Machine learning with tree tensor networks, CP rank constraints, and tensor dropout.

Tensor networks developed in the context of condensed matter physics try to approximate order-N tensors with a reduced number of degrees of freedom that is only polynomial in N and arranged as a network of partially contracted smaller tensors. As we have recently demonstrated in the context of quantum many-body physics, computation costs can be further substantially reduced by imposing constraints on the canonical polyadic (CP) rank of the tensors in such networks. Here, we demonstrate how tree tensor networks (TTN) with CP rank constraints and tensor dropout can be used in machine learning. The approach is found to outperform other tensor-network-based methods in Fashion-MNIST image classification. A low-rank TTN classifier with branching ratio b = 4 reaches a test set accuracy of 90.3% with low computation costs. Consisting of mostly linear elements, tensor network classifiers avoid the vanishing gradient problem of deep neural networks. The CP rank constraints have additional advantages: The number of parameters can be decreased and tuned more freely to control overfitting, improve generalization properties, and reduce computation costs. They allow us to employ trees with large branching ratios, substantially improving the representation power.

Criticality and Phase Classification for Quadratic Open Quantum Many-Body Systems.

We study the steady states of translation-invariant open quantum many-body systems governed by Lindblad master equations, where the Hamiltonian is quadratic in the ladder operators, and the Lindblad operators are either linear or quadratic and Hermitian. These systems are called quasifree and quadratic, respectively. We find that steady states of one-dimensional systems with finite-range interactions necessarily have exponentially decaying Green's functions. For the quasifree case without quadratic Lindblad operators, we show that fermionic systems with finite-range interactions are noncritical for any number of spatial dimensions and provide bounds on the correlation lengths. Quasifree bosonic systems can be critical in D>1 dimensions. Last, we address the question of phase transitions in quadratic systems and find that, without symmetry constraints beyond invariance under single-particle basis and particle-hole transformations, all gapped Liouvillians belong to the same phase.

The 3-triangle method preserves the posterior tibial slope during high tibial valgus osteotomy: first preliminary data using a mathematical model.

PURPOSE: Despite much improved preoperative planning techniques accurate intraoperative assessment of the high tibial valgus osteotomy (HTO) remains challenging and often results in coronal over- and under-corrections as well as unintended changes of the posterior tibial slope. Noyes et al. reported a novel method for accurate intraoperative coronal and sagittal alignment correction based on a three-dimensional mathematical model. This is the first study examining preliminary data via the proposed Noyes approach for accurate intraoperative coronal and sagittal alignment correction during HTO. METHODS: From 2016 to 2020 a total of 24 patients (27 knees) underwent HTO applying the proposed Noyes method (Noyes-Group). Radiographic data was analyzed retrospectively and matched to patients that underwent HTO using the conventional method, i.e., gradual medial opening using a bone spreader under fluoroscopic control (Conventional-Group). All operative procedures were performed by an experienced surgeon at a single orthopaedic university center. RESULTS: From the preoperative to the postoperative visit no statistically significant changes of the posterior tibial slope were noted in the Noyes-Group compared to a significant increase in the Conventional-Group (p = 0.01). Regarding the axial alignment no significant differences between both groups were observed pre- and postoperatively. The number of over- and under-corrections did not differ significantly between both groups. Linear regression analysis showed a significant correlation of the postoperative medial proximal tibial angle (MPTA) with the position of the weightbearing line on the tibial plateau. CONCLUSION: The 3-triangle method by Noyes seems to be a promising approach for preservation of the posterior tibial slope during HTO.

Sweeping-beam technique with electrons for large treatment areas as total skin irradiation : Dosimetric and technical aspects of a modified Stanford technique.

