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PurposeIn total knee arthroplasty (TKA), knee phenotypes including joint line obliquity are of interest regarding surgical realignment strategies. The hypothesis of this study is that better clinical results, including decreased postoperative knee pain, will be observed for patients with a restored knee phenotype.MethodsA retrospective analysis was performed on prospective data, including 1078 primary osteoarthritic knees in 936 patients. The male:female ratio was 780:298, mean age at surgery was 71.3 years ± 8.0. International Knee Society Scores and standardized long-leg radiographs (LLR) were collected preoperatively and at 2 years follow-up after TKA. Patients were categorized using the Coronal Plane Alignment of the Knee (CPAK) classification including the lateral distal femoral angle (LDFA) and medial proximal tibial angle (MPTA) measured on LLR by a single observer, allowing knee phenotypes to be categorized considering the arithmetic hip–knee–ankle (aHKA) angle (MPTA-LDFA) as measure of constitutional alignment, and joint line obliquity (JLO) (MPTA + LDFA). Clinical results were compared between patients with surgically restored preoperative constitutional knee phenotype to patients without restored constitutional knee phenotypes. Descriptive data analysis such as means, standard deviations and ranges were performed. T tests for independent samples were performed to compare group differences. Comparisons of categorical data were performed using the χ2 test. Significance was set at p < 0.05.ResultsA third of patients (33.4%) had constitutional knee varus with apex distal JLO. 63.5% of patients had preoperative apex distal JLO. Postoperatively, 57.8% of patients had a neutral HKA (− 2° to 2°) and a neutral JLO (− 3° and 3°), with only 18% of patients with restored constitutional knee phenotype. Of these patients, statistically less postoperative pain was observed in patients where apex distal JLO was restored compared to non-restored apex distal JLO (pain score 46.7 vs. 44.6; p = 0.02) without clinical relevance. Other categories of restored JLO or arithmetic HKA angle were not associated with improved outcomes.ConclusionThis study showed that performing mechanical alignment for primary TKA resulted in most cases in a change of the preoperative knee phenotype. These results emphasize the relevance of considering joint line obliquity to better understand preoperative knee deformity and better restore knee phenotypes with a more personalized realignment strategy to potentially improve TKA postoperative results.Level of evidenceIII.

Purpose The purpose of this study was to understand if differences exist between computed tomography (CT) and long leg radiographs (LLR) when defining coronal plane alignment of the lower limb in total knee arthroplasty (TKA). It aimed to identify any such differences between the two imaging modalities by quantifying constitutional limb alignment (arithmetic hip–knee–ankle angle (aHKA), joint line obliquity (JLO) and Coronal Plane Alignment of the Knee (CPAK) type within the same population. Methods A retrospective radiographic study compared pre-operative LLR and CT measurements in patients undergoing robotic-assisted TKA. The aHKA, JLO and CPAK types were calculated after measuring the medial proximal tibial angle (MPTA) and lateral distal femoral angle (LDFA). The primary outcomes were the mean differences in aHKA (MPTA−LDFA), JLO (MPTA + LDFA) and proportions of CPAK types between LLR and CT groups. The secondary outcomes were the differences in CT-derived MPTA values based on four different tibial sagittal landmarks. Results After exclusions, 465 imaging sets were analysed in 394 patients. There was a statistically significant mean difference between LLR and CT, respectively, for both MPTA (87.5° vs. 86.2°; p  < 0.01) and LDFA (88.7° vs. 87.3°; p  < 0.01). There were also statistically significant differences for aHKA (− 0.2° vs. − 1.1°) and JLO (175.1° vs. 173.4°) for LLR and CT, respectively (both p  < 0.01). CT increased the proportion of patients with CPAK Type I (constitutional varus aHKA, apex distal JLO) and CPAK Type II (neutral aHKA, apex distal JLO), and decreased numbers of CPAK Types III–VI. There were significant mean differences in the MPTA using varying sagittal landmarks. Conclusion Alignment determined by LLRs underestimates the magnitude of both constitutional varus alignment and joint line obliquity compared to CT, differences that notably increase the proportions of patients included in CPAK Types I and II. These distinctions are primarily due to underestimation of proximal tibial varus when measured on LLRs compared to CT, which more specifically defines articular weight-bearing points. Level of evidence III.

