Surgical anatomy of the nail unit

Anatomic and Histological Features of the Extensor Digitorum Longus Tendon Insertion in the Proximal Nail Matrix of the Second Toe

Background: Anatomic and histological landmarks of the extensor digitorum longus (EDL) tendon insertion in the proximal nail matrix may be key aspects during surgery exposure in order to avoid permanent nail deformities. Objective: The main purpose was to determine the anatomic and histological features of the EDL’s insertion to the proximal nail matrix of the second toe. Methods: A sample of fifty second toes from fresh-frozen human cadavers was included in this study. Using X25-magnification, the proximal nail matrix limits and distal EDL tendon bony insertions were anatomically and histologically detailed. Results: The second toes’ EDLs were deeply located with respect to the nail matrix and extended superficially and dorsally to the distal phalanx in all human cadavers. The second toe distal nail matrix was not attached to the dorsal part of the distal phalanx base periosteum. Conclusions: The EDL is located plantar and directly underneath to the proximal nail matrix as well as dorsally to the bone. The proximal edge of the nail matrix and bed in human cadaver second toes are placed dorsally and overlap the distal EDL insertion. These anatomic and histological features should be used as reference landmarks during digital surgery and invasive procedures.

Anatomic Association of the Proximal Fingernail Matrix to the Extensor Pollicis Longus Tendon: A Morphological and Histological Study

BACKGROUND

Extensor tendon disorders may cause severe functional impairments, and there is a lack of knowledge about their anatomic associations with the proximal fingernail matrix.

OBJECTIVE

To delineate the association between the distal extensor pollicis longus tendon (EPLT) insertion and the limit of the fingernail matrix in the thumb.

METHODS

The limit of the fingernail matrix and the distal bony insertion of the EPLT were identified in five thumbs from fresh-frozen human cadavers. An additional five thumbs were fixed and the longitudinal thumb sections were histologically analyzed.

RESULTS

The terminal limit of the matrix and fingernail was dorsal and overlapped to the EPL tendon, which was located between the fingernail matrix and the phalanx, and extended dorsally to the distal section of the terminal phalanx in all ten thumb bodies.

CONCLUSION

The fingernail matrix is not directly inserted into the periosteum of the dorsal section of the base to the distal phalanx, because this anatomic relationship is separated by the deep fibers of the EPLT.

Nail unit ultrasound: a complete guide of the nail diseases

INTRODUCTION

The nails have a functional and esthetic importance for patients. Almost always, the nail disorders are diagnosed on the basis of clinical findings, but imaging methods may be required for a better assessment. These imaging methods, such as ultrasound and magnetic resonance, may help to establish an accurate diagnosis. Magnetic resonance imaging is not widely available and sometimes may be very expensive; that is why, ultrasound is an excellent imaging modality. Our objective is to expose the nail unit anatomy, the nail unit anatomy in ultrasound, and some of the frequent pathologies found in our daily practice.

METHODS

A review of the literature was done to review the anatomy, technical aspects, and different findings in normal and abnormal nail unit ultrasound.

RESULTS

Ultrasound offers an appropriate alternative for the evaluation of the nail unit, allows a real-time evaluation of each one of the components of the nail unit with an optimal visualization of these structures, and allows the evaluation of the thickness of the components, the vascularity, and blood flow by Doppler application. In addition, the nail unit disorder, such as infectious diseases, inflammatory and rheumatologic conditions, nail tumors, among others, may be assessed, not only in the diagnosis but also in the follow-up. Pre-surgical evaluation, surgical follow-up, and some procedures, such as biopsies, may be done by this technique.

CONCLUSIONS

Ultrasound is an excellent technique for evaluation of normal anatomy, diagnosis, and follow-up of patients with nail unit diseases. This is an alternative for other imaging methods and may be used for an accurate diagnosis approach.

Current Topics in Nail Surgery

Background:

Nail surgery can be performed in an office-based dermatology practice with a limited amount of specialized equipment and training. Several excellent reviews have been published in recent years that detail the techniques of nail surgery for both the novice and the experienced practitioner.

Objective:

In this article recent developments in nail surgery are discussed. Topics that are treated include the general principles of nail surgery, including epidemiologic issues, studies of nail anatomy, instrumentation, and anesthesia. The reconstruction of injuries and congenital defects involving the nail is explained, and the role of the hand surgeon clarified. Appropriate removal of tumours and cysts is considered, with special attention to the management of malignant lesions. The controversy regarding more or less conservative management of melanonychia striata is addressed, and the need for early diagnosis of subungual melanoma is emphasized. Other topics are surgical management of ingrown nails and onychomycosis. Newer areas of nail surgery, such as laser surgery of the nail, psycho-dermatology of the nail, and the role of primary care physicians in simple nail surgery are also examined.

Anatomic relationship of the proximal nail matrix to the extensor hallucis longus tendon insertion

BACKGROUND

The purpose of this study was to delineate the relationship of the terminal extensor hallucis longus tendon insertion to the proximal limit of the nail matrix of the great toe.

