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The posterior cruciate ligament (PCL) represents an intra-articular structure composed of two distinct bundles. Considering the anterior and posterior meniscofemoral ligaments, a total of four ligamentous fibre bundles of the posterior knee complex act synergistically to restrain posterior and rotatory tibial loads. Injury mechanisms associated with high-energy trauma and accompanying injury patterns may complicate the diagnostic evaluation and accuracy. Therefore, a thorough and systematic diagnostic workup is necessary to assess the severity of the PCL injury and to initiate an appropriate treatment approach. Since structural damage to the PCL occurs in more than one third of trauma patients experiencing acute knee injury with hemarthrosis, background knowledge for management of PCL injuries is important. In Part 1 of the evidence-based update on management of primary and recurrent PCL injuries, the anatomical, biomechanical, and diagnostic principles are presented. This paper aims to convey the anatomical and biomechanical knowledge needed for accurate diagnosis to facilitate subsequent decision-making in the treatment of PCL injuries. Level of evidence V.

Purpose To compare the biomechanical properties of the graft during PCL reconstruction by three-dimensional finite element analysis of the PCL trans-tibial reconstruction technique with three different tibial bony channel exit positioning points, to determine which method of positioning is better able to avoid wear and tear between the graft and bony channel, and to reduce the failure rate of the PCL reconstruction. Methods This is a study limited to computational simulation and based on data from a single anatomical model. Thirty-year-old male volunteers were selected. A three-dimensional knee joint model consisting of the distal femur, the proximal tibiofibula and the posterior cruciate ligament was established based on CT scanning and three-dimensional reconstruction of the left knee joint. According to the different positioning points of the tibial tunnel exit, the PCL model of tibial side PCL anatomical region center point reconstruction, the PCL model of Fanelli suggested point (i.e., 10 mm below and 5 mm lateral to the PCL anatomical point) reconstruction, and the PCL model of tibial side posterior posterior joint capsule distal anticompromise and posterior mediastinum reference positioning point (i.e., 5 mm above the posterior capsule distal retropubic, 5 mm medial to the posterior mediastinum) reconstruction were established (respectively designated as Model 1, Model 2, and Model 3). The diameter of the entire graft was set uniformly at 7 mm. With the knee flexed at 90° and the midpoint of the line connecting the medial and lateral apexes of the tibial intercondylar ridge as the reference point, a standardized backward thrust displacement of 5 mm was applied to simulate a posterior knee drawer test with all proximal femoral degrees of freedom constrained. The model overall Mises stress, tibial plateau Mises stress, PCL Mises stress, PCL contact Cpress stress, PCL contact stress and PCL contact effective area were measured. Results Simulated posterior drawer tests demonstrated that Model 3 exhibited a substantial reduction in PCL contact Cpress stress (22.57 MPa) compared to Model 1 (32.93 MPa) and Model 2 (29.86 MPa). Additionally, the ratio of contact force (277.48 N) to effective graft-tibial contact area (50.19 mm²), representing the contact force per unit area, was also the lowest in Model 3 compared to Model 1 (213.88 N/17.65 mm²) and Model 2 (470.77 N/63.75 mm²). These findings indicate that Model 3 significantly reduced frictional loads between the graft and tibia, highlighting its biomechanical optimization potential. Further analysis revealed that Model 3 also displayed the lowest tibial plateau Mises stress (48.80 MPa). However, its PCL tensile stress (69.71 MPa) was significantly higher than that of Model 1 (41.03 MPa) and Model 2 (40.90 MPa), suggesting that while Model 3 minimizes friction dependency, it primarily transfers loads through graft tension. Conclusion Compared with the anatomic regional center point and Fanelli point reconstruction PCL, the grafts of the soft tissue reference tibial localization reconstruction PCL method were subjected to greater tensile forces, but they had significantly lower friction with the tibia and were able to reduce contact wear with the tibia. This can enhance long-term patient outcomes. Our study offers crucial biomechanical evidence for optimizing tunnel positioning in PCL reconstruction, propelling the advancement of surgical techniques.

The posterior reversible encephalopathy syndrome (PRES) is a neurological disorder of (sub)acute onset characterized by varied neurological symptoms, which may include headache, impaired visual acuity or visual field deficits, disorders of consciousness, confusion, seizures, and focal neurological deficits. In a majority of patients the clinical presentation includes elevated arterial blood pressure up to hypertensive emergencies. Neuroimaging, in particular magnetic resonance imaging, frequently shows a distinctive parieto-occipital pattern with a symmetric distribution of changes reflecting vasogenic edema. PRES frequently develops in the context of cytotoxic medication, (pre)eclampsia, sepsis, renal disease or autoimmune disorders. The treatment is symptomatic and is determined by the underlying condition. The overall prognosis is favorable, since clinical symptoms as well as imaging lesions are reversible in most patients. However, neurological sequelae including long-term epilepsy may persist in individual cases.

