A retrospective case‒control study approved by the institutional review board was conducted among patients who had undergone total knee arthroplasty at our hospital. The clinical data and soft tissue data on preoperative anteroposterior and lateral X-rays of the knee joint collected before knee total knee arthroplasty were compared.
Patients: We reviewed the clinical databases of multiple medical centers at our hospital and collected data on total number of knee replacement surgeries performed at all medical centers from January 2019 to December 2020. The age of patients at the time of reoperation was limited to 65–80 years to reduce the impact of age on knee prognosis. As a result, we collected a total of 1263 total knee replacements performed on 1045 patients and followed them for 20 to 44 months, with a follow-up deadline of August 2022. Patients who had incomplete medical records, incomplete height and weight data that could not be used to calculate BMI data, or who could not be tracked during follow-up were excluded. The remaining 964 patients underwent 1141 total knee replacements. The imaging data of the patients were examined. Patients who participated in the data collection were required to have anteroposterior and lateral views of the knee joint collected within one year before surgery at the corresponding medical center. The images could be recognized and accurately measured in the Any image viewing system or Uniweb image viewing system. All anteroposterior and lateral views of the knee joint had markers to accurately adjust the zoom ratio of the image to accurately measure the thickness of bones and related soft tissues. All patients who did not meet the above imaging requirements could not be included in the study. At this point, we still had a total of 761 total knee replacements performed on 625 patients included in the study. [Figure 1]
Control:
All patients included in the study underwent total knee replacement surgery performed by joint surgeons with more than 10 years of experience who had completed more than 150 total knee replacements. All patients included in the study successfully completed the surgery and were discharged after meeting the discharge requirements. 1. Patient characteristics at admission, including sex, height, weight, past medical history, ASA score, and side of surgery, were collected. 2. Patient age at surgery and imaging data taken within one year before surgery were collected. The imaging data included measurable anteroposterior and lateral views of the patient’s knee joint. The image size is calibrated using a 30 mm or 50 mm marker recorded on the image when the image is taken. The patient’s knee joint was flexed at 10°-40° when taking the lateral view. The Medcom AnyPacs2.0 system or EBM technologies Uniweb Server system can be used for accurate measurement.
The thickness of bones and related soft tissues is accurately measured. The measurements included the following: 1 Anterior femur subcutaneous tissue thickness. On the lateral view of the knee joint, the upper edge of the femoral condyle was located, and the thickness was measured 3 cm above the upper edge of the femoral condyle to locate the measurement section. The distance from the surface of the quadriceps to the surface of the skin on the measurement section was measured and defined as the thickness of the anterior femur subcutaneous tissue. 2 Anterior tibia soft tissue thickness: On the lateral view of the knee joint, the tibial tuberosity was found, and the distance from the surface of the tibial tuberosity to the skin, defined as the anterior tibia soft tissue thickness, was measured. 3 Antepatellar soft tissue thickness: On the lateral view of the knee joint, the midpoint position on the anterior surface of the patella was located, and a perpendicular line was drawn through it. The distance from this perpendicular line from the midpoint on the surface of the patella to the skin was measured and defined as the antepatellar soft tissue thickness. 4 Patellar bone thickness: There are many bone spurs on the patella, but bone spurs only play a stabilizing role in joint movement in the extension area. Therefore, on the lateral view of the knee joint, the solid thickness at the midpoint of the anterior surface of the patella was measured. 5 Medial knee subcutaneous tissue thickness: On the anteroposterior view of the knee joint, the midpoint on the medial side of the femoral condyle was located as a plane, and the distance from the upper surface of the medial collateral ligament to the skin on the medial side of the knee joint on this plane, defined as the medial knee subcutaneous tissue thickness, was measured. 6 Femoral condyle width: On the anteroposterior view of the knee joint, bone spurs were removed from the femoral condyles, and the line between the midpoint on the inner edge of the medial femoral condyle and the midpoint on the outer edge of the lateral femoral condyle, defined as the width between the two femoral condyles, was measured. 7 Antepatellar soft tissue ratio: The ratio of the antepatellar soft tissue thickness to the patellar bone thickness on the left or right lower limb image of the patient. 8 Medial knee tissue to femoral condyle ratio: The ratio of the thickness of the medial knee subcutaneous tissue to the width of the femoral condyle on the left or right lower limb image of the patient. [Figure 2] The first six imaging data points were measured for each patient and then calculated to obtain the latter two ratios.
3. Postoperative readmission and reoperation data for complications were collected with follow-up periods between 20 and 44 months and a follow-up record deadline of July 31, 2022. Patients who were diagnosed with postoperative complications or other diseases directly related to total knee arthroplasty after readmission during follow-up; patient readmission status, reoperation status and patient death status (all known follow-up patients survived). If a patient experienced readmission or reoperation related to the joint, the clinical diagnosis of postoperative complications was recorded. If there were multiple postoperative readmission events, they were also recorded.
Evaluate:
To determine whether the patient’s preoperative BMI and soft tissue indicators on preoperative anteroposterior and lateral views of the knee joint are associated with postoperative complications leading to readmission, we divided the 761 joint replacements into 22 patients with readmission and 739 patients without readmission complications. The IBM SPSS Statistics 26.0 system was used to perform independent sample t tests on the two sets of data. First, the Levene test for homogeneity of variance was performed to determine whether the variances of the two sets of data were equal. If the data were equal, a t test was used. If the variances were different, a corrected t test was used to compare whether there was a significant difference between the two groups.
Finally, to determine the effect of soft tissue measurement indicators and whether they are associated with BMI and patient weight, patients were matched according to BMI and weight using propensity score matching (PSM) (1:n) for patients with readmission complications. The IBM SPSS Statistics 26.0 system was used to perform paired sample T tests on the two sets of data to compare the differences between the sample group and the readmission complication group.