Improvement in clinical outcomes following arthroscopic all-inside medial lateral ligament reconstruction for rotational ankle instability

PURPOSE

Rotational ankle instability can be diagnosed in up to 18% of cases of chronic lateral ankle instability. It is characterised by an abnormal increase of talar rotation within the tibiofibular mortise, due to an injury in the most anterior component of the deltoid ligament secondary to a chronic deficiency of the lateral collateral ligament. The aim of this prospective observational study was to investigate the clinical outcomes following arthroscopic all-inside medial and lateral ligament reconstruction for rotational ankle instability.

METHODS

A prospective observational study of consecutive patients undergoing arthroscopic all-inside medial and lateral ligament reconstruction for rotational ankle instability with minimum 6-month follow-up. The primary outcome was a validated patient-reported outcome measure (PROM), the Manchester-Oxford Foot Questionnaire. Secondary outcomes included the EQ-5D, European Foot and Ankle Society score and complications.

RESULTS

Between 2020 and 2023, 12 patients underwent primary arthroscopic all-inside medial and lateral ligament reconstruction for rotational ankle instability with pre- and post-operative PROMs available for all 12 patients. The mean ± standard deviation age was 33.9 ± 7.2 years and the mean follow-up was 1.9 ± 1.2 (range: 0.5-3.8, interquartile range: 0.9-3.0) years. There was a significant improvement in all Manchester-Oxford Foot Questionnaire domain scores (p < 0.05): Index 53.1 ± 19.1 to 26.4 ± 27.6, Pain 46.7 ± 20.3 to 26.2 ± 26.8, Walking/Standing 58.7 ± 26.0 to 27.0 ± 30.0 and Social Interaction 51.2 ± 19.5 to 25.6 ± 30.1. There were improvements in EQ-5D-5L Index, VAS and VAS Pain; however, these were not statistically significant. There was one complication-a superficial peroneal nerve injury which resolved with a corticosteroid injection.

CONCLUSION

The arthroscopic all-inside medial and lateral ligament reconstruction technique is a reliable and safe method for treating rotational ankle instability, demonstrating significant improvement in PROMs at a mean 1.9-year follow-up.

LEVEL OF EVIDENCE

Level IV.

Cartiva interpositional arthroplasty versus arthrodesis in the treatment of Hallux rigidus: A retrospective comparative study with mean 2 year follow up

BACKGROUND

Hallux rigidus is a common condition characterised by first metatarsophalangeal joint (MTPJ) degeneration, pain and limited range of motion (ROM). The gold standard surgical treatment is arthrodesis, providing good pain relief, but sacrifices ROM. The Cartiva synthetic cartilage implant (SCI) has been utilised as an interpositional arthroplasty, aiming to reduce pain whilst preserving range of motion. Current evidence for Cartiva SCI is limited. The aim was to evaluate the clinical outcomes of Cartiva SCI compared to arthrodesis undertaken in our centre.

METHODS

A retrospective cohort study was conducted, enrolling all adult patients who underwent primary first MTPJ SCI arthroplasty or arthrodesis for the treatment hallux rigidus. The primary outcome was a validated patient-reported outcome measure (PROM), the Manchester-Oxford Foot Questionnaire (MOXFQ). Secondary outcomes included EQ-5D, complication rates, VAS Pain and FAAM (ADL).

RESULTS

Between 2017 and 2020 there were 33 cases divided into two groups (17 Cartiva SCI, 16 arthrodesis, mean age 59.0 ± 9.9 years) with a mean follow up of 2.3 years. There was no statistically significant difference in any of the MOXFQ, EQ-5D, VAS Pain or FAAM (ADL) outcome scores between the Arthrodesis and SCI groups (p > 0.05). The mean MOXFQ Index score was 7.2 ± 6.4 for the SCI group and 3.9 ± 5.8 for the Arthrodesis group at final follow up (p = 0.15). Although complications were high in both groups, the overall hallux reoperation rate was 29.4 % in the SCI cohort and 0.0 % for arthrodesis.

CONCLUSION

This retrospective comparative study found no significant superiority of Cartiva SCI over arthrodesis in terms of PROMs. Due to the higher rate of further surgical intervention in the SCI cohort, we recommend arthrodesis as the preferred surgical option for hallux rigidus.

LEVEL OF EVIDENCE

III.

Activity-dependent compartmentalization of dendritic mitochondria morphology through local regulation of fusion-fission balance in neurons in vivo

Neuronal mitochondria play important roles beyond ATP generation, including Ca2+ uptake, and therefore have instructive roles in synaptic function and neuronal response properties. Mitochondrial morphology differs significantly between the axon and dendrites of a given neuronal subtype, but in CA1 pyramidal neurons (PNs) of the hippocampus, mitochondria within the dendritic arbor also display a remarkable degree of subcellular, layer-specific compartmentalization. In the dendrites of these neurons, mitochondria morphology ranges from highly fused and elongated in the apical tuft, to more fragmented in the apical oblique and basal dendritic compartments, and thus occupy a smaller fraction of dendritic volume than in the apical tuft. However, the molecular mechanisms underlying this striking degree of subcellular compartmentalization of mitochondria morphology are unknown, precluding the assessment of its impact on neuronal function. Here, we demonstrate that this compartment-specific morphology of dendritic mitochondria requires activity-dependent, Ca2+ and Camkk2-dependent activation of AMPK and its ability to phosphorylate two direct effectors: the pro-fission Drp1 receptor Mff and the recently identified anti-fusion, Opa1-inhibiting protein, Mtfr1l. Our study uncovers a signaling pathway underlying the subcellular compartmentalization of mitochondrial morphology in dendrites of neurons in vivo through spatially precise and activity-dependent regulation of mitochondria fission/fusion balance.

Metformin treatment results in distinctive skeletal muscle mitochondrial remodeling in rats with different intrinsic aerobic capacities

The rationale for the use of metformin as a treatment to slow aging was largely based on data collected from metabolically unhealthy individuals. For healthspan extension metformin will also be used in periods of good health. To understand potential context specificity of metformin treatment on skeletal muscle, we used a rat model (HCR/LCR) with a divide in intrinsic aerobic capacity. Outcomes of metformin treatment differed based on baseline intrinsic mitochondrial function, oxidative capacity of the muscle (gastroc vs soleus), and the mitochondrial population (IMF vs SS). Metformin caused lower ADP-stimulated respiration in LCRs, with less of a change in HCRs. However, a washout of metformin resulted in an unexpected doubling of respiratory capacity in HCRs. These improvements in respiratory capacity were accompanied by mitochondrial remodeling that included increases in protein synthesis and changes in morphology. Our findings raise questions about whether the positive findings of metformin treatment are broadly applicable.

