Posterior Research Articles

The influence of muscle forces and external loads on cruciate ligament strain.

We know it is important to avoid excessive strain on reconstructed ligaments, but we do not know how individual muscles affect cruciate ligament strain. To answer this, we studied the effect of muscle forces and external loads on cruciate ligament strain. Nine cadaveric knee joints were tested in an apparatus that allowed unconstrained knee joint motion. Quadriceps, hamstring, and gastrocnemius muscle forces were simulated. Additionally, external loads were applied such as varus-internal or valgus-external rotation forces. Cruciate ligament strain was recorded at different knee flexion angles. Activation of the gastrocnemius muscle significantly (P < 0.05) strained the posterior cruciate ligament at flexion angles larger than 40 degrees. Quadriceps muscle activation significantly strained the anterior cruciate ligament when the knee was flexed 20 degrees to 60 degrees (P < 0.01) and reduced the strain on the posterior cruciate ligament in the same flexion range (P < 0.05). Activation of the hamstring muscles strained the posterior cruciate ligament when the knee was flexed 70 degrees to 110 degrees (P < 0.05). Combined varus and internal rotation forces significantly increased anterior cruciate ligament strain throughout the flexion range (P < 0.05). The results suggest that to minimize strain on the ligament after posterior cruciate ligament surgery, strong gastrocnemius muscle contractions should be avoided beyond 30 degrees of knee flexion. The study also calls into question the use of vigorous quadriceps exercises in the range of 20 degrees to 60 degrees of knee flexion after anterior cruciate ligament reconstruction.

Electrophysiological properties of efferent pathways from the subfornical organ to the hypothalamic paraventricular nucleus: Comparison between SHR and WKY

The impor tance of efferent pathways from the subfornica l organ (SFO) to the hypothalamic pa r aven t r i cu l a r nuc leus (PVN) for genera t ing a cent ra l ly media ted pressor response and for cont ro l l ing vasopress in (VP) release from the pos ter ior p i tu i t a ry has been suggested by the experimental observations in several lines. In the present study, we recorded extracellular single-unit activities of SFO neurons that were antidromically activated by electrical s t imulat ion of the PVN in urethane-anesthet ized spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats, and compared them. The spontaneous firing rate was significantly higher and the absolute refractory period was significantly shorter in SHR. There was no significant differences in the threshold, latency conduction velocity of antidromic activation between two groups of subjects. The effects of intravenous injection of angiotensin II (ANG II) on the excitability of SFO neurons projecting to the PVN were investigated. In both SHR and WKY, ANG II caused an increase in the excitability of SFO neurons. The magni tude of excitation to ANGII was much greater in SHR than in WKY. We also compared the responsivity of physically active neurohypophyseal neurons (putative VP-secreting neurons) in the PVN in response to electrical stimulation (1.2 X threshold) of the SFO. In SHR and WKY, SFO stimulation produced excitation or inhibition of the activity of putative VP-secreting PVN neurons. The magnitude of excitation was much greater in SHR than in WKY. These results imply that the alteration in the electophysiological properties of SFO projections to the PVN may contribute, in part, to hypertension.

Role of the medial structures in the intact and anterior cruciate ligament-deficient knee. Limits of motion in the human knee.

We measured motion limits in human cadaveric knees before and after sectioning the anterior cruciate ligament and the medial structures. Sectioning the medial collateral ligament in an anterior cruciate ligament-deficient knee increased the anterior translation limit at 90 degrees of flexion but not at 30 degrees of flexion. The tibia displaced straight anteriorly without exhibiting the coupled internal rotation that occurred in intact and anterior cruciate ligament-deficient knees. A lateral 15 N-m abduction moment produced a coupled external rotation in the medial collateral ligament-deficient knee. This was in marked contrast to intact, anterior cruciate ligament-deficient, or combined medial collateral ligament and anterior cruciate ligament-deficient knees, in which an abduction moment produced a coupled internal rotation. Sectioning only the medial collateral ligament caused a small but significant increase in the abduction rotation limit, whereas larger increases in the abduction rotation limit occurred when the posterior oblique ligament and posterior medial capsule were cut in addition to the medial collateral ligament. Cutting the medial collateral ligament increased the external rotation limit. The increase was independent of whether the anterior cruciate ligament was intact or sectioned. Subsequent cutting of the posterior oblique ligament and posterior medial capsule further increased the external rotation limit.

