Does the Level and Complexity of Femur Fracture Determine Intramedullary Peak Pressures During Reamed Femoral Nailing? A Prospective Study

OBJECTIVES

To investigate femoral intramedullary (IM) pressures during reamed antegrade nailing and to determine whether fracture level and/or complexity affect peak pressures.

METHODS

DESIGN

Prospective, nonrandomized observational cohort.

SETTING

Single level I trauma center.

PATIENT SELECTION CRITERIA

Patients presenting with femur fractures (OTA/AO 31A3; 32A; 32B; 32C; 33A2; 33A3), requiring antegrade IM nail fixation, were included in this study. Excluded were minors and patients presenting with hemodynamic instability, a reduced level of consciousness and intoxication. Femurs were divided into thirds based on preoperative radiological measurements and allocated to 3 groups based on fracture location: Proximal (A), middle (B), and distal (C) third femur fractures. Fracture complexity was also documented.

OUTCOME MEASURES AND COMPARISONS

Peak IM pressures of proximal, middle, and distal third femoral fractures were compared during antegrade femoral IM nail fixation.

RESULTS

Twenty-two fractures in 21 patients were enrolled and treated over a 4-month period with a distribution of fracture locations of group A = 12, group B = 6, and group C = 4. Measured mean resting distal IM pressures were significantly higher ( P < 0.05) in proximal fractures (group A: 52.5 mm Hg) than in middle and distal third fractures (group B: 36.6 mm Hg and group C: 27.5 mm Hg). Greatest peak pressures were generated during the first ream in groups A and B, occurring distal to the fracture in all cases. Group A averaged 363.8 mm Hg (300-420), group B 174.2 mm Hg (160-200), and group C 98.8 mm Hg (90-100). There was a significant difference comparing group A with B and C combined ( P < 0.01) and group A with B ( P < 0.05) and C ( P < 0.05]) individually. Group A consisted of 6 comminuted and 6 simple fracture configurations. Mean peak pressures in these subgroups differed significantly: 329 mm Hg (300-370) versus 398 mm Hg (370-430), respectively ( P < 0.05). Complex fractures in study groups B and C did not have significantly different peak pressures compared with simple fractures ( P > 0.05).

CONCLUSIONS

Both the fracture location and comminution affect peak IM pressures during reamed antegrade femoral nailing. Proximal, simple fracture configurations resulted in significantly higher pressures when compared with more distal and comminuted fracture configurations.

LEVEL OF EVIDENCE

Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Evaluating Basic Knee Arthroscopy Skills in Orthopaedic Trainees in a Limited-Resource Setting

Orthopaedic training in Southern Africa is largely focused on trauma, although elective procedures, such as knee arthroscopy, are increasing. This is especially true in the private sector where most trainees will practice. The primary aim of this study was to assess the arthroscopic competency of orthopaedic trainees in a setting of limited resources.

Methods

A prospective observational cohort study was conducted. Orthopaedic trainees of a Southern African university hospital performed basic arthroscopy on a knee model. Their surgical competency was assessed by 2 surgeons proficient in arthroscopy using the modified Basic Knee Arthroscopy Skill Scoring System (mBAKSSS).

Results

A total of 16 trainees (12 male) were included (6 junior and 10 senior trainees). The median age of participants was 36 (34.8-37) years. The median mBAKSSS was 28.0 (20.3-32.5) but showed a large variability (12.0-42.5). The overall reliability was excellent with Cronbach's alpha of 0.91 and interclass correlation of 0.91 (95% confidence interval 0.75-0.97).

Conclusions

The average knee arthroscopy proficiency of our trainees is comparable with that of international training programs, but there was great variability with inconsistent skills among the trainees. This calls for improved and reproducible arthroscopy training and skills transfer, exposure to procedures, and ongoing assessment.

Level of Evidence

II (prospective observational cohort study).

Paediatric ankle cartilage lesions: Proceedings of the International Consensus Meeting on Cartilage Repair of the Ankle

BACKGROUND

The evidence supporting best practice guidelines in the field of cartilage repair of the ankle are based on both low quality and low levels of evidence. Therefore, an international consensus group of experts was convened to collaboratively advance toward consensus opinions based on the best available evidence on key topics within cartilage repair of the ankle. The purpose of this article is to report the consensus statements on "Pediatric Ankle Cartilage Lesions" developed at the 2019 International Consensus Meeting on Cartilage Repair of the Ankle.