Most axonal mitochondria in cortical pyramidal neurons lack mitochondrial DNA and consume ATP

In neurons of the mammalian central nervous system (CNS), axonal mitochondria are thought to be indispensable for supplying ATP during energy-consuming processes such as neurotransmitter release. Here, we demonstrate using multiple, independent, in vitro and in vivo approaches that the majority (~80-90%) of axonal mitochondria in cortical pyramidal neurons (CPNs), lack mitochondrial DNA (mtDNA). Using dynamic, optical imaging analysis of genetically encoded sensors for mitochondrial matrix ATP and pH, we demonstrate that in axons of CPNs, but not in their dendrites, mitochondrial complex V (ATP synthase) functions in a reverse way, consuming ATP and protruding H+ out of the matrix to maintain mitochondrial membrane potential. Our results demonstrate that in mammalian CPNs, axonal mitochondria do not play a major role in ATP supply, despite playing other functions critical to regulating neurotransmission such as Ca2+ buffering.

Tourniquet use in ankle arthroscopy: A systematic review

BACKGROUND

Ankle arthroscopy is commonly performed using a thigh tourniquet and is thought to improve visibility and reduce operative time. However, the current evidence is unclear as to whether the use of a tourniquet provides these benefits. The aim of this study was to investigate whether there is any clinical benefit of using a tourniquet in ankle arthroscopy.

METHODS

A systematic review following PRISMA guidelines was undertaken. All clinical studies published in Medline, Embase, PubMed and the Cochrane Library Database from inception until January 2023 reporting on the use of a tourniquet in ankle arthroscopy were included.

RESULTS

180 studies were identified of which 3 (164 patients) met the inclusion criteria. All studies showed no statistically significant difference in mean surgical time and complication rate between the tourniquet and non-tourniquet groups. Overall, the quality of the evidence was moderate to poor without data in favour or against the routine use of tourniquets in ankle arthroscopy.

CONCLUSION

The current literature suggests that there are no significant differences in mean surgical time and complication rate between the tourniquet and non-tourniquet groups.

Activity-dependent subcellular compartmentalization of dendritic mitochondria structure in CA1 pyramidal neurons

Neuronal mitochondria play important roles beyond ATP generation, including Ca2+ uptake, and therefore have instructive roles in synaptic function and neuronal response properties. Mitochondrial morphology differs significantly in the axon and dendrites of a given neuronal subtype, but in CA1 pyramidal neurons (PNs) of the hippocampus, mitochondria within the dendritic arbor also display a remarkable degree of subcellular, layer-specific compartmentalization. In the dendrites of these neurons, mitochondria morphology ranges from highly fused and elongated in the apical tuft, to more fragmented in the apical oblique and basal dendritic compartments, and thus occupy a smaller fraction of dendritic volume than in the apical tuft. However, the molecular mechanisms underlying this striking degree of subcellular compartmentalization of mitochondria morphology are unknown, precluding the assessment of its impact on neuronal function. Here, we demonstrate that this compartment-specific morphology of dendritic mitochondria requires activity-dependent, Camkk2-dependent activation of AMPK and its ability to phosphorylate two direct effectors: the pro-fission Drp1 receptor Mff and the recently identified anti-fusion, Opa1-inhibiting protein, Mtfr1l. Our study uncovers a new activity-dependent molecular mechanism underlying the extreme subcellular compartmentalization of mitochondrial morphology in dendrites of neurons in vivo through spatially precise regulation of mitochondria fission/fusion balance.

Neuronal deletion of MnSOD in mice leads to demyelination, inflammation and progressive paralysis that mimics phenotypes associated with progressive multiple sclerosis

Neuronal oxidative stress has been implicated in aging and neurodegenerative disease. Here we investigated the impact of elevated oxidative stress induced in mouse spinal cord by deletion of Mn-Superoxide dismutase (MnSOD) using a neuron specific Cre recombinase in Sod2 floxed mice (i-mn-Sod2 KO). Sod2 deletion in spinal cord neurons was associated with mitochondrial alterations and peroxide generation. Phenotypically, i-mn-Sod2 KO mice experienced hindlimb paralysis and clasping behavior associated with extensive demyelination and reduced nerve conduction velocity, axonal degeneration, enhanced blood brain barrier permeability, elevated inflammatory cytokines, microglia activation, infiltration of neutrophils and necroptosis in spinal cord. In contrast, spinal cord motor neuron number, innervation of neuromuscular junctions, muscle mass, and contractile function were not altered. Overall, our findings show that loss of MnSOD in spinal cord promotes a phenotype of demyelination, inflammation and progressive paralysis that mimics phenotypes associated with progressive multiple sclerosis.

Exercise and mitochondrial remodeling to prevent age-related neurodegeneration

Healthy brain activity requires precise ion and energy management creating a strong reliance on mitochondrial function. Age-related neurodegeneration leads to a decline in mitochondrial function and increased oxidative stress, with associated declines in mitochondrial mass, respiration capacity, and respiration efficiency. The interdependent processes of mitochondrial protein turnover and mitochondrial dynamics, known together as mitochondrial remodeling, play essential roles in mitochondrial health and therefore brain function. This mini-review describes the role of mitochondria in neurodegeneration and brain health, current practices for assessing both aspects of mitochondrial remodeling, and how exercise mitigates the adverse effects of aging in the brain. Exercise training elicits functional adaptations to improve brain health, and current literature strongly suggests that mitochondrial remodeling plays a vital role in these positive adaptations. Despite substantial implications that the two aspects of mitochondrial remodeling are interdependent, very few investigations have simultaneously measured mitochondrial dynamics and protein synthesis. An improved understanding of the partnership between mitochondrial protein turnover and mitochondrial dynamics will provide a better understanding of their role in both brain health and disease, as well as how they induce protection following exercise.

The Learning Curve of Third-Generation Percutaneous Chevron and Akin Osteotomy (PECA) for Hallux Valgus

The learning curve to reach technical proficiency for third-generation percutaneous or minimally invasive chevron and Akin osteotomies (PECA/MICA) is recognized to be steep however it is poorly defined in the literature. This study is a retrospective review of the first 58 consecutive PECA cases of a single surgeon. The primary outcome was the number of cases required to reach technical proficiency as defined by the operation time. Secondary outcomes included radiation exposure, radiographic deformity correction, and complication rates. Between November 2017 and March 2019, 61 consecutive PECA cases were performed with outcome data available for 58 of these (95%). Technical proficiency was reached after 38 cases. Operation time and radiation exposure significantly decreased after this transition point (p < .05). There was no difference in complication rate or radiographic deformity correction regardless of position along the learning curve (p > .05). In conclusion, the mean number of cases required to reach technical proficiency in third-generation PECA is 38 cases. The complication rate does not correlate to the number of cases performed, therefore surgeons interested in learning minimally invasive surgery can be reassured that there is unlikely to be an additional risk of harm to a patient during the learning curve.

