Instability usually occurs because of surgical error and/or poor prosthesis selection and often results in revision surgery an average of 4 years after the primary arthroplasty [21]. Severe instability can result in dislocation. In a 2014 review of 781 cases of prosthesis failure, Sharkey et al [12] found that instability represented the third most common cause of prosthesis failure overall, accounting for 7.5% of all cases. The concepts of instability, malalignment, and loosening in TKA are closely interrelated [117]. When malalignment of the joint is created at the time of surgery, minor degrees of instability can become a significant problem. By the same token, instability, ongoing over time, can give rise to malalignment, which, in turn, can lead to loosening. Although ligamentous balance/imbalance plays a role in joint instability, it is not the only factor accounting for stability [118]. 3-Phase Bone Scan Knee There is insufficient evidence to support routine use of Tc-99m 3-phase bone scans for the assessment of instability. CT Arthrography Knee CT joint arthrography can assess for lucency with contrast accumulation at the bone/cement/hardware interface. These areas of lucency are not specific for infection versus mechanical loosening. Imaging After Total Knee Arthroplasty CT Knee With IV Contrast CT with IV contrast is not useful for the assessment of aseptic loosening, osteolysis, or instability. CT Knee Without and With IV Contrast CT without and with IV contrast is not useful for the assessment of aseptic loosening, osteolysis, or instability. CT Knee Without IV Contrast Particularly when metal artifact reduction techniques are used, CT can be used to show the extent and width of lucent zones that may be less apparent on radiographs [20]. MRI and CT have both been shown to be more sensitive for detection of osteolysis than radiographs [116].
Imaging After Total Knee Arthroplasty. Instability usually occurs because of surgical error and/or poor prosthesis selection and often results in revision surgery an average of 4 years after the primary arthroplasty [21]. Severe instability can result in dislocation. In a 2014 review of 781 cases of prosthesis failure, Sharkey et al [12] found that instability represented the third most common cause of prosthesis failure overall, accounting for 7.5% of all cases. The concepts of instability, malalignment, and loosening in TKA are closely interrelated [117]. When malalignment of the joint is created at the time of surgery, minor degrees of instability can become a significant problem. By the same token, instability, ongoing over time, can give rise to malalignment, which, in turn, can lead to loosening. Although ligamentous balance/imbalance plays a role in joint instability, it is not the only factor accounting for stability [118]. 3-Phase Bone Scan Knee There is insufficient evidence to support routine use of Tc-99m 3-phase bone scans for the assessment of instability. CT Arthrography Knee CT joint arthrography can assess for lucency with contrast accumulation at the bone/cement/hardware interface. These areas of lucency are not specific for infection versus mechanical loosening. Imaging After Total Knee Arthroplasty CT Knee With IV Contrast CT with IV contrast is not useful for the assessment of aseptic loosening, osteolysis, or instability. CT Knee Without and With IV Contrast CT without and with IV contrast is not useful for the assessment of aseptic loosening, osteolysis, or instability. CT Knee Without IV Contrast Particularly when metal artifact reduction techniques are used, CT can be used to show the extent and width of lucent zones that may be less apparent on radiographs [20]. MRI and CT have both been shown to be more sensitive for detection of osteolysis than radiographs [116].