Biomedical subjects

S M Stover

Publications and source records attributed to S M Stover.

At least 37 records · Page 2Linked to original sources

PubMed1999

Effect of surgical technique and use of a rigid centralizing device on stem positioning and geometric reconstruction in the sagittal plane during total hip replacement in canine cadavers.

OBJECTIVE: To determine the effect of surgical technique and use of a rigid centralizing device on stem positioning and geometric reconstruction in the sagittal plane during total hip replacement in dogs. SAMPLE POPULATION: Bilateral femurs from 8 adult mixed-breed canine cadavers. PROCEDURE: Femurs were prepared for femoral stem implantation, using 4 variations in technique. Proximal femoral reconstruction and femoral stem positioning were evaluated on radiographs. RESULTS: Implants evaluated in this study accurately reconstructed displacement of the femoral head of the intact canine femur in the sagittal plane. Centralization of the distal aspect of the stem was optimized by use of an undersized femoral stem. Ostectomy at the level of the lesser trochanter resulted in the smallest diaphysis-to-implant angle. Anteversion and retroversion of implants significantly decreased the distance between the distal tip of the implant and the adjacent cortex, compared with normoversion. The centralizing device significantly increased the minimum distance between the distal tip of the implant and adjacent cortex but did not improve the odds of actually centralizing the tip of the implant. CONCLUSIONS AND CLINICAL RELEVANCE: Malpositioning of implants in the sagittal plane may be minimized through ostectomy at the lesser trochanter and use of an undersized implant positioned in normoversion. Use of a polymethylmethacrylate centralizing device will help eliminate contact between the implant tip and adjacent cortex. Implantation of an undersized femoral component, avoidance of substantial anteversion or retroversion, and use of a rigid centralizing device are recommended when using the prosthesis described-for total hip replacement of dogs.

Animals↗

PubMed1998

Association between long periods without high-speed workouts and risk of complete humeral or pelvic fracture in thoroughbred racehorses: 54 cases (1991-1994).

OBJECTIVE: To determine whether a two-month or longer period without official high-speed workouts (lay-up) is associated with humeral or pelvic fracture in Thoroughbred racehorses. DESIGN: Reprospective study. ANIMALS: Thoroughbred racehorses in California that were euthanatized because of a complete humeral or pelvic fracture. PROCEDURE: Age, sex, activity, number of lay-ups, number of days from a race or official timed workout to fracture, number of days from end of last lay-up to fracture, mean duration of lay-ups, and total number of days in race training were compared between horses with humeral fractures and horses with pelvic fractures. A case-crossover study was used to estimate relative risk for fracture of the humerus or pelvis occurring within hazard periods of 10 and 21 days following lay-up, compared with periods following more regular participation in official racing or timed workout events. RESULTS: Horses with pelvic fractures were more often female, older, and had 0 or > or = 2 lay-ups. Horses with humeral fractures were typically 3-year-old males that had 1 lay-up. Horses with pelvic fractures had more total days in race training, fewer days from last exercise event to fracture, and a greater number of days from end of last lay-up to fracture than horses with humeral fractures. Return from lay-up was strongly associated with risk for humeral fracture during hazard periods of 10 and 21 days (relative risk = 71 and 45, respectively). CLINICAL IMPLICATIONS: Risk of humeral fracture may be reduced if horses are cautiously reintroduced into race training after lay-up.

Animals↗

PubMed1998

Lateral approach for arthrocentesis of the distal interphalangeal joint in horses.

OBJECTIVE: To determine anatomic landmarks for a lateral approach for arthrocentesis of the proximopalmarolateral aspect of the distal interphalangeal (DIP) joint in horses and the likelihood of entering synovial structures other than the DIP joint through this approach. DESIGN: Prospective study. SAMPLE POPULATION: Paired forelimbs of 8 cadavers and 12 horses. PROCEDURE: Anatomic preparations were used to determine anatomic landmarks. Positive-contrast arthrography was used to determine which structures were entered. RESULTS: Landmarks for the lateral approach included a depression in the proximal border of the lateral ungular cartilage and the palmar border of the middle phalanx. Use of the lateral approach for arthrography resulted in deposition of contrast material exclusively in the DIP joint in only 13 of 20 limbs, whereas use of the dorsal approach resulted in deposition of contrast material exclusively in the DIP joint in 20 of 20 limbs. CLINICAL IMPLICATIONS: The lateral approach is an alternative to the conventional dorsal approach to the DIP joint in horses, however, inadvertent entry into adjacent synovial structures is a possible complication. The lateral approach provides an additional portal for through-and-through lavage and arthroscopic access to the palmar aspect of the DIP joint.

