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POSITIONING FOR ORTHOPEDIC SURGERY

Patients are placed in a variety of positions for orthopedic procedures (see Chapter 28 ). Improper positioning may result in intraoperative or postoperative problems such as those described subsequently.

Air embolism (see Chapter 53 ) can occur when the operative field is above the level of the heart. This is
TABLE 61-3 -- Anesthetic problems of the prone position
Airway
Endotracheal tube kinking or dislodgement
Edema of upper airway in prolonged cases may cause postoperative respiratory obstruction
Blood Vessels
Arterial or venous occlusion of the upper extremity (check with pulse oximeter on the finger)
Kinking of the femoral vein with marked flexion of the hips, which may predispose to postoperative deep vein thrombosis
During lumbar laminectomy, increased abdominal pressure may elevate epidural venous pressure, contributing to intraoperative bleeding
Nerves
Brachial plexus stretch or compression
Ulnar nerve compression due to pressure medial to the olecranon
Peroneal nerve compression due to lateral pressure over the head of the fibula
Lateral femoral cutaneous nerve trauma due to pressure over the iliac crest
Head and Neck
Gross hyperflexion or hyperextension of the neck[278] [279]
External pressure over the eyes may result in retinal injury due to compression[28] [139] [280]
Lack of lubrication or coverage of eyes may result in corneal abrasion
Headrest may cause pressure injury of supraorbital nerve.
Excessive rotation of the neck may contribute to brachial plexus problems or kinking of the vertebral artery[281]
Lumbar Spine
Excessive lordosis may lead to neurologic injury[282] [283]

a potential problem in surgery of the cervical spine or the shoulder in the sitting position, in total-hip replacement in the lateral decubitus position, or in lumbar spinal surgery in the prone position. Air embolism should be considered if untoward circulatory compromise occurs in any of these settings, although it is rare.[21] [22] [23] [24]

Stretch or malposition of joints may occur during anesthesia and may account for a variety of nonspecific postoperative discomforts in the back or the extremities. Patients with rheumatoid arthritis, osteoporosis, osteogenesis imperfecta, or contractures must be carefully positioned to avoid ligamentous or bony injury.

Direct pressure, especially over bony prominences, may cause tissue ischemia or necrosis, particularly after prolonged surgery when hypotensive anesthesia is used. Direct pressure on the soft tissues of the orbit when lying prone may lead to retinal artery occlusion,[25] [26] [27] [28] and direct pressure over other peripheral nerves may result in postoperative neurapraxia.[29] [30] [31] [32]

The veins and arteries supplying the upper or lower extremity may be compressed. Prolonged venous obstruction at the axillary vein is best alleviated with an axillary roll positioned beneath the upper thorax.

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TABLE 61-4 -- Sites of peripheral nerve injury in orthopedics
Nerve Injury Site * Cause Comment
Upper extremity

  Brachial plexus Abduction, external rotation, or extension of shoulder Usually resolves within several months

Traction of shoulder
  Ulnar nerve Pressure at the elbow Common

Traction of C8-T1 dermatomes over the 1st rib Postoperative palsy results in numbness of ring and fifth fingers
  Radial nerve Pressure behind the arm Results in wristdrop
  Anterior interosseous nerve Pressure at the distal elbow laterally Bandages or external pressure[284]
Head

  Supraorbital nerve Pressure on the supraorbital ridge when lying prone Results in numbness of forehead
Lower extremity

  Lateral femoral cutaneous nerve of the thigh Pressure over anterior iliac crest in lateral or prone position or over lateral thigh Results in numbness of the lateral aspect of the thigh and knee
  Femoral nerve Pressure to the groin of the dependent limb in the lateral decubitus position Results in numbness of the anterior thigh and medial aspect of lower leg
  Common peroneal nerve Pressure below the head of the fibula May be caused by compartment syndrome


Results in footdrop
Ankle Pressure from Esmarch bandage Pressures beneath Esmarch bandage can be much higher than believed
*Checklist:
  1. Check for preoperative nerve dysfunction.
  2. Check tourniquet problems (duration and pressure).
  3. Check postoperative position, splints, tight bandages; rule out compartment syndrome.
  4. Check intraoperative surgical factors.
  5. Risk of neurapraxia is more common in prolonged surgery.




Similarly, with patients in the lateral decubitus position, stabilizing posts must be positioned carefully over the groin so as not to interfere with venous return at the level of the femoral vein. Arterial obstruction of a limb may be checked by the use of a pulse oximeter[33] or by palpating the pulse of a distal artery. Venous obstruction may lead to a compartment syndrome with edema, neuropraxia, elevation of creatine phosphokinase level, and myoglobinuria postoperatively.[34]

Positioning of the rheumatoid patient is very important; care must be taken to avoid flexing the neck excessively. Regional anesthesia is particularly suitable for these patients, because neck stability can be maintained by the patients themselves, particularly if only light or moderate sedation is given. Other joints that should not be moved beyond the normal range of motion are protected by the conscious patient. Excessive motion may occur when these patients are moved in the anesthetized, paralyzed state, resulting in neuropraxia, joint dislocation or stretch, or muscle trauma.

The prone position in particular may lead to a variety of episodes of minor or major trauma,[35] [36] which are listed in Table 61-3 . Visual loss may occur in the prone position through a number of different mechanisms (see "Thoracolumbar Spinal Surgery"). Malpositioning of the extremities may lead to various stretch or compression-induced neurapraxias,[29] [30] [31] [32] as described in Table 61-4 .

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