Effects of immobilization followed by remobilization on mineral density, histomorphometric features, and formation of the bones of the metacarpophalangeal joint in horses

A Systematic Review of Animal Models of Disuse-Induced Bone Loss

OBJECTIVE

Several different animal models are used to study disuse-induced bone loss. This systematic review aims to give a comprehensive overview of the animal models of disuse-induced bone loss and provide a detailed narrative synthesis of each unique animal model.

METHODS

PubMed and Embase were systematically searched for animal models of disuse from inception to November 30, 2019. In addition, Google Scholar and personal file archives were searched for relevant publications not indexed in PubMed or Embase. Two reviewers independently reviewed titles and abstracts for full-text inclusion. Data were extracted using a predefined extraction scheme to ensure standardization.

RESULTS

1964 titles and abstracts were screened of which 653 full-text articles were included. The most common animal species used to model disuse were rats (59%) and mice (30%). Males (53%) where used in the majority of the studies and genetically modified animals accounted for 7%. Twelve different methods to induce disuse were identified. The most frequently used methods were hindlimb unloading (44%), neurectomy (15%), bandages and orthoses (15%), and botulinum toxin (9%). The median time of disuse was 21 days (quartiles: 14 days, 36 days) and the median number of animals per group subjected to disuse was 10 (quartiles: 7, 14). Random group allocation was reported in 43% of the studies. Fewer than 5% of the studies justified the number of animals per group by a sample size calculation to ensure adequate statistical power.

CONCLUSION

Multiple animal models of disuse-induced bone loss exist, and several species of animals have successfully been studied. The complexity of disuse-induced bone loss warrants rigid research study designs. This systematic review emphasized the need for standardization of animal disuse research and reporting.

Sprint Exercise of Juvenile Animals Does Not Impact Cartilage Glycosaminoglycan or Synovial Fluid Neopeptide Collagenase Cleavage of Type I and II Collagen Content

Short sprints performed during growth can increase bone strength, mineral density, and cortical widths, but their impact on joint health is not fully understood. Some studies have found joints of young animals are damaged by forced sprints, while others found confinement hindered joint development. This study aimed to determine the impact of short sprints on synovial fluid neopeptide collagenase cleavage of type I and II collagen (C1,2C) and cartilage glycosaminoglycan (GAG) content. Calves were used as a model for young horses in this terminal study. Twenty-four Holstein bull calves were assigned to treatment groups of 1, 3, 5, or 0 days/week of sprinting (n = 6). A sprint consisted of an individual calf being walked from its stall and down a 71-m concrete aisle, at the end of which the calf was released, and encouraged to sprint towards the barn. Calves remained on treatment for 6 weeks and were euthanized on day 42. Immediately posteuthanasia synovial fluid was sampled from the middle carpal joint and cartilage discs sampled from 9 locations on the carpal bones. Analysis was performed in SAS 9.4 with fixed effects of treatment and bone. There were no differences in C1,2C or GAG concentrations between treatments (P = .73 and P = .96, respectively), but there was a difference between individual carpal bone GAG concentration (P = .03). Short sprints for 6 weeks during growth did not impact middle carpal joint C1,2C or carpal bone GAG content, and should be permitted given the benefits to bone health.

Surgical Repair of a Unicortical Condylar Fracture in a Thoroughbred Racehorse Using a Bioabsorbable Screw

Surgical repair of unicortical fractures of the distal condyles of the third metacarpal/metatarsal bones (MCIII/MTIII) has been described. In the present case, a bioabsorbable screw was used to stabilize a unicortical fracture in the palmar aspect of the medial condyle of MCIII in a National Hunt Thoroughbred racehorse. The clinical, radiographic, and magnetic resonance imaging findings before and after surgery were recorded. Eighteen weeks after surgery, the lameness had resolved and the bone surrounding the fracture had recovered its normal architecture. One year after surgery, the horse was in training, showed no recurrence of the primary lesion and was considered a "racing prospect" by the trainer. The use of a bioabsorbable screw in this case was associated with a successful outcome and is worthy of further investigation.