METHODS

Forty-three international experts in cartilage repair of the ankle representing 20 countries convened to participate in a process based on the Delphi method of achieving consensus. Questions and statements were drafted within four working groups focusing on specific topics within cartilage repair of the ankle, after which a comprehensive literature review was performed and the available evidence for each statement was graded. Discussion and debate occurred in cases where statements were not agreed upon in unanimous fashion within the working groups. A final vote was then held, and the strength of consensus was characterised as follows: consensus: 51-74%; strong consensus: 75-99%; unanimous: 100%.

RESULTS

A total of 12 statements on paediatric ankle cartilage lesions reached consensus during the 2019 International Consensus Meeting on Cartilage Repair of the Ankle. Five achieved unanimous support, and seven reached strong consensus (>75% agreement). All statements reached at least 84% agreement.

CONCLUSIONS

This international consensus derived from leaders in the field will assist clinicians with the management of paediatric ankle cartilage lesions.

Osteochondral Lesions of the Tibial Plafond and Ankle Instability With Ankle Cartilage Lesions: Proceedings of the International Consensus Meeting on Cartilage Repair of the Ankle

BACKGROUND

An international consensus group of experts was convened to collaboratively advance toward consensus opinions based on the best available evidence on key topics within cartilage repair of the ankle. The purpose of this article is to present the consensus statements on osteochondral lesions of the tibial plafond (OLTP) and on ankle instability with ankle cartilage lesions developed at the 2019 International Consensus Meeting on Cartilage Repair of the Ankle.

METHODS

Forty-three experts in cartilage repair of the ankle were convened and participated in a process based on the Delphi method of achieving consensus. Questions and statements were drafted within 4 working groups focusing on specific topics within cartilage repair of the ankle, after which a comprehensive literature review was performed and the available evidence for each statement was graded. Discussion and debate occurred in cases where statements were not agreed on in unanimous fashion within the working groups. A final vote was then held.

RESULTS

A total of 11 statements on OLTP reached consensus. Four achieved unanimous support and 7 reached strong consensus (greater than 75% agreement). A total of 8 statements on ankle instability with ankle cartilage lesions reached consensus during the 2019 International Consensus Meeting on Cartilage Repair of the Ankle. One achieved unanimous support, and seven reached strong consensus (greater than 75% agreement).

CONCLUSION

These consensus statements may assist clinicians in the management of these difficult clinical pathologies.

LEVEL OF EVIDENCE

Level V, mechanism-based reasoning.

Total Talar Replacements Short-Medium Term Case Series, South Africa 2019

There are few surgical options available to manage complex talar pathology that result in predictably acceptable functional and patient satisfaction scores. Recently, total talar replacement has gained popularity as a viable option. This study presents the clinical outcomes of a case series of total talar replacements in South Africa. A review of data for 8 (N = 8) consecutive patients who underwent total talus replacement between July 2014 and August 2018 was performed. The American Orthopedic Foot and Ankle Society hindfoot score was used to assess clinical function and the Short Form-36 was used to assess patient satisfaction. Patient demographics as well as data on pathology, range of motion, gait analysis, and radiological outcomes were included. The mean age was 46 (range, 23-71) years. Pathologies included trauma, avascular necrosis, and tumors. The mean duration of follow-up was 23 (range, 12-49) months. The mean American Orthopedic Foot and Ankle Society score was 79.25 (range, 69-88) and the mean Short Form-36 satisfaction score was 83.25 (range, 60-93). No revision surgeries have been performed to date. Seven patients demonstrated a mildly abnormal gait and 1 revealed a moderately abnormal gait. The patient with the longest duration of follow-up showed radiological changes of tibial wear, although he remained symptom free. Our experience with the patients described in this report leads us to believe that total talar replacement is a viable surgical option in appropriately selected patients with end-stage talar pathology in the short to medium term, without compromising future salvage options.

