Leaving hip rotation out of a conventional 3D gait model improves discrimination of pathological gait in cerebral palsy: A novel neural network analysis.

BACKGROUND: Complex clinical gait analysis results can be expressed as single number gait deviations by applying multivariate processing methods. The original Movement Deviation Profile (MDP) quantifies the deviation of abnormal gait using the most trusted nine dynamic joint angles of lower limbs. RESEARCH QUESTION: Which subset of joint angles maximises the ability of the MDP to separate abnormal gait from normality? What is the effect of using the best subset in a large group of patients, and in individuals? METHODS: A self-organising neural network was trained using normal gait data from 166 controls, and then the MDP of 1923 patients with cerebral palsy (3846 legs) was calculated. The same procedure was repeated with 511 combinations of the nine joint angles. The standardised distances of abnormal gait from normality were then calculated as log-transformed Z-scores to select the best combination. A mixed design ANOVA was used to assess how removing the least discriminating angle improved the separation of patients from controls. The effect of using the optimal subset of angles was also quantified for each individual leg by comparing the change in MDP to the independent FAQ levels of patients. RESULTS: Removal of hip rotation significantly (p<0.0005) increased the separation of the patient group from normality (ΔZ-score 0.24) and also at FAQ levels 7-10 (ΔZ-score 0.38, 0.27, 0.22, 0.14). The MDP of individual patients changed in a wider range of -4.65 to 1.12 Z-scores and their change matched their independent FAQ scores, with less functional patients moving further from, and more functional patients moving closer to normality. SIGNIFICANCE: In existing gait databases we recommend excluding hip rotation from data used to calculate the MDP. Alternatively, the calculation of hip rotation can be improved by post-hoc correction, but the ultimate solution is to use more accurate and reliable models of hip rotation.

The effect of distal femoral extension osteotomy on muscle lengths after surgery.

PURPOSE: The distal femoral extension osteotomy (DFEO) is often used in the treatment of crouch gait to help compensate for knee flexion contractures. The effects of DFEO on skeletal and muscle lengths are incompletely understood, but are important to consider in planning concomitant surgeries such as patellar tendon advancement (PTA). Therefore, the purpose of this study was to quantify the changes in femur, quadriceps, and hamstring lengths with DFEO, and to determine the sensitivity to surgical factors such as wedge location and magnitude. METHODS: A musculoskeletal model with six degrees of freedom tibiofemoral and patellofemoral joints was used for analysis. A wedge was removed from the distal femur and the remaining bone segments were plated together to simulate the DFEO. After simulating the knee's post-operative equilibrium, the surgically-induced changes in muscle and bone lengths were analysed. RESULTS: Relative to the pre-operative state, DFEO stretches the hamstrings while shortening the femur and quadriceps. A more posterior wedge apex location (i.e. creation of a cuneiform wedge) diminished the stretch of the hamstrings, but induced greater shortening of the femur and quadriceps. More proximal wedge locations necessitated greater translation of the distal fragment to maintain the knee joint axis. CONCLUSION: Reduced quadriceps length after DFEO shown in this study is consistent with the need for simultaneous PTA. The induced hamstring stretch also may represent a potential mechanism for post-operative nerve palsies. Overall, the numerical results provide a firmer basis for planning the specifics of DFEO such that desired muscle lengths and joint alignment are achieved.

Quantifying gait deviations in individuals with rheumatoid arthritis using the Gait Deviation Index.

OBJECTIVES: In this study we evaluated the usability of the Gait Deviation Index (GDI), an index that summarizes the amount of deviation in movement from a standard norm, in adults with rheumatoid arthritis (RA). The aims of the study were to evaluate the ability of the GDI to identify gait deviations, assess inter-trial repeatability, and examine the relationship between the GDI and walking speed, physical disability, and pain. METHOD: Sixty-three adults with RA and 59 adults with typical gait patterns were included in this retrospective case-control study. Following a three-dimensional gait analysis (3DGA), representative gait cycles were selected and GDI scores calculated. To evaluate the effect of walking speed, GDI scores were calculated using both a free-speed and a speed-matched reference set. Physical disability was assessed using the Health Assessment Questionnaire (HAQ) and subjects rated their pain during walking. RESULTS: Adults with RA had significantly increased gait deviations compared to healthy individuals, as shown by lower GDI scores [87.9 (SD = 8.7) vs. 99.4 (SD = 8.3), p < 0.001]. This difference was also seen when adjusting for walking speed [91.7 (SD = 9.0) vs. 99.9 (SD = 8.6), p < 0.001]. It was estimated that a change of ≥ 5 GDI units was required to account for natural variation in gait. There was no evident relationship between GDI and low/high RA-related physical disability and pain. CONCLUSIONS: The GDI seems to useful for identifying and summarizing gait deviations in individuals with RA. Thus, we consider that the GDI provides an overall measure of gait deviation that may reflect lower extremity pathology and may help clinicians to understand the impact of RA on gait dynamics.

