Upper Limb Journal Post (#1)

Tendons of the Hand

     Within the structure of the hand there are many specialized units that allow extensive articulation and movement. Some of the more prominent features of a dissected hand include tendons. The hand is composed of a tight network of tendons that include examples such as flexor digitorum superficialis (FDS) tendon and the  flexor digitorum profundus (FDP) tendon. Tendons such as these within the hand are encased in sheaths (e.g. FDS & FDP are encased in the common flexor sheath). The common flexor sheath is deep to the flexor retinaculum, and the tendons (FDS & FDP) enter the central part of the hand. An important aspect of the sheath is the various types that enable various movements of the hand. For example, the digital synovial sheaths allows for the tendons to move when the fingers flex.

     This topic allows a segue to a pathology associated with these sheaths within the hand. A common occurrence is when a tendon within the hand becomes inflamed and prevents movement within the sheath, this is known as Tenosynovitis or "Trigger Finger". This most often occurs in either digit #1 or #2 and usually only occurs singularly. However, if the patient has certain comorbid disorders, such as arthritis or diabetes, multiplicity (either more than one digit involved or repeat of occurrence)  may occur. In general, 95% of all trigger finger patient cases can be solved by non-operative procedures. However, repeat offenses may find surgery as an unavoidable consequence.  



Innervation of the Hand

     Another aspect of the hand that is worth mentioning is of the hand's expanse of innervation. Very few places in the human body present as much branching and complexity as the nerves in the hand. Three main nerves constitute  the primary composition of innervation of the hand. These three nerves include the Radian, Ulnar, and Median nerves. Each of the these nerves have several branches each, but in general these nerve are localized to certain aspects of the posterior and anterior views of the hand. These innervations, as mentioned, contain branches of nerve plexuses, and contain fibers from more than one spinal cord segment. 


     Interestingly, a pathology that is associated with Radial nerve injury is the "wrist drop". This is interesting because the Radial nerve doesn't supply any muscles in the hand, but Radial nerve injury in the arm can cause serious hand instability. This is because the damage to the Radial nerve can cause paralysis of the extensor muscles of the forearm. However, despite how debilitating this sounds, usually the restriction of movement is minimal, even in serious injuries.


Lymphatics of the Upper Limb

     Arguably one of the most common oversights in the upper limbs may be the Lymphatic drainage. In general the Lymphatic system is an overflow system that gives drainage to excess fluids within every system in the body. Within the upper extremity the there is an expansive system of drainage, which are composed of smaller subunits. One of the main examples of this system  are the superficial lymphatic vessels that originate from the lymphatic plexuses. These ascend mostly to superficial veins such as the basilic and cephalic veins of the arm. Then some of these vessels enter various lymph nodes such as the cubital, humeral axillary, and apical axillary lymph nodes. Aside from the superficial vessels, there is another category, the Deep lymphatic vessels. These are far outnumbered by the superficial, but these terminate only in the humeral axillary lymph nodes.

     This discussion of lymphatics can lead to many types of pathology, but one in particular is Lymphedema. This is a disorder that is characterized by excess fluid builup due to congenital developmental abnormalities within the lymphatic system itself. There are two main categories for the disorder, Primary and Secondary. The Primary (Sporadic) subtype is when there is hypoplastic or hyperplastic involvement of the proximal or distal lymphatics. Whereas, the Secondary (Induced) subtype refers to when there is obstruction and/or inflammation due to trauma or other disease.  Essentially the disorder is chronic. However, consistent elevations of the limb (s) affected may aid in temporary symptom relief.

References:

1.)      Moore Keith L., Dalley Arthur F., Agur Anne M.R., "Chapter 6: Upper Limb". Lippincott Williams & Wilkins. Clinically Oriented Anatomy, 6e. 2010

2.)      Wheeless' Textbook of Orthopedics

3.)      Rapp Joseph H, Owens Christopher D, Johnson Meshell D, "Chapter 12. Blood Vessel & Lymphatic Disorders" (Chapter). McPhee SJ, Papadakis MA: CURRENT Medical Diagnosis & Treatment 2011: http://www.accessmedicine.com/content.aspx?aID=777652.

4.)      Wolff K, Johnson RA, "Section 16. Skin Signs of Vascular Insufficiency" (Chapter). Wolff K, Johnson RA: Fitzpatrick's Color Atlas & Synopsis of Clinical Dermatology, 6e: http://www.accessmedicine.com/content.aspx?aID=5189520.