Outcomes of primary fusion in high-energy Lisfranc injuries at a tertiary state hospital

ABSTRACT BACKGROUND: High-energy Lisfranc injuries are relatively uncommon but can lead to severe disability and morbidity. Primary fusion is a treatment option that can improve outcomes and reduce the reoperation rate. The aim of this study was to evaluate our series of primary fusions for high-energy Lisfranc injuries, looking specifically at type of fusion, time to union, non-union rates, reoperation rates and quality of reduction METHODS: Patients who underwent surgery for Lisfranc injuries were identified from the REDCap surgical database and then retrieved from records. Only cases of primary fusion in adults were included. We excluded low-energy sprains and athletic injuries, ipsilateral lower limb injuries and cases where reduction and fixation were done. Radiographs were analysed from the iSite Enterprise PACS system (Philips® RESULTS: Between 2013 and 2018, 12 cases of high-energy Lisfranc injuries were identified where primary fusion was done. Seven patients (58%) underwent fusion of the first, second and third tarsometatarsal (TMT) joints. The first and second TMT joints were fused in only one case (8%), and the second and third TMT joints were fused in four cases (33%). Only one patient (8%) had removal of implants. Compression plating was the technique of choice used for fusion. There was l0o% union rate and average time to union was 84 days. Acceptable reduction was observed in nine cases (75%). Three cases (25%) of malreduction were found, among which one patient had pre-existing hallux valgus CONCLUSION: The majority of patients who underwent primary fusion of at least one TMT joint had good radiological outcome. Further studies with better clinical follow-up are needed Level of evidence: Level 4 Keywords: Lisfranc, tarsometatarsal, outcome, fusion

Scaffold-Based Therapies: Proceedings of the International Consensus Meeting on Cartilage Repair of the Ankle

BACKGROUND

The evidence supporting best practice guidelines in the field of cartilage repair of the ankle are based on both low quality and low levels of evidence. Therefore, an international consensus group of experts was convened to collaboratively advance toward consensus opinions based on the best available evidence on key topics within cartilage repair of the ankle. The purpose of this article is to report the consensus statements on "Scaffold-Based Therapies" developed at the 2017 International Consensus Meeting on Cartilage Repair of the Ankle.

METHODS

Seventy-five international experts in cartilage repair of the ankle representing 25 countries and 1 territory were convened and participated in a process based on the Delphi method of achieving consensus. Questions and statements were drafted within 11 working groups focusing on specific topics within cartilage repair of the ankle, after which a comprehensive literature review was performed and the available evidence for each statement was graded. Discussion and debate occurred in cases where statements were not agreed upon in unanimous fashion within the working groups. A final vote was then held, and the strength of consensus was characterized as follows: consensus, 51% to 74%; strong consensus, 75% to 99%; unanimous, 100%.

RESULTS

A total of 9 statements on scaffold-based therapies reached consensus during the 2017 International Consensus Meeting on Cartilage Repair of the Ankle. One achieved unanimous support, 8 reached strong consensus (greater than 75% agreement), and 1 was removed because of redundancy in the information provided. All statements reached at least 80% agreement.

CONCLUSIONS

This international consensus derived from leaders in the field will assist clinicians with applying scaffold-based therapies as a treatment strategy for osteochondral lesions of the talus.

LEVEL OF EVIDENCE

Level V, expert opinion.

Post-treatment Follow-up, Imaging, and Outcome Scores: Proceedings of the International Consensus Meeting on Cartilage Repair of the Ankle

BACKGROUND

The evidence supporting best practice guidelines in the field of cartilage repair of the ankle are based on both low quality and low levels of evidence. Therefore, an international consensus group of experts was convened to collaboratively advance toward consensus opinions based on the best available evidence on key topics within cartilage repair of the ankle. The purpose of this article is to report the consensus statements on Post-treatment Follow-up, Imaging and Outcome Scores developed at the 2017 International Consensus Meeting on Cartilage Repair of the Ankle.

METHODS

Seventy-five international experts in cartilage repair of the ankle representing 25 countries and 1 territory were convened and participated in a process based on the Delphi method of achieving consensus. Questions and statements were drafted within 11 working groups focusing on specific topics within cartilage repair of the ankle, after which a comprehensive literature review was performed and the available evidence for each statement was graded. Discussion and debate occurred in cases where statements were not agreed on in unanimous fashion within the working groups. A final vote was then held, and the strength of consensus was characterized as follows: consensus, 51% to 74%; strong consensus, 75% to 99%; unanimous, 100%.

RESULTS

A total of 12 statements on Post-treatment Follow-up, Imaging, and Outcome Scores reached consensus during the 2017 International Consensus Meeting on Cartilage Repair of the Ankle. All 12 statements reached strong consensus (greater than 75% agreement).

