Table of Contents:
Displaced femoral neck fractures are common injuries in the elderly population worldwide with the highest incidence in Europe and North America. Due to demographic change and the high prevalence of osteoporosis, the number of femoral neck fractures will continue to rise. Osteoporosis is an important risk factor for hip fractures, because even low energy traumas can result in fractures of the proximal femur in those with osteoporosis. In contrast, the leading cause of femoral neck fractures in young patients is high impact trauma with an axial compression of the femur.
The diagnosis of a femoral neck fracture is based on the clinical examination and radiographs of the hip and pelvis. To decide on the individual‘s therapy, the classification introduced by Garden is used. The operative treatment is the gold standard for treating femoral neck fractures; conservative treatment is limited to rare cases. The options include using osteosynthesis, such as cannulated screws and the dynamic compression screw, or replacing the hip joint with a prosthesis. An ongoing controversy exists regarding the use of total- or hemiarthroplasty.
The prognosis and the postoperative quality of life depend on several parameters. Reconstructing the biomechanics of the hip, especially the femoral offset (FO), is an important factor. The FO is the distance between the shaft axis of the femur and the orthogonal to the center of the rotation of femoral head. This influences the function of the hip abductors. The impact of the correct restoration of the FO on the functional outcome in patients receiving total hip arthroplasty for osteoarthritis is well studied. However, a paucity of knowledge exists regarding the biomechanics after the implantation of a hemiendoprosthesis for displaced femoral neck fractures. This study examined the correlation between reconstructed FO and the functional outcome 12 months after displaced femoral neck fractures treated by hemiarthroplasty in elderly patients.
The femoral offset (FO) of 126 prospectively enrolled patients with a mean age of 82 years was analyzed on plain radiographs. The FO was correlated with the results of the Harris Hip Score (HHS) as a primary outcome measure with the instrumental activities of daily living- (IADL) score and the timed up and go test (TUG) as secondary outcome measures. Since measuring the FO exclusively with plain radiographs is inaccurate and the FO is therefore often underestimated, the FO was calibrated with the size of the head of the prosthesis. Afterwards, the calibrated results were corrected for rotation by means of a currently developed formula of Lechler et al. and the results were correlated with the clinical data. The mean projected FO (FOP) was 36.8 mm, but after correcting for rotational error the mean reconstructed FORC was 41.1mm (p < 0.0001). At 12 months postoperatively, the mean HHS was 68 points, mean TUG 39 s and mean IADL was 3.6 points. A significant positive correlation was found between the FORC and HHS as well as the FORC and IADL, but not between the FORC and TUG. Following adjustment for confounding variables such as sex, age and ASA physical status grade, there was a significant trend toward a positive correlation between the FORC and HHS and a significant correlation between the FORC and IADL. Again, there was no correlation between the FO and TUG in the multivariate analysis.
Surgical complications were observed in 12.7% of all patients, whereas 6.3% needed a revision surgery and only 3 of those patients suffered a dislocation.
Taken together, the results, which include a significant correlation between the FORC and IADL, underscore the importance of the restoration of the correct length of the femoral offset in patients receiving hemiarthroplasty for femoral neck fractures. However, more studies with prospective interventional study designs are needed to clarify the exact interaction between femoral offset and postoperative function in this patient population.