Arcuate Complex Research Articles

Morphology of kisspeptin-producing nuclei in the rat hypothalamus

ВACKGROUND: The article is devoted to the stereo-morphological analysis of the nuclei of the hypothalamus, synthesizing proteins of the kisspeptin family, regulating sexual differentiation various parts of the extended kisspeptin-producing nuclei of the hypothalamus and the features of their asymmetry in mature rats. The morphology of various parts of extended kisspeptin-producing nuclei of the hypothalamus remains poorly understood, which significantly complicates the choice of their reference zone, from which planning and implementation of morphological studies should begin, related to the evaluation of the effectiveness of therapeutic correction of various forms of hypogonadism.
 AIM: Determination of the main source of regulatory peptides of the kisspeptin family based on the analysis of the number, area of neuron bodies and volumetric characteristics of the kisspeptin-producing nuclei of the hypothalamus.
 MATERIALS AND METHODS: We studied 50 frontal paraffin sections of KPNs of 8 intact sexually mature male rats obtained as a result of a standard technique for their preparation and staining by the Nissl method. As a result, we carried out volumetric reconstruction of the largest nucleus of the arcuate complex the medial arcuate nucleus and the large periventricular nucleus, after which the number and area of neurosecretory cell bodies were determined in 5 frontal planes of these nuclei. To determine the proportion of kisspeptin-producing neurons in the total number of neurons in the kisspeptin-producing nuclei of the hypothalamus, we also performed the subsequent quantitative and morphometric characterization of their kisspeptin-producing neurons (after immunohistochemical staining, the identification of kisspeptin-kisspeptin granules. Statistical data processing was performed using the GraphPad PRISM 6.0 program, determining and lower quartiles. Differences were considered significant at p 0.01.
 RESULTS: Subdivisions of the nuclei, which are the main source of these regulatory proteins, have been identified. The caudal part of the medial arcuate nucleus (at the level of bregma 3.6 mm) and the anterior part of the periventricular nucleus (at the level of bregma 0.2 mm) are subdivisions of the corresponding kisspeptin-producing nuclei of the hypothalamus of the kisspeptin-producing nuclei of the hypothalamus, containing the largest number of neurosecretory cells and the bodies of their largest largest area. The number and area of neurons in the left-sided and right-sided parts of the hypothalamic kisspeptin-producing nuclei of the hypothalamus did not differ significantly. In this regard, the listed left-sided and right-sided subdivisions of the kisspeptin-producing kisspeptin-producing nuclei of the hypothalamus of the were proposed as standards for their subsequent morphological studies, which are important for assessing the effectiveness of therapeutic correction of various forms of hypogonadism.
 CONCLUSIONS: The left-sided and right-sided caudal parts of the medial arcuate hypothalamic nucleus and the anterior parts of the periventricular hypothalamic nucleus are proposed as a reference for their subsequent morphological studies related to the evaluation of the effectiveness of therapeutic correction of various forms of hypogonadism. as the main sources of regulatory proteins of the kisspeptin family.

Structural features of ghrelin-producing endocrine cells and their reactive changes after experimental stress

The work is devoted to the analysis of reactive changes in ghrelin-producing endocrine cells (HPEC) in the main areas of production of this regulatory peptide – in the stomach and hypothalamus during modeling of psycho-emotional stress and after replacement therapy. Reactive HPECs in experimental post stress disorder models have not previously been specifically studied. Meanwhile, the practice of modeling stress to establish the effectiveness of therapeutic interventions suggests the feasibility of obtaining new and informative criteria for assessing the degree of its impairment and therapeutic effect. The purpose of the study was to establish quantitative features and reactive changes in the GPEC of the stomach and hypothalamus in a model of psychogenic stress. Material and methods. We studied paraffin sections of the hypothalamus and the mucous membrane of the cardial part of the stomach in four groups of mature male rats. The first group (n=5) consisted of intact rats. The rest of the animals were subjected to a single emotional stress. In the nostrils of animals of two experimental groups (n=5 in each), 12 hours after stress, 20 μg of a solution of ghrelin (GHRL, Tocris, Gr. Brit.) and a peptide antagonist of ghrelin receptors ([D-Lys3]-GHRP-6, Tocris, Gr. Brit.). On the 4th day, animals were selected for the main control group (n=5). The number of endocrinocytes in the lateral part of the nuclei of the arcuate complex was counted over an area of 0,01 mm2, in the fundic glands of the stomach – over an area of 0,015 mm2; the area of endocrinocyte bodies was determined using the Imagescope program (Electronic analysis, Russia). The median, upper and lower quartiles, and the significance of their differences in the compared groups (using the nonparametric Mann–Whitney test) were measured using the GraphPad PRISM 6.0 program (GraphPad Software, USA). Differences were considered significant at p<0,01. Results. During a short-term experience of psychogenic stress, the number of viable gastric and hypothalamic HPECs decreased by 2,5 and 3,8 times (respectively; p<0.001), and their body area decreased by 1,5 and 1,6 times (p<0,001). Pharmacological methods of correction did not significantly affect these parameters of HPEC (p>0,05).

