Congenital Malalignment of the Great Toenail, the Disappearing Nail Bed, and Distal Phalanx Deviation: A Review

Importance: Congenital malalignment of the great toenail (CMGT) is an idiopathic deviation of the nail apparatus. CMGT predisposes patients to recurrent stress forces, microtrauma, and secondary complications. The purpose of this study was to review the current published photographs to determine the relationship between variants of CMGT and the disappearing nail bed (DNB). Observations: A search in PubMed and Google using the terms congenital malalignment of the great toenail, disappearing nail bed, and lateral nail deviation was performed. Of the 53 photographs found in a total of 35 articles, 23 were disqualified due to low picture resolution or poor angle. The remaining 30 photographs were evaluated. Pure nail malalignment with associated dystrophy and DNB was found in 22 of 30 photographs. Four of 30 cases demonstrated pure deviation of the distal phalanx, with nail dystrophy but minimal DNB. The remaining 4 cases demonstrated a combination of toe deviation and nail unit deviation with varying degrees of DNB. Conclusions and Relevance: DNB was associated with all forms of pure CMGT. Moreover, a variant of malalignment of the distal phalanx was noted in 8 photographs. This has potential implications for further studies and treatment to correct secondary complications.


Introduction
Congenital malalignment of the great toenail (CMGT) is an idiopathic lateral deviation of the nail apparatus. The displacement of the nail unit may result in recurrent microtrauma leading to various nail pathologies including retronychia, paronychia, onycholysis, onychomadesis, and onychomycosis [1][2][3]. CMGT was first reported in the 1970s [4,5]. There may be a similar pathophysiologic basis to nail dystrophy associated with hallux valgus (malalignment of the MTP) and CMGT associated with the lateral displacement of the distal digit (see Fig. 1a-c). One of the end results of chronic onycholysis in CMGT is epithelization of part of the nail bed. This has been termed the disappearing nail bed (DNB) [6]. Nail pathologies are often difficult to treat due to the requirement of long-term patient compliance and recurrent macro-or microtrauma. Further insight into CMGT concerning treatment and clinical presentation provides the possibility of offering the best possible solutions for patients. One of this article's main goals is to better understand the pathophysiology of CMGT. This may lead to more efficacious forms of treatment. Certainly successful resolution in some cases has been documented. A review of all published cases of CMGT was performed to assess its association with underlying lateral displacement of the distal phalange, nail dystrophy, and DNB.

Methods
A search in PubMed and Google for reports up to January 31, 2021, was (with no restriction on earliest search date) performed by the authors. Search terms used were congenital malalignment of the great toenail, disappearing nail bed, and lateral nail deviation.
Thirty-five articles reporting or reviewing cases of CMGT from 1978 to 2019 were identified. All cases with clinical photographs published were included in this review [1,2,4,. Duplicate images were not included. When multiple photographs of the same patient were available, the image that most clearly demonstrated features of CMGT was used in the assessment. Photographs were analyzed for the presence of CMGT, lateral deviation at the interphalangeal joint of the great toe, nail dystrophy, and DNB.
Fifty-three clinical photographs were included in the final set for review separately by each author. Of these photographs, 23 were disqualified because of the angle of the image which made it difficult to assess or the image demonstrated poor resolution. Of the remaining photographs, the digits were evaluated for nail alignment, toe alignment, nail dystrophy, and DNB.

Discussion/Observations
Nail unit malalignment in the setting of a straight digit was identified in 22 of 30 (73%) photographs. In each case, the CMGT was associated with nail dystrophy and a DNB. Of the 8 remaining images, 4 cases (13%) demonstrated only deviation of the distal phalanx, with no DNB associated. The remaining 4 cases (13%) demonstrated a combination of toe deviation and nail unit deviation, with varying levels of DNB being seen with each. Radiologic images were not present in any of the cases which would have been the best way to confirm bone deviation. Pathophysiology CMGT is an idiopathic lateral deviation of the nail apparatus. It is most often a congenital/inherited disorder. The displacement of the nail unit increases risks of recurrent microtrauma leading to various nail pathologies including retronychia, paronychia, onycholysis, onychomadesis, and onychomycosis [1][2][3]. The microtrauma of the mispositioned nails produces torque that damages the nail matrix and nail bed. There may be a similar pathophysiologic basis to nail dystrophy associated with hallux valgus (malalignment of the MTP) and CMGT associated with either the lateral displacement of the distal digit or lateral deviation of the toenail in the setting of a straight digit (see Fig. 1). Walking, crawling, and trauma from footwear impacting a malaligned toenail create torsion stress forces that would not be present in a normally positioned nail (see Fig. 2).

Clinical Presentation
Patients with CMGT dystrophy often present with dystrophic nails related to recurrent retronychia, paronychia, onychomycosis, or onychomadesis. One of the end results of chronic onycholysis in CMGT is the DNB [6]. DNB is a relatively new concept, with the first article being published in 2005 and the second being published in 2017. It has been seen in chronic cases of onychomycosis and advancing age [6,35]. In this study, DNB was identified in all presumably due to the same mechanisms noted above. While this study demonstrated that the majority of patients have straight toes, deviation of the distal phalanx was present in 4 cases (13%) which has not been noted previously.

Assessment and Diagnosis
In patients with nail dystrophy of the great toenail, the alignment of the great toenail and the digit itself should be evaluated. Physical evaluation of the misalignment of the nail unit in the setting of a normally aligned digit delineates a diagnosis of classic CMGT. The distal digit is laterally displaced, and the nail is growing parallel with the bone in a variant best termed MDP of the great toe. The presence of DNB in a patient, though highly sensitive in the set of photographs studied, is not specific to CMGT.

Treatment and Prognosis
Treatment options should focus on reducing the mechanical stress impacting the nail by wearing well-fitted footwear, trimming at-risk nails, and even surgical removal or realignment of the toenail [36]. In some cases, CMGT may spontaneously resolve, but many patients will continue to have continuing complications such as pain with ambulation [21].

Further Discussion
The Nail Unit or the Digit This review of all published photographs demonstrated a new variant of CMGT that has not been previously recognized. In 4 of 30 patients, the toenail is properly oriented parallel to the axis of the toe, but the distal phalanx itself is malaligned, and the nail is therefore deviated by proxy. MDP leads to the same abnormal forces on the nail and the same onycholysis, DNB, and nail dystrophy. In fact, the same forces would seemingly be present on the nail in hallux valgus where the entire digit is laterally displaced.
In 4 additional patients, there was a combination of both lateral displacement of the distal phalanx and nail unit malalignment. Further research should focus on these 2 subsets of CMGT to determine their frequency and the severity of nail changes in each situation.
Therefore, when considering treatment, especially with pure phalangeal deviation, alignment of the distal toe may prove helpful in the manner bunion surgery can be performed to realign hallux valgus [37]. In theory, this procedure might minimize the trauma that produces nail dystrophy. This should be studied further as more cases of distal phalangeal deviation are recognized and evaluated clinically.

Limitations
This study was limited by the wide variation in quality of photographs in publications describing CMGT. Furthermore, many of the clinical pictures were taken at angles that made it difficult to determine orientation of the distal interphalangeal joint. Radiologic images to confirm the joint alignment were not available in any published case. Gathering a series of cases of CMGT with radiologic imaging and careful photography may well lead to a better understanding of the pathophysiologic basis of CMGT, the DNB, and the presence of MDP.