title: Sled fixation for horizontal medial malleolus fractures.
abstract: BACKGROUND
  Horizontal fractures of the medial malleolus occur through exertion of various rotational forces on the ankle, including supination--external rotation, pronation--external rotation, and pronation-abduction. Many methods of fixation are employed for these fractures, but the optimal fixation construct remains unclear.
  
  
  METHODS
  Horizontal medial malleolus osteotomies were performed in synthetic distal tibiae and randomized into two fixation groups: 1) two parallel unicortical cancellous screws or 2) medial malleolar sled fixation. Specimens were subjected to offset axial tension loading and tracked using high-resolution video. Clinical failure was defined as 2mm of articular displacement.
  
  
  RESULTS
  There were statistically significant increases in mean stiffness (127% higher, P=0.0007) and mean force to clinical failure (52% higher, P=0.0002) with the medial malleolar sled. The mean stiffness in offset tension loading was 232 (SD 83) N/mm for medial malleolar sled and 102 (SD 20) N/mm for parallel unicortical cancellous screws. The mean force to clinical failure was 595 (SD 112) N for medial malleolar sled and 392 (SD 34) N for unicortical screws. In addition, the medial malleolar sled demonstrated elastic recoil to pre-testing alignment while the unicortical screws did not.
  
  
  CONCLUSIONS
  Medial malleolar sled fixation was significantly stiffer and required more force to clinical failure than parallel unicortical cancellous screws. A medial malleolar sled requires more dissection to apply surgically, but provides significantly more initial fixation strength. Additionally, a medial malleolar sled acts like a tension band in its ability to capture comminuted fragments while being low profile enough to minimize soft tissue irritation.
authors.affiliation: University of California Davis Medical Center, Sacramento, CA, USA.
authors.forename: Adam M
authors.initials: AM
authors.lastname: Wegner
authors.affiliation: University of California Davis Medical Center, Sacramento, CA, USA.
authors.forename: Philip R
authors.initials: PR
authors.lastname: Wolinsky
authors.affiliation: Stanford University School of Medicine, Stanford, CA, USA.
authors.forename: Robin Z
authors.initials: RZ
authors.lastname: Cheng
authors.affiliation: University of California Davis Medical Center, Sacramento, CA, USA.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Robbins
authors.affiliation: University of California Davis, Davis, CA, USA.
authors.forename: Tanya C
authors.initials: TC
authors.lastname: Garcia
authors.affiliation: Stanford University School of Medicine, Stanford, CA, USA. Electronic address: dfa@stanford.edu.
authors.forename: Derek F
authors.initials: DF
authors.lastname: Amanatullah
mesh_terms: D064386:Ankle Fractures / Q000503:physiopathology / Q000601:surgery*; D000843:Ankle Joint / Q000601:surgery; D001696:Biomechanical Phenomena; D001863:Bone Screws; D005593:Fracture Fixation, Internal / Q000379:methods*; D006801:Humans; D010027:Osteotomy; D011403:Pronation / Q000502:physiology; D013314:Stress, Mechanical; D013484:Supination / Q000502:physiology; D013978:Tibial Fractures / Q000601:surgery*
keywords: Biomechanical study; Horizontal fracture; Internal fixation; Medial malleolar sled; Medial malleolus; Pronation-abduction; Pronation-external rotation; Supination-external rotation