This study asks whether there are discernable links between precision gripping, tool behaviors, and hand morphology in modern hominoids, which may guide functional interpretation of early hominid hand morphology. Findings from a three-pronged investigation answer this question in the affirmative, as follows: (1) Experimental manufacture of early prehistoric tools provides evidence of connections between distinctive human precision grips and effective tool making. (A connection is not found between the "fine" thumb/index finger pad precision grip and early tool making.) (2) Manipulative behavior studies of chimpanzees, hamadryas baboons, and human show that human precision grips are distinguished by the greater force with which objects may be secured by the thumb and fingers of one hand (precision pinching) and the ability to adjust the orientation of gripped objects through movements at joints distal to the wrist (precision handling). (3) Morphological studies reveal eight featured distinctive of modern humans which facilitate use of these grips. Among these features are substantially larger moment arms for intrinsic muscles that stabilize the proximal thumb joints. Examination of evidence for these reveals that three of the eight features occur in Australopithecus afarensis, but limited thumb mobility would have compromised tool making. Also, Olduvai hand morphology strongly suggests a capacity for stone tool making. However, functional and behavioral implications of Sterkfontein and Swartkrans hand morphology are less clear. At present, no single skeletal feature can be safely relied upon as an indicator of distinctively human capabilities for precision gripping or tool making in fossil hominids.

Precision grips, hand morphology, and tools.

Surveys of performing musicians indicate that almost half of them experience playing-related medical problems, some of which threaten or end their careers. Overuse injuries involving the muscle--tendon unit are the most common problem, with symptoms ranging from mild pain while the musician is playing to pain severe enough to preclude any use of the affected hand. String players are the most commonly affected, and percussionists the least. The most important predisposing characteristic is the use of repetitive movements during long hours of practice, but awkward body positions mandated by the shape and weight of the instrument, the technical difficulty of the repertoire, and unfamiliar instruments may also play a part. Women are more commonly affected than men. Rest is the cornerstone of therapy. Neural impingement syndromes affecting the median or ulnar nerves or the thoracic outlet affect many musicians. Focal dystonias may involve part or all of a hand or the muscles forming the embouchure (the position of the lips in wind players). These are very resistant to therapy and may terminate or drastically alter a career. Stress, especially performance anxiety, may impede performance. Beta-adrenergic blocking agents prevent the symptoms of performance anxiety and are frequently used by musicians without medical supervision. A recognition of the unique problems of musician-patients has led to the formation of successful specialty clinics in a number of cities.

Medical problems of musicians.

Thirty-nine patients with a clinical diagnosis of the pronator teres syndrome were seen during a seven-year period. They typically complained of aching discomfort in the forearm, weakness in the hand, and numbness in the thumb and index finger. Cyclic stress usually brought on the symptoms. The distinctive physical finding was tenderness over the proximal part of the pronator teres, which was aggravated by resisted pronation of the forearm, flexion of the elbow, and occasionally by resisted contraction of the flexor superficialis of the long finger. Electrophysiological testing of the median nerve showed abnormalities in a few patients, but localization of the abnormality was possible only rarely. Intraoperative recordings showed some improvement shortly after release of the median nerve in six of the ten forearms that were tested. Surgical exploration of thirty-six forearms in thirty-two patients showed intramuscular tendinous bands in the pronator, indentation of the muscle belly of the flexor superficialis in most forearms. Vascular and muscular abnormalities were seen occasionally. Of the thirty-six operations, twenty-eight gave good or excellent results; five, fair; and in three patients the symptoms were unchanged. The cause of failure was either inadequate decompression or misdiagnosis.

The pronator teres syndrome: compressive neuropathy of the median nerve.

The discovery of fossil hand bones from an early human ancestor at Olduvai Gorge in 1960, at the same level as primitive stone tools, generated a debate about the role of tools in the evolution of the human hand that has raged to the present day. Could the Olduvai hand have made the tools? Did the human hand evolve as an adaptation to tool making and tool use? The debate has been fueled by anatomical studies comparing living and fossil human and nonhuman primate hands, and by experimental observations. These have assessed the relative abilities of apes and humans to manufacture the Oldowan tools, but consensus has been hampered by disagreements about how to translate experimental data from living species into quantitative models for predicting the performance of fossil hands. Such models are now beginning to take shape as new techniques are applied to the capture, management and analysis of data on kinetic and kinematic variables ranging from hand joint structure, muscle mechanics, and the distribution and density of bone to joint movements and muscle recruitment during manipulative behaviour. The systematic comparative studies are highlighting a functional complex of features in the human hand facilitating a distinctive repertoire of grips that are apparently more effective for stone tool making than grips characterising various nonhuman primate species. The new techniques are identifying skeletal variables whose form may provide clues to the potential of fossil hominid hands for one-handed firm precision grips and fine precision manoeuvering movements, both of which are essential for habitual and effective tool making and tool use.

https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1469-7580.2000.19710121.x

Evolution of the human hand: approaches to acquiring, analysing and interpreting the anatomical evidence.

Hand function and tool behavior in early hominids

Median nerve compression in the proximal forearm is relatively uncommon. This study reviews 71 cases over a 20 year period. Of the 71 in this series, 51 were treated surgically. The time of onset to definitive treatment ranged from 6 months to 5 years, with an average of 9 months. The ages of patients varied from 15 to 56 years and there were 13 males and 58 females. Past criteria for making the diagnosis are reviewed and an added series of clinical observations is made, including three definitive stress tests. In all cases surgically treated compression of the median nerve has been found at one of three levels, in the following order of frequency: the pronator teres, the flexor superficialis arch, and the lacertus fibrosus. Follow-up has been from 6 months to 19 years and four cases in the series were considered to be failures.

Median nerve entrapment syndrome in the proximal forearm

This study illustrates, with the use of laboratory material, personal observations, and available paleoanthropologic material, the evolutionary changes in the distal phalanx, division of the pulp into a proximal and distal region, and the uniqueness of passive hyperextension of the distal phalanx in modern man.

Richard K. Johnson

Papers

Median nerve entrapment syndrome in the proximal forearm

Form, function, and evolution of the distal phalanx.

Soft-tissue injuries of the forearm and hand.