MATERIAL AND METHODS

Fifty fresh-frozen human cadaver great toes with no evidence of trauma (average age, 62.5 years; 29 males and 21 females) were used for this study. Under 25X magnification, the proximal limit of the nail matrix and the terminal bony insertion of the extensor hallucis longus tendons were identified. The distance from the terminal tendon insertion to the nail matrix was ascertained using precision calipers, an optical microscope, and autocad(®) software for windows. Twenty-five great toes were placed in a neutral formalin solution and further analysed by histological longitudinal-sections. The specimens were stained with haematoxylin and eosin and examined microscopically to determine the presence of the extensor hallucis longus tendon along the dorsal aspect of the distal phalanx of each great toe.

RESULTS

The main result we found in great toes was that the extensor tendon is between the matrix and the phalanx and extends dorsally to the distal aspect of the distal phalanx in all, 100%, specimens. The nail matrix of the great toe is not attached to the periosteum of the dorsal aspect of the base of the distal phalanx as is the case for fingers, because the extensor hallucis tendon is plantar or directly underneath the nail matrix and the tendon is dorsal to the bone.

CONCLUSIONS

We have found that the extensor tendon is between the matrix and the phalanx and extends dorsally to the distal aspect of the distal phalanx. The nail matrix of the great toe is not attached to the periosteum of the dorsal aspect of the base of distal phalanx as is the case in fingers, because the extensor hallucis tendon is plantar or directly underneath the nail matrix and the tendon is dorsal to the bone. Our anatomic study demonstrates that the proximal limit of the matrix and nail bed of the human great toe are dorsal and overlapping the terminal extensor hallucis longus tendon until its distal bony insertion in all specimens.

The effect of humidity on the fracture properties of human fingernails

Fingernails are a characteristic anatomical feature of primates and their function is dictated by the environment in which they are utilised. The present study examined the mechanical properties of human fingernails as a function of relative humidity (RH) and the subsequent moisture content of the nail material. Nail clippings were stored at a range of RH values and then weighed in order to determine their moisture content. There was a non-linear relationship between the moisture content of nails and the RH of their local environment. The in vivo moisture content of nails, measured from 55%to 80% RH, was between 14% and 30%, similar to other keratinous materials such as claws, hooves and feathers. Cutting tests on the nail samples showed that the work of fracture was between 11 and 22 kJ m–2, rising to a peak at 55% RH and falling at higher and lower humidities. At all RH values there was anisotropy within the nail between the proximal and lateral directions, the work of fracture being greater proximally. This anisotropy was greatest at 55% RH, at which point the proximal work of fracture was double the lateral value. These results suggest that the mechanical behaviour of human fingernails is optimised at in vivo conditions; they resist tearing most strongly under these conditions and particularly resist tearing into the nail bed. At more extreme humidity levels the fracture properties of the nail deteriorate; they are brittle when fully dry and fracture and split when wet.

Strain in the nail at fingertip compression

PURPOSE

Distribution of nail strain due to compressive force in the finger pulp was investigated.

METHODS

Nail strain of the right index finger of 10 healthy men was measured using three strain gauges with two axes. Each nail strain was measured along the longitudinal and the transverse axis using sensor interface. Three CCD cameras recorded the compressive force and the fingertip deformation. Each subject pressed the right index finger with 30 degrees, 45 degrees and 60 degrees in the contact angle, with the compressive force increased from 0 to 14 N.

RESULTS

When the contact angle was 30 degrees, the strain along the transverse axis increased according to the compressive force increased. The proximal-radial-transverse strain at compressive force of 13 N was significantly (P<0.01) larger than the proximal-ulnar-transverse strain. At the same compressive force, the distal-central-transverse strain was significantly (P<0.05) larger than the proximal-ulnar-transverse strain. The proximal-radial-transverse strain was significantly (P<0.01) larger than the proximal-radial-longitudinal strain. In the contact angle of 45 degrees and 60 degrees, same results were gained.

CONCLUSION

Nail strain due to compressive force in the finger pulp was different between the rectangular axes, between the distal and the proximal parts of the nail, and between the radial and the ulnar sides.

The fracture properties and mechanical design of human fingernails

Fingernails are a characteristic feature of primates, and are composed of three layers of the fibrous composite keratin. This study examined the structure and fracture properties of human fingernails to determine how they resist bending forces while preventing fractures running longitudinally into the nail bed. Nail clippings were first torn manually to examine the preferred crack direction. Next, scissor cutting tests were carried out to compare the fracture toughness of central and outer areas in both the transverse and longitudinal direction. The fracture toughness of each of the three isolated layers was also measured in this way to determine their relative contributions to the toughness. Finally, the structure was examined by carrying out scanning electron microscopy of free fracture surfaces and polarized light microscopy of nail sections. When nails were torn, cracks were always diverted transversely, parallel to the free edge of the nail. Cutting tests showed that this occurred because the energy to cut nails transversely, at approximately 3 kJ m(-2), was about half that needed (approx. 6 kJ m(-2)) to cut them longitudinally. This anisotropy was imparted by the thick intermediate layer, which comprises long, narrow cells that are oriented transversely; the energy needed to cut this layer transversely was only a quarter of that needed to cut it longitudinally. In contrast the tile-like cells in the thinner dorsal and ventral layers showed isotropic behaviour. They probably act to increase the nail's bending strength, and as they wrap around the edge of the nail, they also help prevent cracks from forming. These results cast light on the mechanical behaviour and care of fingernails.

