Joel M. Press

The Role of Core Stability in Athletic Function

The importance of function of the central core of the body for stabilisation and force generation in all sports activities is being increasingly recognised. ‘Core stability’ is seen as being pivotal for efficient biomechanical function to maximise force generation and minimise joint loads in all types of activities ranging from running to throwing. However, there is less clarity about what exactly constitutes ‘the core’, either anatomically or physiologically, and physical evaluation of core function is also variable.‘Core stability’ is defined as the ability to control the position and motion of the trunk over the pelvis to allow optimum production, transfer and control of force and motion to the terminal segment in integrated athletic activities. Core muscle activity is best understood as the pre-programmed integration of local, single-joint muscles and multi-joint muscles to provide stability and produce motion. This results in proximal stability for distal mobility, a proximal to distal patterning of generation of force, and the creation of interactive moments that move and protect distal joints. Evaluation of the core should be dynamic, and include evaluation of the specific functions (trunk control over the planted leg) and directions of motions (three-planar activity). Rehabilitation should include the restoring of the core itself, but also include the core as the base for extremity function.

Incidence of Intravascular Uptake in Lumbar Spinal Injection Procedures

STUDY DESIGNnMulticenter, prospective, observational study.nnnOBJECTIVESnTo document the incidence of and factors associated with intravascular uptake during lumbar spinal injection procedures.nnnSUMMARY OF BACKGROUND DATAnIn prior reports, the incidence of inadvertent intravascular needle placement during contrast-enhanced, fluoroscopically guided lumbar spinal injection procedures has been incidentally noted to range from 6.4% to 9.2%. We present the first systematic prospective documentation of intravascular uptake of contrast dye during different types of lumbar injection procedures.nnnMETHODSnFifteen interventional spine physicians in seven centers recorded data regarding intravascular uptake during 1219 contrast-enhanced, fluoroscopically guided lumbar spinal injection procedures.nnnRESULTSnThe overall incidence of intravascular uptake during lumbar spinal injection procedures as determined by contrast enhanced fluoroscopic observation is 8.5%. Caudal and transforaminal routes have the highest rates at 10.9% and 10.8%, respectively, followed by zygapophyseal joint (6.1%), sacroiliac joint (5.3%), and translaminar (1.9%) injections. Intravascular uptake is twice as likely to occur in those patients over rather than under 50 years of age. Preinjection aspiration failed to produce a flashback of blood in 74% of cases that proved to be intravascular upon injection of contrast dye.nnnCONCLUSIONnThe incidence of intravascular uptake during lumbar spinal injection procedures is approximately 8.5%. The route of injection and the age of the patient greatly affect this rate. Absence of flashback of blood upon preinjection aspiration does not predict extravascular needle placement. Contrast-enhanced, fluoroscopic guidance is recommended when doing lumbar spinal injection procedures to prevent inadvertent intravascular uptake of injectate.

In vivo noninvasive evaluation of abnormal patellar tracking during squatting in patients with patellofemoral pain

BACKGROUNDnPatellofemoral pain syndrome is one of the most common knee problems and may be related to abnormal patellar tracking. Our purpose was to compare, in vivo and noninvasively, the patellar tracking patterns in symptomatic patients with patellofemoral pain and those in healthy subjects during squatting. We tested the hypothesis that patients with patellofemoral pain exhibit characteristic patterns of patellar tracking that are different from those of healthy subjects.nnnMETHODSnThree-dimensional patellar kinematics were recorded in vivo with use of a custom-molded patellar clamp and an optoelectronic motion capture system in ten healthy subjects and nine subjects with patellofemoral pain. The position of osseous knee landmarks was digitized while subjects stood upright, and then patellofemoral kinematics were recorded during squatting. The tracking technique was validated with use of both in vitro and in vivo methodologies, and the average absolute error was <1.2 degrees and <1.1 mm.nnnRESULTSnAt 90 degrees of knee flexion, the patella showed lateral spin (the distal pole of the patella rotated laterally) in subjects with patellofemoral pain (mean and standard deviation, -10.13 degrees +/- 2.24 degrees) and medial spin in healthy subjects (mean, 4.71 degrees +/- 1.17 degrees) (p < 0.001). At 90 degrees of knee flexion, the patella demonstrated significantly more lateral translation in subjects with patellofemoral pain (mean, 5.05 +/- 3.73 mm) than in healthy subjects (mean, -4.93 +/- 3.93 mm) (p < 0.001).nnnCONCLUSIONSnKinematic differences between healthy subjects and subjects with patellofemoral pain were demonstrated through a large, dynamic range of knee flexion angles. Increased lateral patellar translation and lateral patellar spin in subjects with patellofemoral pain suggest that the patella is not adequately balanced during functional activities in this group. Prospective studies are needed to identify when patellofemoral pain-related changes begin to occur and to determine the risk for the development of patellofemoral pain in individuals with abnormal kinematics.

