JOA - 2026-03-30 - Journal Article
Patello-femoral Tracking Optimization in Robotic-Assisted Total Knee Arthroplasty.
Reddy H, Di Gangi C, DeGuzman G, Schaffer O, Rozell JC, Hepinstall MS, Meftah M
Topics
Key Takeaway
All three patella-related complications (including two reoperations) in 932 RA-TKA cases occurred exclusively in the valgus-internal rotation femoral component cohort (Val-IR, 15% of cases), despite no significant difference in KOOS JR or PROMIS scores at one year across alignment groups.
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Summary
This study examined the effect of femoral component rotation (internal vs. external relative to TEA) and coronal alignment (varus vs. valgus) on patellar tracking complications and PROMs in 932 CT-based RA-TKA cases using a single-radius femoral component with a 6° trochlear sulcus angle. Cases were stratified into four groups: Var-ER (48%), Val-ER (26%), Var-IR (11%), and Val-IR (15%), with mean femoral rotation ranging from 2.8° ER to -1.0° IR. All three patella-related complications occurred in the Val-IR cohort (P<0.001), while KOOS JR at 6 weeks was lowest in Var-ER (52.3, P=0.039), but no significant PROMs differences persisted at 3 months or 1 year.
Key Limitation
With only three patella-related complications, the study is critically underpowered to define a quantitative internal rotation threshold or valgus magnitude beyond which patellar complication risk becomes unacceptable.
Original Abstract
BACKGROUND
Robotic-assisted total knee arthroplasty (RA-TKA) allows for intraoperative component positioning to personalize alignment and gaps. However, traditional trochlear designs not optimized for patellar tracking in kinematic alignment result in femoral internal rotation relative to the surgical transepicondylar axis (TEA). We sought to determine the femoral component alignment's effect on patellar tracking in RA-TKA.
METHODS
We retrospectively reviewed 932 RA-TKA cases performed from January 2023 to August 2024 using a computed tomography (CT)-based robotic platform with a single radius femoral component with a 6° trochlear sulcus angle. Femoral rotation was defined as internal (IR) and external (ER) relative to TEA. Femoral coronal alignment was defined as varus (Var) or valgus (Val) relative to the mechanical axis. Patient-reported outcomes were collected at six weeks, three months, and one year postoperatively. Outcomes were analyzed using one-way analyses of variance and Chi-square tests.
RESULTS
There were 445 (48%) Var-ER, 242 (26%) Val-ER, 105 (11%) Var-IR, and 141 (15%) Val-IR cases. Mean femoral component rotation (° external) was Var-ER: 2.8° (range, 0.2 to 6.5); Val-ER: 2.4° (range, 0.1 to 5.0); Var-IR: -0.6° (range, -3.4 to 0); and Val-IR: -1.0° (range, -4.2 to 0). There were three patella-related complications, two of which had further reoperations, all of which occurred in the Val-IR cohort (P < 0.001). Knee Injury and Osteoarthritis Outcome for Joint Replacement (KOOS, JR) at six weeks was lowest in the Var-ER cohort (52.3, P < 0.039). Planned femoral IR had no statistically significant impact on three-month and one-year KOOS, JR scores; there were no differences in Patient-Reported Outcomes Measurement Information System (PROMIS) scores at postoperative intervals studied.
CONCLUSION
Planned femoral IR was not associated with statistically significant differences in patient-reported outcomes beyond six weeks postoperatively. However, all patella-related complications occurred in the Val-IR cohort. We caution surgeons against placing excessive combined valgus and IR with femoral implants designed with narrower trochlear sulcus angles.