Tibial Shear Force Research Articles

Biomechanical Evaluation of Different Fixation Methods for Tibial Eminence Fractures

Background Tibial eminence fractures have become more common, but the best method of fixing these fractures arthroscopically has not been elucidated. Objective The objective of this study is to assess the stability of different fixation methods for tibial eminence fractures. Study Design Controlled laboratory study. Methods The authors evaluated the initial fixation strength of 4 different fixation techniques for tibial eminence fractures (2 screws, 1 screw, suture fixation with 1 mm Ethibond, and suture fixation with No. 5 FiberWire) using single cycle and cyclic loading tests. The tests were performed by loading the knee with an anterior tibial shear force. Results Suture cerclage with the FiberWire showed significantly higher maximum load (599.6 N) and stiffness (36.99 N/mm) than all other fixation methods tested. The lowest maximum load in the single cycle loading test was observed in the group with 2 screws (1 screw, 371.2 N; 2 screws, 249.8 N). The lowest stiffness was found in the Ethibond group (14.5 N/mm). After 1000 cycles of loading, the maximum load of the FiberWire fixation was significantly higher than the maximum load of the Ethibond fixation (399.4 N), the fixation with 1 screw (354.2 N), and the fixation with 2 screws (301.5 N). Conclusion These biomechanical data suggest that under cyclic loading conditions, suture fixation of tibial eminence fractures provides more fixation strength than screw fixation. Clinical Relevance A second screw has no positive effect on the biomechanical characteristics of screw fixation.

The influence of gender-specific loading patterns of the stop-jump task on anterior cruciate ligament strain

Studies have shown that women are at higher risk of sustaining noncontact anterior cruciate ligament (ACL) injuries in specific sports. Recent gait studies of athletic tasks have documented that gender differences in knee movement, muscle activation, and external loading patterns exist. The objective of this study was to determine in a knee cadaver model if application of female-specific loading and movement patterns characterised in vivo for a stop-jump task cause higher ACL strains than male patterns. Gender-specific loading patterns of the landing phase of the vertical stop-jump task were applied to seven cadaver knees using published kinetic/kinematic results for recreational athletes. Loads applied consecutively included: tibial compression, quadriceps, hamstrings, external posterior tibial shear, and tibial torque. Knee flexion was fixed based on the kinematic data. Strain of the ACL was monitored by means of a differential variable reluctance transducer installed on the anterior-medial bundle of the ACL. The ACL strain was significantly increased (P<0.05) for the female loading pattern relative to the male loading pattern after the posterior tibial shear force was applied, and showed a similar trend (P=0.1) to be increased after the final tibial torque was applied. This study suggests that female motor control strategies used during the stop-jump task may place higher strains on the ACL than male strategies, thus putting females at greater risk of ACL injury. We believe these results suggest the potential effectiveness of using training programs to modify motor control strategies and thus modify the risk of injury.

Biomechanics of the rabbit knee and ankle: Muscle, ligament, and joint contact force predictions

Mathematical models of small animals that predict in vivo forces acting on the lower extremities are critical for studies of musculoskeletal biomechanics and diseases. Rabbits are advantageous in this regard because they remodel their cortical bone similar to humans. Here, we enhance a recent mathematical model of the rabbit knee joint to include the loading behavior of individual muscles, ligaments, and joint contact at the knee and ankle during the stance phase of hopping. Geometric data from the hindlimbs of three adult New Zealand white rabbits, combined with previously reported intersegmental forces and moments, were used as inputs to the model. Muscle, ligament, and joint contact forces were computed using optimization techniques assuming that muscle endurance is maximized and ligament strain energy resists tibial shear force along an inclined plateau. Peak forces developed by the quadriceps and gastrocnemius muscle groups and by compressive knee contact were within the range of theoretical and in vivo predictions. Although a minimal force was carried by the anterior cruciate and medial collateral ligaments, force patterns in the posterior cruciate ligament were consistent with in vivo tibial displacement patterns during hopping in rabbits. Overall, our predictions compare favorably with theoretical estimates and in vivo measurements in rabbits, and enhance previous models by providing individual muscle, ligament, and joint contact information to predict in vivo forces acting on the lower extremities in rabbits.