Posterior ossification of the shoulder: the Bennett lesion. Etiology, diagnosis, and treatment.

We report a series of ossific lesions of the posterior inferior glenoid in a group of elite baseball players. We hope to clarify the etiology, diagnosis, and treatment of the Bennett lesion. From August 1985 to August 1991, we identified six professional baseball pitchers and one college pitcher with evidence of ossification of the shoulder on plain radiographs, computed tomography, or magnetic resonance imaging. Arthroscopic examination was performed in all cases. All seven players had identifiable posterior labral injury on arthroscopic examination; six of these seven also had varying degrees of undersurface posterior rotator cuff damage. No anterior tissue damage, anterior instability, or subacromial impingement was noted. No ossification was identified arthroscopically. Intraarticular labral and rotator cuff tears were debrided arthroscopically and patients underwent rehabilitation for 4 to 6 months after surgery. Six of the seven athletes returned to preinjury performance levels; however, one pitcher is no longer playing competitive baseball. The Bennett lesion is an extraarticular posterior ossification associated with posterior labral injury and posterior undersurface rotator cuff damage. It is not, however, a result of traction stresses in the region of the triceps insertion. Recognition is important for identification and treatment of the lesion and associated pathologic damage.

Infraspinatus muscle-splitting incision in posterior shoulder surgery. An anatomic and electromyographic study.

Standard posterior shoulder surgical approaches include infraspinatus tendon detachment and infraspinatus-teres minor interval development. Cadaveric and clinical investigation of a new infraspinatus-splitting approach to the posterior glenohumeral joint was undertaken to assess efficacy in providing exposure, preserving tendon attachment, and avoiding neurologic compromise. Infraspinatus musculotendinous and neural anatomy was examined in 20 cadavers. Four patients with posterior shoulder instability underwent posterior capsulorrhaphy through this infraspinatus-splitting approach, followed by electrodiagnostic testing. Infraspinatus muscle was bipennate in all specimens, the tendinous interval an average 14 mm inferior to the scapular spine at the glenoid rim. The infraspinatus-splitting interval bisected the posterior glenoid rim at its midpoint, whereas the infraspinatusteres minor interval crossed the glenoid rim's lower quarter. The suprascapular nerve provided sole innervation to the infraspinatus muscle in all specimens, entering the infraspinous fossa at the notch as a single trunk 22 mm medial to the glenoid rim. Minimum branching variability was observed. Electrodiagnostic testing showed no evidence of axonal damage or muscle denervation in either infraspinatus pennate bundle. Limiting infraspinatus-splitting dissection medially to 1.5 cm from the posterior glenoid rim prevents damage to any interval-crossing suprascapular nerve branches. Posterior shoulder surgery through a horizontal, longitudinal infraspinatus tendon-splitting approach provides excellent exposure of posterior capsule, labrum, and glenoid, without requiring tendon detachment or causing neurologic compromise.

The effect of joint-compressive load and quadriceps muscle force on knee motion in the intact and anterior cruciate ligament-sectioned knee.

To determine the effect of an externally applied joint-compressive load and a quadriceps muscle force on knee motion, we tested nine intact cadaveric knees and four knees after sectioning of the anterior cruciate ligament. Anteroposterior translation was measured at 0 degrees, 15 degrees, 30 degrees, 45 degrees, and 90 degrees of knee flexion after the application of an anteroposterior force of 100 N, a joint-compressive load of 0, 111, 222, 333, or 444 N, and a quadriceps force of 0 or 133 N. Both a joint-compressive load and a quadriceps force significantly decreased total anteroposterior translation by as much as 50% to 66% in intact knees and 42% to 71% in anterior cruciate ligament-sectioned knees. A substantial anterior translation was also found with the application of a joint-compressive load or a quadriceps force and no anterior force. We termed this translation an anterior neutral-position shift. The anterior neutral-position shift was significantly greater in the ligament-sectioned knees compared with the intact knees, so much so that at flexion angles greater than 15 degrees, the application of a 100-N posterior force could not translate the tibia to the most anterior position achieved in the intact knee with a 100-N anterior force.

