The term “Prosthesis” can be defined as an artificial replica that replaces human damaged or lost body part. In the field of arthroplasty or joint replacement surgery, prosthesis is defined as an artificial joint that replaces the arthritis affected or damaged human articulation (i.e., bone joint). The primary objective of the arthroplasty is to relief patients from arthritis pain in addition with restoring joint functions. Though in most of the cases the reason behind the arthroplasty is the arthritis pain, it’s not only the reason. Human articulations can be damaged by severe impacts or unusual stresses. Prostheses are usually made for human main joints such as hip, knee, elbow, shoulder, wrist etc. Long term results of the arthroplasty depend to a great extent on the quality of prosthesis implantation. The application of the robotics technology in the field of arthroplasty reduces the inaccuracy that occurred in conventional joint replacement surgery such as misalignment, rotation error, resection etc.
On the other hand, in the field of biomechatronics (i.e., the science of fusing artificially intelligent devices with the human body), prosthesis is defined as an artificial substitute for a missing body part. Human limb amputation can causes due to trauma, tumor, congenital, disease, etc. According to biomechatronics, prostheses are considered as those which replace human lost arms and legs. The development of the biomechatronics provides useful technology for the robotic prosthesis. Robotic prosthesis act as an extended body part of the amputee’s by using which amputee’s can be able to perform his/her daily life activities and take care of them by using their own body functions. As a result, robotic prostheses provide an independent life and more productive role of these people in the society.
In addition with the prostheses mentioned above, artificial eyes, teeth, artery, and heart valves are also correctly termed as prostheses.
TRANSHUMERAL PROSTHESIS FOR ABOVE-ELBOW AMPUTEES
“Transhumeral Prosthesis” can be defined as a prosthesis that is designed for the people who have lost their arm just above the elbow joint (i.e., above-elbow amputees). Human arm amputation can caused due to congenital (birth defect), tumor, trauma, disease, etc. circulatory disease, cancer and infections are considered as the major categories of disease which may require surgical removal of human arm. Moreover, the civil wars and more specifically wars in Sri Lanka, Iraq and Afghanistan producing an unprecedented number of amputees. Although nothing can ever become a perfect substitute for a missing arm, the intension of the transhumeral prosthesis is to compensate for the lost functions of the above-elbow (AE) amputees absent arm, so that they can lead an independent life and play more productive role in the society.
HISTORICAL EVOLUTION OF THE PROSTHETIC ARM
Prostheses have been found around for thousands of years, however real advancement and fabrication of the prostheses have started about 500 years ago . According to the medical museum exhibited at the University of Iowa titled “History of Prostheses”, earliest prostheses were used by soldiers dating back to 484 B.C. Hegesistratus; a Persian soldier around 490 B.C. cut off part of his own feet in order to escape from the prison and later replaced it with a wooden foot . In 61 A.D., Pliny the Elder wrote about the Roman General Marcus Sergius who had lost his right arm during the Second Punic War (218-201 B.C.). Later he had replaced that by an iron arm to support his shield and he returned to battle . During the middle ages, 15th and 16th centuries cosmetic prostheses were usually made from iron. At that period, blacksmiths and armor makers designed the prostheses for the soldiers after modeling their suits of armor. In the 16th century, the great French arm surgeon Ambrose Pare, designed several limb prostheses in addition with practicing surgical amputation. In 1818, Peter Baliff appears to have been the first person to introduce the use of the trunk and shoulder girdle muscles as sources of power to move the prosthetic arm. In 1844, the first transhumeral amputation replacement used Baliff’s principle to apply flexion for the elbow joint . The prosthetic arm using this concept is termed as “Mechanical” or “Body Powered” prosthetic arm and still extremely famous among the amputees society. By 1860, the Crimean and Italian campaigns of the French Empire left many soldiers in need of prostheses, and their call was answered by the Comte de Beaufort  . The Comte de Beaufort designed several limb prostheses using the articles of clothing, pulleys and levers. After the World War I and II, a tremendous loss of manpower in USA and Europe served as a catalyst for the rapid development of the prosthetic arm. In 1948, N. Wiener proposed the concept of Cybernetics i.e., the study of control and communication between the human and the machine , which plays an important role later for the development of the prosthetic arm. In 1949, Samuel Anderson created the first electrically powered prosthetic arm using the external power with support from the US Govt. and IBM. The first myoelectric arm was developed by Russians in 1958 and later on Otto Bock Company revealed the commercially available prosthetic arm for general application which was the first made versions of the Russian design .