CONCLUSIONS

This international consensus derived from leaders in the field will assist clinicians with post-treatment follow-up, imaging, and outcome scores after management of a cartilage injury of the ankle in the general population. Moreover, healing, rehabilitation, and final outcomes can be optimized for the individual patient.

Osteochondral Autograft: Proceedings of the International Consensus Meeting on Cartilage Repair of the Ankle

BACKGROUND

Treatment guidelines for cartilage lesions of the talus have been based on both low quality and low levels of evidence. Therefore, an international consensus group of experts was convened to collaboratively advance toward consensus opinions on key topics regarding cartilage lesions of the talus. The purpose of this consensus article is to explain the process and delineate the consensus statements derived from this consensus meeting on the use of "osteochondral autograft" for osteochondral lesions of the talus.

METHODS

Seventy-five international experts in cartilage repair of the ankle representing 25 countries and 1 territory were convened and participated in a process based on the Delphi method of achieving consensus. Questions and statements were drafted within 11 working groups focusing on specific topics within cartilage repair of the ankle, after which a comprehensive literature review was performed and the available evidence for each statement was graded. Discussion and debate occurred in cases where statements were not agreed upon in unanimous fashion within the working groups. A final vote was then held, and the strength of consensus was characterized as follows: consensus, 51% to 74%; strong consensus, 75% to 99%; and unanimous, 100%.

RESULTS

A total of 14 statements on osteochondral autograft reached consensus during the 2017 International Consensus Meeting on Cartilage Repair of the Ankle. Two achieved unanimous support, 11 reached strong consensus (greater than 75% agreement), and 1 achieved consensus. All statements reached at least 67% agreement.

CONCLUSIONS

This international consensus derived from leaders in the field will assist clinicians with osteochondral autograft as a treatment strategy for osteochondral lesions of the talus.

The L5 transverse process fracture revisited. Does its presence predict the pelvis fracture instability?

BACKGROUND

The presence of a L5 transverse process fracture is reported in many texts to be a marker of pelvis fracture instability. There is paucity of literature to support this view. Only two previous studies have been performed on this subject with statistical analysis.

METHODS

We conducted a retrospective cross-sectional review of all abdominopelvic CT scans performed for blunt abdominal trauma in a Level 1 Trauma Unit between January 2012 and August 2013. A total of 203 patients met our inclusion criteria. Fifty four (54) of these patients had an associated pelvis fracture.

RESULTS

Of the 54 patients with pelvis fractures 26 (48%) had an unstable fracture (AO Type B and C) and 28 (52%) had a stable pelvis fracture (AO Type A). Five (19%) of the 26 patients with an unstable pelvis fracture had an associated L5 transverse process fracture. This association was not statistically significant (P=0.724). Seven (12%) of the 28 patients with a stable fracture pattern had an associated L5 transverse process fracture. Three patients (2%) had an L5 transverse fracture in the absence of a demonstrable pelvis fracture. The relative risk of an unstable pelvis fracture in the presence of a L5 transverse process fracture is 1.2 (CI 0.6 2.3).

CONCLUSIONS

The presence of an L5 transverse process fracture on an abdominopelvic CT scan is strongly associated with an underlying pelvis fracture (P<0.001). Statistically, its presence however does not strongly predict instability (P=0.724). The latter finding differs from the previously published studies.

Failure of the Agility total ankle replacement system and the salvage options

The Agility total ankle replacement system was the most commonly performed implant in the United States for more than 20 years and has undergone four generations and seven phases of improvement. Much attention has been placed on intraoperative complications, such as malleolar fracture; nerve or tendon injury; and incision healing-related problems, such as wound coverage and infection. However, it is the intermediate- and long-term complications (ie, aseptic osteolysis, subsidence, component loosening, and progressive malalignment) that require careful consideration, because the revision options remain limited. This article reviews the history of the Agility total ankle replacement system in detail, to understand the revision possibilities available.

An examination of antibacterial and antifungal properties of constituents described in traditional Ulster cures and remedies

Traditional herbal cures and remedies have played an important historical role in the treatment of a variety of illnesses and diseases in Northern Ireland for the last three hundred years. Recently, these have been reviewed in the publication by Linda Ballard from the Ulster Folk and Transport Museum at Cultra, Co. Down, which details the variety of local plants used and for what purpose. From this publication and another related publication, we note the description of several plant species that consistently appear in traditional cures and remedies, particularly used to treat infections and infectious diseases. Unfortunately, although these plants have strong associations with the local historical evidence base, there are very limited and mainly no formal publications in the medical/scientific evidence base, examining their scientific background and clinical efficacy.

