Why Computer Imaging May Be Used Prior To Knee Replacement

Successful treatment of knee problems is aided by gathering as much information as possible about the diseased joint before forming a plan of treatment. Patients who are candidates for a knee replacement may have some form of diagnostic imaging performed as part of the process of determining the best implant for their knee. Your orthopedic surgeon has many diagnostic imaging tools available to help evaluate the extent of your disease.

Diagnosing knee problems

Use of x-rays, a CT (computed tomography) scan, or an MRI (magnetic resonance imaging) will help your doctor document the severity of the problem with your knee, assist with planning a course of treatment and if a TKR is necessary, help with determining the specific type of replacement that will be used.1

The initial visit to your surgeon will probably include routine knee x-rays.  Some will be taken while you are lying on a table and others while you are standing, if you are able to do so. Conventional x-rays are most often used to illustrate problems within your knee but do not necessarily show the extent of damage to soft tissue, cartilage and ligaments.2 For that reason, computer imaging may be requested by your doctor for a more detailed and accurate look into your knee. For evaluation of the cruciate and collateral ligaments, the meniscii, and the articular cartilage of the knee, MRI is preferred.3

Arthritis and computer imaging

When a patient has osteoarthritis, a series of x-rays will document damage to bones within the joint and will show areas of cartilage loss. For many patients, this is adequate information for the surgeon to proceed with the knee replacement. In other cases, the surgeon may decide to use additional imaging to identify anatomic changes  due to osteoarthritis. Both CT and MRI scans are useful in evaluating the extent of changes in detail. These imaging tools show your anatomy in cross-sections, like slices of bread. Other abnormalities that may be shown in an MRI include some forms of soft tissue damage. The MRI exam usually takes about 30 minutes.4

In addition to destroying cartilage, osteoarthritis often results in damage to bone structures. This damage may include the growth of bone spurs or osteophytes which can break off and move freely in the knee joint causing pain and the inability to move. Other bone changes that may occur include sclerosis and cyst formations. To best see bone structures in detail your surgeon may request a CT scan. Occasionally in order to evaluate the meniscus, cartilage and ligaments of the knee, this exam is ordered in conjunction with an injection of contrast media into the joint space prior to acquiring the scan. If so, you will most likely be asked to get up and walk around or otherwise exercise your knee after the injection to distribute the liquid in your knee joint. A CT scan is also often ordered for patients unable to undergo MRI studies.

Patient specific instruments and implants

Custom knee implant patient case sequence (Smith & Nephew)

In recent years computer imaging has been used in the development of customized patient instrumentation (CPI) and customized total knee replacement implants in an effort to further improve the precision of surgical technique, implant placement, and alignment.5 This concept may draw upon pre-op imaging studies such as x-rays, MRI or CT scans that are manipulated in software programs to generate virtual three-dimensional models of your knee joint and leg alignment. The digital recreation of your knee is then used to create customized cutting jigs that uniquely fit your anatomy. In some cases the information will be used to create a custom-fitted implant that will replace your natural knee.

iFit® Image-to-Implant™ Technology (ConforMIS)

As far as accuracy of implant positioning and alignment are concerned, studies indicate that the use of pre-op computer imaging and the development of customized patient instrumentation results in a higher incidence of accurate implant alignment than that of traditional TKR alignment methods.5

As with any new medical technology, the use of computer imaging and the development of customized patient instruments and implants is more expensive than traditional methods and implants.5 Computer imaging also may not yet be covered under some insurance policies in the United States. If future studies indicate computer imaging and CPI contributes significantly to increased patient satisfaction and implant longevity the cost-benefit disparity may cease to be a consideration.

Sources

  1. Pavlov, Helene MD, FACR, Radiologist in Chief at Hospital for Special Surgery “Imaging Studies and Knee Replacement Surgery: What You Need to Know” http://www.huffingtonpost.com/helene-pavlov/imaging-studies-and-knee-_b_823925.html
  2. Koplas, Monica MD; Schils, Jean MD; Sundaram, Murali MD,MBBS; The Cleveland Journal of Medicine “The painful knee: Choosing the right imaging test” http://www.ccjm.org/content/75/5/377.full
  3. WebMD “Using MRI to Diagnose Arthritis” http://www.webmd.com/osteoarthritis/guide/mri-diagnose-arthritis
  4. Chester Knee Clinic & Cartilage Repair Centre “Knee Imaging” http://www.kneeclinic.info/knee_imaging.php
  5. Bugbee, William D.; Mizu-uchi, Hideki; Patil, Shantanu; D’Lima, Darryl “Accuracy of Implant Placement Utilizing Customized Patient Instrumentation in Total Knee Arthroplasty” http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3787656/

image credit: ConforMIS

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