Objective: To evaluate the clinical performance of the Dynamic Helical Hip System (DHHS) spiral blade relative to the Dynamic Hip Screw (DHS) lag screw.
Design: Randomized prospective study.
Setting: One level-2 trauma center and one level-3 trauma center.
Patients: Fifty-one consecutive patients were recruited into the trial. Inclusion criteria included patients over 50 years of age with AO/OTA 31A1 or 31A2 fracture.
Intervention: Surgeries were performed by one of 15 participating community orthopaedic surgeons. The patients were randomized to either a DHHS or DHS implant. Follow-up occurred at two weeks and six weeks and then at six-week intervals until healing occurred.
Main outcome measures: Primary outcome variables included sliding of die implant on the final AP radiographs, failure by cut-out and implant failure.
Results: There were 24 patients in the DHS group and 27 in the DHHS group. There was no difference in age, gender, ASA score, fracture classification or in the quality of reduction measured on the immediate postoperative radiographs (p=0.28) between the two groups. The tip apex distance was 18.7 mm in the DHHS group and 18.5 mm in the DHS group (p=0.40). The DHHS group had average blade sliding of 7.4 mm while the DHS group had an average lag-screw sliding of 7.7 (p=0.45). The DHHS group had two failures by central protrusion of the blade through the femoral head without significant varus collapse or superior migration. One was revised to a DHS and healed, the other was revised to a proximal femoral locking plate, which also failed and eventually required revision to a total hip arthroplasty. Investigation of the implants post failure showed evidence of binding of the blade shaft in the barrel as a mechanism of failure in both cases. No DHS implants cut out in this series, although one patient was revised to a total hip arthroplasty for symptomatic segmental osteonecrosis.
Conclusion: Both implants performed well in a majority of cases. The higher incidence of failure in the DHHS group is concerning, despite the low numbers. The mechanism of failure of the DHHS implant left adequate bone stock for attempts at revision fixation.