Form and exploration of mechanical stability limits in erect stance

The stability limits of erect stance are described as a geometrical structure in a movement space. Mechanical properties and response latency, a neural property, are determining factors for the stability limits. Standing stability limits of adults and young children are compared, and a simple scheme is suggested by means of which infants can discover the stability limits as they learn to stand. The mechanics of different standing movements are discussed because their spatial temporal properties relate directly to their different stability limits. The combination of the stability limits for different movements gives a total set of stability limits, a different structure for adults than for children.

Conditional transitions in gaze dynamics: role of vestibular nuclei in eye-only and eye/head gaze behaviors

The gaze control system governs distinct gaze behaviors, including visual fixation and gaze reorientations. Transitions between these gaze behaviors are frequent and smooth in healthy individuals. This study models these gaze-behavior transitions for different numbers of gaze degrees of freedom. Eye/head gaze behaviors have twice the number of degrees of freedom as eye-only gaze behaviors. Each gaze behavior is observable in the system dynamics and is correlated with neuronal behaviors in several, coordinated neural centers, including the vestibular nuclei. The coordination among the neural centers establishes a sensorimotor state which maintains each gaze behavior. This study develops a mathematical framework for synthesizing the coordination among neural centers in gaze sensorimotor states and focuses on the role of vestibular nuclei neurons in gaze sensorimotor state transitions.

Social barriers to a theoretical neuroscience

Social rather than scientific barriers are impeding neuroscience theory. There are plenty of experimental data and mathematical methods to develop a rigorous, mathematical theory in neuroscience. However, structural mathematical efforts are being suffocated by the requirement to produce numbers immediately. Also theoretical development is tied too closely to one experimental group. The social barriers can be addressed by: (1) judging theory by structural accuracy rather than numerical output; (2) recognizing mathematical theory (not just computational modeling) as a method for producing insight into neurobiological phenomena; (3) funding fundamental theoretical neuroscience and (4) recognizing theoretical neuroscientists as neuroscientists.

Sensory and motor interdependence in postural adjustments

The sensory reafference from a movement depends upon the movement, and the movement chosen depends upon the available senses, as demonstrated by vestibular patients who abandon certain movements. Often, one variable is assumed to be dependent whereas the other is independent; however, sensory and motor dynamics in posture are interdependent as conditions upon each other. This paper applies conditional dynamics to characterize the global structure of interdependence between sensory states and motor strategies in fast postural adjustments. The mathematical formalism incorporates rich but disparate experimental, clinical, and theoretical results about sensory and motor control of posture. The control structures presented include relatively stable anatomical, physiological, and functional structures, both continuous and discrete, leading to a composite functional logic for the coordination of these structures in sensorimotor control. Results include sensorimotor control structures for postural adjustments for healthy subjects and certain types of vestibular patients. The sensorimotor control structures for patients with absent vestibular function suggest implications for management of the deficit.

Identification of head motions by central vestibular neurons receiving linear and angular input

Most naturally occurring displacements of the head in space, due to either an external perturbation of the body or a self-generated, volitional head movement, apply both linear and angular forces to the head. The vestibular system detects linear and angular accelerations of the head separately, but the succeeding control of gaze and posture often relies upon the combined processing of linear and angular motion information. Thus, the output of a secondary neuron may reflect the linear, the angular, or both components of the head motion. Although the vestibular system is typically studied in terms of separate responses to linear and angular acceleration of the head, many secondary and higher-order neurons in the vestibular system do, in fact, receive information from both sets of motion sensors. The present paper develops methods to analyze responses of neurons that receive both types of information, and focuses on responses to sinusoidal motions composed of a linear and an angular component. We show that each neuron has a preferred motion, but a single neuron cannot code for a single motion. However, a pair of neurons can code for a motion by the relative phases of firing-rate modulation. In this way, information about motion is enhanced by neurons combining information about linear and angular motion.

