Indications and Limitations of Resection and Ligaments Repair for Os Subfibulare Based on the Hasegawa Classification
Authors: Hio Naohiro , Taki Masanori , Hasegawa Atsushi 
Published: December 2024

Category:

Ankle; Arthroscopy

Introduction/Purpose:

Os subfibulare (OS) is present in 10-38.5% of chronic ankle instability cases, increasing the risk of talus osteochondral lesions. Despite the lack of consensus on surgical indications and methods for symptomatic, treatment-resistant OS, surgery is often performed. Hasegawa et al. proposed a classification detailing the condition of the os subfibulare and its ligament attachments, indicating effective excision and possible additional surgeries. However, the relationship between classification items, surgical methods, and outcomes remains unclear, with no further studies based on this classification reported. This paper examines the indications and limitations of ligament repair surgery following OS excision, based on the Hasegawa classification.

Methods:

This study analyzed 18 joints treated surgically for os subfibulare (OS) from December 2015 to December 2022, with at least one year of follow-up. Participants included 6 males and 11 females, averaging 21.6 years old, ranging from 12 to 62. The surgical approach involved arthroscopic examination, direct OS removal, and lateral ligament repair. For ligament repairs with potential fibula gaps, dissected extensor retinaculum strips were used for bridging. Additionally, suture tape augmentation was applied in two cases exhibiting overall laxity. Outcome measures assessed were pain via the Visual Analog Scale (VAS), functional status using the Japanese Society for Surgery of the Foot ankle/hindfoot scale (JSSF scale), subjective instability, talar tilting angle (TTA), and anterior drawer stress distance (ADSD), both derived from stress radiographs.

Results:

In a study applying the Hasegawa classification to 17 joints, significant post-surgical improvements were noted in pain (VAS improved from 38.5±26.2 to 6.7±16.4), function (JSSF scale increased from 75.6±9.4 to 94.8±8.4), and subjective instability (reduced from 58.8% to 17.6%). TTA and ADSD showed no significant difference before and after the surgery. However, a detailed analysis of the Hasegawa classification subitems (size, grade, type) revealed that TTA, ADSD, and subjective instability tended to worsen with increased severity in each category, indicating a correlation between the severity of the classification subitems and the degree of postoperative instability or radiographic findings, despite overall significant clinical improvement.

Conclusion:

Surgical outcomes for ligament repair following os subfibulare (OS) excision are generally favorable. However, according to the Hasegawa classification, an increase in the severity of each category tends to result in a rise in both subjective and objective instability postoperatively. Treatment for OS necessitates not only an assessment of the remaining ligament and the size of the OS but also a direct and indirect evaluation of the lateral soft tissue. It is considered that this surgical method is well-suited for cases with mild conditions.