Measurement and observation of the first web space based on morphology and clinical applications.

PURPOSE: To describe and evaluate the anatomical skin shape of the first web space in cadavers and to guide flap design for this area. METHODS: Twelve cadavers (24 hands on both sides) were selected. Marker points were chosen based on the characteristics of the first web for morphological measurement and observation. The morphological characteristics of the first web under the radial or palmar abduction position of the thumb were measured and compared. The best morphologic features and parameters of the first web repairing flap were obtained. RESULTS: When the thumb was in the palmar abduction position, the maximum distance a(p) was 6.78 ± 0.72 cm and the skin area s(p) was 20.09 ± 2.63 cm2, both of which were significantly greater than the distance a(r) of 5.86 ± 0.74 cm and the skin area s(r) of 17.39 ± 2.15 cm2 when the thumb was in the radial abduction position (P < 0.05). There was no significant difference in the length b(r) and b(p) of the long axis of the flap between two different abduction positions (P > 0.05). It is found that the shape of the first web area was not a symmetrical spindle but an irregular quadrilateral inclined to the index finger side. CONCLUSION: The flap design and measurement for the first web space covering should take the maximum palmar abduction position of the thumb as a reference. The asymmetric quadrilateral flap design is more in line with the anatomical and morphological characteristics of the region.

Captive bonobos (Pan paniscus) apply precision grips when using flaked stone tools.

OBJECTIVES: Current evidence suggests that flaked stone tool technologies did not emerge until ~3.3-2.6 million-years-ago (Ma). It is often hypothesized that early hominin (principally Ardipithecus and early Australopithecus) manual anatomy may have prevented an earlier emergence, as the forceful precision grips essential to flake tool-use may have been ineffectively performed by these species. Marzke, Marchant, McGrew, and Reece (2015) observed potentially forceful pad-to-side precision grips being recruited by wild chimpanzees (Pan troglodytes) during feeding behaviors, indicating that Pan-like manual anatomy, and therefore potentially early hominin anatomy, may be capable of effectively securing flake stone tools during their use. MATERIALS AND METHODS: Here, we report on the grips recruited by four captive, human-trained, bonobos (Pan paniscus) during the use of stone and organic tools, including flake stone tools during cutting behaviors. RESULTS: It is revealed that pad-to-side precision grips are frequently recruited by these bonobos when securing stone flakes during cutting actions. In some instances, high forces could have been resisted and applied by the thumb and fingers. DISCUSSION: While our analyzes are preliminary and limited to captive individuals, and Pan is not suggested to secure flakes with the same efficacy as Homo or Australopithecus, it points to early hominins potentially being able to perform the precision grips required to use flake stone tools. In turn, the ability to gain tangible benefits from the effective use of flake tools (i.e., gain energetic returns from processing food resources) may have been - at least anatomically - possible in early Australopithecus and other pre-Early Stone Age hominin species. In turn, hominin manual anatomy may not be a leading restriction on the emergence of the earliest stone tool technologies.

The Sensitivity of the Endpoint Forces of Thumb Extrinsic and Intrinsic Muscles to Changes in Joint Angles, Muscle Moment Arms and Bone Lengths in the Flexed Thumb.

A previous study showed in situ measurements of thumb-tip forces produced by muscles vary substantially among cadaveric specimens. Potential sources of variability include inter-specimen anatomic differences and postural deviations from the nominal posture in which the specimens were tested. This study aimed to theoretically determine the variation in thumb-tip force caused by inter-specimen differences in thumb anatomy and posture. We developed a two-dimensional mathematical model of force production at the thumb tip based on published estimates of muscle moment arms, bone length, and joint angle measurements from nine cadaveric specimens. The model was placed in a flexed posture. Using the model, we calculated variations in magnitude and direction of each muscle's thumb-tip force induced by a ±1 standard deviation (or equivalent) variation in each bone length, the moment arm of the muscle (i.e., anatomic factors), and each joint angle (i.e., postural factor). For most muscles, inter-specimen differences in the metacarpophalangeal (MP) joint angle produced at least a 75% larger variation in thumb-tip force magnitude than that produced by other factors. For all muscles, differences in the interphalangeal joint angle among specimens produced the largest variation in thumb-tip force direction. For some muscles, inter-specimen differences in bone lengths, moment arms, and MP joint angles also produced large variations in thumb-tip force direction. This study suggests deviation from the nominal flexed thumb posture and large measurement variability in muscle moment arms are primary and secondary sources, respectively, of variability in thumb-tip forces produced by the majority of thumb muscles. Further, this study suggests a more careful approach to standardizing the thumb posture would likely improve current measurements of thumb-tip forces.Clinical Relevance- This work describes the influence of anatomic and postural factors on thumb-tip forces that thumb muscles produce. The results of this work have implications for musculoskeletal modeling and surgical reconstruction of grasp.

