The use of physical examination and kneeling X-ray as diagnostic tools of sagittal instability after primary kne arthroplasty

Flexion instability following knee arthroplasty is a serious complication that negatively impacts patient satisfaction and may necessitate revision surgery. Despite its significant effects, there are no definitive criteria for the physical examination and imaging findings that aid in diagnosing flexion instability. In recent years, stress radiography methods have been increasingly used to assist in diagnosis. This study evaluated 119 patients and 145 knees who underwent primary knee arthroplasty using cruciate-sacrificing implants at Hacettepe University Department of Orthopedics and Traumatology between February 2018 and June 2023. Patients' symptoms of knee instability, anterior drawer, posterior sag and Vince tests, Forgotten Joint Score and Knee Society Scores (KSS and fKSS) were assessed. Standard knee radiographs were reviewed. Kneeling radiographs were taken without stress (pre-stress) and with stress applied. The difference (Δ-TPkFA) in the distance between the posterior tibial line and the anterior femoral component between the two kneeling radiographs was measured. A negative correlation was found between patients' fKSS scores and Δ-TPkFA values (p: 0.005). No correlation was found between patients' posterior tibial slope (PTS) and knee scores (p>0.05). Patients were then divided into two groups based on whether they had symptoms of knee instability. There was no significant difference between the groups in terms of average age, follow-up duration, body mass index (BMI), and knee extension strength (p>0.05). Knee scores were significantly lower in the knee instability group (fKSS: 74.9 ± 12.4 vs. 85.1 ± 11.1, p: 0.00). The positivity of the posterior sag sign was significantly higher in the instability group (p: 0.00). However, no difference was found with the anterior drawer test (p: 0.964). The Δ-TPkFA values were -1.2 ± 3.3 mm in the stable knee group and 1.05 ± 3.8 mm in the unstable group (p: 0.001). There was no significant difference between the stable and unstable groups in terms of PTS values (2.5° ± 3.8 and 1.9° ± 3.3, p>0.05). However, a significant difference was found regarding the postoperative and preoperative posterior femoral offset (2.9 ± 4.9 mm and 0.6 ± 4.1 mm, p: 0.019).