Introduction: Lag screw cut-out in gamma nailing is reported between 1,1% and 7.1% in the literature. Searching for predictive factors we performed a retrospective study, and we analyzed our cut-out cases.

Material & Methods: We reviewed our first 1000 gamma nailings. A detailed analysis of the cut-out cases was performed. We focused on fracture type and the technical failures of the primary surgery. Fractures were classified according to AO. Timing of surgery, implant type and an estimated value of osteoporosis on x-ray was investigated. Distance of the tip of the lag screw from the cortical bone, from the ideal central line of the neck and head in AP and lateral view, and precision of reduction was measured and classified. We recorded the direction of cut-out and the occurrence of secondary varus displacement.

Results: We had 29/1000 (2,9%) cut-outs. Average age was: 76 years. 14/29 (48%) AO A2.2 type and 8/29 (28%) A3.3 type fractures were found in the cut out group. Normal collo-diaphyseal angle was achieved in all cases primarily. In 21/29 (72%) the gap between main fragments was narrower than 5 mm, and in 8/29 (28%) it was bigger. The subjective evaluation of the reduction was 2/29 excellent, 9/29 good, 12/29 satisfactory and 6/29 bad. Primary position of the lag screw tip was caudal in 13/29, central in 10/29 and cranial in 6/29 cases. The distance of the lag screw from the central line in frontal/dorsal direction was 0–4 mm in 5/29, 5–9 mm in 12/29, 10–14 mm in 7/29 and 15–19 mm in 5/29 cases. The numbers of too short or too long lag screws were not high in this patient group. The cut out was cranial in 24/29 (83%) cases and central at 5/29 (17%) patients. We recorded 20/29 (68%) secondary varus displacement. We found 2/29 (7%) patients where none of the above mentioned technical problems could be justified.

Conclusion: AO A2.2 and A3.3 fracture type is a predisposing factor. Cut-out appears relatively early. Correct positioning of the lag screw in both views is essential. Leaving the fracture in a significantly displaced position increases the risk of cut out, too. The lag screw migrates mainly cranial with a secondary varus dislocation. With adequate technique the majority of cut-outs can be avoided, but there is a little percentage of the cases when the primary mistake is not obvious. A possible explanation could be osteoporosis, but further investigation is necessary to clarify these unknown factors.