Time to maximum clinical improvement following minimally invasive chevron and Akin osteotomies (MICA) in hallux valgus surgery

BACKGROUND

There is increasing evidence of positive improvement in clinical and radiological outcomes following minimally invasive hallux valgus deformity correction surgery (MIS). This study investigated the rate of improvement in clinical patient reported outcome measures (PROMs) following MIS as this is not well understood.

METHODS

Between July 2014 and July 2019, data was prospectively collected from consecutive patients pre-operatively and at 6, 12, and 24 months following third-generation minimally invasive chevron and Akin osteotomies (MICA). Radiographic deformity and correction was assessed using weight-bearing radiographs pre-operatively and 6 weeks post-operatively. The primary outcome measure was the change in Manchester Oxford Foot Questionnaire (MOXFQ) score at each time point. Secondary outcomes include radiographic deformity correction, health-related quality of life PROMs and exploration of cases where PROMs did not improve.

RESULTS

There were 202 feet with complete PROM data for every time point. There was a statistically significant improvement in MOXFQ Index score at each time point (p < 0.05) following MICA surgery. The majority of the improvement occurred within the first 6 months. A subgroup of 17 feet (8.4%) were identified which had worse MOXFQ Index scores 6 months following MICA. For 14 feet in this subgroup (82.4%), the MOXFQ Index score subsequently improved over time such that by two years, their score had significantly improved compared to their pre-operative score.

CONCLUSION

The majority of PROM improvement with MICA is gained by 6 months post-operatively but further significant improvement can be seen up to 2 years. Those patients who have not improved at 6 months, are likely to do so with time.

LEVEL OF EVIDENCE

IV.

Health-related quality of life in patients with Achilles tendinopathy: Comparison to the general population of the United Kingdom

BACKGROUND

There is little evidence available regarding the impact of Achilles Tendinopathy (AT) on health-related quality of life (HRQOL). The primary aim of this study was to quantify the clinical and health-related quality-of-life patient-reported outcome measures for a population presenting with either mid-substance or insertional Achilles tendinopathy.

METHODS

A prospective comparative observational study of consecutive patients with AT presenting for extracorporeal shockwave therapy (ESWT) at a large teaching hospital. The primary outcome was assessment of a validated health-related quality of life PROMs (Euroqol EQ-5D-5L) and comparison to 2 general UK population datasets. The secondary outcomes were Visual Analogue Pain Scale (VAS-Pain) and two validated foot-specific patient reported outcome measures (Foot Function Index (FFI) and Victorian Institute of Sports Assessment-Achilles (VISA-A)).

RESULTS

Between March 2014 and June 2021, 320 consecutive patients (125 male; 195 female) were diagnosed with AT and referred for a first course of ESWT. EQ-5D-5L PROMs were prospectively collected for 303 of these patients (94.7%). The mean age (± standard deviation(SD)) was 52.1 ± 11.4 years. The mean EQ-5D-5L Index score (mean±SD) for the AT cohort was 0.783 ± 0.131. Patients less than 55 years with AT had a statistically significantly worse quality of life compared with members of the same age group in the general population. The mean VAS-Pain, FFI, VISA-A clinical outcome scores were 6.0 ± 2.3, 49.5 ± 21.2 and 34.1 ± 14.4 respectively. There was a statistically significant moderate correlation between HRQOL and clinical PROMs (VAS-Pain and FFI vs EQ-5D) however there was no correlation with age.

CONCLUSION

This study demonstrates that patients under the age of 55 with AT have a significantly reduced quality of life compared with the general population.

LEVEL OF EVIDENCE

III.

Aβ42 oligomers trigger synaptic loss through CAMKK2-AMPK-dependent effectors coordinating mitochondrial fission and mitophagy

During the early stages of Alzheimer's disease (AD) in both mouse models and human patients, soluble forms of Amyloid-β 1-42 oligomers (Aβ42o) trigger loss of excitatory synapses (synaptotoxicity) in cortical and hippocampal pyramidal neurons (PNs) prior to the formation of insoluble amyloid plaques. In a transgenic AD mouse model, we observed a spatially restricted structural remodeling of mitochondria in the apical tufts of CA1 PNs dendrites corresponding to the dendritic domain where the earliest synaptic loss is detected in vivo. We also observed AMPK over-activation as well as increased fragmentation and loss of mitochondrial biomass in Ngn2-induced neurons derived from a new APP^Swe/Swe knockin human ES cell line. We demonstrate that Aβ42o-dependent over-activation of the CAMKK2-AMPK kinase dyad mediates synaptic loss through coordinated phosphorylation of MFF-dependent mitochondrial fission and ULK2-dependent mitophagy. Our results uncover a unifying stress-response pathway causally linking Aβ42o-dependent structural remodeling of dendritic mitochondria to synaptic loss.

Minimally invasive surgery for severe hallux valgus in 106 feet

BACKGROUND

There is widespread variation in the optimal procedure for correction of severe hallux valgus deformity defined as hallux valgus angle (HVA) (≥40°) and/or 1-2 intermetatarsal angle (IMA) (≥20°). There is limited evidence investigating the clinical or radiological outcomes following treatment of severe hallux valgus deformity with third-generation minimally invasive chevron and Akin osteotomies (MICA).

METHODS

This was a prospective observational single surgeon series of consecutive patients who underwent primary third-generation MICA with screw fixation for severe hallux valgus. The primary outcome was a validated patient reported outcome measure (PROM), the Manchester-Oxford Foot Questionnaire (MOXFQ), assessed minimum 2 years following MICA. Secondary outcomes were radiographic deformity correction (assessed 6 weeks post-operatively), complication rates and other quality of life PROMs (EQ-5D and Visual Analogue Pain Scale).

RESULTS

Between September 2014 and November 2018, 106 consecutive feet (n = 78 patients; 73 female, 5 male) met the inclusion criteria. Prospectively collected pre-operative and 2 year PROM MOXFQ data was available for 86 feet (81.1%). At two years following surgery, the MOXFQ score significantly improved for the Pain, Walking and Standing and Social Interaction domains from 39.2 to 7.5, 38.2 to 5.9 and 48.6 to 5.5, respectively (p < 0.001). Pre- and 6 week post-operative radiographic data was available for all 106 feet. Mean IMA improved from 18.2° to 6.3° (p < 0.001) whilst mean HVA improved from 45.3° to 10.9° (p < 0.001). The complication rate was 18.8% and the screw removal rate was 5.6%.

