Direct Anterior Hip Replacement - Dr. Nasar

I recently performed a direct anterior hip replacement. This is a new approach to hip replacement that preserves the muscles. It usually allows very rapid return of function and patients do not have to worry about dislocation. They can bend over right after surgery without a problem.

Anatomy of the Hip Joint
By Smith & Nephew (Smith & Nephew) [FAL], via Wikimedia Commons

The direct anterior approach uses a small (4") incision in front of the hip. This approach is known for quicker recovery.

Severely Bowed Knee - Complex Knee Replacent with LCCK & Stems

I have come across a few patients recently where their knee arthritis was so severe and has gone on so long that their legs have become severely deformed. In these cases, standard knee replacement implants will not work properly. The ligaments that hold the knee in place can get stretched out in severe cases and when the deformity is corrected and the leg is straightened, the ligaments become incompetent.
In these cases, a constrained type of knee replacement implant must be used. Constrained implants have larger internal supports that hold the implant together and have stems or rods that anchor the implants deep within the bone so that they can absorb the increased forces necessary to hold the knee together. I personally use the Zimmer NexGen LCCK system for these cases.

Here are before and after radiographs (x-rays) of a recent case:

Severely bowed knee with advanced arthritis

Post-operative x-ray showing knee replacement with constrained LCCK implants. 

As you can see in the second set of x-rays, the angulation (deformity) has been corrected with this stemmed implant. It has been one month since surgery and he is doing exceedingly well.

Facebook Groups for Hip Replacement NJ and Knee Replacement NJ

I recently created Facebook groups for patients who are interested in hip and knee replacement surgery to join and share information with each other and to ask questions about surgery and the recovery process.

·         Knee Replacement: https://www.facebook.com/groups/KneeReplacementNJ/

·         Hip Replacement: https://www.facebook.com/groups/HipReplacementNJ/

Feel free to join and share.

How are Hip Implants attached to Bone? Do you use Glue?

The bonding of hip joint replacement parts to bone is very important to the success of the surgery. Patients are often interested in how this is accomplished. This topic has been highly researched in orthopedic journals for many years. Historically, bone cement (poly methyl methacrylate) was used to glue the parts of hip implants to bone.

Methyl-methacrylate By Jynto and Ben Mills [Public domain], via Wikimedia Commons

In general, bone cement is very successful when used as a bonding agent. It needs to be properly prepared and pressurized into the bone and it works well. More recently, researchers have concluded that bone cement can break down over time in active patients. At the same time, orthopedic engineers have designed implants that have a roughened surface that bonds directly to bone without the use of cement. As a result, the orthopedic community has gradually shifted to the use of cement-less,  porous coated implants for hip replacement.
Both the cup and the stem are usually implanted in what we call a "press-fit" manner. That means that the prosthesis is just a little bit larger than the opening in the bone. When the implants are impacted into position, they jam into place and have enough roughness and surface friction that they stay in place and are immediately stable. Usually a patient can put their full weight on the hip immediately after surgery without concern for the implants coming loose. Here is a hip replacement x-ray.

X-ray showing a total hip implant placed without cement or screws. Note that the metallic prosthesis is in direct contact with the bone.

Next I will cover the use of bone cement for knee replacement.

What is a Hip Replacement implant made of? Titanium?

Patients are often curious as to what hip replacement implants are made of. This is an important topic since there are certain materials that have proven to result in long-lasting, well functioning hip replacements. Patients often guess that the prosthesis is made of titanium and they are partially correct. Modern hip replacements generally do have at least some titanium parts. Hip replacements are usually made up of four component parts, each of which can be made of a different material.
1. Cup or Acetabular component - usually made of Titanium or Tantalum both of which are porous and integrate well with bone
2. Liner - Polyethylene which is very resistant to wear
3. Head or Ball - Ceramic heads are the best for longevity, Cobalt Chrome can also be used
4. Stem or Femoral prosthesis - Titanium or other porous or roughened metal that allows bone to attach

Here is a diagram:

Next we will discuss the use of bone cement in joint replacement surgery.

What material is a Knee Replacement made of? Titanium?

Another question that I get asked all the time has to do with what the knee replacement implants are made of. Patients often guess that it is made of titanium.

By Pumbaa (original work by Greg Robson) (Application: (generated by script)) [CC-BY-SA-2.0-uk (http://creativecommons.org/licenses/by-sa/2.0/uk/deed.en)], via Wikimedia Commons

The answer is yes, some parts of knee replacements are made of titanium, however, it is more complicated than that.
A knee replacement usually contains four separate parts that are combined. From top to bottom the components are:
1. Femoral component - usually made of Cobalt Chrome
2. Patella component - usually made of Polyethylene
3. Tibial insert - Polyethylene
4. Tibial tray - Titanium or Cobalt Chrome

Here is an illustration:

The reason for the different materials is simple. Metal can not rub on metal so there needs to be polyethylene wherever motion is occurring  The patella rubs on the metal femoral prosthesis, so it is made of polyethylene. The Femoral prosthesis rotates on the tibial insert so the insert is also made of polyethylene. The parts that attach to bone are metal. The reason why the femoral prosthesis is made of cobalt chrome is because it is hard and smooth and therefore causes a low rate of wear. The tibial tray component can be made of either titanium or cobalt chrome since it is not part of the joint, there is no movement involving the tibial tray, it supports the liner and sits on the bone. Titanium is often preferred for metals that come in contact with bone because it is less stiff and more bio-compatible.
I will review the components of a hip replacement implant next.

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.

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: www.Zimmer.com

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.

Outpatient joint replacement, expedited recovery

I recently went to see Mark Hartzband talk in Red Bank about outpatient joint replacement in a surgery center. I missed the first half and he was so kind to send me the PowerPoint file. I don't think outpatient surgery for joint replacement is right for everyone, but in select cases it can be done successfully.

At CentraState, through our Joint Center, we have implement many advancements over the last few years to speed up the recovery process and shorten the hospital stay. We have been using a cocktail of peri-operative medications combined with spinal anesthesia, nerve blocks, intra-operative anesthetic injections, minimally invasive surgery, and a rapid recovery protocol. It seems that Dr, Hartzband is having success with Decadron IV given in the OR and that has been added to our protocol.

We have been using IV Ofirmev (acetaminophen) quite successfully at CentraState and we have been able to cut down on narcotic usage by eliminating the PCA. This has resulted in much fewer issues with post-op nausea and our patients are recovering faster. At this point most patients under 70 years old should be able to be discharged to home in 1-2 days after surgery.