Modular hip hemiarthroplasty for narrow femoral canal – Is it a true Indication?

Ignatius Liew, Khaldoun Bitar, Justin Leong, Nameer Choudry, James Fountain

Background: The modular prosthesis is sometimes favoured for sizing options in narrow femoral canals despite no advantage in clinical outcomes with higher cost for displaced intracapsular femoral neck fractures. This study aimed to investigate factors affecting surgeons’ choice of using modular hip hemiarthroplasty instead of monoblock design and to determine whether it was justifiable.

Methods: All femoral neck fractures from March 2013 to December 2016 were reviewed. Modular hemiarthroplasty performed for a narrow femoral canal were included, with a patient-matched group of patients who had undergone monoblock hemiarthroplasty. Satisfactory lateralisation and alignment of the femoral stem were measured. Patients who received modular hemiarthroplasty were templated on radiographs using TraumaCad for Stryker® ETS design.

Results: A total of 553 hemiarthroplasty were performed, of which 27 were modular hemiarthroplasty performed for narrow canals, with a ratio of modular to monoblock was 1:18. Average head side for monoblock and modular hemiarthroplasty were 46.7mm±3.6 and 44.07±1.5 (p=0.001) respectively. There were 4 malaligned stems in monoblock group versus 14 in the modular group (p=0.008). 18 (7mm±2.9) patients had unsatisfactory lateralisation in the Modular group as compared to 8 (4.7mm±3.9) in the monoblock (p=0.029). 24 patients were classified as Dorr A and B in the Modular group as compared to 18 in the monoblock (P=0.006). 2 (7%) patients who did not achieve 2mm cement mantle on templating.

Conclusion: Patients perceived to have narrow femoral canals intraoperatively should not be immediately converted to a modular implant prior to a thorough check of the position of the implant. Female patients with small femoral head size, Dorr A and B need careful planning. Surgical techniques should be explored through education in achieving lateralisation during femoral stem preparation to avoid prolonged anaesthetic time and achieving cost saving.