Myocardial cell hypertrophy after myocardial infarction with reperfusion in dogs.

The potential role of myocardial cell hypertrophy in the ischemic zone in the mechanism of late recovery of regional contractile function after myocardial infarction followed by reperfusion has not been examined. Eight chronically instrumented, conscious dogs were subjected to 90-120 minutes of circumflex coronary artery occlusion followed by reperfusion. The thickness and function of the anterior (AT) and posterior (PT) walls was measured by ultrasonic gauges at control, during occlusion, and after reperfusion. After 3 weeks, cross-sectional areas of surviving cells were determined from subepicardial (epi), midwall (mid), and subendocardial (endo) regions in six dogs and compared with those from six animals without infarction, including three sham-operated control dogs. PT systolic wall thickening showed dyskinesia during occlusion but recovered after reperfusion to 48% of control at 1 week and 67% at 3 weeks. End-diastolic thickness of the PT wall increased markedly after reperfusion, but AT and PT walls were only slightly thicker (p = NS) than in control dogs at 3 weeks. Cross-sectional areas of reperfused dogs in the infarct region averaged 279 (PTepi), 291 (PTmid), and 317 microns 2 (PTendo) and were significantly larger than in control animals (237 [PTepi], 241 [PTmid], and 233 microns 2 [PTendo]). PT cell areas were significantly larger than AT cells, ENDO cell areas were larger than EPI cells (both p < 0.05), and ENDO cells of the AT wall were larger than those of noninfarcted dogs (p < 0.05). In dogs with myocardial infarction followed by reperfusion, the cross-sectional areas of cells in the infarcted PT wall were larger than those in the noninfarcted AT wall, and within both the infarcted and noninfarcted zones, cell areas were larger in the endocardial than the epicardial region. In all regions of the infarcted wall and in the ENDO region of the noninfarcted wall, cell areas were generally larger than those of control dogs without infarction, and the control dogs showed no transmural differences in cell areas. The mechanisms responsible for this significant remodeling of the reperfused infarcted zone, which involves myocardial cellular hypertrophy, are unknown, but it is possible that hypertrophy of surviving regions of the infarcted wall played a role in the late recovery of regional function that accompanied this hypertrophic response.

Measurements of length and tension patterns during reconstruction of the posterior cruciate ligament.

The twofold purpose of this study was to develop an intraoperative technique to assess isometric positioning of posterior cruciate ligament grafts and to demonstrate the rationale for postoperative immobilization of the knee in full extension after a posterior cruciate ligament reconstruction. Multiple femoral fixation sites were selected on the medial intercondylar notch and the posterior cruciate ligament substitute was assessed for changes in length and tension at each of these sites during knee flexion from 0 degree to 120 degrees. The most isometric and isotonic femoral fixation site was localized over a small area slightly distal to the center of the medial intercondylar notch surface. This isometric point can be identified intraoperatively using recognizable surface markers within the knee. When a posterior stress was applied to the proximal tibia, the posterior cruciate ligament substitute showed the least increase in tension and length when the knee was locked in full extension for all of the potential femoral attachment sites assessed. This suggests that postoperative immobilization should be maintained in full extension to limit the stress placed on the posterior cruciate ligament reconstruction.

Force displacement characteristics of the posterior cruciate ligament.

The percent force changes in the posterior cruciate ligament were calculated using a previously validated computerized knee model after the femoral insertion sites were varied 2.5 and 5.0 mm in an anterior, posterior distal, anterior distal, and posterior distal direction. The tibial insertion sites were also varied 2.5 and 5.0 mm in the medial, lateral, proximal, and distal directions. Percent force changes were measured over a range of 0 degree to 90 degrees. These insertion sites simulated potential surgical placement errors. Results of this study demonstrated that the greatest percent force changes in the posterior cruciate ligament were at full extension. The greatest absolute percent force change between 0 degree and 90 degrees of flexion was with a femoral insertion of the posterior cruciate ligament placed 5 mm anterior to its normal attachment site, which resulted in a 39% change in the posterior cruciate ligament force. Distal femoral site attachment had the least effect (10% at 5.0 mm). Alterations at the tibial attachment site were less sensitive than on the femur; the greatest absolute percent force changes occurred with medial and lateral attachment sites (14% and 15%, respectively, at 5.0 mm). A minimal amount of percent force changes were seen between 45 degrees and 75 degrees of knee flexion in all positions tested for both tibial and femoral attachment sites. This model suggests that, like the anterior cruciate ligament, the force in the posterior cruciate ligament is also sensitive to attachment site position. As in anterior cruciate ligament studies, the femoral attachment site was found to be more sensitive.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term study of anterior cruciate ligament reconstruction for chronic instability using the central one-third patellar tendon and a lateral extraarticular tenodesis.