An investigation of the action of the hamstring muscles during standing in crouch using functional electrical stimulation (FES).

The hamstring muscle moment arms indicate that they act as hip extensors and knee flexors. Previous work using induced acceleration (IA) analysis and functional electrical stimulation (FES) has, however, revealed counter-intuitive muscle actions, particularly for biarticular muscles during the stance phase of normal gait. In conditions such as cerebral palsy the hamstrings have been associated with the development of pathological gait patterns, particularly crouch gait. This study examines the role of these muscles in the control of crouched standing postures. Five unimpaired adult subjects had their muscles stimulated during quiet standing in different degrees of crouch. Kinematic and kinetic changes were observed and measured using a 3D motion analysis system. The hamstring muscles were shown to act strongly to retrovert the pelvis and extend the hip. The action at the knee changes as crouch increases, moving from flexing to extending.

A nondimensional normalization scheme for oxygen utilization data.

The total oxygen required for gait (gross utilization) is a widely used indicator of locomotor efficiency. The standard scheme of mass normalization (dividing gross utilization by mass) is intended to eliminate confounding effects that arise from variations in age and size. Despite its prevalence, mass normalization has been shown to be inadequate, as the normalized quantity retains a marked dependence on clinically relevant factors. The current study proposes a new scheme for normalizing oxygen utilization data. The new scheme, called net-nondimensional normalization, is based on the use of net oxygen utilization (gross-rest) and nondimensional gait variables. Measures of statistical significance are employed to demonstrate that net nondimensional normalization is superior to mass normalization. Net nondimensional oxygen utilization is shown to be largely independent of the relevant physiological and anatomical factors, and is therefore well suited for studies where an independent measure of gait efficiency is needed.

Deepithelialization of a complex ventral hernia for completely extraperitoneal Rives-Stoppa herniorrhaphy.

Peritoneal incisions made during abdominal surgery are associated with numerous postoperative complications. Laparoscopic procedures are extraperitoneal, but they do not always provide adequate exposure of the defect nor room for manipulation. We suggest a de-epithelialization approach prior to mesh placement for the repair of large ventral hernias as a means of achieving a completely extraperitoneal ventral herniorrhaphy.

A tool for quantifying hip flexor function during gait.

An index to measure the change in hip flexor function after hip surgery was developed in the Motion Analysis Laboratory at Gillette Children's Specialty Healthcare (GCSH). The hip flexor index (HFI) utilizes principal component analysis applied to five kinematic and kinetic variables collected during normal acquisition of gait data. A single index number is derived that describes accurately the overall hip function. Initial clinical validation was carried out using a data set of 23 normal controls and six patients with a diagnosis of cerebral palsy. The patients were all independent ambulators who had undergone orthopedic hip surgery. The controls were used to establish patterns of interdependency between selected gait parameters and form a basis for the index number. The HFI based surgical outcome was compared to the subjective rating of six clinicians. The clinicians were versed in gait analysis and were blinded to the HFI based outcome. The HFI measure of post-operative change in hip function was found to correspond well with the subjective clinical evaluation. A valid tool such as the HFI can be used to objectify clinical impressions of change in hip function, and can thereby assist researchers with statistical and outcome analysis of interdependent and redundant gait variables.

An index for quantifying deviations from normal gait.

A method is derived to calculate the amount by which a subject's gait deviates from an average normal profile, and to represent this deviation as a single number. The method uses principal component analysis to derive a set of 16 independent variables from 16 selected gait variables. The sum of the square of these 16 independent variables is interpreted as the deviation of the subject's gait from normal. Statistical tests of the method's validity and an initial demonstration of its clinical utility are included. It is found that using this index, increasing clinical involvement corresponds to increasing index score.

Distraction osteogenesis.

Distraction osteogenesis is a surgical technique originally used to lengthen the long bones without bone grafting. An osteotomy is created and by slowly separating the two segments with specially fabricated hardware, the biological distractant will grow with the bone and calcify into mature bone once the appropriate length has been achieved. Distraction techniques have been used in the human facial bone area for the past 10 years. This article reviews the basic uses of distraction osteogenesis, the pros and cons, and possible future techniques.

The oral and maxillofacial surgeon's role in the care of patients with cleft lip and palate deformities.

