original article Wien Klin Wochenschr (2019) 131:216–220 https://doi.org/10.1007/s00508-019-1483-8 Sexual dimorphism in the anatomy of the ulnar collateral thumb ligament Martin F. Vierhapper · Gabriela K. Muschitz · Stefan Hacker · Sandra E. Boesmueller · Michael Pretterklieber · Hugo B. Kitzinger Received: 29 August 2018 / Accepted: 13 March 2019 / Published online: 1 April 2019 © Springer-Verlag GmbH Austria, part of Springer Nature 2019 Summary Background Treatment of ruptured ulnar collateral thumb metacarpophalangeal (MCP) joint ligaments (UCL) necessitate a profound anatomic knowledge for optimal surgical repair in order to preserve range of motion and ensure postoperative joint stability. Therefore, knowledge of the angle between the UCL and the longitudinal axis of the first metacarpal bone could be useful. Methods In this study 46 ulnar collateral thumb MCP joint ligaments in 15 male and 15 female embalmed anatomic specimens were dissected and the angles between the longitudinal axis of the first metacarpal This work was presented at the annual meeting of the Austrian society of plastic and reconstructive surgery in October 2016 in Innsbruck M. F. Vierhapper, MD () Division of Plastic and Reconstructive Surgery, Department of Surgery, Wilhelminenspital Vienna, Montlearstraße 37, 1160 Vienna, Austria martinvierhapper@gmx.at G. K. Muschitz, MD, PhD Vienna, Austria S. Hacker, MD Clinic for Facial Plastic Surgery, Marienhospital Stuttgart, Stuttgart, Germany S. E. Boesmueller, MD, PhD Department of Trauma Surgery, AUVA trauma hospital Meidling Vienna, Medical University of Vienna, Kundratstraße 27, 1120 Vienna, Austria M. Pretterklieber, MD, PhD Center of Anatomy and Cell Biology, Department of Applied Anatomy, Medical University of Vienna, Währinger Straße 13, 1090 Vienna, Austria H. B. Kitzinger, MD, PhD Laudongasse 25, 1080 Vienna, Austria bone and the proper (PUCL) as well as the accessory ulnar collateral thumb MCP ligament (AUCL) were measured. Results In male specimens the angle for the PUCL measured on average 133.5° (±2.35°) and 122.75° (±3.8°) for the AUCL. A significantly different angle was measured for female specimens which showed on average 137.88° (±3.51°) for the PUCL and 128.65° (±4.14°) for the AUCL. Conclusions Optimal surgical repair or reconstruc- tion of torn ulnar collateral thumb MCP joint liga- ments should aim for an angle of approximately 135° in PUCL and 126° in AUCL in relation to the longitu- dinal axis of the metacarpal bone. Differences in men and women should be considered if possible. Level of evidence IV (anatomic study). Keywords Ulnar collateral ligament thumb · Thumb metacarpophalangeal joint · Anatomic sexual dimor- phism · Collateral ligament thumb Introduction Injuries to the metacarpophalangeal (MCP) joint of the thumb are very common. Most often the ulnar collateral ligament is affected while other traumatic lesions, such as distortion or rupture of the radial col- lateral ligament are rare [1–4]. Treatment often in- volves operative refixation or reconstruction. Knowl- edge of the anatomic situation is essential for opera- tive success. Sexual dimorphism has attracted grow- ing attention during the last years in anatomy and traumatology. Previous studies on ligamentous knee repair described differences for men and women [5]. This anatomic study describes the angle between the ulnar collateral ligament (UCL) complex and the lon- gitudinal axis of the metacarpal bone showing sexual 216 Sexual dimorphism in the anatomy of the ulnar collateral thumb ligament K