Imageless robotic total knee arthroplasty determines similar coronal plane alignment of the knee (CPAK) parameters to long leg radiographs.

BACKGROUND: The coronal plane alignment of the knee (CPAK) classification was first developed using long leg radiographs (LLR) and has since been reported using image-based and imageless robotic total knee arthroplasty (TKA) systems. However, the correspondence between imageless robotics and LLR-derived CPAK parameters has yet to be investigated. This study therefore examined the differences in CPAK parameters determined with LLR and imageless robotic navigation using either generic or optimized cartilage wear assumptions. METHODS: Medial proximal tibial angle (MPTA) and lateral distal femoral angle (LDFA) were determined from the intraoperative registration data of 61 imageless robotic TKAs using either a generic 2 mm literature-based wear assumption (Navlit) or an optimized wear assumption (Navopt) found using an error minimization algorithm. MPTA and LDFA were also measured from preoperative LLR by two observers and intraclass correlation coefficients (ICCs) were calculated. MPTA, LDFA, joint line obliquity (JLO), and arithmetic hip-knee-ankle angle (aHKA) were compared between the robotic and the average LLR measurements over the two observers. RESULTS: ICCs between observers for LLR were over 0.95 for MPTA, LDFA, JLO, and aHKA, indicating excellent agreement. Mean CPAK differences were not significant between LLR and Navlit (all differences within 0.6°, P > 0.1) or Navopt (all within 0.1°, P > 0.83). Mean absolute errors (MAE) between LLR and Navlit were: LDFA = 1.4°, MPTA = 2.0°, JLO = 2.1°, and aHKA = 2.7°. Compared to LLR, the generic wear classified 88% and the optimized wear classified 94% of knees within one CPAK group. Bland-Altman comparisons reported good agreement for LLR vs. Navlit and Navopt, with > 95% and > 91.8% of measurements within the limits of agreement across all CPAK parameters, respectively. CONCLUSIONS: Imageless robotic navigation data can be used to calculate CPAK parameters for arthritic knees undergoing TKA with good agreement to LLR. Generic wear assumptions determined MPTA and LDFA with MAE within 2° and optimizing wear assumptions showed negligible improvement.

Patient reported outcome measures correlate with step-count in total hip arthroplasty.

BACKGROUND: Passive smartphone-based apps are becoming more common for measuring patient progress after total hip arthroplasty (THA). Optimum activity levels during early THA recovery have not been well documented. OBJECTIVES: Correlations between step-count and patient reported outcome measures (PROMs) during early recovery were explored. This study also investigated how demographics impact step-count during early post-operative recovery. METHODS: Smartphone captured step-count data from 666 THA patients was retrospectively reviewed. Mean age was 64 ± 11 years. 55% were female. Mean BMI was 29 ± 8kg/m2. Mean daily step-count was calculated for each patient over four time-windows: 60 days prior to surgery (preop), 42-49 days postop (6 weeks), 91-98 days postop (3 months), and 183-197 days postop (6 months). Spearman correlation coefficients and linear regression were used to assess the association between PROMs (HOOS-12, HOOS-Jr, and UCLA) were performed. Patients were separated into three step-count levels: low (< 2500 steps/day), medium (2500-5500 steps/day), and high (> 5500 steps/day). Age > 65 years, BMI > 35 kg/m2, and sex were used for demographic comparisons. Post hoc analyses were performed using Welch's unequal variances t-tests, or Wilcoxon rank-sum tests, both with Bonferroni corrections, where appropriate when comparing between groups. Chi-squared analyses were also used when comparing categorical variables. RESULTS: UCLA correlated with step-count at all time-windows (p< 0.001). HOOS12-Function correlated with step-count preoperatively, at 6 weeks, and at 3 months (p< 0.001). High step-count individuals had improved UCLA scores compared to low step-count individuals preoperatively (Δ1.5, p< 0.001), at 6 weeks (Δ0.9, p< 0.001), at 3 months (Δ1.4, p< 0.001), and at 6 months (Δ1.4, p< 0.001). High step-count individuals had improved HOOS12-Function scores compared to low step-count individuals preoperatively (Δ9.6, p< 0.001), at 6 weeks (Δ5.3, p< 0.001), and at 3 months (Δ6.1, p< 0.001). Males had greater step-count at all time points (p< 0.001). Younger patients and low BMI patients had greater step-count across all time points (p< 0.001). CONCLUSION: High step-count improved PROMs scores compared to low step-count. Early post-operative step-count was significantly impacted by age, sex, and BMI. Generic recovery profiles may not be appropriate across diverse populations.

Restricted Inverse Kinematic Alignment Better Restores the Native Joint Line Orientation While Achieving Similar Balance, Laxity, and Arithmetic Hip-Knee-Ankle Angle to Gap Balancing Total Knee Arthroplasty.

Background: Both restricted inverse kinematic alignment (iKA) and gap balancing aim for a balanced total knee arthroplasty by adjusting femoral component position based on ligamentous gaps. However, iKA targets a native tibial joint line vs resecting perpendicular to the mechanical axis. This study compares how these 2 techniques impact the balance and laxity throughout flexion and joint line obliquity (JLO), arithmetic hip-knee-ankle angle (aHKA), and the coronal plane alignment of the knee (CPAK). Methods: Two surgeons performed 75 robot-assisted iKA total knee arthroplasties. A digital joint tensioner collected laxity data throughout flexion before femoral resection. The femoral component position was determined using predictive gap-planning to optimize the balance throughout flexion. Planned gap balancing (pGB) simulations were performed for each case using neutral tibial resections. Mediolateral balance, laxity, and CPAK were compared among pGB, planned iKA (piKA), and final iKA. Results: Both piKA and pGB had similar mediolateral balance and laxity, with mean differences <0.4 mm. piKA had a lower mean absolute difference from native JLO than pGB (3 ± 2° vs 7 ± 4°, P < .001). aHKA was similar (P > .05) between pGB and piKA. piKA recreated a more native CPAK distribution, with types I-V being the most common ones, while most pGB knees were of type V, VII, and III. Final iKA and piKA had similar mediolateral balance and laxity, with a root-mean-square error <1.4 mm. Conclusions: Although balance, laxity, and aHKA were similar between piKA and pGB, piKA better restored native JLO and CPAK phenotypes. The neutral tibial resection moved most pGB knees into types V, VII, and III. Surgeons should appreciate how the alignment strategy affects knee phenotypes.

