Comparative anatomical measurements of osseous structures in the ovine and human knee

A wear model to predict damage of reconstructed ACL

Impingement with surrounding tissues is a major cause of failure of anterior cruciate ligament reconstruction. However, the complexity of the knee kinematics and anatomical variations make it difficult to predict the occurrence of contact and the extent of the resulting damage. Here we hypothesise that a description of wear between the reconstructed ligament and adjacent structures captures the in vivo damage produced with physiological loadings. To test this, we performed an in vivo study on a sheep model and investigated the role of different sources of damage: overstretching, excessive twist, excessive compression, and wear. Seven sheep underwent cranial cruciate ligament reconstruction using a tendon autograft. Necropsy observations and pull-out force measurements performed postoperatively at three months showed high variability across specimens of the extent and location of graft damage. Using 3D digital models of each stifle based on X-ray imaging and kinematics measurements, we determined the relative displacements between the graft and the surrounding bones and computed a wear index describing the work of friction forces underwent by the graft during a full flexion-extension movement. While tensile strain, angle of twist and impingement volume showed no correlation with pull-out force (ρ = -0.321, p = 0.498), the wear index showed a strong negative correlation (r = -0.902, p = 0.006). Moreover, contour maps showing the distribution of wear on the graft were consistent with the observations of damage during the necropsy. These results demonstrate that wear is a good proxy of graft damage. The proposed wear index could be used in implant design and surgery planning to minimise the risk of implant failure. Its application to sheep can provide a way to increase preclinical testing efficiency.

Subchondral Drilling Independent of Drill Hole Number Improves Articular Cartilage Repair and Reduces Subchondral Bone Alterations Compared With Debridement in Adult Sheep

BACKGROUND

Subchondral drilling is an established marrow stimulation technique for small cartilage defects, but whether drilling is required at all and if the drill hole density affects repair remains unclear.

HYPOTHESES

Osteochondral repair is improved when the subchondral bone is perforated by a higher number of drill holes per unit area, and drilling is superior to defect debridement alone.

STUDY DESIGN

Controlled laboratory study.

METHODS

Rectangular full-thickness chondral defects (4 × 8 mm) were created in the trochlea of adult sheep (N = 16), debrided down to the subchondral bone plate without further treatment as controls (no treatment; n = 7) or treated with either 2 or 6 (n = 7 each) subchondral drill holes (diameter, 1.0 mm; depth, 10.0 mm). Osteochondral repair was assessed at 6 months postoperatively by standardized (semi-)quantitative macroscopic, histological, immunohistochemical, biochemical, and micro-computed tomography analyses.

RESULTS

Compared with defect debridement alone, histological overall cartilaginous repair tissue quality (P = .025) and the macroscopic aspect of the adjacent cartilage (P≤ .032) were improved after both drilling densities. Only drilling with 6 holes increased type 2 collagen content in the repair tissue compared with controls (P = .038). After debridement, bone mineral density was significantly decreased in the subchondral bone plate (P≤ .015) and the subarticular spongiosa (P≤ .041) compared with both drilling groups. Debridement also significantly increased intralesional osteophyte sectional area compared with drilling (P≤ .034). No other differences in osteochondral repair existed between subchondral drilling with 6 or 2 drill holes.

CONCLUSION

Subchondral drilling independent of drill hole density significantly improves structural cartilage repair compared with sole defect debridement of full-thickness cartilage defects in sheep after 6 months. Subchondral drilling also leads to a better reconstitution of the subchondral bone compartment below the defects. Simultaneously, drilling reduced the formation of intralesional osteophytes caused by osseous overgrowth compared with debridement.

CLINICAL RELEVANCE

These results have important clinical implications, as they support subchondral drilling independent of drill hole number but discourage debridement alone for the treatment of small cartilage defects. Clinical studies are warranted to further quantify the effects of subchondral drilling in similar settings.

Anatomical features for an adequate choice of the experimental animal model in biomedicine: III. Ferret, goat, sheep, and horse

The anatomical characteristics of each of the many species today employed in biomedical research are very important when selecting the correct animal model(s), especially for conducting translational research. In previous papers, these features have been considered for fish (D'Angelo et al. Ann. Anat, 2016, 205:75), the most common laboratory rodents, rabbits, and pigs (Lossi et al. 2016). I here follow this line of discussion by dealing with the importance of proper knowledge of ferrets, goats, sheep, and horses' main anatomical features in translational research.

Correlation of the Histological ICRS II Score and the 3D MOCART Score for the Analysis of Aged Osteochondral Regenerates in a Large Animal Model

OBJECTIVE

Reliable outcome measures are essential to predict the success of cartilage repair techniques. Histology is probably the gold standard, but magnetic resonance imaging (MRI) has the potential to decrease the need for invasive histological biopsies. The 3D magnetic resonance observation of cartilage repair tissue (MOCART) score is a reliable yet elaborate tool. Moreover, literature is controversial concerning the correlation of histology and MRI.

DESIGN

To test the applicability of the International Cartilage Regeneration and Joint Preservation Society (ICRS) II and MOCART 3D score for the evaluation of aged osteochondral regenerates in a large animal model, and to identify correlating histological and MRI parameters. Osteochondral defects in medial femoral condyles of n = 12 adult sheep were reconstructed with biodegradable bilayer implants. About 19.5 months postoperation, n = 10 joints were analyzed with MRI (3D MOCART score). Histological samples were analyzed using the ICRS II score; both pre- and post-training. The intraclass correlation coefficient, the inter-rater reliability, and the 95% confidence interval were calculated. Matching histological and MRI parameters were tested for correlation.

RESULTS

We found a statistically significant correlation of all histological parameters. MRI parameters reflecting "overall" assessments had very strong inter-rater correlations. Statistically significant strong correlations were found for the MRI parameters defect filling, cartilage interface, bone interface, and surface. For defect overall (MRI) and overall assessment (ICRS II), we found a significant yet mild correlation.

CONCLUSIONS

The ICRS II and the 3D MOCART score are applicable to aged osteochondral regenerates. Prior training on the scoring systems is essential. Select MRI and histological parameters correlate; however, the only statistically significant correlation was found for overall assessment.

OA foundations - experimental models of osteoarthritis

Osteoarthritis (OA) is increasingly recognised as a disease of diverse phenotypes with variable clinical presentation, progression, and response to therapeutic intervention. This same diversity is readily apparent in the many animal models of OA. However, model selection, study design, and interpretation of resultant findings, are not routinely done in the context of the target human (or veterinary) patient OA sub-population or phenotype. This review discusses the selection and use of animal models of OA in discovery and therapeutic-development research. Beyond evaluation of the different animal models on offer, this review suggests focussing the approach to OA-animal model selection on study objective(s), alignment of available models with OA-patient sub-types, and the resources available to achieve valid and translatable results. How this approach impacts model selection is discussed and an experimental design checklist for selecting the optimal model(s) is proposed. This approach should act as a guide to new researchers and a reminder to those already in the field, as to issues that need to be considered before embarking on in vivo pre-clinical research. The ultimate purpose of using an OA animal model is to provide the best possible evidence if, how, when and where a molecule, pathway, cell or process is important in clinical disease. By definition this requires both model and study outcomes to align with and be predictive of outcomes in patients. Keeping this at the forefront of research using pre-clinical OA models, will go a long way to improving the quality of evidence and its translational value.

