Planning a Total Knee Revision
3 min read
Case presented by Krishna Tripuraneni, MD Orthopaedic Total Joint Replacement Surgeon at New Mexico Orthopaedics in Albuquerque.
Krishna Tripuraneni, MD is a fellowship-trained orthopaedic surgeon at New Mexico Orthopaedics in Albuquerque, NM specializing in total knee and hip replacement. He uses digital pre-operative planning to prepare all of his total joint procedures and has been using OrthoView for six years.
Establish a surgical plan for a total knee revision
The patient was an 86-year-old woman who was the primary caregiver for her husband and had previously been an active person in the local community. She was experiencing increasing right knee pain and deformity and was unable to walk without the use of a cane. Even mundane daily activities were considerably more challenging as a result of her right knee pain and swelling.
A physical examination revealed antero-posterior and medial instability with 10-degree hyperextension to 90-degree flexion. Due to gross component loosening on radiographs and functional limitations, a revision knee procedure was planned.
OrthoView preoperative planning software
Using the OrthoView preoperative planning solution, the following preoperative considerations were identified and incorporated into the surgical plan:
- It was identified that stemmed components were required for both the tibia and the femur.
- We determined that a tibial augment was required as a result of the varus failure of the tibial component and medial tibial bone loss.
- The offset value provided by the software identified that an offset tibial component was required to avoid an abutment of the cortex by the tibial stem.
- We were able to assess how the pre-operative plan would affect the joint line and determined that it would maintain it reasonably well.
In revision cases, the existing femoral and tibial component positions are ignored, and bony landmarks are used to identify where to place the femoral and tibial preoperative planning tools.
There appeared to be a significant amount of osteolysis in the femur. Metaphyseal cones or allograft were considered for bone stock restoration/substitution, but were eventually not needed.
The pre-operative planning software allows the width of the femur and tibia to be assessed for proper component sizing, which is important as size is the primary focus, rather than angles. Intramedullary guides are used to restore the mechanical axis. Also key with revisions is identifying where the articular surfaces of the revision components would lie, in relation to the shaft. Further, it is helpful to determine pre-operatively the offset of the tibial component (more so than that of the femoral component), as this can help intra-operatively to reduce the need for trialing of various tibial stems.
The tibial AP axis indicates that an offset tibial stem will be needed.
During the templating stage, varying stem sizes are trialed to ensure bony defects will be bypassed by at least two cortical diameters.
Templating on the lateral view permits assessment of the proposed joint line. Augments can readily be added to the distal femur or tibia if the templated polyethylene size is too large, or the joint line is too high or low, based on bony landmarks.
Precision planning for a more predictable patient outcome
Planning this case preoperatively with OrthoView enabled me (Krishna Tripuraneni) to identify several key factors easily: the point at which to stop reaming (to avoid an intraoperative fracture), suitable stem sizes (diameter and length), as well as additional component sizes, the offset requirements for the stem, and the size of stem extension needed to obtain diaphyseal engagement. Digital preoperative planning also made it quick and easy to establish the mechanical alignment of the leg with the use of the SmartKnee Wizard.
- As there was intra-operative hyperextension, tibial augments and a 17 mm polyethylene were used to balance the extension space (in addition to distal femoral augments), which caused the joint line to be raised by a few millimeters.
- A hybrid cementation technique was used for this case.
- The post-operative ROM at the one-year follow up was found to be 0-115 degrees.
Materialise OrthoView is a digital templating solution used by orthopaedic surgeons to create detailed preoperative plans quickly and easily from digital x-ray images. Materialise OrthoView facilitates digital planning and templating for joint arthroplasty and revisions, trauma, limb deformity correction, osteotomy and spinal assessment and is chosen by hospitals worldwide to complete their target of film-free radiology.
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