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Purpose The purpose of this study was to visualise the influence of alignment strategy on bone resection in varus knee phenotypes. The hypothesis was that different amounts of bone resection would be required depending on the alignment strategy chosen. Through visualisation of the corresponding bone sections, it was hypothesised, it would be possible to assess which of the different alignment strategies would require the least amount of change to the soft tissues for the chosen phenotype, whilst still ensuring acceptable alignment of the components, and thus could be considered the most ideal alignment strategy. Methods Simulations of the different alignment strategies (mechanical, anatomical, constrained kinematic and unconstrained kinematic) in relation to their bone resections were performed on five common exemplary varus knee phenotypes. VAR HKA 174° VAR FMA 87° VAR TMA 84°, VAR HKA 174° VAR FMA 90° NEU TMA 87°, VAR HKA 174° NEU FMA 93° VAR TMA 84° , VAR HKA 177° NEU FMA 93° NEU TMA 87° and VAR HKA 177° VAL FMA 96° VAR TMA 81°. The phenotype system used categorises knees based on overall limb alignment (i.e. hip knee angle) but also takes into account joint line obliquity (i.e. TKA and FMA) and has been applied in the global orthopaedic community since its introduction in 2019. The simulations are based on long-leg radiographs under load. It is assumed that a change of 1° in the alignment of the joint line corresponds to a displacement of the distal condyle by 1 mm. Results In the most common phenotype VAR HKA 174° NEU FMA 93° VAR TMA 84°, a mechanical alignment would result in an asymmetric elevation of the tibial medial joint line by 6 mm and a lateral distalisation of the femoral condyle by 3 mm, an anatomical alignment only by 0 and 3 mm, a restricted by 3 and 3 mm, respectively, whilst a kinematic alignment would result in no change in joint line obliquity. In the similarly common phenotype 2 VAR HKA 174° VAR FMA 90° NEU TMA 87° with the same HKA, the changes are considerably less with only 3 mm asymmetric height change on one joint side, respectively, and no change in restricted or kinematic alignment. Conclusion This study shows that significantly different amounts of bone resection are required depending on the varus phenotype and the alignment strategy chosen. Based on the simulations performed, it can, therefore, be assumed that an individual decision for the respective phenotype is more important than the dogmatically correct alignment strategy. By including such simulations, the modern orthopaedic surgeon can now avoid biomechanically inferior alignments and still obtain the most natural possible knee alignment for the patient.

Medicine has been under a constant change. The latest strong and permanent trend in most of the medical fields is personalized medicine. Personalized medicine or theragnostics means targeting your diagnostics and treatment more towards the individual patient than to the mean of your patient population. In contrast, historical and current knee arthroplasty alignment and implantation concepts followed and still follow a systematic approach, mostly the mechanical alignment concept. However, the wind of change has yet arrived in total knee arthroplasty. If one would have asked knee arthroplasty surgeons about their preferred alignment concept following ten years ago, it predominantly would have been mechanical alignment. The most personalized alignment concept in the past was anatomical alignment, which still is a systematic approach and leads to a neutral mechanical alignment, however, puts the tibial joint line in 3° varus and the femoral one in 3° valgus.

Acetabular bone defect quantification and classification is still challenging. The objectives of this study were to suggest and define parameters for the quantification of acetabular bone defects, to analyze 50 bone defects and to present the results and correlations between the defined parameters. The analysis was based on CT-data of pelvises with acetabular bone defects and their reconstruction via a statistical shape model. Based on this data, bone volume loss and new bone formation were analyzed in four sectors (cranial roof, anterior column, posterior column, and medial wall). In addition, ovality of the acetabulum, lateral center-edge angle, implant migration, and presence of wall defects were analyzed and correlations between the different parameters were assessed. Bone volume loss was found in all sectors and was multidirectional in most cases. Highest relative bone volume loss was found in the medial wall with median and [25, 75]-percentile values of 72.8 [50.6, 95.0] %. Ovality, given as the length to width ratio of the acetabulum, was 1.3 [1.1, 1.4] with a maximum of 2.0, which indicated an oval shape of the defect acetabulum. Lateral center-edge angle was 30.4° [21.5°, 40.4°], which indicated a wide range of roof coverage in the defect acetabulum. Total implant migration was 25.3 [14.8, 32.7] mm, whereby cranial was the most common direction. 49/50 cases showed a wall defect in at least one sector. It was observed that implant migration in cranial direction was associated with relative bone volume loss in cranial roof (R = 0.74) and ovality (R = 0.67). Within this study, 50 pelvises with acetabular bone defects were successfully analyzed using six parameters. This could provide the basis for a novel classification concept which would represent a quantitative, objective, unambiguous, and reproducible classification approach for acetabular bone defects.

