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In this paper we are interested in lifting a prescribed group of automorphisms of a finite graph via regular covering projections. Let Γ\\Gamma be a finite graph and let Aut(Γ)\\mathrm {Aut}(\\Gamma ) be the automorphism group of Γ\\Gamma. It is well known that we can always find a finite graph Γ~\\tilde {\\Gamma } and a regular covering projection ℘:Γ~→Γ\\wp \\colon \\tilde {\\Gamma } \\to \\Gamma such that Aut(Γ)\\mathrm {Aut}(\\Gamma ) lifts along ℘\\wp. However, for constructing peculiar examples and in applications it is often important, given a subgroup GG of Aut(Γ)\\mathrm {Aut}(\\Gamma ), to find ℘\\wp along which GG lifts but no further automorphism of Γ\\Gamma does, or even that Aut(Γ~)\\mathrm {Aut}(\\tilde {\\Gamma }) is the lift of GG. In this paper, we address these problems.

Background To determine if temporizing cast immobilization is a safe alternative to external fixator (ex-fix) in ankle fracture-dislocations with delayed surgery or moderate soft-tissue injury, we analysed the early complications and re-dislocation rates of cast immobilization in relation to ex-fix in patients sustaining these injuries. Methods All skeletally mature patients with a closed ankle fracture-dislocation and a minimum 6-months follow-up treated between 2007 and 2017 were included. Baseline demographics, comorbidities, injury description, treatment history and complications were assessed. Results In 160 patients (94 female; mean age 50 years) with 162 ankle fracture-dislocations, 35 underwent primary ex-fix and 127 temporizing cast immobilizations. Loss of reduction (LOR) was observed in 25 cases (19.7%) and 19 (15.0%) were converted to ex-fix. The rate of surgical site infections (ex-fix: 11.1% vs cast: 4.6%) and skin necrosis (ex-fix: 7.4% vs cast: 6.5%) did not differ significantly between groups ( p  = 0.122 and p  = 0.825). Temporizing cast immobilization led to an on average 2.7 days earlier definite surgery and 5.0 days shorter hospitalization when compared to ex-fix ( p  < 0.001). Posterior malleolus fragment (PMF) size predicted LOR with ≥ 22.5% being the threshold for critical PMF-size ( p  < 0.001). Conclusion Temporizing cast immobilization was a safe option for those ankle fracture-dislocations in which immediate definite treatment was not possible. Those temporized in a cast underwent definite fixation earlier than those with a fix-ex and had a complication rate no worse than the ex-fix patients. PMF-size was an important predictor for LOR. Primary ex-fix seems appropriate for those with ≥ 22.5% PMF-size. Trial registration The study does not meet the criteria of a prospective, clinical trial. There was no registration.

Graphical Abstract

Background The aim of this retrospective monocentric study was to investigate the outcomes of surgically treated intra-articular calcaneus fractures in a maximum care trauma center. Methods One hundred forty patients who had undergone surgery for intra-articular calcaneal fractures between 2002 and 2013 were included. One hundred fourteen cases with 129 fractures were eligible to participate in the study of which 80 were available for a clinical and radiological follow-up. 34 patients were followed up by telephone interview only. Outcome measures included the American Orthopaedic Foot and Ankle Society (AOFAS) hindfoot score, Short Form 36 Health Status Survey (SF-36), complications, and subsequent surgeries. Results Mean follow-up was 91 months (range 12–183). The overall complication rate was 29% (37/129 ft). Disturbed wound healing (11%) and infection (5%) occurred most commonly. Non-union (4%) only occurred in smokers ( p  = 0.02). A high rate of posttraumatic subtalar arthritis (77%) and need for subsequent subtalar fusion (18%) without independent risk factors for subsequent subtalar fusion was found. The revision rate was high (60%) after primary fusion. Mean AOFAS-hindfoot score was 74 (Sanders I: 99, Sanders II: 74, Sanders III: 77, Sanders IV: 70). The postoperative Boehler angle improved significantly in all subgroups ( p  < 0.01). Patients with a decreased Boehler angle between postoperative images and the follow-up had significantly lower AOFAS hindfoot scores ( p  < 0.01). Conclusions Our data can aid decision-making in the treatment of calcaneal fractures. We advocate to use primary subtalar fusion with caution due to the high revision rate. Smoking status should always be considered. Level of evidence: Level III, retrospective cohort study.