CLASSIFICATION OF THE PROSTHETIC ARM
Prosthetic arms can be grouped into three general categories:
1) Non-functional or Cosmetic Prosthetic Arm – As the name implies functioning of these prostheses has less priority than the appearance, weight, wearing comfort and easy handling. These are the oldest and available for 2000 years. Though cosmetic prostheses offer a more natural look and feel, they sacrifice functionality and versatility while also being relatively expensive .
2) Mechanical or Body Powered Prosthetic Arm – The power to operate these prostheses comes from the user’s own body. In this system, the user wears a harness that translates the shoulder motion into elbow flexion motion and action of gravity force generates the elbow extension motion. The earliest model of this prosthetic arm was the Ballif arm . These prosthetic arms are light weight and less expensive than the others however it requires large amount of forces to actually move the elbow .
3) Externally Powered Prosthetic Arm – Most advanced commercially available prosthetic arm in which power to operate the prosthetic arm comes from the external sources such as electric motor and battery pack. Most of these prostheses are operated by using user’s stump arm muscles EMG signals. This type of prostheses provides greater proximal functions, increased cosmetic appeal but also tend to be much heavier and expensive than any of the other categories .
Present State and Proposed Transhumeral Prosthesis
Recent progress in biomechatronics technology brings a lot of benefit to increase the mobility of above-elbow (AE) amputees in their daily life activities. A transhumeral or AE prosthetic arm is used to compensate for the lost functions of the AE amputees absent arm. A number of commercial prosthetic arms have been developed since last few decades. However, many amputees have not used them due to the discrepancy between their expectations and the reality. The main factors causing a loss of interest in presently available prosthetic arms include low functionality and poor controllability .
Since the concept of Cybernetics proposed by N. Wiener , a number of research works have already been carried out and are ongoing for the development of prosthetic arm. At present, Utah arm, Boston Elbow, and Otto Bock are considered as the pioneers in this field which are shown in Fig. 1 -. However, currently, commercial prosthesis available on the market for the AE amputees provides a limited DOF. Most of these prostheses provide elbow flexion-extension motion with a terminal device attached at the end. In addition to the elbow motion, some prostheses provide forearm supination-pronation motion and a single DOF at the terminal device for grasping object. Some passive DOF, which are useful to generate an optimal pre-determined configuration during performing certain tasks , are sometimes included in the prostheses. Commercially available expensive cosmetic prostheses offer a more natural appearance and simple control. However, their dexterity is relatively very poor compared to the human arm. Human arm generates precise and complex motions during daily life activities which are almost impossible to be generated by using a limited DOF prosthetic arm. As a result, the presently available commercial prostheses have failed to gain wide acceptance among AE amputees.
Figure 1: Commercially Available Externally Powered AE Prosthetic Arm .
In order to improve the quality of life of AE amputees and to increase their mobility in daily life activities (like, eating, drinking, dressing, brushing etc.), a 5 DOF externally powered transhumeral prosthesis is proposed in this thesis. The prosthesis is designed to generate elbow flexion-extension, forearm supination-pronation, wrist flexion-extension and radial-ulnar deviation, and hand grasp-release motion. Currently, no commercial transhumeral prosthesis provides a combination of wrist flexion-extension and radial-ulnar deviation motion, which have uttermost importance to perform daily life activities. In recent years, a number of prostheses capable of generating multi-DOF motion have been proposed for upper limb amputees , -. However, none of these provide a combination of forearm and 2 DOF wrist motion with the exception of an arm designed for above-wrist amputees to provide wrist flexion-extension and forearm motion .
Bio-Mechanics of Human Upper Limb
Before develop a robotic arm system to mimic to the human arm, the physics of the human upper limb should be thoroughly studied. Accordingly the upper limb mainly consists of three major components, the shoulder complex, elbow complex and wrist joint. Mainly the shoulder complex is built with three bones, clavicle, scapula and humerus and four articulations: the glenohumeral, acromioclavicular, sternoclavicular and scapulothoracic, with the thorax as a stable base.