Ultrasound assessment of sheep stifle joint undergone lipopolysaccharide-induced synovitis

Abstract Synovitis can be induced in animals through the application of bacterial wall lipopolysaccharide and has similar signs to naturally-occurring synovitis. Several studies have been using the sheep species as an experimental model to understand osteoarticular diseases of the femorotibiopatellar (FTP) joint in humans. There are echographic studies on the standardization of normality of the femorotibiopatellar joint in sheep. However, there is a gap in the literature for changes such as acute synovitis. The objective was to serially describe the sonographic aspects of the synovitis process induced by intra-articular infiltration of Escherichia coli (E. coli) lipopolysaccharide in the femorotibiopatellar joint of sheep. Twelve healthy crossbred sheep (Santa Inês x Dorper) were used. Induction of synovitis was performed only in the right FTP joints, which were serially evaluated using ultrasound examination at baseline moment (M0) and 12 (M12), 24 (M24), 48 (M48), 72 (M72), and 120 (M120) hours after lipopolysaccharide infiltration for synovitis induction. Intra-articular application of E. coli lipopolysaccharide resulted in one or more echographic signs of synovitis (increased synovial fluid volume, folding of the synovial membrane, and cellularity in the joint cavity), which were identified early, 12 hours after inoculation, and regressed over the evaluated times (p=0.0001) until disappearing after 120 hours of inoculation.

Ultrassonografia da articulação femorotibiopatelar em ovinos submetidos à indução de sinovite por lipopolissacarídeos

Resumo A sinovite pode ser induzida em animais por meio da aplicação de lipopolissacarídeo de parede bacteriana, e apresenta sinais semelhantes à sinovite causada de forma natural. Diversos estudos têm sido realizados utilizando a espécie ovina como modelo experimental na compreensão das enfermidades osteoarticulares da articulação femorotibiopatelar (FTP) em humanos. Existem estudos ecográficos quanto a padronização da normalidade da articulação femorotibiopatelar em ovinos. Porém, para as alterações, como a sinovite aguda há lacuna na literatura. Objetivou-se descrever, de forma seriada, os aspectos ultrassonográficos do processo de sinovite induzida por infiltração intra-articular de lipopolissacarídeo de Escherichia coli (E. coli) na articulação femorotibiopatelar de ovinos. Foram utilizados 12 ovinos mestiços (Santa Inês x Dorper), hígidos. A indução da sinovite foi realizada apenas nas articulações FTP direitas, as quais foram avaliadas, por meio do exame ultrassonográfico de forma seriada, nos momentos basal (M0) e às 12 (M12), 24 (M24), 48 (M48), 72 (M72) e 120 (M120) horas após a infiltração com lipopolissacarídeo para a indução de sinovite. A aplicação intra-articular de lipopolissacarídeo de E. coli resultou em um ou mais sinais ecográficos de sinovite (aumento de volume do fluido sinovial, pregueamento da membrana sinovial e celularidade na cavidade articular), os quais foram identificados precocemente, 12 horas após a inoculação, e regrediram ao longo dos tempos avaliados (p=0,0001), até desaparecerem após 120 horas da inoculação.

Morphological and morphometric features of knee joint in wild boar (Sus scrofa)

In the study, it was aimed to reveal the structure of the knee joint anatomically and morphometrically in the wild pig known as the ancestor of the domestic pig. In the study, the left and right knee joints of mature 10 wild boars were used as material. For this purpose, the materials were fixed with 10% formaldehyde solution. Macroanatomical and morphometrical examinations of bones, menisci and ligaments involved in joint formation were performed after fixation. Trochlea and condyles of femur were examined, and various measurements were made. Trochlear labia were found to be the same size, and the condyles did not show a significant difference in size. The shape of lateral condyle of the tibia was trapezoid, and the shape of medial condyle was triangular. Moreover, the lateral intercondylar tubercule was higher according to the medial one. The presence of a shallow groove on the tibial tuberosity was detected. It was found that the width difference between apex and base was more pronounced on the anterior and lateral surface of the patella. Joint surface of the fibula was found to be flat in all materials. The menisci were 'C' shape, but the medial meniscus is more convex than the lateral one. It was observed that the outer edges were thick, while the inner edges were thin. Ligaments of the knee joint were well developed. When the findings of the study were compared with the literature, domestication seemed to have no significant effect in terms of the morphologic properties of the knee joint of wild boar.

Comparative anatomy and morphology of the knee in translational models for articular cartilage disorders. Part I: Large animals

BACKGROUND

The human knee is a complex joint, and affected by a variety of articular cartilage disorders. Large animal models are critical to model the complex disease mechanisms affecting a functional joint. Species-dependent differences highly affect the results of a pre-clinical study and need to be considered, necessitating specific knowledge not only of macroscopic and microscopic anatomical and pathological aspects, but also characteristics of their individual gait and joint movements.

METHODS

Literature search in Pubmed.

RESULTS AND DISCUSSION

This narrative review summarizes the most relevant anatomical structural and functional characteristics of the knee (stifle) joints of the major translational large animal species, comprising dogs, (mini)pigs, sheep, goats, and horses in comparison with humans. Specific characteristics of each species, including kinematical gait parameters are provided. Considering these multifactorial dimensions will allow to select the appropriate model for answering the research questions in a clinically relevant fashion.

Systematic Postoperative Assessment of a Minimally-Invasive Sheep Model for the Treatment of Osteochondral Defects

To assess the clinical course of a sheep stifle joint model for osteochondral (OC) defects, medial femoral condyles (MFC) were exposed without patella luxation using medial parapatellar skin (3–4 cm) and deep incisions (2–3 cm). Two defects (7 mm diameter; 10 mm depth; OC punch) were left empty or refilled with osteochondral autologous transplantation cylinders (OATS) and explanted after six weeks. Incision-to-suture time, anesthesia time, and postoperative wound or impairment scores were compared to those in sham-operated animals. Implant performance was assessed by X-ray, micro-computed tomography, histology, and immunohistology (collagens 1, 2; aggrecan). There were no surgery-related infections or patellar luxations. Operation, anesthesia, and time to complete stand were short (0.5, 1.4, and 1.5 h, respectively). The wound trauma score was low (0.4 of maximally 4; day 7). Empty-defect and OATS animals reached an impairment score of 0 significantly later than sham animals (7.4 and 4.0 days, respectively, versus 1.5 days). Empty defects showed incomplete healing and dedifferentiation/heterotopic differentiation; OATS-filled defects displayed advanced bone healing with remaining cartilage gaps and orthotopic expression of bone and cartilage markers. Minimally-invasive, medial parapatellar surgery of OC defects on the sheep MFC allows rapid and low-trauma recovery and appears well-suited for implant testing.

Relative Surface Velocity of the Tibiofemoral Joint and Its Relation to the Development of Osteoarthritis After Joint Injury

The relative velocity of the tibiofemoral surfaces during gait before and after partial-ACL and full MCL transection (p-ACL/MCL Tx) was examined in an ovine model (N = 5) and the relation between the variation in the relative sliding velocity component and gross morphological damage was investigated. We defined the in vivo kinematics of the tibiofemoral joints by using an instrumented spatial linkage and then determining the relative velocity components on the reconstructed femoral condyle surfaces. One major finding was that the magnitude of the relative velocity components was relatively high during the initial stance period of the gait and oscillated with a decaying envelope. Interestingly, for most subjects, the highest value of relative sliding velocity occurred during the stance phase, and not swing. The magnitude of the relative velocity components was increased in 3/5 subjects during stance after an injury. For the lateral compartment, there was a significant correlation (p value = 0.005) between the joint gross morphological damage and the increase in the maximum relative sliding velocity during stance. For the medial compartment, there was a trend (p value < 0.1) between the joint gross morphological score and the increase in the maximum relative sliding velocity during stance, 20 weeks after injury. In conclusion, a connection between an increase in the relative surface velocity and gross morphological damage might be due to an increase in the normal stress and the plowing friction between the surfaces.

