Background: Robotic-assisted unicompartmental knee arthroplasty (UKA) enhances the precision of component alignment compared to conventional techniques. Although various robotic systems exist, direct comparisons assessing their relative clinical performance remain limited. The purpose of this study is to provide a comparison between image-based and imageless robotic UKA. Methods: A systematic review was conducted in accordance with PRISMA guidelines. Five databases were searched: PubMed (via MEDLINE), Epistemonikos, Cochrane Library, Web of Science, and Scopus. Inclusion criteria were (1) studies comparing rUKA and cUKA with radiologic parameters and revision rates (prospective or retrospective), (2) human subjects, (3) meta-analyses for cross-referencing, and (4) English language. Data collected included (1) pre- and postoperative radiologic parameters, (2) radiologic outliers, and (3) revisions and their causes. A random-effects meta-analysis was employed to enable a generalizable comparison. Mean differences (MDs) with 95% confidence intervals (CIs) were calculated for continuous variables, and log odds ratios (LORs) with 95% CIs for binary outcomes. Results: Image-based robotic UKA was associated with fewer joint line height outliers (LOR = 3.5, 95% CI: 0.69–6.30, p = 0.015) using a 2° threshold. HKA outliers (thresholds 2–3°) were also reduced (LOR = 0.6, 95% CI: 0.09–1.19, p = 0.024). Posterior tibial and posterior femoral implant fit were significantly lower with image-based systems (LOR = 1.7, 95% CI: 1.37–2.03, respectively, LOR = 1.7, 95% CI: 1.29–1.91; p < 0.001 for both). No significant differences in revision rates were observed. Conclusions: Image-based robotic systems may result in fewer outliers in key radiologic parameters, including hip–knee angle, joint-line height, posterior tibial, and posterior femoral fit, though reporting remains highly heterogeneous.

Purpose: Registry data suggests that robotic-assisted unicompartmental knee arthroplasty (rUKA) significantly reduces all-cause revisions compared to conventional implantation (cUKA). This study aims to compare joint line-related parameters and their reconstruction accuracy between rUKA and cUKA. Methods: Five databases were searched using a pre-defined strategy and inclusion criteria: (1) comparative studies reporting radiological outcomes, (2) human studies, (3) English language, and (4) meta-analyses for cross-referencing. Cadaveric or saw-bone studies were excluded. Data extracted included demographics data, pre- and postoperative radiological parameters (HKA, MPTA, LDFA, posterior tibial slope, femoral sagittal angle, joint line height, implant congruency), and outliers. A random-effects meta-analysis was conducted using mean difference (MD) and odds ratio (OR) as main effect estimators. Risk of bias was assessed using the Newcastle-Ottawa Scale (NOS), and publication bias was evaluated with funnel plots. Results: A total of 18 studies assessing 2470 patients (1112 rUKA, 1358 cUKA) were included in the analysis. No significant baseline differences were found in age, sex, BMI, follow-up period, MPTA, LDFA, or tibial slope. Postoperative radiological parameters showed no significant differences between groups for HKA, LDFA, MPTA, or tibial slope ( p > 0.05). Joint line height was significantly lower in cUKA compared to rUKA (MD = -1.37 mm, 95% CI: -2.06 to -0.69, p < 0.001). Outlier analysis revealed that rUKA had significantly fewer outliers across relevant radiological parameters, including HKA, joint line height, tibial slope, femoral flexion, femoral implant congruency, and medial, anterior, and posterior tibial congruency. Conclusion: Reporting pre- and postoperative mean alignment parameters undermines patient-specific anatomy reconstruction with advanced technologies. Outlier reporting showed significant variability, with limited evidence supporting its clinical relevance. Future studies should focus on patient-specific reconstruction and define clinical thresholds for outliers.

Preoperative planning of total knee arthroplasty is usually performed using knee-centred computed tomography (CT) data sets. The disadvantage of these data sets is having no account of the biomechanical axis of the lower extremity, known as Mikulicz line. It aligns the femoral head to the middle of the talocrural joint. For optimal prosthesis arrangement, the knee CT data set must therefore be brought in congruency with this line of loading to achieve the best results and eliminate rotational malalignments.This study aims to establish a relation between the knee-centred clinical coordinate system (CCS) and a biomechanical coordinate system (BCS) based on the Mikulicz line. CT data sets of 45 lower extremities were evaluated. Using VG Studio Max, a visualisation and measurement software program; each CT data set was aligned according to the CCS and BCS. After superimposing both the aligned data sets, the deviations of both coordinate systems in all three planes were measured with the centre of the knee defined as the origin. For the coronal plane, the CCS was demonstrated to be 2.54° in adduction compared to the BCS [standard deviation (SD) = 1.8°]. In sagittal view, the CCS was demonstrated to be 0.3° retroversed (SD = 3.27°). Finally, the deviation in the axial plane showed an outward rotation of 3.39° (SD = 1.99°). The alignment as well as the measurements demonstrated high intraobserver and interobserver reproducibility. Both coordinate systems can be established in knee-centred CT data sets in a reproducible manner. Clearly, the CCS differs significantly from the BCS describing the biomechanical axis, but mathematical-based adaptations and corrections can be performed. The findings of this study allow a mathematical conversion of a knee CT to the biomechanical axis of the leg.

The principles of the hip arthroplasty, as we know them today, were established about 60 years ago by Sir John Charnley. Replacement of the hip joint became one of the most successful and safest therapeutic procedures. Hip arthroplasty has been shown to yield good long-term results without complications. Over the last 20 years, the development and establishment of minimally invasive operation techniques has contributed to rapid changes. Additionally, perioperative patient management was optimized. Improvements in the material and tribology of the implants led to promising developments. Nonetheless, analysis of possible complications, shows potential for further developments, for example in cup geometry. Enhanced training concepts for surgeons, operation simulators, simple navigation aids for component positioning can surely achieve improvements in surgical safety.