Animals↗

PubMed1998

Relationship between race start characteristics and risk of catastrophic injury in thoroughbreds: 78 cases (1992).

OBJECTIVE: To investigate relationships of several racehorse characteristics and race conditions with risk of a catastrophic musculoskeletal injury (CMI) resulting in euthanasia in Thoroughbreds during racing in California in 1992. DESIGN: Retrospective longitudinal study. ANIMALS: Thoroughbreds that incurred CMI during racing and all California race entrants in 1992. PROCEDURE: Necropsy records were reviewed, and race start information was obtained. Incidence risk of CMI/1,000 race entrants was estimated. Relationships between CMI during racing and race-meet, entrant age and sex, race type and length, and racing surface type and condition were evaluated by use of logistic regression. RESULTS: Incidence risk of CMI was 1.7/1,000 entrants. A higher risk of CMI was found at 2 fair race-meets, with incidence risks of 4.9 and 5.5/1,000 entrants. Risk of injury in male horses was 1.7 times greater than that in female horses, and influence of age on risk depended on race type. Risk of injury for horses 2 to 5 years old was two times greater for claiming horses than for maiden horses. Race length or racing surface type (dirt vs turf) or condition (fast, muddy, yielding) were not significantly associated with risk of CMI. CLINICAL IMPLICATIONS: Incidence of CMI was similar among 12 of 14 major and fair race-meets and among various race lengths and racing surface types and conditions, whereas incidence of CMI was influenced by entrant age and sex as well as race type. Investigators should consider controlling for age and sex, race-meet, and race type whenever possible in studies of risk of CMI.

Age Factors↗

PubMed1998

A case-crossover study of intensive racing and training schedules and risk of catastrophic musculoskeletal injury and lay-up in California thoroughbred racehorses.

The objective of this study was to investigate the relationship between intensive racing and training schedules and risk of either catastrophic musculoskeletal injury (CMI) or lay-up from racing in California Thoroughbreds. Thoroughbred racehorses that sustained a CMI during racing or training and either were subsequently euthanized or died on a California racetrack during 1991 and 1992 were studied using a case-crossover study design. Each study subject (case) provided its own self-matched control information in the form of 'typical' exposure frequency, determined or estimated from historic information. Periods of rapid average daily accumulation of high-speed exercise distance were identified for each horse from official race and training histories with a sliding 60-day window. Those window frames containing an average daily rate of distance accumulation exceeding 75th percentile cutoff values were classified as exposed frames followed by 30 days of increased risk, or hazard periods. All remaining days (excluding periods of layoff from racing) were considered non-hazard time at risk. The relative risk (RR) of CMI within 30 days following a period of rapid accumulation of high-speed exercise distance (during a hazard period) was 4.2 (95% confidence interval [CI] = 3.0, 5.8). Of these 214 cases, 84 (39%) were injured during a hazard period whereas on average only 22% of total career time at risk was hazard time for these horses. A second analysis was performed for horses with at least 1 lay-up period from racing of > or = 60 days. RR for a lay-up beginning during a hazard period was estimated for the last lay-up experienced by each horse. The RR for lay-up beginning during a hazard period was 4.8 (95% CI = 2.9, 8.1). Of these 98 cases, 32 (33%) of the lay-ups began during a hazard period whereas on average, only 22% of at-risk time up to last lay-up was hazard time for these horses.

Age Distribution↗

PubMed1998

Ex vivo simulation of in vivo strain distributions in the equine metacarpus.

