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IN A NUTSHELL – PROCEDURES & IMPLANTS


Cemented hip replacement:

The acetabular and femoral components are cemented to the bone with a special type of bone cement.

Uncemented hip replacement:

The acetabular and femoral components have a surface finish on the outside (like a porous surface) which allows the components to osseo-integrate with the bone. Usually the components are “press-fit” into the bone but occasionally screws are used to fix the cup.

Alternative bearings:

Bearing surfaces made up of high wear resistance materials including cross-linked poly, ceramics, metal on metal.

Cross-linked poly:

The original poly (plastic) used as a bearing surface is made up of high molecular weight polyethylene. This is one of the weak links in joint replacement as the plastic wear debris can cause tissue reaction (osteolysis), gradually leading to loosening of the implant (aseptic loosening). Different manufacturers are using various techniques to increase the cross-linking between the poly chains and thus improving the wear properties.

 

Ceramics:

In the context of joint replacement, the ceramics are used as bearing surfaces mainly in hip replacements. Modern ceramics (delta ceramics) are very strong and manufactures with high precision and fracture risk of the ceramics are very rare now, although in rare instances it can still occur. Occasionally some patients may also have squeaking.

MOM (metal on metal) bearings:

Although MOM bearing has been used even in the 1960’s, in the past decade MOM bearings have had a renewed interest with advent of modern hip resurfacing. The MOM bearing resurfacing and hip replacement allow larger sized ball to be used in the hip replacement, decreasing the risk of dislocation and probably allow higher activity level. Although the wear rate is minimal, some patients may develop reaction to the metal ions/particles leading to fluid collection in the hip joint and loosening of the implant.

Hip resurfacing:

Considered to be a bone conserving option in younger patients where the femoral neck is preserved (unlike total hip replacement) and the femoral head is merely resurfaced. In addition dislocation rate is almost nil. Has a somewhat higher early failure rate compared to total hip replacement. It is made up of metal on metal bearings. Some people may develop an allergic reaction to the metal and can lead to fluid collection around the hip joint and loosening. Other complication like femoral neck fracture can occur.

Large diameter head THR (anatomical head THR):

The size of the ball in the hip replacement is almost the same size of the patient’s femur. Usually made of metal on metal bearings.  The advantages being almost nil dislocation and possibly better range of motion. Some people may develop an allergic reaction to the metal and can lead to fluid collection around the hip joint and loosening. Recently ceramic on ceramic bearings are also being introduced.

Aseptic loosening:

Often associated with metal on plastic (poly) articulation. The plastic wear debris lead to a foreign body reaction which cause bone loss (osteolysis) leading to loosening of the implants

Periprosthetic fracture:

Fracture occurring either in the  vicinity of the prosthesis. While some of them may occur at the time of surgery, majority occur when the bone becomes weak due to osteoporosis and also due to osteolysis and loosening of the prosthesis. Even when there is no severe pain, it may be appropriate to consider revision surgery if there is a suggestion of impending periprosthetic fracture.

Dislocated hip replacement:

There are many reasons for a hip replacement to dislocate including the component position, patient compliance and the “ball size” . While dislocations as a complication can not be eliminated completely, the dislocation rate could be reduced by accurate component positioning and using larger size ball.

Revision hip replacement:

Done for various reasons including infection, loosening, dislocation etc., This entails more complex surgery with more complex instrumentation and implants than primary hip replacement. With the advances in the technical know-how, instrumentation and implants, revision knee replacements can give fairly reasonable improvement in function.

Trabecular metal:

A porous tantalum structure which has similar porosity of cancellous bone. This is being increasingly used in revision surgery for example revision hip replacement as it has excellent osseo-integration potential.

Total knee replacement:

The femur and the tibia are resurfaced and the femroal and tibial components (metal) are usually cemented in place. A plastic (poly) insert is placed in between the two surfaces (can be fixed or mobile bearing). The patella may or may not be resurfaced with a plastic component.

Unicompartmental knee replacement:

In some patients with isolated medial compartmental arthritis, only that part of the knee joint is replaced preserving the rest of the unaffected joint.

Patellofemoral arthroplasty:

In some patients, the arthritis mainly occurs in the patellofemoral compartment. In those patients a patellofemoral joint replacement could be considered preserving the rest of the knee.

Computer Assisted Surgery:

Use of computer guided navigation to assist the surgeon in performing procedures like knee replacement and hip replacement. This improves the accuracy.

Minimally invasive knee replacement:

Essentially this involves a muscle sparing approach to do the knee replacement. Some studies have shown early functional improvement compared to traditional approach.

Accelerated rehabilitation:

With multi-modal analgesia and appropriate patient education, physiotherapy etc., the rehabilitation can be fast tracked to decrease the length of stay.

 

2 Hours Post Op

Accelerated Rehabilitation

Revision knee replacement:

Done for various reasons including infection, loosening, malposition etc., This entails more complex surgery with more complex instrumentation and implants than primary knee arthroplasty. With the advances in the technical know-how, instrumentation and implants, revision knee replacements can give fairly reasonable improvement in function.

Personalised Knee Replacements:

A very recent technique where a MRI scan of the patients knee along with hip and ankle is done and a computer software creates a 3 dimensional model of the patients knee. The surgeon then preoperatively plans the surgery again using computer software. This plan is then converted into a 3 dimensional plastic template for that specific patient. The surgeon then uses the template to carry out the bone resection as per the preoperative planning without the need for the conventional jigs and thus reducing the chance of “outliers”

Skyline view:

Images the knee cap and the patellofemoral joint. Unfortunately many of the x-ray departments do not do the skyline view routinely when knee x-rays are requested and at least in some instances, when the arthritis is predominantly in the patellofemoral compartment, the x-rays are often reported as showing only early/minimal arthritis in the knee! Only when the skyline view is done the reason for the patients significant knee symptom becomes obvious. Please see an example below.

Calibrated x-rays:

When plain x-rays are done, they are usually magnified (because the beam of the x-ray diverges from the source to the x-ray plate). Surgeons usually template the provisional size of the hip and knee prosthesis prior to surgery. If the magnification factor is not taken into account, the templating will be grossly inaccurate. It is more so with the digital x-rays where the images are resized to fit best in a computer screen. With calibrated x-rays, a radio opaque ball is placed in a appropriate place and this allows the digital templating software to take into account the magnification  factor when templating. Please note that the calibrated x-rays are needed mainly for patients who may need joint replacement. If the GP’s could request calibrated x-rays when they suspect hip or knee arthritis, then a further set of calibrated x-rays could be avoided.  

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