Computer Assisted Orthopaedic Surgery (Knee)

Computer assisted orthopaedic surgery (CAOS) is a surgical technology that assists surgeons through creation and display of images showing the replacement components in their relationships to the bones and ligaments of the joint being replaced. CAOS is also called Imaged Guided Surgery or Surgical Navigation. CAOS has two basic components:

  1. A special camera designed to see the surgical joint and limb and create a picture or image of the hip or knee
  2. Computer programs which integrate these images with surgical information and assist the surgeon during the operation

CAOS can use actual images of the joint (X-Rays/fluoroscopic, ultrasound or CT images) or can create virtual images of the damaged joint. The camera and computer are given information by the surgeon about the normal and abnormal anatomic landmarks of the joint and limb. This information can be transmitted in several ways. Some CAOS systems use special cameras to identify and record the position of photo reflective spheres or infra-red light emitting devices. Some other systems use ultrasonic devises to identify bony landmarks. The surgeon uses the computer generated information and images to accurately and reproducibly reconstruct the damaged joint and limb.


  • Potential benefits of using CAS/Robotics in joint replacement surgery include:
  • Computer organized and directed surgical work flow
  • Potential improved reliability of sizing and positioning of joint implants
  • Documentation of limb/joint anatomy and deformity
  • Data storage for research and outcome analysis
  • Potential improved accuracy of reconstructed limb length
  • Potential improved accuracy of prosthetic component alignment
  • Potential impact on functional outcomes and implant durability


  • Potential disadvantages of using CAS/Robotics in joint replacement surgery include:
  • Increased time required to perform the operation
  • Increased hospital costs from the additional equipment, software and surgical time
  • Risk of fractures or infections related to the pins and their incisions (wounds) needed to attach the reference arrays to the bones (< 1% complication rate)
  • Potential need for additional imaging before surgery (such as CT scans) to provide landmarks for surgical planning

While these technologies can be used in any patient, it is especially helpful in those patients who have specific bone deformities or have hardware from previous surgeries.
CAS/Robotic surgery can help the surgeon align the patient’s bone and implants with great accuracy. Robotics are currently most commonly used for partial knee replacements, with technologies advancing for total knee and hip replacements and other applications.

For CAS and robotic surgery, anatomic landmarks are registered on the computer and guide the surgical procedure. The same metal, plastic, and/or ceramic implants are used in surgery as replacements without CAS and robots.

Recovery after total hip replacement, total knee replacement, and partial knee replacement after using Computer Assisted Surgery and Robotic Surgery is the same as surgical procedures where they are not used. Please refer to those sections


Hip and Knee Patients

  1. Computer organized and directed surgical work flow
  2. Improved reliability of sizing and positioning of joint implants
  3. Added information about ligament and muscle balancing
  4. Improved documentation of limb/joint anatomy and deformity
  5. Enhanced data storage for research and outcome analysis
  6. Added information during less invasive surgical approaches

Hip Replacement Patients

  1. Improved reliability of reconstructed limb length
  2. Improved reliability of prosthetic component alignment
  3. Fewer prosthetic hip joint dislocations

Knee Replacement Patients

  1. Increased reliability of limb alignment
  2. Decreased surgical trauma by eliminating instrumentation of the canals (hollow centers) of the femur (thigh bone) or tibia (shin bone)

Potential Disadvantages of CAOS for Patients

  1. Increased time required to perform the operation
  2. Additional incisions (wounds) required for attachment of the reference arrays (holding the reflective spheres or emitting devises) attached to the bones about the joint
  3. Increased hospital costs from the additional equipment, software and surgical time
  4. Increased incidence of fractures or infections related to the pins and their incisions (wounds) needed to attach the reflective or emitting devises to the bones (less than 1% reported complication rate)

Potential Complications

Reported CAOS complications are very infrequent (less than 1%). Complications have been reported related to the pins used to attach the photo reflective or emitting devises to the bone. These complications include occasional pin site fractures and pin site infections. If infection involves the new joint this type of problem can be very serious.

What Patients Should Consider

CAOS is an evolving surgical technology. The surgical indications, added values for patients, limitations of the technique and complications are currently being studied. Like any surgical technology, evaluation of the surgeon’s and the surgical team’s knowledge and experience is important. Since CAOS is a recent technology used in total joint replacement surgery, it will take several years to determine if the long term outcomes of CAOS joint replacement patients are improved.

CAOS techniques can be bypassed during surgery if computer malfunction occurs. Anatomical and mechanical references can be used to confirm or substitute for computer based decisions. CAOS has some potential advantages and disadvantages for patients. There are also some important unknown factors and outcomes of CAOS. All CAOS systems work on different assumptions and computer algorithms. The patient should take into consideration the experience of the surgeon and if special training utilizing these systems has been undertaken by their surgeon. These systems rely on accurate input of anatomical and surgical landmarks by the surgeon and are only as accurate as the data that are provided.

Unknown Surgical Factors and Outcomes

  1. Reliability of CAOS techniques by less experienced or infrequent CAOS users.
  2. Impact on overall patient outcomes and patient satisfaction
  3. Impact on prosthetic joint longevity and durability
  4. Decreased frequency of revision surgeries


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