CONCLUSION

This study has demonstrated third-generation MICA for the treatment of severe hallux valgus deformity enables substantial deformity correction and is associated with significant improvements in clinical PROMs 2 years following surgery.

The impact of hallux valgus on function and quality of life in females

BACKGROUND

The effect of hallux valgus (HV) on health-related quality of life (HRQOL) and the relationship between radiographic severity of deformity and patient reported outcome measures (PROMs) is poorly understood. The aim of this study was to compare the HRQOL of female patients with HV to the UK population. The secondary aim was to assess the correlation between PROMs, including HRQOL, with radiographic severity of deformity.

METHODS

Weight bearing radiographic data (hallux valgus (HVA) angle; intermetatarsal (IM) angle) were measured in consecutive female patients presenting with HV. Each patient prospectively completed the Euroqol EQ-5D-5L questionnaire (EQ-5D), Visual Analogue Scale for Pain (VAS-Pain) and Manchester Oxford Foot Questionnaire (MOXFQ). Data were stratified into age ranges and compared with an EQ-5D United Kingdom general population reference dataset. Pearson R correlation values were calculated for the PROMs and radiographic deformity.

RESULTS

Between July 2015 and March 2020, 425 consecutive female patients presented with HV for consideration for surgery. EQ-5D-5L data were prospectively collected for 396 of these patients (93.2%). Females less than 65 years with HV had a statistically significantly worse quality of life compared with females of the same age group in the general population. Above the age of 65, there was no statistically significant difference in EQ-5D-5L Index score between the two groups. Younger females reported higher VAS-Pain scores compared to older patients with 91% of patients reporting some degree of pain symptoms. There was a moderate correlation with MOXFQ Index score and EQ-5D-5L Index (R = -0.51, p < 0.001) and VAS-Pain scores (R = 0.54, p < 0.001). There was no correlation between radiographic HV deformity and HRQOL measures or MOXFQ scores although it was noted that there was a trend of increasing HVA/IMA with age.

CONCLUSION

Female patients presenting with HV deformity have a significantly reduced quality of life compared with the UK general population. The radiographic severity of deformity did not correlate with HRQOL measures or foot and ankle specific PROMs. Foot and ankle specific clinical PROMsmoderately correlate with HRQOL and may be a better marker of the negative effect of symptomatic hallux valgus deformity on quality of life.

LEVEL OF EVIDENCE

III.

Hallux valgus surgery in children with cerebral palsy: A systematic review

BACKGROUND

Children with cerebral palsy are highly likely to develop foot deformities, some of which may require surgical intervention. Hallux valgus is a common forefoot deformity which can cause issues with pain, footwear, orthotic splints and soft tissues. It remains unclear what the optimal surgical treatment is for children with cerebral palsy and hallux valgus deformity.

OBJECTIVE

To systematically review studies reporting the clinical and radiological outcomes of surgical correction of hallux valgus deformity in children with cerebral palsy.

METHODS

A systematic review of studies published in electronic databases (Medline, Embase, Pubmed and Cochrane library) from inception until January 2021. Keywords related to hallux valgus and cerebral palsy were included.

RESULTS

58 studies were identified of which 7 met the criteria for inclusion. 200 feet in 134 patients with a mean age of 13.5 years were included, with a mean follow up period of 43 months. A range of clinical and radiographic outcomes were assessed. A treatment framework for the assessment and management of hallux valgus in children with cerebral palsy based on the published evidence is presented.

CONCLUSION

Non-ambulant children with cerebral palsy with symptomatic hallux valgus should primarily undergo first MTPJ arthrodesis whilst those who are ambulant should undergo first metatarsal osteotomy± soft tissue correction.

Clinical outcomes following surgical management of insertional Achilles tendinopathy using a double-row suture bridge technique with mean two-year follow-up

BACKGROUND

The clinical outcomes following surgical management of insertional Achilles tendinopathy (IAT) vary depending on the surgical technique used to reattach the Achilles tendon following debridement. The aim of this study was to investigate the clinical outcomes of patients with IAT who underwent surgical management with a double-row suture bridge technique used to reattach the Achilles tendon.

METHODS

A retrospective review of consecutive patients diagnosed with IAT, who underwent surgical management utilising a double-row suture bridge technique (Arthex Speedbridge), and a minimum of 3-month follow-up were included. The primary outcome was the Manchester-Oxford Foot Questionnaire (MOXFQ) Index score which is a patient reported outcome measure (PROM). Secondary outcomes included EuroQol EQ-5D-5L health-related quality of life PROM and complication rates.

RESULTS

Between July 2013 and June 2020, 50 consecutive patients (23 male; 27 female) were included. The mean age (± standard deviation) was 52.3 ± 11.3 (range 29.0-84.3). Pre- and post-operative PROM data were available for all cases. The mean follow-up was 2.4 ± 1.9 years. The MOXFQ Index score improved from 48.5 to 12.4 (p < 0.01), EQ-5D-5L improved from 2.7 ± 0.46 to 1.2 ± 0.37 (p < 0.01), and EQ-VAS improved from 48.0 ± 18.4 to 84.1 ± 12.6 (p < 0.01). Four patients had complications which were of minimal clinical relevance and caused no deviation from routine recovery. There were no cases of tendon rupture.

CONCLUSION

This study has demonstrated that surgical management of IAT is safe and effective with clinical improvement in both clinical and general health-related quality of life outcome PROMs.

LEVEL OF EVIDENCE

IV.

The intra-muscular course and distribution of the anterior interosseous nerve within pronator quadratus: An anatomical study

BACKGROUND

The anterior interosseous nerve (AIN) is a terminal motor branch of the median nerve innervating the following three muscles from proximal to distal: Flexor pollicis longus (FPL), the radial half of flexor digitorum profundus (FDP), and the pronator quadratus (PQ). The aim of this study was to define the course of the AIN within the PQ to aid surgeons performing distal radial procedures.

METHODS

Ten embalmed cadaveric forearms were dissected to identify the path of the AIN within PQ. An en-bloc excision of the PQ with its supplying AIN and vasculature was performed to identify a safe zone where PQ can be elevated without damaging AIN. A scoping literature search was performed to identify other studies reporting the path of AIN through PQ.

RESULTS

The mean distance from the radial border of the radius perpendicular to the point at which the AIN enters the PQ was 22.3 mm (range 21-24 mm). The mean distance from the distal wrist crease to the AIN entering PQ was 74.3 mm (range 59-84 mm). The mean number of nerve branches to PQ was 5.2 (range 3-8). In all specimens, the AIN was found to lie on the radial side of the anterior interosseous artery (AIA).