Knee Avulsion Injuries: What can I Get From a CT?

Acute bone and soft-tissue injuries to the knee are commonly seen in emergency departments as well as in the outpatient clinic. Most commonly, these injuries result from a direct blow, a fall, or a twisting injury. Prompt and accurate diagnosis relies heavily on imaging and is mandatory to facilitate adequate management and prevent potential complications [1]. Radiographs are usually the initial imaging modality in the evaluation of the acutely injured knee but have a low yield. Computed Tomography (CT) may be performed as the next imaging study for the evaluation of suspected radiographically occult fractures. In patients with radiographic diagnosis of knee fracture, CT is frequently performed for further classification and characterization of the fracture severity and for prediction or diagnosis of associated meniscal and ligamentous injuries [12]. The knee has numerous tendinous, ligamentous, and meniscal attachments, which make it particularly vulnerable to avulsion injuries after trauma. These include avulsions of the anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL), Segond (small bony avulsion of the anterolateral ligament at the lateral tibial rim that indicates a ACL tear) and reverse Segond (small medial tibial avulsion fracture that indicates a PCL tear) fractures, fibular head avulsion fracture, arcuate complex avulsion, fracture avulsions of the medial collateral ligament, iliotibial band avulsion, avulsions of the semimembranosus, and quadriceps tendons, and patellar sleeve fractures. In the setting of acute twisting trauma to the knee, CT scan has high sensitivity and specificity in detecting bony avulsion fractures and a high negative predictive value for excluding ligamentous injuries (e.g.: ACL avulsion fracture) [3] (Figure 1). Radiologists should recognize the pattern of these injuries and their underlying mechanism to understand the substantial damage that it frequently represents. This presentation will outline the imaging appearances of common knee avulsion fractures. Specific examples will be used to highlight clinical relevance and learning points.

Posterolateral Rotatory Knee Instability-MRI Evaluation of Anatomic Landmarks for Tibial Drill Tunnel Placement in Open and Arthroscopic Popliteus Tendon Reconstruction.

Anatomic reconstruction of the popliteus tendon and arcuate complex results in superior functional and a biomechanically more stable outcome compared with extra-anatomic techniques in posterolateral rotatory knee instability. Although specific characteristics of the femoral and fibular footprint of the anatomic posterolateral reconstruction have been described, data for tibial tunnel placement while popliteus tendon reconstruction do not exist. The purpose of this study was to quantify reasonable parameters, which could be used in arthroscopy, fluoroscopy, or open surgery to determine the anatomic tibial drill tunnel position in popliteus tendon reconstruction. Thirty magnetic resonance images of 30 patients with an intact posterolateral corner (PLC) were analyzed to specify the ideal point for tibial fixation of a popliteus tendon graft with respect to 17 bony, cartilaginous, and ligamentous anatomic landmarks. The ideal point for tibial fixation was defined as the musculotendinous junction of the popliteus tendon near to the insertion of the popliteofibular ligament. In the coronal plane, the ideal tibial fixation was located at the crossing of a tangent to the fibular head, parallel to the joint line with a tangent to the medial border of the fibular head, and vertical to the joint line with a deviation of less than 1 mm. It was located 0.26 (±1.91) mm superior to the distal edge and 11.75 (±2.66) mm lateral to the lateral edge of the tibial posterior cruciate ligament footprint and only 8.68 (±2.81) mm lateral to the lateral edge of the neurovascular bundle. Interrater reliability to detect the correct position of the popliteus tendon graft footprint was almost perfect. The position for tibial drill tunnel placement in anatomic popliteus tendon reconstruction showed low interindividual differences. The present findings of the quantified anatomic landmarks might improve open, fluoroscopy, or arthroscopy guided PLC reconstruction.