A pathological Neandertal thumb phalanx from Moula-Guercy (France).

OBJECTIVE: To discuss a Neandertal pathological adult first pollical proximal phalanx (I2-104) from the Baume de Moula-Guercy (Ardèche, France) and evaluate the possible causes of this pathology. METHODS: Macroscopic analyses of external features, as well as CT imaging, were used in the analysis RESULTS: The presence of asymmetric eburnation on the distal epiphysis associated with an osteophyte on the palmar surface, as well as the absence of periosteal bone reaction visible on CT images, is consistent with osteoarthritis. CONCLUSION: Osteoarthritis (OA) can have different origins and the cause is difficult to identify. The pathology of the Moula-Guercy I2-104 phalanx may be due to a genetic predisposition for OA known in Neandertals and associated with short limb bones. The OA could have been aggravated by the age of this individual and by an inflammatory reaction caused by repeated movements and intense vibrations provoked by high-frequency knapping or by other use of the hands SIGNIFICANCE: The I2-104 phalanx is the first Neandertal pollical phalanx known to display OA, although joints of this bone are frequently affected by this pathology in modern humans. Thus, greater insight into the presence and consequences of Neandertal behaviors is offered LIMITATION: It is impossible to give a definitive conclusion on the cause(s) of the OA in this case. SUGGESTIONS FOR FURTHER RESEARCH: More data is needed concerning OA within Neandertals and its relationship with behavior and genetics.

Morphometric study of percutaneous A1 pulley of thumb release.

Through anatomy, microscope, histopathology, and simulating needle knife operation on specimens, to accumulate the relevant parameters of the A1 pulley of thumb, and to provide an anatomical evidence for the needle knife therapy of stenosing flexor tenosynovitis. A total of 20 fingers were selected from 20 intact adult upper limb specimens, a small amount of emerald green waterproof dye was injected from the needle insertion point, dissected layer by layer, and the A1 pulley and neurovascular bundle were observed. Observe the loosening of the thumb A1 pulley after 5 and 10 times of simulated needle knife cutting on the specimen; observe the relationship between the needle knife entry point and the A1 pulley under the thumb extension and abduction, and the thumb extension neutral position respectively; further observe the histological characteristics, and the relationship between needle entry point and A1 pulley by microscope. ① In general observation, the A1 pulleys of each finger were transverse fibers perpendicular to the flexor tendon, tough in texture, connected with synovial fibers at the proximal end. It is difficult to distinguish, and connected with oblique fibers at the distal end. ② The release rate of the thumb A1 pulley after 5 and 10 times of simulated needle knife cutting on the specimen were (40.46 ± 2.22)% and (63.52 ± 4.49)%, respectively. ③ In the neutral position of the thumb straightening, the needle entry point is 3.06 ± 0.14 mm from the proximal side of the proximal edge of the A1 pulley, which overlaps with the needle entry point where the thumb is straight and abducted. ④ Observed under a microscope, the A1 pulley is a dense transverse fiber with a pale yellow dense connective tissue, both ends are continuous with the synovial fibers. It is thin and translucent, and loose connective tissue. The A1 pulley is a dense transverse fiber with a pale yellow dense connective tissue. The anatomical key points of the needle knife therapy lie in the extended and abducted position of the thumb. Currently, it is believed that cutting the proximal edge of the A1 pulley is sufficient, and there is no need to cut the entire A1 pulley.

Human thumb consists of three phalanges and lacks metacarpal? A morphometric study on the long bones of the hand.