PURPOSE: Total skin electron beam therapy (TSEBT) is still a technical and therapeutic challenge today. Thus, we developed TSEBT using a sweeping-beam technique. METHODS: For treatment delivery, a linear accelerator Versa HD (ELEKTA, Stockholm, Sweden) with high-dose-rate electrons (HDRE) was used with a dose rate of 9000 MU/min. Dosimetry quality assurance was performed by multiple measurements with film dosimetry, 2D array, and Roos chamber. RESULTS: Clinical experience shows that treatment durations of 75 to 90 min are usual for the Stanford technique without using HDRE. With this new sweeping-beam irradiation technique, the total treatment time of a daily fraction could be reduced to 20 min while keeping over- and underdosing low. The treatment area is about 60 cmâ€¯× 200 cm and the dose distribution is uniform within 2% and 5% in vertical and horizontal directions, respectively. Initially, the electron energy of 6 MeV is reduced to 3.2 MeV by 1­cm polymethylmethacrylat (PMMA) scatter and the irradiation conditions of a source-surface distance (SSD) of 350 cm. The photon contamination drops to under 1%. CONCLUSION: These results show that the mean dose to total skin varies between 1.3 and 1.8 Gy. The sweeping-beam technique with electrons has a homogeneous dose distribution in connection with a short treatment time.

Eigenstate Entanglement: Crossover from the Ground State to Volume Laws.

For the typical quantum many-body systems that obey the eigenstate thermalization hypothesis (ETH), we argue that the entanglement entropy of (almost) all energy eigenstates is described by a single crossover function. The ETH implies that the crossover functions can be deduced from subsystem entropies of thermal ensembles and have universal properties. These functions capture the full crossover from the ground-state entanglement regime at low energies and small subsystem size (area or log-area law) to the extensive volume-law regime at high energies or large subsystem size. For critical one-dimensional systems, a universal scaling function follows from conformal field theory and can be adapted for nonlinear dispersions. We use it to also deduce the crossover scaling function for Fermi liquids in d>1 dimensions. The analytical results are complemented by numerics for large noninteracting systems of fermions in d≤3 dimensions and have also been confirmed for bosonic systems and nonintegrable spin chains.

Focal cartilage defects of the lateral compartment do influence the outcome after high tibial valgus osteotomy.

INTRODUCTION: High tibial medial open-wedge valgus osteotomy (HTO) is a well-established procedure for unicompartimental medial osteoarthritis of the young and active patient. However, the influence of cartilage defects of the lateral compartment on the total outcome remains obscure. METHODS: From 2005 to 2012, a total of 63 patients underwent HTO for medial osteoarthritis of the knee at a single university orthopaedic center. Baseline data as well as intraoperative findings, including the grade and location of cartilage lesions, were evaluated retrospectively. Two groups were formed regarding the integrity of the lateral tibiofemoral compartment as measured by the Outerbridge score (group A: no lateral cartilage defects, group B: mild to moderate lateral cartilage defects). Functional outcome was assessed using the Knee and Osteoarthritis Outcome Score (KOOS), including its five subscores. RESULTS: Comparing pre- and postoperative data, we identified an overall benefit of the HTO procedure as measured by the KOOS. Group A (no lateral cartilage defects) showed an increase in all five KOOS subscores (p = 0.00-0.01), whereas for group B (mild to moderate lateral cartilage defects), only two KOOS subscores revealed a significant increase (p = 0.03-0.04). There was also a statistically significant difference in the total KOOS score with higher values for group A at the postoperative visit. Cartilage defects with a higher Outerbridge score were associated with lower postoperative KOOS subscores. DISCUSSION: Mild to moderate cartilage defects of the lateral compartment humble the total outcome after HTO procedure. Thus, indication for HTO should be made very carefully if any degree of lateral cartilage degeneration is present.

Why compromise the patella? Five-year follow-up results of medial patellofemoral ligament reconstruction with soft tissue patellar fixation.

PURPOSE: This study investigates the redislocation rate and functional outcome at a minimum follow-up of five years after medial patellofemoral ligament (MPFL) reconstruction with soft tissue patellar fixation for patella instability. METHODS: Patients were retrospectively identified and knees were evaluated for trochlea dysplasia according to Dejour, for presence of patella alta and for presence of cartilage lesion at surgery. At a minimum follow-up of five years, information about an incident of redislocation was obtained. Kujala, Lysholm, and Tegner questionnaires as well as range of motion were used to measure functional outcome. RESULTS: Eighty-nine knees were included. Follow-up rate for redislocation was 79.8% and for functional outcome 58.4%. After a mean follow-up of 5.8 years, the redislocation rate was 5.6%. There was significant improvement of the Kujala score (68.8 to 88.2, p = 0.000) and of the Lysholm score (71.3 to 88.4, p = 0.000). Range of motion at follow-up was 149.0° (115-165). 77.5% of the knees had patella alta and 52.9% trochlear dysplasia types B, C, or D. Patellar cartilage legions were present in 54.2%. Redislocations occurred in knees with trochlear dysplasia type C in combination with patella alta. CONCLUSION: MPFL reconstruction with soft tissue patellar fixation leads to significant improvement of knee function and low midterm redislocation rate. Patients with high-grade trochlear dysplasia should be considered for additional osseous correction.