Large Animal Models for Anterior Cruciate Ligament Research

Large animal (non-rodent mammal) models are commonly used in ACL research, but no species is currently considered the gold standard. Important considerations when selecting a large animal model include anatomical differences, the natural course of ACL pathology in that species, and biomechanical differences between humans and the chosen model. This article summarizes recent reports related to anatomy, pathology, and biomechanics of the ACL for large animal species (dog, goat, sheep, pig, and rabbit) commonly used in ACL research. Each species has unique features and benefits as well as potential drawbacks, which are highlighted in this review. This information may be useful in the selection process when designing future studies.

Anatomical feature of knee joint in Aachen minipig as a novel miniature pig line for experimental research in orthopaedics

BACKGROUND

The pig is a commonly used large animal model, since pigs share anatomical and physiological similarities with humans. In contrast to other experimental pig lines the Aachen minipig, as a robust novel minipig does not require housing with any barrier. To estimate transferability of results to human conditions, pig lines should be thoroughly characterized.

PURPOSE

Therefore, we analyzed the anatomical pecularities of the knee joint of the novel "Aachen minipig" line raised for experimental conditions.

METHODS

Eight knee joints of four adult Aachen minipigs were dissected measuring the dimensions of typical landmarks using a digital caliper. Hybrid pig and human knee joints served as controls. Cartilage of the Aachen minipig (trochlear groove, femoral condyles, menisci) were assessed histologically.

RESULTS

The Aachen minipig shared its knee joint anatomy with the hybrid pig. In comparison to humans, peculiarities of the pig were demonstrated in the Aachen minipig: the lateral meniscus and the lateral tibial joint surface were significantly longer than the medial counterparts. The fibular head was covered by fibrocartilage and completely integrated into the lateral lower joint surface. The cartilage at the joint areas usually used for cartilage repair studies was in average 0.66±0.04mm thick. The porcine anterior cruciate ligament (ACL) attached with two bundles at the anterior tibial plateau separated from each other by the lateral anterior meniscotibial ligament. Aachen minipig articular and meniscal cartilage presented the typical histoarchitecture.

CONCLUSIONS

The Aachen minipig reflects porcine anatomical peculiarities, which should be considered, especially for meniscus and ACL reconstruction.

Three-dimensional in vivo kinematics and finite helical axis variables of the ovine stifle joint following partial anterior cruciate ligament transection

Partial anterior cruciate ligament (p-ACL) rupture is a common injury, but the impact of a p-ACL injury on in vivo joint kinematics has yet to be determined in an animal model. The in vivo kinematics of the ovine stifle joint were assessed during 'normal' gait, and at 20 and 40 weeks after p-ACL transection (Tx). Gross morphological scoring of the knee was conducted. p-ACL Tx creates significant progressive post-traumatic osteoarthritis (PTOA)-like damage by 40 weeks. Statistically significant increases for flexion angles at hoof-strike (HS) and mid-stance (MST) were seen at 20 weeks post p-ACL Tx and the HS and hoof-off (HO) points at 40 weeks post p-ACL-Tx, therefore increased flexion angles occurred during stance phase. Statistically significant increases in posterior tibial shift at the mid-flexion (MF) and mid-extension (ME) points were seen during the swing phase of the gait cycle at 40 weeks post p-ACL Tx. Correlation analysis showed a strong and significant correlation between kinematic changes (instabilities) and gross morphological score in the inferior-superior direction at 40 weeks post p-ACL Tx at MST, HO, and MF. Further, there was a significant correlation between change in gross morphological combined score (ΔGCS) and the change in location of the helical axis in the anterior direction (ΔsAP) after p-ACL Tx for all points analyzed through the gait cycle. This study quantified in vivo joint kinematics before and after p-ACL Tx knee injury during gait, and demonstrated that a p-ACL knee injury leads to both PTOA-like damage and kinematic changes.

Structure-Function relationships of equine menisci

Meniscal pathologies are among the most common injuries of the femorotibial joint in both human and equine patients. Pathological forces and ensuing injuries of the cranial horn of the equine medial meniscus are considered analogous to those observed in the human posterior medial horn. Biomechanical properties of human menisci are site- and depth- specific. However, the influence of equine meniscus topography and composition on its biomechanical properties is yet unknown. A better understanding of equine meniscus composition and biomechanics could advance not only veterinary therapies for meniscus degeneration or injuries, but also further substantiate the horse as suitable translational animal model for (human) meniscus tissue engineering. Therefore, the aim of this study was to investigate the composition and structure of the equine knee meniscus in a site- and age-specific manner and their relationship with potential site-specific biomechanical properties. The meniscus architecture was investigated histologically. Biomechanical testing included evaluation of the shore hardness (SH), stiffness and energy loss of the menisci. The SH was found to be subjected to both age and site-specific changes, with an overall higher SH of the tibial meniscus surface and increase in SH with age. Stiffness and energy loss showed neither site nor age related significant differences. The macroscopic and histologic similarities between equine and human menisci described in this study, support continued research in this field.

Stem Cells for Cartilage Repair: Preclinical Studies and Insights in Translational Animal Models and Outcome Measures

Due to the restricted intrinsic capacity of resident chondrocytes to regenerate the lost cartilage postinjury, stem cell-based therapies have been proposed as a novel therapeutic approach for cartilage repair. Moreover, stem cell-based therapies using mesenchymal stem cells (MSCs) or induced pluripotent stem cells (iPSCs) have been used successfully in preclinical and clinical settings. Despite these promising reports, the exact mechanisms underlying stem cell-mediated cartilage repair remain uncertain. Stem cells can contribute to cartilage repair via chondrogenic differentiation, via immunomodulation, or by the production of paracrine factors and extracellular vesicles. But before novel cell-based therapies for cartilage repair can be introduced into the clinic, rigorous testing in preclinical animal models is required. Preclinical models used in regenerative cartilage studies include murine, lapine, caprine, ovine, porcine, canine, and equine models, each associated with its specific advantages and limitations. This review presents a summary of recent in vitro data and from in vivo preclinical studies justifying the use of MSCs and iPSCs in cartilage tissue engineering. Moreover, the advantages and disadvantages of utilizing small and large animals will be discussed, while also describing suitable outcome measures for evaluating cartilage repair.

