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Finger flexion initiated at the distal and proximal interphalangeal joint level forces the extensor tendon to move distally. Therefore, the interosseous hood fixed to the extensor apparatus moves distally, too. The proximal part of the hood which is located at the level of the metacarpal head during extension of the finger slides distally along the basis of the proximal phalanx. Due to the much smaller cross-section of the phalanx compared to the metacarpal head, the palmar border of the interosseous hood is shifted palmarly. This produces a two-fold effect concerning the metacarpophalangeal joint. First, it leads to an increasing flexion moment of the intrinsic muscles during flexion of the metacarpophalangeal joint. Second, the same mechanism improves the ability of abduction and adduction in the metacarpophalangeal joint during extension of the finger. In this position, the proximal part of the interosseous hood covers the metacarpal head and the strong palmar bundles of the hood are pushed to the ulnar and radial sides resulting in a greater distance to the abduction/adduction axis of the MP-joint. The other effect concerns the proximal interphalangeal joint. The described transformation of the interosseous hood during flexion especially of its proximal part causes a curved deformation of the strong palmar border of the interosseous hood. The power of the intrinsic muscles inserting at the interosseous hood is passed along this smooth curve on its way to the dorsal side of the proximal interphalangeal joint thus allowing a continuous extension of the proximal interphalangeal joint in all flexion phases of the MP-joint. The typical transformation of the interosseous hood is regulated by the form of the underlying bone and ligament apparatus and can be understood as a passive mechanism effecting in a senseful change of muscle function as the active element during finger flexion and extension. These not yet described morphological data concerning the transformation of the interosseous hood during finger flexion and the functional interpretation complete the former described mechanism of flexion by Landsmeer (1955) and Landsmeer and Long (1965).

Percutaneous application of Kirschner wires, fixator pins, or other implants near the metacarpophalangeal joint may lead to postoperative disability of movement with subsequent joint stiffness. To determine the best location for the application of implants into the metacarpal head and the basis of the proximal phalanx, 57 Kirschner wires were introduced into the metacarpal head and into the bases of the proximal phalanx and the resulting stiffness has been measured. Kirschner wires inserted at the level of the dorsal tubercle or proximal to the tubercle, do not lead to a noteworthy stiffness. Whenever possible, this tubercle should be taken as the distal border for inserting implants. If the position of the fracture line makes it necessary to implant wires into the metacarpal head itself, a more dorsal application is preferable. If a palmar placement cannot be avoided, the implantation should be done in neutral position of the metacarpophalangeal joint, because a transfixation of the tense collateral ligament in flexion leads to a maximum of postoperative stiffness. The application of wires into the basis of the proximal phalanx does not influence the range of movement of the metacarpophalangeal joint.

Cartilage and bone as supportive tissues are submitted to mechanical stresses and react to these in a very specific manner. Functional adaptation to the quality and magnitude of the acting forces is the result. In this article, the basic principles of functional adaptation of cartilage and bone will be presented. On the basis of these principles, promising functional concepts and clinical treatments may be established; this will be shown by some examples concerning the hand.

The four ulnar metacarpal bones are connected to each other at their proximal and distal ends by strong ligaments. The second and fifth metacarpal bones are the frame of the metacarpus. Surgically, this is of great importance. A fracture of these two bones often requires stabilization, whereas a fracture of the third and fourth metacarpal bones with intact ligaments seldom requires surgery except in cases of severe fragment dislocation. Using external fixation for these purposes it seems to be of utmost interest to define secure pintracks through the soft tissue. In an anatomical study using formalin fixed specimen it clearly could be demonstrated that the second and fifth metacarpal bones are best suited for external fixation. The second metacarpal bone should always be fixed from the radial side because the fixator pins can be inserted within a wide range of angles without the risk of violating the extensor tendons. Variations of tendons and ligaments are seldom located on the radial side of the second metacarpal bone and therefore, finger movement is unhindered after pin application. A similar consideration is true for the fifth metacarpal bone which should be fixed from the ulnar side. With respect to the extensor tendon which covers the entire dorsal surface of the fifth metacarpal bone, the angle of the pins should be 40 to 90 degrees from the dorsal side. For the third metacarpal bone, fixation from the radial side is preferable taking topographical and biomechanical considerations into account. The radial corridor to the fourth metacarpal bone is smaller than the ulnar corridor, but there is much less morphological variability of the extensor tendons than on the ulnar side where strong fibres often cross the fourth intermetacarpal space. Because in the proximal fourth of the metacarpal bones the tendons are located very close to each other, a small skin incision and preparation to the bone surface is advisable to exclude violation of the tendons when inserting fixator screws into the third and fourth metacarpal bones. Using formalin-alcohol fixed cadaver specimens for the research gives an idea of the anatomical situation in the dorsal metacarpus but cannot answer the question whether the tendons in the lax subcutaneous tissue of the living will automatically slip aside when the fixator pin approaches. This should be item to subsequent studies in fresh frozen specimens and follow-up studies in a larger amount of patients treated with external fixation.