Purpose This study aimed to compare the biomechanical properties of the popliteus bypass against the Larson technique for the reconstruction of a combined posterolateral corner and posterior cruciate ligament injury. Methods In 18 human cadaver knees, the kinematics for 134 N posterior loads, 10 Nm varus loads, and 5 Nm external rotational loads in 0°, 20°, 30°, 60,° and 90° of knee flexion were measured using a robotic and optical tracking system. The (1) posterior cruciate ligament, (2) meniscofibular/-tibial fibers, (3) popliteofibular ligament (PFL), (4) popliteotibial fascicle, (5) popliteus tendon, and (6) lateral collateral ligament were cut, and the measurements were repeated. The knees underwent posterior cruciate ligament reconstruction, and were randomized into two groups. Group PB (Popliteus Bypass; n  = 9) underwent a lateral collateral ligament and popliteus bypass reconstruction and was compared to Group FS (Fibular Sling; n  = 9) which underwent the Larson technique. Results Varus angulation, posterior translation, and external rotation increased after dissection ( p  < 0.01). The varus angulation was effectively reduced in both groups and did not significantly differ from the intact knee. No significant differences were found between the groups. Posterior translation was reduced by both techniques ( p  < 0.01), but none of the groups had restored stability to the intact state ( p  < 0.02), with the exception of group PB at 0°. No significant differences were found between the two groups. The two techniques revealed major differences in their abilities to reduce external rotational instability. Group PB had less external rotational instability compared to Group FS ( p  < 0.03). Only Group PB had restored rotational instability compared to the state of the intact knee ( p  < 0.04) at all degrees of flexion. Conclusion The popliteus bypass for posterolateral reconstruction has superior biomechanical properties related to external rotational stability compared to the Larson technique. Therefore, the popliteus bypass may have a positive influence on the clinical outcome. This needs to be proven through clinical trials.

Purpose The K-line, which is a virtual line that connects the midpoints of the anteroposterior diameter of the spinal canal at C2 and C7 in a plain lateral radiogram, is a useful preoperative predictive indicator for sufficient decompression by laminoplasty (LMP) for ossification of the posterior longitudinal ligament (OPLL). K-line is defined as (+) when the peak of OPLL does not exceed the K-line, and is defined as (–) when the peak of OPLL exceeds the K-line. For patients with K-line (–) OPLL, LMP often results in poor outcome. The aim of the present study was to compare the clinical outcome of LMP, posterior decompression with instrumented fusion (PDF) and anterior decompression and fusion (ADF) for patients with K-line (–) OPLL. Methods The present study included patients who underwent surgical treatment including LMP, PDF and ADF for K-line (–) cervical OPLL. We retrospectively compared the clinical outcome of those patients in terms of Japanese Orthopedic Association score (JOA score) recovery rate. Results JOA score recovery rate was significantly higher in the ADF group compared with that in the LMP group and the PDF group. The JOA score recovery rate in the PDF group was significantly higher than that in the LMP group. Conclusions LMP should not be used for K-line (–) cervical OPLL. ADF is one of the suitable surgical treatments for K-line (–) OPLL. Both ADF and PDF are applicable for K-line (–) OPLL according to indications set by each institute and surgical decisions.

Almost two decades have elapsed since posterior reversible encephalopathy syndrome (PRES) was described in an influential case series. This usually reversible clinical syndrome is becoming increasingly recognised, in large part because of improved and more readily available brain imaging. Although the pathophysiological changes underlying PRES are not fully understood, endothelial dysfunction is a key factor. A diagnosis of PRES should be considered in the setting of acute neurological symptoms in patients with renal failure, blood pressure fluctuations, use of cytotoxic drugs, autoimmune disorders, or eclampsia. Characteristic radiographic findings include bilateral regions of subcortical vasogenic oedema that resolve within days or weeks. The presence of haemorrhage, restricted diffusion, contrast enhancement, and vasoconstriction are all compatible with a diagnosis. In most cases, PRES resolves spontaneously and patients show both clinical and radiological improvements. The range of symptoms that can comprise the syndrome might be broader than usually thought. In its mild form, this disorder might cause only one clinical symptom (headache or seizure) and radiographically might show few areas of vasogenic oedema or even normal brain imaging in some rare cases. In severe forms, PRES might cause substantial morbidity and even mortality, most often as a result of acute haemorrhage or massive posterior fossa oedema causing obstructive hydrocephalus or brainstem compression.

