Robotic-Arm-Assisted Lateral Unicompartmental Knee Arthroplasty with a Fixed-Bearing Implant.

Background: Approximately 5% to 10% of patients with knee arthritis have isolated lateral compartment arthritis; however, lateral unicompartmental knee arthroplasty (UKA) comprises just 1% of all knee arthroplasties¹. This low proportion is partly because of the perceived complexity of lateral UKA and concerns over implant longevity and survivorship compared with total knee arthroplasty (TKA)^2,3. With an improved understanding of knee kinematics alongside advances in implant design and tools to aid in appropriate restoration of limb alignment, lateral UKA can be an appealing surgical alternative to TKA for certain patients with lateral knee arthritis^4,5. In appropriately selected patients, lateral UKA has been associated with reduced osseous and soft-tissue resection, more natural knee kinematics, less pain, shorter hospitalization, decreased blood loss and infection rates, and excellent survivorship and patient-reported outcomes^6-9.

Description: This surgical approach and technique described for lateral UKA utilizes robotic-arm assistance and modern fixed-bearing implants¹⁰. The specific steps involve appropriate patient evaluation and selection, extensive radiographic and computed-tomography-based preoperative templating, a lateral parapatellar approach, intraoperative confirmation of component position and alignment, and robotic-arm assistance to perform osseous resections to achieve limb alignment and kinematic targets¹⁰. Final implants are cemented in place, and patients typically are discharged home on the day of surgery¹⁰.

Alternatives: Nonoperative treatment for end-stage knee arthritis includes weight loss, activity modification, assistive devices, bracing, nonsteroidal anti-inflammatory medications, and various injections¹¹. Alternative surgical treatments include TKA⁴ and, in certain patients, an offloading periarticular osteotomy¹².

Rationale: Lateral UKA is an appealing surgical option for nonobese patients who have disabling knee pain isolated to the lateral compartment, good preoperative range of motion, and a passively correctable valgus limb deformity^10,13.

Expected outcomes: Patients are typically discharged home on the day of surgery, or occasionally on postoperative day 1 if medical comorbidities dictate hospital monitoring overnight¹⁰. Patients return to light activities, including walking, immediately postoperatively. By 3 months postoperatively, patients will generally have returned to all desired activities⁹. The mid-term outcomes of this procedure, as performed by the corresponding author, have been published recently^14,15. The 5-year survivorship of 171 lateral UKAs was 97.7%, with 72.8% of patients reporting that they were very satisfied with their procedure and 19.8%, that they were satisfied¹⁴. Only 3.8% of patients reported dissatisfaction with their lateral UKA¹⁴. The mean Knee Injury and Osteoarthritis Outcome Score (KOOS) and standard deviation were 85.6 ± 14.3¹⁴. These outcomes did not differ from those observed in 802 medial UKAs, which showed a survivorship of 97.8% and KOOS of 84.3 ± 15.9¹⁴. These findings are generally in line with previously published studies, which have demonstrated excellent survivorship and patient-reported outcomes with fixed-bearing lateral UKA^16-19.

Important tips: Component position and alignment are critical to achieve target knee kinematics.Target postoperative alignment is 1° to 4° of valgus.A meticulous cementation technique is required for optimal fixation and avoidance of excess residual cement in the posterior knee.

Acronyms and abbreviations: ACL = anterior cruciate ligamentAP = anteroposteriorBMI = body mass indexCT = computed tomographyCAT = computed axial tomographyIT = iliotibialKOOS JR = Knee Injury and Osteoarthritis Outcome Score for Joint ReplacementMCL = medial collateral ligamentMRI = magnetic resonance imagingOR = operating roomPFJ = patellofemoral jointpoly = polyethyleneROM = range of motionTKA = total knee arthroplastyUKA = unicompartmental knee arthroplasty.