Physiologic effects of long-term immobilization of the equine distal limb

OBJECTIVE

To describe the effects of distal limb immobilization and remobilization in the equine metacarpophalangeal joint.

STUDY DESIGN

Randomized, prospective experimental study.

ANIMALS

Eight healthy, skeletally mature horses.

METHODS

One forelimb of each horse was immobilized in a fiberglass cast for 8 weeks; this was followed by 12 weeks of a treadmill-based training program after the cast had been removed. Clinical examinations, radiography, computed tomography (CT), nuclear scintigraphy, MRI, and histomorphometry were used to examine the third metacarpal (MC3), proximal phalanx, proximal sesamoid bones, and associated soft tissues in each horse. Serum and synovial fluid were collected for biomarker analyses.

RESULTS

Distal limb immobilization resulted in persistent lameness (P < .001), effusion (P = .002), and a decreased range of motion (P = .012) as well as radiographically visible fragments (P = .036) in the cast forelimb. Bone density was decreased (P < .001) in MC3 according to CT, and trabecular bone fluid was increased (P < .001) according to MRI in the cast forelimb. The cast forelimbs had a change (P = .009) in the appearance of the deep digital flexor tendon according to MRI immediately after removal of the cast. Numerous clinical, radiographic, CT, and MR abnormalities were visible at the end of the study period.

CONCLUSION

Eights weeks of cast immobilization induced changes in bone, cartilage, and periarticular soft tissues that were not reversed after 12 weeks of remobilization.

CLINICAL SIGNIFICANCE

Cast application should be used judiciously in horses with musculoskeletal injuries, balancing appropriate stabilization with potential morbidity secondary to cast placement.

Calves, as a model for juvenile horses, need only one sprint per week to experience increased bone strength

Previous research has determined that maintaining young animals in stalls is detrimental to their bone health, while the addition of 50 to 82-m sprints 5 d/week aids in counteracting the reduction of bone strength from confinement. The current research aims to determine if 1 or 3 d/week of sprinting affords the same benefits to bone as 5 d/week of sprinting compared to animals confined with no sprinting. Twenty-four Holstein bull calves were obtained from the Michigan State University Dairy Cattle Teaching and Research Center. At 9 wk of age, calves were randomly assigned to treatments of 1, 3, or 5 d/week of sprint exercise, or to the confined control group sprinted 0 d/week. Each treatment had 6 calves. Individual sprinting bouts included a single sprint down a 71-m concrete aisle. For the duration of the 6-wk study, calves were housed at the MSU Beef Cattle Teaching and Research Center in stalls which afforded calves room to stand, lay down, and turn around. Serum was collected weekly via jugular venipuncture to obtain concentrations of osteocalcin (OC) and C-telopeptide crosslaps of type I collagen (CTX-1)—markers of bone formation and degradation, respectively. Sprints were videotaped weekly to determine stride frequency and sprint velocity. On day 42, calves were humanely euthanized at the Michigan State University Meat Lab and both front limbs were immediately harvested. Computed tomography scans and mechanical testing were performed on the left fused third and fourth metacarpal bones. Serum OC concentration was greatest for calves sprinted 5 d/week (P < 0.001). Calves sprinted 5 d/week had both greater stride frequency (P < 0.05) and lower sprint velocity (P < 0.05). All exercise treatments experienced greater dorsal cortical widths compared to control animals (P < 0.01). Through mechanical testing, fracture forces of all sprinting treatments were determined to be greater than the control treatment (P < 0.02). Results from this study support that sprinting 1, 3, or 5 d/week during growth can increase bone health and cause favorable alterations in bone markers. While all exercise treatments had over a 20% increase to fracture force, calves sprinted 1 d/week sprinted only 426 m over the 6-wk study and still experienced over a 20% increase in bone strength compared to confined calves. This study demonstrates the remarkably few strides at speed needed to enhance bone strength and emphasizes the danger to skeletal strength if sprinting opportunities are not afforded.