Reliable landmarks for precise topographical analyses of pathological structural changes of the ovine tibial plateau in 2-D and 3-D subspaces

Selecting identical topographical locations to analyse pathological structural changes of the osteochondral unit in translational models remains difficult. The specific aim of the study was to provide objectively defined reference points on the ovine tibial plateau based on 2-D sections of micro-CT images useful for reproducible sample harvesting and as standardized landmarks for landmark-based 3-D image registration. We propose 5 reference points, 11 reference lines and 12 subregions that are detectable macroscopically and on 2-D micro-CT sections. Their value was confirmed applying landmark-based rigid and affine 3-D registration methods. Intra- and interobserver comparison showed high reliabilities, and constant positions (standard errors < 1%). Spatial patterns of the thicknesses of the articular cartilage and subchondral bone plate were revealed by measurements in 96 individual points of the tibial plateau. As a case study, pathological phenomena 6 months following OA induction in vivo such as osteophytes and areas of OA development were mapped to the individual subregions. These new reference points and subregions are directly identifiable on tibial plateau specimens or macroscopic images, enabling a precise topographical location of pathological structural changes of the osteochondral unit in both 2-D and 3-D subspaces in a region-appropriate fashion relevant for translational investigations.

* The Ovine Model for Meniscus Tissue Engineering: Considerations of Anatomy, Function, Implantation, and Evaluation

Meniscus injuries represent one of the most-common intra-articular knee injuries. The current treatment options include meniscectomy and allograft transplantation, both with poor long-term outcomes. Therefore, there is a need for regenerative techniques to restore meniscal function. To preclinically test scaffolds for meniscus replacement, large animal models need to be established and standardized. This review establishes the anatomical and compositional similarities between human and sheep menisci and provides guidance for implantation and evaluation of such devices. The ovine meniscus represents a scaled-down version of the human meniscus, with only slight structural differences that can be addressed during device fabrication. Implantation protocols in sheep remain a challenge, as the meniscus cannot be visualized with the arthroscopic-assisted procedures commonly performed in human patients. Thus, we recommend the appropriate implantation protocols for meniscus visualization, ligamentous restoration, and surgical fixation of both total and partial meniscus replacement devices. Last, due to the lack of standardization in evaluation techniques, we recommend a comprehensive battery of tests to evaluate the efficacy of meniscus replacement implants. We recommend other investigators utilize these surgical and testing techniques to establish the ovine model as the gold standard for preclinical evaluation of meniscus replacement devices.

White-Tailed Deer as an Ex Vivo Knee Model: Joint Morphometry and ACL Rupture Strength

Animal joints are valuable proxies for those of humans in biomechanical studies, however commonly used quadruped knees differ greatly from human knees in scale and morphometry. To test the suitability of the cervine stifle joint (deer knee) as a laboratory model, gross morphometry, ACL cross section, and ACL rupture strength were measured and compared to values previously reported for the knees of humans and commonly studied animals. Twelve knee joints from wild white-tailed deer were tested. Several morphometry parameters, including bicondylar width (53.5 ± 3.0 mm) and notch width (14.7 ± 2.5 mm), showed a high degree of similarity to those of the human knee, while both medial (16.7 ± 2.1°) and lateral (17.6 ± 4.7°) tibial slopes were steeper than in humans but less steep than other quadrupeds. The median ACL rupture force (2054 N, 95% CI 2017-2256 N), mean stiffness (260 ± 166 N/mm), mean length (33 ± 7 mm), and mean cross sectional area (44.8 ± 18.3 mm²) were also comparable to previously reported values for human knees. In our limited sample size, no significant sexual dimorphism in strength or morphometry was observed (p ≥ 0.05 for all parameters), though female specimens generally had steeper tibial slopes (lateral: p = 0.52, medial: p = 0.07). Our results suggest that the deer knee may be a suitable model for ex vivo studies of ACL rupture and repair.

Surgical induced models of joint degeneration in the ovine stifle: Magnetic resonance imaging and histological assessment

BACKGROUND

The purposes of this study were to (1) validate and assess the reliability of a modified magnetic resonance semi-quantitative score (sheep Magnetic Resonance osteoarthritis Knee Score (sMOAKS)) to evaluate joint degeneration in the ovine knee and to (2) investigate whether the transection of the anterior cruciate ligament (ACL), isolated or in combination with meniscal injuries, reproduce the degenerative changes described in the meniscectomized sheep.

METHODS

Twenty sheep were randomly subjected to one of the following injuries to induce osteoarthritis (OA): ACL transection (ACLt), mid-body transection of the medial meniscus, ACLt combined with complete medial meniscectomy and complete medial meniscectomy. OA assessment was performed eight weeks postoperatively with sMOAKS, Mankin and Osteoarthritis Research Society International (OARSI) histological scores.

RESULTS

sMOAKS showed very good to excellent reliability (kappa=0.61 to 1.0) for the majority of features evaluated. sMOAKS revealed small differences between groups (p<0.05) being the ACLt group the most affected. We observed a strong positive correlation between the three scales in the evaluation of femoro-tibial articular cartilage (AC) (r=0.829, r=0.917, r=0.879).

CONCLUSIONS

sMOAKS is a reliable semi-quantitative Magnetic Resonance (MR) scale to evaluate and quantify the effect of different OA induction lesions in the ovine knee and presents a high correlation with Mankin and OARSI scales in the evaluation of femoro-tibial AC. Although minor differences were observed between the different surgical procedures for the induction of OA, ACLt proved to be the intervention that produced the highest amount of degeneration eight weeks postoperatively.

LEVEL OF EVIDENCE

II.

The Odocoileus virginianus Femur: Mechanical Behavior and Morphology

Biomechanical research relies heavily on laboratory evaluation and testing with osseous animal structures. While many femora models are currently in use, including those of the European red deer (Cervus elaphus), the Odocoileus virginianus femur remains undocumented, despite its regional abundance in North America. The objective of this study was to compare biomechanical and morphological properties of the Odocoileus virginianus femur with those of the human and commonly used animal models. Sixteen pairs of fresh-frozen cervine femora (10 male, 6 female, aged 2.1 ± 0.9 years) were used for this study. Axial and torsional stiffnesses (whole bone) were calculated following compression and torsion to failure tests (at rates of 0.1 mm/sec and 0.2°/sec). Lengths, angles, femoral head diameter and position, periosteal and endosteal diaphyseal dimensions, and condylar dimensions were measured. The results show that the cervine femur is closer in length, axial and torsional stiffness, torsional strength, and overall morphology to the human femur than many other commonly used animal femora models; additional morphological measurements are comparable to many other species’ femora. The distal bicondylar width of 59.3mm suggests that cervine femora may be excellent models for use in total knee replacement simulations. Furthermore, the cervine femoral head is more ovoid than other commonly-used models for hip research, making it a more suitable model for studies of hip implants. Thus, with further, more application-specific investigations, the cervine femur could be a suitable model for biomechanical research, including the study of ballistic injuries and orthopaedic device development.

Ligament and meniscus loading in the ovine stifle joint during normal gait

BACKGROUND

The ovine stifle joint is an ideal preclinical model to study knee joint biomechanics. Knowledge of the ovine ligamentous and meniscal loading during normal gait is currently limited.

METHODS

The in vivo kinematics of the ovine stifle joint (N=4) were measured during "normal" gait using a highly accurate instrumented spatial linkage (ISL, 0.3±0.2mm). These motions were reproduced in vitro using a unique robotic testing platform and the loads carried by the anterior/posterior cruciate ligaments (ACL/PCL), medial/lateral collateral ligaments (MCL/LCL), and medial/lateral menisci (MM/LM) during gait were determined.

