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Background: Semi-constrained implants are developed to reduce the detrimental impact of constrained implants in patients with complex primary total knee arthroplasty (TKA). However, the outcomes of TKA using semi-constrained implants are mainly unknown. Objectives: This study aims to report the short-term outcomes and complications of primary TKA in patients managed with a semi-constrained implant. Methods: Twenty-three patients (33 knees) who underwent TKA with semi-constrained implants were included in this study. The outcomes of patients were evaluated radiographically and clinically. Clinical evaluation was performed using the knee society score (KSS) and oxford knee score (OKS) at 6 and 12 months. The subjective satisfaction of the patients was also evaluated at 6 and 12 months using yes/no questions. Postoperative complications were inspected through the patient's medical records. Results: The study population included six men and 17 women with a mean age of 70.7±7.6 years. The mean follow-up of the patients was 12.5±4.8 months. The average postoperative tibiofemoral alignment was 0.26±1.1° of valgus (ranging from 3° of valgus to 2° of varus). The mean KSS of the patients were 93.8±8.1 and 94.7±8.3 at 6 and 12 months, respectively. The mean OKS of the patients were 43.6±3.7 and 44.1±3.8 at 6 and 12 months, respectively. All patients were satisfied with the surgery at 6 and 12 months. No postoperative complications were recorded during the follow-up period. Conclusion: The use of a semi-constrained prosthesis is safe and effective as a primary implant in TKA patients having severe deformity or ligamentous laxity. [ABSTRACT FROM AUTHOR]

Purpose: Revision constrained-condylar total knee arthroplasty (CCK-TKA) is often used to provide additional mechanical constraint after failure of a primary TKA. However, it is unknown how much this translates to a reliance on soft-tissue support. The aim of this study was therefore to compare the laxity of a native knee to the CCK-TKA implanted state and quantify how medial soft-tissues stabilise the knee following CCK-TKA.Methods: Ten intact cadaveric knees were tested in a robotic system at 0°, 30°, 60° and 90° flexion with ± 90  N anterior-posterior force, ± 8 Nm varus-valgus and ± 5 Nm internal-external torques. A fixed-bearing CCK-TKA was implanted and the laxity tests were repeated with the soft tissues intact and after sequential cutting. The deep and superficial medial collateral ligaments (dMCL, sMCL) and posteromedial capsule (PMC) were sequentially transected and the percentage contributions of each structure to restraining the applied loads were calculated.Results: Implanting a CCK-TKA did not alter anterior-posterior laxity from that of the original native knee, but it significantly decreased internal-external and varus-valgus rotational laxity (p < 0.05). Post CCK-TKA, the sMCL restrained 34% of the tibial displacing load in anterior drawer, 16% in internal rotation, 17% in external rotation and 53% in valgus, across the flexion angles tested. The dMCL restrained 11% of the valgus rotation moment.Conclusions: With a fully-competent sMCL in-vitro, a fixed-bearing CCK-TKA knee provided more rotational constraint than the native knee. The robotic test data showed that both the soft-tissues and the semi-constrained implant restrained rotational knee laxity. Therefore, in clinical practice, a fixed-bearing CCK-TKA knee could be indicated for use in a knee with lax, less-competent medial soft tissues.Level Of Evidence: Controlled laboratory study. [ABSTRACT FROM AUTHOR]

Revision total knee arthroplasty (TKA) in prosthetic joint infections (PJI) is a challenging problem. We evaluated our institutional experience with a semi-constrained implant placed in a PJI setting. Seventy-eight TKAs in 75 patients with a history of a PJI were identified. The average follow-up was 7.5 years. Twenty-three (29%) underwent repeat revision surgery. Five and 10 year survivals were 71% and 64%, respectively. The most common reason for repeat revision surgery was recurrent infection (78%). Smoking and elevated BMI increased the risk of repeat revision surgery. Significant improvements were maintained long term in pain and range of motion ( P < 0.01 and P = 0.02). In the absence of repeat infection, long term pain relief and improved function may be expected with the semi-constrained implant. [ABSTRACT FROM AUTHOR]