Timing of secondary vestibular neuron responses to a range of rotational head movements

Secondary vestibular neurons exhibit a wide variety of responses to a head movement, with the response of each secondary neuron depending upon the particular primary afferents converging onto it. A single head movement is thereby registered in a distributed manner. This paper focuses on implications of afferent convergence to the relative timing of secondary neuron response modulation during rotational movements about a combination of horizontal axes. In particular, the neurons of interest are those that receive input from afferents innervating the vertical semicircular canals, and the movements of interest are those that have a sinusoidal component about one vertical canal axis and a sinusoidal component about another, approximately orthogonal, vertical canal axis. Under these conditions, the present research shows that it is possible for two or more secondary neurons to have a different relative timing of response (i.e., different relative phase of the periodic modulation in firing rate) for different head movements, and for the neurons to switch their order of response for different movements. For particular head movements, those same neurons will respond in phase. From the point of view of the nervous system, the relative timing of neuron responses may tell which movement is taking place, but with certain restrictions as discussed in the present paper. Shown here is that, among those head movements for which the two components of rotation may be at any phase relative to one another and have any relative amplitude, an in-phase response of just two neurons cannot identify a single motion. Two neurons that respond in phase for one motion must respond in phase for an entire range of motions; all motions in that range are thus response-equivalent, in the sense that the pair of neurons cannot distinguish between the two motions. On the other hand, an in-phase response of three neurons can identify a single motion, for certain patterns of primary afferent convergence.

Organizing sensory information for postural control in altered sensory environments

Healthy human subjects can maintain adequate balance despite distorted somatosensory or visual feedback or vestibular feedback distorted by a peripheral vestibular disorder. Although it is not precisely known how this sensorimotor integration task is achieved, the nervous system coordinates information from multiple sensory systems to produce motor commands differently in different sensory environments. These different ways of coordinating sensory information and motor commands can be thought of as "sensorimotor states". The way the nervous system distributes the monitoring of postural sway among states is analysed in this paper as a logical structure of transitions between states. The form of the transition structure is specified and distinguished from a finite state machine. The hypothesis that the nervous system could use a transition structure to maintain balance is tested by developing transition structures which are consistent with a set of experimental observations of postural control in healthy subjects and three groups of patients with peripheral vestibular disease.

The stomatogastric nervous system: a formal approach

A discrete mathematical formalism (d-space) which is specifically designed to investigate discrete aspects of behavior is applied to the foregut of decapod crustacea. This approach differs from continuous modeling techniques in that the analysis determines a structure in which the observed behavior of the foregut is constrained. A notation for the implementation of the formalism is developed as well as a coordinate system natural to the functioning of the gastric mill. The formalism is used to organize previous observations that suggest potential courses of further experimental investigation. A detailed analysis of observed chewing modes of the gastric mill is presented, along with a discussion of the overall organization of the interrelationships between these modes. The investigation also addresses the relationship between behavioral modes of a pyloric muscle found in the shrimp Palaemon. Two alternative hypotheses are presented to describe the relationship of the behavioral components of the gastric mill: an interlaced control scheme in which the components are freely exchanged, and a top-down control system where the chewing modes are rigidly separated into packages. Flow through regions of state space in time is found to be important in determining the relations between the discrete behavioral components. The behavior of the foregut, like that of other motor control systems, is shown to fit naturally into the d-space formalism.

Dynamics of the sit-to-stand movement

The strategies of the sit-to-stand movement are investigated by describing the movement in terms of the topology of an associated phase diagram. Kinematic constraints are applied to describe movement sequences, thus reducing the dimension of the phase space. This dimensional reduction allows us to apply theorems of topological dynamics for two-dimensional systems to arrive at a classification of six possible movement strategies, distinguished by the topology of their corresponding phase portrait. Since movement is treated in terms of topological structure rather than specific trajectories, individual variations are automatically included, and the approach is by nature model independent. Pathological movement is investigated, and this method clarifies how subtle abnormalities in movement lead to difficulties in achieving a stable stance upon rising from a seated position.

