Related Experiment Video
Updated: Apr 7, 2026
In Vitro Application of a Wireless Sensor in Flexion-Extension Gap Balance of Unicompartmental Knee Arthroplasty
Published on: May 5, 2023
Sagittal Femoral Component Flexion in Primary Total Knee Arthroplasty: Is There a Clinically Relevant Inflection
Ozan Altun1, Süleyman Albayrak1
1Department of Orthopedics and Traumatology, Cankiri State Hospital, Cankiri, Turkey.
Background:
The purpose of our study was to determine whether sagittal malalignment of the femoral component after primary total knee arthroplasty (TKA) has a flexion threshold beyond which postoperative clinical outcomes deteriorate.
Methods:
This retrospective cohort included 235 consecutive primary TKA patients operated on by a single surgeon with at least 12 months of follow-up. All procedures were performed using a conventional manual instrumentation technique. All knees received the same cemented, posterior-stabilized implant. Femoral component flexion was measured on standardized lateral radiographs as the angle between the long axis of the component and the distal femoral mechanical axis. Patients were categorized into low (0 to 2.5°), medium (2.6 to 5.5°), and high (5.6° or greater) flexion groups. At 12 months, pain, function, and patellofemoral symptoms were evaluated using the visual analog scale, Western Ontario and McMaster Universities Osteoarthritis Index, Knee Society Score, Kujala score, and a four-point satisfaction scale. Group comparisons and regression analyses, including nonlinear and piecewise models with a knot at 6°, were performed.
Results:
Medium flexion produced the most favorable outcomes, whereas excessive flexion was associated with significantly higher pain, worse Western Ontario and McMaster Universities Osteoarthritis Index score and Knee Society Score, and lower satisfaction. Spline regression demonstrated no meaningful change in outcomes between 0 and 6°, but greater than 6°, each additional degree of flexion resulted in progressive deterioration, particularly in patellofemoral function. Flexion angle remained associated with anterior knee symptoms after adjustment for age, body mass index, and follow-up duration.
Conclusions:
Sagittal femoral component flexion was independently associated with patellofemoral symptoms and showed a significant nonlinear relationship with postoperative pain and functional outcomes after primary TKA in a single-surgeon series using a single posterior-stabilized implant design. A mid-range flexion of approximately 3 to 5° appears safest, while flexion greater than 6° represents a clinically relevant inflection point beyond which clinical outcomes decline.
Level Of Evidence:
Level III.
More Related Videos
08:15Three-Dimensional Preoperative Virtual Planning in Derotational Proximal Femoral Osteotomy
Published on: February 17, 2023
09:51The Transition to an Anterior-Based Muscle Sparing Approach Improves Early Postoperative Function but is Associated with a Learning Curve
Published on: September 7, 2022
Related Concept Videos
01:23Knee Joint
A total of seven ligaments support the knee joint. The patellar ligament, which is also attached to the quadriceps femoris...
01:16Bones of the Lower Limb: Femur and Patella
01:23Muscles that Move the Leg
Anterior Compartment
The quadriceps femoris, the most visible muscle of the anterior compartment, is integral for leg extension and thigh flexion. It is formed by merging four distinct muscles — the vastus lateralis, vastus medialis, vastus intermedius, and rectus femoris. The quadriceps tendon, a shared tendon of the four quadriceps muscles, is affixed...