Buttoningyour shirt, picking up a penny, turning a door knob, and brushing your teethare just a few movements we take for granted. These movements activatedifferent patterns of prehension. Prehension is the act of taking hold,seizing, or grasping. There are twotypes of prehension, the power grip and the precision grip. The power grip isused when an object must be held with a lot of force. A power grip includes anisometric contraction with no movement happening between the hand and theobject being held. It is used to lift heavier objects. A precision grip, sometimesreferred to as precision prehension, is used when an object is beingmanipulated in a finer type of movement, like holding a pencil.
With prehension,the way the hand and fingers are positioned depends on the weight, size, andshape of an object and how the object is going to be used including determiningthe grip. Some of the grips include: The hook grip ranges from the second through the fifth finger flexedaround an object in a hook like form. With the thumb not involved, it includesthe MCP joints in extension, and the PIP and DIP joints in some degree offlexion. This technique is used most often in sports like weight lifting, orlifting a piece of luggage where you need a secure grip for heavy loadsThespherical grip includes the thumb and fingers abducted and spread apart aroundan object. The palm is usually not involved with the finger positioning.
Movements that can be done with the spherical grip are holding a ball andopening the lid on a jar.Thelumbrical grip, also known as the plate grip, is mostly used when somethingneeds to be help horizontally like holding a plate or a tray. It is named bythe action of the lumbrical muscles flexing the MCP joints, while extending theIP joints. WithPad-to-pad grip, the IP and MCP joints of the finger are flexed and the thumbis abducted the distal joints are extended bringing the thumb and the pads ofthe finger together. This grasp is sometimes used to hold a piece of paper, oran index card.Theside-to-side grip is considered one of the weaker grips. It requires adductionof the index finger and abduction of the middle finger. It is most frequentlyused to hold a cigarette or even a pencil which is a secondary motion.
In thisgrip the thumb is not involved, so its possible to do with the absence of athumb.Prior to taking hold,seizing or grasping, the person will use vision to determine the restrictiveconditions of the environment in which the action will occur. Some of the common restrictions include,distance, location, size of object, and the spatial orientation of the object. Ifthe reach is exaggerated, the reach will occur without sensory feedback withmaking vision provide information of the displacement and velocity of theobject. For an example, if you were told to find a marker in a bag of crumpledpaper, with your hand sensation being intact, you would easily find it withoutlooking, because you can feel the difference between the marker and paper.
Ifyour hand sensation were not intact, you would have to dump the bag, and rely onyour visual to get you the marker. Hand sensations are provided by the radial,median and ulnar nerves. These nerves differentiate from person to person. Theradial nerves sup ply the muscles on the back of the arms to the skin of theforearms and hands, and the ulnar nervesare branches that come fromthe cervical nerves, which supply impulses to and from the muscles of theforearms and hands. The median nerve goes down the full length of the arm intothe hands as it branches off the brachial plexus and starts before the thirdpart of the axillary artery at the lateral side. The median nerve is one of themain nerves in the arm.
It’s in charge of controlling the forearm and hand muscles,allowing for the thumb, the wrist, and fingers to bend and move around. Injuryto nerves in the hand are often caused by trauma, with the area being cut,overstretched, crushed or burned, damaging the nerve ending.It’s the most often to getinjured with the wound being at the axilla. With it injured, the potential toabduct and oppose the thumb may be lost resulting in the lack of prehension abilitieslike, the lumbar grip to hold plates, the side-to-side grip to hold a cigaretteor pencil, and the spherical grip to open the top of a jar.
As a conclusion a Physicaltherapy assistant should understand the importance of prehension. Prehension isneeded in different situations, for instance, as a PTA we need to educate andmake sure our patients are able to complete continuous activities. For example, being able to grasp onto anydevices needed for ambulation and/or balance, using grasping for transfers, andbeing able to grasp and stand at the parallel bars safely, etc. Prehension is important for physical therapistassistant to continue to help people restore, maintain and promote overallfitness and health.