Midline Approach

MIDLINE APPROACH

USES

This is a utilitarian approach that is useful for all tendon work, nerve repair, and artery repair work in the arm. It is also useful for fracture repair work on the distal radius that entails using a volar plate.

ADVANTAGES

This is an extensile exposure that can be extended as far as necessary in either direction.

DISADVANTAGES

The major disadvantage is that the neurovascular structures of the forearm are at risk with this approach, and they must be identified and protected.

STRUCTURES AT RISK

The median nerve is the major structure at risk with this midline approach. The nerve is underneath the sublimis tendon throughout most of its course through the forearm, but comes to the surface in the distal forearm along the radial side of the sublimis tendons. It gives off the palmar cutaneous branch typically on its radial side, which runs parallel to the nerve and proceeds to the skin of the palm over the thenar eminence.

On the radial side of the flexor carpi radialis is the radial artery. This artery is usually out of the way and is protected by retracting the flexor carpi radialis tendon and artery in a radial direction.

On the ulnar side of the forearm, just inside the flexor carpi ulnaris tendon and muscle, is the ulnar artery and nerve. These structures are at risk any time the profundis tendons are exposed. They need to be identified and protected prior to opening the fascia of the profundis muscle.

In the very depth of the wound, the anterior interosseous nerve runs along the interosseous membrane. It is the nerve supply to the flexor pollicis longus and to the pronator quadratus, both of which are very important muscles. There should be no dissection or stripping done of the tissue on the anterior aspect of the interosseous membrane, to prevent injury to this nerve. All stripping should be done directly over the radius itself.

TECHNIQUE

A straight midline incision is made, typically centered over the palmaris longus tendon, and it is carried through the subcutaneous tissue. The tendon of the palmaris longus is identified and retracted in either direction, whichever seems convenient. The fascia on its underlying surface is what covers the flexor digitorum sublimis muscles. This fascia should be opened in the midline on the proximal end of the incision in the region where the reddish coloration of the muscles is clearly visible. This is a safe area in which to open this fascia. If you are too far distal, you risk damaging the median nerve. Once the sublimis is mobilized, it is possible to see the median nerve on its undersurface coming up to the superficial layers at the wrist joint itself.

To expose the flexor digitorum profundis tendons, it is usually easier to retract the median nerve and sublimis in a radial direction, and the ulnar neurovascular structures and the flexor carpi ulnaris in an ulnar direction. This retraction exposes the profundis muscle and tendons.

If the goal is to place a volar plate on the radius, then the median nerve along with all of the other neurovascular structures, except the radial artery, are retracted in an ulnar direction. Care must be taken not to damage the palmar cutaneous nerve. The pronator quadratus then needs to be stripped from its insertion onto the radius to expose the bone itself.

TRICKS

The major trick to entering the forearm safely is to identify the palmaris longus and to come through the skin directly over that tendon. The tendon can be sacrificed without any functional loss to the patient. The fascia overlying the sublimis is opened over the muscle. As long as you can clearly see the reddish color of the muscle, you will not have to worry about damaging the median nerve.

The trick to protecting the radial artery is to realize that it is moving in a dorsoradial direction and to take it in that direction when retracting. Taking the flexor carpi radialis in that direction also provides some protection for the radial artery.

The main trick to protecting the ulnar neurovascular structures is to approach the flexor carpi ulnaris from the subcutaneous side. Because the nerve and artery are underneath the muscle, this puts the muscle between you and the nerve as you make your approach.

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