Robotic-Assisted Conversion of Unicompartmental Knee Arthroplasty to Total Knee Arthroplasty
Authors: Piuzzi Nicolas S. , Huffman Nickelas , Lancaster Alex , Deren Matthew E. 
Published: December 2024

Background:
Unicompartmental knee arthroplasty (UKA) procedures have become much more common in the United States in recent years, with >40,000 UKAs performed annually
1
. However, it is estimated that 10% to 40% of UKAs fail and thus require conversion to total knee arthroplasty (TKA)
2–5
. In the field of total joint arthroplasty, robotic-assisted surgeries have demonstrated advantages such as better accuracy and precision of implant positioning and improved restoration of a neutral mechanical axis
6–9
. These advantages may be useful in UKA to TKA conversion surgeries, as the use of robotic assistance may result in improved bone preservation.

Description:
Robotic-assisted TKA is performed with the patient in the supine position, under spinal anesthesia, and with use of a tourniquet. A limited incision is made approximately 1 cm medial to a standard midline incision, through the previous UKA incision. A medial parapatellar arthrotomy and partial synovectomy are performed. Array pins are placed in a standard fashion: intra-incisional in the femoral diaphysis and extra-incisional in the distal tibial diaphysis. Femoral and tibial bone registration is performed, along with functional knee balancing to adjust implant positioning. The robotic arm-assisted system is then utilized to achieve the planned bone resections. After completing all bone cuts, trial components are inserted. Trial reduction is then performed, and knee extension, stability, and range of motion are assessed. The final implant is cemented into place. We utilize a cruciate-retaining TKA implant. No augments are required.

Alternatives:
An alternative treatment option is manual UKA to TKA conversion.

Rationale:
Robotic-assisted conversion of UKA to TKA is especially useful for patients requiring bone preservation. For example, 1 case series found that the use of robotic-assisted conversion of UKA to TKA resulted in a decreased use of augments and a smaller average polyethylene insert thickness compared with manual conversion. Furthermore, mechanical bone loss may occur secondary to implant loosening. Thus, in patients with aseptic loosening, robotic-assisted conversion of UKA to TKA may be useful
10
.

Expected Outcomes:
Results of robotic-assisted conversion of UKA to TKA have thus far been excellent. In a study of 4 patients undergoing robotic-assisted conversion of UKA to TKA, all patients experienced uneventful recoveries without any need for subsequent re-revision
10
. In a case report of a robotic-assisted conversion of UKA to TKA, the patient was pain-free at both 6 months and 1 year postoperatively, with a range of motion of 0° to 120° at 6 months and 0° to 130° at 1 year, and excellent component alignment on radiographs at 1 year
11
. In another case report, the patient had full range of motion and a normal, painless gait at 1 year postoperatively
12
. When comparing manual versus robotic-assisted conversion, 1 study found no difference in postoperative range of motion or complications among the 28 patients assessed
13
.

Important Tips:

Ensure accurate soft-tissue balancing prior to implant removal and osseous resection.Augments can easily be cut by executing the initial cut, then moving the resection depth either 5 or 10 mm deeper. The cut is then performed only in the compartment that needs an augment. Augment cutting is usually performed in a stepwise fashion to avoid excessive resection in the other compartments in order to preserve native bone.Having revision implants with increased constraint and metaphyseal fixation available is important during these cases because, as in any revision surgery, unexpected events can lead to the need for other implant choices.

Acronyms and Abbreviations:

UKA = unicompartmental knee arthroplastyRA = robotic-assistedTKA = total knee arthroplastyROM = range of motionCT = computed tomographyPCL = posterior cruciate ligamentDVT = deep venous thrombosisVTE = venous thromboembolism