Abstract
The unacceptable failure rate of cemented femoral revisions led to many different cementless femoral designs employing fixation in the damaged proximal femur with biological coatings limited to this area. The results of these devices were uniformly poor and were abandoned for the most part by the mid 1990's.
Fully porous coated devices employing distal fixation in the diaphysis emerged as the gold standard for revisions with several authors reporting greater than 90% success rate at 8–10 years of follow-up. Surgical techniques and ease of insertion improved with the introduction of the extended trochanteric osteotomy as well as curved, long, fully porous coated stems with diameters up to 23 mm. The limits of these stems were stretched to include any stem diameter in which even 1–2 cm of diaphyseal contact could be achieved. When diaphyseal fixation was not possible (Type IV), the alternatives were either impaction grafting or allograft prosthetic composite (APC).
As the results of fully porous coated stems were very carefully scrutinised, it became apparent that certain types of bone loss did not yield the most satisfactory results both clinically and radiographically.
When less than 4 cm of diaphyseal press fit (Type IIIB) was achieved, mechanical failure rate (MFR) was over 25%. It also became apparent that even when there was 4–6 cm. diaphyseal contact (Type IIIA), and the stem diameter was 18 mm or greater, post-op pain and function scores were significantly less than those with smaller diameter stems. This was probably due to poorer quality bone.
Many of these Type IIIA and Type IIIB femurs had severe proximal torsional remodeling leading to marked distortion of anteversion. This made judging the amount of anteversion to apply to the stem at the time of insertion very difficult, leading to higher rates of dislocation. These distortions were not present in Type I and Type II femurs.
This chain of events which was a combination of minimal diaphyseal fixation, excessively stiff stems and higher dislocation rates led to the conversion to modular type stems when these conditions existed.
For the past 8 years, low modulus taper stems of the Wagner design have been used for almost all Type IIIA and Type IIIB bone defects. The taper design with fluted splines allows for fixation when there is less than 2 cm of diaphysis.
The results in these femurs even with diameters of up to 26 mm have led to very low M.F.R.'s and significantly less thigh pain. Independent anteversion adjustment is also a hug advantage in these modular stems. Similar success rates, albeit with less follow-up, have been noted in Type IV femurs.
