Review Question - QID 218152

This patient is an elderly community ambulator with poor proximal femur bone stock (Dorr C femur; illustration A). They are indicated for a total hip arthroplasty and PMMA cement should be utilized to achieve femoral stem fixation (Answer A).

Within the United States, the vast majority of primary total hip arthroplasty (THA) implants are placed using the press-fit technique for both the acetabular and femoral components. Polymethylmethacrylate (PMMA) cement’s biomechanical properties render it highly resistant to compressive loads, but poorly resistant to shearing loads. For this reason, the utilization of cement to achieve acetabular fixation is highly discouraged, as it has been proven to result in significant risk for aseptic loosening (secondary to shearing loads) and poor long-term survivorship. The femoral component is ideally placed to ensure long-term biologic fixation, however, some patients lack adequate bone stock required to achieve this biologic fixation (i.e. Dorr C femurs). Therefore, utilizing PMMA in elderly cohorts with poor bone stock to achieve femoral stem fixation is prudent and has been shown to have equivalent long-term implant survivorship.

Scanelli and colleagues provided an overview of cementing femoral components in hip arthroplasty. They highlight the lower early risk for periprosthetic fractures when cementing hemiarthroplasty implants for elderly femoral neck fractures. The authors report similar risk reduction when cementing femoral implants in elderly (75+ years) elective total hip arthroplasty. They conclude by discussing optimal cementing techniques and how to avoid pitfalls in the operative theatre.

Lindahl provided a short overview of the epidemiology of periprosthetic femur fractures, particularly in Sweden. The author noted the gradual increase in femoral-sided periprosthetic fractures with the introduction of uncemented stems. They further observed an even higher risk for femoral-sided periprosthetic fractures during uncemented revision cases. The author concludes that surgeons should take extra precautions when using uncemented stems in patients with poor bone stock.

Figure A demonstrates AP radiographic imaging of a patient with moderate left-sided hip arthritis, thin metadiaphyseal cortices, and a capacious femoral canal consistent with a Dorr C classification. Illustration A demonstrates the Dorr classification which is often utilized when determining the optimal femoral implant in the setting of hip arthroplasty.

Incorrect Answers:
Answer 2: Cementing the acetabular cup has been shown to have significantly higher rates of revision for aseptic loosening compared to impacted acetabular cups ± screw fixation. Therefore, cementing acetabular cups is no longer recommended.
Answer 3: Femoral-cemented primary total hip arthroplasty is cost-effective with proven optimal long-term survival rates in the older population. While they could be utilized in the primary setting, diaphyseal-engaging femoral implants should be reserved if a need for revision arises in the future.
Answer 4: Mixing more than 1g of antibiotics per 40g bag of cement compromises the mechanical strength of the cement and is not recommended for infectious prophylaxis in primary hip and knee arthroplasty. Mixing up to 4.5g of antibiotics per 40g bag of cement is indicated when placing an antibiotic spacer for the treatment of periprosthetic joint infections.
Answer 5. Even when cementing a femoral stem, the canal should be prepared with broaching to achieve near-maximal implant fit within the metaphysis. Simply cementing the smallest size stem is not advised because this approach risks obtaining a non-supportive cement mantle in weak cancellous bone. Even thinner (2-3mm) cement mantles have adequate structural integrity to handle the compressive forces required.