Background. The aim of this study was to evaluate causes and results of revision surgery in unstable total knee arthroplasties. Methods. We retrospectively reviewed 24 knees that underwent a revision arthroplasty for unstable total knee arthroplasty. The average follow-up period was 33.8 months. We classified the instability and analyzed the treatment according to its cases. Stress radiographs, postoperative component position and joint level were measured. Clinical outcomes were assessed using the score and range of motion of the Hospital for Special Surgery (HSS). Results. Causes of instability included coronal instability with posteromedial polyethylene wear and lateral laxity in 13 knees(Fig. 1) and coronal instability with posteromedial polyethylene wear in 6 knees(Fig. 2), coronal and sagittal instability in 3 knees including post breakage in 1 knee(Fig. 3), global instability in 1 knee(Fig. 4) and flexion instability in 1 knee. Mean preoperative/postoperative varus and valgus angles were 5.8°/3.2° (p = 0.713) and 22.5°/5.6° (p = 0.032). Mean postoperative α, β, γ, δ angle were 5.34°, 89.65°, 2.74°, 6.77°. Mean changes of joint levels were from 14.1 mm to 13.6 mm from fibular head (p = 0.82). The mean HSS score improved from 53.4 to 89.2 (p = 0.04). The average range of motion was changed from 123° to 122° (p = 0.82). Conclusions. Revision total knee arthroplasty with or without a more constrained prosthesis will be a definite solution for an unstable total knee arthroplasty. The solution according to the causes is very important and seems to have a chance of avoidance of unnecessary over-constrained implant selection in revision surgery for total knee instability

Background:. To evaluate causes and results of revision arthroplasties in unstable total knee arthroplasties. Methods:. We retrospectively reviewed 24 knees that underwent revision arthroplasty for unstable total knee arthroplasty from December 2004 to December 2010. The mean age was 71.0(range, 54–85) years and the average follow-up period was 33.8 months (range, 6–70). The mean interval between the primary TKA and revision TKA was 82.5 months (range, 14–228). We classified the instability and analyzed the treatment according to its cases. Stress radiographs, postoperative component position and joint level were measured. Joint line position was measured using the fibular head as the reference point. Clinical outcomes were assessed using the Hospital for Special Surgery (HSS) score and range of motion. Wilcoxon sign rank test was employed for statistical analysis, and when p-value was over 0.05, it was analyzed as having statistical significances. Results:. Causes of instability included coronal instability with medial laxity in 13 knees (Fig. 1) and with polyethylene wear in 6 knees, coronal and sagittal instability in 3 knees including post breakage in 1 knee (Fig. 2, Fig. 3), global instability in 1 knee, and flexion instability in 1 knee. Mean preoperative/postoperative varus and valgus angles were 5.8°/3.2°(p = 0.713) and 22.5°/5.6°(p = 0.032). Mean postoperative α, β, γ, δ angle were 5.34°, 89.65°, 2.74°, 6.77°. Mean change of Joint levels were form 14.1 mm to 13.6 mm from fibular head (p = 0.82). The mean HSS score improved from 53.4 to 89.2(p = 0.04). The average range of motion was changed from 123° to 122°(p = 0.82). Conclusions:. Revision total knee arthroplasty with more constrained prosthesis was a very effective. The solution according to the causes is very important in revision surgery for unstable arthroplasty

Stability after TKA is essential for knee function and patient satisfaction. Stability may be marginally more important even than alignment because “stability” means there will be ONE alignment, whereas INSTABILITY means there will be many alignments of the joint, usually the worst one for any loading pattern. Whereas alignment results from the orientation and size of implants, stability depends on all of these, plus soft tissue integrity and in many cases, surgical alteration. Ligament releases (and rarely reconstructions) will certainly be required if alignment is changed with the arthroplasty. Instability may be a subtle or flagrant problem. The “Instabilities” are: . i. Varus- valgus. ii. Plane of motion- Flexion. iii. Plane of Motion-Extension. Varus-valgus instability is the prototype and while it may originate exclusively from the failure of soft tissue, knee alignment and dynamic forces outside the knee joint such as hip abductor dysfunction, scoliois and tibialis posterior rupture may be implicated. A comprehensive approach will be needed. Flexion instability, most simply stated results from a flexion gap that exceeds the dimensions of the extension gap. It will result most commonly after surgery for the patient with a fixed flexion contracture whose knee extends fully because a relatively thin polyethylene insert has been selected. So-called “mid-flexion” instability (implying stability in extension and flexion) has not yet been thoroughly characterised. Extension instability includes all failures of the extensor mechanism (rupture, maltracking and weakness) which are better characterised as “buckling” under a separate topic. Recurvatum has received little attention but can generate the most destructive forces leading to knee arthroplasty failure. In general begins as a compensatory mechanism for relative extensor weakness. All treatment of the unstable TKA must characterise the mode(s) of failure above and correct the underlying cause. Surgical technique will be extremely important, followed eventually by implant selection