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Background: This study compared the early rehabilitation progress of patients undergoing robotic-assisted medial unicompartmental knee arthroplasty (mUKA) and robotic-assisted kinematically aligned total knee arthroplasty (rKA-TKA), focusing on daily activity by step-count measurements. Methods: A retrospective analysis of prospectively collected data from 88 patients (53 rKA-TKA and 35 mUKA) was conducted. Patients wore Garmin Vivofit® 4 activity trackers pre and postoperatively. Daily step counts were analyzed, and clinical outcomes were assessed using various scores, including the Knee Society Score (KSS) and Forgotten Joint Score (FJS). Results: Preoperative median daily step counts were comparable between groups (rKA-TKA: 3988 and mUKA: 4315; p = 0.128). At 6 and 7 weeks post-surgery, the mUKA group showed significantly higher median step counts (3741 and 4730) compared to the rKA-TKA group (2370 and 2910), with p-values of 0.015 and 0.048, respectively. The mUKA group reached 86.7% of their preoperative step count at week 6 and 100% at week 7, while the rKA-TKA group achieved 59.4% and 73%, respectively. Both groups surpassed their preoperative activity levels by week 9. Clinical outcomes at 2 months and 1 year post-surgery showed no significant differences between groups. Conclusions: While both the mUKA and rKA-TKA patients achieved their preoperative daily activity levels within nine weeks post-surgery, the mUKA patients reached this milestone approximately two weeks earlier. This study demonstrates a clinical benefit of mUKA in terms of faster postoperative remobilization, even when compared to kinematically aligned robotic-assisted TKA.

PurposeDetermining the point at which a valgus deformity requires a more invasive therapy—in this case PS TKA—is surgically challenging. Retaining the posterior cruciate ligament has both advantages and disadvantages. The aim was to evaluate the failure rate and clinical outcomes.Methods248 patients with valgus gonarthrosis underwent surgical treatment: 167 CR TKA cases and 81 PS TKA cases. The KOOS and the OKS were recorded, and 201 patients (133 CR, 68 PS) were recruited into the retrospective study. The influence of BMI and degree of preoperative valgus deformity on the clinical outcome was determined. The revision rate was documented and analysed.ResultsOf 201 patients, 10 required revision surgery owing to instability (10/133 CR, 0/68 PS). Based on the KOOS and the OKS, no significant difference between CR TKA and PS TKA was found. BMI and degree of valgus deformity had no effect on the clinical outcome.ConclusionsNo difference in the clinical outcome between the CR and PS TKA patients was found. In the CR group, significantly more patients showed ‘excellent’ OKS than in the PS group. However, 8.0% of the patients in the CR group and none in the PS group underwent surgery due to instability. A higher rate of dissatisfied patients in the CR group is likely. In our clinic, we no longer perform CR TKA for valgus cases.

Background. Late-onset chronic (low-grade) periprosthetic joint infections are often accompanied by unspecific symptoms, false-negative cultures or nonspecific low values of serum biomarkers. This may lead to the unintended implantation of a revision prosthesis into an infected surgical site with the risk of short-term failure developing again. Conversely, false diagnosis of joint infection may result in multistage revision procedures, which expose the patient to unnecessary surgical procedures and inappropriate antibiotic treatment. Here, we investigated whether circulating biomarkers can preoperatively distinguish between aseptic prosthesis loosening and low-grade joint infection, and which biomarker combinations are most accurate. Methods. Inclusion criteria for the study were indication for revision arthroplasty due to aseptic implant failure, acute high-grade infection, or (suspected) low-grade infection. C-reactive protein (CRP), procalcitonin, tumor necrosis factor α, interleukin 6 (IL-6), interleukin 10, and lipopolysaccharide binding protein were assessed preoperatively in the serum of 98 adult patients. Results. The classification tree method revealed IL-6 and CRP as the most suitable biomarker combination for the discrimination of aseptic loosening vs low-grade joint infection. The combination of IL-6 >5.12 pg/mL and CRP >0.3 mg/dL correctly identified 15 of 16 patients as having low-grade infection (94%) whereas just one patient was aseptic (6%). Conclusions. This is the first comprehensive prospective clinical study to our knowledge investigating the significance of a combined biomarker approach in differentiating between aseptic prosthesis loosening and low-grade joint infection. CRP plus IL-6 seems to be the most helpful combination for preoperative discrimination of aseptic loosening vs low-grade joint infection.