The objective of this study was to examine several simple ex vivo loading conditions for the equine metacarpus, and to evaluate their ability to reproduce the mid-diaphyseal bone surface strain distributions previously reported in vivo at the walk and trot. Distributed axial compressive loads, and 9 different axial compressive point loads at -7.5 kN and -15 kN were applied to metacarpal-distal carpal bone preparations from 6 Thoroughbred horses, aged 1-5 years. The resulting dorsal, medial, palmar, and lateral mid-diaphyseal bone surface axial and shear strains were compared with previously reported in vivo surface strain distributions using a root mean square error (RMSE) protocol. The effects of loading condition and load magnitude on RMSE were assessed with a mixed-model analysis of variance. There were significant differences between loading conditions, and, in most cases, between load magnitudes, in the fit of the ex vivo to the in vivo strain distributions. In vivo mid-diaphyseal bone surface strain distributions at the walk can be well approximated ex vivo by a distributed axial compressive load, or by a point load positioned 0.5 cm medial to the sagittal midline, at -7.5 kN loads. In vivo mid-diaphyseal bone surface strain distributions at the trot can be well approximated by the -15 kN loads applied to the same locations. These simplified loading conditions can be used in designing biologically relevant loading protocols for ex vivo mechanical testing studies, as well as in developing boundary conditions for finite element analysis. As such, these loading conditions may be considered as tools to be used as a means of replicating in vivo loading conditions during the initial design and testing stages in the development of fracture fixation devices, as well as in the theoretical mechanical analysis of the metacarpal structure.

Analysis of Variance↗

PubMed1998

Stress fractures of the vertebral lamina and pelvis in Thoroughbred racehorses.

Thirty-six Thoroughbred racehorses that died at California racetracks between October 1993 and July 1994 were evaluated for stress fractures in the caudal portion of the thoracic and lumbosacral regions of the spine and the pelvis. The lumbosacral spine and pelvis were collected, debrided of soft tissues and examined visually for the presence of an incomplete fracture line and focal periosteal proliferation, characteristic of a stress fracture. Sixty-one per cent of specimens had evidence of stress fracture in the caudal portion of the thoracic and lumbosacral regions of the spine and the pelvis. Vertebral lamina stress fractures were found in 50% of specimens and were positively associated with the severity of dorsal spinous process impingement and overall severity of articular process degenerative changes. Pelvic stress fractures affected 28 % of specimens and occurred more frequently in older horses. Pelvic stress fractures were positively associated with the severity of lumbar transverse process impingement and several ilial articular surface degenerative changes. A high prevalence of vertebral and pelvic stress fractures was noted in this sample of Thoroughbred racehorses that died because of unrelated injuries. Vertebral and pelvic stress fractures need to be considered in the clinical evaluation of horses with back problems or hindlimb lameness. Undiagnosed stress fractures of the vertebrae or pelvis could be a significant cause of poor performance and lameness in Thoroughbred racehorses.

Age Factors↗

PubMed1998

Effect of hoof trimming on the occurrence of distal phalangeal palmar process fractures in foals.

This study sought to determine if extensive trimming of the front hooves of foals results in a higher incidence of palmar process fractures compared to untrimmed foals, and to characterise the clinical course of foals with palmar process fractures with physical findings, hoof measurements and radiography. Twenty foals age 4-8 weeks of multiple breeds were examined every 2 weeks over a 12 week period. Ten foals had both front hooves extensively trimmed every 4 weeks, while 10 foals remained untrimmed. Palmar process fractures occurred in 4 trimmed and 3 untrimmed foals. Four foals with fractures had brief lameness (Grades I-II/V) and hoof tester sensitivity was found inconsistently with fractures. All foals with fractures were sound at the end of the study. Fractures healed based on radiographic evaluations in an average of 8.4 weeks. Two of 3 foals with fractures developed club-footed conformation. None of the measured hoof parameters significantly differed between foals with and without fractures. We conclude that extensive trimming of the heels did not appear to affect the occurrence of palmar process fractures in this group of foals.

Animals↗

PubMed1998

Transverse plane evaluation of the effects of surgical technique on stem positioning and geometry of reconstruction in canine total hip replacement.

OBJECTIVES: To test whether femoral ostectomy level, subtrochanteric bone mass removal, and stemsize selection significantly affect stem positioning in canine total hip replacement, and to determine ability of the femoral stem component to restore geometry of the normal femoral head and neck. SAMPLE POPULATION: Femurs from 8 adult mixed-breed canine cadavers. PROCEDURE: Femurs were systematically prepared, using 8 combinations of 3 surgical preparation techniques that included level of ostectomy (cervical isthmus vs lesser trochanter), subtrochanteric bone block removal, and femoral stem size (recommended, undersized). Computer-aided analysis of specimen photographs was used to evaluate femoral head offset and position and variability of femoral stem positioning for each of the preparation combinations. RESULTS: Original femoral head offset and position were reconstructed to within a mean of 0.052 and 0.031 cm, respectively, using an undersized femoral stem after ostectomy at the level of the lesser trochanter. Implantation of an undersized femoral stem after subtrochanteric bone block removal improved ability to centralize the distal tip of the implant and reduce the angle between the femoral diaphyseal and implant axes. Ostectomy at the level of the cervical isthmus tended to force femoral implants into a varus position, and ostectomy at the level of the lesser trochanter tended to force implants into a valgus position. CONCLUSIONS: Geometry of normal canine femurs was most closely reconstructed by implantation of an undersized femoral component after ostectomy at the level of the lesser trochanter. Implantation of an undersized femoral component after subtrochanteric bone block removal resulted in the best alignment and centralization of the stem.

