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KIRNER'S DEFORMITY

Introduction

Kirner’s deformity, first described in 1927, is a rare bony defect characterized by radial and volar deviation of the distal phalanges of the fifth digits. Most patients are 8–14 year old children.  Girls are affected more frequently than boys (5:1). It is usually sporadic but may be inherited as an autosomal dominant trait with incomplete penetrance. Function is mostly unhindered. There is no pain; therefore, the deformity produces mainly cosmetic repercussions. Spontaneous resolution of Kirner’s deformity has never been reported. Lack of treatment results in fusion of the epiphyses and a lifelong deformity.

Pathophysiology

  • The fundamental etiology is cartilage growth in abnormal dimensions.
  • Suggested mechanisms include:
    • Abnormal distal insertion of the FDP tendon
    • Aseptic necrosis affecting the epiphysis and not the diaphysis
    • Epiphysiolysis, such as in slipped capital femoral epiphysis
    • Osteochondritis
    • Osteomalacia
    • Volar extension of the physeal plate of the distal phalanx
  • Progression of the deformity appears to cease after the epiphyseal growth plate closes.

Related Anatomy

  • The deviation involves only the diaphysis, with preservation of the epiphyseal, metaphyseal and articular alignment.
  • The physeal plate tends to be widened, and the diaphysis is sharply narrowed with a loss of normal trabecular bone structure.
  • Both radial flexion deformities and volar flexion of the distal phalanges range from 5–50°.
  • Subluxation at the distal interphalangeal (DIP) joint may also be seen.

Incidence and Related Conditions

  • Kirner’s deformity is extremely rare. In a 1972 survey of 3000 patients, incidence was 1 in 410.
  • As of 1986, only 63 cases had been reported in the literature.

Differential Diagnosis

  • Camptodactyly
  • Clinodactyly
  • Fracture (eg, physeal, Salter-Harris)
  • Frostbite
  • Infection
  • Osteomyelitis
  • Other congenital deformity
  • Trauma
ICD-10 Codes

  • KIRNER'S DEFORMITY

    Diagnostic Guide Name

    KIRNER'S DEFORMITY

    ICD 10 Diagnosis, Single Code, Left Code, Right Code and Bilateral Code

    DIAGNOSISSINGLE CODE ONLYLEFTRIGHTBILATERAL (If Available)
    KIRNER'S DEFORMITY M20.092M20.091 

    ICD-10 Reference

    Reproduced from the International statistical classification of diseases and related health problems, 10th revision, Fifth edition, 2016. Geneva, World Health Organization, 2016 https://apps.who.int/iris/handle/10665/246208

Clinical Presentation Photos and Related Diagrams
  • Kirner's Deformity of distal phalanx (arrow)
    Kirner's Deformity of distal phalanx (arrow)
Symptoms
Curving of the tip of the little fingers
Curving of the terminal phalanges of the little fingers
No pain, redness, or tenderness
Typical History

The typical patient is a young female child who presents with a complaint about the appearance of the small finger. There may be a history of difficulty with handwriting, typing, or playing a musical instrument. On questioning, the patient will describe progressive curvature of the distal aspect of the fifth finger over several months. There will be no history of injury or trauma. Fever and erythema will be absent. There may be no family history of a similar anomaly. 

Positive Tests, Exams or Signs
Work-up Options
Treatment Options
Conservative
  • Observation
  • Splinting, before growth spurt and epiphyses fusion, to mitigate progression
    • In a 1986 case, 16 months of splinting straightened a 12-year-old girl’s small fingers before her growth spurt. Diaphyseal deviation was "substantially reduced."
Operative
  • Distal detachment of the FDP tendon
  • Distraction lengthening
  • Osteotomy (most common)
  • Amputation (very rare and only in skeletally mature patients with severe deformity) 
Treatment Photos and Diagrams
  • Kirner's Deformity of distal phalanx with closing wedge osteotomy outlined. (arrow)
    Kirner's Deformity of distal phalanx with closing wedge osteotomy outlined. (arrow)
  • Kirner's Deformity of distal phalanx corrected by a closing wedge osteotomy internally fixed with a K-wire. (arrow)
    Kirner's Deformity of distal phalanx corrected by a closing wedge osteotomy internally fixed with a K-wire. (arrow)
Complications
  • Recurrent or persistent deformity after surgery.
Outcomes
  • Osteotomy provides moderate results: some curvature may remain (eg, 35° post surgery, increasing to 52° at 58 months and remaining at that angle).
  • Patients are generally satisfied with the cosmetic improvement attained. 
Key Educational Points
  • Kirner’s deformity may be more common than reported; as a minor disorder, it receives little attention. Occurrence of Kirner’s deformity in fingers other than the little finger is extremely rare.
  • The bowing site depends on patient age: the epiphyseal line in juveniles, the diaphysis in juveniles or adolescents, and the distal tip in adults.
  • Parent and patient compliance with continuous splinting, including regular follow-up to monitor improvement and adjust the splint, is critical to its success.
  • Classic observations include:
    • Bilateral, symmetrical involvement
    • The right side seems to be affected more severely, but no correlation with handedness has been shown.
    • Extensor lag of the DIP joint
    • Shortening of the terminal phalanx of the little fingers
    • Pronounced convexity of the fingernails causing a "parrot beak" disfiguration
  • X-rays are diagnostic and show:
    • Ventral and radial angulation of the terminal phalanx relative to the middle phalanx
    • Deviation in the diaphysis only; epiphysis, metaphysis, and all other joints are normally positioned
    • Physeal plate may be widened with sharply narrowed and sclerosed diaphysis
References

New Articles

  1. Adeb M, Hayashi D, Kumar Y. Kirner's deformity of the fifth finger: a case report. BMC Musculoskelet Disord 2016;17(1):440. PMID: 27769216
  2. Fairbank SM, Rozen WM, Coombs CJ. The pathogenesis of Kirner’s deformity: A clinical, radiological and histological study. J Hand Surg Eur Vol 2015;40(6):633-7. PMID: 25274771

Reviews

  1. Aucourt J, Budzik JF, Manouvrier-Hanu S, et al. Congenital malformations of the hand and forearm in children: what radiologists should know. Semin Musculoskelet Radiol 2012;16(2):146-58. PMID: 22648430
  2. Freiberg A, Forrest C. Kirner's deformity: a review of the literature and case presentation. J Hand Surg Am 1986;11:28-32. PMID: 3944436

Classics

  1. David TJ, Burwood RL. The nature and inheritance of Kirner's deformity. J Med Genet 1972;9(4):430-3. PMID: 4646550
  2. Dykes RG. Kirner's deformity of the little finger. J Bone Joint Surg Br 1978;60(1):58-60. PMID: 627580
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