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. 2025 Jun 4:33:101732.
doi: 10.1016/j.artd.2025.101732. eCollection 2025 Jun.

Mid-Flexion Sagittal Stability of Total Knee Arthroplasty Implanted With Kinematic Alignment: A Quantitative Radiographic Laxity Study With Single-Radius Posterior-Stabilized and Condylar-Stabilized Implants

Lauren K Holbrook  1 , Emma N Horton  1 , David F Scott  1   2
Affiliations

Mid-Flexion Sagittal Stability of Total Knee Arthroplasty Implanted With Kinematic Alignment: A Quantitative Radiographic Laxity Study With Single-Radius Posterior-Stabilized and Condylar-Stabilized Implants

Lauren K Holbrook et al. Arthroplast Today. .

Abstract

Background: Stability between full extension and 90° of flexion is crucial for successful outcomes in total knee arthroplasty (TKA). Thus, we compared the sagittal/anteroposterior (AP) stability of knees implanted with single-radius condylar-stabilized (CS) vs posterior-stabilized (PS) devices from a randomized, prospective study. We hypothesized that the implant group with superior sagittal/AP stability would exhibit better clinical outcomes.

Methods: Sixty-five patients underwent primary TKA with a PS (n = 28) or CS (n = 37) device. Outcomes collected 5-7 years postoperatively included Knee Society (KS) Scores, range of motion (ROM), the Lower Extremity Activity Scale, the Forgotten Joint Score, and mechanical and anatomic alignment. Sagittal/AP stability was evaluated in 45° and 90° of flexion via stress radiographs.

Results: The CS and PS groups averaged 85.8 and 77.3 months post-TKA, respectively, at evaluation. The CS group demonstrated greater mean AP laxity, especially in 45° mid-flexion. Alignment, ROM, and patient-reported outcome scores were similar. However, women in the CS group demonstrated inferior mean KS Function (P = .02) and Total Composite scores (P < .01) compared to women in the PS group. These scores were not significantly different for men or the combined groups.

Conclusions: Mid-flexion sagittal/AP laxity was substantial in both implant groups. With the limited population available, the greater laxity observed in patients with CS implants did not correspond to differences in Forgotten Joint Score, Lower Extremity Activity Scale, ROM, or alignment; however, the difference between the KS Function and Total Composite scores in women revealed an inverse relationship between sagittal laxity and clinical outcomes.

Level of evidence: I.

Keywords: Kinematic alignment; Mid-flexion laxity; Total knee arthroplasty.

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Figures

Figure 1
Figure 1
Participant selection flowchart.
Figure 2
Figure 2
Patients with CS implants exhibited greater mean total anteroposterior (AP) displacement (mm) in 45° and 90° of flexion. Statistical significance was determined by a Student’s t-test. CS, condylar-stabilized.
Figure 3
Figure 3
Condylar-stabilized (CS) implant (a) anterior and (b) posterior displacement at 45° flexion.
Figure 4
Figure 4
Posterior-stabilized implant (PS) (a) anterior and (b) posterior displacement at 45° flexion.
Figure 5
Figure 5
Women with PS implants achieved better mean Knee Society Function Scores than women with CS implants. Statistical significance was determined by a Student’s t-test. CS, condylar-stabilized; PS, posterior-stabilized.
Figure 6
Figure 6
Patients with PS implants achieved better mean total Knee Society Scores than women with CS implants. Statistical significance was determined by a Student’s t-test. CS, condylar-stabilized; PS, posterior-stabilized.
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