Biomedical subjects

Young-Kyu Kim

Publications and source records attributed to Young-Kyu Kim.

5 recordsLinked to original sources

PubMed2005

Biomechanics of the shoulder in youth baseball pitchers: implications for the development of proximal humeral epiphysiolysis and humeral retrotorsion.

BACKGROUND: The effects of repetitive throwing on the shoulders of developing athletes are not well understood because of the paucity of data describing the biomechanics of youth pitchers and the plasticity of the developing skeleton. HYPOTHESIS: The direction and magnitude of the stresses that exist at the proximal humeral physis during the fastball pitching motion are consistent with the development of proximal humeral epiphysiolysis (Little League shoulder) and/or humeral retro-torsion. STUDY DESIGN: Descriptive laboratory study. METHODS: A total of 14 elite youth baseball pitchers (mean age, 12.1 +/- 0.4 years) were filmed from the front and dominant side while throwing fastballs in a simulated game. The net force and torque acting on the humerus throughout the throwing motion were calculated using standard biomechanical techniques. RESULTS: The external rotation torque about the long axis of the humerus reached a peak value of 17.7 +/- 3.5 N.m (2.7% +/- 0.3% body weight x height) just before maximum shoulder external rotation. A shoulder distraction force of 214.7 +/- 47.2 N (49.8% +/- 8.3% body weight) occurred at, or just after, ball release. CONCLUSION: Shear stress arising from the high torque late in the arm-cocking phase is large enough to lead to deformation of the weak proximal humeral epiphyseal cartilage, causing either humeral retrotorsion or proximal humeral epiphysiolysis over time. The stresses generated by the external rotation torque are much greater than those caused by distraction forces generated during the pitching motion of youth baseball pitchers. CLINICAL RELEVANCE: The motion of throwing fastballs by youth baseball pitchers results in force components consistent with proposed mechanisms for 2 clinical entities.

Baseball↗

PubMed2004

Quantitative high-resolution on-line NMR spectroscopy in reaction and process monitoring.

On-line nuclear magnetic resonance spectroscopy (on-line NMR) is a powerful technique for reaction and process monitoring. Different set-ups for direct coupling of reaction and separation equipment with on-line NMR spectroscopy are described. NMR spectroscopy can be used to obtain both qualitative and quantitative information from complex reacting multicomponent mixtures for equilibrium or reaction kinetic studies. Commercial NMR probes can be used at pressures up to 35 MPa and temperatures up to 400 K. Applications are presented for studies of equilibria and kinetics of complex formaldehyde-containing mixtures as well as homogeneously and heterogeneously catalyzed esterification kinetics. Direct coupling of a thin-film evaporator is described as an example for the benefits of on-line NMR spectroscopy in process monitoring.

Journal Article↗

PubMed2004

A soft tissue attempt to stabilize the multiply operated glenohumeral joint with multidirectional instability.

Treating patients with multidirectional instability who have had multiple failed stabilization procedures is a challenging problem. These patients have disability from instability and pain. Final treatment may be glenohumeral narthrodesis. We report on the results of a soft tissue operation for treatment of multidirectional instability in multiply operated shoulders. Since 1994, 28 patients have had what we term the kitchen sink operation for treatment of refractory multidirectional instability. After exclusion of patients with collagen abnormality, 10 patients who had at least three previous stabilizations were identified with recalcitrant multidirectional instability. The kitchen sink operation encompasses a humeral-based inferior capsular shift, Nicola biceps tenodesis, and coracohumeral ligament and rotator interval augmentation and/or reconstruction. All patients were immobilized for 8 weeks postoperatively. Minimum clinical and radiographic followup was 2 years (range, 2-6 years). Preoperatively, all patients had incapacitating pain and instability. Postoperatively, five patients (50%) had significant improvement of pain, and nine patients (90%) had successful reduction of instability. Four of the five patients with persistent disabling pain needed glenohumeral fusions. The kitchen sink operation is a final attempt to stabilize the shoulder with multidirectional instability. This procedure reduces instability (especially inferior) associated with multidirectional instability. However, pain remains unremitting in 50% of patients, therefore a glenohumeral arthrodesis may be needed as a last option.

Adult↗

PubMed2004

Humeral torque in professional baseball pitchers.

BACKGROUND: Spontaneous fracture of the humeral shaft in throwers is a rare but well-known phenomenon. Although it has been hypothesized that the biomechanics of the throw cause such fractures, it is not clear how or when the fractures occur in the pitching motion. METHODS: The torque acting about the long axis of the humerus was calculated in 25 professional baseball pitchers throwing in game situations. RESULTS: Peak humeral axial torque reached a mean value of 92 +/- 16 Nm near the time of maximum shoulder external rotation at the end of the cocking phase. This torque tended to externally rotate the distal end of the humerus relative to its proximal end. The direction of the torque was consistent with the external rotation spiral fractures of the humerus noted to occur in throwers. The magnitude of the peak humeral torque averaged 48% of the theoretical torsional strength of the humerus, suggesting that repetitive stress plays a role in humeral shaft fractures. CONCLUSIONS: Fractures are most likely to occur near the time of maximum shoulder external rotation when humeral torque peaks. Pitchers whose elbows were more extended at stride foot contact tended to have lower peak humeral torques.

Adult↗

PubMed2003

Quantitative on-line high-resolution NMR spectroscopy in process engineering applications.

In many technical processes, complex multicomponent mixtures have to be handled, for example, in reaction or separation equipment. High-resolution NMR spectroscopy is an excellent tool to study these mixtures and gain insight in their behavior in the processes. For on-line studies under process conditions, flow NMR probes can be used in a wide range of temperature and pressure. A major challenge in engineering applications of NMR spectroscopy is the need for quantitative evaluation. Flow rates, recovery times, and other parameters of the on-line NMR experiments have to be optimized for this purpose. Since it is generally prohibitive to use deuterated solvents in engineering applications, suitable techniques for field homogenization and solvent signal suppression are needed. Two examples for the application of on-line NMR spectroscopic experiments in process engineering are presented, studies on chemical equilibria and reaction kinetics of the technically important system formaldehyde-water-methanol and investigations on reactive gas absorption of CO(2) in aqueous solutions of monoethanolamine.

Journal Article↗