Perhaps no conditions other than cleft lip and palate and oral cancer assemble teams of dentists and physicians intensely focused on treatment and rehabilitation. The oral and maxillofacial surgeon's role is often pivotal especially in the 20-year term of care for the child born with a cleft lip and palate deformity (CLPD). Issues of basic orofacial functions of mastication, respiration and communication overlay human considerations of self-esteem and image. From the moment of birth the child with a CLPD is special and challenged. Early issues concern parent and family acceptance and insuring basic life functions. While not generally a part of the immediate surgical unit, the OMFS often provides surgical consultation, educational and emotional support for the family. A clear picture must be painted of the treatment that will unfold over the next two decades. Realistic optimism is the watchword. Indeed, today there is every reason to anticipate an outcome that will result in a balanced, functional and esthetic face.

Decreased length of stay for patients with colorectal cancer: implications of DRG use.

Hospital length of stay (LOS) has declined significantly at Mt. Sinai Hospital with the advent of diagnosis-related groups (DRGs). Patients with colorectal cancer who were operated on before and after the implementation of the DRG were compared to determine whether the shorter LOS reflected changes in the patient population or changes in the way patients were being treated. Both preoperative and postoperative LOS declined significantly for DRG patients. The decreased LOS for DRG patients could not be attributed to a decreased severity of disease because DRG patients presented with significantly more advanced tumors. The DRG patients had significantly less operative blood loss; shorter, less extensive procedures; fewer transfusion; shorter specimen lengths; shorter margins of resection; and fewer postoperative complications than the pre-DRG patients. Other measures of disease severity (i.e., admission hematocrit, tumor differentiation, and tumor size) and patient mix (i.e., age and sex) did not change. These results suggest that with the use of DRGs, surgeons may have modified certain aspects of treatment for colorectal cancer in an attempt to shorten LOS.

Chondrocytes in culture produce a mechanically functional tissue.

A mechanically testable tissue was grown in vitro from rabbit chondrocytes that were initially plated at high density (approximately 80,000 cells/cm2). The DNA, collagen, and proteoglycan content, as well as the tissue thickness, tensile stiffness, and synthesis rates, were measured at 4, 6, and 8 weeks. The biochemical properties were similar to those for immature cartilage, with predominantly type-II collagen produced; this indicated that the cells retained their chondrocytic phenotype. The tissue formed a coherent mechanical layer with testable tensile stiffness as early as 4 weeks. The tensile elastic modulus reached 1.3 MPa at 8 weeks, which is in the range of values for native cartilage from the midzone. Collagen density was approximately 24 mg/ml at 8 weeks, which is about one-half the value for native cartilage, and the collagen fibril diameters were smaller. Chondrocytes in culture responded to culture conditions and were stimulated by cytokine interleukin-1beta. When culture conditions were varied to RPMI nutrient medium with lower fetal bovine serum and higher ascorbic acid concentrations, the thickness decreased and the modulus increased significantly. Interleukin-1beta, added to the 8-week culture for 2 weeks, caused a decrease of 60% in thickness, a decrease of 81% in proteoglycan content, and a decrease of 31% in collagen content; this is similar to the response of cartilage explants to interleukin-1beta. This cartilage analog may be useful as a model system to study structure-function relationships in cartilage or as cartilage-replacement tissue.

Using neural networks to identify patients unlikely to achieve a reduction in bodily pain after total hip replacement surgery.

OBJECTIVES: Fourteen patient-provided variables were chosen as potential predictors for improvement after total hip replacement surgery. These variables included patient demographic information, as well as preoperative physical function. METHODS: A neural network was trained to predict the relative success of total hip replacement surgery using this presurgical patient survey information. The outcome measure was improvement in the Medical Outcomes Study 36 Short Form Health Survey pain score between the preoperative assessment and the 1-year postoperative assessment. For the study sample, 221 patients were selected who had complete information for the composite outcome variable. A backpropagation feedforward neural network was trained to predict the output variable using the jackknife method. RESULTS: Performance of the neural network was assessed by calculating the area under the receiver operating characteristic curve for the network's ability to predict whether the pain score was improved after total hip replacement surgery. The observed area under the receiver operating characteristic curve was 0.79. For comparison, a linear regression model built using the same data had a receiver operating characteristic area of 0.74 (P = 0.23). CONCLUSIONS: This research therefore showed the ability of neural networks to predict the success of total hip replacement more accurately. Our results further indicate that it may be possible to predict which patients are at greatest risk of a poor outcome.

A microstructural model for the elastic response of articular cartilage.