Development of an equine groove model to induce metacarpophalangeal osteoarthritis: a pilot study on 6 horses

The aim of this work was to develop an equine metacarpophalangeal joint model that induces osteoarthritis that is not primarily mediated by instability or inflammation. The study involved six Standardbred horses. Standardized cartilage surface damage or “grooves” were created arthroscopically on the distal dorsal aspect of the lateral and medial metacarpal condyles of a randomly chosen limb. The contralateral limb was sham operated. After 2 weeks of stall rest, horses were trotted 30 minutes every other day for 8 weeks, then evaluated for lameness and radiographed. Synovial fluid was analyzed for cytology and biomarkers. At 10 weeks post-surgery, horses were euthanized for macroscopic and histologic joint evaluation. Arthroscopic grooving allowed precise and identical damage to the cartilage of all animals. Under the controlled exercise regime, this osteoarthritis groove model displayed significant radiographic, macroscopic, and microscopic degenerative and reactive changes. Histology demonstrated consistent surgically induced grooves limited to non-calcified cartilage and accompanied by secondary adjacent cartilage lesions, chondrocyte necrosis, chondrocyte clusters, cartilage matrix softening, fissuring, mild subchondral bone inflammation, edema, and osteoblastic margination. Synovial fluid biochemistry and cytology demonstrated significantly elevated total protein without an increase in prostaglandin E2, neutrophils, or chondrocytes. This equine metacarpophalangeal groove model demonstrated that standardized non-calcified cartilage damage accompanied by exercise triggered altered osteochondral morphology and cartilage degeneration with minimal or inefficient repair and little inflammatory response. This model, if validated, would allow for assessment of disease processes and the effects of therapy.

A review of translational animal models for knee osteoarthritis

Knee osteoarthritis remains a tremendous public health concern, both in terms of health-related quality of life and financial burden of disease. Translational research is a critical step towards understanding and mitigating the long-term effects of this disease process. Animal models provide practical and clinically relevant ways to study both the natural history and response to treatment of knee osteoarthritis. Many factors including size, cost, and method of inducing osteoarthritis are important considerations for choosing an appropriate animal model. Smaller animals are useful because of their ease of use and cost, while larger animals are advantageous because of their anatomical similarity to humans. This evidence-based review will compare and contrast several different animal models for knee osteoarthritis. Our goal is to inform the clinician about current research models, in order to facilitate the transfer of knowledge from the "bench" to the "bedside."

The horse as a model of naturally occurring osteoarthritis

Osteoarthritis (OA) is an important cause of pain, disability and economic loss in humans, and is similarly important in the horse. Recent knowledge on post-traumatic OA has suggested opportunities for early intervention, but it is difficult to identify the appropriate time of these interventions. The horse provides two useful mechanisms to answer these questions: 1) extensive experience with clinical OA in horses; and 2) use of a consistently predictable model of OA that can help study early pathobiological events, define targets for therapeutic intervention and then test these putative therapies. This paper summarises the syndromes of clinical OA in horses including pathogenesis, diagnosis and treatment, and details controlled studies of various treatment options using an equine model of clinical OA.

The OARSI histopathology initiative - recommendations for histological assessments of osteoarthritis in the horse

OBJECTIVE

Equine models of osteoarthritis (OA) have been used to investigate pathogenic pathways of OA and evaluate therapeutic candidates for naturally occurring equine OA which is a significant clinical disease in the horse. This review focuses on the macroscopic and microscopic criteria for assessing naturally occurring OA in the equine metacarpophalangeal joint as well as the osteochondral fragment-exercise model of OA in the equine middle carpal joint.

METHODS

A review was conducted of all published OA studies using horses and the most common macroscopic and microscopic scoring systems were summarized. Recommendations regarding methods of OA assessment in the horse have been made based on published studies.

RESULTS

A modified Mankin scoring system is recommended for semi-quantitative histological assessment of OA in horses due to its already widespread use and similarity to other scoring systems. Recommendations are also provided for histological scoring of synovitis and macroscopic lesions of OA as well as changes in the calcified cartilage and subchondral bone of naturally occurring OA.

CONCLUSIONS

The proposed system for assessment of equine articular tissues provides a useful method to quantify OA change. It is believed that addition of quantitative tracing onto plastic and macroscopic measurement as recently described would be an improvement for overall assessment of articular cartilage change.

