Association of a Wider Medial Gap (Medial Laxity) in Flexion with Self-Reported Knee Instability After Medial-Pivot Total Knee Arthroplasty

Abstract

Background:Medial-pivot total knee arthroplasty (TKA) is designed with high articular conformity in the medial compartment in order to achieve stability. The subjective outcome of patients has been reported to be good postoperatively; however, the association between the objective and subjective knee stability and the influence of subjective stability on the overall outcomes of TKA remained unknown. Our hypothesis was that postoperative flexion joint-gap imbalance could affect subjective knee instability following TKA in medial-pivot prostheses. The purpose of this study was to analyze the association between the joint gap in flexion and subjective knee instability and between subjective knee instability and outcomes following medial-pivot TKA.Methods:A total of 769 patients who underwent primary TKA with use of medial-pivot prostheses were enrolled. Clinical outcomes included knee range of motion, Knee Society Score-2011 (KSS-2011), Forgotten Joint Score-12 (FJS-12), patient-reported subjective knee instability, and axial knee radiography to assess flexion joint-gap balance measured at the final follow-up. Clinical outcomes were compared between patients with and without subjective knee instability. Moreover, associated factors were analyzed for postoperative subjective knee instability.Results:Overall, 177 patients (23%) reported experiencing postoperative subjective knee instability. Knee flexion (p = 0.04); KSS-2011 symptom (p<0.001), satisfaction (p<0.001), expectation (p=0.008), and activity (p<0.001) subscales; and FJS-12 (p < 0.001) were significantly worse in patients with subjective knee instability. The KSS-2011 subjective score differences were greater than the minimal clinically important difference. Older age at the time of surgery (odds ratio, 1.04; p = 0.04) and a wider postoperative joint gap in flexion on the medial side (odds ratio, 1.21; p = 0.001) were significant risk factors for subjective knee instability. A gap angle of −2.9° (i.e., medial laxity) was the threshold to predict postoperative knee instability (sensitivity, 0.29; specificity, 0.91).Conclusions:Postoperative flexion joint-gap laxity on the medial side following medial-pivot TKA affected the patient-reported subjective knee instability scores. Postoperative KSS-2011 subjective scores following medial-pivot TKA were poorer in patients with subjective knee instability.Level of Evidence:Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Navigated functional alignment total knee arthroplasty achieves reliable, reproducible and accurate results with high patient satisfaction

“…A key difference of FA over KA and other nMA’s is that FA not only attempts to realign the knee in the coronal plane in extension but also aims to do the same in flexion alignment, which typically receives less attention as it is more challenging to measure flexion alignment pre‐operatively and post‐operatively. Predicting and realigning the knee through its ROM curve allows the soft tissue to maintain appropriate tension, restore normal kinematic features such as medial pivot, and avoid flexion instability [26, 27]. Additionally, FA accepts that a compromise on implant alignment or position may be required to restore suitable kinematics.…”

Does diabetes mellitus impair the clinical results of total knee arthroplasty under enhanced recovery after surgery?

“…The FJS-12 scale was created in recent years to evaluate the degree of knee joint forgotten, existing studies have found that multiple factors have negative correlations with FJS-12 after surgery, such as preoperative depression, postoperative patellar subluxation [ 41 ] and knee instability [ 42 ]. Recent studies have found that the FJS-12 score of diabetic patients is lower than that of non-diabetic patients 1 year after surgery, and the difference is more obvious in female patients [ 43 ].…”

Joint gap produced by manual stress is dependent on the surgeon’s experience and is smaller in flexion in robotic-assisted total knee arthroplasty

“…Since the accuracy of the bone cut is increasing owing to the development of the navigation and robot systems [15], such inter-surgeon diference may have signiicant clinical relevance in robotic-assisted TKAs. Because the medial lexion gap is a reliable indicator of softtissue balancing and is associated with patient satisfaction and patient-reported subjective scores after TKA [1,16,19], manual stress measurements in navigation and robot systems must be improved [4,21,22].…”

“…Accurate soft-tissue balancing is important in achieving a good clinical outcome, patient satisfaction, and a long-term implant survival after total knee arthroplasty (TKA) [1,3,5,11,19]. Joint gap measurement is most commonly performed under static conditions, with the knee extended and performing a 90° lexion using a gap tensioner/spreader [18].…”