A model of articular cartilage is developed in which the continuum stiffness tensor is related to the tissue's microstructure. The model consists of bilinear elastic fibers embedded in an elastic matrix. Homogenization techniques are used to relate this level of organization to the macroscopic response of the tissue. The model includes the effects of spatial orientation of fibers, pre-stress in the fibers and matrix resulting from matrix swelling, slipping at the interface between the fibers and the matrix, fiber buckling in compression, and deformation-induced fiber reorientation. The model predicts increased axial stiffness with increasing stretch due to fiber reorientation, reduced axial and shear stiffness with slipping between fiber and matrix and a sensitivity of the tissue response to the swelling pressure in the matrix, the matrix modulus and the bonding of the fiber matrix interface.

Effect of ethanol on subthreshold currents of Aplysia pacemaker neurons.

The subthreshold currents in bursting pacemaker neurons of the Aplysia abdominal ganglion were individually studied with the voltage clamp technique for sensitivity to 4% ethanol. The most prevalent effect of ethanol on unclamped bursting neurons was a hyperpolarization. This was shown to be due to a decrease of a voltage independent inward leakage current. Direct measurement of the Na-dependent slow inward current showed that this current was eliminated by 4% ethanol. Direct measurement of the Ca-dependent slow inward current showed that this current was substantially reduced by 4% ethanol. Injection of EGTA into cell bodies did not eliminate the ethanol-induced block of the slow inward calcium current. Thus, ethanol cannot be reducing the Ca-dependent slow inward current solely by an increase of internal calcium concentration. The effect of ethanol on voltage dependent outward current was measured by blockage of all inward current. The peak outward current was increased by ethanol. The rate of inactivation of this outward current was also increased. Calcium activated potassium current (IK(Ca)) is particularly complicated in its response to ethanol because it is dependent on both Ca and voltage for its activation. The level of IK(Ca) elicited in response to constant Ca injection was increased by ethanol treatment. The level of this current as activated by voltage clamp pulses was either increased or decreased depending on the neuron type. Ca2+ activated potassium conductance increased e-fold for a 26 mV depolarization in membrane holding potential. Ethanol decreased this voltage dependence to e-fold for a 55 mV change in potential. This result was interpreted to mean that ethanol shifted an effective Ca2+ binding site of these channels from about halfway through the membrane field to one quarter of the way across. The same theoretical approach allowed the further conclusion that ethanol caused an increased internal free calcium concentration probably by decreasing calcium binding by intracellular buffers.

Voltage clamp analysis of ethanol effects on pacemaker currents of Aplysia neurons.

The effect of 4% ethanol on pacemaker currents of Aplysia neurons was studied under voltage clamp. In normal seawater the n-shape in the I-V disappeared and outward current increased. Ion substitution and drug blocking experiments determined that leakage current and the slow inward calcium current were decreased and that the outward currents, IA and IK, were increased. This knowledge can be used to explain ethanol effects on spontaneous firing patterns.

The metabolism of zomepirac sodium. I. Disposition in laboratory animals and man.

Zomepirac sodium (ZS) is an orally active, nonnarcotic, analgesic agent. The disposition and pharmacokinetics of zomepirac (Z) were studied in rats, mice, rabbits, hamsters, rhesus monkeys, and healthy human subjects. Z was rapidly and completely absorbed by all animal species and man. Dose-related linear increases in the area under the curve for plasma Z vs. time were noted after increasing po doses of ZS to mice (2.5--7.5 mg/kg), rats (0.5--10 mg/kg), and rhesus monkeys (5--40 mg/kg). Daily administration of ZS to rats (10 mg/kg/day for 10 days) caused no biologically significant changes in the pharmacokinetic profile for Z. Assessment of Z's absolute bioavailability in monkeys (10 mg/kg, iv vs. po) indicated that po doses of ZS were completely bioavailable (F = 1.12 +/- 0.40). Plasma clearance ranged from ca. 4.5 ml/min/kg for the female hamster, rhesus monkey, and man to as low as 0.30 ml/min/kg for rats, mice, and rabbits. Terminal elimination half-lives averaged 5.3--6.6 hr for mouse, 2.8--6.5 hr for rat, 2.5 hr for rabbit, 2.3 hr for hamster, 12.7--25.5 hr for rhesus monkey, and 4 hr for man. The major route of excretion for Z and its metabolites was via the kidneys for all animals and man with the balance appearing in feces. Biliary excretion was qualitatively observed in rhesus monkeys and quantitated in rats (23.6% of dose in 27 hr). Formation of the acyl glucuronide of Z was the major metabolic pathway in man and rhesus monkey, was substantial in the mouse, was very minor in the rat and rabbit, and was nonexistent in the hamster. Rat, mouse, and hamster hydroxylate the 4-methyl group on the pyrrole ring to give hydroxyzomepirac (a biologically inactive metabolite), a minor metabolite in man and nonexistent in the rhesus monkey. The rodents also cleave Z to form 4-chlorobenzoic acid and its conjugates, minor metabolites in man and rhesus monkey.