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Diagnosing nail matrix diseases requires knowledge of the nail matrix function and anatomy. This allows recognition of the clinical manifestations and assessment of potential surgical risk. Nail signs depend on the location within the matrix (proximal or distal) and the intensity, duration, and extent of the insult. Proximal matrix involvement includes nail surface irregularities (longitudinal lines, transverse lines, roughness of the nail surface, pitting, and superficial brittleness), whereas distal matrix insult induces longitudinal or transverse chromonychia. Clinical signs are described and their main causes are listed to enable readers to diagnose matrix disease from the nail's clinical features., (Copyright © 2015 Elsevier Inc. All rights reserved.)

The nail apparatus contains tissues of various echogenicities and is thus well suited for ultrasound examination. Furthermore, ultrasonography is widely available and non-invasive and may therefore be used for longitudinal studies of tissues and diseases. Characteristic ultrasound pictures can be seen in psoriasis, cysts, vascular abnormalities,and other nail diseases. Ultrasound examination can visualize and quantify morphologic and functional aspects of nail biology.

Nail surgery is an integral part of dermatologic surgery. An in-depth knowledge of the anatomy, biology, physiology, and gross pathology of the entire nail unit is essential. In particular, knowledge of nail histopathology is necessary to perform diagnostic nail biopsies and other nail procedures correctly.

This article provides a description of the growth and anatomic structure of the human nails.

Nail disorders are often given little regard in clinical practice. The myriad relations between nail disease and other disease entities merits each practitioner's attention. Whether the cause is heritable, infectious, post-traumatic, environmental, neoplastic, biomechanical, or secondary to systemic disease, podiatrists are in a unique position to examine, properly diagnose, and treat nail disorders.

The nail unit is distinctive for human beings. Developmentally, the fetus demonstrates cranial and caudal paired anlage of the upper and lower extremities. The leg bud develops a foot plate and eventually toe rays that are first notched, later webbed, and then develop into separate toes. Distal on the toe, the primitive nail unit appears and eventually moves dorsal. When developed fully, the nail unit consists of the nail plate, nail bed, ungualabia, eponychium, hyponychium, lunula, and nail matrix. These structures are associated intimately with the terminal or ungual phalanges of the foot's five toes.

Nail bed and fingertip injuries are commonly seen in the Emergency Department. Each of these injuries must be evaluated carefully not only for the acute situation but for the possible long-term effects. Nail bed injuries must be appropriately diagnosed and treated initially because a secondary repair is often unsatisfactory. Fingertip injuries must provide the patient with a sensitive fingertip with sufficient length for effective use of the finger. The initial care and treatment are vital for the best patient outcome.

The characteristic gross and microanatomic components of the nail unit are described specifically and in relation to surrounding digital anatomy, including its specialized vascular supply. In addition, major steps in the development of the nail unit, and factors in growth of the nail, are outlined.

The primary care physician has a profound influence on the prevention of deformity and disability resulting from fingernail injuries. Prompt recognition and precise repair of the disrupted nailbed consistently result in successful nail restoration. For injuries with a substantial subungual hematoma or a displaced phalangeal fracture, optimal treatment requires removal of the nailplate, reduction of the fracture, and meticulous repair of the nailbed. Even with severely fragmented or avulsion injuries, the results of an accurate primary repair are generally far superior to those of corrective surgery for established fingernail deformities. Skillful primary repair is the best method of managing the vast majority of fingernail injuries.

In this review an attempt has been made to clarify the etiology, pathogenesis, and therapy of brittle fingernails. Hopefully, this discussion will enable the clinician to better understand, evaluate and manage patients with this disorder.

The physician entrusted with the management of the injured hand must possess knowledge of the functional anatomy of the upper limb. Necessary also is the ability to correlate the surface topography, underlying soft tissues, and the x-ray image as well as the results of individual tests for the functional integrity of skin, vessels, muscle-tendon units, skeleton, joints, and nerves.

The CO2 laser has facilitated the treatment of many toenail conditions. Satisfactory wound healing and cure rates have been equivalent to current standards of treatment. Pain was markedly diminished as compared with pain in traditional methods of treatment, and time until comfortable ambulation was dramatically shortened. Healing times were consistent with those in other methods of treatment. The protocol for CO2 treatment of nail conditions has been thoroughly described. Evaluation of 50 patients after 4 years from treatment date is tabulated. The CO2 laser must be strongly considered as a treatment modality for toenail pathology. Because of markedly reduced pain, minimal disability, and satisfactory long-term results, the laser is becoming a valuable treatment of choice for pathologic conditions of the nail.

The nail plate lies under the proximal nail fold and over the matrix, nail bed, and hyponychium. The nail plate is made by the matrix. Although the few cells the nail bed contributes to the nail plate do not increase the bulk of the plate, they are important in attaching the plate to the bed. The interrelationships of the components of the nail and knowledge about their normal function are reviewed.

Introductory sections on why and how to biopsy the nail unit and on the handling and processing of the specimen are followed by a presentation of normal histologic findings. These are contrasted with the abnormal changes in infections, especially fungal, of the nail unit, and in skin diseases that may affect the nail, especially psoriasis and lichen planus. Benign and malignant neoplasms that may occur beneath or around the nail, including melanoma, conclude the discussion.

Evaluation of dystrophic nails must include a thorough assessment of the patient's occupation. Unless this is done, it will not be possible to ascertain the correct diagnosis, and without this, successful therapy is impossible. The spectrum of clinical change exhibited by the nails is limited so that every effort must be made to ensure accuracy.