A Review of the Complex, Delicate Anatomy of the Hand
It might surprise you to know that the hand is the most commonly injured part of the body. Serious injuries like tendon injuries require treatment by an experienced hand surgeon. Surgeons know how complex and delicate the anatomic structures of the hand are. They understand the need for very careful surgical technique when repairing, reconstructing, transferring, or grafting a tendon.

In this article, the extensor tendons of the hand are featured. The authors review the anatomy of each one and discuss the complexities of surgery for tendon transfers. Included in the discussion are the following tendons: extensor digitorum communis, extensor indicis proprius, extensor digiti minimi, extensor proprius indicis, extensor digitorum brevis manus, extensor pollicus brevis, extensor pollicis longus, and extensor medii proprius.

Tendon transfer refers to taking one tendon and moving it to function in place of another. This is done most often when a tendon has been injured, the nerve to the tendon has been damaged, or there is a defect of the tendon from rheumatoid arthritis. But tendon transfers (or using tendon as a graft) are not as simple as they sound.

For example, sometimes a tendon originates (or begins) in a slightly different place than expected. Most tendons start from an attachment directly to the bone. But in some cases, the insertion point could be a ligament instead of the bone. Or the origination could be from the soft tissue over the bone.

If even a single tendon slip is taken from the wrong tendon, it can affect the movement and strength of the finger and/or hand. Likewise, if the surgeon chooses a weaker tendon for a transfer to a stronger tendon that has been injured, the result can be a significant loss of hand function.

In yet another example, the authors point how the extensor indicis proprius (EIP) has many connections to the extensor digitorum communis (EDC). EDC is the main tendon that extends all the fingers. The connection between these two tendons must be carefully cut to avoid losing the benefit of the EIP as a tendon transfer.

There are also thin bands of tissue that connect the extensor digitorum communis (EDC) tendons. These are called the juncturae tendinum. The full function of the juncturae tendinum is not completely understood but it is clear that the anatomy can be quite different from one person to another. The authors provide a detailed description of this anatomic structure and description of what is known so far about how it works. Even rare anomalies (differences or variations) of the juncturae tendinum anatomy are important for the hand surgeon to be aware of.

In summary, this review article featuring the extensor tendons of the hand will benefit any surgeon who is evaluating a patient with a hand injury. Knowing how many and what kind of anatomical differences that can occur from patient to patient is essential when planning hand surgery. Known anatomic and functional variations of the extensor tendons are described and discussed keeping in mind how these may affect decisions before and during tendon transfers.
References
Kevin Chen, et al. Extensors of the Hand. In Current Orthopaedic Practice. March/April 2013. Vol. 24. No. 2. Pp. 189-196.