The shape of self-motion perception--II. framework and principles for simple and complex motion

There have been numerous experimental studies on human perception and misperception of self-motion and orientation relative to the earth, each focusing on one or a few types of motion. We present a formal framework encompassing many types of motion and including all angular and linear components of velocity and acceleration. Using a mathematically rigorous presentation, the framework defines the space of all possible motions, the map from motion to sensor status, the space containing each possible status of the sensors, and the map from sensor status to perceived motion. The shape of the full perceptual map from actual motion to perceived motion is investigated with the framework, using formal theory and a number of published experimental results. Two principles of simple motion perception and four principles of complex motion perception are presented. The framework also distinguishes the roles of physics and the nervous system in the process of self-motion perception for both simple and complex motions. The present rigorous development of the self-motion perception framework allows the scientist to compare and contrast results from many studies with differing types of motion. The six principles formalized here comprise a foundation with which to explain and predict perceptual phenomena, both those observed in the past and those to be encountered in the future. The framework is especially aimed to expand our capacity to investigate complex motions such as those encountered in everyday life or in unusual motion environments.

The shape of self-motion perception--I. Equivalence classification for sustained motions

Two completely different motions of a subject relative to the earth can induce exactly the same stimuli to the vestibular, somatosensory and visual systems. When this happens, the subject may experience disorientation and misperception of self-motion. We have identified large classes of motions that are perceptually equivalent, i.e. indistinguishable by the subject, under three sets of conditions: no vision, with vision and earth-fixed visual surround, and with vision during possible movement of the visual surround. For each of these sets of conditions, we have developed a classification of all sustained motions according to their perceptual equivalences. The result is a complete list of the possible misperceptions of sustained motion due to equivalence of the forces and other direct stimuli to the sensors under the given conditions. This research expands the range of possible experiments by including all components of linear and angular velocity and acceleration. Many of the predictions in this paper can be tested experimentally. In addition, the equivalence classes developed here predict perceptual phenomena in unusual motion environments that are difficult or impossible to investigate in the laboratory.

Forms of early walking

Children in the first weeks of independent locomotion display a wide variety of walking forms. The walking forms differ in mechanical strategy and concern with balance. Three extreme walking forms are presented: the Twister, who uses trunk twist, the Faller, who uses gravity, and the Stepper, who remains balanced as much as possible. Each walking form is presented as a "d-space", a mathematical format combining continuous and discrete aspects, developed to express the sequence and pattern of a movement without the inappropriate precision of a physical trajectory. The three d-spaces represent analyses of three extreme modes of early walking. They are used to generate the variety of early walking forms and to predict mixtures of mechanical strategies as children mature and converge to more similar walking forms over the first few months of independent locomotion.

Navigating a set of discrete regions in body position space

This paper defines a mathematical object that expresses physiological aspects of motor control, besides physical aspects. Based on observations in human development and rehabilitation, this paper lays a foundation for unifying discrete with continuous aspects of motor control. Discreteness in motor control arises from the fact that movements are planned by the organism, based on movement limits set by the organism, the task, and the environment, rather than following simply from physical laws. This paper defines two relations, an ordering and a contiguity relation, between discrete regions of joint space crossed with physical space, to make a d-space. Within the d-space, a particular body and physical position is represented by a completely ordered set, a coincidence. A trajectory through a continuous space is represented by a coincidence sequence. Examples are drawn mostly from human locomotion, with particular interest in balance. Only in certain regions of body and physical position space can a body maintain balance, for example, a standing human. Slow steps proceed from one balanced region to another. A poset (partially ordered set) of sets of steps and its relationship to a person's balance regions can be used in the study of development or rehabilitation.

Detail, proportion, and foci among face receptive fields of climbing fiber responses in the cat cerebellum

This paper reports a theoretical analysis of the transformation from a tactile stimulus of the face to climbing fiber responses in three regions of the cat cerebellum. The database consisted of climbing fiber receptive fields on the face from 75 responses from the anterior lobe, 33 responses from the paramedian lobule (PML), and 52 responses from the crus IIp of the anesthetized cat. The receptive fields were similar in being composed of discrete areas on the skin, or skin compartments. The regional differences in the configurations of the receptive fields were reflected in which compartments most often combined to form receptive fields. Each region had a distinct pattern of the preponderance of skin compartments that combined to form receptive fields, and yet the preponderant compartments were all chosen from one composite set of compartments that applied to all three regions. The climbing fiber representation of the face differed over the three regions (1) in the parts of the face that were represented; (2) in the frequency with which certain areas were included in the receptive fields; and (3) in the details of the face that could be distinguished by differing ensembles of climbing fiber responses. The majority of the climbing fiber receptive fields from either the anterior lobe or the crus IIp were unique to the region, whereas the majority of the receptive fields of responses from the PML were encountered in one or both of the other regions. Overlapping all face receptive fields from each of the three regions revealed that the receptive fields were differentially focused on or around the cornea, nose, or chin. In the anterior lobe, the face receptive fields mainly included the chin (43%) and the glabrous tip of the nose (40%), but few included the cornea (1%). In the PML, the receptive fields included the cornea (24%) and the chin (58%), but none included the nose. In the crus IIp, the cornea was included in the greatest number (37%) of receptive fields, whereas the nose and the chin were included equally (24%). The different sets of climbing fiber receptive fields in each of the three regions afforded the regions differing abilities to distinguish among complex patterns of stimuli, depending on the portion of the face stimulated.

