ADVANTAGES
This approach allows access to the medial side of the humerus without coming directly over the neurovascular bundle.
DISADVANTAGES
Because the anterior humerus is overlaid by the biceps and brachioradialis, this approach requires either splitting or retracting large muscles.
STRUCTURES AT RISK
The musculocutaneous nerve, which crosses from medial to lateral, innervating the biceps and the brachialis muscle and continuing down as the lateral antebrachial cutaneous nerve of the forearm, can be damaged in the more proximal part of this approach. The musculocutaneous nerve runs along the undersurface of the biceps in the region of the pectoralis major insertion and then innervates the biceps and the brachialis before moving in a lateral direction. If you are splitting the biceps down the middle, or retracting it in a medial direction and cutting down to the humerus, it is possible that you will damage this nerve.
The medial neurovascular bundle is potentially at risk with this approach. These structures lie just medial to the humerus and perhaps slightly posterior to it. They are clearly posterior to the biceps. By approaching the humerus through the biceps fascia, you have a layer protecting the neurovascular bundle.
TECHNIQUE
An incision is made, usually on the anterior medial aspect of the arm, just on the medial side of the biceps and carried through the subcutaneous tissue. The biceps can be retracted either medially or laterally. In the upper end of the approach in the region of the tendinous portion of the long head of the biceps, it is retracted medially. In the midshaft, it is retracted laterally. If the goal is to reach the proximal biceps for tenodesis, then you need to carry the incision into the deltopectoral groove area, retracting the deltoid laterally and the pectoralis medially. The biceps tendon will be seen underneath those muscles, directly anterior to the humerus.
If the goal is to reach the medial humerus in the midshaft region, then the biceps would be retracted laterally. The brachialis would be split as much as is necessary for the exposure. Ideally, the brachialis could also be retracted in its entirety in a lateral direction.
Care must be taken when in the proximal portion of the incision not to damage the musculocutaneous nerve. The nerve typically comes from underneath the coracobrachialis muscle and enters the biceps 5 to 10 cm distal to the coracoid. It can be easily identified at the level of the pectoralis major insertion by lifting the biceps anteriorly. The nerve is typically about the size of a shoelace and runs on the under surface of the biceps. By the time you reach the midshaft humerus, the nerve is already well into the muscle and moving laterally. Retraction of the muscles laterally then takes the nerve with it, providing protection for the nerve.
TRICKS
The major trick to this approach is identifying the biceps. Once you know where it is, opening its fascia and retracting it laterally and continuing the approach toward the humerus will keep you safely away from the more medial neurovascular bundle.
The other trick concerns the musculocutaneous nerve. In the midhumerus, the biceps and brachialis can be retracted laterally, but in the proximal arm in the region of the pectoralis major, it is probably safer to retract them medially, taking the nerve toward the medial side with the muscle.
If the dissection to the anterior humerus is proximal to where the nerve exits the coracobrachialis and comes underneath the biceps, then medial retraction is the wiser choice. Medial retraction is generally done for a proximal biceps tendon tenodesis. Remember that the musculocutaneous nerve can be within 5 cm of the coracoid process as it courses from medial to lateral.
HOW TO TELL IF YOU ARE LOST
As with many approaches, it is difficult to get lost when you are coming directly down on the bone. The key landmark is the medial border of the biceps. Once you have that retracted out of the way, then the neurovascular structures are medial and posterior to it and should be protected. The brachialis muscle, which is surprisingly big, underlies the biceps, and sometimes it is difficult to tell one from the other. It is not usually necessary to do so, however, and you can simply approach directly onto the humerus.
If you are lost too far medially, you will encounter the neurovascular structures. Care must be taken with this approach because you are trying to come along the medial border of the biceps so that you can protect the musculocutaneous nerve by retracting it laterally, which is what puts the main neurovascular structures at risk. Staying inside the biceps fascia provides protection. If you are not inside the biceps fascia, you are lost.
FIGURE 7–1 The skin incision.
FIGURE 7–2 The underlying coracobrachialis deep to the subcutaneous tissue. The area at the bottom of the coracobrachialis muscle, which looks to be more yellow in color and perhaps fatty, is the region of the neurovascular bundle, and should be avoided.
FIGURE 7–3 The coracobrachialis fascia open. The lower border of the coracobrachialis is apparent, as is the area of the neurovascular bundle immediately inferior to the coracobrachialis. This is the correct interval to go down to the humerus, because the coracobrachialis provides protection from the neurovascular bundle.
FIGURE 7–4 The biceps being retracted anteriorly. The musculocutaneous nerve is on the undersurface of the biceps and is easily identified in this location.
FIGURE 7–5 The coracobrachialis and neurovascular bundle retracted posteriorly and the musculocutaneous nerve and biceps retracted anteriorly, exposing the shaft. This dissection can then be carried as far distally as is necessary in that same plane because the musculocutaneous nerve is already safe and out of the way.
FIGURE 7–6 The interval between the coracobrachialis and the main neurovascular bundle. If, as you are making this approach, this is the picture that you see, then you are going too far in a posterior direction, which is a great risk. This risk is avoided by proceeding far enough laterally that you can tell the biceps from the coracobrachialis muscle.
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LATERAL APPROACH TO THE HUMERUS
USES
This approach is used primarily for fracture work.
ADVANTAGES
This approach is internervous because the anterior musculature of the biceps and brachialis is innervated