Bone contact forces on the distal tibia during the stance phase of running

Although the tibia is a common site of stress fractures in runners, the loading of the tibia during running is not well understood. An integrated experimental and modeling approach was therefore used to estimate the bone contact forces acting on the distal end of the tibia during the stance phase of running, and the contributions of external and internal sources to these forces. Motion capture and force plate data were recorded for 10 male runners as they ran at 3.5–4 m/s. From these data, the joint reaction force (JRF), muscle forces, and bone contact force on the tibia were computed at the ankle using inverse dynamics and optimization methods. The distal end of the tibia was compressed and sheared posteriorly throughout most of stance, with respective peak forces of 9.00±1.13 and 0.57±0.18 body weights occurring during mid stance. Internal muscle forces were the primary source of tibial compression, whereas the JRF was the primary source of tibial shear due to the forward inclination of the leg relative to the external ground reaction force. The muscle forces and JRF both acted to compress the tibia, but induced tibial shear forces in opposing directions during stance, magnifying tibial compression and reducing tibial shear. The superposition of the peak compressive and posterior shear forces at mid stance may contribute to stress fractures in the posterior face of the tibia. The implications are that changes in running technique could potentially reduce stress fracture risk.

Neuromuscular Control of the Knee during a Resisted Single-Limb Squat Exercise

Background Closed kinetic chain exercises such as single-limb squats are preferred for knee rehabilitation. A complete understanding of the neuromuscular control of the knee during the single-limb squat is essential to increase the efficiency of rehabilitation programs. Hypothesis Performing a controlled single-limb squat with resistance to knee flexion and extension will increase the coactivation of the hamstring muscle group, thus reducing the quadriceps/hamstrings ratio. Study Design Descriptive laboratory study. Methods A total of 15 healthy human subjects (7 women, 8 men) performed controlled single-limb squats in a custom mechanical device that provided resistance to both flexion and extension. Subjects performed the task at 3 levels of resistance, set as a percentage of body weight. Surface electromyographic recordings from 7 muscles (gluteus medius, rectus femoris, vastus medialis oblique, vastus lateralis, biceps femoris, semitendinosus, and medial gastrocnemius) were collected during the task. Results Biceps femoris activity during knee flexion increased from approximately 12% maximum voluntary isometric contractions during low resistance (0% body weight) to approximately 27% maximum voluntary isometric contractions during high resistance (8% body weight). Although the quadriceps had greater activity than the hamstrings at all levels of resistance, the quadriceps/hamstrings ratio declined significantly with resistance (F2,27 = 29.05; P=. 012) from 3.0 at low resistance to 2.32 at the highest resistance. Conclusions Performing controlled resisted single-limb squats may help to simultaneously strengthen the quadriceps and facilitate coactivation of the hamstrings, thus reducing anterior tibial shear forces. The coactivation may also increase the dynamic control of the knee joint. Clinical Relevance The typical single-limb squat exercise performed in the clinic does not usually control for bidirectional resistance and knee joint excursion. As seen in this study, controlled single-limb squats at increased levels of resistance help to increase the coactivation of the hamstring muscles, which is essential to optimize neuromuscular control of the knee.

Effect of Fatigue on Knee Kinetics and Kinematics in Stop-Jump Tasks

Background Altered motor control strategies in landing and jumping maneuvers are a potential mechanism of noncontact anterior cruciate ligament injury. There are biomechanical differences between male and female athletes in the landing phase of stop-jump tasks. Fatigue is a risk factor in musculoskeletal injuries. Hypothesis Lower extremity muscle fatigue alters the knee kinetics and kinematics during the landing phase of 3 stop-jump tasks and increases an athlete's risk of anterior cruciate ligament injury. Study Design Controlled laboratory study. Methods Three-dimensional videography and force plate data were collected for 20 recreational athletes (10 male and 10 female athletes) performing 3 stop-jump tasks before and after completing a fatigue exercise. Knee joint angles and resultant forces and moments were calculated. Results Both male and female subjects had significantly increased peak proximal tibial anterior shear forces (P =. 01), increased valgus moments (P =. 03), and decreased knee flexion angles (P =. 03) during landings of all 3 stop-jump tasks when fatigued. Fatigue did not significantly affect the peak knee extension moment for male or female athletes. Conclusion Fatigued recreational athletes demonstrate altered motor control strategies, which may increase anterior tibial shear force, strain on the anterior cruciate ligament, and risk of injury for both female and male subjects. Clinic Relevance Fatigued athletes may have an increased risk of noncontact anterior cruciate ligament injury.