Purpose of Review This review provides an updated discussion on the clinical presentation, diagnosis and radiographic features, mechanisms, associations and epidemiology, treatment, and prognosis of posterior reversible encephalopathy syndrome (PRES). Headache is common in PRES, though headache associated with PRES was not identified as a separate entity in the 2018 International Classification of Headache Disorders. Here, we review the relevant literature and suggest criteria for consideration of its inclusion. Recent Findings COVID-19 has been identified as a potential risk factor for PRES, with a prevalence of 1–4% in patients with SARS-CoV-2 infection undergoing neuroimaging, thus making a discussion of its identification and treatment particularly timely given the ongoing global pandemic at the time of this writing. Summary PRES is a neuro-clinical syndrome with specific imaging findings. The clinical manifestations of PRES include headache, seizures, encephalopathy, visual disturbances, and focal neurologic deficits. Associations with PRES include renal failure, preeclampsia and eclampsia, autoimmune conditions, and immunosuppression. PRES is theorized to be a syndrome of disordered autoregulation and endothelial dysfunction resulting in preferential hyperperfusion of the posterior circulation. Treatment typically focuses on treating the underlying cause and removal of the offending agents.

Over two decades have passed since posterior reversible encephalopathy syndrome (PRES) was first described in 1996. It has becoming increasingly recognised because of improved and more readily available imaging modality. The exact pathophysiological mechanism is not completely understood and remains controversial at present. Precise diagnosis is essential to guide prompt, proper management. Our ability of differentiating it from other acute neurological disorders is likely to improve as we learnt more about the spectrum of this entity in the last 20 years. We emphasise the importance of recognising its diagnostic criteria and biomarker, which would be of great relevance to either outcome evaluation or study design. PRES has a favourable prognosis generally, but neurological sequelae and even fatalities can occur, especially in severe forms that might cause substantial morbidity and even mortality, particularly when the syndrome is complicated by intracranial haemorrhage or brain infarction. In this review, the pathophysiology, approach to diagnosis, some controversies as to the prognosis, as well as the future research direction of PRES are described.

Ossification of the posterior longitudinal ligament (OPLL) can cause severe and irreversible paralysis in not only the cervical spine but also the thoracolumbar spine. To date, however, the prevalence and distribution of OPLL in the whole spine has not been precisely evaluated in patients with cervical OPLL. Therefore, we conducted a multi-center study to comprehensively evaluate the prevalence and distribution of OPLL using multi-detector computed tomography (CT) images in the whole spine and to analyze what factors predict the presence of ossified lesions in the thoracolumbar spine in patients who were diagnosed with cervical OPLL by plain X-ray. Three hundred and twenty-two patients with a diagnosis of cervical OPLL underwent CT imaging of the whole spine. The sum of the levels in which OPLL was present in the whole spine was defined as the OP-index and used to evaluate the extent of ossification. The distribution of OPLL in the whole spine was compared between male and female subjects. In addition, a multiple regression model was used to ascertain related factors that affected the OP-index. Among patients with cervical OPLL, women tended to have more ossified lesions in the thoracolumbar spine than did men. A multiple regression model revealed that the OP-index was significantly correlated with the cervical OP-index, sex (female), and body mass index. Furthermore, the prevalence of thoracolumbar OPLL in patients with a cervical OP-index ≥ 10 was 7.8 times greater than that in patients with a cervical OP-index ≤ 5. The results of this study reveal that the extent of OPLL in the whole spine is significantly associated with the extent of cervical OPLL, female sex, and obesity.

Summary The prevalence of radiographic cervical ossification of the posterior longitudinal ligament (OPLL) in 1,562 Japanese from a population-based cohort was 1.9 %. The presence of OPLL showed a significant association with the femoral neck bone mineral density (BMD), presence of diffuse idiopathic skeletal hyperostosis (DISH) and plasma pentosidine levels. Only one new case of radiographic OPLL was detected, but OPLL progressed in all affected subjects. Introduction The purpose of this study was to clarify the prevalence and progression of radiographic OPLL and the associated factors, using the population-based cohort Research on Osteoarthritis/osteoporosis Against Disability (ROAD). Methods In the ROAD study, 1,690 participants underwent X-ray examination of the entire spine and both knees. Radiographic OPLL, lumbar spondylosis, knee osteoarthritis and DISH were diagnosed by a single, well-experienced orthopaedic surgeon. An interviewer-administered questionnaire and tests for anthropometric measurements were administered, and the BMDs of the lumbar spine and proximal femur were determined. A new OPLL case was considered if heterotopic ossification in the posterior longitudinal ligament was absent at baseline but present during follow-up. Progression was defined as an increase in the maximum length or width of the ossification at follow-up over that at baseline. Results Radiographic OPLL was detected in 30 (17 men, 13 women) of 1,562 individuals who underwent X-ray examination of the cervical spine (prevalence = 1.9 %). Its prevalence was significantly higher in men than in women ( p  = 0.007), but no association with age was observed. In a logistic regression analysis, OPLL showed a significant association with the femoral neck BMD, presence of DISH and plasma pentosidine levels. Only one new case of radiographic OPLL was detected, but OPLL progressed in all affected subjects. Conclusion This population-based study clarified the prevalence of radiographic OPLL in the Japanese population as well as its progression. OPLL showed significant association with plasma pentosidine levels, BMD and DISH.