PURPOSE: For many years, it was thought that the thumb consists of just two phalanges that differentiate it from the other four medial triphalangeal fingers. But there are some old reports that few former scientists believed the thumb has three phalanges and it lacked a metacarpal, and the thumb metacarpal is a phalanx. So this anthropometric study was carried out by investigating the morphology of the long bones of the hand and correlations between the thumb metacarpal and other miniature long bones of the hand. METHODS: We studied anterior-posterior X-ray images of the right hands of 80 individuals from 18 to 65 years old. The exploration targets were the length of all metacarpals (MC), proximal phalanges (PP), middle phalanges (MP), and distal phalanges (DP). Friedman Repeated Measures Analysis of Variance and Dunn's post hoc test were carried out to compare the means of all variables. The correlation between all quantitative factors was done by Spearman Rank Correlation (Spearman's Rho) coefficient. RESULTS: Our results showed that the length of the phalanges and the total length of the fingers are independent of the related metacarpal length (P < 0.001). Also, the thumb metacarpal length in comparison to all bones of the hand was significantly different from all long bones of the hand except the proximal phalanx of the middle finger (P = 1). CONCLUSION: Based on the morphology of the long bones of the hand and the high similarity between the thumb metacarpal and phalanges especially the proximal phalanx of the middle finger, it can be suggested that the current thumb metacarpal is a proximal phalanx of the thumb.

Pointing in a different direction: a case of bilateral absence of extensor indicis.

Understanding anatomical variations as well as normal anatomy of the muscles and tendons of the hand is vital for successful clinical evaluation and surgery. A number of extensor muscle and tendon variations have been reported in the literature, including duplication, triplication, and absence. We report a rare anatomical variation that includes bilateral absence of the extensor indicis (EI) muscles and bilateral duplication of the extensor digitorum (ED) tendon to the second digit in the forearm of an 83-year-old male cadaver during routine upper limbs dissection. In the present case, only three muscles were present in the deep compartment: extensor pollicis longus (EPL), extensor pollicis brevis (EPB), and abductor pollicis longus (APL) with bilateral absence of EI. The reported prevalence of bilateral absence of EI muscle and tendon ranges from 0.5% to 3.5%. The prevalence of an additional index tendon arising bilaterally from the ED muscle belly is 3.2% of the population. Extension of the index finger is governed by the actions of EI and ED. However, the four tendons of ED are linked to each other by juncturae tendinum, restricting independent extension of the digits in certain postures, e.g. when the hand is fisted. With fisted hand, EI controls extension of the index finger. Clinically, EI tendons are used for tendon reconstruction procedures to restore function to the hand and thumb after trauma or tendon rupture. This report highlights the importance of anticipating anatomical variations and conducting pre-operative evaluations to confirm the presence of EI when planning tendon transfer procedures.

An Anatomical Evaluation of the Trapezium and Its Relationship to Basilar Joint Osteophytic Change.

BACKGROUND: To perform a comprehensive osteologic investigation into trapezium anatomy and investigate the relationship between anatomical factors and osteophyte formation, focusing on sex-specific differences. METHODS: This was a cadaveric study involving 1233 trapezia and first metacarpals. Two subgroups ("Control" and "Main Study") were established. The "Control" cohort was used to identify features of the trapezium in specimens devoid of osteophytic change. The prevalence and severity of osteophytic change were investigated in the "Main Study" cohort. Sex differences were specifically assessed. Regression analyses were used to identify factors associated with osteophyte formation. RESULTS: Three discrete surface morphologies exist at the trapezium trapeziometacarpal (TM) facet: heart, quadrilateral, and bean. Controlling for height, men have a larger trapezium TM facet surface area. However, the trapezium assumes the same off-center saddle shape in both sexes. The presence of osteophytes at the basilar joint is a common finding; no differences in osteologic prevalence exist between sexes. The progression of osteophytic change complements the radiographic Eaton-Littler classification system. The trapezium TM facet increases the surface area with incremental osteophyte involvement, with the degree of surface area expansion correlated with increases in the severity of osteophytic change. Increased age, increased surface area, bean morphology, and decreased volar joint depth are associated with more severe osteophyte formation. CONCLUSIONS: Anatomical features of the trapezium may contribute to osteophyte development. Although the prevalence of osteophytic disease appears equal between sexes, sex differences exist in some anatomical parameters. These differences may help explain the increased prevalence of symptomatic basilar joint disease in women.

Human evolution: Thumbs up for efficiency.

Modelling a muscle key to flexing the thumb, a new study suggests that the powerful opposability that characterises the dextrous human hand evolved in some of our fossil relatives about two million years ago - a time when tool use became more important.

Biomechanics of the human thumb and the evolution of dexterity.