Layer-by-Layer Anatomy of the Anterolateral Complex of the Knee

Injuries to the anterior cruciate ligament can be associated with anterolateral capsular injuries. Recently, these capsular tears have been suggested to play an important role in rotatory knee instability. A critical review of the anterolateral complex of the knee is necessary to clarify nomenclatures of same structures and the complex anatomy of anterolateral side of the knee. In addition to the lateral collateral ligament and the arcuate complex, the iliotibial band (ITB) is an important lateral structure. It consists of different layers, namely, the superficial, middle, deep, and capsulo-osseous layers. Further, in a subset of patients, a capsular thickening, that is, the mid-third capsular ligament can be observed. Biomechanically, the functional unit of the ITB with its deeper layers between the firm attachment on the distal lateral femoral metaphysis (Kaplan fibers) and Gerdy tubercle was shown to contribute the most to resist internal tibial rotation. Therefore, the ITB and its deeper layers as well as the mid-third capsular ligament should be referred to collectively as the anterolateral complex.

Knee Injury - Soccer

HISTORY: A 17-year-old female high school soccer player presented a few hours after sustaining a right knee injury during a game. At minute 80, she suffered a varus blow to the anteromedial aspect of the knee from a sliding tackle on her planted, fully extended leg. She heard an audible pop and had immediate anterolateral knee pain and swelling with significant instability. PHYSICAL EXAMINATION: Antalgic gait with large knee effusion noted on inspection. Focal tenderness over lateral joint line and fibular head. Range of motion (ROM) at the knee limited by pain to 0-100 degrees. Strength testing 4/5 with knee flexion and extension, 0/5 with ankle dorsiflexion and extensor hallucis longus, 5/5 with plantar flexion. Sensation to light touch decreased in lateral lower leg and dorsum of the foot. 2+ Dorsalis pedis and popliteal pulses and <2s capillary refill in toes. Provocative testing significant for positive Lachman’s, posterior drawer, varus stress and dial test. Valgus stress and McMurray’s were negative. DIFFERENTIAL DIAGNOSIS: 1. Combined ligamentous tear 2. Acute Fracture 3. Meniscal injury TEST AND RESULTS: Anterior-posterior and lateral knee X-ray: ---Fibular head avulsion fracture. MRI without contrast of the knee: ---Arcuate complex avulsion fracture with complete disruption of the posterior cruciate ligament (PCL), anterior cruciate ligament (ACL) and concomitant posterolateral corner (PLC) injury. FINAL WORKING DIAGNOSIS: 1. Grade III sprain of ACL and PCL 2. Arcuate complex avulsion fracture with PLC injury. 3. Common Peroneal Nerve Mononeuropathy TREATMENT AND OUTCOMES: 1. Immediate cessation of physical activity with non-weight bearing status of right lower extremity. The patient was provided with crutches and placed in a knee immobilizer brace. 2. Isometric quad strengthening initiated for the first 9 days to help reduce swelling and prevent muscle atrophy. 3. On day 10, the patient had simultaneous reconstruction of her ACL and PCL followed by surgical repair of the fibular head. 4. Electrodiagnostics at week 4 confirmed right common peroneal nerve mononeuropathy below the fibular head and the patient was provided with an ankle foot orthosis. 5. Returned to sports after 14 months of challenging rehab when she regained full, painless ROM and strength in her knee and ankle dorsiflexors.

Aminostratigraphy and sea-level history of the Pleistocene Bridgewater Formation, Mount Gambier region, southern Australia