PurposeIt is known that in uni-compartmental knee arthroplasty (UKA) low-volume surgeons have a higher complication and revision rate than high-volume surgeons. Further, robotic-assisted UKA leads to lower early revision rate as well as fewer limb and joint line outliers compared to conventional UKA. The purpose of this study was to retrospectively analyze the outliers’ and revision rate of low-volume UKA surgeons with different robotic systems at short-term follow-up.MethodsIn this case–control study, 103 robotic-assisted UKAs were included. The procedures were performed between 2016 and 2019 from two low-volume UKA surgeons with an imageless (IL) (63 patients) and image-based (IB) (40 patients) robotic system. Alignment outliers, joint line (JL) reconstruction, complication and revision rates of the two different robotic systems were analyzed. The minimum follow-up was two years. Outliers were defined as a postoperative valgus malalignment greater than 182°. The surgery time for all procedures was evaluated.ResultsThe overall revision rate was 3.9% (4 of 103). Two occurred in the IB group (5.0%) and two in the IL group (3.2%). No valgus malalignment outliers were observed in both groups. The mean JL was not distalized by more than 2 mm in both groups (IL: 1.3 ± 1.6 mm vs. IB: 1.8 ± 0.9 mm, p value 0.08). The IL procedures had a significant lower mean surgery time (55 ± 13 min vs. 68 ± 14, p value 0.001).ConclusionRobotic-assisted UKA is a safe procedure in the hand of low-volume UKA surgeons. Robotic-assisted UKA minimizes overcorrection into valgus mal-alignment. Low revision rates are observed at short-term follow-up for robotic-assisted UKA. The choice of the different robotic systems has no impact on the outcome.

PurposeFlexion of the femoral component in 5° increments downsizes the femoral component, decreases the proximal reach and surface area of the trochlea, delays the engagement of the patella during flexion, and is associated with a higher risk of patellar-femoral instability after kinematically aligned TKA. The present study evaluated flexion of the femoral component after use of two kinematic alignment instrumentation systems. We determined whether a distal cutting block attached to a positioning rod inserted perpendicular to the distal femoral joint line in the axial plane and 8–10 cm into the distal femur anterior and posterior to the distal cortex of the femur in the sagittal plane or a femoral patient-specific cutting guide sets the femoral component in more natural flexion.MethodsFlexion of the femoral component was measured with respect to the sagittal femoral anatomic axis of the distal diaphysis and the sagittal femoral axis on rotationally controlled long-leg lateral computer scanograms. Measurements were performed on 53 consecutive patients treated with a kinematically aligned TKA performed with a distal cutting block attached to a positioning rod, and 53 consecutive patients treated with a kinematically aligned TKA performed with a femoral patient-specific cutting guide.ResultsThe average flexion and variability (±standard deviation) of the femoral component of patients treated with a positioning rod was 1° ± 2° and 7° ± 4° with respect to the anatomic and mechanical axes, respectively, which was 5° less than the average flexion of the femoral component of patients treated with a femoral patient-specific cutting guide of 6° ± 4° and 12° ± 5° (p = 0.0001, p = 0.0001, respectively).ConclusionsBecause a distal cutting block attached to a positioning rod sets the femoral component in 5° less flexion and with less variability than a femoral patient-specific cutting guide, we prefer this instrumentation system when performing kinematically aligned TKA to reduce the risk of patellar-femoral instability. Each surgeon should determine the repeatability of setting the flexion of the femoral component with this instrumentation system.

