Wegner AM, MD, PhD, Wolinsky PR, MD, Cheng RZ, B.S., Robbins MA, BS, Garcia TC, MS, Amanatullah DF, MD, PhD

Clinical Biomechanics, 42, 92-96, February 2017

Background: Horizontal fractures of the medial malleolus occur through various rotational forces of the ankle, including supination-external rotation, pronation-external rotation, and pronation abductionc. Many methods of fixation are employed for these fractures, but the optimal fixation construct remains unclear.

Methods: Horizontal medial malleolus osteotomies were perfomred in synthetic distal tibiae. Tibiae were randomized into two fixation groups: 1) two parralel unicortical cancellous screws or 2) medial malleolar sled fixation. Specimens were subjected to offset axial tension laoding and tracked using high-resolution video. Clinical failure was defined as 2 mm of articular displacement.

Findings: There was a statistically significant increase (115% higher) in mean stiffness with the medial malleolar sled (p <0.001). The mean stiffness in offset tension loading was 232 (SD 83) N/mm of medial malleolar sled and 102 (SD 20) N/mm for parallel unicortical cancellous screws. There was a statistically significant increase (52% higher) in mean force to clinical failure with the medial malleolar sled (p = 0.001). The mean force to clinical failure was 595 (SD 112) N for the medial malleolar sled and 392 (SD 34) N for parallel unicortical cancellous screws.

Interpretation: Medial malleolar sled fixation was significantly stiffer and required more force to clinical failure than parallel unicortical cancellous screws. A medial malleolar sled rquired more dissection to apply surgically, but provides significanly more initial fixation strenght. Additionally, a medial malleolar sled acts like a tension band in its ability to capture comminuted fragments w hile being low profile enough to minimize soft tissue irritation.

Keywords: horizontal fracture, pronation-external rotation, medial malleolous, medial malleolar sled, internal fixation, biomechanical study

1. Two constructs were tested for fixation of horizontal medial malleolus fractures
2. Medial mallolar sled was compared to two parallel unicortical cancellous screws
3. The medial mallelolar sled was stiffer and had greater load at 2mm displacement
4. Medial Malleolar sled demonstrated elastic recoil to pre-testing alignment