A geochronological framework based on amino acid racemisation (AAR) and constrained by previously reported optically stimulated luminescence (OSL) ages is presented for the evolution and paleosea-level record of the Pleistocene Bridgewater Formation of the Mount Gambier region, of southern Australia. Within the study area, the Bridgewater Formation is represented by late early Pleistocene [Marine Isotope Stage (MIS) 23 at 933 ka] to Holocene barrier shoreline successions deposited during sea-level highstands. Regional monotonic uplift (0.13 mm yr–1) and pervasive calcrete development during the Pleistocene have preserved the sequence of calcarenite (mixed quartz-skeletal carbonate sand) shoreline complexes from denudation. AAR analyses confirm that the barriers generally increase in age landwards and correlate with sea-level highstands associated with interglacials as defined by the marine oxygen isotope record. AAR analyses on the benthic foraminifer Elphidium crispum have proved more reliable than the whole-rock method in extending the age range of AAR dating of these relict shoreline successions. Paleosea-levels from the coastal plain are as follows: MIS 7, –9 ± 2 m; MIS 9, 4 ± 1 m; and a minimum sea-level of 2 ± 2 m is derived for MIS 11. Paleosea-level could not be determined for MIS 15, 19 or 23 as diagnostic sea-level indicators were not identified within these sedimentary successions. Dismal Range, dated at 933 ± 145 ka (MIS 23), represents a correlative feature to the East Naracoorte Range but is some 25 km seaward of the Kanawinka Fault compared with the same barrier at Naracoorte. Mingbool Range (788 ± 18 ka) is of similar age to the West Naracoorte Range (MIS 19) and formed as an arcuate shoreline complex that became attached to the higher relief of the area represented by the Mount Burr Volcanic Province. The higher topographical relief resulted from crustal doming of the Oligo-Miocene Gambier Limestone caused by the intrusion of magma associated with the volcanic province. The AAR age of 788 ± 118 ka for Mingbool Range indicates that the Mount Burr volcanics predate the deposition of this shoreline complex.

The Rovuma Delta deep-water fold-and-thrust belt, offshore Mozambique

We interpret two-dimensional seismic reflection data from the Rovuma Delta basin deep-water fold-and-thrust belts. Two major arcuate complexes with different architecture and extent are identified. While in the northern Palma arcuate complex a multitude of steep, east-dipping thrust-related fold anticlines formed above a single main detachment, in the southern Mocimboa arcuate complex multiple detachments resulted in the formation of thrust duplexes. In between the two arcuate domains, only few thrust-related fold anticlines developed. Our interpretation of the Rovuma basin is a linked system of up-dip extension and down-dip compression that is mainly driven by gravity tectonics. Sediment loading and a hinterland uplift due to the development of the East African Rift System since the Oligocene is proposed as origin of the delta. It is shown that the main, seaward-dipping detachment in Early Cenozoic strata is likely under-compacted and overpressured shale. Conversely, shale diapirism is questionable since the shape and location of such structures in the fold-and-thrust-belts appear simply indicating steeply dipping imbricated folds, rooted by a near vertical thrust. We suggest that mainly a different rheology and thickness and thus efficiency of the shale detachment across the delta resulted in different morphologies and geometries of the deep-water fold-and-thrust-belts. • The Rovuma Delta is a linked system of up-dip extension and down-dip compression • Two arcuate complexes with different architecture and extend: Palma and Mocimboa • The southern Mocimboa complex shows multiple detachments with thrust duplexes • DWFTBs are formed by gravity-driven under thick seaward-dipping shale detachment

Fto immunoreactivity is widespread in the rodent brain and abundant in feeding-related sites, but the number of Fto-positive cells is not affected by changes in energy balance

A single nucleotide polymorphism in the FTO gene is associated with obesity in humans. Evidence gathered in animals mainly relates energy homeostasis to the central FTO mRNA levels, but our knowledge of the Fto protein distribution and regulation is limited. Fto, a demethylase and transcriptional coactivator, is thought to regulate expression of other genes. Herein, we examined Fto immunoreactivity (IR) in the mouse and rat brain with emphasis on sites governing energy balance. We also studied whether energy status affects central Fto IR. We report that Fto IR, limited to nuclear profiles, is widespread in the brain, in- and outside feeding circuits; it shows a very similar distribution in feeding-related sites in mice and rats. Several areas regulating energy homeostasis display enhanced intensity of Fto staining: the arcuate, paraventricular, supraoptic, dorsomedial, ventromedial nuclei, and dorsal vagal complex. Some regions mediating feeding reward, including the bed nucleus of the stria terminalis, have ample Fto IR. We found that differences in energy status between rats fed ad libitum, deprived or refed following deprivation, did not affect the number of Fto-positive nuclei in 10 sites governing consumption for energy or reward. We conclude that Fto IR, widespread in the rodent brain, is particularly abundant in feeding circuits, but the number of Fto-positive neurons is unaffected by changes in energy balance.