CONCLUSIONS

The AIN courses on the deep surface of the PQ in a longitudinal proximal to distal direction. A 'safe zone' was identified within 20 mm of the radial border of the distal radius, which may be utilised by surgeons in a muscle-splitting approach to the distal radius.

Neuronal mitochondrial morphology is significantly affected by both fixative and oxygen level during perfusion

Neurons in the brain have a uniquely polarized structure consisting of multiple dendrites and a single axon generated from a cell body. Interestingly, intracellular mitochondria also show strikingly polarized morphologies along the dendrites and axons: in cortical pyramidal neurons (PNs), dendritic mitochondria have a long and tubular shape, while axonal mitochondria are small and circular. Mitochondria play important roles in each compartment of the neuron by generating adenosine triphosphate (ATP) and buffering calcium, thereby affecting synaptic transmission and neuronal development. In addition, mitochondrial shape, and thereby function, is dynamically altered by environmental stressors such as oxidative stress or in various neurodegenerative diseases including Alzheimer's disease and Parkinson's disease. Although the importance of altered mitochondrial shape has been claimed by multiple studies, methods for studying this stress-sensitive organelle have not been standardized. Here we address pertinent steps that influence mitochondrial morphology during experimental processes. We demonstrate that fixative solutions containing only paraformaldehyde (PFA), or that introduce hypoxic conditions during the procedure, induce dramatic fragmentation of mitochondria both in vitro and in vivo. This disruption was not observed following the use of glutaraldehyde (GA) addition or oxygen supplementation, respectively. Finally, using pre-formed fibril α-synuclein treated neurons, we show fixative choice can alter experimental outcomes. Specifically, α-synuclein-induced mitochondrial remodeling could not be observed with PFA only fixation as fixation itself caused mitochondrial fragmentation. Our study provides optimized methods for examining mitochondrial morphology in neurons and demonstrates that fixation conditions are critical when investigating the underlying cellular mechanisms involving mitochondria in physiological and neurodegenerative disease models.

The patient perspective, experience and satisfaction of day case unicompartmental knee arthroplasty: A short-term mixed-methods study

BACKGROUND

Day case unicompartmental knee arthroplasty (UKA) is increasingly being performed worldwide. When performed in the appropriate patient, day case UKA has been demonstrated to be safe, cost effective and improve resource allocation. Limited evidence highlights increased patient satisfaction of day case UKA when compared with inpatient UKA. A detailed study of the patient perspective, experience and satisfaction following day case UKA has not been described before.

METHODS

A retrospective case series review of 21 consecutive patients (19 unilateral, 2 bilateral) undergoing day case UKA in an elective orthopaedic centre was undertaken. A qualitative and quantitative patient assessment of the day case UKA experience was administered. A five-point Likert scale satisfaction questionnaire, Oxford Knee Score (OKS) and open-ended interview was undertaken. The qualitative responses underwent thematic analysis.

RESULTS

One hundred percent of patients expressed satisfaction (76.2% completely satisfied, 33.8% moderately satisfied) with day case UKA. The majority of patients (90.5%) reported that if they had to undergo UKA again they would prefer a day case over an inpatient procedure. Patients consider surgical outcome, physiotherapy provision, discharge planning, postoperative medications and follow up as key aspects of day case UKA care. One patient was re-admitted following discharge.

CONCLUSIONS

The present study demonstrates a high level of patient satisfaction with day case UKA. The results reported herein are subject to the study limitations of sample size, recall bias and inclusion criteria. We recommend that the themes identified by patients are addressed through a multidisciplinary approach with well-defined clinical pathways for a high-quality patient-centred experience.

Mitochondrial biogenesis in developing astrocytes regulates astrocyte maturation and synapse formation

The mechanisms controlling the post-natal maturation of astrocytes play a crucial role in ensuring correct synaptogenesis. We show that mitochondrial biogenesis in developing astrocytes is necessary for coordinating post-natal astrocyte maturation and synaptogenesis. The astrocytic mitochondrial biogenesis depends on the transient upregulation of metabolic regulator peroxisome proliferator-activated receptor gamma (PPARγ) co-activator 1α (PGC-1α), which is controlled by metabotropic glutamate receptor 5 (mGluR5). At tissue level, the loss or downregulation of astrocytic PGC-1α sustains astrocyte proliferation, dampens astrocyte morphogenesis, and impairs the formation and function of neighboring synapses, whereas its genetic re-expression is sufficient to restore the mitochondria compartment and correct astroglial and synaptic defects. Our findings show that the developmental enhancement of mitochondrial biogenesis in astrocytes is a critical mechanism controlling astrocyte maturation and supporting synaptogenesis, thus suggesting that astrocytic mitochondria may be a therapeutic target in the case of neurodevelopmental and psychiatric disorders characterized by impaired synaptogenesis.

Modified Broström repair with suture tape augmentation for lateral ankle instability: A systematic review

BACKGROUND

There is increasing interest in augmentation of modified Broström repairs for lateral ankle instability with a prosthetic reconstruction using suture tape internal bracing. The aim of this study was to investigate if suture tape augmentation resulted in improved clinical and radiological outcomes compared to a standard modified Broström repair alone.

METHODS

A systematic review following PRISMA guidelines was undertaken. All clinical studies published in Medline, Embase, Pubmed and the Cochrane Library Database from inception until January 2020 reporting on the use of suture tape augmentation to a modified Broström repair for lateral ankle instability.

RESULTS

78 studies were identified of which 10 (assessing 333 patients) met the criteria for inclusion. Mean follow up was 24.8 months (range 6-52 months). All studies showed a statistically significant improvement across multiple clinical outcome measures post-surgery in both suture tape augmentation and modified Broström groups, however there were no statistically significant inter-group differences. Pooled results suggested there may be a reduction in recurrence of instability with suture tape augmentation when compared to modified Broström repair alone (p < 0.05). Overall quality of evidence was moderate to poor with limited data to support use of suture tape augmentation.

CONCLUSION

Clinical and radiographic outcomes using a suture tape internal bracing for lateral ankle instability are excellent, and are equivalent to standard treatment across multiple clinical and radiographic assessment measures. There is minimal evidence to suggest functional outcomes are better, or recurrence rates are lower than modified Broström repair alone.

PROSPERO REGISTRY

CRD42020169876.

LEVEL OF EVIDENCE

II.