Assessment of the mineral density and mineral content of the equine third metacarpal and first phalanx bone by dual energy x-ray absorptiometry

In the first part of this methodological study eleven metacarpi of 9 skeletally normal horses were examined from 4 directions by dual energy x-ray absorptiometry (DXA). The differences between the dorsopalmar-palmarodorsal and lateromedial-mediolateral (opposite sites) bone mineral density (BMD) values were found to be nonsignificant. In the second part of the study the precision of the Norland XR-26 densitometer was tested by measuring 34 metacarpal bones and 34 proximal phalanges, each of them three times, from a single direction. The difference between the individual measurements of the first phalanges and of the metacarpal bones originating from the right or the left side of the same horse were not significant, nor did the age or breed have a significant effect on BMD or bone mineral content (BMC). However, both BMD and BMC are greater in the metacarpal bones than in the proximal phalanges and are higher in geldings than in mares or to stallions, while the BMD or BMC values of mares and stallions did not differ from each other significantly. These data point to the necessity of further BMD studies in a higher number of patients.

Correlation of signal attenuation-based quantitative magnetic resonance imaging with quantitative computed tomographic measurements of subchondral bone mineral density in metacarpophalangeal joints of horses

OBJECTIVE

To evaluate the ability of signal attenuation-based quantitative magnetic resonance imaging (QMRI) to estimate subchondral bone mineral density (BMD) as assessed via quantitative computed tomography (QCT) in osteoarthritic joints of horses.

SAMPLE POPULATION

20 metacarpophalangeal joints from 10 horse cadavers.

PROCEDURES

Magnetic resonance (MR) images (dorsal and transverse T1-weighted gradient recalled echo [GRE] and dorsal T2*-weighted GRE fast imaging employing steady-state acquisition [T2*-FIESTA]) and transverse single-slice computed tomographic (CT) images of the joints were acquired. Magnetic resonance signal intensity (SI) and CT attenuation were quantified in 6 regions of interest (ROIs) in the subchondral bone of third metacarpal condyles. Separate ROIs were established in the air close to the joint and used to generate corrected ratios and SIs. Computed tomographic attenuation was corrected by use of a calibration phantom to obtain a K(2)HPO(4)-equivalent density of bone. Correlations between QMRI performed with different MR imaging sequences and QCT measurements were evaluated. The intraobserver repeatability of ROI measurements was tested for each modality.

RESULTS

Measurement repeatability was excellent for QCT (R(2) = 98.3%) and QMRI (R(2) = 98.8%). Transverse (R(2) = 77%) or dorsal (R(2) = 77%) T1-weighted GRE and QCT BMD measurements were negatively correlated, as were dorsal T2*-FIESTA and QCT (R(2) = 80%) measurements. Decreased bone SI during MR imaging linearly reflected increased BMD.

CONCLUSIONS AND CLINICAL RELEVANCE

Results of this ex vivo study suggested that signal attenuation-based QMRI was a reliable, clinically applicable method for indirect estimation of subchondral BMD in osteoarthritic metacarpophalangeal joints of horses.

Distal limb cast sores in horses: risk factors and early detection using thermography

REASONS FOR PERFORMING STUDY

There is a lack of evidence-based data on the prevalence, outcome and risk factors of distal limb cast sores, and no objective tool has been described for the early detection of cast sores.

OBJECTIVES

To investigate the prevalence, location, outcome and risk factors of cast sores after application of a distal limb cast and to determine whether static thermography of the cast is a valuable tool for the assessment of sores.

METHODS

A prospective study was conducted on horses treated with a distal limb cast. At each cast removal, cast sores were graded as superficial sores (SS), deep dermal sores (DS) or full thickness skin ulcerations (FS). In several cases, a thermographic evaluation of the cast was performed immediately prior to removal and differences in temperature (AT) between the coolest point of the cast and 2 cast regions predisposed for sore development (dorsoproximal mc/mtIII and palmar/plantar fetlock) were calculated.

