Qualitative and quantitative measurement of the anterior and posterior meniscal root attachments of the New Zealand white rabbit
© Civitarese et al. 2016
Received: 18 January 2016
Accepted: 24 February 2016
Published: 29 February 2016
The purpose of this study was to quantify the meniscal root anatomy of the New Zealand white rabbit to better understand this animal model for future in vitro and in vivo joint degeneration studies.
Ten non-paired fresh frozen New Zealand white rabbit knee stifle joints were carefully disarticulated for this study. Measurements were made for all bony landmarks and ligamentous structure attachment sites on the tibial plateau. The following soft tissue structures were consistently identified in the rabbit stifle joint: the anterior root attachment of the lateral meniscus, the anterior root attachment of the medial meniscus, the anterior cruciate ligament, the posterior root attachment of the medial meniscus, the ligament of Wrisberg, the posterior cruciate ligament, and the posterior meniscotibial ligament. The following bony landmarks were consistently identified: the extensor digitorum longus groove, the medial tibial eminence, the center of the tibial tuberosity, and the lateral tibial eminence.
The center of the anterior cruciate ligament and the medial tibial eminence apex were found to be 3.4 ± 0.3 mm (2.9–3.6) and 6.1 ± 0.6 mm (5.1–7.0) respectively from the center of the medical anterior root attachment. The center of the anterior cruciate ligament and the lateral tibial eminence apex were found to be 2.1 ± 0.5 mm (1.2–2.7) and 7.0 ± 0.6 mm (6.4–8.2) respectively from the center of the lateral anterior root attachment. The center of the posterior cruciate ligament and the medial tibial eminence apex were found to be 2.0 ± 0.7 mm (0.5–2.6) and 1.8 ± 0.4 mm (1.2–2.4) respectively from the center of the medial posterior root attachment.
This study augments our understanding of the comparative anatomy of the rabbit stifle joint. This information will be useful for future biomechanical, surgical, and in vitro studies utilizing the rabbit stifle as a model for human knee joint degenerative diseases.
KeywordsMeniscal roots Meniscus Rabbit stifle Anatomy New Zealand white rabbits
It has only become recently recognized that the meniscal root attachments provide an essential role in knee joint health (Bhatia et al. 2014). By attaching the menisci to the tibial plateau, the meniscal roots facilitate the dispersion of axial loads into hoop stresses (Bhatia et al. 2014). In addition, biomechanical studies have reported that meniscal root tears significantly alter tibiofemoral contact mechanics, leading to the potential rapid progression of osteoarthritis (Allaire et al. 2008; Padalecki et al. 2014; LaPrade et al. 2014). The natural history of osteoarthritis is logistically difficult to monitor and study in humans, especially because there are few objective diagnostic tools for the early stages of the disease. Studies have reported that rabbits can serve as a useful animal model for studying knee osteoarthritis due to the similarities between the human knee and rabbit stifle, (Crum et al. 2003) and they also incur less costs and housing than other larger animal models (Arnoczky et al. 2010). Previous studies have used rabbits to study the effects of a complete medial meniscectomy on the development of osteoarthritis and have reported comparable effects in shorter time periods than humans after meniscectomy (Messner et al. 2000; Hoch et al. 1983). However, the effectiveness of a rabbit model as a translational model for meniscal root tears needs to be further investigated and compared to recent anatomical studies on the human meniscal roots (Johannsen et al. 2012; LaPrade et al. 2014; Proffen et al. 2012; Brody et al. 2007). Before in vivo experiments in rabbits are carried out, the anatomy of the meniscal roots needs to be understood to determine the feasibility of translating the findings into clinically significant results for humans.
The purpose of this study was to quantitatively define the meniscal root anatomy in New Zealand white rabbits modeling previous meniscal root anatomy studies in humans (Johannsen et al. 2012; LaPrade et al. 2014). Reproducible and consistent measurements for the meniscal root attachments and their proximity to bony landmarks will provide an anatomic basis for further translational research in a New Zealand white rabbit model. It was hypothesized that the quantitative anatomy of the New Zealand white rabbit stifle would be reproducible and thus confirm the usage of this species for future animal research on the progression of osteoarthritis following meniscal root tears.
This study was exempt from Institutional Review Board approval at our institution. Ten non-paired fresh-frozen skeletally mature adult New Zealand white rabbit stifles were dissected for an anatomical study of the stifle meniscal root attachments. The hind limb of the rabbit was disarticulated at the tibiofemoral joint with careful attention afforded to preserving the tibial attachment footprint sites. Bony landmarks of the tibia and the attachment sites of the medial and lateral menisci, anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) were identified.
A single observer performed all measurements for each specimen once and a magnifying lens was used to increase precision during point selection. Relevant ligament attachments, meniscal roots, and osseous landmarks were manually selected with a fine point stylus tip for mapping with a portable three dimensional coordinate measuring device with a manufacturer-reported point-repeatability of 0.025 mm (7315 Romer Absolute Arm, Hexagon Metrology, North Kingstown, RI). The geometrical centers of all root and ligament attachment sites were determined by finding the center of eight data points outlining each footprint. Relevant distance and area calculations were then performed from the collected data using custom software (MATLAB R2014, MathWorks, Natick, Massachusetts, USA).
The coordinate system of the tibia was defined by the collection of a series of points to establish superior-inferior, medial-lateral and anterior-posterior axes. Three series of circumferential points around the tibial diaphysis were used to establish the superior-inferior axis. The medial-lateral axis was defined by selecting the most medial and lateral points on the tibial plateau. A perpendicular line intersecting the superior-inferior and medial-lateral axes was calculated to determine the alignment of the anterior-posterior axis.
