Fracture Type and Injury-to-Surgery Interval as Risk Factors for Avascular Necrosis of the Femoral Head after Internal Fixation of Intracapsular Femoral Neck Fracture

The aim of the study was to investigate the occurrence of avascular necrosis (AVN) of the femoral head following the osteosynthesis of intracapsular fracture of the femoral neck in relation to the time interval between injury and surgery and the type of fracture.The data of patients with intracapsular fractures of the femoral neck surgically treated in the period from 2001 to 2011 were reviewed. Of 1555 patients treated for this fracture, 125 (7%) underwent osteosynthesis. The evaluated group included 115 patients who came for examination at one-year follow-up. There were 59 (52%) women and 56 (48%) men. Dynamic hip screw (DHS) osteosynthesis with an anti-rotation screw was performed in 103 patients and lag-screw osteosynthesis involving three parallel cannulated cancellous screws was employed in 12 patients. The patients were allocated to groups according to the injury-to-surgery interval and to sub-groups on the basis of the Garden classification of femoral fracture stage.In the group of 58 patients treated within 6 h of injury, AVN developed in 10 (17%). When the type of fracture was considered, 4% of the non-displaced fractures and 30% of the displaced fractures developed AVN. The patients with Garden stage I and II (non-displaced) fractures treated within 6 h of injury had a significantly lower risk of AVN development than those with Garden stage III or IV (displaced) fractures. The group treated between 6 and 24 post-injury hours comprised 21 patients, of whom four (19%) had AVN. In non-displaced and displaced fracture sub-groups, 25% of the patients in the former and 16% in the latter had AVN. The stage of displacement had no effect on AVN development. The two groups together (patients treated by 24 h) had a significantly lower AVN incidence than the patients treated after 24 h (p = 0.0025). In this group of 36 patients, 16 had AVN (44%) and the fracture stage made no significant difference (p = 0.6985; nondisplacement sub-group, 41%; displacement sub-group, 55%).The study showed a significantly lower AVN occurrence in the patients surgically treated within 24 h of injury. In the patients treated within 6 h of injury, AVN incidence was significantly lower in the patients with non-displaced fractures, as compared with those who had displaced fractures. This was not true for the two patient groups treated later (6-24 and later than 24 h) in which the differences between AVN development after non-displaced fractures and that after displaced fractures were similar.