Forty-four patients with symptomatic chronic anterior cruciate ligament instabilities that had been reconstructed with the central one-third patellar tendon and a lateral extraarticular iliotibial band tenodesis were studied at an average followup of 7 years (range, 4 to 10). The cases with associated medial, lateral, or posterior laxity were not included, nor were the cases with more than minimal preoperative degenerative changes. The average age at surgery was 21 years (range, 16 to 33). A postoperative cast was used for 4 weeks. Satisfactory objective stability, which was defined as a KT-1000 side-to-side difference of up to 5 mm at the manual maximum test, was obtained in 37 (84%) of the patients. In 25 patients (57%), stability was restored within normal limits (less than or equal to 3 mm). No deterioration of the KT-1000 stability was noted at two follow-up visits performed by the same examiner (at an average of 4 and 7 years). A return to high-risk sports was possible in 27 (62%) of the patients. Difficulties in regaining a complete range of motion were recorded in 5 (11%) of the patients. A flexion contracture of 5 degrees to 7 degrees was also found in 5 patients. Significant patellofemoral symptoms were present in 4 patients (9%). A 5% to 11% shortening of the patella tendon was observed in 14 (32%) of the knees, but did not correlate with patellar problems. Moderate radiographic changes were noted in eight patients (18%) at followup and correlated with meniscectomy and pain. Overall satisfactory results were obtained in this initial experience in 29 (66%) of the patients.(ABSTRACT TRUNCATED AT 250 WORDS)

馬尾損傷を伴った中下位腰椎，仙椎損傷の検討

Middle-Lower lumbar and sacral spinal injuries are rare. Neurological recovery following cauda equina injury is better than after spinal cord injuries and it is possible for patients with this injury to walk. We reviewed 6 cases with cauda equina injuries. All achiewed good neurological recovery, regaining bladder-rectum function, and sensory (pain) sensation. We treated these patients by post erior decompression and fusion. Full decompression of the nerve tissues and rigid internal skeletal fixation are recommended for this type of injury.

Ultrastructure of giant and small thalamic terminals of cortical origin: a study of the projections from the barrel cortex in mice using Phaseolus vulgaris leuco-agglutinin (PHA-L)

By means of tracing with the lectin Phaseolus-vulgaris leucoagglutinin (PHA-L), we examined in the thalamus of the mouse, the axon terminals of fibers originating in the barrel cortex. Vibratome sections of the brain were subjected to PHA-L immunocytochemistry and processed for light and electron microscopy. We observed small (0.5-0.8 microns in diameter) varicosities of labeled fibers in the nucleus ventrobasalis (VB) and the nucleus posterior (PO) as well as labeled giant terminals (3-5 microns in diameter) in PO. The analysis involved examination of serial sections and computer-aided reconstruction of several terminals. The small varicosities in VB appear to be small axon terminals forming distinct asymmetric synapses with small dendritic profiles. Some labeled terminals are apposed to, but not synaptically related with, the cell bodies of neurons in VB that are retrogradely labeled with PHA-L. The small varicosities seen with the light microscope in PO are terminals forming asymmetric synapses with dendritic shafts. The giant terminals in PO appear as large, vesicle-filled profiles forming part of synaptic glomeruli, i.e. complexes of one corticothalamic terminal engulfing several excrescences of a single dendrite. A giant terminal forms several asymmetric synapses (about 8) with these excrescences, as well as numerous (up to 15) puncta adhaerentia. The glomeruli are enveloped in glial lamellae, and they are often found at the bifurcations of primary dendritic segments. We suggest that the small terminals in VB are in the service of feedback signalling from the barrel cortex to its principal thalamic relay nucleus; the functional importance of this projection may reside in increased spatio-temporal discrimination. We interpret the giant terminals in PO as elements serving feed-forward processing, allowing the barrel cortex to influence, via PO, parts of the motor pathway modulating the animal's ongoing behavior.