Harnessing the osseointegration principle for anchorage of fingernail prostheses

On the basis of this preliminary report series of patients, it seems that the achievement of fixed anchorage for nail prostheses is feasible using the process of osseointegration, the use of standard dental implants, and abutment and maxillofacial rehabilitation laboratory to build the superstructure system. The osseointegrated procedure is relatively simple, cost-effective, and less time-consuming compared with other reconstruction techniques. Using local anesthesia and day-care facilities the operative time was only 35 minutes for the first stage and 15 minutes for the second stage. The attachment should be lifelong, as in the face. Loosening and infection are infrequent.

Hard palate mucosal grafts for defects of the nail bed

The authors present 2 children in whom a hard palate mucosal graft was used for a defect of the nail bed after resecting subungual exostosis. After the tumor was resected with the overriding nail bed, hard palate mucosa without periosteum was grafted to the nail bed defect. In both patients the graft took completely, and within 2 weeks after the operation the patients were able to enjoy activities of daily life, including athletic movement, without any symptoms. Nail growth was uneventful and was complete in 4 or 5 months after the operation without any complications. The authors think that a hard palate mucosal graft is a valid choice for a defect of the nail bed, and the mucosa does not need to be harvested with periosteum. The grafting of hard palate mucosa without periosteum to a defect of the nail bed contributes to a shorter healing time, resulting in a reduction in the period of restriction of movement in activities of daily life, and this is a great advantage in children.

Examination of the anatomic relationship of the proximal germinal nail matrix to the extensor tendon insertion

The purpose of this study was to delineate the relationship of the terminal extensor tendon insertion to the proximal limit of the germinal nail matrix. Sixteen fresh-frozen human cadaver fingers without any evidence of trauma (average age, 55 years; 3 males and 1 female) were used for this study. Under x25 magnification the proximal limit of the germinal nail matrix and the terminal bony insertion of the extensor tendon were identified. The distance from the terminal tendon insertion to the germinal nail matrix was ascertained using precision calipers. The average distance from the terminal extensor tendon insertion to the proximal edge of the germinal nail matrix was found to be 1.2 mm. We conclude that the proximal limit of the germinal matrix is extremely close to the terminal extensor tendon bony insertion. When the extensor tendon insertion is visualized during operative exposures of the dorsum of the distal phalanx, care should be taken to avoid damaging the germinal matrix. Conversely, when the nail bed is being completely excised, visualization of the insertion of the extensor tendon will indicate that further proximal dissection is not required.

Nail surgery

Nail deformities may present as wither medical or cosmetic problems, often requiring surgical intervention. These deformities have a number of etiologic factors including infections, inflammatory disease processes, congenital abnormalities, trauma, tumors, and systemic diseases. This article discusses several nail problems and surgery techniques.

The lunula: a magnetic resonance imagining approach to the subnail matrix area

High-resolution sagittal magnetic resonance images depict an oval area in the dermis beneath the nail matrix that gives a particular signal. This study defines the magnetic resonance imaging characteristics of this area and examines its correlation with the lunula. A high-resolution surface gradient coil specially designed for skin imagining was used on a 1.5 T magnetic resonance unit. The subnail matrix (SNM) areas of 12 subjects had a significantly longer T2 relaxation time and a higher enhancement ratio after injection of gadolinium than did the nail bed dermis. The length of the SNM area distal to the free edge of the proximal nail fold was highly correlated with the length of the lunula (R = 0.98) in 30 fingers and 10 toes. The total length of the SNM area was somewhat correlated with the nail thickness (R = 0.86) in 30 fingers. The histology and microvascularization of the subungual tissue in 21 fingers showed that this SNM area had specific features: The area was composed of loose connective tissue without bundles, and the reticular and subdermal vascular networks had large regular meshes in this oval area. The lunula is shown to be linked to a well-defined area in the underlying dermis with a specific histology and microvascularization.

Dermatologic surgery of the hand. General principles and avoiding complications

Dermatologists and dermatologic surgeons are frequently presented with significant pathology of the hand. Because the hand plays such a unique and important role in man's everyday life, preservation and restoration of its form and function is critical. The hand is both powerful and extremely delicate. Before performing any procedures in this area, dermatologists and dermatologic surgeons must have a clear understanding of the cutaneous and deep anatomy of the hand and digits, as well as a thorough knowledge of the disease process being treated and the modality being used. This article reviews the intricate anatomy, the proper hemostasis and anesthesia, and many of the complications seen in dermatologic surgery and procedures of the hand, digits, and nails. With appropriate preoperative evaluation and precautions, many dermatologic procedures may be safely performed on the hand.