Biomechanics of phalangeal curvature

Phalangeal curvature has been widely cited in primate functional morphology and is one of the key traits in the ongoing debate about whether the locomotion of early hominins included a significant degree of arboreality. This study examines the biomechanics of phalangeal curvature using data on hand posture, muscle recruitment, and anatomical moment arms to develop a finite element (FE) model of a siamang manual proximal phalanx during suspensory grasping. Strain patterns from experiments on intact cadaver forelimbs validated the model. The strain distribution in the curved siamang phalanx FE model was compared to that in a mathematically straight rendition in order to test the hypotheses that curvature: 1) reduces strain and 2) results in lower bending strains but relatively higher compression. In the suspensory posture, joint reaction forces load the articular ends of the phalanx in compression and dorsally, while muscle forces acting through the flexor sheath pull the mid-shaft palmarly. These forces compress the phalanx dorsally and tense it palmarly, effectively bending it 'open.' Strains in the curved model were roughly half that of the straight model despite equivalent lengths, areas, mechanical properties, and loading conditions in the two models. The curved model also experienced a higher ratio of compressive to tensile strains. Curvature reduces strains during grasping hand postures because the curved bone is more closely aligned with the joint reaction forces. Therefore, phalangeal curvature reduces the strains associated with arboreal, and especially suspensory, activity involving flexed digits. These results offer a biomechanical explanation for the observed association between phalangeal curvature and arboreality.     

Middle phalangeal hair in two Mediterranean Spanish populations

Data on middle phalangeal hair (MPH) among unrelated autochtonous individuals from Delta de l'Ebre and Murcia (Spain) show remarkable sexual differences in the Murcia population. The Delta de l'Ebre sample seems to have more pilosity than the Murcia sample. In the Spanish and Mediterranean variation range, Delta de l'Ebre is located between the populations with high pilosity while Murcia females show an extremely low value for this trait.     

Principal component analysis of the elongation of metacarpal and phalangeal bones

A hypothesis that the first principal component computed from the covariance matrix of logarithms reflected the specific growth rates of corresponding bones was taken to analyze the growth pattern of the tubular bones of the hand. The total length of 19 tubular bones of the right hand was measured on standardized radiographs of Japanese children (33 boys, 33 girls). Metacarpals in boys and bones of the fifth digit in girls showed higher growth coefficients. The second, third and fourth proximal, and the third and fourth middle phalanges showed lower coefficients for both sexes. These observations suggest the signs of proximal row dominance in boys and of fifth ray dominance in girls in the elongation of the hand bones. A marked sex difference was found in the fifth middle phalanx. In girls the growth coefficients of this bone was much larger than any other bones, but was moderate in boys.     

Middle phalangeal hair distribution in a Sardinian population sample

Data relating to middle phalangeal hair (MPH) among unrelated individuals of both sexes born and living in Sardinia are presented. The occurrence of MPH is generally manifested on the 3-4-5 digits of both hands in the two sexes. The observed sex differences are statistically non-significant. The Sardinian sample seems to have a marked decrease in the frequency of individuals with MPH with regard to Mediterranean and other European populations.     

The frequency of middle phalangeal hair in Saudi Arabia.

Middle phalangeal hair was found to be present in 71% if Saudi Arabian males. For those exhibiting this trait, the frequency of combinations of digits with hair was similar to the frequency in other populations.     

Contributions to variance in phalangeal growth: estimates from twins

Lengths of the second metacarpal and fourth middle phalanx of a sample of 99 sets of radiographs of twins (45 MZ sets and 54 like-sex DZ sets) are subjected to variance analysis. The purpose is to examine incremental growth status between the appearance of these bones and the fusion of their epiphyses. Grouped data show higher F-ratios and H scores for males in MC2 length and for females in MP4 length. When the data are sub-divided by age (10 and under, older than 10), the later ages show uniformly higher F and H scores than the younger, and males higher than females for all measurements. It is suggested that the influence of the environment is relatively less in later ages, and that X-chromosomal influence plays a part in determining tubular bone growth in the hand-wrist.     

Successful delayed venous drainage in 16 consecutive distal phalangeal replantations

The authors describe, in the first report of this type of replantation surgery, a high success rate using delayed venous anastomosis in 16 consecutive distal phalangeal replantations under digital block. Among these replantations, seven fingers (43.8 percent) showed postoperative venous congestion and five fingers were reoperated on with delayed venous drainage under digital block. All the reoperated fingers were successfully drained by additional single or double venous drainage with a vein graft. As a result, 13 fingers survived (81.3 percent success rate). All operations were performed under a digital block.     

Human chondrocyte cell lines from articular cartilage of metatarsal phalangeal joints

Chondrocytes can be isolated from human adult cartilage from metatarsal phalangeal joints. After enzymatic digestion to isolate viable cells, confluent monolayers were obtained 2-4 weeks after the start of cell division. Chondrocytes cultures, initiated and maintained in HAM's F12 with bovine fetal serum without the addition of other growth factors, produced in vitro a matrix rich in collagen and proteoglycans. Although several studies reported phenotypic instability, our results showed that the cell retain for more than 5 months in culture their differentiated characteristics, including the ability to produce cartilage-specific molecules. Chondrocyte cell lines should be useful in studying the functions of these cells from normal and abnormal tissue and for pharmacological studies in vitro.     

A note on the distribution of middle phalangeal hair among Tibetans

In the present paper the frequencies of individuals without middle phalangeal hair was found as 55.75% in the Tibetan males and 68.61% in females. Sex differences were noticed in the present sample. Populations of Mongoloid affinity seems to have a marked increase in the frequency of individuals without phalangeal hair and the present Tibetan sample reflects this tendency.     