Systematic tool production and use is one of humanity's defining characteristics, possibly originating as early as >3 million years ago.1-3 Although heightened manual dexterity is considered to be intrinsically intertwined with tool use and manufacture, and critical for human evolution, its role in the emergence of early culture remains unclear. Most previous research on this question exclusively relied on direct morphological comparisons between early hominin and modern human skeletal elements, assuming that the degree of a species' dexterity depends on its similarity with the modern human form. Here, we develop a new approach to investigate the efficiency of thumb opposition, a fundamental component of manual dexterity, in several species of fossil hominins. Our work for the first time takes into account soft tissue as well as bone anatomy, integrating virtual modeling of musculus opponens pollicis and its interaction with three-dimensional bone shape form. Results indicate that a fundamental aspect of efficient thumb opposition appeared approximately 2 million years ago, possibly associated with our own genus Homo, and did not characterize Australopithecus, the earliest proposed stone tool maker. This was true also of the late Australopithecus species, Australopithecus sediba, previously found to exhibit human-like thumb proportions. In contrast, later Homo species, including the small-brained Homo naledi, show high levels of thumb opposition dexterity, highlighting the increasing importance of cultural processes and manual dexterity in later human evolution.

Anatomical variations of the extensor tendons of the fetal thumb.

PURPOSE: The extensor pollicis longus (EPL) and brevis (EPB) and abductor pollicis longus (APL) are muscles located in the posterior compartment of the forearm. These muscles allow the thumb to move independently from the other four fingers by attaching to the thumb separately. This study's goal was to investigate the tendon variations and insertions of these muscles. METHODS: Our study was conducted on 43 fetal cadavers (86 upper extremities) aged between 17 and 40 weeks of gestation. This study investigated the tendon numbers and insertions of the EPL, EPB, and APL. RESULTS: The tendon numbers of the EPL and EPB were observed to range between 1 and 2, and the tendon numbers of the APL ranged between 1 and 5. The EPL was found to insert into the distal phalanx via the dorsal aponeurosis in all extremities. It was observed that the EPB tendons inserted into the proximal phalanx, distal phalanx, and dorsal aponeurosis. It was determined that the APL tendons inserted into the basis of the first metacarpal, abductor pollicis brevis, opponens pollicis, and trapezium bone. CONCLUSION: Knowing the tendon variations and insertions of the EPL, EPB, and APL muscles during the fetal period will be useful in planning treatments to correct the congenital thumb anomalies and the loss of function after injury.

The implications of thumb movements for Neanderthal and modern human manipulation.

Much research has debated the technological abilities of Neanderthals relative to those of early modern humans, with a particular focus on subtle differences in thumb morphology and how this may reflect differences in manipulative behaviors in these two species. Here, we provide a novel perspective on this debate through a 3D geometric morphometric analysis of shape covariation between the trapezial and proximal first metacarpal articular surfaces of Neanderthals (Homo neanderthalensis) in comparison to early and recent humans (Homo sapiens). Results show a distinct pattern of shape covariation in Neanderthals, consistent with more extended and adducted thumb postures that may reflect habitual use of grips commonly used for hafted tools. Both Neanderthals and recent humans demonstrate high intraspecific variation in shape covariation. This intraspecific variation is likely the result of genetic and/or developmental differences, but may also reflect, in part, differing functional requirements imposed by the use of varied tool-kits. These results underscore the importance of holistic joint shape analysis for understanding the functional capabilities and evolution of the modern human thumb.

Thumb Metacarpophalangeal Ulnar and Radial Collateral Ligament Injuries.

Thumb metacarpophalangeal collateral ligament injuries are common in athletes and occur via forced abduction or hyperextension. Management primarily depends on the grade of ligamentous injury and the presence of a Stener lesion or large avulsion fracture. Surgeons should consider the athlete's position, hand dominance, duration of season remaining, and goals. Shared decision making regarding timing of surgery is imperative. Acutely, primary ligamentous repair with or without augmentation is achievable. Chronic collateral ligament injuries are effectively treated with ligament reconstruction. Numerous surgical techniques have been described without 1 showing superiority. Postoperative rehabilitation protocols vary based on repair quality and sports-specific considerations.

Anatomical relationship between the sagittal band and extensor tendon of the thumb: a focus on variations of the extensor pollicis brevis tendon insertion.