IntroductionRobot-assisted surgery (RAS) and kinematic alignment (KA) are being increasingly adopted to improve patient outcomes in total knee arthroplasty (TKA). There is uncertainty around the individual or combined effect of these concepts compared with computer-assisted surgery (CAS) and mechanical alignment (MA), respectively. This study aims to assess the effectiveness of RAS, KA or both to improve clinical outcomes, functional measures, radiographic precision and prosthetic survivorship when compared with current gold standards of surgical care.Methods and analysisA national registry-nested, multicentre, double-blinded, 2×2 factorial, randomised trial will be undertaken with 300 patients undergoing primary unilateral TKA performed by 15 surgeons. The primary outcome will be the between-group differences in postoperative change over 2 years in the mean Knee injury and Osteoarthritis Outcome Score (KOOS-12), comparing first, RAS to CAS as its control, and second, KA to MA as its control. Secondary outcomes will include other knee-specific and general health patient-reported outcome measures (PROMs), intraoperative pressure loads as a measure of soft tissue balance, 6-month postoperative functional outcomes, radiological precision using CT imaging, complications and long-term prosthetic survivorship. The contribution of each patient’s unique coronal plane alignment of the knee phenotype to primary and secondary PROMs will be investigated. OMERACT-OARSI criteria and Patient Acceptable Symptom State outcome score thresholds for the KOOS-12 and Oxford Knee Score will be used in secondary analyses. Primary intention-to-treat and secondary per-protocol analyses will be performed. Statistical analysis will include a generalised linear mixed model for repeated measures for continuous KOOS-12 scores. Kaplan-Meier estimates with adjusted HRs of implant survivorship will be calculated.Ethics and disseminationEthics approval was obtained from Sydney Local Health District-Royal Prince Alfred Hospital (Approval X20-0494 and 2020/ETH02896 10.24/DEC20). Results will be submitted for publication in a peer-reviewed journal and presented in national, state and international meetings.Trial registration numberACTRN12621000205831.

Purpose Kinematically aligned total knee arthroplasty (KA TKA) relies on precise determination of constitutional alignment to set resection targets. The arithmetic hip-knee-ankle angle (aHKA) is a radiographic method to estimate constitutional alignment following onset of arthritis. Intraoperatively, constitutional alignment may also be approximated using navigation-based angular measurements of deformity correction, termed the stressed HKA (sHKA). This study aimed to investigate the relationship between these methods of estimating constitutional alignment to better understand their utility in KA TKA. Methods A radiological and intraoperative computer-assisted navigation study was undertaken comparing measurements of the aHKA using radiographs and computed tomography (CT-aHKA) to the sHKA in 88 TKAs meeting the inclusion criteria. The primary outcome was the difference in the paired means between the three methods to determine constitutional alignment (aHKA, CT-aHKA, sHKA). Secondary outcomes included testing agreement across measurements using Bland-Altman plots and analysis of subgroup differences based on different patterns of compartmental arthritis. Results There were no statistically significant differences between any paired comparison or across groups (aHKA vs. sHKA: 0.1°, p  = 0.817; aHKA vs. CT-aHKA: 0.3°, p  = 0.643; CT-aHKA vs. sHKA: 0.2°, p  = 0.722; ANOVA, p  = 0.845). Bland-Altman plots were consistent with good agreement for all comparisons, with approximately 95% of values within limits of agreement. There was no difference in the three paired comparisons (aHKA, CT-aHKA, and sHKA) for knees with medial compartment arthritis. However, these findings were not replicated in knees with lateral compartment arthritis. Conclusions There was no significant difference between the arithmetic HKA (whether obtained using CT or radiographs) and the stressed HKA in this analysis. These findings further validate the preoperative arithmetic method and support use of the intraoperative stressed HKA as techniques to restore constitutional lower limb alignment in KA TKA. Level of evidence III.