Instruction of Jump-Landing Technique Using Videotape Feedback

Background Anterior cruciate ligament injury prevention programs have used videotapes of jump-landing technique as a key instructional component to improve landing performance. Hypothesis All videotape feedback model groups will increase knee flexion angles at initial contact and overall knee flexion motion and decrease peak vertical ground reaction forces and peak proximal anterior tibial shear forces to a greater extent than will a nonfeedback group. The secondary hypothesis is that the videotape feedback using the combination of the expert and self models will create the greatest change in each variable. Study Design Controlled laboratory study. Methods Knee kinematics and kinetics of college-aged recreational athletes randomly placed in 3 different videotape feedback model groups (expert only, self only, combination of expert and self) and a nonfeedback group were collected while participants performed a basketball jump-landing task on 3 testing occasions. Results All feedback groups significantly increased knee angular displacement flexion angles [F(6,70) = 8.03, P =. 001] and decreased peak vertical ground reaction forces [F(6,78) = 2.68, P =. 021] during performance and retention tests. The self and combination groups significantly increased knee angular displacement flexion angles more than the control group did; the expert model group did not change significantly more than the control group did. All feedback groups and the nonfeedback group significantly reduced peak vertical forces across performance and retention tests. There were no statistically significant changes in knee flexion angle at initial ground contact (P =. 111) and peak proximal anterior tibial shear forces (P =. 509) for both testing sessions for each group. Conclusion The use of self or combination videotape feedback is most useful for increasing knee angular displacement flexion angles and reducing peak vertical forces during landing. Clinical Relevance The use of self or combination modeling is more effective than is expert-only modeling for the implementation of instructional programs aimed at reducing the risk of jump-landing anterior cruciate ligament injuries.

Age and Gender Effects on Lower Extremity Kinetics of Youth Soccer Players Performing a Stop-Jump Task

1064 Several investigators have speculated that anterior cruciate ligament (ACL) injuries frequently occur during the stop-jump phase of movement tasks, yet minimal data exists in comparing lower extremity motion patterns between different age groups and gender performing stop-jump tasks. PURPOSE: To compare knee kinetics of male and female youth soccer players to determine if there are motion pattern differences between gender and age groups (11–16 yrs.) when performing a stop-jump task. METHODS: Knee kinetics of 30 female (age = 13.80 ± 1.76 yrs, height = 1.58 ± .09 m, weight = 49.89 ± 10.19 kg) and 26 male (age = 13.54 ± 1.79 yrs, height = 1.63 ± .11 m, weight = 52.90 ± 13.25 kg) youth soccer players were collected. Subjects took a three-step approach and performed a stop-jump maneuver to “head” an imaginary soccer ball. The dependent variables (normalized to bodyweight and height) were proximal anterior tibial shear force maximum and at initial foot contact; knee flexion (+)/extension (−) and varus (+)/valgus (−) moments at maximum proximal anterior tibial shear force and at initial foot contact during a stop-jump task. RESULTS: Preliminary analyses were performed using a stepwise multiple regression analysis on each dependent variable for age and gender effects to evaluate the motion pattern trends. A significant gender effect was found for proximal anterior tibial shear force at initial foot contact and knee flexion/extension moment at initial foot contact. Females demonstrated greater proximal anterior tibial shear force at initial foot contact and greater knee extensor moment at initial foot contact as compared to males. A significant age effect was found for knee varus/valgus moment at maximum proximal anterior tibial shear force and at initial foot contact. Younger aged youth soccer players demonstrated a smaller knee valgus moment at maximum proximal anterior tibial shear force, while older aged players demonstrated a greater knee valgus moment. Younger aged players demonstrated greater knee valgus moment at initial foot contact, while older aged players demonstrated a knee varus moment. No statistical difference was found for maximum proximal anterior tibial shear force, but the data indicate a trend that females had increased shear force as compared to their male counterparts. CONCLUSIONS: These findings suggest that age and gender differences occur in youth soccer players' lower extremity motion patterns when performing a stop-jump task. The findings of this study provide a basis for further research comparing age and gender jump-landing differences, which may be valuable for the development of noncontact ACL injury prevention programs.