The sagittal band of the finger is an aponeurosis-like structure surrounding the metacarpophalangeal joint. Sagittal band rupture causes extensor tendon dislocation from the dorsal side of the metacarpophalangeal joint. The thumb has two extensor tendons: extensor pollicis longus and extensor pollicis brevis tendons. Multiple studies have reported variations of extensor pollicis brevis tendon insertion. However, it remains unclear how the thumb sagittal band envelopes the extensor pollicis longus and extensor pollicis brevis tendons. This study investigated the anatomical relationship between the sagittal band and the two extensor tendons of the thumb. One hundred hands (47 right, 53 left) from 54 cadavers were examined to assess the detailed structure of the thumb sagittal band and extensor pollicis longus and extensor pollicis brevis tendons. We found that the thumb sagittal band enveloped both the tendons either separately (type I) or collectively (type II). Thirty-four cases (34.0%) were type I and 66 cases (66.0%) were type II. The extensor pollicis longus and extensor pollicis brevis tendons enveloped in the type I thumb sagittal band were inserted on different sites, respectively, whereas those tendons enveloped in the type II thumb sagittal band were inserted on the same sites. This study demonstrated that differences in the type of thumb sagittal band are closely associated with variations in extensor pollicis brevis tendon insertion. We predicted that these differences contribute to the sliding distance between the extensor pollicis brevis and extensor pollicis longus tendons and affect the pathophysiology of extensor tendon dislocation.

Biometry of thenar muscle origins on the flexor retinaculum.

The transverse carpal ligament (TCL), the main part of the flexor retinaculum, serves as an anchor for the thenar muscles: abductor pollicis brevis (APB), superficial head of the flexor pollicis brevis (sFPB), and opponens pollicis (OPP). Biomechanically, the thenar muscles rely on their TCL anchoring to transmit muscle contractions distally for thumb force and motion production, and reciprocally, muscle contraction interacts with the TCL at the proximal end through the origins. However, scarce knowledge exists regarding the distribution pattern of the thenar muscle origins. The purpose of this study was to understand the anatomical interface between the thenar muscles and TCL by examining the origin distributions of the individual muscles. Ten cadaveric specimens were dissected for digitization of the muscle origins and TCL volar surface. Digitized data were used for mesh reconstruction and calculation of surface areas and centroids. The origin areas for APB, sFPB, and OPP were 105.8 ± 30.3, 64.6 ± 15.2, and 245.9 ± 70.7 mm2 , respectively. The surface area of the TCL was 386.2 ± 86.9 mm2 . The origin areas of APB and OPP on the TCL were comparable, 18.4 ± 4.8% and 17.3 ± 9.6% of the TCL area, respectively. The origin locations for APB, sFPB, and OPP were in proximal-radial quadrant of the TCL, on distal aponeurosis outside the TCL, and around the ridge of trapezium, respectively. The knowledge of the anatomical interface provides a foundation for the understanding of biomechanical interactions between the muscles and ligaments and pathomechanical implications.

A primate with a Panda's thumb: The anatomy of the pseudothumb of Daubentonia madagascariensis.

OBJECTIVES: Accessory digits have evolved independently within several mammalian lineages. Most notable among these is the pseudothumb of the giant panda, which has long been considered one of the most extraordinary examples of contingent evolution. To date, no primate has been documented to possess such an adaptation. Here, we investigate the presence of this structure within the aye-aye (Daubentonia madagascariensis), a species renowned for several other specialized morphological adaptations in the hand, including a morphologically unique third digit. MATERIALS AND METHODS: We combine physical dissection techniques with digital imaging processes across a sample of seven individuals (six adults and one immature individual) to describe and visualize the anatomy of the wrist and hand within the aye-aye. RESULTS: A distinct pseudothumb, which consists of both a bony component (an expanded radial sesamoid) and a dense cartilaginous extension (the "prepollex") was observed in all specimens. We demonstrate that this pseudodigit receives muscular attachments from three muscles, which collectively have the potential to enable abduction, adduction, and opposition. Finally, we demonstrate that the pseudothumb possesses its own distinct pad within the palm, complete with independent dermatoglyphs. DISCUSSION: Pseudothumbs have been suggested to improve palmar dexterity in taxa with overly -generalized first digits (e.g., pandas) and to widen the hand for digging (e.g., some fossorial moles), but the aye-aye's pseudothumb represents what we believe is a heretofore unrecognized third functional role: its accessory digit compensates for overspecialization of its fingers for non-gripping functions (in this case, the aye-aye's unique "tap foraging" practices).