MFF-dependent mitochondrial fission regulates presynaptic release and axon branching by limiting axonal mitochondria size

Neurons display extreme degrees of polarization, including compartment-specific organelle morphology. In cortical, long-range projecting, pyramidal neurons (PNs), dendritic mitochondria are long and tubular whereas axonal mitochondria display uniformly short length. Here we explored the functional significance of maintaining small mitochondria for axonal development in vitro and in vivo. We report that the Drp1 'receptor' Mitochondrial fission factor (MFF) is required for determining the size of mitochondria entering the axon and then for maintenance of their size along the distal portions of the axon without affecting their trafficking properties, presynaptic capture, membrane potential or ability to generate ATP. Strikingly, this increase in presynaptic mitochondrial size upon MFF downregulation augments their capacity for Ca²⁺ ([Ca²⁺]_m) uptake during neurotransmission, leading to reduced presynaptic [Ca²⁺]_c accumulation, decreased presynaptic release and terminal axon branching. Our results uncover a novel mechanism controlling neurotransmitter release and axon branching through fission-dependent regulation of presynaptic mitochondrial size.

Haploinsufficiency of autism spectrum disorder candidate gene NUAK1 impairs cortical development and behavior in mice

Recently, numerous rare de novo mutations have been identified in patients diagnosed with autism spectrum disorders (ASD). However, despite the predicted loss-of-function nature of some of these de novo mutations, the affected individuals are heterozygous carriers, which would suggest that most of these candidate genes are haploinsufficient and/or lead to expression of dominant-negative forms of the protein. Here, we tested this hypothesis with the candidate ASD gene Nuak1 that we previously identified for its role in the development of cortical connectivity. We report that Nuak1 is haploinsufficient in mice with regard to its function in cortical development. Furthermore Nuak1^+/− mice show a combination of abnormal behavioral traits ranging from defective spatial memory consolidation, defects in social novelty (but not social preference) and abnormal sensorimotor gating. Overall, our results demonstrate that Nuak1 haploinsufficiency leads to defects in the development of cortical connectivity and a complex array of behavorial deficits.

Nuak1 is an autism spectrum disorder candidate gene. Here the authors report behavioral and cortical development in mice heterozygous for Nuak1, suggesting loss of function mutations in one copy of Nuak1 may contribute to neurodevelopmental disorders.

Structure and Function of an Actin-Based Filter in the Proximal Axon

The essential organization of microtubules within neurons has been described; however, less is known about how neuronal actin is arranged and the functional implications of its arrangement. Here, we describe, in live cells, an actin-based structure in the proximal axon that selectively prevents some proteins from entering the axon while allowing the passage of others. Concentrated patches of actin in proximal axons are present shortly after axonal specification in rat and zebrafish neurons imaged live, and they mark positions where anterogradely traveling vesicles carrying dendritic proteins halt and reverse. Patches colocalize with the ARP2/3 complex, and when ARP2/3-mediated nucleation is blocked, a dendritic protein mislocalizes to the axon. Patches are highly dynamic, with few persisting longer than 30 min. In neurons in culture and in vivo, actin appears to form a contiguous, semipermeable barrier, despite its apparently sparse distribution, preventing axonal localization of constitutively active myosin Va but not myosin VI.

Emerging roles of mitochondria in synaptic transmission and neurodegeneration

Mitochondria play numerous critical physiological functions in neurons including ATP production, Ca2+ regulation, lipid synthesis, ROS signaling, and the ability to trigger apoptosis. Recently developed technologies, including in vivo 2-photon imaging in awake behaving mice revealed that unlike in the peripheral nervous system (PNS), mitochondrial transport decreases strikingly along the axons of adult neurons of the central nervous system (CNS). Furthermore, the improvements of genetically-encoded biosensors have enabled precise monitoring of the spatial and temporal impact of mitochondria on Ca2+, ATP and ROS homeostasis in a compartment-specific manner. Here, we discuss recent findings that begin to unravel novel physiological and pathophysiological properties of neuronal mitochondria at synapses. We also suggest new directions in the exploration of mitochondrial function in synaptic transmission, plasticity and neurodegeneration.

Impaired Mitochondrial Dynamics and Mitophagy in Neuronal Models of Tuberous Sclerosis Complex

Tuberous sclerosis complex (TSC) is a neurodevelopmental disease caused by TSC1 or TSC2 mutations and subsequent activation of the mTORC1 kinase. Upon mTORC1 activation, anabolic metabolism, which requires mitochondria, is induced, yet at the same time the principal pathway for mitochondrial turnover, autophagy, is compromised. How mTORC1 activation impacts mitochondrial turnover in neurons remains unknown. Here, we demonstrate impaired mitochondrial homeostasis in neuronal in vitro and in vivo models of TSC. We find that Tsc1/2-deficient neurons accumulate mitochondria in cell bodies, but are depleted of axonal mitochondria, including those supporting presynaptic sites. Axonal and global mitophagy of damaged mitochondria is impaired, suggesting that decreased turnover may act upstream of impaired mitochondrial metabolism. Importantly, blocking mTORC1 or inducing mTOR-independent autophagy restores mitochondrial homeostasis. Our study clarifies the complex relationship between the TSC-mTORC1 pathway, autophagy, and mitophagy, and defines mitochondrial homeostasis as a therapeutic target for TSC and related diseases.

Virus-Enabled Optimization and Delivery of the Genetic Machinery for Efficient Unnatural Amino Acid Mutagenesis in Mammalian Cells and Tissues

Unnatural amino acid (UAA) mutagenesis of recombinant proteins in live mammalian cells requires coexpression of the mutant target, as well as an engineered tRNA/aminoacyl-tRNA synthetase pair. The ability to readily determine the optimal relative expression levels of these three genetic components for efficient expression of the UAA-modified target is highly desirable, but remains challenging to accomplish. Here we report a facile strategy to achieve this by taking advantage of the efficient gene-delivery by a baculovirus vector, which enables systematic variation of the expression level of each genetic component in a population-wide manner. Insights gained from this study led to the design of an optimal expression system, which can be delivered into mammalian cells by a single baculovirus vector to provide significantly improved UAA incorporation efficiency at a low virus load. Furthermore, this optimized baculovirus vector was shown to enable efficient UAA mutagenesis of proteins expressed in mouse brain tissue.