Sex Differences in Lower Extremity Kinetics and Kinematics during Landing

1578 Anterior cruciate ligament (ACL) injuries occur relatively more frequently in female athletes than in male athletes. Recently, altered landing techniques (less knee flexion angle) in female athletes have been reported to be associated with an increase in ACL loading. However, the mechanism(s) responsible for ACL injuries and sex differences in landing techniques remain unclear. PURPOSE: To compare the kinetics and kinematics of females with those of males during two landing movements: vertical jump (VJ) and horizontal jump (HJ). METHODS: Kinetic and kinematic data were recorded during landing by 12 male and 11 female college students. Initial and peak joint angles of hip, knee, and ankle in a sagittal plane, and the time to reach peak knee flexion were determined from the kinematic data. Peak values for hip, knee, and ankle moments and powers, ground reaction force, and anterior tibial shear force were determined and normalized to body mass. Repeated measures ANOVA was used to identify sex related differences. RESULTS: During VJ, time to reach maximum knee flexion was lower for females (183 ± 36ms vs. 224 ± 36ms, p = 0.01), whereas other variables did not differ. During HJ, knee moments (3.10 ± 1.13Nm vs. 2.25 ± 0.57Nm, p = 0.04), knee power (−23 ± 6.8W/kg vs. −16 ± 6.8W/kg, p = 0.03) and time to reach peak knee flexion (female: 187 ± 33ms vs. 217 ± 35ms, p = 0.05) were significantly greater in males. CONCLUSIONS: Males and females in this study exhibited similar landing kinematics, suggesting that the kinematics per se are not responsible for the increased ACL injury rate of females. However, our results suggest that altered energy dissipation in females, as demonstrated by different time to reach maximum knee flexion, may represent a possible mechanism for increased ACL injury rates in female athletes.

Sex Differences in Lower Extremity Kinetics and Kinematics during Landing

1578 Anterior cruciate ligament (ACL) injuries occur relatively more frequently in female athletes than in male athletes. Recently, altered landing techniques (less knee flexion angle) in female athletes have been reported to be associated with an increase in ACL loading. However, the mechanism(s) responsible for ACL injuries and sex differences in landing techniques remain unclear. PURPOSE: To compare the kinetics and kinematics of females with those of males during two landing movements: vertical jump (VJ) and horizontal jump (HJ). METHODS: Kinetic and kinematic data were recorded during landing by 12 male and 11 female college students. Initial and peak joint angles of hip, knee, and ankle in a sagittal plane, and the time to reach peak knee flexion were determined from the kinematic data. Peak values for hip, knee, and ankle moments and powers, ground reaction force, and anterior tibial shear force were determined and normalized to body mass. Repeated measures ANOVA was used to identify sex related differences. RESULTS: During VJ, time to reach maximum knee flexion was lower for females (183 ± 36ms vs. 224 ± 36ms, p = 0.01), whereas other variables did not differ. During HJ, knee moments (3.10 ± 1.13Nm vs. 2.25 ± 0.57Nm, p = 0.04), knee power (−23 ± 6.8W/kg vs. −16 ± 6.8W/kg, p = 0.03) and time to reach peak knee flexion (female: 187 ± 33ms vs. 217 ± 35ms, p = 0.05) were significantly greater in males. CONCLUSIONS: Males and females in this study exhibited similar landing kinematics, suggesting that the kinematics per se are not responsible for the increased ACL injury rate of females. However, our results suggest that altered energy dissipation in females, as demonstrated by different time to reach maximum knee flexion, may represent a possible mechanism for increased ACL injury rates in female athletes.

Are hamstrings activated to counteract shear forces during isometric knee extension efforts in healthy subjects?

The hamstring muscles have the potential to counteract anterior shear forces at the knee joint by co-contracting during knee extension efforts. Such a muscle recruitment pattern might protect the anterior cruciate ligament (ACL) by reducing its strain. In this study we investigated to what extent co-activation of the knee flexors during extension efforts is compatible with the hypothesis that this co-activation serves to counteract anterior tibial shear forces during isometric knee extension efforts in healthy subjects. To this aim, it is investigated whether co-activation varies with the required knee extension moment, with the knee joint angle, and with the position of the external flexing force relative to the knee joint. With unaltered moment and muscle activation, distal positioning of the flexing force on the tibia causes higher resultant (muscular plus external) forward shear forces at the knee as compared to proximal positioning. In ten subjects, knee flexor and extensor EMG was measured during a quasi-isometric positioning task for a range (5–50 degrees) of knee flexion angles. It was found that the co-activation of the knee flexors increased with the extension moment, but this increase was less than proportional ( p<0.001). The extension moment increased 2.7 to 3.4 times, whereas the activation of Biceps Femoris and Semitendinosus increased only a factor 1.3 to 2.0 (joint angle dependent). Furthermore, a strong increase in co-activation was seen near full extension of the knee joint. The position of the external extension load on the tibia did not affect the level of co-contraction. It is argued that these results do not suggest a recruitment pattern that is directed at reduction of anterior shear forces in the knee joint during sub-maximal isometric knee extension efforts in healthy subjects.