Avulsion Fractures of the Knee: Imaging Findings and Clinical Significance

The knee is an intricate joint with numerous tendinous, ligamentous, and meniscal attachments, which make it particularly vulnerable to complex injuries after trauma. A variety of avulsion fractures of the knee can occur, including Segond and reverse Segond fractures; avulsions of the anterior and posterior cruciate ligaments; arcuate complex avulsion; iliotibial band avulsion; avulsions of the biceps femoris, semimembranosus, and quadriceps tendons; Sinding-Larsen-Johansson syndrome; and Osgood-Schlatter disease. These fractures often have a subtle appearance at conventional radiography, which is typically the first imaging modality performed in these cases. Advanced imaging modalities, particularly magnetic resonance imaging, are helpful and can provide valuable additional information for adequately defining the extent of damage. The onus is on the radiologist to identify the pattern of injury and to understand the substantial underlying damage that it frequently represents. Conveying this information to the referring clinician is crucial and represents the first step toward additional evaluation and probable orthopedic referral. By recognizing the significance of these injuries at initial presentation, radiologists can facilitate appropriate patient work-up and prevent the chronic morbidity associated with delayed treatment.

Surgical Treatment of Chronic Posterolateral Rotatory Instability of the Knee Using Capsular Procedures

Chronic posterolateral rotatory instability of the knee was introduced as a diagnostic classification by Hughston and associates in the early 1970s and occurs as a result of dysfunctional healing of a strained arcuate complex, causing a patulous posterolateral capsuloligamentous complex to exist. This capsular redundancy allows varying degrees of recurvatum and adduction instability during single-limb stance. Eradication of the redundant pouch with a capsular shift-type reconstruction has been shown to eliminate the instability and hold up under long-term follow-up studies. Understanding the complex normal and injured anatomy of the posterolateral corner of the knee is essential for effective reconstruction of this instability.

Avulsion fracture of the head of the fibula (the "arcuate" sign): MR imaging findings predictive of injuries to the posterolateral ligaments and posterior cruciate ligament.

The purpose of this study was to describe the significance of an avulsion fracture of the head of the fibula ("arcuate" sign) and its association with injuries of the knee on MR imaging. We conducted a retrospective search of 2318 patients who underwent conventional radiography and MR imaging after an episode of knee trauma. Patients were included in this study if they had an avulsion fracture of the head of the fibula revealed on conventional radiography and underwent arthroscopy. Thirteen patients, all of whom were men, satisfied the inclusion criteria. Ten patients underwent further explorative surgery. The clinical, radiographic, MR imaging, and surgical findings were then reviewed. The avulsion fracture of the styloid process of the fibular head was apparently related to injuries of the arcuate complex in all 13 patients. Radiographically, the bony fragment was horizontally oriented and similar in size in most patients, ranging from 8 to 10 mm in length and from 2 to 5 mm in width. On MR imaging, the fibular avulsion was identified in 11 of the 13 patients. The other two patients had marrow edema in the fibular styloid process, although the avulsion fracture was not evident. All patients had injuries of the posterior cruciate ligament (six tibial avulsions, seven midsubstance tears). No patient had a tear of the anterior cruciate ligament. Disruption of the lateral collateral ligament was evident in seven patients, and one patient had a tear of the popliteal tendon. During surgery, six patients had disruption of the arcuate complex, but this disruption could not be identified on the MR images. An avulsion fracture of the fibular head generally involves the styloid process and causes injury of some of the major stabilizers in the posterolateral corner. Avulsion fractures are strongly associated with disruption of the posterior cruciate ligament.

Posterolateral stabilizers of the knee: anatomy and injuries assessed with MR imaging.

