We have found that people are often interested to learn of the various anatomical features unique to the hand that enhance a human’s ability to grasp and hold on to things. This ability to firmly grasp and hold with significant strength enables the human to use tools and engage in the myriad functions of daily living. These unique anatomical features include:
- Crossing Anatomical Arches: The medial and lateral longitudinal arches, run the length of the entire hand and place the hand in a cupping shape. This naturally facilitates wrapping one’s fingers around an object. The transverse arch runs perpendicular to the metatarsals. Here the metacarpophylangeal (MCP) joints of the little and ring fingers are quite mobile. This enables them to wrap around the bottom of an object more fully. The greater stability of the MCP joints of the middle and index fingers, allows for a firmer grip. This dual capability of mobility and stability among the four different fingers, maximizes the gripping and holding potential of the hand.
- An Elongated Opposable Thumb: Gripping or grasping requires the application of a force-counter force. The carpometacarpal (CMC) joint of the thumb is a joint that can move in all three planes of motion. This combined with the human’s elongated thumb, allows for complete opposition to the other four fingers. A total of five muscles are involved in applying the force and movement to position and flex the thumb for opposition to the fingers.
- A Built in Finger Flexor Pulley System: There are two major muscles originating in the forearm, and each provides four tendons that go to all four fingers. The unique “pulley” feature occurs when the deeper flexor digitorum profundus muscle tendons emerge and pass through the split tendons of the more superficial flexor digitorum superficialis muscle tendons. The location where the deeper tendons emerge through the split tendons of the more superficial tendons creates a pulley system that increases the mechanical advantage and the resultant force it can produce in flexing the four fingers for gripping and holding objects.
- A Palm with Anchored Skin: Unlike the skin on the back of the hand, the skin on the palm is anchored, via tiny ligaments, to the underlying palmar aponeurosis, a tough connective tissue covering most of the palm. Consequently, when holding something heavy the skin on the palm stays put, anchored in place, and does not slide downward under the weight of the object being held. If the human grip were backward, the skin on the back of the hand, which is not anchored down, would move about and hinder grip. However, because we don’t grip with the back of our hand, but rather flex our fingers through a good range of motion, we need movement on the back of the hand, and stationary skin on the palm for gripping.
When you collectively consider these unique features that are designed to maximize hand grip strength and finger range of motion, it makes sense that achieving or maintaining proper grip strength is a primary focus in the rehabilitation efforts of those having suffered hand and/or finger trauma.
Lynn Perkes is a full-time faculty member at Brigham Young University-Idaho teaching courses in Kinesiology and Biomechanics, Applied Kinesiology and Assessment, Therapeutic Exercise, and Physical Therapist Assistant classes. He writes part time for ProhealthcareProducts.com, which sells healthcare, therapy, fitness, and personal protective equipment products.