RESULTS

Mean +/- s.d. total casting time of 70 horses was 31 +/- 18 days. Overall, 57 legs (81%) developed at least SS. Twenty-four legs (34%) ultimately developed DS and one horse had an FS. Multivariable analysis showed that the severity of sores was positively associated with increasing age (OR: 1.111, P = 0.028), a normal (vs. swollen) limb (OR: 3387, P = 0.023) and an increase in total casting time (OR per week: 1.363, P = 0.002). The thermographic evaluation (35 casts) revealed that the severity of sores was positively associated with increasing deltaT (OR: 2.100, P = 0.0005). The optimal cut-off values for the presence of SS and DS were set at, respectively, deltaT = 23 and 43 degrees C.

CONCLUSION AND POTENTIAL RELEVANCE

Distal limb cast is a safe coaptation technique with increasing risk of developing sores with time. Thermography is a valuable and rapid clinical tool to monitor the development of cast sores.

Pharmacological effects of tiludronate in horses after long-term immobilization

INTRODUCTION

Tiludronate, a bisphosphonate, has recently been introduced in veterinary medicine to treat orthopedic conditions in the horse. This study was designed to evaluate its effects on biochemical biomarkers of bone metabolism and on bone density and structure in an experimental model of disuse osteoporosis induced by cast application in horses.

METHODS

Two groups of eight horses were immobilized during 8 weeks. The first group (P-group) received a placebo, and the second group (T-group) received tiludronate 1 mg/kg by slow IV infusion. Both treatments were administered twice, 28 days apart. Immobilization consisted of stall rest with the left forelimb packed in a fiberglass cast. It was followed by a 4-week remobilization period and an 8-week standardized training protocol. One biomarker of bone resorption, the C-telopeptides of type I collagen cross-links (CTX-1) and one biomarker of bone formation, the bone isoenzyme of alkaline phosphatase (bone ALP), were assessed. Metacarpus III (MCIII) bone mineral density (BMD) and speed of sound (SOS) were evaluated respectively by dual energy X-ray absorptiometry (DEXA) and quantitative ultrasonography (QUS). Lameness was regularly assessed during the remobilization and training periods. Group- and time-related effects were tested by analysis of variance on repeated measurements.

RESULTS

A rapid, transient and significant decrease in CTX-1 concentration was seen after each treatment in the T-group only. No significant differences between groups were seen in the evolution of bone ALP activity. At the end of the experiment, the loss of MCIII BMD measured by DEXA in the immobilized limb was significantly less in the T-group than in the P-group. The MCIII SOS measured by QUS did not significantly vary within or between groups throughout the study.

DISCUSSION AND CONCLUSIONS

Tiludronate was found to significantly reduce bone resorption during immobilization, as well as to prevent long-term osteopenia in the immobilized limb. Disuse osteopenia did not affect the lateral superficial cortex of MCIII.

The response of bone, articular cartilage and tendon to exercise in the horse

Horses can gallop within hours of birth, and may begin training for athletic competition while still growing. This review cites studies on the effects of exercise on bone, tendon and articular cartilage, as detected by clinical and research imaging techniques, tissue biochemical analysis and microscopy of various kinds. For bone, alterations in bone mineral content, mineral density and the morphology of the mineralized tissue are the most common end-points. Apparent bone density increases slightly after athletic training in the cortex, but substantially in the major load paths of the epiphyses and cuboidal bones, despite the lower material density of the new bone, which is deposited subperiosteally and on internal surfaces without prior osteoclastic resorption. With training of greater intensity, adaptive change is supervened by patho-anatomical change in the form of microdamage and frank lesions. In tendon, collagen fibril diameter distribution changes significantly during growth, but not after early training. The exact amount and type of protracted training that does cause reduction in mass average diameter (an early sign of progressive microdamage) have not been defined. Training is associated with an increase in the cross-sectional area of some tendons, possibly owing to slightly greater water content of non-collagenous or newly synthesized matrix. Early training may be associated with greater thickness of hyaline but not calcified articular cartilage, at least in some sites. The age at which adaptation of cartilage to biomechanical influences can occur may thus extend beyond very early life. However, cartilage appears to be the most susceptible of the three tissues to pathological alteration. The effect of training exercise on the anatomical or patho-anatomical features of connective tissue structures is affected by the timing, type and amount of natural or imposed exercise during growth and development which precedes the training.

