A Sagittal Patellar Angle Linear Equation Reflecting Patellofemoral Kinematics: Evaluation of Patellar Height at any Degree of Knee Flexion Angle.

OBJECTIVE: To confirm whether a novel sagittal patellar angle linear equation used for evaluating patellar height by calculating expected sagittal patellar angle (SPA) at any degree of knee flexion angle is suitable for patients older than 17 years and its reliability compared with other commonly used methods. METHODS: From September 2016 to September 2019, a total number of 202 consecutive outpatients' knee lateral X-ray radiographs were retrospectively measured and evaluated using a recently proposed linear equation Y = 1.94 + 0.74 × knee flexion(KF) angle. Patients were divided by ages into ayounger group, whose ages were between 17-49 years, and an older group, whose ages were older than 49 years, which has not been validated in the original study. Parameters such as KF, SPA, patella and patella tendon length and so on were measured on computer with picture archiving and communication system by two independent observers at an interval of 1 month. Insall-Salvati (IS) index, Caton-Deschamps (CD) index and Y value, correlation coefficients were calculated and compared using SPSS 22.0 software. RESULTS: In the younger group, 143 patients (165 knees) were included, ages were 17-49 (31.62 ± 11.38) years, males/females were 70 (48.95%)/73 (51.05%), left knees/right knees were 83 (50.30%)/82 (49.70%), mean value of Y was 31.50° ± 10.07°, and SPA was 34.38° ± 12.38°, mean value of IS was 1.06 ± 0.17, mean value of CD was 1.04 ± 0.18. While in older group, 59 patients (78 knees) were included, ages were 50-60 (mean 54.61 ± 2.99) years, there were 32 males (54.24%) and 27 females (45.76%), 42 knees were left (53.85%) and 36 knees were right (46.15%), mean values of Y and SPA were 25.90° ± 11.55° and 29.36° ± 14.22°, mean IS index in older group was 1.06 ± 0.18, mean CD index was 1.00 ± 0.16. Intra- and inter-observer reliabilities of Y in younger and older groups were 0.999, 0.999, 1.000 and 0.999, meaning high reliability and reproducibility, but low Pearson's correlation coefficients with IS and CD index were showed as -0.213 and - 0.216 in younger group and - 0.113 and - 0.316 in older group. CONCLUSIONS: In patients older than 17 years, the linear equation Y = 1.94 + 0.74 × KF is a reliable and practical method to evaluate SPA regardless of age and knee flexion angle, but has weak correlation coefficients with the IS and CD index.

A Retrospective Study of the Risk Factors for Postoperative Foot or Ankle Pain in 90 Patients with Varus Osteoarthritis of the Knee who Underwent Total Knee Arthroplasty.

BACKGROUND The reasons for foot and ankle pain following total knee arthroplasty (TKA) for knee varus osteoarthritis are unknown. This retrospective study aimed to investigate the risk factors for postoperative foot and ankle pain in patients with varus osteoarthritis of the knee who underwent TKA. MATERIAL AND METHODS We enrolled 90 patients who underwent TKA for varus knee osteoarthritis. The visual analog scale (VAS) was used to evaluate patients' foot or ankle pain before and after surgery. The correlation between independent variables (eg, age, sex, body mass index [BMI], ankle osteoarthritis, and varus angle) and foot and ankle pain in patients with osteoarthritis of the knee was measured. Moreover, radiological changes were compared between the groups with and without worsened pain. RESULTS No significant difference in VAS was found between patients <60 and ≥60 years of age (P>0.05). Male sex and BMI <30 kg/m² were weakly correlated with preoperative foot or ankle pain. However, patients with varus of ≥6° and preexisting ankle osteoarthritis had a higher incidence of foot or ankle pain before surgery. Moreover, no significant differences in radiological changes were found between the groups with and without worsened foot or ankle pain after surgery (P>0.05). CONCLUSIONS In male patients with osteoarthritis of the knee, a BMI <30 kg/m², varus of <6°, and no preexisting ankle osteoarthritis were protective factors for foot and ankle pain. TKA corrected knee and ankle malalignment. Therefore, postoperative foot and ankle pain was not associated only with TKA surgery.