Secondary centers of ossification of the human toes: exceptional polymorphism and evolutionary perspectives

Technical keys in maximizing finger proximal interphalangeal joint motion after vascularized toe joint transfers

Vascularized toe joint transfers to the fingers have been performed for more than four decades, but their outcomes are not comparable with implant arthroplasty. Limited range of motion and extensor deficits of about 30° remain major problems with the constructed joints. We observed that the central extensor tendon of the toe is often attenuated proximally in its course on the dorsum of the proximal interphalangeal joint. A tight repair of the toe extensors to finger extensors limits joint motion. We reviewed our surgical techniques with this consideration. Thirty-eight fingers that we followed for 6 to 123 months had active range of motion of the reconstructed proximal interphalangeal joint in the finger of 58° (range 17°-76°) with an extensor deficit of 18° (range 0°-30°). We consider that the extensor mechanism and central slip insertion to the middle phalanx must be reconstructed meticulously to improve joint motion and decrease extension lag, and design of a lateral skin flap paddle to better cover vessels and allow extensor repairs.

Prevalence of toe symphalangism in Hong Kong Chinese population

Objective:

To explore the prevalence and variations of toe symphalangism in the Hong Kong Chinese population.

Methods:

A retrospective review of foot radiographs taken in Chinese adult patients admitted to United Christian Hospital from 1 January, 2016 to 31 December, 2016. Exclusion criteria include (1) previous toe amputation, (2) skeletal immaturity, (3) severe deformity, and (4) repeated attendance. The frequencies were compared by χ 2 test.

Result:

A total of 1364 foot radiographs were reviewed. Six-hundred sixty radiographs were excluded. A total of 704 radiographs were included in this study. There were total 849 feet reviewed (left: 290, right: 269, bilateral: 145). Their mean age (± standard deviation) was 59.5 ± 14.2 years. The prevalence of 2nd, 3rd, 4th, and 5th toe symphalangism was 0.2%, 0.8%, 9.9%, and 76.7%, respectively. The prevalence resembles Asian population. There was no significant difference in the prevalence associated with the following factors: (1) gender and (2) left versus right foot. There was no 4th toe symphalangism without 5th toe involvement. In the 145 bilateral feet radiographs, asymmetrical distribution of toe symphalangism was found in 8.2%. Second toe symphalangism is rare (0.24%).

Conclusion:

This is the first study in Hong Kong to report prevalence of toe symphalangism in Chinese population. There is a high prevalence rate of 5th toe symphalangism in the Hong Kong Chinese Population. This implies less flexible lesser toes in the Chinese population with higher risks of development of deformities. The clinical implication of such findings needs further research.

The prevalence and ossification pattern of the biphalangeal and triphalangeal lateral toes

Purpose

Biphalangealism of the toes is an exclusively human phenomenon. The aim of this study was to evaluate the development of the lateral toes in childhood by following the ossification pattern of the phalanges.

Methods

Foot radiographs of 913 adults have been evaluated for biphalangealism of 3rd to 5th toe. The pediatric group, aged 6–15 years of age, was assessed for the number of ossification centers in the foot.

Results

In adults, the mean prevalence of biphalangealism in the 5th toe was 41.39%, in the 4th toe was 2.15%, and in the 3rd toe was 0.48%. In children, 45% feet had four ossification centers in the 5th toe. The epiphysis center of the middle and distal phalanx was missing. In the 4th toe, four centers were present in of 2.47% of cases. Those values are similar to the prevalence of the biphalangeal toes in adult population. The remaining toes had 5 or 6 ossification centers. In the 5-center toe, the epiphysis of the middle phalanx was missing.

Conclusion

A missing distal phalanx epiphyseal ossification center is considered indicative of a biphalangeal toe, and the toes with 5 or 6 ossification centers are indicative of triphalangeal toes. The reason for such evolution of the lateral toes is still debated, but the differences in anatomy most likely have no impact on foot function.

Non-metric variation of the middle phalanges of the human toes (II-V): long/short types and their evolutionary significance

The human lateral toes are characterised by extreme reduction compared with other primates, and in particular other hominoids. Some phalangeal non-metric variants have been well identified in humans, in particular: triphalangeal/biphalangeal patterns, and the presence/absence of phalangeal secondary centres of ossification. The purpose of the present study was to describe and analyse an original non-metric variation of the middle phalanges of the lateral toes. The material consisted of 2541 foot radiographs that came from 2541 different European adult individuals. Two morphological types of the middle phalanx were defined as a simple binary trait: long type (L) and short type (S). In feet with a triphalangeal pattern in all lateral toes (1413 cases), a mediolateral increasing gradient was observed in the occurrence of type S: 8.1% in II; 30.7% in III; 68.4% in IV; and 99.1% in V. In feet with a biphalangeal pattern in one or more lateral toes (III-V; 1128 cases), type S occurred more frequently than in triphalangeal feet. Of the 30 theoretical arrangements of the L/S types in the lateral toes (II-V) in a complete foot, only 13 patterns were observed. Seven patterns represented 95.6% of the population: LLSS (20.9%), LLLS (17.1%), LSS (15.9%), SSS (14.5%), LSSS (12.7%), LLS (10.1%) and SSSS (4.4%). Type L can be interpreted as the primitive pattern (plesiomorphy), and type S as a derived pattern (apomorphy) that seems specific to the human species (i.e. autapomorphy). Within the specific evolution of the human foot in relation to the acquisition of constant erect posture and bipedalism, the short type of the middle phalanges can reasonably be considered as directly linked to the reduction of the lateral toes.

Normal genetic variation of the human foot: Part 2: Population variance, epigenetic mechanisms, and developmental constraint in function

Congenital deformities of the foot have been reported to correlate with regulatory epigenetic mechanisms that are also responsible for the timing and sequencing of developmental growth of the lower limb. Developmental variance of normal morphologic features has also been shown to vary between populations despite the retention of human foot characteristics. The molecular evidence for genetically controlled expressions of common evolved physical features is highly suggestive of regulatory control mechanisms that act together with developmental constraints to homogenize the retained functional characteristics of the foot. Genetic variance in morphologic features and functional plasticity when linked to morphometric change during gait may prove influential in clarifying kinematic and kinetic relationships.