The purpose of this study is to investigate carpal kinematics with respect to the pisotriquetral joint, before and after pisi-form excision. Five cadaver-hands were studied and a custom-designed plexi-glass-fixation device was used to standardize the wrists for exact passive movements in flexion and extension as well as in ulnar and radial abduction. Five sets of motion were registered before and after excision of the pisiform. Motion of the triquetrum and pisiform were studied by 3D-Motion Analysing Software System (peak 54). The results indicated that the excision of the pisiform does have an influence on the kinematics of the wrist. The movement of the triquetrum was increased after removal of the pisiform. Although the differences in measurement were only a few of millimetres and degrees, we know from the dorsal and palmar intercalated segment instabilities that even minor instabilities can act as a predisposing factor for arthrosis. Therefore, the excision of pisiform must be carefully considered. The common joint between the triquetrum and pisiform supports and indicates relation of their movements. However, the correlation for flexion/extension and radial deviation was high, an obvious correlation of the movements for ulnar deviation was not verifiable.

Although the relevance of capillary and gliding spaces of the back of the hand and the finger located dorsal to the extensor aponeurosis in the metacarpo-phalangeal region between the layers of the subdermal connective tissue is often emphasized clinically in inflammatory and acute traumatic occurrences, hardly any information has been published concerning the morphology of these spaces. By means of plastic-injection techniques, varying configurations of capillary spaces in the distal region of the dorsum manus of cadavers were found. The deep connective tissue spaces located dorsal to the extensor aponeurosis were shown to have proximal connections to the dorsal tendon sheaths of the carpus, whereas superficial gliding spaces tended to vary in their expanse depending on the subcutaneous and epifascial septa. The deep as well as the superficial capillary gliding spaces are adapted as mobilizing and limiting structures for the movements of the metacarpo-phalangeal joints and the various mechanical stresses of the skin of the back of the hand. A high degree of exactness in the reconstruction of the marginal elements of such functional spaces appears to be of special importance with regard to a total restoration of the functional capability of the metacarpo-phalangeal joint region.

Alterations of the spatial geometry of the carpal tunnel and its contents during dynamic stress situations of the wrist are of importance in clarifying morphological causes of a carpal tunnel syndrome. In order to demonstrate the changes occurring in the form of the carpal tunnel and the location of its contents during wrist movement, casts of the carpal tunnel were produced from the hands of cadavers in flexed and extended positions. The casts were then morphometrically analyzed and the movements of the median nerve and the flexor tendons were examined radiologically. The investigation showed that a delicate equilibrium exists between the capacity of the carpal tunnel--whose hourglass shape typically changes to suit dynamic stress situations--and the volume of its contents. Spatial processes extending from the carpal tunnel wall or emanating from the structures contained within the carpal tunnel may exceed the system's ability to compensate for extreme positioning of the wrist and thus induce compression symptoms of the median nerve.

In the following study, the basal joint of the thumb and its neighboring joints of 100 anatomical specimens were inspected radiologically and macroscopically for arthrotic alterations. The comparison of the radiological and macroscopic findings showed that early arthrotic joint alterations cannot be diagnosed by radiograms. Virtually half of the specimens examined demonstrated arthrotic lesions of the basal joint of the thumb, whereas the trapezio-scaphoidal and trapezoido-scaphoidal joints were only affected in one-third of the specimens. Two-thirds of the cases with manifest arthrosis of the metacarpophalangeal joint of the thumb demonstrated additional arthrotic changes in the joints between the scaphoid, trapezium, and trapezoideum. No macroscopic evidence of arthrotic alterations in the remaining radial carpal bones were observed. The architecture of the capsular and ligamentous apparatus as well as the individual variations in the scaphoid bone have both been discussed as possible causes of these phenomena, as were polyarthrotic or secondary arthrotic processes.