Clinical scores and motion-capturing gait analysis are today’s gold standard for outcome measurement after knee arthroplasty, although they are criticized for bias and their ability to reflect patients’ actual quality of life has been questioned. In this context, mobile gait analysis systems have been introduced to overcome some of these limitations. This study used a previously developed mobile gait analysis system comprising three inertial sensor units to evaluate daily activities and sports. The sensors were taped to the lumbosacral junction and the thigh and shank of the affected limb. The annotated raw data was evaluated using our validated proprietary software. Six patients undergoing knee arthroplasty were examined the day before and 12 months after surgery. All patients reported a satisfactory outcome, although four patients still had limitations in their desired activities. In this context, feasible running speed demonstrated a good correlation with reported impairments in sports-related activities. Notably, knee flexion angle while descending stairs and the ability to stop abruptly when running exhibited good correlation with the clinical stability and proprioception of the knee. Moreover, fatigue effects were displayed in some patients. The introduced system appears to be suitable for outcome measurement after knee arthroplasty and has the potential to overcome some of the limitations of stationary gait labs while gathering additional meaningful parameters regarding the force limits of the knee.

IntroductionIn the recent years modular partial knee prosthesis with the opportunity to combine unicompartmental tibiofemoral (UKA) and patellofemoral prosthesis (PFJ) were introduced to the clinics. To date, little is known about the biomechanics of these bi-cruciate retaining prosthetic designs. Aim of this study was to evaluate the influence of a PFJ in bicompartmental arthroplasty (UKA + PFJ) on patella tracking and retropatella pressure distribution.MethodsA dynamic in vitro knee kinemator simulating an isokinetic extension cycle of the knee was used on eight knee specimen. Patella tracking and patellofemoral contact pressure were evaluated using pressure sensitive films after implantation of a medial UNI and after subsequent implantation of a PFJ.ResultsWhereas the area contact pressure remained the same after PFJ implantation, the contact area was reduced significantly and significantly elevated peak pressures were determined in deep flexion and close to extension. The patella tracking was not significantly altered, however, effects of edge loading could be shown.ConclusionWhen using PFJ prosthesis, one must be aware of altered pressure introduction on the retropatella surface compared to the physiological situation. The elevated peak pressures and reduced contact area may be an argument for patella resurfacing and the problems of edge loading indicate that care must be taken on the correct implantation of the device with no implant overhang.

Aims and Objectives: The debate of cruciate retaining (CR) versus posterior stabilized (PS) designs in total knee arthroplasty (TKA) is ongoing. With the posterior cruciate ligament retained, the TKA is supposed to function better in terms of proprioception, balance and kinematics. In contrast to that, PS designs are supposed to lead to higher degrees of flexion and a better femoral rollback. It is known, that the preoperative deformity negatively correlates with inferior results following TKA. When balancing a valgus knee, Ranawat et al. suggest to address the PCL in the first place. It is known that in 60% of valgus knees 1-2 soft tissue releases are necessary in order to achieve neutral alignment. Up to date no study exists, reporting the outcome of CR versus PS TKA in valgus knees. Thus, it was purpose of this study to evaluate the mid term outcome of CR versus PS TKA for the treatment of valgus OA in groups between 3°-6° of valgus, 7-10° of valgus and >10° of valgus. Materials and Methods: With the KOOS score as the primary endpoint, a sample size of 117 cases (78 CR and 39 PS) was needed in order to get a statistical power of 80%.Between 01-2011 and 03-2014 a total of 248 patients with a preoperative valgus >3° were treated with a CR TKA (167 cases) or a PS TKA (81 cases) of the same manufacturer (Stryker Triathlon, Stryker, Kalamazoo USA). CR patients were divided into the following groups: Preoperative valgus >3°-6°, 7°-10° and >10°. PS patients were divided into the following groups: Preoperative valgus >3°-6°, 7°-10° and >10°. The KOOS Score and the Oxford Knee score was collected at the time of follow up. For the CR and PS group failure rates and failure etiologies were analyzed. Patients demographics and were collected as well. Results: 141 patients were included into this study (97 CR and 44 PS cases). The CR group had a mean follow up of 57 weeks, the PS group had a follow up of 52weeks. In the CR group, 11/97 (11%) patients were revised due to a.p. instability, whereas 2/44 (5%) patients were revised in the PS group due to infection or aseptic loosening. There was no difference regarding OKS and the KOOS score between the two groups. Further, there was no difference regarding patients demographics and no correlation between the BMI and the clinical outcome. Conclusion: The most important findings of this study are that the CR group showed a significant higher early revision rate, whereas the clinical mid term follow up results are equal. The CR version of the used system showed significantly higher early failure due to a.p. instability.

