A Randomized Controlled Trial of the Difference in Sagittal Angle of the Lower Limbs Between Healthy Individuals and Patients With Osteoarthritis

I. Clinical Research Background As China enters an aging society, the elderly population is increasing, leading to a rise in knee joint disease patients. Total knee arthroplasty is an effective treatment for joint disorders, alleviating knee pain, restoring function, and improving quality of life.The objectives of total knee arthroplasty are to relieve pain, restore function, and ensure a long-lasting implant. Achieving good alignment is crucial for patient recovery after total knee arthroplasty. The alignment of the lower limb in the sagittal plane is important for assessing whether the limb is extended or not, which also guides the sagittal alignment during TKA. Currently, there is limited research on the sagittal alignment of the lower limb, and there is no clear definition of whether the lower limb should be extended in this plane. Additionally, existing studies lack a clear method for assessing sagittal alignment in both normal individuals and patients with OA. Consequently, there is an urgent need to establish a classification standard for sagittal alignment of the lower limb, applicable to clinical and TKA surgical evaluations.

II. Content of Clinical Trials (I) Overall Design and Sample Size This study is a prospective clinical investigation, encompassing two groups: ① Healthy Group: Non-osteoarthritis (OA) patients who underwent sagittal plane EOS examinations at the People's Liberation Army General Hospital between September 2024 and September 2026. ② OA Group: OA patients who underwent sagittal plane EOS examinations at the same hospital from September 2024 to September 2026. The sagittal alignment angles on the EOS radiographs of the subjects were measured to establish a classification system for extension or non-extension.

(II) Randomization and Control in the Study Randomized controlled trial. (III) Content From September 2024 to September 2026, at the Chinese PLA General Hospital, a cohort of 200 non-lower limb-related non-osteoarthritis (OA) patients who underwent sagittal plane EOS imaging was studied. Basic demographic data, including age, weight, and height, were recorded. An experienced researcher measured angles such as the modified mechanical axis angle, femoral anterior bowing angle, and tibial plateau posterior slope angle. The collected data underwent statistical analysis to determine the 95% normal distribution ranges for these angles, thereby establishing the sagittal plane ranges for 'extension,' 'overextension,' and 'extension-limited' in the knee joint. Additionally, 200 OA patients attending the director's outpatient clinic were measured by the researcher and taken to the radiology department for sagittal plane imaging according to the established EOS requirements. The same three angles were measured and recorded, and the aforementioned classification was used to assess whether the OA patients were in extension or not. The differences between the two groups were then compared.

III: Trial Procedure (I) Subject Enrollment Physicians selected subjects who underwent EOS imaging at our hospital from September 2024 to September 2026, and screened them based on inclusion and exclusion criteria. If a patient met the inclusion criteria, the details of the research project were thoroughly explained to them, and they were required to sign the relevant informed consent form.

(II) Methodology Subjects who met the inclusion criteria and underwent sagittal EOS examinations at the Radiology Department of the First Medical Center of the Chinese PLA General Hospital from September 2024 to September 2026 were included in the study. Imaging data were collected under the following conditions: ① the radiographer stood on one leg; ② the two femoral condyles coincided on the lateral radiograph. Basic demographic information, including age, weight, and height, was recorded. An experienced researcher measured angles such as the modified mechanical axis angle, femoral anterior bowing angle, and tibial plateau posterior slope angle. The obtained data were subjected to statistical analysis to determine the 95% normal distribution range values for these three angles, thereby establishing the angular ranges for "extension," "hyperextension," and "limited extension" of the knee joint in the sagittal plane. A total of 200 OA patients attending the outpatient clinic of director were measured by the researcher, who then brought them to the radiology department to undergo sagittal radiography according to the established EOS imaging requirements. The same three angles were measured and recorded, and the aforementioned classification was used to evaluate whether the OA patients were in extension or not. The differences between the two groups were compared.