RESULTS

Considerable inter-subject variability in tissue loads was observed. The load in the ACL was near zero at hoof-strike (0% gait) and reached a peak (100 to 300N) during early-stance (~10% gait). The PCL reached a peak load (200 to 500N) just after hoof-strike (~5% gait) and was mostly unloaded throughout the remainder of stance. Load in the MCL was substantially lower than the cruciate ligaments, reaching a maximum of 50 to 100N near the beginning of stance. The LCL carried a negligible amount of load through the entire gait cycle. There was also a major contribution of the MM and LM to load transfer from the femur to the tibia during normal gait. The total meniscal load reached a maximum average between 350 and 550N during gait.

CONCLUSION

Knowledge of joint function during normal motion is essential for understanding normal and pathologic joint states. The considerable variability in the magnitudes and patterns of tissue loads among animals simulates clinical variability in humans.

LEVEL OF EVIDENCE

III.

Small-Diameter Awls Improve Articular Cartilage Repair After Microfracture Treatment in a Translational Animal Model

BACKGROUND

Microfracture is the most commonly applied arthroscopic marrow stimulation procedure.

HYPOTHESIS

Articular cartilage repair is improved when the subchondral bone is perforated by small-diameter microfracture awls compared with larger awls.

STUDY DESIGN

Controlled laboratory study.

METHODS

Standardized rectangular (4 × 8 mm) full-thickness chondral defects (N = 24) were created in the medial femoral condyle of 16 adult sheep and debrided down to the subchondral bone plate. Three treatment groups (n = 8 defects each) were tested: 6 microfracture perforations using small-diameter awls (1.0 mm; group 1), large-diameter awls (1.2 mm; group 2), or without perforations (debridement control; group 3). Osteochondral repair was assessed at 6 months in vivo using established macroscopic, histological, immunohistochemical, biochemical, and micro-computed tomography analyses.

RESULTS

Compared with control defects, histological cartilage repair was always improved after both microfracture techniques (P < .023). Application of 1.0-mm microfracture awls led to a significantly improved histological overall repair tissue quality (7.02 ± 0.70 vs 9.03 ± 0.69; P = .008) and surface grading (1.05 ± 0.28 vs 2.10 ± 0.19; P = .001) compared with larger awls. The small-diameter awl decreased relative bone volume of the subarticular spongiosa (bone volume/tissue volume ratio: 23.81% ± 3.37% vs 30.58% ± 2.46%; P = .011). Subchondral bone cysts and intralesional osteophytes were frequently observed after either microfracture treatment. Macroscopic grading, DNA, proteoglycan, and type I and type II collagen contents as well as degenerative changes within the adjacent cartilage remained unaffected by the awl diameter.

CONCLUSION

Small-diameter microfracture awls improve articular cartilage repair in the translational sheep model more effectively than do larger awls.

CLINICAL RELEVANCE

These data support the use of small microfracture instruments for the surgical treatment of cartilage defects and warrant prolonged clinical investigations.

High resolution MRI imaging at 9.4 Tesla of the osteochondral unit in a translational model of articular cartilage repair

Background

Non-destructive structural evaluation of the osteochondral unit is challenging. Here, the capability of high-field magnetic resonance imaging (μMRI) at 9.4 Tesla (T) was explored to examine osteochondral repair ex vivo in a preclinical large animal model. A specific aim of this study was to detect recently described alterations of the subchondral bone associated with cartilage repair.

Methods

Osteochondral samples of medial femoral condyles from adult ewes containing full-thickness articular cartilage defects treated with marrow stimulation were obtained after 6 month in vivo and scanned in a 9.4 T μMRI. Ex vivo imaging of small osteochondral samples (typical volume: 1–2 cm³) at μMRI was optimised by variation of repetition time (TR), time echo (TE), flip angle (FA), spatial resolution and number of excitations (NEX) from standard MultiSliceMultiEcho (MSME) and three-dimensional (3D) spoiled GradientEcho (SGE) sequences.

Results

A 3D SGE sequence with the parameters: TR = 10 ms, TE = 3 ms, FA = 10 °, voxel size = 120 × 120 × 120 μm³ and NEX = 10 resulted in the best fitting for sample size, image quality, scanning time and artifacts. An isovolumetric voxel shape allowed for multiplanar reconstructions. Within the osteochondral unit articular cartilage, cartilaginous repair tissue and bone marrow could clearly be distinguished from the subchondral bone plate and subarticular spongiosa. Specific alterations of the osteochondral unit associated with cartilage repair such as persistent drill holes, subchondral bone cysts, sclerosis of the subchondral bone plate and of the subarticular spongiosa and intralesional osteophytes were precisely detected.

Conclusions

High resolution, non-destructive ex vivo analysis of the entire osteochondral unit in a preclinical large animal model that is sufficient for further analyses is possible using μMRI at 9.4 T. In particular, 9.4 T is capable of accurately depicting alterations of the subchondral bone that are associated with osteochondral repair.

Increased meniscal loading after anterior cruciate ligament transection in vivo: a longitudinal study in sheep

INTRODUCTION

Meniscal injury has been well documented as a frequent consequence of both acute and chronic ACL deficiency. The purpose of this study was to evaluate the effect of ACL deficiency on meniscal loads in vivo and determine how these loads would change over time after ACL injury.

METHODS

The in vivo kinematics of the stifle joint of five sheep were measured during normal gait, as well as 4 and 20 weeks after ACL transection. A unique robotic testing platform was then programmed to reproduce all the previously recorded kinematics and the loads carried by medial and lateral menisci during gait were estimated.

RESULTS

The results demonstrated a significant increase in both medial and lateral meniscal loads 20 weeks following ACL transection, mainly during mid-stance phase of gait (p = 0.007 and p = 0.003, respectively), with interesting inter-subject variability. A moderate correlation (R(2) ≥ 0.5) between in situ meniscal loads and anterior tibial translations was also detected over time after injury, increased translations post injury generally corresponded to larger meniscal loads.

CONCLUSION

The dramatic increase in meniscal loads long term post ACL transection probably explains the meniscal changes or injuries reported clinically in many chronic ACL-deficient knees.

Cervine tibia morphology and mechanical strength: a suitable tibia model?

Animal models for orthopaedic implant testing are well-established but morphologically dissimilar to human tibiae; notably, most are shorter. The purpose of this study was to quantitatively evaluate the morphology and mechanical properties of the cervine tibia, particularly with regard to its suitability for testing orthopaedic implants. Two endosteal and eleven periosteal measurements were made on 15 cervine tibiae. The mechanical strength in axial compression and torsion was measured using 11 tibiae. The cervine tibia is morphologically similar to the human tibia and more closely matches the length of the human tibia than current tibia models (ovine, porcine, and caprine). The distal epiphysis dimensions are notably different, but no more so than the current tibia models. The torsional stiffness of the cervine tibia is within the range of previously reported values for human tibiae. Furthermore, in many regions, cervine tibiae are abundant and locally available at a low cost. Given these mechanical and morphological data, coupled with potential cost savings if regionally available, the cervine tibia may be an appropriate model for orthopaedic implant testing.

Small subchondral drill holes improve marrow stimulation of articular cartilage defects

BACKGROUND

Subchondral drilling is an established marrow stimulation technique.

HYPOTHESIS

Osteochondral repair is improved when the subchondral bone is perforated with small drill holes, reflecting the physiological subchondral trabecular distance.

STUDY DESIGN

Controlled laboratory study.