Aggressive Quadriceps Loading Can Induce Noncontact Anterior Cruciate Ligament Injury

Background The force responsible for noncontact anterior cruciate ligament (ACL) injuries remains controversial. The patella tendon to tibial shaft angle causes an anterior tibial shear force with quadriceps activation. Hypothesis An aggressive quadriceps contraction can injure the ACL. Methods The authors characterized noncontact ACL injury and kinematics with aggressive quadriceps loading. Thirteen freshfrozen knees were potted in a jig held in 20 ° of flexion while a 4500 N quadriceps contraction was simulated. Knee kinematics were recorded. A KT-1000 arthrometer and a simulated active quadriceps test assessed anterior displacement. Statistics were performed using paired t tests and 1-way analysis of variance. Results Kinematics revealed the following mean values: anterior displacement, 19.5 mm; valgus, 2.3 °; and internal rotation, 5.5 °. Mean KT-1000 and active quadriceps test differences were 4.0 mm and 2.7 mm, respectively (statistically significant P = .002 and P = .002). Six knees showed gross ACL injury at the femoral insertion. Based on ACL injury, KT-1000 differences were statistically significant (P = .029). Conclusions Aggressive quadriceps loading, with the knee in slight flexion, produces significant anterior tibial translation and ACL injury. This suggests that the quadriceps is the intrinsic force in noncontact ACL injuries, producing a model for further investigation.

Comparison of shear forces and ligament loading in the healthy and ACL-deficient knee during gait

The purpose of this study was to predict and explain the pattern of shear force and ligament loading in the ACL-deficient knee during walking, and to compare these results to similar calculations for the healthy knee. Musculoskeletal modeling and computer simulation were combined to calculate ligament forces in the ACL-deficient knee during walking. Joint angles, ground-reaction forces, and the corresponding lower-extremity muscle forces obtained from a whole-body dynamic optimization simulation of walking were input into a second three-dimensional model of the lower extremity that represented the knee as a six degree-of-freedom spatial joint. Anterior tibial translation (ATT) increased throughout the stance phase of gait when the model ACL was removed. The medial collateral ligament (MCL) was the primary restraint to ATT in the ACL-deficient knee. Peak force in the MCL was three times greater in the ACL-deficient knee than in the ACL-intact knee; however, peak force sustained by the MCL in the ACL-deficient knee was limited by the magnitude of the total anterior shear force applied to the tibia. A decrease in anterior tibial shear force was brought about by a decrease in the patellar tendon angle resulting from the increase in ATT. These results suggest that while the MCL acts as the primary restraint to ATT in the ACL-deficient knee, changes in patellar tendon angle reduce total anterior shear force at the knee.

Long-term supplementation of various dietary lipids alters bone mineral content, mechanical properties and histological characteristics of Japanese quail

The purpose of this study was to investigate the effects of long-term supplementation of fat in the diets on the fatty acid composition, chemical, mechanical, and histological properties of tibial bone. Month-old male Japanese quail were fed a basal diet containing either soybean oil (SBO), hydrogenated soybean oil (HSBO), chicken fat (CF), or menhaden fish oil (FO) at 50 g/kg of the diet and maintained on these diets for 7 mo. Lipid treatments did not affect body weight, food intake, tibial length, or diameter. The FO diet group had the highest percentage of tibial ash, and both the FO and HSBO significantly increased tibial mineral content compared to those given SBO or CF. The type and amount of fatty acids in the diets had a profound influence on fatty acid composition of lipids in tibial cortical bones. Quail fed FO had the highest concentration of (n-3) fatty acids, and those fed SBO were highest in (n-6) fatty acids. The HSBO diet, containing high level of trans-fatty acids, led to the accumulation of these fatty acids in bone. In quail, long-term supplementation of FO or HSBO increased tibial shear force and shear stress and improved histological cortical thickness and density when compared to those given SBO or CF. These results suggest that long-term exposure to a FO or HSBO diet have a significant beneficial effect on bone metabolism.