In vivo load sharing among the quadriceps components

Knee extension is always performed with coordinated contractions of multiple quadriceps muscle components: however, how the load is shared among them under normal and pathological conditions is unclear. We hypothesized that: the absolute moment generated by each quadriceps component increases with the total knee extension moment; the relative contribution and its dependence on the total knee extension moment are different for different quadriceps components; and the centrally located large vastus intermedius (VI) is favored by the central nervous system at low levels of activation. Electrical stimulation was used to activate each quadriceps component selectively in six human subjects. The relationship between the knee extension moment generated by an individual quadriceps component and the corresponding compound muscular action potential (M‐wave) over various contraction levels was established for each quadriceps component. This relationship was used to calibrate the corresponding EMG signal and determine load sharing among quadriceps components during submaximal isometric voluntary knee extension. The VI contributed the most (51.8–39.6%) and vastus medialis the least (9.5–12.2%) to knee extension moment (P < 0.05). As the knee extension moment increased, the relative contribution of the VI decreased (P = 0.017) while the relation contribution of the vastus lateralis and medialis increased (P ≤ 0.012). The absolute moment generated by each quadriceps component always increased with the total knee extension moment (P < 0.002). Our in vivo approach determined subject‐ and condition‐specific load sharing among individual muscles and showed that the central nervous system utilized the centrally located, uniarticular VI in submaximal isometric knee extension.

The Effect of Long-Distance Bicycling on Ulnar and Median Nerves An Electrophysiologic Evaluation of Cyclist Palsy

Background Distal ulnar neuropathies have been identified in cyclists because of prolonged grip pressures on handlebars. The so-called cyclist palsy has been postulated to be an entrapment neuropathy of the ulnar nerve in the Guyon canal of the wrist. Previous studies utilizing nerve conduction studies have typically been either case reports or small case series. Hypothesis Electrophysiologic changes will be present in the ulnar and median nerves after a long-distance multiday cycling event. Study Design Cohort study; Level of evidence, 2. Methods A total of 28 adult hands from 14 subjects underwent median and ulnar motor and sensory nerve conductions, which were performed on both hands before and after a 6-day, 420-mile bike tour. A ride questionnaire was also administered after the ride, evaluating the experience level of the cyclist, equipment issues, hand position, and symptoms during the ride. Results Distal motor latencies of the deep branch of the ulnar nerve to the first dorsal interosseous were significantly prolonged after the long-distance cycling event. The median motor and sensory studies as well as the ulnar sensory and motor studies of the abductor digiti minimi did not change significantly. Electrophysiologic and symptomatic worsening of carpal tunnel syndrome was observed in 3 hands, with the onset of carpal tunnel syndrome in 1 hand after the ride. Conclusion Long-distance cycling may promote physiologic changes in the deep branch of the ulnar nerve and exacerbate symptoms of carpal tunnel syndrome.

The national jockey injury study: an analysis of injuries to professional horse-racing jockeys.

While there have been numerous reports in the literature of accidents in equestrian sports, no comprehensive study has been conducted to ascertain the nature and incidence of injuries incurred by professional horse-racing jockeys. A survey was conducted to determine the types of injuries to jockeys and racing-related health concerns, including weight reduction methods. The questionnaire was completed by 706 professional jockeys actively competing at United States racetracks between July and October 1990 about injuries they had sustained in their careers. More than 1,700 injuries were reported. Fractures (n = 1,113) accounted for 64% of the total. The most common cause of injury was becoming unseated, followed by the horse falling. Relationships between characteristics of jockeys and injuries were evaluated. There were significant numbers of serious injuries with prolonged periods of not riding. Recommendations for improving jockey safety are made.

Biomechanical effects of sitting with adjustable ischial and lumbar support on occupational low back pain: evaluation of sitting load and back muscle activity.