METHODS

A rectangular full-thickness chondral defect was created in the trochlea of adult sheep (n = 13) and treated with 6 subchondral drillings of either 1.0 mm (reflective of the trabecular distance) or 1.8 mm in diameter. Osteochondral repair was assessed after 6 months in vivo by macroscopic, histological, and immunohistochemical analyses and by micro-computed tomography.

RESULTS

The application of 1.0-mm subchondral drill holes led to significantly improved histological matrix staining, cellular morphological characteristics, subchondral bone reconstitution, and average total histological score as well as significantly higher immunoreactivity to type II collagen and reduced immunoreactivity to type I collagen in the repair tissue compared with 1.8-mm drill holes. Analysis of osteoarthritic changes in the cartilage adjacent to the defects revealed no significant differences between treatment groups. Restoration of the microstructure of the subchondral bone plate below the chondral defects was significantly improved after 1.0-mm compared to 1.8-mm drilling, as shown by higher bone volume and reduced thickening of the subchondral bone plate. Likewise, the microarchitecture of the drilled subarticular spongiosa was better restored after 1.0-mm drilling, indicated by significantly higher bone volume and more and thinner trabeculae. Moreover, the bone mineral density of the subchondral bone in 1.0-mm drill holes was similar to the adjacent subchondral bone, whereas it was significantly reduced in 1.8-mm drill holes. No significant correlations existed between cartilage and subchondral bone repair.

CONCLUSION

Small subchondral drill holes that reflect the physiological trabecular distance improve osteochondral repair in a translational model more effectively than larger drill holes.

CLINICAL RELEVANCE

These results have important implications for the use of subchondral drilling for marrow stimulation, as they support the use of small-diameter bone-cutting devices.

Arthroscopy of the normal cadaveric ovine femorotibial joint: a systematic approach to the cranial and caudal compartments

OBJECTIVES

Preclinical studies using large animal models play an intergral part in translational research. For this study, our objectives were: to develop and validate arthroscopic approaches to four compartments of the stifle joint as determined via the gross and arthroscopic anatomy of the cranial and caudal aspects of the joint.

METHODS

Cadaveric hindlimbs (n = 39) were harvested from mature ewes. The anatomy was examined by tissue dissection (n = 6), transverse sections (n = 4), and computed tomography (n = 4). The joint was arthroscopically explored in 25 hindlimbs.

RESULTS

A cranio-medial portal was created medial to the patellar ligament. The cranio-lateral portal was made medial to the extensor digitorum longus tendon. The medial femoral condyle was visible, as well as the cranial cruciate ligament, caudal cruciate ligament and both menisci with the intermeniscal ligament. Valgus stress improved visibility of the caudal horn of the medial meniscus and tibial plateau. To explore the caudal compartments, a portal was created 1 cm proximal to the most caudal aspect of the tibial condyle. Both femoral condyles, menisci, caudal cruciate ligament, the popliteal tendon and the menisco-femoral ligament were visible. The common peroneal nerve and popliteal artery and vein are vulnerable structures to injury during arthroscopy.

CLINICAL SIGNIFICANCE

The arthroscopic approach developed in this research is ideal to evaluate the ovine stifle joint.

Decreased posterior cruciate and altered collateral ligament loading following ACL transection: a longitudinal study in the ovine model

Although ACL deficiency is shown to lead to joint degeneration, few quantitative data are reported on its effect on soft tissue structures surrounding the knee joint, specifically, the posterior cruciate and collateral ligaments. The kinematics of the stifle joint of sheep (N = 5) were measured during "normal" gait, as well as 4 and 20 weeks after ACL transection. These motions were reproduced using a unique robotic manipulator and the loads borne by PCL, MCL, and LCL during gait were determined. Our results demonstrated a significant decrease in mean PCL loads 20 weeks post-ACL injury, at hoof-strike (0% of gait, p = 0.034), hoof-off (66% of gait, p = 0.006), peak-swing (85% of gait, p = 0.026), and extension-before-hoof-strike (95% of gait, p = 0.028). Mean MCL loads did not significantly increase following ACL transection, maybe due to large between-animal variation. Finally, mean LCL loads indicated a significant decrease (p < 0.047) at 20 weeks across the entire gait cycle. From a clinical perspective, the load redistributions observed in cruciate and collateral ligaments following ACL injury indicate that these tissues can carry/adapt to the altered mechanical environment of the joint. The considerable variability in the magnitudes of change following ACL injury among animals also simulates clinical variability in humans after trauma.

[Experimental induction of Perthes disease in lambs]

OBJECTIVE

To establish a simple, reproducible and safe experimental model, for the development of ischemic vascular necrosis of the hip in the lamb.

MATERIAL AND METHODS

We used 15 lambs (10 males and 5 females) aged four weeks, divided into a control group (7 animals) and an experimental group (8 animals) producing ischemia in the proximal femur. Standard radiography and MRI were performed. The animals were euthanised at the 4th, 8th and 12th weeks after surgery. The femoral heads were extracted and measured and a histological analysis was performed with hematoxylin-eosin staining.

RESULTS

Decreased height and increased width of the femoral head was observed in the X-Rays, particularly after the 4th week. We did not observe any changes in the height of the lateral pillar or trochanteric distance. The experimental group showed macroscopical hypertrophy and progressive flattening of the head. At 4 weeks necrotic areas in articular cartilage were observed, bone marrow was dense and the growth cartilage height was lower. The vessels were thickened by proliferation of the medial and adventitia layers. At 8 weeks, we found fibrosis in the subchondral bone with thinned and devitalized angiogenesis fat areas. The articular cartilage showed irregularities. At 12 weeks the closure of the physis was noted, as well as chondral areas in the trabecular bone and fat cells in the methaphysis.

CONCLUSION

Although the histological changes are consistent with necrosis of the femoral head, the images obtained did not resemble Perthes disease, so we do not advise this experimental model for the study of this disease.

Primary and secondary restraints of human and ovine knees for simulated in vivo gait kinematics

Knee soft tissue structures are frequently injured, leading to the development of osteoarthritis even with treatment. Understanding how these structures contribute to knee function during activities of daily living (ADLs) is crucial in creating more effective treatments. This study was designed to determine the role of different knee structures during a simulated ADL in both human knees and ovine stifle joints. A six degree-of-freedom robot was used to reproduce each species' in vivo gait while measuring three-dimensional joint forces and torques. Using a semi-randomized selective cutting method, we determined the primary and secondary structures contributing to the forces and torques along and about each anatomical axis. In both species, the bony interaction, ACL, and medial meniscus provided most of the force contributions during stance, whereas the ovine MCL, human bone, and ACLs of both species were the key contributors during swing. This study contributes to our overarching goal of establishing functional tissue engineering parameters for knee structures by further validating biomechanical similarities between the ovine model and the human to provide a platform for measuring biomechanics during an in vivo ADL. These parameters will be used to develop more effective treatments for knee injuries to reduce or eliminate the incidence of osteoarthritis.

Biomechanical comparison of menisci from different species and artificial constructs

Background

Loss of meniscal tissue is correlated with early osteoarthritis but few data exist regarding detailed biomechanical properties (e.g. viscoelastic behavior) of menisci in different species commonly used as animal models. The purpose of the current study was to biomechanically characterize bovine, ovine, and porcine menisci (each n = 6, midpart of the medial meniscus) and compare their properties to that of normal and degenerated human menisci (n = 6) and two commercially available artificial scaffolds (each n = 3).