Purpose Key concepts in total knee arthroplasty include restoration of limb alignment and soft-tissue balance. Although differences in balance have been reported amongst mechanical alignment (MA), kinematic alignment (KA) and functional alignment (FA) techniques, it remains unclear whether there are differences in gap imbalance or resection thicknesses when comparing different constitutional alignment subgroups. Methods MA (measured resection technique), KA (matched resections technique) and FA (technique based on the restricted KA boundaries) were compared in 116 consecutive patients undergoing 137 robotic-assisted cruciate-retaining total knee arthroplasties. The primary outcome was the proportion of balanced gaps (differential laxities ≤ 2 mm) for extension, flexion, medial and lateral gap measurements. Manual pre-resection laxity measurements were obtained for MA and KA and manual post-resection measurements were obtained for FA in 10° and in 90° of knee flexion. Secondary outcomes were resection depths and implant alignment. All outcomes were analysed per constitutional coronal alignment and joint line obliquity subgroups. Results The proportions of balance in all four gap measurements were 54.7%, 66.4% and 96.5%, with MA, KA and FA, respectively. Across all constitutional alignment types, FA achieved the highest proportion of balance. MA resected the least amount of bone from the medial tibial plateau. KA had femoral components in most valgus and most internally rotated, tibial components in most varus and was the most bone-preserving for the posteromedial femoral condyle. FA had the most externally rotated femoral components and was most bone-preserving for the distal femoral resections. Conclusion The study shows that implant alignment to the mechanical axis or joint line anatomy (equal resections) alone does not guarantee a balanced total knee arthroplasty. FA resulted in the highest proportion of balanced knees across all analysed subgroups. Future research will consider whether one alignment philosophy leads to superior outcomes for different constitutional alignment subgroups. Level of evidence Level II.

Purpose Restricted kinematic alignment (rKA) in total knee arthroplasty (TKA) aims to restore native soft tissue laxities while limiting alignment extremes that risk prosthetic failure. However, there is no consensus where restricted boundaries (RB) should be set. This study aims to determine the proportion of limbs in which constitutional alignment and joint line obliquity (JLO) would be restored with various RB scenarios, to inform decision making in rKA TKA. Methods The mechanical hip–knee–ankle (mHKA) angle, arithmetic hip–knee–ankle (aHKA) angle, lateral distal femoral angle (LDFA) and medial proximal tibial angle (MPTA) were measured on radiographs of 500 normal knees. Incrementally wider RBs were then applied. The proportion of limbs within each increment was determined when RBs were applied only to HKA, or to HKA, LDFA and MPTA together. In addition, the proportion of limbs within published adjusted mechanical alignment (aMA) and rKA protocols were determined, as well as those within one, two and three standard deviations of the means for HKA, LDFA and MPTA. Results When restrictions to mHKA alone were applied, 74.0% and 97.8% of knees were captured with boundaries of ± 3° and ± 6° respectively. However, when the same boundaries to HKA were also applied to MPTA and LDFA, 36.2% and 91.0% of knees were captured respectively, highlighting the limiting effect that JLO has on restoration of normal knee phenotypes. When comparing previously published boundaries, aMA of 0° ± 3° captured 36.2%; rKA of 0° ± 3 for HKA and 85° to 95° for LDFA/MPTA captured 67.8%; rKA of − 5° to 4° HKA and 86°–93° for LDFA/MPTA captured 63%; and rKA of − 6° to + 3° for HKA and 84°–93° for LDFA/MPTA captured 85.4%. Conclusion The greatest proportions of normal knee phenotypes were captured with boundaries that were centred around population means for HKA and JLO. Further, these findings demonstrate that restricting the JLO has a significant limiting influence on restoration of normal knee phenotypes beyond that of restricting HKA alone. Level of evidence III.

Purpose Biomechanical studies suggest that PF tracking is not reliably restored to physiological values in TKA despite surgical technique optimization. A clinical observation is that current TKA designs may not replicate anterior femoral offset. The aim was to examine the intraoperative resection thicknesses of the anterior femoral condyles during TKA and correlate these findings relative to modern prostheses. Methods This was a retrospective analysis of 199 patients who underwent 233 TKAs using a single implant design with measured anterior femoral condylar resection thicknesses. The aim was to restore posterior condylar offset whilst minimizing overstuffing of the anterior compartment of the knee by choosing the smallest prosthesis to allow for the maximal anterior resection as close to the cortex without inducing notching. Prosthetic measurements from 7 commonly used TKAs were collected by analysis of 3D models of median sized explants. Results An average of 7.9 mm (SD 2.5 mm, range 2–16.5 mm) and 11.5 mm (SD 2.5 mm, range 2–21 mm) was resected from the medial and lateral aspects of the anterior femur, respectively. The average anterior flange thickness for the prosthesis data set was 6.6 mm (SD 0.6 mm, range 6.1–7.9 mm) medially and 7.6 mm (SD 0.7 mm, range 6.8–9.0 mm) laterally. Comparison across patients who received the median prosthesis size of 5 (SD 1.3, range 2–8) was inadequately restored by 1.4 mm ( p  < 0.00001) medially and 3.4 mm ( p  < 0.00001) laterally. Conclusion Host anatomy is not routinely restored during TKA. The surgical teaching to aim for an anterior femoral osteotomy close to the anterior cortex will result in understuffing of the PFJ and based on current prosthesis designs, the risk of overstuffing is not as significant as once believed. Future prostheses and surgical techniques should aim to restore not only posterior femoral but also anterior femoral offset. Level of evidence IV, Case series.