The only point of skeletal attachment of the upper extremity to the trunk occurs at the sternoclavicular (SC) joint. At this joint the clavicle joints to the sternum, the middle bones of the rib cages. The clavicle is connected to the scapula at its distal end via the acromioclavicular (AC) joint. At this joint, most of the movements of the scapula on the clavicle occur, and the joint handles large contact stresses as a result of high axial loads that are transmitted through the joint.
The scapula interfaces with the thorax via the scapulothoracic (ST) joint. This is not a typical articulation, connecting bone to bone. Rather, it is a physiological joint containing neurovascular, muscular, and bursal structures that allow for a smooth motion of the scapula on the thorax. The final articulation in the shoulder complex is the shoulder complex is the shoulder joint, or the glenohumeral (GH) joint. Motions of the shoulder joint are represented by the movements of the arm. This is a synovial ball-and-socket joint that offers the greatest range of motion and movement potential of any joint in the body.
The shoulder complex can be mimic to a ball-and-socket joint and can be modeled accordingly. The proximal part of the humerus, humeral head and the female part of the scapula, glenoid cavity respectively act as the ball and the socket of the joint. The main motion of the shoulder joints are shoulder flexion/extension, shoulder abduction/adduction and internal/external rotation. During this each motion, the position of the centre of rotation of the shoulder joint changes.
The distal part of the humerus is connected to the elbow joint or the radioulnar joint. The elbow is considered a stable joint, with structural integrity, good ligamentous support, and good muscular support. It consists of three bones of the arm and the forearm, humerus, radius and ulna. Movements between the forearm and the arm takes place at the ulnohumeral and radio-humeral articulations, and movements between the radius and the ulna take place at the radioulnar articulations.
The ulnohumeral joint is the articulation between the ulna and the humerus and is the major contributing joint to flexion and extension of the forearm. The joint is the union between the spool-like trochlea on the distal end of the humerus and the trochlear notch on the ulna. The second joint participating in flexion and extension motion of the forearm is the radiohumeral joint. At the distal end of the humerus is the articulating surface for this joint, the capitulum, which is supheroidal and covered with cartilages on the anterior and inferior surface. The top of the round radial head butts up against the capitulum, allowing radial movement around the humerus during flexion and extension. The capitulum acts as a buttress for lateral compression and the other rotational forces absorbed during throwing and other rapid forearm movements. The third articulation, the radioulnar joint, establishes movement between the radius and the ulna in pronation and supination. There are actually two radioulnar articulations, the superior in the elbow joint region and the inferior near the wrist. Also, midway between the elbow and the wrist is another fibrous connection between the radius and the ulnar, recognized by some as a third radioulnar articulation.
The hand is primarily used for manipulation activities requiring very fine movements incorporating a wide variety of hand and finger postures. Consequently, there is much interplay between the wrist joint positions and efficiency of finger actions. The hand region has many stable yet very mobile segments, with complex muscle and joint actions. The wrist consists of 10 small carpal bones but can be functionally divided into the radiocarpal and the midcarpal joints. The radiocarpal joint is the articulation where movement of the whole hand occurs. The radiocarpal joint involves the broad distal end of the radius and two carpals, the scaphoid and the lunate. There is also minimal contact and involvement with the trinquetrum. This ellipsoid joint allows movement in two planes: flexion-extension and radial-ulnar flexion. It should be noted that wrist extension and radial and ulnar flexion primarily occur at the radiocarpal joint but a good portion of the wrist flexion is developed at the midcarpal joints
Wrist motions are generated around an instantaneous center. The path of the centrode is small, however, customarily, the displacement of the instantaneous center of rotation is ignored and the rotation axes for the flexion/extension and ulna/radial deviation are considered to be fixed. The axes pass through the capitate, a carpal bone articulating with the third metacarpal. Although it is considered that wrist joint motions are generated with respect to the two axes, some research  has proved that the motions are generated with respect to four axes. The wrist flexion axis and the extension axis are different. Similarly the radial deviation axis and the ulnar deviation axis are also different. Therefore, the 2DOF of the wrist are through four axes. Although flexion and extension motions have different axes they are intersected in a point in capitates. Similarly, radial and ulnar deviations axes are also intersected. When we consider that flexion and extension motions have one axis and similarly ulnar and radial deviations have one axis, the slight offset of the rotational axes of the flexion/extension and the radial/ulnar deviation is approximately 5 mm , .
In addition the motion ranges of the upper limb are as follows.
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