New evaluation indices for rotational knee angles in standing anteroposterior knee radiographs

BACKGROUND: Identifying the time course of rotational knee alignment is crucial for elucidating the etiology in knee osteoarthritis. OBJECTIVE: The aim of this study was to propose new rotational indices for calculating the change in relative rotational angles between the femur and tibia in standing anteroposterior (AP) radiographs. METHODS: Forty healthy elderly volunteers (20 women and 20 men; mean age, 70 ± 6 years) were assessed. The evaluation parameters were as follows: (1) femoral rotational index: the distance between the sphere center of the medial posterior femoral condyle and the lateral edge of the patella, and (2) tibial rotational index: the distance between the medial eminence of the tibia and the lateral edge of the fibula head. The indices were standardized by the diameter of the sphere of the medial posterior femoral condyle. This study (1) identified the relationship between changes in rotational indices and the simulated rotational knee angles in the standing position, (2) proposed a regression equation for the change in relative rotational angles between the femur and tibia in standing AP radiographs, and (3) verified the accuracy of the regression equation. RESULTS: The rotational indices increased in direct proportion to simulated rotational knee angles (femoral index: r > 0.9,p < 0.0001; tibial index: r > 0.9, p < 0.0001). Based on the results, the regression equation with the accuracy of 0.45 ± 0.26° was determined. CONCLUSIONS: The proposed regression equations can potentially predict the change in relative rotational angles between the femur and tibia in a pair of standing AP radiographs taken at different dates in longitudinal studies.

Decreasing Posterior Femoral Condyle Offset Improves Intraoperative Correction of Flexion Contracture in Total Knee Arthroplasty

Multiple intraoperative strategies are described to achieve full extension in total knee arthroplasty, but only a few studies have assessed the effect of the flexion gap on intraoperative improvement in flexion contracture. The aim of this study was to determine whether posterior condylar offset, in isolation, independently affects extension at the time of total knee arthroplasty.Two hundred and seventy-eight patients who underwent total knee arthroplasty for knee osteoarthritis and flexion contracture ≥ 5 degrees between January 2008 and July 2018 were included in this study. Patients with other factors that could affect knee extension at the time of surgery were excluded. We recorded the thickness of posterior femoral condyle bone resected as well as the thickness of the posterior femoral component chosen for each patient. Patients' knee extension was recorded under anesthetic, prior to resection and intraoperatively after total knee replacement.Average thickness of bone resection for the posteromedial femur was 12.64 ± 1.65 mm and for the posterolateral femur was 10.38 ± 1.52 mm. Using a linear regression model, we found that changes in posterior offset and implant downsizing influenced correction of fixed flexion deformity at the time of surgery. When patients had a combined posteromedial and posterolateral offset 2 mm thinner than the thickness of bone resected, there was an average correction of 3.5 degrees of flexion contracture.Our study demonstrated that posterior femoral condyle offset is an independent variable affecting correction of flexion contracture at the time of surgery in a gap balanced cruciate-retaining total knee arthroplasty. Level of evidence Level IV evidence

Radiographic Landmarks for Femoral Tunnel Positioning in Lateral Extra-articular Tenodesis Procedures

Background: Lateral extra-articular tenodesis (LET) is being increasingly performed as an additional procedure in both primary and revision anterior cruciate ligament reconstruction in patients with excessive anterolateral rotatory instability. Consistent guidelines for femoral tunnel placement would aid in intraoperative reproducible graft placement and postoperative evaluation of LET procedures. Purpose: To determine radiographic landmarks of a recently described isometric femoral attachment area in LET procedures with reference to consistent radiographic reference lines. Study Design: Descriptive laboratory study. Methods: Ten fresh-frozen cadaveric knees were dissected. The footprints of the lateral femoral epicondyle (LFE) apex and the deep aspects of the iliotibial tract, with its Kaplan fiber attachments (KFAs) on the distal femur, were marked with a 2.5-mm steel ball. True lateral radiographic images were taken. Mean absolute LFE and KFA distances were measured from the posterior cortex line (anterior-posterior direction) and from the perpendicular line intersecting the contact of the posterior femoral condyle (proximal-distal direction), respectively. Furthermore, positions were measured relative to the femur width. Finally, radiographic descriptions of an isometric femoral attachment area were developed. Results: The mean LFE and KFA positions were found to be 4 ± 4 mm posterior and 4 ± 3 mm anterior to the posterior cortex line, and 6 ± 4 mm distal and 20 ± 5 mm proximal to the perpendicular line intersecting the posterior femoral condyle, respectively. The mean LFE and KFA locations, relative to the femur width, were found at –12% and 11% (anterior-posterior) and –17% and 59% (proximal-distal), respectively. Femoral tunnel placement on or posterior to the femoral cortex line and proximal to the posterior femoral condyle within a 10-mm distance ensures that the tunnel remains safely located in the isometric zone. Conclusion: Radiographic landmarks for an isometric femoral tunnel placement in LET procedures were described. Clinical Relevance: These findings may help to intraoperatively guide surgeons for an accurate, reproducible femoral tunnel placement and to reduce the potential risk of tunnel misplacement, as well as to aid in the postoperative evaluation of LET procedures in patients with residual complaints.

Safety, Feasibility, and Radiographic Outcomes of the Anterior Meniscal Takedown Technique to Approach Chondral Defects on the Tibia and Posterior Femoral Condyle: A Matched Control Study

Objective Takedown of the anterior meniscus to facilitate exposure of the cartilage defects located on the tibial plateau and/or posterior femoral condyle with subsequent reattachment is being performed clinically; however, clinical evidence is lacking to support the safety of this technique. The aim of this study was therefore to investigate whether meniscal extrusion develops after patients undergo meniscus takedown and transosseous refixation during autologous chondrocyte implantation (ACI). Design We analyzed data from 124 patients with a mean follow-up of 6.8 ± 2.5 years. Sixty-two patients who underwent (ACI) with anterior meniscus takedown and refixation by the senior surgeon (TM), were compared with a matched control group of patients who underwent ACI without meniscus takedown. Meniscal extrusion was investigated by measuring the absolute value and the relative percentage of extrusion (RPE) on 1.5-T magnetic resonance images (MRI) at final follow-up. The number of menisci with radial displacement greater or lesser than 3 mm was determined. In cases where a preoperative MRI was available, both pre- and postoperative meniscal extrusion was evaluated ( n = 30) in those patients undergoing meniscal takedown. Results There was no significant difference in either absolute meniscus extrusion, RPE, or extrusion rate in patients with and without meniscus takedown. Among patients with meniscal takedown and both pre- and postoperative MRI scans, absolute meniscus extrusion, RPE, and extrusion rate showed no significant differences. Conclusion Meniscal takedown and subsequent transosseous refixation is a safe and effective technique for exposure of the tibial plateau and posterior femoral condyle.