Is debridement beneficial for focal cartilage defects of the knee: data from the German Cartilage Registry (KnorpelRegister DGOU).

INTRODUCTION: Focal cartilage defects of the knee are often treated with arthroscopic debridement. Existing literature discussing the benefit of debridement for small articular cartilage lesions is scarce, especially if the debridement was not part of a combined operative cartilage procedure including meniscal and ligament repair. The purpose of this study was to examine the patients´ benefit after arthroscopic debridement for the treatment of isolated focal chondral defects with or without partial meniscus resection. MATERIALS AND METHODS: Baseline (preoperative data) and 12-month follow-up of the five Knee Osteoarthritis Outcome Score (KOOS) subscores and the Numeric Rating Scale (NRS) for pain were analyzed in 126 patients undergoing debridement for focal chondral defects of the knee from the German Cartilage Registry. Sub-analysis for patients receiving isolated debridement and debridement with concomitant partial resection of meniscal pathologies was performed. Thus, four subgroups were created according to the treated defect size and presence of meniscal pathologies: "debridement-only < 2 cm2", "debridement-only > 2 cm2", "debridement and partial meniscus resection < 2 cm2" and "debridement and partial meniscus resection > 2 cm2". RESULTS: KOOS-subscores showed a significant increase from baseline to follow-up evaluation (p = 0.017-0.037) within the 126 patients. Sub-analysis showed significant improvement of all five KOOS-subscores in all three subgroups, except for the "debridement and partial meniscus resection > 2 cm2"-group: in this group the KOOS subscores symptoms and sports showed no significant improvement. The NRS scores revealed no significant changes from baseline to 12-month follow-up within the four subgroups. CONCLUSION: An overall benefit of arthroscopic debridement for focal cartilage lesions of the knee could be conducted. Isolated cartilage defects seem to benefit from debridement irrespectively of size. In patients with large cartilage defects (> 2 cm2) and concurrent meniscal pathology expectation to improvement should be humbled. Effective reduction of pain by arthroscopic debridement remains unclear.

[Indications and techniques of arthroscopic anterior and lateral acromioplasty]. / Aktuelle Indikationen und Techniken der arthroskopischen anterioren und lateralen Akromioplastik.

OBJECTIVE: Arthroscopic anterior acromioplasty (AAAP) for treatment of symptomatic subacromial spur. Arthroscopic lateral acromioplasty (ALAP) to reduce a pathological critical shoulder angle (CSA) and prevent rotator cuff re-tear after reconstruction. INDICATIONS: AAAP is indicated for acromial impingement due to an anterolateral acromial spur with or without bursa-sided rotator cuff lesion. ALAP is indicated concomitant to arthroscopic rotator cuff repair if the CSA is pathologically increased. RELATIVE CONTRAINDICATIONS: Irreparable rotator cuff tear with acetabularization of the acromion due to anterosuperior escape of the humeral head or symptomatic os acromiale can contraindicate for AAAP. Dehiscence of the origin of the deltoid muscle or symptomatic os acromiale can contraindicate for ALAP. SURGICAL TECHNIQUE: To preform AAAP, arthroscopic subacromial decompression is followed by anterolateral resection of an acromion spur or ossification of the coracoacromial ligament. To perform ALAP, arthroscopic subacromial decompression and reconstruction of a rotator cuff-tear is followed by reduction of a pathologically increased CSA by resection of the lateral edge of the acromion. POSTOPERATIVE MANAGEMENT: After isolated AAAP, physiotherapy can be performed without restriction. After AAAP or ALAP combined with rotator cuff repair, immobilization in a brace is recommended. The use of pain medication should be standardized and adapted to individual pain levels.

