Saturday, April 27, 2013

Hip Replacement Implant Selection

There are many considerations that go into choosing the best implants for each patient. For most patients I prefer to use the Zimmer Alloclassic Zweymuller stem for the femoral prosthesis. The Alloclassic is a simple, flat-sided, grit-blasted, titanium design that has been around for over 30 years. It has unparalleled results with many studies reporting over 99% survival rate. See product brochure for more information. In addition to having a very high success rate, the Alloclassic is easy to implant and versatile enough to be used in different bone types and anatomic variations. It is implanted using a pneumatic broaching tool called the affectionately known as the "Woodpecker."
Here is a picture of the Alloclassic stem from the Zimmer website:
For the cup I usually use the Zimmer Trabecular Metal (TM) Shell with Longevity Cross-Linked Polyethylene liners. The TM cup grips the bone with an amazing bond and is immediately stable without requiring screw fixation. The Longevity liners have excellent wear characteristics. Here is a picture of the TM cup from the Zimmer website:
For selection of femoral heads, the new generation ceramic designs are far superior to the older metal heads. I use the Biolox Delta Ceramic femoral heads, usually in the 36 mm size. They are tough, smooth, inert, and unlikely to dislocate. Another picture from the Zimmer Website:
These components work very well for my patients and I use them in most cases. There are exceptions. Revision cases often require the use of a fully porous coated stem or modular stems for more complex cases.

Thursday, April 25, 2013

Knee Replacement Implant Selection

I am always asked by patients what implants do I use for knee and hip replacement.

For knee replacement, I most commonly use the NexGen LPS (Legacy Knee Posterior Stabilized) Flex femoral component. This is a high flexion, posterior stabilized design and comes in a "female" and gender neutral design. The "female" design is labeled GSF. I use the cemented version of this component.
For the tibial side, I use the Zimmer NexGen stemmed tibial component with Prolong highly crosslinked polyethylene LPS Flex tibial insert and patella.
The NexGen line of knee implants has an excellent track record and the new additions of the gender specific and high flexion designs have offered more options to match implants to patient anatomy and demands. There have been some issues with products in the NexGen family, specifically with the cementless components and the MIS tibia which I do not use.
Here is a picture of the LPS Flex knee from the Zimmer website:
There are situations when I prefer to use the LPS (non-flex) femoral component. This is sometimes selected for very stiff knees where there is no benefit to the high flexion capabilities. In cases where there is severe deformity with anticipated instability, I will often plan on using the LPS femoral component since it is much easier to convert to a LCCK (Legacy Constrained Condylar) knee system to provide stability to the knee if necessary. 
Here is a picture of the LCCK knee from the Zimmer website:

I will review hip implant selection in my next installment.