Animals↗

PubMed1998

Hoof size, shape, and balance as possible risk factors for catastrophic musculoskeletal injury of Thoroughbred racehorses.

OBJECTIVE: To evaluate hoof size, shape, and balance as risk factors for catastrophic musculoskeletal injuries (CMI), including suspensory apparatus failure (SAF) and cannon bone condylar fracture (CDY) in Thoroughbred racehorses. ANIMALS: 95 Thoroughbred racehorses that died between 1994 and 1996. PROCEDURE: 38 quantitative measures of hoof size, shape, and balance were obtained from orthogonal digital images of the hoof and were compared between case horses with forelimb CMI (70), SAF (43), and CDY (10) injuries and control horses whose death was unrelated to the musculoskeletal system (non-CMI, 25). Comparison of group means between cases and controls was done using ANOVA, and multivariable logistic regression was used to estimate odds ratios. RESULTS: Odds of CMI were 0.62 times lower for a 5mm increase in ground surface width difference and 0.49 times lower for a 100-mm2 increase in sole area difference. Odds of SAF were 6.75 times greater with a 10 degrees increase in toe-heel angle difference and 0.58 times lower with a 100-mm2 increase in sole area difference. Odds of CDY were 0.26 times lower with a 3 degrees increase in toe angle, 0.15 times lower with a 5-mm increase in lateral ground surface width, and 0.35 times lower with a 100-mm2 increase in sole area difference. CLINICAL RELEVANCE: Decreasing the difference between toe and heel angles should decrease risk of SAF for Thoroughbred racehorses and should be considered in addition to increasing toe angle alone to help prevent catastrophic injury. Trimming the hoof to perfect mediolateral symmetry may not be a sound approach to avoiding injury.

Animals↗

PubMed1997

Model of flexural fatigue damage accumulation for cortical bone.

Analytical models that predict modulus degradation in cortical bone subjected to uniaxial fatigue loading in tension and compression are presented. On the basis of experimental observations, damage was modeled as self-limiting for tension but not for compression. These mechanistic uniaxial damage models were then developed into a model for flexural fatigue of cortical bone based on laminated beam theory. The unknown coefficients in the uniaxial damage models were obtained by successfully fitting the resulting equations to uniaxial fatigue data from the literature on human cortical bone in tension and compression. Then, the predictions of the flexural model for the behavior of human cortical bone were compared with experimental results from a small but independent set of specimens tested at three different ranges of load in our laboratory. The behavior of the modulus degradation curves and the flexural fatigue lives of the specimens were in excellent agreement with the predictions of the model.

Bone and Bones↗

PubMed1997

Residual strength of equine bone is not reduced by intense fatigue loading: implications for stress fracture.

Fatigue or stress fractures are an important clinical problem in humans as well as racehorses. An important question in this context is, when a bone experiences fatigue damage during extreme use, how much is it weakened compared to its original state? Since there are very limited data on this question and stress fractures are common in racehorses, we sought to determine the effect of fatigue loading on the monotonic strength of equine cortical bone. Beams were machined from the dorsal, medial and lateral cortices of the third metacarpal bones of six thoroughbred racehorses. Beams from left and right bones were assigned to control and fatigue groups, respectively (N = 18 each). The fatigue group was cyclically loaded in three-point bending at 2 Hz for 100,000 cycles at 0-5000 microstrain while submerged in saline at 37 degrees C. These beams, as well as those in the control group, were then monotonically loaded to failure in three-point bending. The monotonic load-deflection curves were analyzed for differences using three-factor (fatigue loading, anatomic region, and horse) analysis of variance. The mean failure load was 3% less in the fatigue group, but this reduction was only marginally significant. Neither elastic modulus nor yield strength was significantly affected by the fatigue loading. The principal effects of fatigue loading were on post-yield behavior (yield being based on a 0.02% offset criterion). The work done and the load increase between yield and failure were both significantly reduced. All the variables except post-yield deflection were significantly affected by anatomic region. In summary, loading equivalent to a lifetime of racing does not significantly weaken equine cortical bone ex vivo. The clinical implication of this may be that the biological repair of fatigue damage can actually contribute to stress fracture if pressed too far.

