Kirners deformity - a systematic review and surgery recommendations.

Background: Kirner deformity is a rare anomaly of the little finger in adolescents, characterized by a deformity of the distal phalanx and a radiologically L-shaped epiphysis, along with palmar and radial angulation of the distal phalanx. Due to the rarity of these pathological findings, there are no systematic literature reviews available. This work serves as an overview of the clinical presentation, frequency and age distributions, as well as possible conservative and surgical treatment options.

Methods: We present five cases of patients with Kirner's deformity of the little finger who underwent surgical treatment. A partial tenotomy of the flexor digitorum profundus tendon from the metaphyseal/diaphyseal distal phalanx was performed. In one case, a dorsal epiphysiodesis was also carried out. Additionally, a systematic review of the literature on Kirner's deformity was conducted, summarizing the prevalence, previously used surgical treatment options, and epidemiological data.

Results: In the presented cases, the detachment of the FDP tendon and dorsal epiphysiodesis resulted in a good functional and aesthetic outcome. Regarding the epidemiological distribution of Kirner deformity, it is noted that significantly more females are affected than males (63% vs. 36%). The average age at presentation in the respective clinic was 9.36 years (± 2.5). In more than half of all reported cases, the deformity was bilateral. Surgical intervention was performed in only 7.4% of cases, which included FDP detachment or corrective osteotomies. More than 90% of patients were treated conservatively.

Conclusion: Kirner's deformity is a rare condition affecting adolescents. In cases where functional limitations or pain symptoms are present, we recommend surgical intervention via detachment of the FDP tendon. If the deformity is an incidental finding without functional or aesthetic limitations, conservative therapy with a corrective splint can be initiated. From our perspective, early surgical treatment before the age of 12 improves both the long-term functional and aesthetic outcomes.