The geology and geophysics of Kuiper Belt object (486958) Arrokoth

The Cold Classical Kuiper Belt, a class of small bodies in undisturbed orbits beyond Neptune, is composed of primitive objects preserving information about Solar System formation. In January 2019, the New Horizons spacecraft flew past one of these objects, the 36-kilometer-long contact binary (486958) Arrokoth (provisional designation 2014 MU₆₉). Images from the flyby show that Arrokoth has no detectable rings, and no satellites (larger than 180 meters in diameter) within a radius of 8000 kilometers. Arrokoth has a lightly cratered, smooth surface with complex geological features, unlike those on previously visited Solar System bodies. The density of impact craters indicates the surface dates from the formation of the Solar System. The two lobes of the contact binary have closely aligned poles and equators, constraining their accretion mechanism.

Initial results from the New Horizons exploration of 2014 MU69, a small Kuiper Belt object

The Kuiper Belt is a distant region of the outer Solar System. On 1 January 2019, the New Horizons spacecraft flew close to (486958) 2014 MU₆₉, a cold classical Kuiper Belt object approximately 30 kilometers in diameter. Such objects have never been substantially heated by the Sun and are therefore well preserved since their formation. We describe initial results from these encounter observations. MU₆₉ is a bilobed contact binary with a flattened shape, discrete geological units, and noticeable albedo heterogeneity. However, there is little surface color or compositional heterogeneity. No evidence for satellites, rings or other dust structures, a gas coma, or solar wind interactions was detected. MU₆₉'s origin appears consistent with pebble cloud collapse followed by a low-velocity merger of its two lobes.

Ninety-day complications following the Latarjet procedure

BACKGROUND

The purpose of this study was to describe the rate and type of complications occurring within 90 days following the Latarjet procedure for anterior glenohumeral instability.

METHODS

Consecutive patients undergoing the Latarjet procedure by fellowship-trained surgeons from a single institution between 2007 and 2016 were included for analysis. Indications for the Latarjet procedure included primary or recurrent anterior instability with clinically significant anterior glenoid bone loss and/or failed prior arthroscopic stabilization. Patients undergoing the Latarjet procedure after prior glenoid bone grafting were excluded. All complications that occurred within 90 days of surgery were analyzed and correlated with demographic factors.

RESULTS

A total of 146 consecutive patients (146 shoulders) were included. Of these patients, 11 were lost to follow-up and 2 were excluded for having undergone prior open bone grafting. Among the remaining 133 patients (average age, 28.5 ± 11.8 years; 75% male patients), 10 total complications occurred within 90 days of surgery, for an overall short-term complication rate of 7.5%. Of these 10 complications, 6 required subsequent surgery, with recurrent instability in 2 cases (overall rate, 1.50%), infection in 2 (overall rate, 1.50%), musculocutaneous nerve palsy in 1 (overall rate, 0.75%), and postoperative pain in 1 (overall rate, 0.75%). The remaining 4 complications were transient, resolving with nonoperative treatment. No cases of hardware failure or graft osteolysis were reported.

CONCLUSIONS

The overall 90-day complication rate following the Latarjet procedure for anterior shoulder stabilization was 7.5%. In 6 of the 10 cases, complications led to subsequent surgery, including recurrent instability in 2, while in the remaining 4 cases, the complications were transient and resolved with nonoperative treatment.

Variability in the Contour of Cadaveric Anterior and Posterior Glenoids Based on Ipsilateral 3-Dimensional Computed Tomography Reconstructions: Implications for Clinical Estimation of Bone Loss

PURPOSE

To compare differences in the contour of the anterior and posterior glenoid in 3-dimensional computed tomography reconstructions as a reason for variability in estimating glenoid bone loss.

METHODS

Three reviewers digitally placed 11 points (1 at 6 o'clock, 5 from 3 to 6 o'clock, and 5 from 6 to 9 o'clock) along the inferior half of glenoid 3-dimensional computed tomography reconstructions of 32 cadaveric specimens. A best-fit circle for the whole glenoid was determined from all 11 points. The anterior 6 points determined an anterior-based circle, as for estimation of posterior bone loss. The posterior 6 points determined a posterior-based circle, as for estimation of anterior bone loss. The area and radii were determined for all circles. Individual intraclass correlations were used to evaluate reliability. Paired t-tests and Wilcoxon signed rank tests were used to compare areas and radii of the anterior and posterior circles relative to the best-fit glenoid circle. Significance was defined as P < .05.

RESULTS

There was good-to-excellent inter-rater reliability for the overall best-fit circle (intraclass correlation coefficient [ICC] = 0.97 [95% confidence interval (CI), 0.95-0.99]), anterior circle (ICC = 0.82 [95% CI, 0.71-0.90]), and posterior circle (ICC = 0.78 [95% CI, 0.65-0.88]). The average area of the posterior-based circle was significantly greater than the area of the best-fit circle for the intact glenoid (111% [95% CI, 104.3%-117.7%]; P = .0016). The average radius of the posterior-based circle was significantly larger than the radius of the intact glenoid (105% [95% CI, 101.7%-108.3%]; P = .0042). There were no significant differences between the average area (96% [95% CI, 89.0%-103.0%]; P = .16) and average radius (97% [95% CI, 93.5%-100.5%]; P = .19) for the anterior-based circle relative to the actual whole glenoid.