Maternal dietary lipids alter bone chemical composition, mechanical properties, and histological characteristics of progeny of Japanese quail

This study evaluated the effects of maternal dietary lipids on chemical components and mechanical and histological properties of tibia in progeny of Japanese quail fed different dietary lipids. Laying hens were fed a basal diet containing either soybean oil (SBO), hydrogenated soybean oil (HSBO), chicken fat (CF), or menhaden fish oil (FO) at 50 g/kg of the diet. The various maternal dietary lipid treatments did not affect growth of progeny at any developmental stage. There were no differences in tibial length, diameter, or collagen content. Tibial percentage ash was significantly higher in newly hatched progeny from hens fed the FO and HSBO diets. The levels of tibial deoxypyridinoline and total pyridinium crosslinks were higher in the FO and HSBO groups at hatch. At 7 d of age, the tibial deoxypyridinoline links remained higher in the FO group compared to the CF and SBO groups. Likewise, progeny from hens consuming the FO or HSBO diet had higher tibial shear force and stiffness at 7 and 14 d of age. There were no pronounced differences in tibial fracture energy and deflection among treatments. Maternal FO or HSBO enlarged the cartilaginous proliferative and hypertrophic zones of the tibial proximal end in newly hatched quail, which was accompanied by a thicker cortical bone in the diaphysis. However, the width of the hypertrophic zones tended to be smaller in these two groups coupled with improvement in trabecular density and cortical thickness in the proximal end and cortical density in the diaphysis at 3 wk of age. These results suggest that maternal dietary lipids altered bone development by influencing organic matrix quality and mineralization in embryos.

In vitro forces in the normal and cruciate-deficient knee during simulated squatting motion.

Three orthogonal components of the tibiofemoral and patellofemoral forces were measured simultaneously for knees with intact cruciate ligaments (nine knees), following anterior cruciate ligament resection (six knees), and subsequent posterior cruciate ligament resection (six knees). The knees were loaded using an experimental protocol that modeled static double-leg squat. The mean compressive tibial force increased with flexion angle. The mean anteroposterior tibial shear force acted posteriorly on the tibia below 50 deg flexion and anteriorly above 55 deg. Mediolateral shear forces were low compared to the other force components and tended to be directed medially on both the patella and tibia. The mean value of the ratio of the resultant tibial force divided by the quadriceps force decreased with increasing flexion angle and was between 0.6 and 0.7 above 70 deg flexion. The mean value of the ratio of the resultant tibiofemoral contact force divided by the resultant patellofemoral contact force decreased with increasing flexion and was between 0.8 and 1.0 above 55 deg flexion. Cruciate ligament resection resulted in no significant changes in the patellar contact forces. Following resection of the anterior cruciate ligament, the tibial anteroposterior shear force was directed anteriorly over all flexion angles tested. Subsequent resection of the posterior cruciate ligament resulted in an approximately 10 percent increase in the quadriceps tendon and tibial compressive force.

Prediction of muscle recruitment and its effect on joint reaction forces during knee exercises.

This study examined the hypothesis that muscle recruitment of the tibiofemoral joint and joint reaction forces during isometric and isokinetic exercises depends on the existing degrees of freedom of the knee and the direction and type of external load applied during exercise. When three-dimensional knee joint rotation was considered (three degrees of freedom), antagonistic muscle activities were predicted using an inverse dynamic problem formulation and muscle modeling optimization procedures. The results showed that the antagonistic activities of flexors during knee flexion/extension exercise increased the joint compressive forces and decreased the anterior tibial shear forces. Comparison of different knee joint modeling assumptions indicated that modeling a single degree of freedom in flexion/extension for the knee will underestimate the antagonistic muscle function.

Soybeans transformed with a fungal phytase gene improve phosphorus availability for broilers

Male broilers (n = 416) were used to compare the efficacy of providing dietary phytase either as a commercial supplement or as a recombinant protein in transformed soybean. From 7 to 21 d of age, broilers were fed a basal diet containing 0.20% nonphytate P (nP) with additional supplementation by fungal phytase as Natuphos or as raw transformed soybeans expressing recombinant phytase at 400, 800, or 1,200 U/kg. For comparison, broilers were also fed the basal diet containing 0.08, 0.16, or 0.24 added nP. The basal diet was fed as the negative control. Diets were consumed ad libitum as a mash. All excreta were collected from each pen from 18 through 20 d of age, and the birds were killed at 21 d of age. Supplementing the basal diet with nP linearly increased body weight gain, feed efficiency, feed intake, toe ash weight and percentage, and tibia shear force and energy. Phosphorus digestibility decreased linearly as nP level increased, but P excretion increased. Dietary phytase linearly increased growth rate, feed intake, toe ash weight and percentage, tibia shear force and energy, and P digestibility, whereas excretion was decreased. Except for P digestibility, there was no difference in efficacy of responses for performance, bone mineralization, and P excretion between the two sources of phytase. It appears from this study that phytase can improve growth performance of broilers fed low nP diets when provided either as a commercial supplement or in the form of transformed seeds.

