Lefèvre Nicolas, Moussa Mohamad K, Chahal Ahmad, Meyer Alain, Grimaud Olivier, Khalaf Zeinab M, Alayane Ali, Bohu Yoann, Hardy Alexandre
Clinique du Sport, Paris, France.
Department of Orthopedic Surgery, Group Hospitalier Sélestat Obernai, Séléstat, Alsace, France.
Knee Surg Sports Traumatol Arthrosc. 2025 Feb;33(2):739-749. doi: 10.1002/ksa.12437. Epub 2024 Aug 22.
To introduce a new magnetic resonance imaging (MRI) sign, termed the Cobra sign, and identify its diagnostic metrics. The secondary aim was to demonstrate that this sign can be a source of false evaluation of tendon retraction in patients with proximal hamstring avulsion injury.
This retrospective cohort study targeted patients surgically treated for proximal hamstring avulsion injury from January 2019 to June 2023. The MRI Cobra sign was defined as a wavy curved T2-hypointense band with the free end folding distally over itself, resembling a cobra head. The primary outcome measure was the characterization of the Cobra sign in patients with proximal hamstring avulsion injury. The secondary outcome was the association of this sign with tendon retraction. The study included 81 proximal hamstring avulsion injury patients (mean age of 45.7, SD = 13.9), with 41 (50.6%) complete avulsions, 33 semimembranosus, and 7 conjoint tendons.
The MRI Cobra sign was found in 25 patients (17 semimembranosus and 8 complete). It was confirmed surgically only in semimembranosus cases. It demonstrated 51.5% sensitivity and 83.3% specificity for isolated semimembranosus avulsions, with a significant positive likelihood ratio of 3.0. MRI retraction was 10.05 cm (±3.0), reducing to 7.9 cm (±2.5) on surgical measurement (mean difference = 2.0 cm, p < 0.001). The regression analysis confirmed MRI retraction's influence on the Cobra sign, with a 1.4 odds increase per unit (p < 0.001). In linear regression analysis, each unit increase in MRI retraction corresponded to a 79% increase in surgical retraction (coefficient 0.7, t = 11.1, p < 0.001).
The Cobra sign demonstrated acceptable diagnostic accuracy for isolated semimembranosus avulsion, with a high specificity of 83.3%, a low sensitivity of 51.5%, and a positive likelihood ratio of 3.0. The presence of the Cobra sign indicates an overestimated MRI retraction by approximately 21%.
Level III.
介绍一种新的磁共振成像（MRI）征象，即眼镜蛇征，并确定其诊断指标。次要目的是证明该征象可能是导致腘绳肌近端撕脱伤患者肌腱回缩评估错误的原因。
这项回顾性队列研究针对2019年1月至2023年6月接受手术治疗的腘绳肌近端撕脱伤患者。MRI眼镜蛇征定义为一条波浪状弯曲的T2低信号带，其游离端向远端自身折叠，形似眼镜蛇头。主要结局指标是腘绳肌近端撕脱伤患者的眼镜蛇征特征。次要结局是该征象与肌腱回缩的关联。该研究纳入了81例腘绳肌近端撕脱伤患者（平均年龄45.7岁，标准差=13.9），其中41例（50.6%）为完全撕脱，33例为半膜肌撕脱，7例为联合肌腱撕脱。
25例患者发现MRI眼镜蛇征（17例半膜肌撕脱和8例完全撕脱）。仅在半膜肌病例中通过手术得到证实。对于孤立的半膜肌撕脱，其敏感性为51.5%，特异性为83.3%，阳性似然比为3.0。MRI测量的回缩为10.05 cm（±3.0），手术测量时降至7.9 cm（±2.5）（平均差异=2.0 cm，p<0.001）。回归分析证实MRI回缩对眼镜蛇征有影响，每单位增加1.4倍的优势比（p<0.001）。在线性回归分析中，MRI回缩每增加一个单位，手术回缩增加79%（系数0.7，t=11.1，p<0.001）。
眼镜蛇征对孤立的半膜肌撕脱显示出可接受的诊断准确性，特异性高（83.3%），敏感性低（51.5%），阳性似然比为3.0。眼镜蛇征的出现表明MRI回缩高估了约21%。
三级。