[Virtual arthroscopy : Gaming or training concept of the future]. / Virtuelle Arthroskopie : Computerspiel oder Weiterbildungskonzept der Zukunft?

Arthroscopy is a technically challenging surgical procedure with a relatively shallow learning curve compared to open procedures. To become an expert special cognitive and manual abilities have to be acquired and trained. The current situation in further medical education combined with the increasing economic pressure in the medical field does not leave enough room for a time-consuming training in arthroscopic techniques. A structured simulation training could be an alternative solution to this problem. The benefits of arthroscopic simulation training are meanwhile well documented. The complex tasks that an expert carries out during arthroscopy can be fragmented into more simple and elementary exercises and can be trained in a stress-free environment outside the operation room. An essential advantage of simulation training is the assessment of objective measurement parameters during the individual exercises. These parameters can be used to evaluate the learning process and performance of arthroscopic tasks. The aim of this review is to reflect the current state of simulation technology in arthroscopy and to show how simulator training can be meaningfully and effectively integrated into arthroscopic further training, exemplified by a modern medical further education concept.

Fundamental Limitations for Measurements in Quantum Many-Body Systems.

Dynamical measurement schemes are an important tool for the investigation of quantum many-body systems, especially in the age of quantum simulation. Here, we address the question whether generic measurements can be implemented efficiently if we have access to a certain set of experimentally realizable measurements and can extend it through time evolution. For the latter, two scenarios are considered: (a) evolution according to unitary circuits and (b) evolution due to Hamiltonians that we can control in a time-dependent fashion. We find that the time needed to realize a certain measurement to a predefined accuracy scales in general exponentially with the system size-posing a fundamental limitation. The argument is based on the construction of ϵ-packings for manifolds of observables with identical spectra and a comparison of their cardinalities to those of ϵ-coverings for quantum circuits and unitary time-evolution operators. The former is related to the study of Grassmann manifolds.

Surgical technique and clinical outcome of arthroscopic shoulder stabilization via suture anchors using the lasso-loop stitch.

During arthroscopic Bankart-repair the lasso-loop-stitch can be used. The clinical outcome of this technical modification to a broadly used procedure is not known. We followed-up 24 patients treated with this technique over 30 months. We found an excellent clinical outcome in 96% of all cases. The average Rowe-score was 96.3 points. The mean QuickDash was 2.8 points. Using the lasso-loop-stitch in arthroscopic Bankart-repair is safe and results in very good clinical outcomes. It might lead to an accentuated labral bump and enables secure knot-tying with knot-positioning away from the articular cartilage while avoiding the suture cutting through the tissue.

Mesenchymal Stem Cells Isolated from the Anterior Cruciate Ligament: Characterization and Comparison of Cells from Young and Old Donors.

PURPOSE: Mesenchymal stem cells (MSCs) isolated from the anterior cruciate ligament (ACL) share multiple characteristics of bone marrow-derived mesenchymal stem cells (BMSCs), allowing their use for regenerative therapies. Injuries to the ACL can affect people of all ages. This study assesses whether the regenerative potential of ACL-derived MSCs (ACL-MSCs) from old donors is as high as the potential of ACL-MSCs from young donors. MATERIALS AND METHODS: ACL-MSCs were isolated from ACL tissues obtained from young and old donors at the time of ACL reconstruction or arthroplasty. Proliferative capacity, multilineage differentiation potential (chondrogenic, osteogenic, and adipogenic lineages), and transcriptome-wide gene expression were assessed and compared between young and old donors. BMSCs of middle-aged donors served as an additional comparator. RESULTS: No substantial differences between ACL-MSCs from young and old donors were observed in their proliferative capacity and multilineage differentiation potential. The latter did not substantially differ between both ACL-MSC groups and BMSCs. Differential expression of genes related to the cytoskeleton and to protein dephosphorylation amongst other pathways was detected between ACL-MSCs from young and old donors. CONCLUSIONS: Regenerative potential of ACL-MSCs from old donors was not substantially lower than that from young donors, suggesting that regenerative therapies of ACL tears are feasible in both age groups. In vivo studies of the effect of age on the efficacy of such therapies are needed.

Matrix product algorithm for stochastic dynamics on networks applied to nonequilibrium Glauber dynamics.