Purpose Total knee arthroplasty (TKA) designs evolve continuously to improve patient outcomes. However, incidences of radiolucent lines (RLL) in the latest TKA system have recently been reported, raising concerns. The purpose of the current study was to compare radiographic outcomes of this new TKA implant to its predecessor design. Methods A group of 100 patients undergoing TKA using the newer design (Attune) was matched by age and gender to 191 patients with the classic design (LCS). All patients underwent computer-navigated primary TKA by the same surgeon using the same technique. Radiographs were taken before discharge, and 2 and 12 months postoperatively. Radiographic analysis was performed independently by three assessors, using the Modern Knee Society Radiographic Evaluation System and Methodology (MKSRES). Results At 12 months postoperatively, the incidence of RLL did not statistically differ between the two implants (14%, n  = 14 Attune vs. 8% n  = 17 LCS, n.s.). The posterior femoral flange was most commonly affected (12%; n  = 12 Attune vs. 7.9%; n  = 15 LCS, n.s.) followed by the anterior flange (1%; n  = 1 Attune vs. 3.1%; n  = 6 LCS, n.s.). The tibial baseplate was only affected in 1% ( n  = 1) of the Attune and 2.6% ( n  = 5) of the LCS (n.s.). Conclusion At 12 months follow-up we found no significant difference in RLL between the two implants. Both Attune and LCS TKA systems showed RLL predominantly at the posterior femoral flange. The reasons for the RLL remain a matter of speculation; however, shortcomings in surgical and cementing techniques seem to be more important than implant-related factors. Level of evidence III

Background Proximal femoral replacement (PFR) is a technically demanding procedure commonly performed to restore extensive, oncological or non-oncological bone defects in a severely debilitated patient collective. Depending on different indications, a varying outcome has been reported. The aim of the study was to assess the functional outcomes and complication rates of PFR with the modular Munich-Luebeck (MML) femoral megaprosthesis (ESKA/Orthodynamics, Luebeck, Germany), and to highlight outcome differences in patients treated for failed revision total hip arthroplasty (THA) or malignant bone disease. Methods A retrospective review of patients treated with PFR for failed THA or malignant tumor disease between 2000 and 2012 was performed. Patient satisfaction, functional outcome (VAS, SF-12, MSTS, WOMAC, TESS), complications and failure types (Henderson’s failure classification) were assessed. A Kaplan-Meier analysis determined implant survival. Results Fifty-eight patients (age: 69.9 years, BMI: 26.7 kg/m 2 , mean follow-up: 66 months) were included. The mean SF-12 (physical / mental) was 37.9 / 48.4. MSTS averaged 68% at final follow-up, while mean WOMAC and TESS scored 37.8 and 59.5. TESS and WOMAC scores demonstrated significantly worse outcomes in the revision group (RG) compared to the tumor group (TG). Overall complication rate was 43.1%, and dislocation was the most common complication (27.6%). Implant survival rates were 83% (RG) and 85% (TG; p  = n.s.) at 5 years, while 10-year survival was 57% (RG) and 85% (TG, p  < 0.05). Conclusions PFR is a salvage procedure for restoration of mechanical integrity and limb preservation after extensive bone loss. Complications rates are considerably high. Functional outcomes and 10-year implant survival rate were worse in the RG compared to the TG. Strict indications and disease-specific patient education are essential in preoperative planning and prognosis.

Graphical Abstract

Let Γ\\Gamma be a connected GG-arc-transitive graph, let uvuv be an arc of Γ\\Gamma and let LL be the permutation group induced by the action of the vertex-stabiliser GvG_v on the neighbourhood Γ(v)\\Gamma (v). We study the problem of bounding |Guv||G_{uv}| in terms of LL and the order of Γ\\Gamma.

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It has long been known that there exist finite connected tetravalent arc-transitive graphs with arbitrarily large vertex-stabilizers. However, beside a well-known family of exceptional graphs, related to the lexicographic product of a cycle with an edgeless graph on two vertices, only a few such infinite families of graphs are known. In this paper, we present two more families of tetravalent arc-transitive graphs with large vertex-stabilizers, each significant for its own reason.