Analysis of Variance↗

PubMed1997

Artifactual nonlinearity due to wear grooves and friction in four-point bending experiments of cortical bone.

Experiments and analyses were performed to determine the cause of a nonlinear force-deflection response observed in four-point flexural fatigue of beams of cortical bone machined from the mid-diaphysis of the equine third metacarpus. Observable grooves which formed on the beam surface at supports and load noses were found to be the primary cause of the nonlinearity. An additional geometric nonlinearity at large deflections revealed by finite element modeling may be minimized by using the smallest diameter supports and load noses recommended in ASTM 790. However, frictional constraint of the beams at the load noses and supports can occur at low load levels and should be avoided by using roller-bearing supports and load noses, or some equivalent method.

Animals↗

PubMed1997

The distribution of material properties in the equine third metacarpal bone serves to enhance sagittal bending.

The distribution of material properties within the equine third metacarpal bone (MC3), and its possible effect on the mechanics of the structure, was quantitatively evaluated using single-load-to-failure compressive materials testing of specimens from ten horses. Bone samples from six regions within five proximodistal levels of MC3 were milled into right cylinders and compressed at a strain rate of 0.01 s-1. Diaphyseal MC3 bone material was stiffer, stronger, deformed less to yield and failure, and absorbed more energy to yield, than metaphyseal cortical bone material. Lateral and medial MC3 cortical bone material was stiffer and deformed less to yield and failure, than dorsal and palmar material. This distribution of material properties appears to increase the structural compliance in the sagittal plane, and may serve to enhance the predictability of the strain distribution during normal locomotion, as is provided in other bones by a sagittal curvature.

Animals↗

PubMed1997

Development and validation of a series of three-dimensional finite element models of the equine metacarpus.

Three-dimensional finite element (FE) models of the left metacarpi of five adult horses were developed from quantitative computed tomography data, using the algorithms of Keyak et al. (1990, J Biomed. Engng 12, 389-397). The metacarpi were then equipped with 12 rosette strain gauges and loaded non-destructively in a mechanical testing machine. The bones and the models were loaded in axial compression, with the load evenly distributed across the distal row of carpal bones, and with a point load placed mediad to the sagittal midline, to a load equivalent to three times body weight (-15 kN); and in sagittal four-point bending to -2 kN. Maximum and minimum principal strains from the models were compared with those at the strain gauge rosettes. There were significant (p < 0.001) and strong (0.69 < r < 0.90) correlations between predicted and observed surface principal strains, most often resolving as second- or third-order polynomial relationships. In most cases, particularly at extreme strain magnitudes, the models tended to overestimate the observed strain magnitudes. These data suggest that the models are robust and accurate predictors of surface strains. Validation of these models lends further support for the use of this method of automated three-dimensional FE modeling, with its emphasis on accurate, individualized portrayal of structural geometry and material distribution, in research applications, and specifically for the use of these models in the study of the biology and mechanics of the equine metacarpus.

Animals↗

PubMed1997

Changes in canine cortical and cancellous bone mechanical properties following immobilization and remobilization with exercise.