The "Pathology" of the Natural Conjugate Prior Density in the Regression Model

In a Bayesian analysis of the linear regression model, one may have prior information on a subset of the regression coefficients, but one has usually no prior information on the error variance. If one incorporates this kind of information in a natural conjugate prior density, under certain conditions the pos terior mean of the coefficients on which one is informative is equal to the prior mean, and the posterior mean of the coefficients on which one is not informative is equal to a constrained least squares estimator. The value of the posterior covariance matrix is also studied. We discuss and illustrate how to avoid getting posterior results too close to the "pathological" results summarized above.

Regulation of Basal Corticotropin-Releasing Hormone and Arginine Vasopressin Messenger Ribonucleic Acid Expression in the Paraventricular Nucleus: Effects of Selective Hypothalamic Deafferentations*

There exists considerable evidence to suggest that CRH and arginine vasopressin (AVP)-secreting parvocellular neurosecretory neurons of the hypothalamic paraventricular nucleus (PVN) are central integrators of negative feedback effects evoked by circulating glucocorticoid hormones. Most evidence suggests that these neurons may be receptive to circulating glucocorticoid levels, either via glucocorticoid receptors indigenous to these cells and/or via extrahypothalamic glucocorticoid-receptive neurons interacting with the PVN secretory cell. In an effort to address this issue, we performed anterior (ANT), posterior (POST) and total (TOT) deafferentations of the PVN region in male Sprague-Dawley rats using microknives fashioned from narrow-gauge spinal needles. Effective knife cuts were verified immunohistochemically, and deemed acceptable only if they avoided damage to the PVN proper and fibers of CRH and AVP-containing neurons coursing through the hypothalamus en route to the median eminence, while effectively eliminating neuronal input into the PVN region. Subsequent to surgery, levels of mRNA encoding for CRH and AVP in the parvocellular and magnocellular PVN were assayed via semiquantitative in situ hybridization histochemistry. Results indicate that TOT deafferentations resulted in significant increases in CRH mRNA expression in the PVN, and a slight but noticeable induction of AVP mRNA in the medial parvocellular but not posterior magnocellular divisions of the PVN. ANT lesions also produced an up-regulation of CRH and AVP mRNA relative to operated control rats. POST lesions did not produce a clear induction in either CRH or AVP mRNA. The data indicate that in the absence of neuronal input coming from anterior structures, CRH mRNA expression is up-regulated, suggesting that local effects of glucocorticoids on the PVN neuron are ineffective in maintaining normal CRH mRNA expression. These results support a role for neuronal feedback in regulation of the CRH neuron. The limited up-regulation (compared with adrenalectomized rats) of AVP mRNA in the TOT group suggests that while neuronal input may have some control of AVP mRNA expression, local glucocorticoid feedback is clearly able to restrict AVP message to levels considerably less than those seen in steroid-deficient animals. Analysis of knife-cut effects on plasma corticosterone and ACTH levels reveals that POST and TOT, but not ANT, deafferentations prohibit the secretory activity of the hypothalamo-pituitary-adrenocortical (HPA) axis seen pursuant to the anesthesia/thoracotomy in lesion and operated control groups.(ABSTRACT TRUNCATED AT 400 WORDS)

Description of a new ecuadorean gnamptogenys species (hymenoptera: formicidae), with a discussion on the status of the alfaria group

Description of a new ecuadorean gnamptogenys species (hymenoptera: formicidae), with a discussion on the status of the alfaria group

Anatomical Considerations in Obtaining Arterial Access

Arterial cannulation and catheterization are routine parts of medical care in intensive care units for neo nates, children, and adults. In this review I describe the anatomical landmarks that facilitate successful catheteri zation of the radial, ulnar, brachial, axillary, femoral, pos terior tibial, dorsalis pedis, umbilical, and superficial temporal arteries. Criteria for selection of each of these arteries for catheterization are discussed. Risks of arte rial puncture or catheterization include hemorrhage, thrombosis, infection, and vascular compromise to sur rounding structures. These risks are reviewed with ref erence to each of the arteries described.