Arthrography of the proximal wrist joint does not provide details regarding the shape and the extension of the recessus ulnaris. The recessus located between the ulnocarpal disc and the meniscus homologue as a diverticulum of the articular lining was examined in 61 wrists by arthrography and dissection. Using the Pleximon-injection technique, specimens of the proximal wrist cavity allowed a systematic description of morphology and topography of the ulnar recessus. The shape and location of the ulnar recessus show variations, but a sacciform recessus, which usually bears a close relationship to the ulnar styloid process, is the most common. The comparison of arthrographic and morphologic findings allows an assessment of the credibility of arthrographic depictions of the wrist as regards the clinically relevant close relationship to the recessus ulnaris.

Anatomic characteristics of the lunate and the pisiform were compared in order to support the use of a pisiform transposition in advanced stages of Kienböck's disease. Fifty lunate and pisiform bone pairs served for morphological and functional investigations. In view of the present results, the pisiform, after a rotation of 90 degrees, should be implanted in the lunate cavity with its longitudinal diameter oriented in the dorsopalmar plane. Despite the small pisiform volume, maintenance of carpal height is assured by its relatively large dorsopalmar diameter. The rotated position takes advantage of existing cancellous structures and improves the conditions of force transmission. Measurements comparing the radii of curvature of the original lunate and the substitute pisiform surfaces show a good correspondence proximally and a reduction of the articular congruity distally, due to the flatness of the pisiform surface.

Apart from the first carpometacarpal joint, the fifth carpometacarpal joint is of importance in gripping and cupping the hand. The present study describes the functional anatomy of the fifth carpometacarpal joint considering morphological and experimental findings. Shape and extension of the cartilaginous articular surface of 50 metacarpal bases show characteristics of a saddle joint. The differences between the dorso-palmar and ulno-radial curvature of the articular surface suggest a main direction of motion in the fifth carpometacarpal joint around an ulno-radial axis. Flexion in this joint ranges from 10 to 15 degrees. After maximal flexion, a supinatory rotation of the metacarpal bone ranging from 10 to 15 degrees is measured. Because of the transverse arched configuration of the carpal bones, the flexion of the fifth metacarpal bone produces opposition towards the thumb. A simultaneous supinatory rotation supports this opposition movement.

An anatomic variation of the median nerve is demonstrated in a female patient suffering from carpal tunnel syndrome subsequent to a distal radius fracture with malalignment and reflex sympathetic dystrophy. The median nerve coursed anterior to the superficial flexor tendons from proximal ulnar toward the distal radial region of the distal forearm, giving off an ulnar branch just 2.5 cm proximal to the flexor retinaculum. This case proves that in the distal forearm, branches of the median nerve can be found both radial and ulnar to the midline.

The dorsal approach to the metacarpal bones is through the peritendinous connective tissue of the extensor tendons. Knowledge of the vascular supply of the distal parts of these tendons, between the distal end of the tendon sheath and the tendon's osseous insertion is important, especially with respect to atraumatic technique. The course and distribution of the vessels to the extensor tendons II-V were investigated. Superficial and deep layers of connective tissue were found to contain blood vessels. The superficial vessels reach the dorsal aspect of the extensor tendon, originating from subcutaneous arteries and the large arteries of the hand. The deep vessels reach the lateropalmar aspect of the tendons and originate from the peritendinous muscular arteries. Vessel distribution suggests a direct relationship between the number of nourishing arteries and the tendon surface area. The vascular supply to the unsheathed parts of the extensor tendons shows morphological adaptations to differential mechanical stress during tendon excursion.

Assessing radial and ulnar rotational deformities quantitatively by routine diagnosis after healed distal forearm fractures is very difficult. A method to obtain information about direction and graduation of malrotation is described. This method is based on discovering topographic changes of skeletal points by CT. Rotational angles of intact forearm bones are measured on anatomic specimen and in vivo using epiphyseal and diaphyseal axes of the radius and the ulna. Normal rotation of intact forearm bones varies in a specific manner. The radius presents less variations than the ulna. A morphological index of radial and ulnar rotation is not given because of the great individuality of diaphyseal rotation. Both radii of a single individuum show a very small rotational difference. Therefore a verification of malrotation is indicated by comparison to the intact opposite radius. Higher rotational graduations on the left side have to be noted.

