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Purpose Achieving a balanced knee is accepted as an important goal in total knee arthroplasty; however, the deinition of ideal balance remains controversial. This study therefore endeavoured to determine: (1) whether medio-lateral gap balance in extension, midlexion, and lexion are associated with improved outcome scores at one-year post-operatively and (2) whether these relationships can be used to identify windows of optimal gap balance throughout lexion. Methods 135 patients were enrolled in a multicenter, multi-surgeon, prospective investigation using a robot-assisted surgical platform and posterior cruciate ligament sacriicing gap balancing technique. Joint gaps were measured under a controlled tension of 70-90 N from 10°-90° lexion. Linear correlations between joint gaps and one-year KOOS outcomes were investigated. KOOS Pain and Activities of Daily Living sub-scores were used to deine clinically relevant joint gap target thresholds in extension, midlexion, and lexion. Gap thresholds were then combined to investigate the synergistic efects of satisfying multiple targets. Results Signiicant linear correlations were found throughout extension, midlexion, and lexion. Joint gap thresholds of an equally balanced or tighter medial compartment in extension, medial laxity ± 1 mm compared to the inal insert thickness in midlexion, and a medio-lateral imbalance of less than 1.5 mm in lexion generated subgroups that reported signiicantly improved KOOS pain scores at one year (median ∆ = 8.3, 5.6 and 2.8 points, respectively). Combining any two targets resulted in further improved outcomes, with the greatest improvement observed when all three targets were satisied (median ∆ = 11.2, p = 0.002). Conclusion Gap thresholds identiied in this study provide clinically relevant and achievable targets for optimising soft tissue balance in posterior cruciate ligament sacriicing gap balancing total knee arthroplasty. When all three balance windows were achieved, clinically meaningful pain improvement was observed. Level of Evidence Level II.

Plasma immersion ion implantation (PIII) is used in this study to improve the surface bioactivity of polyether ether ketone (PEEK) by modifying the chemical structure and introducing radicals. The kinetic properties of the treated surface are characterised here, allowing for tuning of the PIII process in order to produce PEEK with optimised bioactivity. The optimum PIII ion fluence for PEEK is determined to be 1 × 1016 ions/cm2. A model is proposed that accounts for the decay of radicals, nitrogen loss, oxygen incorporation and changes in surface energy within the structure. The model is based on the premise that there is a distribution of local chemical environments produced by PIII. The distribution of chemical environments results in a bioactive surface that has a long shelf life, compatible with clinical needs.

Plasma immersion ion implantation (PIII) is used to modify the surface properties of polyether ether ketone for biomedical applications. Modifications to the mechanical and chemical properties are characterized as a function of ion fluence (treatment time) to determine the suitability of the treated surfaces for biological applications. Young's modulus and elastic recovery were found to increase with respect to treatment time at the surface from 4.4 to 5.2 MPa and from 0.49 to 0.68, respectively. The mechanical properties varied continuously with depth, forming a graded layer where the mechanical properties returned to untreated values deep within the layer. The treated surface layer exhibited cracking under cyclical loads, associated with an increased modulus due to dehydrogenation and cross-linking; however, it did not show any sign of delamination, indicating that the modified layer is well integrated with the substrate, a critical factor for bioactive surface coatings. The oxygen concentration remained unchanged at the surface; however, in contrast to ion implanted polymers containing only carbon and hydrogen, the oxygen concentration within the treated layer was found to decrease. This effect is attributed to UV exposure and suggests that PIII treatments can modify the surface to far greater depths than previously reported. Protein immobilization on PIII treated surfaces was found to be independent of treatment time, indicating that the surface mechanical properties can be tuned for specific applications without affecting the protein coverage. Our findings on the mechanical properties demonstrate such treatments render PEEK well suited for use in orthopedic implantable devices.

Slow appositional growth of bone in vivo is a major problem associated with polyether ether ketone (PEEK) based orthopaedic implants. Early stage promotion of osteoblast activity, particularly bone nodule formation, would help to improve contact between PEEK implantable materials and the surrounding bone tissue. To improve interactions with bone cells, we explored here the use of plasma immersion ion implantation (PIII) treatment of PEEK to covalently immobilize biomolecules to the surface. In this study, a single step process was used to covalently immobilize tropoelastin on the surface of PIII modified PEEK through reactions with radicals generated by the treatment. Improved bioactivity was observed using the human osteoblast-like cell line, SAOS-2. Cells on surfaces that were PIII-treated or tropoelastin-coated exhibited improved attachment, spreading, proliferation, and bone nodule formation compared to cells on untreated samples. Surfaces that were both PIII-treated and tropoelastin-coated triggered the most favorable osteoblast-like responses. Surface treatment or tropoelastin coating did not alter alkaline phosphatase gene expression and activity of bound cells but did influence the expression of other bone markers including osteocalcin, osteonectin, and collagen I. We conclude that the surface modification of PEEK improves osteoblast interactions, particularly with respect to bone apposition, and enhances the orthopedic utility of PEEK.

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