Relationship of Anterior Cruciate Ligament Volume and T2* Relaxation Time to Anterior Knee Laxity.

Background: High anterior knee laxity (AKL) has been prospectively identified as a risk factor for anterior cruciate ligament (ACL) injuries. Given that ACL morphometry and structural composition have the potential to influence ligamentous strength, understanding how these factors are associated with greater AKL is warranted.

Hypothesis: Smaller ACL volumes combined with longer T2* relaxation times would collectively predict greater AKL.

ACL Size and Notch Width Between ACLR and Healthy Individuals: A Pilot Study.

Background: Given the relatively high risk of contralateral anterior cruciate ligament (ACL) injury in patients with ACL reconstruction (ACLR), there is a need to understand intrinsic risk factors that may contribute to contralateral injury.

Hypothesis: The ACLR group would have smaller ACL volume and a narrower femoral notch width than healthy individuals after accounting for relevant anthropometrics.

Study Design: Cross-sectional study.

Sex Comparisons of In Vivo Anterior Cruciate Ligament Morphometry.

Context: Females have consistently higher anterior cruciate ligament (ACL) injury rates than males. The reasons for this disparity are not fully understood. Whereas ACL morphometric characteristics are associated with injury risk and females have a smaller absolute ACL size, comprehensive sex comparisons that adequately account for sex differences in body mass index (BMI) have been limited.

A subsequent movement alters lower extremity muscle activity and kinetics in drop jumps vs. drop landings.

Drop landings and drop jumps are common training exercises and injury research model tasks. Drop landings have a single landing, whereas drop jumps include a subsequent jump after initial landing. With the expected ground impact, instant and landing surface suggested to modulate landing neuromechanics, muscle activity, and kinetics should be the same in both tasks when landing from the same height onto the same surface.

A preliminary multifactorial approach describing the relationships among lower extremity alignment, hip muscle activation, and lower extremity joint excursion.

Context: Multiple factors have been suggested to increase the risk of faulty dynamic alignments that predict noncontact anterior cruciate ligament injury. Few researchers have examined this relationship using an integrated, multifactorial approach.

Objective: To describe the relationship among static lower extremity alignment (LEA), hip muscle activation, and hip and knee motion during a single-leg squat.

Lower body stiffness and muscle activity differences between female dancers and basketball players during drop jumps.

Background: Anterior cruciate ligament (ACL) injuries often occur during landing, with female athletes at higher injury risk than male athletes. Interestingly, female dancers have lower ACL injury rates than do female athletes in general.

Hypothesis: Female dancers will have earlier and greater lower extremity muscle activity and higher sagittal knee joint and leg stiffness than will female basketball players.

A comparison of cyclic variations in anterior knee laxity, genu recurvatum, and general joint laxity across the menstrual cycle.

Changes in anterior knee laxity (AKL), genu recurvatum (GR) and general joint laxity (GJL) were quantified across days of the early follicular and early luteal phases of the menstrual cycle in 66 females, and the similarity in their pattern of cyclic variations examined. Laxity was measured on each of the first 6 days of menses (M1-M6) and the first 8 days following ovulation (L1-L8) over two cycles. The largest mean differences were observed between L5 and L8 for AKL (0.

Knee joint laxity and its cyclic variation influence tibiofemoral motion during weight acceptance.

Purpose: to better understand how sex differences in anterior knee laxity (AKL) affect knee joint biomechanics, we examined the consequence of greater absolute baseline (males and females) and cyclic increases in AKL during the menstrual cycle (females) on anterior tibial translation (ATT) as the knee transitioned from non-weight-bearing to weight-bearing conditions, while also controlling for genu recurvatum (GR).

Methods: males and females (71 females and 48 males, aged 18-30 yr) were measured for AKL and GR and underwent measurement of ATT. Women were tested on the days of their cycle when AKL was at its minimum (T1) and maximum (T2); males were matched in time to a female with similar AKL.

Varus/valgus and internal/external torsional knee joint stiffness differs between sexes.

Background: Torsional joint stiffness is thought to play a role in the observed sex bias in noncontact anterior cruciate ligament injury rates.

Hypothesis: Women will exhibit lower torsional stiffness values of the knee in response to varus/valgus and internal/external rotations than will men.

Study Design: Controlled laboratory study.

Triple-hop distance as a valid predictor of lower limb strength and power.

Context: Hop tests are functional tests that reportedly require strength, power, and postural stability to perform. The extent to which a triple-hop distance (THD) test measures each of these characteristics is relatively unknown.

Objective: To determine the extent to which the THD predicts performance on clinical measures of power, strength, and balance in athletic individuals.

Phonophoresis and the absorption of dexamethasone in the presence of an occlusive dressing.

Context: Phonophoresis is purported to represent a method to apply topical medications through the skin to treat soft tissue injuries and inflammatory conditions. Few data are available to demonstrate the clinical effectiveness of the treatment.

Objective: To determine the effect of ultrasound on the transcutaneous absorption of dexamethasone when occluded with a dressing.

Sex differences in lower extremity biomechanics during single leg landings.

Background: Females have an increased incident rate of anterior cruciate ligament tears compared to males. Biomechanical strategies to decelerate the body in the vertical direction have been implicated as a contributing cause. This study determined if females would exhibit single leg landing strategies characterized by decreased amounts of hip, knee, and ankle flexion resulting in greater vertical ground reaction forces and altered energy absorption patterns when compared to males.

