Purpose of the study: Osteosynthesis material adapted to a mini-invasive approach certainly reduces surgical trauma. The purpose of this work was to establish the osteosynthesis equivalence for pertrochanteric fractures using a dynamic hip screw, inserted according to the conventional technique versus a mini-invasive screw system (MISS), in terms of healing without loss of reduction.

Material and methods: This was a prospective pilot study in a single centre. From May 2006 to April 2007, 78 patients (mean age 83 years, 70% women) were included (38 MISS, 40 DHS). There was one exclusion criteria: poor reduction on the orthopaedic table before incision. Radiographic and clinical follow-up for six months. The main outcome was the quality of the reduction and healing at three months.

Results: Eight patients were lost to follow-up and two had died at three months. The two groups were comparable regarding mean age, ASA, fracture type, operator experience, and centring of the head screw. In the MISS group, there was a 20% reduction in blood loss, a shorter incision (9 cm) and shorter operative time (16 min). The differences were not significant. The healing rate without loss of reduction at three months was the same in both groups: 82%. There were three revisions in the MISS group: one infection and two material disassemblies. This problem disappeared with the addition of a locking screw on the nail. There were no revisions for haematoma.

Discussion: There were several biases. The series was not really randomised because the type of material used depended on the availability of the instrument sets. The MISS implant evolved during the course of the study. The operators were more familiar with the DHS. Inclusion criteria were too restrictive. Multiple-injury patients with bleeding had a false impact on blood loss data. None of the differences were statistically significant. Revision for infection was not directly attributable to the material. Nail locking never failed after use of the locking screw.

Conclusion: The main outcome was validated: the healing rate without reduction at three months is equivalent with the two methods (82%). A multicentric study should be conducted to confirm that the mini-incision and the MISS reduces blood loss. It could be expected that this mini-invasive approach will become the rule for osteosynthesis of these fractures with a dynamic hip screw.