Ultrasound catheter placement for deep posterior compartment pressure measurements in chronic compartment syndrome

Medial shin pain, often referred to as shin splints, is a common but difficult to diagnose entity in many athletes. Chronic deep posterior compartment syndrome as a cause of medial leg pain is still controversial. The problems of deep posterior compartment pressure measurement contribute to this controversy. These problems include safety of catheter insertion and the possibility that the patient has more than one deep posterior compartment. In this paper, we present a new technique for catheter placement in which continuous ultrasound guidance is used. This technique allows for the safe placement of the catheter into the deep posterior compartment and for documentation of catheter tip location.

Heparin reversal protocol

protamine administration during cardiopulmonary bypass. However, this method is very cumbersome for routine use in the operating theatre. Three years ago, 1 made an algebraic analysis of the Bull curve in the same way as Dr. Pounder pointed out, and wrote a basic program for a pocket computer. Since then we have used this easy-to-handle and safe system during all the extracorporeal procedures performed in our institution (750 cases a year). To estimate the reliability of this program I compared the baseline ACT (Activated Clotting Time) before heparin and the ACT twenty minutes after protamine administration in a consecutive series of a hundred patients scheduled for elective coronary revascularization. Using a paired Student's t test, I could not demonstrate a statistically significant difference (P = 0.35). To avoid inappropriate conclusions from these analyses, a calculation of statistical power was performed a poster ior i . 4 If a variation in ACT-level of five seconds is assumed to have no clinical relevance, analysis of this sample (100 subjects) showed with 95 per cent confidence that the ACT returned to its baseline level using this

Electrolytic but not ibotenic acid lesions of the posterior cingulate cortex produce transitory facilitation of learning in mice

The rate of acquisition of 12 Hebb-Williams mazes was studied after restricted bilateral lesions of the anterior (ANT) or posterior (POST) cingulate cortex in BALB/c mice. In a first experiment, animals with electrolytic lesions were tested with the different mazes at 3 time intervals between 19 and 48 days after surgery. The rate of acquisition in POST-lesioned mice was observed to be facilitated at the 2 first time intervals (between days 19–22 and 32–35), but this effect was reversed (impairment) when the test was carried out between 45–48 days postsurgery; no significant effects were observed in ANT-lesioned mice. In a second experiment, the same behavioral paradigm was used in mice with restricted ibotenic acid lesions of the POST cingulate cortex. These lesions had no significant effects on the acquisition of the mazes. A third experiment was carried out to test if the postoperative delay itself contributed to the long latency of the impairment observed in Expt. I. No impairment of acquisition was observed when POST cingulate lesioned animals underwent their first learning session between 45–48 days after surgery; in contrast, a significant facilitation of the performance was observed at this time. These results suggest an involvement of the posterior cingulate cortex, and in particular the cingulum bundle, both in acquisition and long-term memory processes.

Organization of the projections from barrel cortex to thalamus in mice studied with Phaseolus vulgaris-leucoagglutinin and HRP.

In order to elucidate the geometric organization of projections from the barrel cortex to the thalamus, iontophoretic injections of the anterograde tracer Phaseolus vulgaris-leucoagglutinin were made. The injections were confined to one barrel column (i.e. barrel in layer IV + cortical tissue above and below it). Axonal terminations could be demonstrated in three thalamic nuclei: reticularis (RT), ventrobasalis (VB) and posterior (PO). Anterograde terminal labelling was obtained in RT + VB; in PO only; or in RT + VB + PO. The terminals labelled in PO were much larger than those in RT and VB. The termination areas in RT, VB and PO were shaped like rods which have a rostro-caudal orientation. These cortico-thalamic projections are discretely and topographically organized. The clearest such arrangement was found in VB. Here, projections from the A row of barrels in BF terminate dorsally, whereas those from the C row end ventrally. Barrel A1 projects to the lateral part of VB, whereas A4, to more medial parts; other rows are arranged similarly. These results were compared with the distribution of thalamo-cortical projection neurons that were labelled after iontophoretic HRP injections in individual barrels. We concluded that the corticothalamic projections originating from one barrel column contact an are of barreloids in VB.