Arthroscopic Quantitative Measurement of Medial Clear Space for Deltoid Injury of the Ankle: A Cadaveric Comparative Study With Stress Radiography

Background: The deltoid ligament (DL) is an important stabilizer of the ankle. DL injury of varying severity can occur alone or with syndesmotic injury and fibular fracture. Limited diagnostic tools are available to assess DL injury quantitatively. Purpose: To establish an arthroscopic quantitative assessment of DL injury and to compare its performance with that of external rotation stress (ERS) and gravity stress (GS) radiography. Study Design: Controlled laboratory study. Methods: In total, 24 cadaveric lower extremities were divided into 4 groups: group 1 consisted of intact DL, group 2 of superficial DL disruption, group 3 of deep DL disruption, and group 4 of complete DL (superficial and deep) disruption. All specimens underwent sequential sectioning of syndesmotic ligaments, and medial clear space (MCS) was measured with ankle arthroscopy, ERS radiography, and GS radiography at different stages of syndesmotic sectioning. Results: For noninjured deltoid (group 1) and injured deltoid (groups 2-4), area under the receiver operating characteristic curve (AUC) of measurement of MCS was 0.939 for arthroscopy, 0.932 for ERS radiography, and 0.874 for GS radiography, with a significant difference between arthroscopy and GS radiography (P =.014). For incomplete deltoid injury (groups 1-3) and complete deltoid injury (group 4), the AUC of MCS was 0.811 for arthroscopy, 0.656 for ERS radiography, and 0.721 for GS radiography, with a significant difference between arthroscopy and ERS radiography (P <.001) and between arthroscopy and GS radiography (P =.035). For all stages of syndesmotic sectioning, cutoff values of arthroscopic MCS with intact fibula were ≤2.5 mm for intact DL, between 2.5 and 3.5 mm for partial DL injury (superficial or deep), and ≥3.5 mm for complete DL injury. Arthroscopy was unable to detect a difference between superficial deltoid injury (group 2) and deep deltoid injury (group 3) in partial DL injury, with a measured MCS between 2.5 and 3.5 mm. The intraclass correlation coefficient of interrater reliability was 0.975 for arthroscopy, 0.917 for ERS radiography, and 0.811 for GS radiography. Conclusion: Arthroscopic MCS measurement can differentiate intact DL, partial DL injury, and complete DL injury. Compared with ERS and GS radiography, arthroscopic MCS measurement has greater accuracy with excellent interrater reliability. Clinical Relevance: For patients with suspected DL injury, arthroscopic MCS is useful for determining deltoid lesion severity based on defined cutoff values for consideration in preoperative planning to improve surgical outcomes.