Purpose Clinical outcome of TKA remains unsatisfactory in 20% of the cases. Navigation has added accuracy in terms of alignment, but has improved clinical outcome only in small series with gap-balanced techniques. Reason for that could be that conventional gap balanced TKA determines gaps in extension and 90° of flexion only. Furthermore, measurement is only static. Therefore, the accuracy of a new dynamic navigation software which allows gap assessment throughout the entire range of motion was tested. The purpose of this study was to investigate the accuracy and reliability of dynamic gap testing during gap-balanced TKA. Methods In two different centres, a total of 65 TKA procedures were performed in a tibia-first, gap-balanced technique using a new CAS software. At the same and at different time points of surgery, two different surgeons performed gap measurement to provide inter-observer reliability data and repeated gap measurement to provide intra-observer reliability data. These gap measurements were performed throughout the entire ROM under dynamic stress testing to detect maximum gap values. Results CAS surgery was able to produce correct coronal alignment in 96.4% of the cases (within 3° mechanical alignment). Both inter-observer and intra-observer reliabilities were excellent for gap values throughout the entire ROM. Inter-observer bias of deviation 0.05; 95% limits of agreement of − 2.1 to + 2.21 mm. Intra-observer bias of deviation 0.09; 95% limits of agreement of − 2.27 to + 2.44 mm. Conclusions This new CAS software in combination with the presented dynamic gap measurement provides accurate gap values and therefore facilitates balancing TKA. This technique works reproducibly for different surgeons and has proven robustness also for repeated measurements of any surgeon in this study.

Background Osteoarthritis (OA) is one of the most common disabilities in the elderly. When conservative management fails, total joint arthroplasty (TJA) is the treatment of choice for end-stage OA. Since quality and durability of implants has steadily improved, pre -and postsurgical processes moved into the focus of research. Hence, eHealth approaches offer an opportunity to provide a more available continuity of care. Regarding individualized pre-, peri-, and postsurgical stages, eHealth is expected to improve patient engagement, self-care, and outcomes across the surgical pathway. Aim of this study is to evaluate the effectiveness of the eHealth application “alley” as an adjuvant intervention to TJA. The app provides comprehensive information to empower patient with hip or knee OA to prepare and accompany them for their TJA surgery. Our primary hypothesis is that the pre- and postoperative adjuvant use of the eHealth application “alley” (intervention group, IG) leads to improved functional outcome. Methods Prospective, randomized, controlled, multi-center trial including n  = 200 patients diagnosed with hip and n  = 200 patients with knee OA ( n  = 200) scheduled for TJA. Patients of both groups will be randomly assigned to one of two study arms. Patients in the intervention group will receive access to the functions of the “alley” app. The app presents informative (e.g., information about osteoarthritis), organizational (e.g., information about medical rehabilitation), and emotional/empowerment (e.g., information about the relationship between mood and pain) content. Patients evaluate their condition and functional level by means of standardized digitally questionnaires. Patients in the control group will not receive any functions of the app. Assessments will be performed at baseline before, 10 days after, 1 months after, 3 months after, 6 months after, and 12 months after TJA. Primary outcome is change from baseline measured by the Hip Osteoarthritis Outcome Score or Knee injury and Osteoarthritis Outcome Score 3 months after TJA. The statistical analysis ( t -test for independent variables with effect size Cohen’s d ) is performed separately for patients with TKA and THA. Discussion Overall, the study aims to improve the understanding of the benefits of eHealth applications in the treatment of elderly patients with knee or hip arthroplasty. The approach is novel since a health care companion is combined with a digital information platform enabling direct and continuous feedback from the patients to the therapeutic treatment team. As the study investigate the effectiveness under everyday conditions, it is not feasible to control whether the patients in the IG read the educational information of the app respectively the control group consume additional information from other sources. However, this increases the external validity of the study if significant effects for the app can be demonstrated. Trial registration German Clinical Trials Register: DRKS00025608. Registered on 21 June 2021.