Restricted kinematic alignment achieves similar relative lateral laxity and greater joint line obliquity compared to gap balancing TKA.

PURPOSE: The purpose of this study was to compare ligament balance and laxity profiles achieved throughout flexion in restricted kinematic alignment (rKA) and gap balancing (GB). rKA and GB both aim to improve soft tissue balance and reduce ligament releases in total knee arthroplasty (TKA). METHODS: One surgeon performed 68 rKA, another performed 73 GB TKAs using the same CR implant and robotic system. rKA limited femoral valgus and tibial varus to 6°, with tibial recuts performed to achieve balance. GB limited tibial varus and femoral valgus to 2°, with femoral resections adjusted to achieve mediolateral balance throughout flexion using predictive-gap planning software. Final joint laxity was measured using a robotic ligament tensioner. Statistical analyses were performed to compare differences in mediolateral balance and joint laxity throughout flexion. Further analyses compared alignment, joint line elevation and orientation (JLO), and frequency of ligament releases and bone recuts. RESULTS: Both techniques reported greater lateral laxity throughout flexion, with GB reporting improved mediolateral balance from 10° to 45° flexion. GB resected 1.7 mm more distal femur (p ≤ 0.001) and had greater overall laxity than rKA throughout flexion (p ≤ 0.01). rKA increased JLO by 2.5° and 3° on the femur and tibia (p ≤ 0.001). Pre-operative and post-operative coronal alignment were similar across both techniques. rKA had a higher tibial recut rate: 26.5% vs 1.4%, p < 0.001. CONCLUSIONS: rKA and GB both report lateral laxity but with different JLO and elevation. Use of a predictive-gap GB workflow resulted in greater mediolateral gap symmetry with fewer recuts. LEVEL OF EVIDENCE: III, retrospective cohort study.

Two-year migration characteristics of a novel cementless femoral stem: a radiostereometric analysis and clinical outcomes study.

BACKGROUND: Radiostereometric analysis (RSA) is an established high precision tool enabling us to detect early implant migration in total hip arthroplasty. The aim of this study is to present the RSA and clinical results of a new cementless hip stem and to compare those with established benchmarks. METHODS: A total of 45 patients (46 hips) undergoing total hip arthroplasty were available for full radiographic and clinical assessment at 2 years post-operatively. Mean patient age was 69 (range 43-85) years and mean body mass index was 29 (range 21-38) kg/m2 . RSA was undertaken at day 1, 6 weeks, 6 months and 1 and 2 years post-operatively. Oxford hip score and EQ-5D-5L scores were recorded preoperatively and at the same other time points. Results were compared to published data of established implants. RESULTS: At 2 years, mean subsidence and retroversion were 0.61 mm (standard deviation 0.7 mm, range -0.19 to 3.06 mm) and 0.44° (standard deviation 0.81°, range 0.98 to 3.29°), respectively. Stem migration occurred primarily in the first 6 weeks with no detectable subsidence or rotation at 6 months or 2 years. Mean Oxford hip score and EQ-5D-5L improved from 18.6 to 44.7, and 69 to 86, respectively. There was one cup-only revision and no revisions for stem loosening. CONCLUSION: RSA serves as an accurate measure of femoral stem stability early in the post-operative period. Our data confirm that stability occurs as early as 6 weeks and is sustained at 2 years. The Paragon stem demonstrates stability parameters at 2 years that exceed other established benchmark implants.

Total knee arthroplasty after patellectomy: A meta-analysis of case-control studies.

BACKGROUND: Post-patellectomy patients represent a specific subset of patients who can develop painful and disabling knee osteoarthritis that requires Total Knee Arthroplasty (TKA). The aim of this study was to conduct a meta-analysis comparing the outcome of TKA in patients with previous patellectomy to those with an intact patella. METHODS: A systematic search of electronic databases (PubMed, Medline, Embase, and Cochrane Library) was performed. Data on study setting, type of implant, outcome and associated complications were extracted. Quality assessment was performed using the Newcastle-Ottawa Scale. Random effects meta-analyses were used to combine the results of included studies. RESULTS: Seven case-control studies were found that met the search criteria. Compared to patients with an intact patella, patients with a previous patellectomy were less likely to have an 'excellent' or 'good' outcome (OR: 0.3, 95% CI: 0.14 to 0.65). The weighted mean post-operative knee flexion arc was 6.58° less in patients with a previous patellectomy (95% CI: -12.79, -0.37). The risk of complication occurring in a patella-deficient knee was higher, with a pooled OR of 1.97 (95% CI=1.10 to 3.51). CONCLUSIONS: The current evidence that compares the outcome of knee arthroplasty in patients with a previous patellectomy to patients with an intact patella is mostly based on TKAs performed in the 1980s and 1990s. Total knee replacement in patients with an intact patella results in superior outcomes compared to those with a previous patellectomy. In patients with a previous patellectomy, the arc of flexion is slightly less and the complication rate is significantly higher.