Reciprocal inhibition, synergies, and movements

This paper presents a conceptual scheme relating discrete motor entities, such as muscles, joints, synergies and reflexes, to a continuous space of movements. Synergies are first derived as combinations of muscles, with reference to Ia reciprocal inhibition. Derived synergies may be modified into bases (in the linear space sense) for movements. The empirical example discussed is human postural synergies. The methods presented provide a relatively simple means for describing the control of bending and twisting movements about a joint by multiple muscles, joined by modifiable spinal interconnections.

Rules of combination that generate climbing fiber tactile receptive fields

Climbing fiber tactile receptive fields in the anterior lobe of the cat's cerebellum are found to have regularities of shape, independent of their relative position on the cerebellar cortex. The shape regularities can be expressed as rules of combination that generate the receptive field shapes. Both face and paw receptive fields are unions of a certain set of skin areas called compartments. Face receptive fields are generated by taking the union of a seed compartment and another compartment in a binary relation to it, called CF-contiguity. Paw receptive fields are formed in a similar iterative fashion, with the constraint that anatomically equivalent areas be included on all toes involved in the receptive field. This paper specifies rules of combination that both reproduce observed receptive fields and also predict receptive fields that have not yet been observed. Because of the regularities of shape among the climbing fiber tactile receptive fields, the rules of combination can be used to predict ensemble activation in response to tactile stimulation.

Stimulus classification by ensembles of climbing fiber receptive fields

Although the local structure of the cerebellum is fairly uniform and its inputs are often widely shared, outputs from different regions of the cerebellar cortex reach different parts of the cerebellar and vestibular nuclei, which can affect the rest of the nervous system in different ways. In this review, we explain how different ensembles of climbing fiber responses in the anterior lobe and paramedian lobule can be generated by a tactile stimulus to the distal hindpaw. Apart from differing in degree of activation, the cortical regions differ also in the detailed pattern of the activation transmitted. The anterior lobe can distinguish a greater diversity of stimuli to various skin surfaces than can the paramedian median lobule. This differential classification of particular stimulus arrays by the two cerebellar regions could produce distinct patterns of neuronal activity in various corticonuclear compartments.

Patterns of intersection among climbing fiber receptive fields

Peripheral receptive fields of climbing fiber responses from the anterior lobe of the cat display large intersections and distinct organizations. Receptive fields of the extremities and face have boundaries that follow the lines of a grid. Receptive fields of the tail and ventral trunk and some of the receptive fields on the extremities form concentric sets, which can be completely ordered by inclusion. Receptive fields along the spine form a chain, which indicates rostrocaudal position. Such regularities among the intersections, especially in the grid organization, allow the receptive fields to encode combinations and alternative combinations of skin locations as a pianist might distinguish chords rather than notes.

Invariant structure in locomotion

Biological systems are hypothesized to control behavior with reference to invariants, because this would allow the variable but robust accomplishment of tasks observed in biological behaviors. Invariants for legged locomotion are specified. Combined with observed properties of locomotion, they lead to predictions of forms of control for legged locomotion.

The relation between linear extent and velocity in drawing movements

The speed of execution of complex movements depends on both the local, differential properties of the trajectory and on some of its more global metric parameters. The effects of these global factors were studied in free, writing-like movements with either piece-wise constant, or regularly changing curvature. It is demonstrated that the tangential velocity of the pen's tip is tightly correlated, through a power function, with the total linear extent of the trajectory (perimeter). Thus, a strong tendency exists to keep the execution time of these complex trajectories independent of the movement size (isochrony). Furthermore, it is shown that the average tangential velocity over identifiable segments of the trajectory also depends on the corresponding average curvature. The implications of these results vis-à-vis the central representation and planning of movements are discussed.