A Comparison between Monoblock and Modular Prosthesis in Hip Hemi-arthroplasty regarding the Development of Intra-Operative Peri-prosthetic Femur Fracture in the Elderly

Introduction:
Hip hemiarthroplasty is considered the treatment of choice for displaced femoral neck fractures in elderly less active patients. Hemiarthroplasty prosthesis can be divided into monoblock and modular. The latter has a variety of stem sizes, neck types, head sizes and lengths, whereas, the variability in monoblock prosthesis is usually limited only to head size. This results in better control of leg length, offset and a more stable fixation for the modular, more expensive prosthesis. An intraoperative periprosthetic femur fracture is an important surgical complication.

Aims:
Our primary aim is to compare between monoblock and modular prosthesis regarding intraoperative periprosthetic femur fractures. Our secondary aim is to assess patient related and surgical technique related risk factors for the development of this complication.

Materials and Methods:
Inclusion criteria included patients older than 65 years of age who had a displaced femoral neck fracture and were operated for hip hemiarthroplasty between the years 2014-2018. Until 12.2015 monoblock hemiarthroplasty was performed in our institute, and since then we switched to modular hemiarthroplasty. Patient specific data was collected retrospectively including age, gender, comorbidities (hypertension, ischemic heart disease and diabetes), pre-injury ambulatory status, duration of surgery, surgical approach, use of modular or monoblock prosthesis, surgeon’s experience and type of anesthesia. In addition, radiographs were reviewed and Dor canal type and Calcar to canal ratio (CDR) were calculated for each patient.

Results:
257 patients were enrolled in the study with an average age of 83.7. 118 patients (46%) had a monoblock prosthesis, while 139 (54%) had a modular prosthesis. A total of 22 patients (8.6%) had intraoperative fractures. Fracture prevalence was significantly higher in the modular group compared with the monoblock group (12.2% vs 4.2%, P=0.025). The majority of patients had a Dor A type femoral canal, while the rest had Dor B type canal (70% vs 30%), there were no patients with Dor C canal. There was no difference in fracture prevalence between Dor A and B canal type patients. We didn’t find more fractures in patients with a CDR higher than 0.62. We didn’t find any significant risk factor for developing an intraoperative periprosthetic femur fracture, neither patient wise (age, gender, and comorbidities) nor surgical technique related (surgical approach, type of anesthesia, and surgeon’s experience).

Discussion:
Intraoperative periprosthetic fracture prevalence was significantly higher in the modular patient group compared with the monoblock group. This may be an important advantage of the monoblock prosthesis over the modular prosthesis. In addition, we didn’t find any significant risk factors for developing an intraoperative periprosthetic fracture neither patient nor surgical technique related.