The purpose of this study was to assess cortical and cancellous bone responses to unilateral limb immobilization and, subsequently, to remobilization with exercise, in a young adult canine model. Right forelimbs of 14 1-2-year old mongrel dogs were immobilized in a non-weight-bearing position by a bandage for 16 weeks. Six control dogs were untreated. At 16 weeks, seven immobilized and three control dogs were euthanized. The remaining seven immobilized dogs began a recovery protocol consisting of 16 weeks of kennel confinement (without the right forelimb bandaged) followed by 16 weeks of treadmill exercise conducted three times per week. These seven dogs and three control dogs were euthanized at 48 weeks. Bone mineral density of the proximal radii was determined with dual-energy X-ray absorptiometry and humeral middiaphyseal cross-sectional areas were determined with computed tomography. Humeri were tested in cranio-caudal three-point bending to failure. Cancellous bone cores from the lateral humeral condyles had wet apparent density determined and were tested to failure in compression. Mechanical properties, bone density, and cross-sectional areas were compared between immobilized (right forelimb), contralateral weight bearing (left forelimb), and control forelimbs with Kruskal-Wallis and post hoc tests. At 16 weeks, bone mineral density, cortical load, yield, and stiffness as well as cancellous bone failure stress, yield stress, and modulus were significantly lower (p < 0.02) for immobilized limbs than control limbs. Immobilized limb cancellous bone mechanical properties were 28%-74% of control values, and cortical bone mechanical properties were 71%-98% of control values. After 32 weeks of remobilization, cortical and cancellous bone mechanical properties were not different from control values except that cortical bone failure stress and modulus were significantly higher (p < 0.01) between remobilized and control limbs. In summary, 16 weeks of forelimb immobilization was associated with significantly lower mechanical properties, and with greater differences in cancellous than cortical bone properties. Mechanical properties were not different from control values after 32 weeks of recovery that included 16 weeks of treadmill exercise.

Absorptiometry, Photon↗

PubMed1997

Pregnancy-associated changes in material properties of the third metacarpal cortical bone in mares.

OBJECTIVE: To investigate the effect of late gestation, age, and parity on material properties of third metacarpal (MCIII) cortical bone in mares. ANIMALS: 8 healthy mares (treatment group) that died or were euthanatized within 24 hours after parturition because of foaling complications and 6 age-matched, healthy, nonpregnant mares (control group). PROCEDURES: After random assignment for mechanical testing and microradiography, the dorsal half of transverse mid-diaphyseal sections of each MCIII bone was divided into lateral, dorsal, and medial regions. Cylinders of bone from each of the 3 regions were tested in compression in a single cycle to failure. Contact microradiographic views were taken of 100-microns-thick sections prepared from methylmethacrylate-embedded transverse dorsal region specimens, which were further divided into periosteal, intracortical, and endosteal regions for assessment of bone mineral density and porosity. RESULTS: Postpartum mares had lower yield strain in the dorsal and medial regions and failure strain in the medial region. Increasing parity was associated with decreasing elastic modulus in the dorsal region and yield stress and failure stress in the lateral region. Age and parity were positively correlated (r = 0.865; P = 0.0001), but significant correlations were not found between treatment group and age or between treatment group and parity. Increasing age and parity were associated with increasing porosity in the periosteal region. CONCLUSIONS AND CLINICAL RELEVANCE: On the basis of the material properties evaluated for MCIII cortical bone in late pregnancy, any increased risk for fractures in mares in late gestation may be related to parity or age or both, and less likely to pregnancy pese.

Aging↗

PubMed1997

Effect of maturation and aging on the histomorphometric and biochemical characteristics of equine superficial digital flexor tendon.

OBJECTIVE: To assess tendon morphology and non-reducible crosslink concentration, and associations of these findings with horse age and previously reported mechanical and ultrasonographic findings. SAMPLE POPULATION: Superficial digital flexor tendon samples were obtained from 23 horses aged 2 to 23 years. The tendons had undergone ultrasonography and were submitted to biomechanical testing in the physiologic range prior to sample acquisition. PROCEDURE: Samples were sectioned in a transverse plane; then dorsal, palmar, central, lateral, and medial regions were evaluated for fascicle cross-sectional area (CSA), septal width, and vessel density (the product of vessel numbers and vessel CSA per field). Contiguous samples were analyzed for collagen crosslinking. RESULTS: Central fascicles were significantly larger than fascicles in other tendon regions. Fascicle CSA decreased significantly with increasing age. Because total tendon CSA is unrelated to increasing age, fascicle numbers appeared to increase with increasing age. Regional or age effects on septal width were not found. There was no age or regional effect on vessel numbers, density, or fractional area. Fascicle CSA was positively correlated with total tendon CSA; fascicle CSA was negatively correlated with elastic modulus. Hydroxypiridinium concentration tended to increase with increasing horse age; this effect was associated with a positive correlation between hydroxypiridinium values and elastic modulus. CONCLUSIONS: Equine superficial digital flexor tendon undergoes an increase in structural organization and an increase in nonreducible crosslinks with maturation and aging. These changes are associated with an increase in elastic modulus.

Aging↗