Analysis of vertical and horizontal offsets in displaced femoral neck fracture in elderly treated with indigenous bicentric bipolar hip device

Abstract

Objectives: To analyze the effect of indigenous bicentric bipolar prosthesis on horizontal and vertical offsets in fracture neck of femur when compared to contralateral normal hip and to evaluate functional outcomes. We hypothesized that our non-modular bipolar device restores satisfactory offsets in such patients.

Methods: All active elderly patients with displaced fracture NOF having contralateral normal hip were included. We used an indigenous bicentric bipolar hip-prosthesis, which is a non-modular single-piece device in all cases by lateral Hardinge approach. Postoperative radiograph AP view was taken in 15° internal rotation to decrease the effect of limb rotation on offset. CT scan was also used to evaluate offsets using ADW4.6 ADVANCED GE optima 128 slice software system. Subjects were followed for a minimum of 12 months postoperatively and functional outcome of effect of offsets change were evaluated by modified Harris Hip Score.

Results: There is minimal difference in horizontal and vertical offset after bicentric bipolar hemi-replacement which is statistically insignificant supporting our hypothesis. The clinical outcomes were good to fair according to modified Harris Hip Score. The mean value of horizontal offset after our bipolar hemireplacement was 42.4 ± 2.04 mm and of normal hip was 41.8 ± 1.81 mm and P-value=0.08 in plain radiographs and value of horizontal offset in CT scan was 40.73 ± 0.27on bipolar side and 41.19 ± 0.77 on normal side. Vertical offset after bicentric bipolar was 32.67 ± 2.85 mm and vertical offset of normal hip was 32.53 ± 2.73 mm. Mean 9.77 ± 1.09 mm of calcar was preserved. Modified Harris Hip Score at 6 and 12 months postoperatively was 75.78 ± 4.16 and 79.53 ± 3.95 respectively. There was no incidence of hip dislocation.

Conclusion: Our study data clearly demonstrates that vertical and horizontal offsets are effectively maintained by the indigenous bicentric hip device. There was insignificant change in offsets as compared to contralateral normal side due to its design modifications. Indigenous bicentric non-modular bipolar device offers an excellent option for femur neck fractures in elderly patients in resource constrained situations. It allows rapid rehabilitation due to reduced surgical time, minimal blood loss and early return to function and activities of daily living.

Keywords: Bicentric; Bipolar; Femur; Fracture; Hemiarthroplasty; Neck; Offset.

Fig. 1

Post-operative AP radiograph of pelvis in 15° internal rotation of lower limbs: (a) uncemented stem and (b) cemented stem designs of the bicentric bipolar hip device.

Fig. 2

a & b. Case examples comparing horizontal offset in postoperative CT scan on bipolar in situ side and contralateral normal hip. Metallic artifact can make offset measurement on implant side difficult. The head and its center are marked by the software. The lateral point is marked by extrapolation from the center of the medullary canal. This is independent of rotation of limb (in radiographs it is rotation dependant).