Effects of Supplemental Phytase and Phosphorus on Histological and Other Tibial Bone Characteristics and Performances of Broilers Fed Semi-Purified Diets

Two trials with day-old chicks were conducted to investigate the effects of supplemental phytase (Natuphos®) on histological, mechanical, and chemical properties of tibia, and performances of broilers fed semi-purified diets containing soybean meal as the only organic P source [0.11% nonphytate P (nP)]. Dietary treatments in Trial 1 were: 1) 0.20% nP, 2) Diet 1 + 800 U of phytase/kg of diet, 3) 0.27% nP, 4) Diet 3 + 600 U of phytase, 5) 0.34% nP, 6) Diet 5 + 400 U of phytase. Supplemental phytase and inorganic P increased tibial length (P < 0.01), shear force (P < 0.001), shear stress (P < 0.05), ash content (P < 0.001), and BW gain and feed intake (P < 0.001) during Trial 1. The hypertrophic zone width at the proximal end of the tibia was decreased (P < 0.05), and the tibial width (P < 0.05) of the long axis of the tibia was increased by the phytase and P supplementation. Supplemental phytase enlarged the cartilaginous and proliferative zones of the tibial proximal end (P < 0.05), and an increase in nP levels produced similar effects. Supplementation of phytase and P also tended to improve the orderliness of development and arrangement of cartilage and bone cells. Dietary treatments in Trial 2 were: 1) 0.27% nP, 2) Diet 1 + 350 U of phytase, 3) Diet 1 + 1,050 U of phytase, 4) 0.45% nP, 5) 0.54% nP, 6) Diet 5 + 1,050 U of phytase. Broilers fed diets containing relatively high levels of nP and phytase supplementation in Trial 2 gave results similar to those observed in Trial 1. Marked improvements (P < 0.05) in the ash content, shear force, shear stress, length of tibia, BW gain, and feed intake, and reduced hypertrophic zone width were achieved for broilers fed the P-deficient diet supplemented with phytase. Also, supplemental phytase tended to increase the width of cartilaginous and proliferative zones, to increase trabecular bone density, and to improve the orderliness of development and mineralization of cartilage and bone cells. In summary, supplementing a low-nP diet with inorganic P or phytase resulted in similar beneficial effects on bone development.

An Evaluation of Various Response Criteria in Assessing Biological Availability of Phosphorus for Broilers

The relative bioavailability of P from seven sources was determined in relation to a standard dicalcium phosphate dihydrate (CaHPO4.2 O) in a 21-d assay involving 1,320 broiler male chicks using several response criteria. The seven sources (Lucaphos-48, Lucaphos-40, Rukana, Cefkaphos-N, phosphoric acid, monocalcium phosphate monohydrate, or Biophos) were added to the basal diet (.40% total P and 1.10% Ca) at levels to supply .05, .08, .12, .17, .23, and .32% P. Two additional levels (.44 and .66%) of P from dicalcium phosphate dihydrate were included for the standards. The criteria selected to evaluate included tibia ash, tibia specific gravity, tibia shear force, toe shear force, and metatarsal shear force. Other criteria: weight, length, diameter, and volume of tibia; weight, volume, and specific gravity of metatarsus; and weight, volume, and specific gravity of toe were not selected because their response to increasing P levels were inconsistent and quite variable. Nonlinear (asymptotic and sigmoidal) regression equations were fitted to the data for the selected criteria because they were a better fit of the data than linear equations. The ratios of regression coefficients were used to determine the bioavailability of various test phosphates relative to the reference standard. The results indicated that the response criteria used for the determination will considerably influence the relative bioavailability estimates of a P source. Body weight gain and toe ash percentage were found to be an equally or a more sensitive criteria for assessment of P availability than tibia ash. Tibia specific gravity, tibia shear force, toe shear force, and metatarsal shear force were of limited value as response criteria in P bioavailability assays based on standard error and difference required for significance.