Purpose The purpose of this study was to investigate the dynamic gap widths of valgus knees in extension and flexion to evaluate the influence of deformity on gap differences and to find out whether different ligamentous subtypes in valgus knees exist. Methods Dynamic gap widths of 1000 consecutive total knee arthroplasty (TKA) patients were measured at different flexion angles by applying a computer-assisted surgery (CAS) technique. 198 knees showed a valgus deformity and were assessed regarding its degree of fulfillment of the following criteria of valgus knee: 1. Medial extension gap greater than lateral; 2. Medial flexion gap greater than lateral; 3. Flexion gap greater than extension gap. A single-factor ANOVA subgroup analysis was performed, based on the amount of deformity. The effect of other patient factors (age, gender, weight) on gap differences was investigated. Results The medial extension gap (3.7 ± 2.2 mm) was significantly ( p  < 0.01) larger than the lateral extension gap (1.1 ± 2.9 mm). The amount of deformity correlated highly with gap difference in extension ( r 2  = 0.67) but not in flexion. In 92.4% (183), the flexion gap (6.2 ± 3.1 mm) was significantly ( p  < 0.01) larger than the extension gap (2.4 ± 2.3 mm). Only 29.3% (58) of patients met all three criteria, this was mainly due to the fact that in flexion the medial gap was larger than the lateral in only 35.4% (70). Patient factors showed no significant influences (NS) on the gap widths. Conclusion Valgus knees show large variability in terms of gap widths. The extent of deformity correlates highly with gap difference in extension, but not in other flexion angles. Vast majority of valgus knees were valgus in extension only. Because of this variability, it should be aimed for an individualized balancing technique based on intraoperative gap sizes. Level of Evidence Level III.

Purpose To achieve a higher level of satisfaction in patients having undergone Total Knee Arthroplasty (TKA), a more personalized approach has been discussed recently. It can be assumed that a more profound knowledge of bony morphology and ligamentous situation would be beneficial. While CT/MRI can give 3D information on bone morphology, the understanding of the ligamentous situation in different flexion angles is still incomplete. In this study, the dynamic gap widths of a large number of varus knees were assessed in various flexion angles, to find out whether all varus knees behave similar or have more individual soft tissue patterns. Additionally, it was investigated whether the amount of varus deformity or other patient factors have an effect on joint gap widths. Methods A series of 1000 consecutive TKA patients, including their CAS data and patient records were analyzed. Joint gap widths in multiple flexion angles (0°, 30°, 60°, 90°) were measured in mm and differences between the joint gaps were compared. A “standard” varus knee was defined as follows: (1) Lateral extension gap greater than medial, (2) lateral flexion gap greater than medial, and (3) flexion gap greater than extension gap. The percentage of fulfillment was tested for each and all criteria. To measure the influence of varus deformity on gap width difference, three subgroups were formed based on the deformity. Data were analyzed at 0°, 30°, 60° and 90° flexion. The effect of patient factors (gender, BMI, age) on gap sizes was tested by performing subgroup analyses. Results Only 444 of 680 (65%) patients met all three varus knee criteria. The lateral extension gap (4.1 mm) was significantly larger than the medial extension gap (0.6 mm) in 657 (97%) patients and the gap difference highly correlated with the amount of varus deformity ( r 2  = 0.62). In all flexion positions, however, no correlation between gap differences and varus deformity existed. Women had significantly larger extension and flexion gaps. Age and BMI showed no significant effect on gap widths. Conclusion Varus knees show a large inter-individual variability regarding gap widths and gap differences. The amount of varus deformity correlates highly with the medio-lateral gap difference in extension, but not in any flexion angle. As varus knees are not all alike, a uniform surgical technique will not treat all varus knees adequately and the individual gap sizes need to be analyzed and addressed accordingly with an individualized balancing technique. Which final balancing goal should be achieved needs to be analyzed in future studies. Level of evidence Level III.

Background The posterior cruciate ligament (PCL) plays an important role in maintaining physiological kinematics and function of the knee joint. To date mainly in-vitro models or combined magnetic resonance and fluoroscopic systems have been used for quantifying the importance of the PCL. We hypothesized, that both tibiofemoral and patellofemoral kinematic patterns are changed in PCL-deficient knees, which is increased by isometric muscle flexion. Therefore the aim of this study was to simultaneously investigate tibiofemoral and patellofemoral 3D kinematics in patients suffering from PCL deficiency during different knee flexion angles and under neuromuscular activation. Methods We enrolled 12 patients with isolated PCL-insufficiency as well as 20 healthy volunteers. Sagittal MR-images of the knee joint were acquired in different positions of the knee joint (0°, 30°, 90° flexion, with and without flexing isometric muscle activity) on a 0.2 Tesla open MR-scanner. After segmentation of the patella, femur and tibia local coordinate systems were established to define the spatial position of these structures in relation to each other. Results At full extension and 30° flexion no significant difference was observed in PCL-deficient knee joints neither for tibiofemoral nor for patellofemoral kinematics. At 90° flexion the femur of PCL-deficient patients was positioned significantly more anteriorly in relation to the tibia and both, the patellar tilt and the patellar shift to the lateral side, significantly increased compared to healthy knee joints. While no significant effect of isometric flexing muscle activity was observed in healthy individuals, in PCL-deficient knee joints an increased paradoxical anterior translation of the femur was observed at 90° flexion compared to the status of muscle relaxation. Conclusions Significant changes in tibiofemoral and patellofemoral joint kinematics occur in patients with isolated PCL-insufficiency above 30 degrees of flexion compared to healthy volunteers. Since this could be one reasonable mechanism in the development of osteoarthritis (OA) our results might help to understand the long-term development of tibiofemoral and/or patellofemoral OA in PCL-insufficient knee joints.

