Dorsal approach to the radius

Introduction

The dorsal approach to the radius, also known as the Thompson approach, provides excellent exposure to the entire dorsal aspect of the radial shaft.

Indications for the Dorsal Approach to the Radius

The primary goal of this approach is to isolate and retract the posterior interosseous nerve before exposing the most proximal parts of the radial shaft. This keeps the nerve under direct observation throughout the subsequent procedure, protecting it from injury.

Uses of the posterior approach to the radius include:

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

Patient Positioning

Place 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 muscles of the forearm.
2. Place the patient’s arm across the chest. Supinate the forearm to expose the extensor muscles. If both the radius and ulna need to be addressed, this position allows easier access to the ulna through a separate incision.

Landmarks and Incision

Landmarks:

• Palpate the lateral epicondyle of the humerus, located just lateral to the olecranon process on the distal humerus. It is a prominent bony landmark, but slightly smaller and less prominent than the medial epicondyle.
• Lister's tubercle (the dorsal radial tubercle) is located about one-third of the way across the dorsum of the wrist from the radial styloid process. It feels like a small, elongated bony prominence or bump.

Incision

Make a straight incision running from a point just anterior to the lateral epicondyle of the humerus (along the back of the forearm) to a point just distal to the ulnar side of Lister's tubercle at the wrist.

Usually, only a portion of this incision is needed for surgery. In the case of a fracture, the incision should be centered over the fracture site. Using an image intensifier can allow for more accurate placement of the incision.

Internervous Plane

Proximal: The internervous plane for the dorsal approach to the radius lies between the extensor carpi radialis brevis (supplied by the radial nerve) and the extensor digitorum communis (supplied by the posterior interosseous nerve). The common aponeurosis of these muscles is the splitting plane.

Distal: The internervous plane for the dorsal approach to the radius lies between the extensor carpi radialis brevis (supplied by the radial nerve) and the extensor pollicis longus (supplied by the posterior interosseous nerve).

Superficial Surgical Dissection

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

Distally, this plane is more apparent, where the abductor pollicis longus and extensor pollicis brevis emerge between the two muscles. Proximally, the extensor carpi radialis brevis and extensor digitorum communis share a common aponeurosis. Continue the dissection proximally, separating the two muscles to expose the upper third of the radial shaft, which is covered by the enveloping supinator muscle.

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

Deep Surgical Dissection

Proximal Third:

The supinator muscle conceals the dorsal side of the upper third of the radius; the posterior interosseous nerve runs within its substance between the superficial and deep heads. The nerve emerges 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.

There are two methods to successfully identify and preserve this nerve during its course through the muscle:

1. Proximal to distal: Release 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 by palpating the nerve. Now, carefully dissect the nerve through the substance of the supinator muscle in a proximal-to-distal direction, carefully preserving the numerous motor branches to the muscle itself.
2. Distal to proximal: Identify the nerve as it exits the supinator. Note that it exits about 1 cm proximal to the distal end of the muscle. Now, trace the nerve proximally through the muscle substance, taking care to preserve all muscular branches.

Once the nerve has been successfully identified and preserved, fully supinate the arm to visualize the anterior surface of the radius. Release the attachment of the supinator muscle from the anterior side of the radius. Subperiosteally elevate the supinator off the bone to expose the proximal third of the radial shaft.

Middle Third

Two muscles, the abductor pollicis longus and extensor pollicis brevis, cover this approach as they cross the dorsal side of the radius before passing distally and radially over the middle third of the radius. To remove them from the bone, make an incision along their upper and lower borders. They can then be easily separated from the underlying radius and retracted either distally or proximally, depending on the exposure required. Plates can be slid under these muscles for fixation if needed.

Distal Third

The separation of the extensor carpi radialis brevis from the extensor pollicis longus has already led directly to the lateral border of the radius.

Extending the Thompson Approach

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

The Thompson approach can be extended proximally to expose the lateral epicondyle of the humerus (see Lateral Approach to the Distal Humerus). However, these extensions are rarely necessary.

Dangers

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

1. Identification of the nerve. In 25% of patients, the posterior interosseous nerve actually contacts the dorsal side of the radius opposite the bicipital tubercle; plates placed high on the dorsum of the radius can entrap the nerve underneath. Identifying and preserving the nerve within the supinator muscle is the only way to ensure it is not trapped under a plate applied for a radial fracture.
2. Protection of the nerve through the supinator muscle. Remove the supinator from the anterior side of the radius and retract it radially, with the nerve still enclosed within its substance. This technique is commonly used in the anterior approach to the radius to expose the anterior surface of the bone. The dorsal part of the radius can be exposed in the same way, but since the posterior interosseous nerve actually contacts the periosteum in one out of four patients, the safest procedure is to fully dissect out the nerve before releasing 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.