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Computer-Assisted Surgical Navigation


Computer-assisted surgery (CAS) of the knee is a new technique used to optimize accuracy. Although CAS joint replacement is identical to the traditional knee replacement, in many ways, exposure and time are fundamentally different. Computer systems are designed with a variety of different applications and qualities. CAS systems require fixing frames around the knee to the lower femur (above the knee) and upper tibia (below the knee). These reference frames are applied to the bone by small pins. Knowing where the positions of the surgical instruments and anatomy during surgery allows the system to make an accurate calculation as well as predictions about all important aspects of the knee replacement surgery, including size, position, alignment, motion, and ligament balance.


Why Surgeons Carry Computers to Operations

A recent meta-analysis combined study has shown two important outcomes after 10 years of use of (CAS) Computer assisted surgery. The first and most important is the absence or reduction in blood loss in CAS. By not violating the cortex of the bone as above describes, the reduction to virtually no transfusions and bloodless surgery is able to be accomplished. The indirect result of this is a slight improvement in outcomes and functions, shorter length of stay, and a measurable improvement in early functional results. The second is an offshoot of the accuracy. It has been now shown by a combination of all of the articles collected over the last 10 years that navigation improves accuracy. When new products and technologies are backed up with this plethora of literature, one can rest assured that that technology is here to stay and there is benefit to using it.

  1. Tomek, , et al, Early Patient Outcomes After Primary Total Knee Arthroplasty with Quadriceps-Sparing Subvastus and Medial Parapatellar Techniques, J Bone Joint Surg. Am 2014;96:907-15
  2. Moskal, et al, Navigated versus Conventional Total Knee Arthroplasty, J Knee Surg. 2014;27:235-248
  3. Cip, et al, Conventional Versus Computer-Assisted Technique for Total Knee Arthroplasty; A minimum of 5-Year Follow-up of 200 Patients in a Prospective Randomized Comparative Trial, J. Cip et al./ The Journal of Arthroplasty 29 (2014) 1795-1802
  4. Merz, et al, Perioperative Differences in Conventional and Computer-Assisted Surgery in Bilateral Total Knee Arthroplasty, Am J Orthop. 2014;43(6):256-261
  5. Lionberger, et al, Patient Specific Instrumentation, The Journal of Arthroplasty 29 (2014) 1699-1704.

Revised 1/20/15

David Lionberger, MD

CAS provides numerous additional advantages beyond accuracy. For example, in older traditional knee replacements, alignment bars and rods are used to align the end of the thigh bone (femur) by pushing metal rods into the bone to gauge alignment. Many of the complications from knee replacement surgery are an indirect result of this maneuver in that they increase the bone pressure producing microembolism of the bone marrow, which may force air and/or fat into the circulatory system. Microembolism is often a subtle problem that can cause temporary confusion, mild breathing trouble, and occasionally respiratory distress following surgery. If these symptoms can be eliminated or at least reduced by the use of the CAS system, while not sacrificing accuracy, it is felt that this may lessen some postoperative complications.

Why is Accuracy Essential?

There are many reasons for why accuracy in performing total knee replacements (TKR) is important. First and foremost, the properly replaced knee when done precisely is more likely to perform better. To the owner, this has obvious ramifications which start the day of surgery. The knee replacement will function better, rehab better, and feel better. However, an even more important aspect of accuracy is the longevity of the implant. Simply speaking, inaccuracy begets failure. If a knee replacement is placed in proper alignment and orientation, it is likely that it will last longer. Even though a TKR may feel and function properly for many years, there is ample evidence in the medical literature of premature failure in improperly aligned TKR. For example, if an alignment is off by more than 3ยบ, there is double the amount of load on the plastic insert. As time goes on, the history of revisions in TKR suggest that at least 25% of failures occur as a result of malalignment.

Surgeons are only human and as such, are subject to their own set of inaccuracies. Even though many orthopedic surgeons specializing in joint replacement perform hundreds of TKRs per year, 20% of the time, we miss the exact alignment despite our best efforts. This is where CAS comes to the rescue. It can reduce (but not eliminate) the inaccuracy to about 5-8% instead of 20%. It makes us better surgeons. Despite countless articles supporting CAS in reducing surgical errors, the insurance companies and Medicare still do not reimburse surgeons for either the extended time and effort or the cost of supplies. Herein lies the ethics lesson; the best time to get a total knee correctly is the first time. As such, I will always encourage (but not force) patients to use navigation in every total knee replacement because I believe it to be the best for my patients. There is however, a fee of 629.00 dollars required before surgery. Medicare and insurance companies do not pay for this service so the patient can elect to use CAS as an option for their replacement. Until then, generosity and grants for research are what keep this technology available.

Total Knee Replacement

Written by David R. Lionberger, MD, 2006

Revised by David R. Lionberger, MD, 2010