The hypothesis of this study was that length, torsion, and axis of a leg phantom can be measured accurately and reproducibly by magnetic resonance imaging (MRI) and that this can be applied to patients with leg deformities. Two phantoms and 30 patients (genu varum, n  = 15; genu valgum, n  = 15) were investigated using an optimized MRI technique. Reference measurements were performed with a micrometer screw and a goniometer. Patient leg length and axis were compared with long radiographs in bipedal stance. Intra- and interobserver reproducibility and accuracy were calculated using the mean absolute difference (MAD) and the 95% confidence interval. In patients, comparisons were done using a paired Student’s t -test. MAD, intraobserver MAD, and interobserver MAD were 0.03, 0.03, 0.04 mm (length); 0.98, 1.2, 0.98° (torsion); and 0.18, 0.23, 0.22° (axis), respectively. In patients, leg length was underestimated by MRI (−2.4 ± 0.7%; 1.9 ± 0.7 cm; P  < 0.001). The hip-knee-ankle angle (HKA) did not show significant differences in varus knees (−0.5 ± 1.0°; P  > 0.05), while it was significantly underestimated in valgus knees (−3.6 ± 2.8°; P  < 0.05). The phantom study revealed that leg length, torsion, and axis can be measured accurately and reproducibly by MRI. Although underestimation of leg length and HKA in valgus knees occurred, this optimized MRI technique can be applied to patients with leg deformities.

Purpose Navigated, gap-balanced adjusted mechanical alignment (AMA) including a 0° varus tibial cut and modification of angles and resections of the femoral cuts to obtain optimal balance accepting minor axis deviations. Objectives of this study were (1) to analyse to what extent AMA achieves the goals for leg alignment and gap balance, and (2) in what percentage non-anatomical cuts are needed to achieve these goals. Methods Out of 1000 total knee arthroplasties (TKA) all varus knees (hip-knee-ankle (HKA) angle < 178°; n  = 680) were included. All surgeries were performed as computer assisted surgery (CAS) in AMA technique. CAS data at the end of surgery were analysed with respect to HKA and gap-sizes. All bone cuts were quantified. Depending on the amount of deformity, a subgroup analysis was performed. It was analysed whether the amount of deformity influences the non-anatomical cuts by correlation analysis. Results AMA reached the goals for postoperative HKA (3° corridor) in 636 cases (93.5%). While extension and flexion gap balance were achieved in more than 653 cases (96%), flexion and extension gap size were equalled in 615 knees (90.4%). The resections of the lateral tibia plateau and distal and posterior medial femoral condyle were anatomical (Tibia: 7.0 ± 1.7 mm; medial condyle distal: 7.8 ± 1.4 mm; medial posterior: 8.2 ± 1.8 mm). The number of non-anatomical resections for those cuts were low; 67 (9.9%); 24 (3.5%); 32 (4.7%). For the medial tibia plateau and the lateral posterior condyle, the cuts were non-anatomical in a high percentage of cases; Tibia: 606 (89.1%), lateral posterior condyle: 398 (58.5%). Moderate but significant correlations were found between resection differences and amount of deformity (medio-lateral: tibia: 0.399; distal femur: 0.310; posterior femur: 0.167). No correlations were found between resection differences and gap values. Conclusion AMA reaches the intended target for HKA and gap balance in over 612 (90%) of cases and maintains the medial femoral condyle anatomically. Non-anatomical tibial resection causes increased external rotation of the femoral component and by that non-anatomical cut of the posterior lateral condyle. Nonanatomical resections of AMA might be one reason for the persisting high rate of unsatisfied patients after TKA. Anatomical and individual alignment philosophies might help to reduce this rate of dissatisfaction.