Sled fixation for horizontal medial malleolus fractures

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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 2 mm of articular displacement.

Findings:

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.

Interpretation:

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.

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