R.Du Hyun RoOrthopedics & Research
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TKAroboticsrestricted kinematic alignmentjoint linegap balancePROMs

2026 · Journal of Arthroplasty

How Are Alignment Changes and Intraoperative Medial and Lateral Gaps Related to 1–2-year Patient-reported Outcomes in Robotic rKA TKA?

Smaller changes in HKA and LDFA were associated with higher 2-year Knee Society Knee Scores (P = 0.001 and 0.013).

Research structure

  1. 01
    Subject

    TKA 69 cross-retaining robot assist implemented with the rKA protocol.

  2. 02
    Methods

    A retrospective cohort analyzed robot-recorded medial and lateral gaps in extension and flexion, and pre- and postoperative HKA, LDFA and MPTA measured with deep learning. Multivariable ANCOVA and ROC analysis assessed associations with 1–2-year PROMs.

  3. 03
    Reported Results

    Smaller changes in HKA and LDFA were associated with higher 2-year Knee Society Knee Scores (P = 0.001 and 0.013).

An explanatory schematic separating the study population, methods, and results. It is not an original paper figure.

Evidence & Original Source

Abstract commentary

Participants and Methods

A retrospective cohort analyzed robot-recorded medial and lateral gaps in extension and flexion, and pre- and postoperative HKA, LDFA and MPTA measured with deep learning. Multivariable ANCOVA and ROC analysis assessed associations with 1–2-year PROMs. TKA 69 cross-retaining robot assist implemented with the rKA protocol.

Main Findings

Smaller changes in HKA and LDFA were associated with higher 2-year Knee Society Knee Scores (P = 0.001 and 0.013). Larger extension lateral gaps (ELG) were associated with higher 2-year FJS (P = 0.001). Larger flexion medial gaps (FMG) were associated with lower WOMAC pain and stiffness scores (P = 0.011 and 0.002). Exploratory ROC thresholds were ΔLDFA < 2.3° (AUC 0.622), ΔHKA < 8.4° (AUC 0.541), ELG ≥ 3.0 mm (AUC 0.658) and FMG ≥ 1.5 mm (AUC 0.716). No revisions occurred.

The point of reading on surgery

The findings support examining femoral joint-line changes together with extension lateral and flexion medial laxity in rKA. They raise a different question from targeting fully symmetrical gaps, but do not establish a causal benefit of an optimal gap.

Limitations

This retrospective study included 69 cases and only early follow-up results. Limited ROC discrimination prevents these cutoffs from being established as universal surgical targets. The authors also called for larger cohorts and longer-term validation.

Let's put it briefly.

What did this study confirm?

Smaller changes in HKA and LDFA were associated with higher 2-year Knee Society Knee Scores (P = 0.001 and 0.013).

Can it be applied directly to individual patients' treatment decisions?

This retrospective study included 69 cases and only early follow-up results. Limited ROC discrimination prevents these cutoffs from being established as universal surgical targets. The authors also called for larger cohorts and longer-term validation.

Keywords

Abstract · Original text

Do Weon Lee, Du Hyun Ro, Hyuk-Soo Han. Limited Femoral Joint-Line Alteration and Preserved Extension Lateral Laxity Enhanced Early Outcomes in Restricted Kinematic Alignment Total Knee Arthroplasty. The Journal of arthroplasty. 2026:S0883-5403(26)00519-X. doi:10.1016/j.arth.2026.05.029.

BACKGROUND

Restricted kinematic alignment (rKA) total knee arthroplasty (TKA) seeks to restore native alignment while limiting excessive correction. The influence of alignment change magnitude and intraoperative gap characteristics on early patient-reported outcome measures (PROMs) after robotic rKA TKA remains unclear.

METHODS

This retrospective cohort study included 69 robotic-arm-assisted cruciate-retaining TKAs performed using an rKA protocol. Intraoperative medial and lateral extension and flexion gaps-extension medial gap, extension lateral gap, flexion medial gap (FMG), and flexion lateral gap-were recorded automatically. Preoperative and postoperative hip-knee-ankle (HKA) angle, lateral distal femoral angle (LDFA), and medial proximal tibial angle were measured using a validated deep learning model. Multivariable analyses of covariance evaluated associations between demographics, baseline alignment, alignment changes, gap characteristics, and PROMs at one and two years.

RESULTS

All PROMs improved postoperatively. Smaller changes in HKA and LDFA were independently associated with higher two-year Knee Society Knee Scores (P = 0.001 and P = 0.013). Greater ELG was associated with a higher two-year Forgotten Joint Score (P = 0.001), whereas greater FMG was associated with lower two-year Western Ontario and McMaster Universities Osteoarthritis Index pain and stiffness scores (P = 0.011 and P = 0.002). Receiver operating characteristic analyses identified changes in LDFA less than 2.3° (area under the curve [AUC] 0.622) and changes in HKA less than 8.4° (AUC 0.541) as thresholds associated with higher Knee Society Knee Score. An ELG ≥ 3.0 mm predicted higher Forgotten Joint Score (AUC 0.658), and FMG ≥ 1.5 mm predicted lower Western Ontario and McMaster Universities Osteoarthritis Index stiffness (AUC 0.716). No revisions occurred.

CONCLUSIONS

In robotic cruciate-retaining rKA TKA, minimizing femoral joint-line alteration and preserving controlled lateral extension laxity, along with mild medial flexion laxity, were associated with modestly improved early outcomes. These findings are exploratory and require validation in larger cohorts with longer follow-up.

Read abstract on PubMed

The original paper.

Limited Femoral Joint-Line Alteration and Preserved Extension Lateral Laxity Enhanced Early Outcomes in Restricted Kinematic Alignment Total Knee Arthroplasty

Do Weon Lee, Du Hyun Ro, Hyuk-Soo Han
Journal of Arthroplasty · 2026

DOI · 10.1016/j.arth.2026.05.029PubMedBased data
The first one examined.