SPECT/CT Assessment of In-Vivo Loading of the Knee Correlates with Polyethylene Deformation in Retrieved Total Knee Arthroplasty

Background: SPECT/CT distribution patterns in patients with total knee replacements have previously been correlated with factors such as time of implantation, implant type and alignment. It is unknown, however, if an increased and more extended bone tracer uptake (BTU) in SPECT/CT, representing loading of the joint, correlates with findings from retrieval studies. The aim of this study was to further understand this subject. Materials and Methods: 62 retrieved TKA were included. SPECT/CT was performed prior to revision. Quantitative and qualitative medio-lateral comparisons of BTU intensity and distribution in the tibia were performed. Retrieval analysis was performed with a micro-CT method to assess the thickness differences between medial and lateral sides of polyethylene inserts with symmetrical designs. Results: In the subgroup of TKA with asymmetrical SPECT/CT distribution, there was a significant correlation between retrieval and medical imaging data (p = 0.0355): patients showing a more extended BTU in the medial compartment also had a significantly thinner insert in the medial compartment, and vice versa in the lateral side. Conclusion: This is the first study comparing BTU distribution patterns and retrieval findings. Our results support the hypothesis that SPECT/CT is able to identify bone activity due to implant position and loading.

Management of instability after primary total knee arthroplasty: an evidence-based review

Background Instability is one of the most common reasons for revision after a total knee replacement. It accounts for 17.4% of all single-stage revision procedures performed in the UK National Joint Registry. Through a careful patient evaluation, physical assessment and review of investigations one can identify the likely type of instability. Aims To critically examine the different types of instability, their presentation and evidence-based management options. Method A comprehensive literature search was conducted to identify articles relevant to the aetiology and management of instability in total knee replacements. Results Instability should be categorised as isolated or global and then, as flexion, mid-flexion, extension or recurvatum types. By identifying the aetiology of instability one can correctly restore balance and stability. Conclusion With careful judgement and meticulous surgical planning, instability can be addressed and revision surgery can provide patients with successful outcomes.

Roughness Digital Characterization and Influence on Wear of Retrieved Knee Components

Tribological performance of knee components are strongly related to the surface characteristics. Primarily, the roughness and its 3D distribution on the surfaces affect the joint performance. One of the main limitations related to the tribological study of knee prostheses is that most of the research studies report in vitro or in silico results, as knee retrievals are difficult to find or are too damaged to be analyzed. This paper is focused on the roughness characterization of retrieved metal femoral components of total knee replacements (TKR) by means of a rugosimeter and involving digital methods to reconstruct the 3D topography of the studied surfaces. The aim of this study is to investigate how changes and distribution of roughness are correlated between the medial vs. the lateral part and how the resulting digital topography can give insights about the wear behavior.

Management of a Complex Supracondylar Periprosthetic Femur Fracture with Intramedullary Strut Allograft and Bilateral Locking Plates

Supracondylar periprosthetic femoral fractures occurring above total knee replacements have been considered a rare entity. However, they continue to increase in frequency with the increasing number of arthroplasties and the improvement in morbidity and mortality in the concerned patient population. The management of periprosthetic distal femoral fractures is a challenging orthopedic problem. In this brief communication, a case of 49-year-old woman with rheumatoid arthritis who sustained a low distal comminuted periprosthetic femoral fracture is presented. Her fracture was eventually managed with an intramedullary fibular strut allograft and bilateral locking plate placement reaching satisfactory healing and restoration of alignment. The primary aim of this report is to provide insight into this novel technique as a successful alternative to other standard surgical options.

Cutoff points of T1 rho / T2 mapping relaxation times distinguishing early-stage and advanced osteoarthritis

IntroductionThe histopathology grading system is the gold post-operative method to evaluate cartilage degeneration in knee osteoarthritis (OA). Magnetic resonance imaging (MRI) T1 rho/T2 mapping imaging can be used as a preoperative detection. An association between histopathology and T1 rho/T2 mapping relaxation times value was suggested in previous research. However, the cutoff point was not determined among different histopathology grades. Our study was to discuss the cutoff point of T1 rho/T2 mapping.Material and methodsT1 rho/T2 mapping images were acquired from 80 samples before total knee replacements. Then the histopathology grading system was applied.ResultsThe mean T1 rho/T2 mapping relaxation times of 80 samples were 39.17 ms and 37.98 ms respectively. Significant differences were found in T1 rho/T2 mapping values between early-stage and advanced OA (P < 0.001). The cutoff point for T1 rho was at 33 ms with a sensitivity of 94.12 (95%CI: 80.3 to 99.3) and a specificity of 91.30 (95%CI: 79.2 to 97.6). The cutoff point for T2 mapping was suggested at 35.04 ms with a sensitivity of 88.24 (95%CI: 72.5 to 96.7) and specificity of 97.83 (95%CI: 88.5 to 99.9). After bootstrap simulation, 95% CI of T1 rho/T2 mapping cutoff point was estimated as 29.36 to 36.32 ms and 34.8 to 35.04 ms respectively. The area under PR curve of T1 rho/T2 mapping was 0.972 (95%CI: 0.925 to 0.992) and 0.949 (95%CI: 0.877 to 0.989) respectively.ConclusionsThe cutoff point of T1 rho relaxation times, which was suggested as 33 ms could be used to distinguish early-stage and advanced OA.