BackgroundCompared to standing posture, sitting decreases lumbar lordosis, increases low back muscle activity, disc pressure, and pressure on the ischium, which are associated with occupational LBP. A sitting device that reduces spinal load and low back muscle activities may help increase sitting comfort and reduce LBP risk. The objective of this study is to investigate the biomechanical effect of sitting with a reduced ischial support and an enhanced lumbar support (Off-Loading) on load, interface pressure and muscle activities.MethodsA laboratory test in low back pain (LBP) and asymptomatic subjects was designed to test the biomechanical effect of using the Off-Loading sitting posture. The load and interface pressure on seat and the backrest, and back muscle activities associated with usual and this Off-Loading posture were recorded and compared between the two postures.ResultsCompared with Normal (sitting upright with full support of the seat and flat backrest) posture, sitting in Off-Loading posture significantly shifted the center of the force and the peak pressure on the seat anteriorly towards the thighs. It also significantly decreased the contact area on the seat and increased that on the backrest. It decreased the lumbar muscle activities significantly. These effects are similar in individuals with and without LBP.ConclusionSitting with reduced ischial support and enhanced lumbar support resulted in reduced sitting load on the lumbar spine and reduced the lumbar muscular activity, which may potentially reduce sitting-related LBP.

The influence of the spine on the shoulder in the throwing athlete

Analysis of shoulder dysfunction in throwing and overhead athletes can no longer be restricted to evaluation of the glenohumeral joint alone. The isolated shoulder is incapable of generating the force necessary to hurl a baseball at velocities of 90-100 miles per hour or serve a tennis ball in excess of 120 miles per hour. The purpose of this paper is to provide a literature based theoretical framework for the role of the spine during these activities. The spine is a pivotal component of the kinematic chain which functions as a transfer link between the lower and upper limbs, a force generator capable of accelerating the arm, and a force attenuator which dampens shear forces at the glenohumeral joint during the deceleration phase of the pitching motion. Side bending and rotation of the cervical spine facilitates visual acquisition of the intended target. Inflexibility of the hip musculature and weakness of the muscles which attach to the thoracolumbar fascia have profound effects upon spine function which secondarily places greater stress upon the glenohumeral joint and rotator cuff. Shoulder rehabilitation and injury prevention programs should include evaluation of and exercise regimens for the lumbar, thoracic and cervical spine.

In vivo patellar tracking induced by individual quadriceps components in individuals with patellofemoral pain

Patellofemoral pain is a common knee disorder with a multi-factorial etiology related to abnormal patellar tracking. Our hypothesis was that the pattern of three-dimensional rotation and translation of the patella induced by selective activation of individual quadriceps components would differ between subjects with patellofemoral pain and healthy subjects. Nine female subjects with patellofemoral pain and seven healthy female subjects underwent electrical stimulation to selectively activate individual quadriceps components (vastus medialis obliquus, VMO; vastus medialis lateralis, VML; vastus lateralis, VL) with the knee at 0 degrees and 20 degrees flexion, while three-dimensional patellar tracking was recorded. Normalized direction of rotation and direction of translation characterized the relative amplitudes of each component of patellar movement. VMO activation in patellofemoral pain caused greater medial patellar rotation (distal patellar pole rotates medially in frontal plane) at both knee positions (p<0.01), and both VMO and VML activation caused increased anterior patellar translation (p<0.001) in patellofemoral pain compared to healthy subjects at 20 degrees knee flexion. VL activation caused more lateral patellar translation (p<0.001) in patellofemoral pain compared to healthy subjects. In healthy subjects the 3-D mechanical action of the VMO is actively modulated with knee flexion angle while such modulation was not observed in PFP subjects. This could be due to anatomical differences in the VMO insertion on the patella and medial quadriceps weakness. Quantitative evaluation of the influence of individual quadriceps components on patellar tracking will aid understanding of the knee extensor mechanism and provide insight into the etiology of patellofemoral pain.

The practical management of Achilles tendinopathy.

The Achilles tendon, named after the legendary warrior and hero of Homer’s Iliad, is the strongest and thickest tendon in the human body. Despite this fact, Achilles tendinopathy is a common overuse injury, particularly in runners and other athletes. Kujala et al showed a 10-fold increase in Achilles injuries in runners compared with age-matched controls. Another study reported the incidence of Achilles tendinopathy in top-level runners as 7% to 9%. The specific factors linking this injury with running include excessive mileage, sudden increase in training intensity, decrease in recovery time, change of running surface, and poor footwear. This injury also is common in athletes who compete in racquet sports, track and field, volleyball, and soccer. Other factors that have been associated with Achilles tendinopathy include various biomechanical deficits, older age, male gender, increased body weight and height, and fluoroquinolone exposure.