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Dorsal Approach to Radius

 Dorsal Approach to Radius

The Dorsal approach to radius also called Thompson approach, provides good access to the entire dorsal aspect of the radial shaft.

See Also: Forearm Muscles Anatomy

Dorsal Approach to Radius Indications

The principal aim of the approach is to isolate and retract the posterior interosseous nerve before exposing the most proximal parts of the radial shaft, keeping the nerve under direct observation during all stages of the subsequent procedure and protecting it from damage.

The uses of the posterior approach to radius include the following:

  1. Open reduction and internal fixation of radial fractures (the approach provides access to the extensor side of the bone; this is the tensile side of the bone, where plates should be placed, if possible).
  2. Treatment of delayed union or nonunion of fractures of the radius
  3. Access to the posterior interosseous nerve; decompression of the nerve as it passes through the arcade of Frohse for nerve paralysis or resistant tennis elbow.
  4. Radial osteotomy.
  5. Treatment of chronic osteomyelitis of the radius.
  6. Biopsy and treatment of bone tumors.

Position of the Patient

Situate the patient in one of two positions:

  1. Place the patient supine on the operating table, with the arm on an arm board. Pronate the patient’s arm to expose the extensor compartment of the forearm.
  2. Place the patient’s arm across the chest. Supinate the forearm to expose its extensor compartment. If the ulna must be approached as well as the radius, this position will allow easier access to the ulna through a separate incision.
Dorsal Approach to Radius-patient position

Landmarks and Incision

Landmarks:

Incision

Make either a straight incision, extending from a point anterior to the lateral epicondyle of the humerus (along the dorsal aspect of the forearm) to a point just distal to the ulnar side of Lister’s tubercle at the wrist.

Normally, only part of this incision is required for any given operation. In cases of fracture, the incision should be centered over the fracture site. Use of an image intensifier may allow more accurate placement of the incision.

thompson approach Incision

Internervous Plane

Proximally, the internervous plane for the Dorsal approach to radius lies between the extensor carpi radialis brevis muscle (which is supplied by the radial nerve) and the extensor digitorum communis muscle (which is supplied by the posterior interosseous nerve). The common aponeurosis of these muscles is the cleavage plane.

Distally, the internervous plane for Dorsal approach to radius lies between the extensor carpi radialis brevis muscle (which is supplied by the radial nerve) and the extensor pollicis longus muscle (which is supplied by the posterior interosseous nerve).

posterior approach to radius Internervous Plane

Superficial Surgical Dissection

Incise the deep fascia in line with the skin incision and identify the space between the extensor carpi radialis brevis and the extensor digitorum communis.

This plane is more obvious distally, where the abductor pollicis longus and the extensor pollicis brevis emerge from between the two muscles. Proximally, the extensor carpi radialis brevis and the extensor digitorum communis share a common aponeurosis Continue the dissection proximally, separating the two muscles to reveal the upper third of the shaft of the radius, which is covered by the enveloping supinator muscle.

Below the abductor pollicis longus and the extensor pollicis brevis, identify the intermuscular plane between the extensor carpi radialis brevis and the extensor pollicis longus. Separating the two muscles exposes the lateral aspect of the shaft of the radius.

Deep Surgical Dissection

Proximal Third:

The supinator muscle cloaks the dorsal aspect of the upper third of the radius; the posterior interosseous nerve runs within its substance between the superficial and deep heads. The nerve emerges from between the superficial and deep heads of the supinator muscle about 1 cm proximal to the distal edge of the muscle. At this point, it divides into branches that supply the extensors of the wrist, fingers, and thumb.

Two methods exist for successfully identifying and preserving this nerve as it traverses the muscle:

  1. Proximal to distal: Detach the origin of the extensor carpi radialis brevis and part of the origin of the extensor carpi radialis longus from the lateral epicondyle and retract these two muscles laterally. Next, identify the posterior interosseous nerve proximal to the proximal end of the supinator muscle by palpating the nerve. Now, carefully dissect the nerve out through the substance of the supinator, in a proximal to distal direction, taking great care to preserve the multiple motor branches to the muscle itself.
  2. Distal to proximal: Identify the nerve as it emerges from the supinator. Note that it emerges about 1 cm proximal to the distal end of the muscle. Now, follow the nerve proximally through the substance of the muscle, taking care to preserve all muscular branches.

When the nerve has been identified and preserved successfully, fully supinate the arm to bring the anterior surface of the radius into view. Detach the insertion of the supinator muscle from the anterior aspect of the radius. Strip the supinator off the bone subperiosteally to expose the proximal third of the shaft of the radius

Middle Third

Two muscles, the abductor pollicis longus and the extensor pollicis brevis, blanket this approach as they cross the dorsal aspect of the radius before heading distally and radially across the middle third of the radius. To retract them off the bone, make an incision along their superior and inferior borders. Then, they can be separated easily from the underlying radius and retracted either distally or proximally, depending on the exposure that is required. Plates can be slid underneath these muscles if required for fixation.

Distal Third

Separating the extensor carpi radialis brevis from the extensor pollicis longus already has led directly onto the lateral border of the radius.

Thompson Approach Enlargement

The Thompson Approach can be extended to the dorsal side of the wrist (see Dorsal Approach to the Wrist).

Thompson Approach can be extended proximally to expose the lateral epicondyle of the humerus (see Lateral Approach to the Distal Humerus). These extensions, however, rarely are required.

Dangers

There are two ways in which to preserve the critical posterior interosseous nerve during the Dorsal approach to radius, which is the key to this dissection:

  1. Identification of the nerve. In 25% of patients, the posterior interosseous nerve actually touches the dorsal aspect of the radius opposite the bicipital tuberosity; plates placed high on the dorsal surface of the radius may trap the nerve underneath. Identifying and preserving the nerve in the supinator muscle is the only means of ensuring that it will not be trapped beneath any plate that is applied for a radial fracture.
  2. Protecting the nerve with the supinator muscle. Strip the supinator off the anterior aspect of the radius and retract it radially, with the nerve still enclosed in its substance. This technique often is used in the anterior approach to the radius, exposing the anterior surface of the bone. The dorsal aspect of the radius can be exposed in the same way, but because the posterior interosseous nerve actually touches the periosteum in one of four patients, the safest procedure is to dissect the nerve out fully before stripping the muscle from the bone.

References

  1. Surgical Exposures in Orthopaedics The Anatomic Approach 4th Edition.
  2. Hashizume H, Nishida K, Nanba Y, Shigeyama Y, Inoue H, Morito Y. Non-traumatic paralysis of the posterior interosseous nerve. J Bone Joint Surg Br. 1996 Sep;78(5):771-6. PMID: 8836068.

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