Ex Vivo Strength Comparison of Bioabsorbable Tendon Plates and Bioabsorbable Suture in a 3-Loop Pulley Pattern for Repair of Transected Flexor Tendons from Horse Cadavers

OBJECTIVE

To test the failure strength and energy of 2 bioabsorbable implants applied to transected deep digital flexor tendons (DDFT) from adult horses.

STUDY DESIGN

Ex vivo biomechanical experiment.

SAMPLE POPULATION

Twelve pairs of deep digital flexor tendons harvested from the forelimbs of fresh equine cadavers.

METHODS

Poly-L-lactic acid tendon plates were custom manufactured for application to the cylindrical surface of an adult equine deep digital flexor tendon. Twelve pairs of DDFTs were transected 2 cm distal to the insertion of the distal check ligament of the deep digital flexor tendon. One tendon of each pair was randomly selected for repair with a biodegradable plate or a 3-loop pulley method. Size 2 polydioxanone suture was used in both repairs. Repairs were tested in tension to failure, with peak force (PF) and total energy (TE) at repair failure recorded in Newtons (N) and Joules (J), respectively. A paired t-test was used for statistical evaluation with a significant level set at P< or = .05.

RESULTS

Mean+/-SD PF for failure of plated tendons (1507.08+/-184.34 N) was significantly greater than for sutured tendons (460.86+/-60.93 N). TE was also significantly greater for failure of plated tendons versus sutured tendons.

CONCLUSIONS

Plate fixation of transected cadaver DDFTs appear to have superior immediate failure strength than 3-loop pulley repairs.

CLINICAL RELEVANCE

Whereas in vivo testing is required, a bioabsorbable tendon plate may provide initial increased strength to support tendon healing and decrease external coaptation requirements.

Evaluation of subchondral bone mineral density associated with articular cartilage structure and integrity in healthy equine joints with different functional demands

OBJECTIVE

To determine and correlate subchondral bone mineral density and overlying cartilage structure and tensile integrity in mature healthy equine stifle (low magnitude loading) and metacarpophalangeal (high magnitude loading) joints.

ANIMALS

8 healthy horses, 2 to 3 years of age.

PROCEDURE

Osteochondral samples were acquired from the medial femoral condyle (FC) and medial trochlear ridge (TR) of the stifle joint and from the dorsal (MC3D) and palmar (MC3P) aspects of the distal medial third metacarpal condyles of the metacarpophalangeal joint. Articular cartilage surface fibrillation (evaluated via India ink staining) and tensile biomechanical properties were determined. The volumetric bone mineral density (vBMD) of the underlying subchondral plate was assessed via dual-energy x-ray absorptiometry.

RESULTS

Cartilage staining (fibrillation), tensile moduli, tensile strength, and vBMD were greater in the MC3D and MC3P locations, compared with the FC and TR locations, whereas tensile strain at failure was less in MC3D and MC3P locations than FC and TR locations. Cartilage tensile moduli correlated positively with vBMD, whereas cartilage staining and tensile strain at failure correlated negatively with vBMD.

CONCLUSIONS AND CLINICAL RELEVANCE

In areas of high joint loading, the subchondral bone had high vBMD and the articular cartilage surface layer had high tensile stiffness but signs of structural wear (fibrillation and low failure strain). The site-dependent variations and relationships in this study support the concept that articular cartilage and subchondral bone normally adapt to physiologic loading in a coordinated way.

Problems in quantifying bone response to exercise in horses: a review

Detecting changes in bone during growth, training, rest from competition (spelling), and disease in horses requires imaging techniques that have a high level of accuracy and precision. Currently, most imaging techniques used in horses do not possess such characteristics and are more suitable for detecting end-stage disease than subtle changes. Some are incapable of detecting changes in bone size. Non-planar techniques should be used for estimating or determining bone strength. This review outlines available imaging techniques and shows why cross-sectional procedures are required to accurately estimate bone strength. If these can be validated and improved for use in the standing horse, serial examination can be used to show the magnitude of changes in bone strength that occur during training or varying management regimens. Such knowledge can then be used to improve training and spelling regimens for equine athletes, hopefully resulting in a reduction in racing or athletic injury.