What is the jack knife position?

The Jack Knife Position

The jack knife position is a surgical positioning technique where the patient is placed prone (face down) with the hips flexed at approximately 90 degrees, creating an inverted V-shape that provides optimal exposure for perianal, rectal, and lower spinal procedures. 1

Key Characteristics and Setup

• The position involves placing the patient prone on an operating table that can be flexed in the middle, with the hips elevated and the head and feet lowered, creating a characteristic inverted V-shape 1, 2
• The position requires a specialized operating table that can be mechanically adjusted to achieve the desired angle, typically with 15-25 degrees of flexion at the hips 2, 3
• Proper positioning requires a minimum of three staff members plus the anesthetist for patients weighing >50 kg to ensure patient safety during the transition to this position 4
• The patient's arms are typically positioned alongside the body or on armboards with careful attention to prevent pressure on the ulnar nerve 5

Clinical Applications

• Commonly used for:
  • Perianal surgeries including hemorrhoidectomy and fistula repair 3
  • Colorectal procedures such as restorative proctocolectomy 2
  • Lower spine surgeries 6
  • Procedures requiring optimal exposure of the perineum and anus 1

Physiological Effects and Considerations

Hemodynamic Effects

• The position causes significant hemodynamic changes including:
  • Initial decrease in cardiac index when moving from supine to prone position 2
  • Slowed heart rate and increased mean arterial pressure in the fully positioned patient 2
  • Return of cardiac index to baseline values after complete positioning with head-down rotation 2

Neurological Considerations

• The position can cause significant neurological effects:
  • Studies show 100% of subjects placed in 25° lateral jack-knife position for 60 minutes developed motor deficits in the non-dependent lower limb 7
  • 98% of subjects experienced sensory abnormalities in the non-dependent lower limb 7
  • These neurological changes are typically transient but require monitoring 7

Respiratory Effects

• The position can compromise respiratory mechanics due to:
  • Abdominal compression limiting diaphragmatic excursion 4
  • Increased pressure on the chest wall 4
  • Higher PEEP levels may be required to maintain adequate lung compliance and prevent atelectasis 4

Anesthetic Management

• Spinal anesthesia can be used for procedures in this position but requires special considerations:
  • Duration of sitting position after spinal injection significantly affects the spread of anesthesia (longer sitting time limits cephalad spread) 3
  • A 10-minute sitting period after spinal injection limits the maximum cephalad spread to T11 level 3
  • Baricity of the anesthetic agent is less important than patient positioning in determining spread 3
  • Continuous monitoring of hemodynamic parameters, respiratory function, and block level is essential 1

Positioning Precautions

• Careful padding of pressure points is essential to prevent nerve injuries and pressure ulcers 4
• The position should be avoided or used with extreme caution in:
  • Patients with severe cardiac disease due to hemodynamic effects 1
  • Obese patients who are at risk for sudden extension of spinal blocks when turned into this position 1
  • Elderly patients who may have compromised hip and back extensor muscle strength 6

Monitoring Requirements

• Continuous monitoring of:
  • Hemodynamic parameters (blood pressure, heart rate) 2
  • Respiratory function 1
  • Level of sensory block when neuraxial anesthesia is used 1
  • Pressure points and peripheral circulation 5

The jack knife position, while valuable for specific surgical procedures, requires careful attention to patient selection, positioning technique, and physiological monitoring to minimize the risk of complications.