Progressive Decrease of Mitochondrial Motility during Maturation of Cortical Axons In Vitro and In Vivo

The importance of mitochondria for neuronal function is evident by the large number of neurodegenerative diseases that have been associated with a disruption of mitochondrial function or transport (reviewed in [1, 2]). Mitochondria are essential for proper biological function as a result of their ability to produce ATP through oxidative phosphorylation, buffer cytoplasmic calcium, regulate lipid biosynthesis, and trigger apoptosis (reviewed in [2]). Efficient transport of mitochondria is thought to be particularly important in neurons in light of their compartmentalization, length of axonal processes, and high-energy requirements (reviewed in [3]). However, the majority of these results were obtained using short-term, in vitro neuronal culture models, and very little is currently known about mitochondrial dynamics in mature axons of the mammalian CNS in vitro or in vivo. Furthermore, recent evidence has demonstrated that mitochondrial immobilization at specific points along the axon, such as presynaptic boutons, play critical roles in axon morphogenesis [4, 5]. We report that as cortical axons mature, motility of mitochondria (but not other cargoes) is dramatically reduced and this coincides with increased localization to presynaptic sites. We also demonstrate using photo-conversion that in vitro mature axons display surprisingly limited long-range mitochondrial transport. Finally, using in vivo two-photon microscopy in anesthetized or awake-behaving mice, we document for the first time that mitochondrial motility is also remarkably low in distal cortical axons in vivo. These results argue that mitochondrial immobilization and presynaptic localization are important hallmarks of mature CNS axons both in vitro and in vivo.

LKB1 Regulates Mitochondria-Dependent Presynaptic Calcium Clearance and Neurotransmitter Release Properties at Excitatory Synapses along Cortical Axons

Individual synapses vary significantly in their neurotransmitter release properties, which underlie complex information processing in neural circuits. Presynaptic Ca2+ homeostasis plays a critical role in specifying neurotransmitter release properties, but the mechanisms regulating synapse-specific Ca2+ homeostasis in the mammalian brain are still poorly understood. Using electrophysiology and genetically encoded Ca2+ sensors targeted to the mitochondrial matrix or to presynaptic boutons of cortical pyramidal neurons, we demonstrate that the presence or absence of mitochondria at presynaptic boutons dictates neurotransmitter release properties through Mitochondrial Calcium Uniporter (MCU)-dependent Ca2+ clearance. We demonstrate that the serine/threonine kinase LKB1 regulates MCU expression, mitochondria-dependent Ca2+ clearance, and thereby, presynaptic release properties. Re-establishment of MCU-dependent mitochondrial Ca2+ uptake at glutamatergic synapses rescues the altered neurotransmitter release properties characterizing LKB1-null cortical axons. Our results provide novel insights into the cellular and molecular mechanisms whereby mitochondria control neurotransmitter release properties in a bouton-specific way through presynaptic Ca2+ clearance.

A change in the trend in dosulepin usage following the introduction of a prescribing indicator but not after two national safety warnings

WHAT IS KNOWN AND OBJECTIVE

The tricyclic antidepressant dosulepin has been associated with an increased risk of toxicity in overdose compared with other antidepressants. In the UK, the MHRA and NICE have issued advice on the prescribing of dosulepin, and a National Prescribing Indicator (NPI) to monitor usage was introduced in Wales in 2011. The aim of this study was to assess whether trends in dosulepin usage in Wales and NE England changed following the two pieces of safety guidance and the introduction of the National Prescribing Indicator in Wales.

METHODS

Primary care dosulepin usage in the 12 months prior to and following MHRA safety advice (in 2007), NICE guideline CG90 (in 2009) and the introduction of the NPI (in 2011) was obtained. Usage was measured using defined daily doses (DDDs) per 1000 prescribing units (PUs). The trends in the 12 months prior to and following the introduction of prescribing advice and the NPI were compared using an autoregressive integrated moving average (ARIMA) model.

RESULTS AND DISCUSSION

In Wales, the trend in dosulepin usage did not change significantly prior to and following the MHRA advice: -0·18 and -0·43 DDDs/1000PUs per month, respectively (P = 0·07), or prior to and following NICE CG90: -0·30 and -0·49 DDDs/1000PUs per month, respectively (P = 0·35). In the 12 months prior to and following the introduction of the NPI, the trend was -0·45 and -0·98 DDDs/1000PUs per month, respectively (P = 0·001). In NE England, the trend did not alter significantly following the NICE advice or the introduction of the NPI in Wales.

WHAT IS NEW AND CONCLUSION

The trend in dosulepin usage in Wales altered significantly following the introduction of the NPI, but not after the other prescribing advice. This association, coupled with the absence of a significant change in NE England over the same period, provided some evidence of the effectiveness of the NPI in prompting a change in prescribing behaviour in Wales.

Metabolism. AMP-activated protein kinase mediates mitochondrial fission in response to energy stress

Mitochondria undergo fragmentation in response to electron transport chain (ETC) poisons and mitochondrial DNA-linked disease mutations, yet how these stimuli mechanistically connect to the mitochondrial fission and fusion machinery is poorly understood. We found that the energy-sensing adenosine monophosphate (AMP)-activated protein kinase (AMPK) is genetically required for cells to undergo rapid mitochondrial fragmentation after treatment with ETC inhibitors. Moreover, direct pharmacological activation of AMPK was sufficient to rapidly promote mitochondrial fragmentation even in the absence of mitochondrial stress. A screen for substrates of AMPK identified mitochondrial fission factor (MFF), a mitochondrial outer-membrane receptor for DRP1, the cytoplasmic guanosine triphosphatase that catalyzes mitochondrial fission. Nonphosphorylatable and phosphomimetic alleles of the AMPK sites in MFF revealed that it is a key effector of AMPK-mediated mitochondrial fission.

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Cell biology in neuroscience: Cellular and molecular mechanisms underlying axon formation, growth, and branching

Proper brain wiring during development is pivotal for adult brain function. Neurons display a high degree of polarization both morphologically and functionally, and this polarization requires the segregation of mRNA, proteins, and lipids into the axonal or somatodendritic domains. Recent discoveries have provided insight into many aspects of the cell biology of axonal development including axon specification during neuronal polarization, axon growth, and terminal axon branching during synaptogenesis.

Terminal axon branching is regulated by the LKB1-NUAK1 kinase pathway via presynaptic mitochondrial capture

The molecular mechanisms underlying the axon arborization of mammalian neurons are poorly understood but are critical for the establishment of functional neural circuits. We identified a pathway defined by two kinases, LKB1 and NUAK1, required for cortical axon branching in vivo. Conditional deletion of LKB1 after axon specification or knockdown of NUAK1 drastically reduced axon branching in vivo, whereas their overexpression was sufficient to increase axon branching. The LKB1-NUAK1 pathway controls mitochondria immobilization in axons. Using manipulation of Syntaphilin, a protein necessary and sufficient to arrest mitochondrial transport specifically in the axon, we demonstrate that the LKB1-NUAK1 kinase pathway regulates axon branching by promoting mitochondria immobilization. Finally, we show that LKB1 and NUAK1 are necessary and sufficient to immobilize mitochondria specifically at nascent presynaptic sites. Our results unravel a link between presynaptic mitochondrial capture and axon branching.