T he posterolateral aspect of the knee contains several ligamentous and tendinous structures that are the primary restraints against varus angulation and external rotation of the tibia. These structures are the fibular collateral ligament (FCL), the arcuate ligament, the popliteus tendon, the popliteofibular ligament, and the fabellofibular ligament [1]. Hughston et al. [2] refer to the first three structures collectively as the arcuate complex. In addition to these static stabilizers, dynamic stabilization of the posterolateral corner of the knee is provided by the popliteus, biceps femoris, and lateral gastrocnemius muscles [2]. Injury to the posterolateral structures may lead to posterolateral rotatory instability of the knee, in which the lateral tibial plateau rotates externally and subluxates posteriorly [3]. Acutely, patients may complain of pain in the posterolateral aspect of the knee and chronically may describe the sensation of the knee giving way in extension [1]. Such injuries often accompany anterior cruciate ligament (ACL) and posterior cniciate ligament (PCL) tears [1] but may be subfle and miSsed by the examiner [2]. Clinically unrecognized posterolateral injury has been suggested as a cause of ACL graft failure [4] as well as instability after PCL repair [5]. Materials and Methods We dissected the posterolateral aspect of an embalmed cadaveric knee obtained from our medical school’s department of anatomy. After identifying and photographing the posterolateral ligaments, we coated them with 120% w/v barium paste (E-ZPaste; E-Z-EM, Westbury, NY) and radiographed the specimen using a detail extremity film-screen combination with 6.4 mA and 60 kV. We also reviewed the reports of all MR imaging examinations of the knee peiformed at our institution over a 2-year period, looking forcases ofinjury to the posterolateral Stabilizers. All Studies were performed on l.5-T units (Signa; General Electric Medical Systerm, Milwaukee, WI, or Gyroscan; Philips Medical Systems, Shelton, CI’) using dedicated extremity coils. The routine protocol consisted of sagiual Spinecho Tl-weighted images (TR rangeiTE range, 500600/15-20), gradient-echo T2-weighted images (600-875/15-20; flip angle, 30#{176}), axial spin-echo Ti-weighted images (500-600/15-20), fat-suppressed fast spin-echo 12-weighted images (17004500/50-90; echo train length, eight), and coronal fat-suppressed fast spin-echo proton densityweighted images (1700-3500/18-40; echo train length, eight). Fat suppression was achieved by frequency-selective presaturation on the Signa unit and spectral inversion recovery on the Gymscan unit. Field of view was 16-20 cm and one to two excitetions were performed. Slice thickness for the sagittal and T2-weighted axial sequences was 3 mm, with no interslice gap on the Sigma unit and a gap ofO3 mm on the Gyroscan unit; the slice thickness on the coronal images was 3-4 mm for both units, with no gap on the Signa unit and a gap ofO.3-0.4 mm on the Gyroscan unit. Matrix size was 256 x 192-256 and 205 x 256 for the Signa and Gyroscan units, respectively.

Shallow Mesozoic layered gabbros of the Shadow Mountains, San Bernardino County, California

Jurassic hornblende gabbros intrude as a conspicuous 9 km 2 arcuate complex within Paleozoic metasedimentary pendants of the Shadow Mountains, San Bernardino County, California. This complex is significant because it: (1) displays evidence of processes active in magma chambers which are crystallizing cumulus phases; (2) resembles many mid-Mesozoic plutons described in the western and central Sierra Nevada and western Mojave desert which may all be petrologically related; and (3) may be used as a diagnostic tectonic marker for Mesozoic tectonic reconstructions of the Mojave Desert and western Cordillera. The gabbroic body is unusual for its compact, near-circular plan, conspicuous banding and layering and reverse geochemical zonation. The mafic complex was intruded as a hydrous magma and was emplaced as a concentric epizonal pluton. Oxygen isotopic data indicate the melt was mantle derived but has been contaminated by assimilation of metasediments. The gabbro was likely generated by reaction of olivine with fractionated melt from the melting of a low MgO basalt under water-saturated conditions. The banding and layering is ascribed to the cyclic ascent of felsic rejected solute along the walls of the chamber and its accumulation near the roof of the complex. Cooling was facilitated by conduction and the presence of pendant rocks at uppermost levels. The Shadow Mountains gabbros resemble other gabbroic bodies of similar Jurassic age throughout the Sierra Nevada, Mojave Desert and Transverse Ranges, California (Lahren and Schweickert, 1994; Miller and Glazner, 1995). These intrusions are useful as markers of subsequent large-scale tectonic crustal displacements affecting the western Mojave Desert and Sierra Nevada. In particular, the Shadow Mountains gabbros show age, mineralogie and textural affinities with correlative gabbroic complexes in the central Sierra Nevada 400 km to the north. All these plutonic bodies may represent subvolcanic sources of the Jurassic-Cretaceous Independence dike swarm in the western Mojave Desert and eastern Sierra Nevada.