Purpose When performing unicondylar knee arthroplasty (UKA), the surgeon can choose between two fundamentally different designs: a mobile-bearing (MB) inlay with high conformity, or a low-conformity, fixed bearing (FB) inlay. There is an ongoing debate in the orthopaedic community about which design is superior. To date, there have been no comparative biomechanical studies regarding each system’s effects on the quadriceps force and the medial contact pressure. The purpose of this study was to investigate these alterations in vitro before and after UKA with two prosthesis systems, representing the MB and FB designs. Methods FB and MB unicondylar knee prosthesis designs were tested in sequence under isokinetic extension in an in vitro simulator. In each case, the required quadriceps extension force was determined before and after implantation of a medial UKA. Furthermore, the tibiofemoral contact pressures were evaluated for both prosthesis designs. Results The quadriceps force maximum was achieved at 106° and 104° of flexion with the FB and MB designs, respectively. Implantation of the FB UKA resulted in a significant increase in the necessary maximum quadriceps force ( p  = 0.006). In addition, implantation of the MB UKA resulted in a significantly higher extension force ( p  = 0.03). The difference between the two groups was statistically significant in deep flexion ( p  = 0.03), with higher forces in MB UKA. Conclusion The MB design showed significantly increased quadriceps extension force compared with the FB inlay in deep flexion. Although the FB design showed higher maximum peak pressures concentrated on a smaller area, the pressure introduction in deep flexion was lower, compared to MB inserts.

Aims and Objectives: Patients with isolated medial gonarthrosis benefit from a treatment with a unicompartmental knee arthroplasty (UKA) compared to a total knee arthroplasty (TKA). They have a shorter rehabilitation time, better function, lower morbidity and a higher satisfaction rate. However, the revision rate is higher than in patients with TKA. Patient selection and the resulting incorrect indication may be one reason. Hamilton et al.’s research group prepared a radiological “decision aid” for the indication of a UKA. The aim of this study was to validate this uncomplicated diagnostic procedure based on intraoperative findings. Materials and Methods: In this prospective study, 85 patients received routinely conventional x-rays. Strictly lateral and anterior-posterior view as well as varus/valgus stress x-rays were taken. Using Hamilton et al.’s “desiscion aid”, the x-ray images were preoperatively evaluated with regard to medial and lateral cartilage damage and the function of the anterior cruciate ligament. The cartilage damage of the individual tibial and femoral compartments was also scaled and documented intraoperatively. The results of the decision aid were validated with regard to the intraoperative findings. Indication-justifying cartilage damage was defined as focal complete cartilage loss. The sensitivity (SEN) and specificity (SPE) of decision aid with regard to cartilage damage in the medial and lateral compartments and the functionality of the anterior cruciate ligament were determined. Results: In the area of the medial compartment, decision aid has a SEN and PES of 79.4% and 82.4% respectively. The SEN and SPE for lateral compartments are 98.5% and 55.0%, respectively. Intact ACLs are correctly diagnosed at 94.7%. Insufficient ACLs at 33.3%. Conclusion: These data suggest that according to our findings, only about 2 out of 10 patients are not reliably diagnosed with medial gonarthrosis. However, about 2 out of 10 patients are diagnosed with medial gonarthrosis, which does not yet have to be treated with UKA. Furthermore, it could be shown that almost all patients with a completely laterally preserved cartilage are also recognized as such. However, every second patient with relevant cartilage damage is not radiologically identified. These data refer only to the radiological findings. Coupled with the patient’s medical history and clinic, the “Desicion Aid” is a very good aid for the correct indication for a UKA.