Methods

Samples were tested in a cyclic, minimally constraint compression–relaxation test with a universal testing machine allowing the characterization of the viscoelastic properties including stiffness, residual force and relative sample compression. T-tests were used to compare the biomechanical parameters of all samples. Significance level was set at p < 0.05.

Results

Throughout cyclic testing stiffness, residual force and relative sample compression increased significantly (p < 0.05) in all tested meniscus samples. From the tested animal meniscus samples the ovine menisci showed the highest biomechanical similarity to human menisci in terms of stiffness (human: 8.54 N/mm ± 1.87, cycle 1; ovine: 11.24 N/mm ± 2.36, cycle 1, p = 0.0528), residual force (human: 2.99 N ± 0.63, cycle 1 vs. ovine 3.24 N ± 0.13, cycle 1, p = 0.364) and relative sample compression (human 19.92% ± 0.63, cycle 1 vs. 18.72% ± 1.84 in ovine samples at cycle 1, p = 0.162). The artificial constructs -as hypothesized- revealed statistically significant inferior biomechanical properties.

Conclusions

For future research the use of ovine meniscus would be desirable showing the highest biomechanical similarities to human meniscus tissue. The significantly different biomechanical properties of the artificial scaffolds highlight the necessity of cellular ingrowth and formation of extracellular matrix to gain viscoelastic properties. As a consequence, a period of unloading (at least partial weight bearing) is necessary, until the remodeling process in the scaffold is sufficient to withstand forces during weight bearing.

Kinematic and kinetic interactions during normal and ACL-deficient gait: a longitudinal in vivo study

The interactions between different tissues within the knee joint and between different kinematic DOF and joint flexion during normal gait were investigated. These interactions change following ACL transection, in both short (4 weeks) and long (20 weeks) term. Ten skeletally mature sheep were used in control (N = 5) and experimental (N = 5) groups. The 6-DOF stifle joint motion was first measured during normal gait. The control group were then euthanized and mounted on a unique robotic testing platform for kinetic measurements. The experimental group underwent ACL transection surgery, and kinematics measurements were repeated 4 and 20 weeks post-operatively. The experimental group were then euthanized and underwent kinetic assessment using the robotic system. Results indicated significant couplings between joint flexion vs. abduction and internal tibial rotation, as well as medial, anterior, and superior tibial translations during both normal and ACL-deficient gait. Distinct kinetic interactions were also observed between different tissues within the knee joint. Direct relationships were found between ACL vs. LM/MM, and PCL vs. MCL loads during normal gait; inverse relationships were detected between ACL vs. PCL and PCL vs. LM/MM loads. These kinetic interaction patterns were considerably altered by ACL injury. Significant inter-subject variability in joint kinematics and tissue loading patterns during gait was also observed. This study provides further understanding of the in vivo function of different tissues within the knee joint and their couplings with joint kinematics during normal gait and over time following ACL transection.

Biological and biomechanical evaluation of the ligament advanced reinforcement system (LARS AC) in a sheep model of anterior cruciate ligament replacement: a 3-month and 12-month study

PURPOSE

The purposes of this study were to assess tissue ingrowth within the Ligament Advanced Reinforcement System (LARS) artificial ligament (LARS AC; LARS, Arc sur Tille, France) and to study the biomechanical characteristics of the reconstructed knees in a sheep model of anterior cruciate ligament (ACL) replacement.

METHODS

Twenty-five female sheep underwent excision of the proximal third of the left ACL and intra-articular joint stabilization with a 44-strand polyethylene terephthalate ligament (mean ultimate tensile failure load, 2,500 N). Animals were killed either 3 or 12 months after surgery. Explanted knees were processed for histology (n = 10) or mechanical tests including tests of laxity and loading to failure in tension (n = 15).

RESULTS

Well-vascularized tissue ingrowth within the artificial ligament was only observed in the portions of the ligament in contact with the host's tissues (native ligament and bone tunnels). Ligament wear was observed in 40% of explanted knees. The ultimate tensile failure loads of the operated knees at both time points were inferior to those of the contralateral, intact knees (144 ± 69 N at 3 months and 260 ± 126 N at 12 months versus 1,241 ± 270 N and 1,218 ± 189 N, respectively) (P < .01). In specimens with intact artificial ligaments, failure occurred by slippage from the bone tunnels in all specimens explanted 3 months postoperatively and in half of the specimens explanted 12 months postoperatively.

CONCLUSIONS

This study provides evidence that the LARS AC has a satisfactory biointegration but that it is not suitable for ACL replacement if uniform tissue ingrowth is contemplated. Despite good clinical performance up to 1 year after implantation, none of the reconstructions approached the mechanical performance of the normal ACL in the ovine model. Partial tearing of the artificial ligament, which led to a significant decrease in ultimate tensile strength, was observed in 40% of cases in the ovine model.

CLINICAL RELEVANCE

The LARS is not a suitable scaffold for ACL replacement. Further animal studies are needed to evaluate its potential for augmentation of ligament repair.

Examination of osteoarthritis and subchondral bone alterations within the stifle joint of an ovariectomised ovine model

The exact relationship between osteoporosis and osteoarthritis is still a matter for debate for many. The ovariectomised ewe is frequently used as a model for osteoporosis, resulting in significant alterations in bone morphometry and turnover in both trabecular and subchondral bone after 1 year. This study examines whether ovariectomy has any impact on development of osteoarthritis within the ovine stifle joint at the same time point. In addition, we investigate whether there are any significant correlations present between articular cartilage degeneration and alterations in microstructural parameters or turnover rates in the underlying bone. Twenty-two sheep were examined in this study; 10 of the sheep underwent ovariectomy and 12 were kept as controls. Five distinctive fluorochrome dyes were administered intravenously at 12-week intervals to both groups, to label sites of bone turnover. All animals were then sacrificed 12 months postoperatively. Although most specimens showed some evidence of osteoarthritis, no measurable difference between the two study groups was detected. Osteoarthritis was associated with a thinning of the subchondral plate, specifically the subchondral cortical bone; however, whereas previous studies have suggested a link between trabecular thinning and osteoarthritis, this was not confirmed. No correlation was found between osteoarthritis and bone turnover rates of either the subchondral trabecular bone or bone plate. In conclusion, despite the fact that ovariectomy results in marked morphological and structural changes in the ovine stifle joint at 1-year postoperatively, no evidence was found to suggest that it plays a direct role in the aetiology of osteoarthritis.

A low morbidity surgical approach to the sheep femoral trochlea

BACKGROUND

The ovine stifle joint is an important location for investigations on the repair of articular cartilage defects in preclinical large animals. The classical medial parapatellar approach to the femoral trochlea is hazardous because of the high risk of postoperative patellar luxation. Here, we describe a low morbidity surgical exposure of the ovine trochlea without the necessity for intraoperative patellar luxation.

METHODS

Bilateral surgical exposure of the femoral trochlea of the sheep stifle joint was performed using the classical medial parapatellar approach with intraoperative lateral patellar luxation and transection of the medial patellar retinaculum in 28 ovine stifle joints. A low morbidity approach was performed bilaterally in 116 joints through a mini-arthrotomy without the need to transect the medial patellar retinaculum or the oblique medial vastus muscle nor surgical patellar luxation. Postoperatively, all 72 animals were monitored to exclude patellar luxations and deep wound infections.

