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Background <p>Talocalcaneal coalition is highly prevalent but diagnostically challenging due to the subtalar joint’s complex anatomy, leading to frequent oversights on conventional radiographs. Existing signs rely primarily on lateral views, with variable sensitivity.</p> Objective <p>To introduce and validate the “gorilla lip” sign on non-weight-bearing anteroposterior (AP) radiographs as a complementary diagnostic marker for talocalcaneal coalition.</p> Materials and methods <p>In this retrospective study, non-weight-bearing AP ankle radiographs of 30 talocalcaneal coalition-confirmed feet (positive group) and 33 normal feet (negative group) from children aged ≤17&#xa0;years were analyzed. The “gorilla lip” sign was defined by sustentaculum tali abnormalities: (1) osseous protuberance ≥50% medial malleolus height, (2) narrowed and rough articular surface, or (3) absent joint space. Three blinded observers independently assessed randomized images twice (2-month interval). Sensitivity, specificity, likelihood ratios, and inter-/intraobserver reliability were calculated.</p> Results <p>Across two evaluations by three observers, sensitivity ranged from 77-93%, and specificity ranged from 85-100%. Positive likelihood ratios were ranging from 5.28 to infinite, indicating a high probability of talocalcaneal coalition when the sign is present, while low negative likelihood ratios (ranging from 0.07 to 0.24) suggest its absence is a strong indicator to rule out talocalcaneal coalition. The sign showed good interobserver reliability (Fleiss kappa, 0.65-0.70) and good to excellent intraobserver reliability (kappa, 0.67-0.87).</p> Conclusions <p>The “gorilla lip” sign is a highly sensitive, specific, and reproducible radiographic marker for diagnosing talocalcaneal coalition on non-weight-bearing AP ankle radiographs. Its application can complement traditional lateral view signs, enhancing diagnostic confidence and potentially reducing unnecessary examinations prompted by misdiagnosis.</p> Graphical abstract <p></p>

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The gorilla lip sign: diagnostic utility of anteroposterior radiographs for pediatric talocalcaneal coalition

  • 期刊论文

  • 发表日期：

    2025年10月21日

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  • Yueqiang Mo,
  • Haodong Li,
  • Peng Huang,
  • Yanhui Jing,
  • Bo Ning,
  • Yuerong Zhang,
  • Dahui Wang

摘要

Background

Talocalcaneal coalition is highly prevalent but diagnostically challenging due to the subtalar joint’s complex anatomy, leading to frequent oversights on conventional radiographs. Existing signs rely primarily on lateral views, with variable sensitivity.

Objective

To introduce and validate the “gorilla lip” sign on non-weight-bearing anteroposterior (AP) radiographs as a complementary diagnostic marker for talocalcaneal coalition.

Materials and methods

In this retrospective study, non-weight-bearing AP ankle radiographs of 30 talocalcaneal coalition-confirmed feet (positive group) and 33 normal feet (negative group) from children aged ≤17 years were analyzed. The “gorilla lip” sign was defined by sustentaculum tali abnormalities: (1) osseous protuberance ≥50% medial malleolus height, (2) narrowed and rough articular surface, or (3) absent joint space. Three blinded observers independently assessed randomized images twice (2-month interval). Sensitivity, specificity, likelihood ratios, and inter-/intraobserver reliability were calculated.

Results

Across two evaluations by three observers, sensitivity ranged from 77-93%, and specificity ranged from 85-100%. Positive likelihood ratios were ranging from 5.28 to infinite, indicating a high probability of talocalcaneal coalition when the sign is present, while low negative likelihood ratios (ranging from 0.07 to 0.24) suggest its absence is a strong indicator to rule out talocalcaneal coalition. The sign showed good interobserver reliability (Fleiss kappa, 0.65-0.70) and good to excellent intraobserver reliability (kappa, 0.67-0.87).

Conclusions

The “gorilla lip” sign is a highly sensitive, specific, and reproducible radiographic marker for diagnosing talocalcaneal coalition on non-weight-bearing AP ankle radiographs. Its application can complement traditional lateral view signs, enhancing diagnostic confidence and potentially reducing unnecessary examinations prompted by misdiagnosis.

Graphical abstract