Distribution of middle phalangeal hair in a population of the south of Spain

In this paper the presence or absence of middle phalangeal hair has been studied in an Andalusian population sample. This sample consists of 245 students from Granada (128 males and 117 females). The frequencies of middle phalangeal hair are similar to those obtained in the Basque population, which show the lowest frequencies so far reported. In our sample no significant sexual or bimanual differences are seen. The most affected finger is the ring-finger, the least affected one is the forefinger. The phenotypes were classified according to the nomenclatures given by Valls and Bernstein.     

Identical phalangeal defects induced by phenytoin and nifedipine suggest fetal hypoxia and vascular disruption behind phenytoin teratogenicity.

In previous experimental studies in rabbits, we have shown that vasodilating drugs (including nifedipine) cause distal digital defects. These defects were preceded by edema, hemorrhage, and finally necrosis of the developed cartilage in the phalanges. The underlying mechanism is most likely a fetal hypoxic response, secondary to maternal hypotension and decreased uteroplacental blood flow. Since phenytoin is known to cause distal digital defects both in man and rabbits, we decided to compare the defects provoked by oral administration of phenytoin (100 mg/kg) versus nifedipine (8.3 mg/kg) to New Zealand White rabbits on days 6-18 of gestation. In order to investigate phase-specificity, phenytoin (150 mg/kg) was given on days 14-17. The result of single dose administration on day 16 of phenytoin (300 mg/kg) versus nifedipine (33.2 mg/kg) was also studied. In this latter experiment maternal heart rate was measured up to 21 hours after phenytoin administration. Phenytoin induced digital defects identical with those produced by nifedipine and caused marked maternal cardiodepression. The defects consisted of a reduction, absence, or abnormal structure of the distal phalanges. The distal phalanx of the fourth digit on the hindpaw was the first to be affected, with inclusion of other phalanges, both on the hind- and forepaws, with increasing dose. The sensitive period for induction and histological appearance of these defects was identical for phenytoin and nifedipine. These results suggest that vascular disruption due to a fetal hypoxic response lies behind phenytoin teratogenicity, as has been shown for vasodilators. A cardiodepressive action on the maternal and fetal hearts, possibly in combination with decreased uteroplacental blood flow, is discussed as a probable factor behind phenytoin teratogenicity.     

Evolutionary and developmental aspects of phalangeal formula variation in pig-nose and soft-shelled turtles (Carettochelyidae and Trionychidae)

In order to examine the evolution of the phalangeal formula in a diverse clade of turtles, including hyperphalangy as a rare condition in this group, we studied 210 specimens representing all extant genera of Trionychidae and their sister taxon, Carettochelyidae. Both groups consist of highly aquatic species with elongated autopods that are either paddle-like (Trionychidae) or transformed to flippers (Carettochelyidae). Phalangeal formulae were obtained mostly by radiographs of alcohol-preserved or dry specimens, as well as by direct counts from skeletons. All trionychids and Carettochelys are pentadactylous, but their phalangeal formulae differ. Carettochelys exhibits the turtle-plesiomorphic state (manus and pes: 2-3-3-3-3), with no variation in adults. Trionychids exhibit intraspecific variation, ranging from 2-3-3-3-2 to 2-3-3-6-5 for the manus, and from 2-3-3-3-2 to 2-3-3-5-3 for the pes. The extant Carettochelys as well as the Middle Eocene Allaeochelys crassesculpta are characterized by an elongation of phalanges, whereas trionychids consistently have shorter phalanges. All trionychid genera exhibit some degree of hyperphalangy in digits IV and V, in both the manus and pes. Phalanges of the clawed digits I–III are very robust compared to phalanges of the non-clawed digits IV and V. The latter contribute significantly to the enlargement of the paddle by their additional phalanges. We hypothesize that this phalangeal pattern is coupled with prolongation of growth processes in the non-clawed digits. The differences in autopod morphology between carettochelyids and trionychids reflect different locomotor patterns related to different natural histories (elongated flippers for high-speed escape in the mainly herbivorous Carettochelys; broad paddles for rapid turns during hunting in the mainly carnivorous trionychids). The autopod of Pelodiscus sinensis is proposed as an experimental model to examine the developmental basis of adult autopod variation.     

A resampling approach and implications for estimating the phalangeal index from unassociated hand bones in fossil primates

Primate fossil assemblages often have metacarpals and phalanges from which functional/behavioral interpretations may be inferred. For example, intrinsic hand proportions can indicate hand function and substrate use. But, estimates of intrinsic hand proportions from unassociated hand elements can be imperfect due to digit misattribution. Although isolated metacarpals can be identified to a specific digit, phalanges are difficult to assign to a specific ray. We used a resampling approach to evaluate how estimates of intrinsic hand proportions are affected by such uncertainty. First, the phalangeal index—intermediate phalanx length plus proximal phalanx length divided by metacarpal length—for the third digit was calculated for associated specimens of terrestrial, semiterrestrial, and arboreal taxa. We then used resampling procedures to generate distributions of “composite digits” based on resampled ratios in which phalanges from the second, fourth, and fifth rays, and from different individuals, were chosen randomly. Results confirm that the phalangeal index for associated third digits significantly discriminates groups. We also found that resampled ratios had significantly lower means, indicating that using composite digits is prone to systematic underestimation. Resampled ratios also generated distributions with greater variance around the means that obscured distinctions between groups, although significant differences between the most arboreal and terrestrial taxa are maintained. We conclude that using unassociated phalanges to calculate a phalangeal index is prone to sampling bias. Nevertheless, a resampling approach has the potential to inform estimates of hand proportions for fossil taxa, provided that the comparative sample is constrained to mimic the fossil composition. Am J Phys Anthropol 151:280–289, 2013. © 2013 Wiley Periodicals, Inc.