Functional and Ambulation Outcome after Femoral Neck Fracture Comparison between Monopolar Monoblock versus Modular Bipolar Prosthesis

Background:
Femoral neck fracture or sub capital fracture of the hip is one of the most common fractures at old age. Optimal prosthesis design for femoral neck fractures is still debatable. The theoretical advantages of the development of bipolar hemiarthroplasty (HA) are better range of motion, lower risk of dislocation and less acetabular wear. Our previous study revealed that only small number of patients achieved good or excellent functional and ambulation score using cementless monoblock monopolar for HA of the hip.

Objective:
The aim of this study was to evaluate hip function and ambulation outcome of HA after sub capital fracture using modular bipolar prosthesis (Corin) versus monoblock monopolar prosthesis (cementless Austin Moore).

Methods:
A retrospective study was conducted between 2011-2018 in the orthopedic department at Ziv Medical Center. Two hundred fifty patients with femoral neck fracture underwent hip HA surgery using modular bipolar prosthesis. The surgical approach was anterolateral or posterolateral. Forty-six of the two hundred fifty patients who underwent hip HA using bipolar prosthesis were able to participate and enrolled to this study.

All patients were followed at the out-patient`s clinic and filled a questionnaire about functional and ambulation before fracture and after rehabilitation period.

The functional outcome was divided into four levels, Poor, Fair, Good and Excellent functional ability. The scale of ambulation ability was 1-7 in which 1 is ambulation with no means and 7 is bed or chair ridden.

Our results were compered to our pervious study conducted on Seventy-nine patients who underwent 84 hip HA with cementless Austin Moore prosthesis at Rambam Health Care Campus.

Results:
The use of bipolar prosthesis showed an average of functional score of 27.97 before fracture and 21.34 after the surgery. The average of ambulation ability before the fracture was 2.78 and 4.02 after rehabilitation. All forty-six patients which were operated using the bipolar prosthesis had no complications nor dislocation, infection or periprosthetic fracture.

Our previous study results using monoblock monopolar prosthesis demonstrated average functional score of 22.87 before the fracture and 10.43 after surgery. The average ambulation ability before the fracture and after rehabilitation was 1.62 and 4.29 respectively. Out of the 320 patients, three prosthetic hip dislocated (0.94%), four were (1.25%) infected and five (1.56%) experienced a periprosthetic fracture.

Conclusion:
This study reveals that the majority of the patients that were treated with bipolar HA prosthesis had achieved fair or good functional score and were independent household ambulatory. These results demonstrated better functional results whereas ambulation ability was similar. Thus, we believe that HA using modular bipolar prosthesis should be done for more ambulated active patients whereas monoblock monopolar prosthesis should be reserved only for old debilitated patients