Trabecular variation in the first metacarpal and manipulation in hominids.

OBJECTIVES: The dexterity of fossil hominins is often inferred by assessing the comparative manual anatomy and behaviors of extant hominids, with a focus on the thumb. The aim of this study is to test whether trabecular structure is consistent with what is currently known about habitually loaded thumb postures across extant hominids. MATERIALS AND METHODS: We analyze first metacarpal (Mc1) subarticular trabecular architecture in humans (Homo sapiens, n = 10), bonobos (Pan paniscus, n = 10), chimpanzees (Pan troglodytes, n = 11), as well as for the first time, gorillas (Gorilla gorilla gorilla, n = 10) and orangutans (Pongo sp., n = 1, Pongo abelii, n = 3 and Pongo pygmaeus, n = 5). Using a combination of subarticular and whole-epiphysis approaches, we test for significant differences in relative trabecular bone volume (RBV/TV) and degree of anisotropy (DA) between species. RESULTS: Humans have significantly greater RBV/TV on the radiopalmar aspects of both the proximal and distal Mc1 subarticular surfaces and greater DA throughout the Mc1 head than other hominids. Nonhuman great apes have greatest RBV/TV on the ulnar aspect of the Mc1 head and the palmar aspect of the Mc1 base. Gorillas possessed significantly lower DA in the Mc1 head than any other taxon in our sample. DISCUSSION: These results are consistent with abduction of the thumb during forceful "pad-to-pad" precision grips in humans and, in nonhuman great apes, a habitually adducted thumb that is typically used in precision and power grips. This comparative context will help infer habitual manipulative and locomotor grips in fossil hominins.

Anatomic Considerations and Reconstruction of the Thumb Flexor Pulley System.

Disruption to the flexor pulley system of the thumb is an infrequent but devastating injury that can lead to significant compromise in both strength and function. Acute rupture leads to pain, weakness, reduced range of motion (ROM), and potential bowstringing of the flexor tendons. Conservative treatment with a pulley ring should be considered in all patients. However, failure of conservative treatment and bowstringing of the thumb are indications for operative intervention. Reconstruction of the oblique pulley system can be performed either in situ or using a free palmaris longus graft. Care should be taken to identify the neurovascular bundles to avoid compression during the reconstruction. Conscious sedation protocols augmented by ultrasound-guided sheath blocks allow the patient to actively and strongly contract the flexor pollicis longus tendon intraoperatively to appropriately tension the construct for optimal results. Rehabilitation should be performed in a stepwise manner beginning with early passive ROM, active ROM, and finally strengthening at around 8 weeks postoperative.

Investigation into reducing anthropomorphic hand degrees of freedom while maintaining human hand grasping functions.

Underactuation is widely used when designing anthropomorphic hand, which involves fewer degrees of actuation than degrees of freedom. However, the similarities between coordinated joint movements and movement variances across different grasp tasks have not been suitably examined. This work suggests a systematic approach to identify the actuation strategy with the minimum number for degrees of actuation for anthropomorphic hands. This work evaluates the correlations of coordinated movements in human hands during 23 grasp tasks to suggest actuation strategies for anthropomorphic hands. Our approach proceeds as follows: first, we find the best description for each coordinated joint movement in each grasp task by using multiple linear regression; then, based on the similarities between joint movements, we classify hand joints into groups by using hierarchical cluster analysis; finally, we reduce the dimensionality of each group of joints by employing principal components analysis. The metacarpophalangeal joints and proximal interphalangeal joints have the best and most consistent description of their coordinated movements across all grasp tasks. The thumb metacarpophalangeal and abduction/adduction between the ring and little fingers exhibit relatively high independence of movement. The distal interphalangeal joints show a high degree of independent movement but not for all grasp tasks. Analysis of the results indicates that for the distal interphalangeal joints, their coordinated movements are better explained when all fingers wrap around the object. Our approach fails to provide more information for the other joints. We conclude that 19 degrees of freedom for an anthropomorphic hand can be reduced to 13 degrees of actuation distributed between six groups of joints. The number of degrees of actuation can be further reduced to six by relaxing the dimensionality reduction criteria. Other resolutions are as follows: (a) the joint coupling scheme should be joint-based rather than finger-based and (b) hand designs may need to include finger abduction/adduction movements.