Posterolateral instability of theknee: treatment using the clancy biceps femoris tenodesis

Posterolateral instability of the knee is perhaps the most challenging injury facing the sports medicine physiciantoday. Diagnosis requires a thorough understanding of the complex anatomy, function, and biomechanics of the posterolateral structures. In isolated cases of posterolateral instability, the physical findings may be subtle and easily overlooked. Similarly, in complex injuries involving the posterolateral structures, the physical findings may be confusing and misdiagnosed as an isolated cruciate ligament injury. Failure to appropriately diagnose and treat a posterolateral injury can lead to significant functional disability and failure of associated ligamentous reconstruction. Optimal results may be achieved if the injury is diagnosed acutely and surgical treatment is carried out promptly with stabilization of the posterolateral structures and any associated ligamentous insufficiencies. The clinical and biomechanical results of the Clancy biceps tenodesis have proven the procedure successful for controlling varus and external rotational laxity. Rerouting of the biceps femoris tendon with tenodesis to the lateral femoral epicondyle creates a new fibular collateral ligament and tightens the posterolateral capsule and arcuate complex. In addition, tenodesis eliminates the dynamic external rotation of the tibia by the biceps femoris muscle, which actively exacerbates posterolateral subluxation. When performed properly, the biceps tenodesis can eliminate posterolateral instability and restore functional stability to the knee.

Major circular structure beneath southern Lake Huron defined from potential field data

Newly compiled and merged Canadian and United States potential field data for the area of southern Lake Huron reveal a large circular structure that has a diameter that may extend to 100 km. The aeromagnetic image shows a circular central high with a diameter of 6 km located at fat 43°14.21′N, long 82°19.88′W, surrounded by a principal ring with a diameter of 50 km and indications of conformable, arcuate structure extending to a diameter of about 100 km. The prevailing, northeast-striking aeromagnetic signature of the Grenville front and adjacent Grenville front tectonic zone is interrupted and may be overprinted by the circular feature. The Bouguer gravity field shows a strong positive anomaly that extends southeast from the Grenville front and terminates in an arcuate complex of positive anomalies that correlate with the aeromagnetic field. The gravity field illustrates the circular structure with an annular low and central high, as well as positive extensions that follow the foliate pattern of magnetic anomalies marking the outer area of the feature. There is no strong evidence of the feature in the bathymetry data of southern Lake Huron, although the general coastline of the southern end of Lake Huron closely follows the outline of the main circular feature. The interruption of the Grenville trends, the clear, regular, circular signature of the feature, and the interpreted magnetic source depths at the Precambrian surface, suggest an event possibly as young as early Paleozoic. In the absence of basement samples, the origin of the feature is unconfirmed. However, the scale and potential field anomaly pattern of the feature are comparable to several of the larger impact structures exposed on the Canadian Shield.

Further Observations on the Isometricity of the Anterior Cruciate Ligament

Six anatomical specimens were used to evaluate the ligament length pattern and mean maximal ligament length change (MMLLC) of the anterior cruciate ligament (ACL) using a ligament replacement with a 6-mm diameter. Three femoral and three tibial attachment sites were selected. Nine different combinations were studied in intact knees and also in knees whose posterior capsule and arcuate ligament complex were sequentially divided, whose menisci were resected, and whose capsule and arcuate complex were repaired. The smallest ligament length change (5.6 mm) was obtained in the intact knee with the anatomic femoral and tibial attachments. Moving the femoral origin either anteriorly or to the over-the-top position significantly increased the MMLLC. Moving the tibial insertion posteriorly had a negligible effect, but changing to an anterior attachment site increased (but not significantly) the MMLLC. Even for anatomically positioned ligaments, the instability caused by sectioning the posterior capsule and arcuate ligament complex increased the MMLLC by more than 80%. Resection of both menisci did not result in a further increase in the MMLLC, but repairing the posterior capsule and arcuate complex restored the length changes to those of the intact knee. These data confirm the importance of precise anatomic placement of the femoral and tibial tunnels when performing intraarticular ACL grafts for anterolateral rotatory instability. The adverse effect of certain other associated instabilities on the ligament length change, even with correct tunnel placement, has been demonstrated and may be one explanation for the variability in the clinical results of these procedures.

Limits of movement in the human knee. Effect of sectioning the posterior cruciate ligament and posterolateral structures.