Purpose. To compare the extent of tibial bone covered by the tibial tray in 6 most commonly used total knee arthroplasty designs in order to strike a balance between mediolateral cortical fit and optimal tibial component rotation. Methods. In 74 men and 27 women aged 17 to 60 (mean, 32) years with suspected soft-tissue injuries, their magnetic resonance images of the knee in full extension were superimposed with scans of the tibial trays of the 6 designs (one asymmetric and 5 symmetric). The tibial coverage by the tray and any posterolateral/posteromedial overhang/underhang were measured. Results. All 6 tray designs achieved tibial bone coverage of over 80%. Only 28% of all trays achieved optimal posterolateral fit, whereas 49% had posterolateral overhang enough to cause popliteal tendon impingement. Although the asymmetric tray provided highest tibial coverage (88%), its rates of relative and absolute posterolateral and posteromedial overhang were also highest (64%). Conclusion. The asymmetric tray provided improved tibial coverage at the expense of posterolateral and posteromedial overhang of the tibial tray.

Background The accuracy of surgeon-defined assessment (SDA) of soft tissue balance in total knee arthroplasty (TKA) is poorly understood despite balance being considered a significant determinant of surgical success. The study’s hypothesis was that intra-operative SDA is a poor predictor of coronal balance in TKA. Methods A prospective, multicenter study assessing accuracy of SDA of balance was conducted in 250 patients (285 TKAs). Eight surgeons and thirteen trainees participated, and all were blinded to sensor measurements. The primary outcome was test accuracy of SDA measured at 10°, 45° and 90° compared to sensor measures as the gold standard test. Cohen’s kappa coefficient was calculated to determine chance-corrected agreement. Secondary outcomes include the relationship of SDA to level of surgical experience, analysis of between-surgeon differences, and the influence of patient and operative factors on SDA accuracy. Results Average accuracy of SDA was 58.3%, 61.2% and 66.5% at 10°, 45° and 90° respectively. Cohen’s kappa coefficient was 0.18 at all angles and rated as “slight agreement”. SDA sensitivities to correctly identify a balanced knee (76.2% at 10°; 82.6% at 45°; 83.2% at 90°) were approximately twice specificities to correctly identify an unbalanced knee (42.6% at 10°; 34.1% at 45°; 41.4% at 90°). Surgical experience (surgeon versus trainee) had no effect on capacity to determine balance. Considerable between-surgeon variability was found (33–65% at 10°, 41–73% at 45°, 55–89% at 90°). Conclusion SDA was a poor predictor of balance, particularly when assessing the unbalanced TKA. Surgeon experience had no effect on test accuracy and considerable between-surgeon variability was recorded. These findings question the accuracy of SDA in TKA. Trial Registration Number : ACTRN# 12618000817246.

Purpose. To evaluate the effect of intra-articular tranexamic acid (TXA) on blood loss after total knee arthroplasty (TKA). Methods. Medical records of 73 men and 93 women (mean age, 68 years) who underwent primary TKA for osteoarthritis and received intra-articular TXA 1500 mg (n=56) or 3000 mg (n=56) or not at all (n=54) were reviewed. Reduction in haemoglobin levels on days 1 and 2 was measured, as were the rates of venous thromboembolism (VTE) and blood transfusion. Results. Reduction in haemoglobin levels on day 2 was significantly greater in controls (35±11 g/dl) than the 1500 mg TXA group (29±9 g/dl, p=0.005) and the 3000 mg TXA group (23±10 g/dl, p±0.001). The difference between the 2 TXA groups was also significant (p=0.002). There was a dose-dependent effect of TXA on blood loss. The rates of VTE and blood transfusion did not differ significantly between groups. Conclusion. Intra-articular administration of TXA is effective in reducing blood loss after TKA, without increasing the risk of VTE.