title: Kinematics analysis of ankle inversion ligamentous sprain injuries in sports: five cases from televised tennis competitions.
abstract: BACKGROUND
  Ankle ligamentous sprain is common in sports. The most direct way to study the mechanism quantitatively is to study real injury cases; however, it is unethical and impractical to produce an injury in the laboratory. A recently developed, model-based image-matching motion analysis technique allows quantitative analysis of real injury incidents captured in televised events and gives important knowledge for the development of injury prevention protocols and equipment. To date, there have been only 4 reported cases, and there is a need to conduct more studies for a better understanding of the mechanism of ankle ligamentous sprain injury.
  
  
  OBJECTIVE
  This study presents 5 cases in tennis and a comparison with 4 previous cases for a better understanding of the mechanism of ankle ligamentous sprain injury.
  
  
  METHODS
  Case series; level of evidence, 4.
  
  
  METHODS
  Five sets of videos showing ankle sprain injuries in televised tennis competition with 2 camera views were collected. The videos were transformed, synchronized, and rendered to a 3-dimensional animation software. The dimensions of the tennis court in each case were obtained to build a virtual environment, and a skeleton model scaled to the injured athlete's height was used for the skeleton matching. Foot strike was determined visually, and the profiles of the ankle joint kinematics were individually presented.
  
  
  RESULTS
  There was a pattern of sudden inversion and internal rotation at the ankle joint, with the peak values ranging from 48°-126° and 35°-99°, respectively. In the sagittal plane, the ankle joint fluctuated between plantar flexion and dorsiflexion within the first 0.50 seconds after foot strike. The peak inversion velocity ranged from 509 to 1488 deg/sec.
  
  
  CONCLUSIONS
  Internal rotation at the ankle joint could be one of the causes of ankle inversion sprain injury, with a slightly inverted ankle joint orientation at landing as the inciting event. To prevent the foot from rolling over the edge to cause a sprain injury, tennis players who do lots of sideward cutting motions should try to land with a neutral ankle orientation and keep the center of pressure from shifting laterally.
authors.affiliation: Department of Orthopaedics and Traumatology, Prince of Wales Hospital, Faculty of Medicine, The Chinese University of Hong Kong, China. dfong@ort.cuhk.edu.hk
authors.forename: Daniel Tik-Pui
authors.initials: DT
authors.lastname: Fong
authors.forename: Sophia Chui-Wai
authors.initials: SC
authors.lastname: Ha
authors.forename: Kam-Ming
authors.initials: KM
authors.lastname: Mok
authors.forename: Christie Wing-Long
authors.initials: CW
authors.lastname: Chan
authors.forename: Kai-Ming
authors.initials: KM
authors.lastname: Chan
mesh_terms: D016512:Ankle Injuries / Q000503:physiopathology*; D001265:Athletic Injuries / Q000503:physiopathology*; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D008023:Ligaments, Articular / Q000293:injuries*; D008297:Male; D008962:Models, Theoretical; D013180:Sprains and Strains / Q000503:physiopathology*; D013715:Tennis / Q000293:injuries*; D014741:Video Recording