RESULTS

The novel approach could be performed easily in all joints and safely exposed the distal two-thirds of the medial and lateral trochlear facet. No postoperative patellar luxations were observed compared to a postoperative patellar luxation rate of 25% experienced with the classical medial parapatellar approach and a re-luxation rate of 80% following revision surgery. No signs of lameness, wound infections, or empyema were observed for both approaches.

CONCLUSIONS

The mini-arthrotomy presented here yields good exposure of the distal ovine femoral trochlea with a lower postoperative morbidity than the classical medial parapatellar approach. It is therefore suitable to create articular cartilage defects on the femoral trochlea without the risk of postoperative patellar luxation.

The preclinical sheep model of high tibial osteotomy relating basic science to the clinics: standards, techniques and pitfalls

PURPOSE

To develop a preclinical large animal model of high tibial osteotomy to study the effect of axial alignment on the lower extremity on specific issues of the knee joint, such as in articular cartilage repair, development of osteoarthritis and meniscal lesions. Preoperative planning, surgical procedure and postoperative care known from humans were adapted to develop a HTO model in the adult sheep.

METHODS

Thirty-five healthy, skeletally mature, female Merino sheep between 2 and 4 years of age underwent a HTO of their right tibia in a medial open-wedge technique inducing a normal (group 1) and an excessive valgus alignment (group 2) and a closed-wedge technique (group 3) inducing a varus alignment with the aim of elucidating the effect of limb alignment on cartilage repair in vivo. Animals were followed up for 6 months.

RESULTS

Solid bone healing and maintenance of correction are most likely if the following surgical principles are respected: (1) medial and longitudinal approach to the proximal tibia; (2) biplanar osteotomy to increase initial rotatory stability regardless of the direction of correction; (3) small, narrow but long implant with locking screws; (4) posterior plate placement to avoid slope changes; (5) use of bicortical screws to account for the brittle bone of the tibial head and to avoid tibial head displacement.

CONCLUSION

Although successful high tibial osteotomy in sheep is complex, the sheep may--because of its similarities with humans--serve as an elegant model to induce axial malalignment in a clinically relevant environment, and osteotomy healing under challenging mechanical conditions.

Subchondral osteopenia and accelerated bone remodelling post-ovariectomy - a possible mechanism for subchondral microfractures in the aetiology of spontaneous osteonecrosis of the knee?

Osteopenia and subchondral microfractures are implicated in the aetiology of spontaneous osteonecrosis of the knee (SPONK). The ovine tibia shows significant alterations of the trabecular architecture within the subchondral bone of the medial tibial plateau post-ovariectomy (OVX), including reduced trabecular bone volume fraction. We hypothesise that accelerated subchondral bone resorption may also play a role in increasing microfracture risk at this site. Twenty-two sheep were examined in this study; 10 of the sheep underwent OVX, while the remainder (n = 13) were kept as controls (CON). Five fluorochrome dyes were administered intravenously at 12-week intervals via the jugular vein to both groups, to label sites of bone turnover. These animals were then killed at 12 months post-operatively. Bone turnover was significantly increased in the OVX group in both trabecular bone (2.024 vs. 1.047 no. mm(-2) ; P = 0.05) and within the subchondral bone plate (4.68 vs. 0.69 no. mm(-2) ; P < 0.001). In addition to the classically described turnover visible along trabecular surfaces, we also found visual evidence of intra-trabecular osteonal remodelling. In conclusion, this study shows significant alterations in bone turnover in both trabecular bone and within the subchondral bone plate at 1 year post-OVX. Remodelling of trabecular bone was due to both classically described hemi-osteonal and intra-trabecular osteonal remodelling. The presence of both localised osteopenia and accelerated bone remodelling within the medial tibial plateau provide a possible mechanism for subchondral microfractures in the aetiology of SPONK. Further utilisation of the OVX ewe may be useful for further study in this field.

Effect of subchondral drilling on the microarchitecture of subchondral bone: analysis in a large animal model at 6 months

BACKGROUND

Marrow stimulation techniques such as subchondral drilling are clinically important treatment options for symptomatic small cartilage defects. Little is known about whether they induce deleterious changes in the subchondral bone.

HYPOTHESIS

Subchondral drilling induces substantial alterations of the microarchitecture of the subchondral bone that persist for a clinically relevant postoperative period in a preclinical large animal model.

STUDY DESIGN

Controlled laboratory study.

METHODS

Standardized full-thickness chondral defects in the medial femoral condyles of 19 sheep were treated by subchondral drilling. Six months postoperatively, the formation of cysts and intralesional osteophytes was evaluated. A standardized methodology was developed to segment the ovine subchondral unit into reproducible volumes of interest (VOIs). Indices of bone structure were determined by micro-computed tomography (micro-CT).

RESULTS

Analysis of the microarchitecture revealed the absence of zonal stratification in the ovine subarticular spongiosa, permitting an unimpeded and simultaneous analysis of the entire subchondral trabecular network. Subchondral drilling led to the formation of subchondral bone cysts (63%) and intralesional osteophytes (26%). Compared with the adjacent unaffected subchondral bone, drilling induced significant alterations in nearly all parameters for the microarchitecture of the subchondral bone plate and the subarticular spongiosa, most importantly in bone volume, bone surface/volume ratio, trabecular thickness, separation, pattern factor, and bone mineral density (BMD) (all P ≤ .01).

CONCLUSION

The data show that the ovine subchondral bone can be reliably evaluated using micro-CT with standardized VOIs. We report that subchondral drilling deteriorates the microarchitecture both of the subchondral bone plate and subarticular spongiosa and decreases BMD. These results suggest that the entire osteochondral unit is altered after drilling for an extended postoperative period.

CLINICAL RELEVANCE

The subchondral bone remains fragile after subchondral drilling for longer durations than previously expected. Further evaluations of structural subchondral bone parameters of patients undergoing marrow stimulation are warranted.

A study of the anatomy and injection techniques of the ovine stifle by positive contrast arthrography, computed tomography arthrography and gross anatomical dissection

Although ovine stifle models are commonly used to study osteoarthritis, meniscal pathology and cruciate ligament injuries and repair, there is little information about the anatomy of the joint or techniques for synovial injections. The objectives of this study were to improve anatomical knowledge of the synovial cavities of the ovine knee and to compare intra-articular injection techniques. Synovial cavities of 24 cadaver hind limbs from 12 adult sheep were investigated by intra-articular resin, positive-contrast arthrography, computed tomography (CT) arthrography and gross anatomical dissection. Communication between femoro-patellar, medial femoro-tibial and lateral femoro-tibial compartments occurred in all cases. The knee joint should be considered as one synovial structure with three communicating compartments. Several unreported features were observed, including a communication between the medial femoro-tibial and lateral femoro-tibial compartments and a latero-caudal recess of the lateral femoro-tibial compartment. No intermeniscal ligament was identified. CT was able to define many anatomical features of the stifle, including the anatomy of the tendinous synovial recess on the lateral aspect of the proximal tibia under the combined tendon of the peroneus tertius, extensor longus digitorum and extensor digiti III proprius. An approach for intra-articular injection into this recess (the subtendinous technique) was assessed and compared with the retropatellar and paraligamentous techniques. All three injection procedures were equally successful, but the subtendinous technique appeared to be most appropriate for synoviocentesis and for injections in therapeutic research protocols with less risk of damaging the articular cartilage.