Custom made knees

SUMMARY


  • nowadays, younger and younger patients are presenting needing knee replacements

  • patients' expectations for improvement in function are now higher than in previous years

  • technical advances have been made in knee replacement prostheses

  • the way that the knee moves ('kinematics') is more complex by far than just a simple hinge joint

  • no two patients have exactly the same knee anatomy

  • it is better to make an implant that fits the patient's knee, rather than have to remove additional bone to make the knee match an off-the-shelf implant

  • new custom made partial knee replacement prostheses are now available that match precisely the geometry of a patients knee, that are bone preserving and that are giving excellent functional outcomes


The functional results after hip replacement surgery are excellent, with an increase in sporting activities post-op. The results for knee replacements are excellent, in terms of pain relief, however, the percentage of patients participating in active exercise (as reported in the scientific literature) actually goes down after knee replacement surgery.

 

How a knee really moves

 

There is a very clear reason for this. The hip joint is a simple ball and socket joint, and it is therefore relatively easy to replicate the joint mechanics with an artificial replacement. The knee joint, however, moves in a far more complex fashion. The knee is not just a simple hinge joint; as the knee bends (flexes), the tibia (shin bone) also rotates, and furthermore the tibia also slides backwards slightly (more so on the outer side than the inner side). The way that the knee moves (it's kinematics) is thus highly complex - far from a simple hinge or a ball and socket joint. This complex movement is guided by a number of factors, including the shapes of the bones, the tension in the various ligaments inside and around the knee, and the pull of the muscles.

 

Studies using real-time X-rays watching knee replacement patients walking post-operatively demonstrate that the artificial joints display very different kinematics compared to a normal knee joint, with the artificial joint sometimes sliding, rolling and clunking around quite considerably. This excessive irregular movement can contribute to increased wear and tear in the artificial joint, which may be a factor in early failure of the knee. Also, due to the shape as well as the movements of most artificial knees, post-operatively patients often find it difficult to flex (bend) the knee up fully.

 

Standard knee replacements, to-date, resurface the ends of the femur (thigh bone) and the tibia (shin bone) with metal surfaces, which are stuck onto the ends of the bones with special bone cement. However, in most knee replacements, the shapes of the prostheses do not accurately replicate the contours of the normal knee. In addition, the main ligament in the knee, the anterior cruciate ligament (ACL) gets removed and is not replaced. In addition, with a standard knee replacement the patient's bone is cut to fit the prosthesis, which is off-the-shelf. The more bone is removed, the less remains for solid fixation of the implant, and also the less bone there will be for any potential future subsequent knee operations, such as revision knee replacement (if the first one wears out or fails).

 

 

 

 Knee prior to procedure

 

 Bone cuts for total knee replacement

 

 Total knee replacement prosthesis in place

 

 Total knee replacement

 

The latest developments

 

Personalised knee implants allow noticeably more bone preservation than traditional knee replacement options, so one is able to preserve bone stock for potential future treatment options. The ConformMIS iUni (the "i" stands for individualised) is a unicompartmental knee resurfacing device designed for patients with arthritic damage limited to either the medial or lateral compartment. It provides patients with a range of partial knee resurfacing options in earlier stages of arthritis.

 

 

 iUni cuts

 

 ConforMIS iUni prosthesis

 

 iUni in-situ

 

 X-ray of iUni in-situ (viewed from side)

 

 X-ray of iUni in-situ (viewed from front)


Many patients who receive a total knee replacement today actually have damage in just one compartment. Total knee replacements require your surgeon to remove healthy tissue from all three compartments. In addition, standard implants require your surgeon to choose from a variety of standard sized implants and to cut your bones to fit the implant. ConforMIS has developed the only personalised unicompartmental knee implant designed to conform precisely to your own unique anatomy. Using iFit technology and information from a standard CT scan, ConforMIS creates a personalised implant designed to resurface just the affected compartment in your knee. 

 

 The knee geometry is determined from CT imaging

 

 3D Computerised Design software from ConforMIS is used

 

 Full precise detailed 3D planning is performed

 

 Personalised instruments and prostheses are manufactured for each individual patient that match precisely the size and geometry of the patient's knee.

Personalised implants offer unique advantages versus traditional knee replacement options - because each ConforMIS device is created specifically for you, the implants exactly mirror the surface contours of your knee, providing far more bone preservation. The implants also provide an anatomic fit with less bone cutting than traditional options. Patients with unicompartmental disease are able to preserve their knee for future treatment options and may also experience faster recovery time and reduced post-operative pain than with traditional total knee replacement. In addition, the unique iJig instrumentation can improve alignment and provide a more natural feel to the knee, which can reduce implant wear and extend longevity.

The advantages of the ConforMIS iUni are:-

• Manufactured for each patient, based on their individual anatomy 
• Minimally invasive, minimally traumatic procedure 
• Bone and cartilage preserving 
• Appropriate for young and active patients 
• Potential for less post-operative pain and shorter post-operative recovery 
• Preserves the ability to move to other treatment options in the future

Should you and your surgeon determine that you are an appropriate candidate for a personalised iUni partial knee replacement, your surgeon will arrange for you to have CT scan of your knee, the results of which will be sent to ConforMIS for review and implant production. Your iUni should then be available approximately six weeks from receipt of the scan. The personalised implant will be shipped to your surgeon along with personalised surgical instruments derived from your CT scan, which guide the surgeon in determining the precise placement of your implant.

 

For more information on the ConforMIS iUni, please CLICK HERE