Full function of finger flexion requires an intact pulley system. After destruction of the pulleys, reconstruction over the metacarpal head (A1) and over the center of the proximal and middle phalanges (A2, A4) should be carried out. Calculations on a computer model suggest that the reconstructed pulley must hold the tendon close to the underlying bone. Width of the pulley and distance from the next proximal or distal joint of the inserted pulley are of minor functional importance. The amount of maximum load on the pulley, exceeding the tension of the tendon, must be considered in operation and postoperative treatment. The extensor pollicis longus tendon lies at the dorsal tubercle (tubercle of Lister) within an osseous gliding surface, where it changes direction. The deviation angle depends on the radiocarpal position and causes, in addition to the usual tension, a pressure stress to that part of the tendon. A graphical analysis of statics, based on X-rays, demonstrates maximum loads on the gliding surface. They can increase in relation to the tension force of the tendon to about 50% in the antero-posterior and to 100% in the radioulnar projection. Densitography of the distal radius shows a maximum of density where the dorsal tubercle is most prominent. Nutritional problems of that tendon are predisposed by that particular mechanical stress. Therefore spontaneous rupture of the extensor pollicis longus tendon in patients with rheumatoid arthritis or after fracture of the distal radius occurs, though infrequently. In the case of immobilization, slight ulnar abduction within the radiocarpal joint remarkably reduces the tension and pressure stresses on the tendon.

Torsion of the metacarpals II to V was measured in 50 pairs of human hand skeletons. The in-situ position of the metacarpals was reconstructed and the influence of the torsion of the morphological radioulnar head axes analysed. It is shown that during flexion of the metacarpophalangeal joint these morphological radioulnar axes serve as functional axes. Because of the specific position of the radioulnar axes through the metacarpal heads, the hand can be divided into three functional units: the thumb; the index and middle fingers; the fourth and fifth fingers. Within such a functional unit, lines perpendicular to the aforementioned radioulnar axes converge. In contrast to earlier investigations, these lines do not intersect at one common point. There are two separate intersections: one for the metacarpals II and III and another for the metacarpals IV and V. The torsion of right and left metacarpals shows significant differences. The lines perpendicular to the radioulnar metacarpal head axes in left hands generally show a more radial deviation, whereas in right hands they run more parallel to the metacarpals' longitudinal axes. This investigation shows that the precision grip of the right hand and the power grip of the left is supported by the morphology of the metacarpal bones. Finally, the clinical significance of our results is pointed out.

The wrist joint is generally stressed by external forces. The resultant of these external forces produces the pressure in the joint which evokes pressure stresses within the supporting tissues of the joint. As was shown by Pauwels (1973) the density of the subchondral bone is adapted to articular stress distribution. The zone of subchondral bone can be seen as the morphological equivalent of the specific joint stress. This paper shows by means of density analyses and pressure measurements that in contrast to earlier opinions joint pressure is transmitted both by the lunate and the scaphoid bones. It seems that the physiological stress is even higher in the scaphoid than in the lunate bone. The force transmission between the lunate and the ulnar disc is less pronounced. The analysis of the lunatal trabecular architecture leads to the suggestion that the lunate is stressed differentially in the radio-ulnar plane. In pathological conditions of the wrist joint (perforation of the disc, ulnar shift, Kienböck's disease, ulna minus variant) the pressure and the density distribution are adapted to the pathomorphology in each case.

Advanced osteoarthrosis of the first carpometacarpal joint is characterized by a subluxation (luxation) of the joint, by an adduction deformity and by hyperextension of the metacarpophalangeal joint of the thumb. This morphological and functional investigation aims to underline the importance of the intrinsic thumb muscles in this complex deformity of the thumb. The vector of the M. abductor pollicis brevis and the physiological cross-section of the thenar muscles were determined in eight osteoarthrotic and ten healthy hands. The superficial head of the M. flexor pollicis brevis and the M. abductor brevis were investigated electromyographically in patients as well as in healthy controls. There is disturbed function of the M. abductor pollicis brevis in cases of arthrosis, caused by a changed vector of the muscle. The physiological cross-section of the superficial head of the M. flexor pollicis brevis is diminished by about fifty per cent. The electromyographic records of patients lead to the conclusion that there is a particular loss of activity in the short flexor and abductor muscles. The muscular alterations taken together cause functional imbalance of the thenar muscles. The abductor muscle is not able to maintain the coordinating system that consists of two straight and one oblique muscle and the Z-deformity of the thumb results.

The influence of inaccurate positioning of the hand and forearm upon the relative lengths of the ulna and radius is investigated systematically in anatomical specimens and living persons. Increased or decreased ulnar lengths could be produced by moving up and down, by tilting or by pronation of the forearm. Extension of the elbow also influences the ulnar variance measurement.

Any analysis of the stability of the distal radio-ulnar joint should consider the extensor carpi ulnaris tendon. The static and kinematic function of this tendon depends on its relationship to the sigmoid notch of the radius. Morphological studies indicate the existence of a gliding surface in the sulcus of the tendon on the dorsal side of the ulnar head.