The effect of displacement on sensitivity to first- and second-order global motion in 5-year-olds and adults

We compared the development of sensitivity to first- versus second-order global motion in 5-year-olds (n=24) and adults (n=24) tested at three displacements (0.1, 0.5 and 1.0 degrees). Sensitivity was measured with Random-Gabor Kinematograms (RGKs) formed with luminance-modulated (first-order) or contrast-modulated (second-order) concentric Gabor patterns. Five-year-olds were less sensitive than adults to the direction of both first- and second-order global motion at every displacement tested. In addition, the immaturity was smallest at the smallest displacement, which required the least spatial integration, and smaller for first-order than for second-order global motion at the middle displacement. The findings suggest that the development of sensitivity to global motion is limited by the development of spatial integration and by different rates of development of sensitivity to first- versus second-order signals.

Myosin-dependent targeting of transmembrane proteins to neuronal dendrites

The distinct electrical properties of axonal and dendritic membranes are largely a result of specific transport of vesicle-bound membrane proteins to each compartment. How this specificity arises is unclear because kinesin motors that transport vesicles cannot autonomously distinguish dendritically projecting microtubules from those projecting axonally. We hypothesized that interaction with a second motor might enable vesicles containing dendritic proteins to preferentially associate with dendritically projecting microtubules and avoid those that project to the axon. Here we show that in rat cortical neurons, localization of several distinct transmembrane proteins to dendrites is dependent on specific myosin motors and an intact actin network. Moreover, fusion with a myosin-binding domain from Melanophilin targeted Channelrhodopsin-2 specifically to the somatodendritic compartment of neurons in mice in vivo. Together, our results suggest that dendritic transmembrane proteins direct the vesicles in which they are transported to avoid the axonal compartment through interaction with myosin motors.

The role of Kif5B in axonal localization of Kv1 K(+) channels

Here we present evidence that the kinesin, Kif5B, is involved in the transportation and axonal targeting of Kv1 channels. We show that a dominant negative variant of Kif5B specifically blocks localization to the axon of expressed, tagged versions of Kv1.3 in cultured cortical slices. In addition, the dominant negative variant of Kif5B blocks axonal localization of endogenous Kv1.1, Kv1.2, and Kv1.4 in cortical neurons in dissociated cultures. We also found evidence that Kif5B interacts with Kv1 channels. Endogenous Kv1.2 colocalized with Kif5B in cortical neurons and coimmunoprecipitated with Kif5B from brain lysate. The T1 domain of Shaker K(+) channels has been shown to play a critical role in targeting the channel to the axon. We have three pieces of evidence to suggest that the T1 domain also mediates interaction between Kv1 channels and Kif5B: Addition of the T1 domain to a heterologous protein, TfR, is sufficient to cause the resulting fusion protein, TfRT1, to colocalize with Kif5B. Also, the T1 domain is necessary for interaction of Kv1.3 with Kif5B in a coimmunoprecipitation assay. Finally, dominant negative variants of Kif5B block axonal targeting of TfRT1, but have no effect on dendritic localization of TfR. Together these data suggest a model where Kif5B interacts with Kv1 channels either directly or indirectly via the T1 domain, causing the channels to be transported to axons.

Neural correlates of processing facial identity based on features versus their spacing

Adults' expertise in recognizing facial identity involves encoding subtle differences among faces in the shape of individual facial features (featural processing) and in the spacing among features (a type of configural processing called sensitivity to second-order relations). We used fMRI to investigate the neural mechanisms that differentiate these two types of processing. Participants made same/different judgments about pairs of faces that differed only in the shape of the eyes and mouth, with minimal differences in spacing (featural blocks), or pairs of faces that had identical features but differed in the positions of those features (spacing blocks). From a localizer scan with faces, objects, and houses, we identified regions with comparatively more activity for faces, including the fusiform face area (FFA) in the right fusiform gyrus, other extrastriate regions, and prefrontal cortices. Contrasts between the featural and spacing conditions revealed distributed patterns of activity differentiating the two conditions. A region of the right fusiform gyrus (near but not overlapping the localized FFA) showed greater activity during the spacing task, along with multiple areas of right frontal cortex, whereas left prefrontal activity increased for featural processing. These patterns of activity were not related to differences in performance between the two tasks. The results indicate that the processing of facial features is distinct from the processing of second-order relations in faces, and that these functions are mediated by separate and lateralized networks involving the right fusiform gyrus, although the FFA as defined from a localizer scan is not differentially involved.

Greater losses in sensitivity to second-order local motion than to first-order local motion after early visual deprivation in humans

We compared sensitivity to first-order versus second-order local motion in patients treated for dense central congenital cataracts in one or both eyes. Amplitude modulation thresholds were measured for discriminating the direction of motion of luminance-modulated (first-order) and contrast modulated (second-order) horizontal sine-wave gratings. Early visual deprivation, whether monocular or binocular, caused losses in sensitivity to both first- and second-order motion, with greater losses for second-order motion than for first-order motion. These findings are consistent with the hypothesis that the two types of motion are processed by different mechanisms and suggest that those mechanisms are differentially sensitive to early visual input.

Discrimination of speed in 5-year-olds and adults: are children up to speed?

We compared thresholds for discriminating changes in speed by 5-year-olds and adults for two reference speeds: 1.5 and 6 degrees s(-1). Both adults and 5-year-olds were more sensitive to changes from the faster than from the slower reference speed. Five-year-olds were less sensitive than adults at both reference speeds but significantly more immature at the slower (1.5 degrees s(-1)) than at the faster (6 degrees s(-1)) reference speed. The findings suggest that the mechanisms underlying speed discrimination are immature in 5-year-olds, especially those that process slower speeds.

Deficits in the processing of local and global motion in very low birthweight children

This study evaluated the impact of premature birth on the development of local and global motion processing in a group of very low birthweight (<1500 g), 5- to 8-year-old children. Sensitivity to first- and second-order local motion stimuli and coherence thresholds for global motion in random dot kinematograms were measured. Relative to full-term controls, premature children showed deficits on all three aspects of motion processing. These problems could not be accounted for by stereo deficits, amblyopia, or attentional problems. A history of mild retinopathy of prematurity and/or intraventricular hemorrhage increased risk, but deficits were observed in some children with no apparent ocular or cerebral pathology. It is important to note that, despite the observed group differences, individual profiles of performance did vary; the results suggest that these three forms of motion processing may involve separate neural mechanisms. These findings serve to increase our understanding of the organization and functional development of motion-processing subsystems in humans, and of the impact of prematurity and associated complications on visual development.