90° Spinning of Polyethylene Inserts in Mobile Bearing Unicompartmental Knee Arthroplasty

<b>Background</b> The objective of this article is to describe for the first time a case of 90^° spin out of a mobile bearing unicompartmental knee arthroplasty (UKA) polyethylene insert. In this report, we present a 57-year-old gentleman with a medial compartment UKA for osteoarthritis in 2017 who developed dislodgement and 90^° rotation subsequent to traumatic injury when he was involved in a bus crash and impacted the anterolateral knee sustaining a valgus type injury 1 week postoperatively. Following the injury, he reported medial knee pain and a sensation of something moving within the joint. He was initially managed conservatively and progressed to full weight bearing; however, he experienced intermittent symptoms of catching and blocking of the joint, as well as medial knee swelling, that inhibited his ability to perform activities involving walking, kneeling, or pivoting. Imaging taken in 2018 show a 90° rotation of the polyethylene insert. These images showed the longitudinal metallic marker on the insert facing in an anteroposterior direction as opposed to the normal medial-lateral orientation. Failing conservative management, he presented to our clinic in 2019 and proceeded for revision of his UKA. Intraoperatively, his insert was reviewed and seen to easily spin on axis. The liner was therefore removed and upsized from a size 5 medium to a size 7 medium insert which provided excellent stability and stopped any further spinning. He has done tremendously well since the operation and reports full range of motion and no concerns. In patients with a history of pain, swelling, or locking following a UKA, it would be prudent to consider insert spinning, as well as the more common dislocation, through confirming the orientation of the metallic insert marker. Revision surgery to correct the spinning defect has proven effective with good resolution of symptoms and return to full range of motion.

Two-stage Reimplantation in Infected Total Knee Arthroplasty by Using Resterilized Femoral and Tibial Components with a New Polyethylene Insert: Report of 4 Cases with at Least 15 Years’ Follow-up

Background. This study evaluates 15 years’ results of the implantation of autoclaved femoral and tibial prosthesis components together with a new same brand polyethylene insert which were used as a temporary articulating spacer in patients with periprosthetic infection of total knee arthroplasty (TKA) in a two-stage reimplantation procedure in 6 patients. Material and methods. The femoral and tibial prostheses of 6 patients with deep chronic periprosthetic infection of TKA who underwent elective two-stage exchange arthroplasty were autoclaved and reinserted with a new polyethylene insert of the same brand and bone cement mixed with tecoplanin in 2004. Results. Four patients were followed for 15 years. They were all female and between 47-70 years old. The infectious agent was meticillin-resistant Staphylococcus aureus (MRSA) in 3 and coagulase negative Staphy­lococcus in one patient. Patients were invited for second stage reimplantation, but they refused to undergo the second stage. Three of them had their second stage reimplantation after 15, 13 and 10 years while one patient was reinfected after 5 years, in 2009, and arthrodesis was performed. They were all happy with the result and infection free at last follow-up. Conclusions. 1. Regarding the results of our patients, reinsertion of autoclaved femoral and tibial prostheses together with a new same brand polyethylene insert with teicoplanin loaded bone cement can be used cautiously in the management of periprosthetic deep infection of TKA. 2. That is because patients might not want the second stage reimplantation. 3. We believe that the refusal of patients to undergo the surgery shows that the single-stage treatment is effective.

Assessment of paradoxical anterior translation in a CR total knee prosthesis coupling dynamic RSA and FE techniques

Purpose The study aims were to assess the kinematic data, Internal-External (IE) rotation, and Antero-Posterior (AP) translation of the contact points between the femoral condyles and polyethylene insert and to develop a combined dynamic RSA-FE (Radiostereometric – Finite Element) model that gives results congruent with the literature. Methods A cohort of 15 patients who underwent cemented cruciate-retaining highly congruent mobile-bearing total knee arthroplasty were analyzed during a sit-to-stand motor task. The kinematical data from Dynamic RSA were used as input for a patient-specific FE model to calculate condylar contact points between the femoral component and polyethylene insert. Results The femoral component showed an overall range about 4 mm of AP translation during the whole motor task, and the majority of the movement was after 40° of flexion. Concerning the IE rotation, the femoral component started from an externally rotate position (− 6.7 ± 10°) at 80° of flexion and performed an internal rotation during the entire motor task. The overall range of the IE rotation was 8.2°. Conclusions During the sit to stand, a slight anterior translation from 40° to 0° of flexion of the femoral component with respect to polyethylene insert, which could represent a paradoxical anterior translation. Despite a paradoxical anterior femoral translation was detected, the implants were found to be stable. Dynamic RSA and FE combined technique could provide information about prosthetic component’s stress and strain distribution and the influence of the different designs during the movement.

Robotic-assisted total knee arthroplasty improves accuracy and precision compared to conventional techniques

Aims Robotic-assisted total knee arthroplasty (RA-TKA) is theoretically more accurate for component positioning than TKA performed with mechanical instruments (M-TKA). Furthermore, the ability to incorporate soft-tissue laxity data into the plan prior to bone resection should reduce variability between the planned polyethylene thickness and the final implanted polyethylene. The purpose of this study was to compare accuracy to plan for component positioning and precision, as demonstrated by deviation from plan for polyethylene insert thickness in measured-resection RA-TKA versus M-TKA. Methods A total of 220 consecutive primary TKAs between May 2016 and November 2018, performed by a single surgeon, were reviewed. Planned coronal plane component alignment and overall limb alignment were all 0° to the mechanical axis; tibial posterior slope was 2°; and polyethylene thickness was 9 mm. For RA-TKA, individual component position was adjusted to assist gap-balancing but planned coronal plane alignment for the femoral and tibial components and overall limb alignment remained 0 ± 3°; planned tibial posterior slope was 1.5°. Mean deviations from plan for each parameter were compared between groups for positioning and size and outliers were assessed. Results In all, 103 M-TKAs and 96 RA-TKAs were included. In RA-TKA versus M-TKA, respectively: mean femoral positioning (0.9° (SD 1.2°) vs 1.7° (SD 1.1°)), mean tibial positioning (0.3° (SD 0.9°) vs 1.3° (SD 1.0°)), mean posterior tibial slope (-0.3° (SD 1.3°) vs 1.7° (SD 1.1°)), and mean mechanical axis limb alignment (1.0° (SD 1.7°) vs 2.7° (SD 1.9°)) all deviated significantly less from the plan (all p < 0.001); significantly fewer knees required a distal femoral recut (10 (10%) vs 22 (22%), p = 0.033); and deviation from planned polyethylene thickness was significantly less (1.4 mm (SD 1.6) vs 2.7 mm (SD 2.2), p < 0.001). Conclusion RA-TKA is significantly more accurate and precise in planning both component positioning and final polyethylene insert thickness. Future studies should investigate whether this increased accuracy and precision has an impact on clinical outcomes. The greater accuracy and reproducibility of RA-TKA may be important as precise new goals for component positioning are developed and can be further individualized to the patient. Cite this article: Bone Joint J 2021;103-B(6 Supple A):74–80.