidelines strongly recommend evaluation for revascularization options by an interdisciplinary care team before amputation 1
   • Goal of revascularization is to provide in-line blood flow to the foot through at least one patent artery 1

Why Other Options Are Less Critical

• Femoral Artery (Option A): While important for overall limb perfusion, its status alone doesn't determine below-knee amputation success as directly as the popliteal artery 1.

• Dorsalis Pedis Artery (Option B): Important for foot perfusion but less critical for below-knee amputation healing since the amputation site is proximal to this vessel 1.

• Profunda Femoris Artery (Option D): Important collateral vessel but not as directly relevant to below-knee amputation site healing as the popliteal artery 1.

Pitfalls to Avoid

1. Relying solely on clinical assessment: Ischemia at the below-knee election site cannot be ruled out by clinical assessment alone 2.

2. Neglecting objective measurements: Doppler signals, pressure measurements, and imaging provide objective data that correlate with healing outcomes 2, 3.

3. Failing to consider revascularization: Guidelines recommend evaluation for revascularization options before amputation in all cases of CLI 1.

4. Overlooking post-amputation care: Planning for rehabilitation and prosthetic fitting should be part of the pre-amputation decision-making process 5.