Measurement of varus-valgus and internal-external rotational knee laxities in vivo--Part II: relationship with anterior-posterior and general joint laxity in males and females.

We examined sex differences in general joint laxity (GJL), and anterior-posterior displacement (ANT-POST), varus-valgus rotation (VR-VL), and internal-external rotation (INT-EXT) knee laxities, and determined whether greater ANT and GJL predicted greater VR-VL and INT-EXT. Twenty subjects were measured for GJL, and scored on a scale of 0-9. ANT and POST were measured using a standard knee arthrometer at 133 N.

Measurement of varus-valgus and internal-external rotational knee laxities in vivo--Part I: assessment of measurement reliability and bilateral asymmetry.

We examined the capabilities of the Vermont Knee Laxity Device (VKLD) in measuring varus (VR)-valgus (VL) and internal (INT)-external (EXT) rotational laxities by quantifying measurement consistency and absolute measurement error (N = 10). Based on the expected measurement error, we then examined side-to-side differences (N = 20). For all measures, the knee was flexed 20 degrees , the thigh securely fixed, and counterweights applied to the thigh and shank to create an initial zero shear and compressive load across the tibiofemoral joint.

Sex-specific abdominal activation strategies during landing.

Context: Control of the trunk segment in landing has been implicated as a contributing factor to the higher incidence of anterior cruciate ligament injuries in females than in males. Investigating the sex-specific abdominal activation strategies during landing lends insight into mechanisms contributing to control of the trunk segment.

Objective: To examine the abdominal activation strategies used by males and females during a landing task.

Energy absorption as a predictor of leg impedance in highly trained females.

Although leg spring stiffness represents active muscular recruitment of the lower extremity during dynamic tasks such as hopping and running, the joint-specific characteristics comprising the damping portion of this measure, leg impedance, are uncertain. The purpose of this investigation was to assess the relationship between leg impedance and energy absorption at the ankle, knee, and hip during early (impact) and late (stabilization) phases of landing. Twenty highly trained female dancers (age = 20.

Fatigue, vertical leg stiffness, and stiffness control strategies in males and females.

Context: Fatigue appears to influence musculoskeletal injury rates during athletic activities, but whether males and females respond differently to fatigue is unknown.

Objective: To determine the influence of fatigue on vertical leg stiffness (K (VERT)) and muscle activation and joint movement strategies and whether healthy males and females respond similarly to fatigue.

Design: Repeated-measures design with all data collected during a single laboratory session.

The independent and interactive effects of navicular drop and quadriceps angle on neuromuscular responses to a weight-bearing perturbation.

Context: Little is known about the effects of static alignment on neuromuscular control of the knee during dynamic motion.

Objective: To evaluate the isolated and combined effects of quadriceps angle (QA) and navicular drop (ND) on neuromuscular responses to a weight-bearing perturbation.

Design: Mixed-model, repeated-measures design.

Mechanisms and management of stress fractures in physically active persons.

Objective: To describe the anatomy of bone and the physiology of bone remodeling as a basis for the proper management of stress fractures in physically active people.

Data Sources: We searched PubMed for the years 1965 through 2000 using the key words stress fracture, bone remodeling, epidemiology, and rehabilitation.

Data Synthesis: Bone undergoes a normal remodeling process in physically active persons.

Nonweight-bearing anterior knee laxity is related to anterior tibial translation during transition from nonweight bearing to weight bearing.

We examined the relationship between anterior knee laxity (AKL), evaluated while the knee was nonweight bearing, and anterior translation of the tibia relative to the femur (ATT), evaluated when the knee transitioned from nonweight-bearing to weight-bearing conditions in response to an applied compressive load at the foot. Twenty subjects with normal knees (10 M, 10 F; 25.2 +/- 4.

Absolute serum hormone levels predict the magnitude of change in anterior knee laxity across the menstrual cycle.

This study aimed to determine whether absolute sex hormone concentrations predict the magnitude of knee joint laxity changes across the menstrual cycle. Twenty-two females (18-30 years, body mass index View Article and Find Full Text PDF

Females recruit quadriceps faster than males at multiple knee flexion angles following a weight-bearing rotary perturbation.

Objective: To compare the effect of knee angle on muscle response times and neuromuscular recruitment patterns between sexes following a perturbation in single leg stance at 10 degrees, 20 degrees, and 30 degrees. We hypothesized that response times would be faster at lesser knee flexion angles and that females would recruit their quadriceps faster than males at all angles.

Design: A repeated-measures design.

Low levels of anterior tibial loading enhance knee extensor reflex response characteristics.

We examined whether neuromuscular reflexes were altered with anterior loads applied to the tibio-femoral joint. A ligament testing device was modified by attaching a reflex hammer to a steel mounted frame to illicit a patellar tendon tap, while anterior directed loads displaced the tibia on the femur. Five trials were acquired while anterior-directed loads (20, 50, 100 N; counterbalanced) were applied to the posterior tibia between 20 N pre (20 N(Pre)) and post (20 N(Post)) baseline conditions on two different days.

Knee ligament behavior following a controlled loading protocol does not differ by menstrual cycle day.

Background: Females experience a disproportionate number of anterior cruciate ligament injuries compared to males. Increased estradiol concentration has been suggested to alter ligament properties and strength. Determining whether the knee responds differently to an external load at various hormonal levels may be helpful in further explaining the gender disparity.