Anatomic safe zone of pin insertion point for distal clavicle fixation

Clavicle fracture is the most common childhood fracture and one of the most common fractures in adults. Only some types of distal clavicular fractures, and dislocation of the acromioclavicular joint, require internal fixation. Many surgeons prefer closed pinning; however, the difficulty inserting many of the various kinds of pins from acromion into the medullary canal, of the distal clavicle, means the likelihood of iatrogenic complications from repeated drilling is heightened. The purpose of the present study was to establish what would be the optimum insertion point and direction for safe intramedullary pinning of the distal clavicle. Embalmed cadaveric shoulders (32) were studied. A bone window was created at the distal one-thirds of the clavicle, approximately 1.5 cm medial from the conoid tuberosity - as wide as could be freely, retrogradely drilled into the medullary canal of the distal clavicle. A 2.0-mm Kirschner wire was inserted until it penetrated the acromion. The point of emergence was recorded as ratio compared with the acromial width and length in coronal and sagittal planes, respectively. K-wire directions were measured as the angle between the K-wire and the reference line from the anterosuperior tubercle of the clavicle to the anterior angle of the acromion. The process was repeated until the acromion fractured 304 drillings were performed on 32 specimens. The length of the sagittal vs.coronal pin insertion point from the anterior vs. lateral borders of the acromion divided by its length vs. width averaged 0.325 +/- 0.04 and 0.397 +/- 0.09, respectively. The angle of the K-wire and the reference was 7.69 +/- 3.04 and 14.59 +/- 4.34 degrees in the coronal and horizontal planes, respectively. At 8 and 10 drillings survival was 0.72 (95%CI: 0.53-0.84) and 0.41 (95%CI: 0.24-0.57), respectively. The optimum pin inserting point for fixation of distal clavicle fracture and acromioclavicular joint dislocation is 32.5% and 39.7% of acromial length and width, respectively. If a 2.0-mm K-wire is used for fixation, drilling should not be repeated drilled more than 8 times to avoid sudden, high risk iatrogenic acromial fracture.