We introduce and apply an efficient method for the precise simulation of stochastic dynamical processes on locally treelike graphs. Networks with cycles are treated in the framework of the cavity method. Such models correspond, for example, to spin-glass systems, Boolean networks, neural networks, or other technological, biological, and social networks. Building upon ideas from quantum many-body theory, our approach is based on a matrix product approximation of the so-called edge messages-conditional probabilities of vertex variable trajectories. Computation costs and accuracy can be tuned by controlling the matrix dimensions of the matrix product edge messages (MPEM) in truncations. In contrast to Monte Carlo simulations, the algorithm has a better error scaling and works for both single instances as well as the thermodynamic limit. We employ it to examine prototypical nonequilibrium Glauber dynamics in the kinetic Ising model. Because of the absence of cancellation effects, observables with small expectation values can be evaluated accurately, allowing for the study of decay processes and temporal correlations.

Arthroskopische Therapie bei spinoglenoidalem Ganglion.

Aims and Indications A paralabral ganglion cyst of the shoulder can cause neuropathy of the inferior branches of the suprascapular nerve. This can lead to atrophy of the infraspinatus muscle. Arthroscopic decompression of the cyst in combination with repair of the associated labrum tear appears to be an effective treatment option. Methods Initially the connection of the cyst to the joint in the area of the posterior rim of the glenoid is identified arthroscopically. Following the decompression of the cyst the labrum tear is repaired to avoid recurrence. The goal is the complete decompression of the ganglion cyst carefully protecting the infraspinatus branch. Concomitant intraarticular pathologies are also addressed. Conclusions In the literature arthroscopic treatment is superior to open surgical treatments. The degree of muscle atrophy at the time of surgery determines the prognosis for functional recovery. There is a lack of long-term outcome studies and publications of larger case series.

Long-term outcome of anterior cruciate ligament tear without reconstruction: a longitudinal prospective study.

PURPOSE: To analyse subjective and objective long-term outcomes of patients with anterior cruciate ligament (ACL)-deficient knees and limited demands regarding sportive activities. This subgroup of patients might be well-treated without ligament reconstruction. METHODS: We included 303 patients with unilateral tears of the ACL and conservative treatment into a prospective study. Mean age at injury was 33.8 (min. 18, max. 66) years. Follow-up was 27.1 (min. 21.3, max. 31.5) years. Follow-up examinations were conducted 12 and 27 years after injury. At the last follow-up we analysed 50 patients completely. To evaluate clinical and radiological outcomes we used the Lysholm score, Tegner activity scale, visual analogue scale for pain (VAS-pain), KOOS and Sherman score. RESULTS: Subjective outcome (Lysholm score and VAS-pain scale) improved between the 12th and 27th year after anterior cruciate ligament tear. At the same time activity level (Tegner activity scale) decreased. Also, arthritis (Sherman score) worsened over time. Twenty-seven years after injury, 90 % of the patients rated their ACL-deficient knee as normal or almost normal; 10 % of the patients rated it as abnormal. The findings of this study show that there is a subgroup of patients with ACL tears who are well treated with physiotherapy alone, not reconstructing the ligament. Also, other authors found this correlation between activity level reduction and better subjective outcome. CONCLUSIONS: Conservative treatment of an ACL tear is a good treatment option for patients with limited demands regarding activity. Patient age, sportive activities and foremost subjective instability symptoms in daily life should be considered when deciding for or against ACL reconstruction.

Case report - calcification of the medial collateral ligament of the knee with simultaneous calcifying tendinitis of the rotator cuff.

BACKGROUND: Calcification of the medial collateral ligament (MCL) of the knee is a very rare disease. We report on a case of a patient with a calcifying lesion within the MCL and simultaneous calcifying tendinitis of the rotator cuff in both shoulders. CASE PRESENTATION: Calcification of the MCL was diagnosed both via x-ray and magnetic resonance imaging (MRI) and was successfully treated surgically. Calcifying tendinitis of the rotator cuff was successfully treated applying conservative methods. CONCLUSION: This is the first case report of a patient suffering from both a calcifying lesion within the medial collateral ligament and calcifying tendinitis of the rotator cuff in both shoulders. Clinical symptoms, radio-morphological characteristics and macroscopic features were very similar and therefore it can be postulated that the underlying pathophysiology is the same in both diseases. Our experience suggests that magnetic resonance imaging and x-ray are invaluable tools for the diagnosis of this inflammatory calcifying disease of the ligament, and that surgical repair provides a good outcome if conservative treatment fails. It seems that calcification of the MCL is more likely to require surgery than calcifying tendinitis of the rotator cuff. However, the exact reason for this remains unclear to date.