CONCLUSIONS

Estimation of anterior glenoid bone loss based on the normal posterior glenoid rim may overestimate glenoid bone loss because of differences in the contour of the anterior and posterior glenoid, whereas estimations of posterior glenoid bone loss based on the anterior rim did not differ significantly from the intact glenoid.

CLINICAL RELEVANCE

A circle based on the remaining intact portion of the injured glenoid may lead to an inaccurate estimate of glenoid bone loss.

Arthroscopic Intramuscular Side-to-Side Repair of an Isolated Infraspinatus Tear

Intramuscular, full-thickness rotator cuff tears are uncommon and present a challenging clinical scenario for repair because traditional suture anchor or transosseous repair techniques are less feasible. The goal of repair is to achieve a tension-free reduction of both ends of the muscle to allow for adequate healing over time. Intramuscular tears of the infraspinatus specifically have rarely been reported. The clinical presentation of these patients can be challenging to interpret, and other causes of rotator cuff dysfunction, including compression to the suprascapular nerve, must be ruled out. In this Technical Note, we describe our technique for arthroscopic side-to-side suture repair of an isolated intramuscular infraspinatus tear.

An All-Arthroscopic, Length-Tensioned Suprapectoral Biceps Tenodesis Technique

Biceps tenodesis remains a popular choice for treating anterior shoulder pain in the setting of primary biceps tendinitis or biceps pain due to concomitant glenohumeral joint pathology. A variety of surgical approaches and fixation construct options are available for biceps tenodesis. The advantages of an all-arthroscopic biceps tenodesis include anatomic maintenance of the length-tension relation with strength preservation and improved cosmetic results. This technique can be technically challenging but allows for a minimally invasive approach to anchor the biceps. In this Technical Note, we describe a suprapectoral biceps tenodesis using an all-arthroscopic approach in the setting of concomitant rotator cuff repair. This technique offers a viable alternative to the open subpectoral biceps tenodesis.

ACL Reconstruction Basics: Quadruple (4-Strand) Hamstring Autograft Harvest

Hamstring tendon autograft remains a popular graft choice for anterior cruciate ligament (ACL) reconstruction. Although there are a variety of autograft and allograft options available for ACL reconstruction, advantages of hamstring tendon autografts include decreased postoperative knee pain and an overall easier surgical recovery compared with bone patellar tendon bone autograft. In addition, 4-stranded (quadruple) hamstring grafts are among the strongest grafts biomechanically (at time equals zero). Although the technique of hamstring autograft harvest is relatively straightforward, it is critical to pay attention to several technical steps to avoid iatrogenic neurovascular damage as well as to avoid premature amputation of the graft while using a tendon stripper. In this Technical Note, we describe a technique of hamstring autograft harvest for ACL reconstruction for a quadruple (4-strand) hamstring graft using the gracilis and semitendinosus tendons.

Intractable reflex audiogenic seizures in Aicardi syndrome

Aicardi syndrome (AS) is a rare disorder which includes the triad of total or partial agenesis of the corpus callosum, infantile spasms, and chorioretinal anomalies. Seizures and electroencephalogram findings observed in AS are polymorphic with both focal and generalized seizures. We first report on a patient affected by AS who presented with reflex audiogenic seizures specifically triggered by the starting tune of a popular television news. No other type of stimuli, either simple or complex, were able to precipitate the seizures in the patient. The severe cortical-subcortical lesions commonly observed in AS are associated with hyperexcitability of the cortices and may well account for the broad electroclinical patterns noted in this group of patients. From our report, the context of these patterns should be extended to include reflex audiogenic seizures.

Efficacy and safety of topiramate in infants according to epilepsy syndromes

Studies of the efficacy of topiramate (TPM) in infants and young children are few. Here we report an open, prospective, and pragmatic study of effectiveness of TPM in terms of epilepsy syndromes, in children aged less than 2 years. The median follow-up period was 11 months. We enrolled 59 children in the study: 22 affected by localization-related epilepsy (LRE), 23 by generalized epilepsy, six by Dravet's syndrome, and eight with unclassifiable epilepsy. TPM was effective (responders showed a decrease of more than 50% in seizure frequency) in 47% of patients, including 13% who were seizure-free at the last visit. TPM was more effective in localization-related epilepsy (48% of responders) than in generalized epilepsy (32% of responders). In the latter group, 19 patients suffered from infantile spasms. Four of six patients with cryptogenic infantile spasms became seizure-free. Of the 13 patients with symptomatic infantile spasms, only one was seizure-free. Results were poor for patients with Dravet's syndrome. In general, TPM was well tolerated. The most frequently reported adverse effects were drowsiness, irritability, hyperthermia, and anorexia. The present study concludes that TPM is effective for a broad range of seizures in infants and young children and represents a valid therapeutic option in this population.