We applied specific forces and moments to the knees of fifteen whole lower limbs of cadavera and measured, with a six degrees-of-freedom electrogoniometer, the position of the tibia at which the ligaments and the geometry of the joint limited motion. The limits were determined for anterior and posterior tibial translation, internal and external rotation, and varus and valgus angulation from zero to 90 degrees of flexion. The limits were measured in the intact knee and then the changes that occurred with removal of the posterior cruciate ligament, the lateral collateral ligament, the popliteus tendon at its femoral attachment, and the arcuate complex were measured. The cutting order was varied, allowing us to determine the changes in the limits that occurred when each structure was cut alone and the amount of motion of the joint that was required for each structure to become taut and to limit additional motion when the other supporting structures had been removed. Removal of only the posterior cruciate ligament increased the limit for posterior tibial translation, with no change in the limits for tibial rotation or varus and valgus angulation. The additional posterior translation was least at full extension and increased progressively, reaching 11.4 millimeters at 90 degrees of flexion. The progressive increase in posterior translation with flexion was apparently due to slackening of the posterior portion of the capsule, as the translation nearly doubled when the posterolateral structures subsequently were removed. Removal of only the posterolateral extra-articular restraints increased the amount of external rotation and varus angulation. The average increase in external rotation depended on the angle of flexion; it was greatest at 30 degrees of flexion and decreased with additional flexion. At 90 degrees of flexion, the intact posterior cruciate ligament limited the increase in external rotation to only 5.3 degrees, less than one-half of the 13.0-degree increase that occurred at 30 degrees of flexion. Subsequent removal of the posterior cruciate ligament markedly increased external rotation at 90 degrees of flexion, resulting in a total increase of 20.9 degrees. The limit for varus angulation was normal as long as the lateral collateral ligament was intact. When the lateral collateral ligament was cut, the limit increased 4.5 degrees (approximately 4.5 millimeters of additional joint opening) when the knee was partially flexed (to 15 degrees).(ABSTRACT TRUNCATED AT 400 WORDS)

The role of the posterolateral and cruciate ligaments in the stability of the human knee. A biomechanical study.

Injury to the posterolateral structures of the knee, including the popliteus tendon and arcuate complex, frequently results in poorly understood patterns of instability. To evaluate the static function of these tissues, we used a mechanical testing apparatus that allowed five degrees of freedom to test seventeen specimens from human cadavera at angles of flexion that ranged from zero to 90 degrees. Selective section of the lateral collateral ligament, popliteus-arcuate (deep) ligament complex, anterior cruciate ligament, and posterior cruciate ligament was performed. At all angles of flexion, the lateral collateral ligament and deep ligament complex functioned together as the principal structures preventing varus rotation and external rotation of the tibia, while the posterior cruciate ligament was the principal structure preventing posterior translation. However, at angles of flexion of 30 degrees or less, the amount of posterior translation after section of only the lateral collateral ligament and the deep structures was similar to that noted after isolated section of the posterior cruciate ligament. Isolated section of the posterior cruciate ligament did not affect varus or external rotation of the tibia at any position of flexion of the knee. When the posterior cruciate ligament was sectioned after the lateral collateral ligament and deep ligament complex had been cut, a large increase in posterior translation and varus rotation resulted at all angles of flexion. In addition, at angles of flexion of more than 30 degrees, external rotation of the tibia also increased. The application of internal tibial torque resulted in no increase in tibial rotation after isolated section of the anterior cruciate ligament or combined section of the lateral collateral ligament and deep ligament complex. However, combined section of all three structures increased internal rotation at 30 and 60 degrees of flexion. The increases in external rotation that were produced by section of the lateral collateral ligament and deep ligament complex were not changed by the addition of the section of the anterior cruciate ligament.

Posterior problems in the knee. Posterior cruciate insufficiency and posterolateral rotatory insufficiency.

During a recent three-year period, 39 patients underwent surgical procedures for lesions of the posterior complex of the knee. The results in 28 followed for greater than six months (average followup, 16 months) are reported; eight are presently in the early rehabilitative phase and three have been lost to followup. In reconstruction for chronic laxity, a semitendinosus replacement of the posterior cruciate ligament with anterior advancement of the lateral arcuate complex is recommended. Use of the medial gastrocnemius tendon is still advised in selected cases. Reconstruction for posterolateral rotatory laxity with an intact posterior cruciate is performed with anterior advancement of the popliteus tendon and the arcuate complex. Pes anserinus transfer, imbrication of the posterior oblique ligament, and biceps tenodesis may be performed as supplemental procedures.