Nail-patella-syndrome in a young patient followed up over 10 years: relevance of the sagittal trochlear septum for patellofemoral pathology.

INTRODUCTION: Nail-patella-syndrome (NPS) is a rare autosomal-dominant inherited disease with pathologies of nails, skeleton, kidneys, and eyes. Linkage to a mutated gene was found. It codes for the transcription-factor LMX1B. In most cases knees are symptomatic. Patients have hypoplastic patellae, which are laterally subluxated. In those individuals a sagittal trochlear fibrous septum was found, dividing the anterior knee-joint-space. In the literature the etiology and clinical significance of this anatomic abnormality is unclear. Based on clinical and intraoperative findings we developed a theory regarding knee pathology in nail-patella-syndrome. Successful treatment via early resection of the septum with sustained good outcome is presented. METHODS: In a symptomatic six-year-old boy with nail-patella-syndrome we resected the fibrous sagittal septum adherent to the trochlea femoris and we balanced the patella via lateral release and medial plication in both knee joints. We analyzed the clinical outcome of this procedure prospectively over 10 years. RESULTS: Postoperatively the hypoplastic patellae stayed centered and stable during further skeletal development. The patient was still pain free with normal range of motion of both operated knee joints after 10 years of follow-up. DISCUSSION: In patients with nail-patella-syndrome and a subluxated or dislocated patella we recommend diagnostics with magnetic-resonance-imaging and early surgical treatment via resection of the trochlear septum and soft-tissue-balancing of the patella. When the septum displaces the patella and prevents physiological articulation of the patella with the trochlea femoris, early septum resection is likely to be important for a good functional outcome and proper development of the patellofemoral joint during growth.

No significant difference in clinical outcome and knee stability between patellar tendon and semitendinosus tendon in anterior cruciate ligament reconstruction.

INTRODUCTION: ACL reconstruction with either patellar tendon or semitendinosus tendon autografts are standard procedures. Between these two grafts might be differences in stability, morbidity, or long-term changes. This study investigates outcomes of ACL reconstruction with patellar tendon versus semitendinosus tendon autografts. We hypothesize no significant differences in clinical outcome and knee stability between both groups. METHODS: In a randomized prospective trial, we operated 62 ACL-deficient patients, 45 males and 17 females with a mean age of 29.8 years (min. 18, max. 44). We reconstructed the ligament using either autologous patellar tendon (n = 31) or semitendinosus tendon (n = 31). After 10 years of follow-up, we investigated 47 patients of the study. For evaluation we used a standard clinical examination including one-leg jump test and KT-1000 instrumental translation measure, visual analog pain scale, IKDC subjective knee form, Lysholm score, Tegner activity scale, and standard X-rays of the knee. RESULTS: The data did not show any significant differences between the two groups. Between 5 and 10 years after ACL reconstruction both groups started to develop degenerative arthritic changes, which were detectable in standard radiographs of the knee. At 10-year follow-up mean IKDC for the BPTB group was 1.8 (min. 1, max. 3) and for the ST group it was 2.2 (min 1, max. 4), p = 0.35. Regarding Tegner activity scale after 10 years, the BPTB group showed a mean score of 5.9 (min. 4, max. 9) versus 5.1 (min. 3, max. 7) in the ST group, p = 0.53. For the Lysholm score the BPTB group reached a mean of 92.0 (min. 63, max. 98) and the ST group 91.8 (min. 62, max. 98) points, p = 0.66. There is a tendency for higher donor site morbidity in the BPTB group than in the ST group, p = 0.07. CONCLUSIONS: Both, patellar tendon and semitendinosus tendon are safe autografts for ACL reconstruction. Regarding graft selection, individual patient-dependent factors should be considered. ACL reconstruction cannot fully restore pre-injury status of knee joint function in the majority of cases.