Directional distances between anatomic landmarks. MTE medial tibial eminence, ACL anterior cruciate ligament, LARA lateral anterior root attachment, EDLG extensor digitorum longus groove, LTE lateral tibial eminence, PCL posterior cruciate ligament
Average Distance ± SD (mm)
To Medial Anterior Root Attachment (MARA)
6.1 ± 0.6
5.1 to 7.0
MTE Apex (anterior-posterior distance)
5.1 ± 0.4
4.5 to 6.1
MTE Apex (inferior-superior distance)
0.8 ± 0.9
(−0.1) to 2.5
MTE Apex (medial-lateral distance)
3.1 ± 0.7
2.1 to 4.2
3.4 ± 0.3
2.9 to 3.6
Anterior - Superior - Lateral
4.6 ± 0.3
4.1 to 5.0
Anterior - Inferior - Lateral
2.6 ± 0.3
2.1 to 3.1
Posterior - Superior - Medial
To Lateral Anterior Root Attachment (LARA)
7.0 ± 0.6
6.4 to 8.2
Anterior - Superior - Medial
LTE Apex (anterior-posterior distance)
5.1 ± 0.9
3.6 to 6.3
LTE Apex (inferior-superior distance)
0.6 ± 1.1
(−0.9) to 2.5
LTE Apex (medial-lateral distance)
4.6 ± 0.6
(−5.3) to (−3.7)
2.1 ± 0.5
1.2 to 2.7
Anterior - Superior - Medial
To Medial Posterior Root Attachment (MPRA)
1.8 ± 0.4
1.2 to 2.4
Posterior - Inferior - Lateral
MTE Apex (anterior-posterior distance)
0.1 ± 0.4
(−0.9) to 0.5
MTE Apex (inferior-superior distance)
1.4 ± 0.6
(−2.3) to (−0.3)
MTE Apex (medial-lateral distance)
0.8 ± 0.7
0.1 to 1.8
2.0 ± 0.7
0.5 to 2.6
Anterior - Superior - Lateral
Tibial plateau attachment site footprint areas
Average Area ± SD, (mm2)
Anterior Cruciate Ligament
8.8 ± 2.6
5.3 to 12.9
Lateral Anterior Root Attachment
2.4 ± 1.6
0.9 to 5.9
Medial Anterior Root Attachment
3.2 ± 1.5
1.3 to 4.9
Medial Posterior Root Attachment
1.8 ± 1.8
1.0 to 3.1
Posterior Cruciate Ligament
4.6 ± 1.5
2.3 to 7.0
Meniscal root anatomy
Ligamentous anatomy relationship
The ACL tibial attachment was located just posterior and lateral to the lateral anterior root attachment (Fig. 1), while the PCL tibial attachment was posterior and lateral to the posterior root attachment of the medial meniscus. Supplemental fibers of the medial anterior root attachment, lateral anterior root attachment, and medial posterior root attachment were too small to differentiate from ACL or PCL fibers.
The most important finding of this study was that the anatomic locations of the medial anterior, lateral anterior, and medial posterior root attachments of the rabbit meniscus were consistently quantitatively described. The New Zealand white rabbit stifle has been reported to resemble the human knee (Proffen et al. 2012; Messner et al. 2001; Messner et al. 2000). Therefore, the findings of this study enhance the current literature by providing a detailed anatomic description of the rabbit meniscus that will support the usage of this model for future in vivo and in vitro translational biomechanical and surgical research.
The results of this study found reproducible measurements of meniscal root attachment sites to reliable osseous and ligamentous landmarks in the rabbit stifle joint. This study found consistent attachment locations for the medial meniscal root attachments and the anterior lateral meniscal attachment. However, the posterior root attachment of the lateral meniscus did not attach to the tibia and blended directly with the ligament of Wrisberg.
In comparing our findings with previously published anatomic investigations, (Crum et al. 2003; Messner and Gao 1998; Proffen et al. 2012) we verified the consistency of several structures related to the menisci of the New Zealand white rabbit stifle. Both the medial tibial plateau and the lateral tibial plateau were convex and sloped posteriorly similar to previous anatomic descriptions (Crum et al. 2003). This study found the posterior meniscotibial ligament to be present in all specimens. In agreement with Crum et al., we found that the lateral posterior meniscus terminates and blends into the ligament of Wrisberg and attaches to the femur via the ligamentous structure (Crum et al. 2003). Proffen et al. found that anterior lateral meniscus root attachment is further medial than the anterior horn attachment of the medial meniscus (Proffen et al. 2012). The results of the present study verify the anatomic spatial relationship between the anterior lateral and medial attachments of the meniscus with a reproducible distance between these two structures.
Comparison of human and New Zealand white rabbit tibial plateau dimensions. Aspect ratios were calculated as medial-lateral distance divided by anterior-posterior distance
Medial Aspect Ratio
Lateral Aspect Ratio
New Zealand white rabbit
Human (Long et al. 2012)
While the New Zealand white rabbit shares many resemblances with the human knee joint, there were also additional noticeable differences. In particular, the rabbit stifle had no visible supplemental meniscal root attachments as noted in the human knee, (Ellman et al. 2014; LaPrade et al. 2014; Johannsen et al. 2012) although this observation may be due to the considerably smaller scale of the New Zealand white rabbit stifle. In addition, there was no meniscal attachment to the anterior lateral tibia where the extensor digitorum longus tendon coursed anterior to the lateral meniscus. Proffen et al. found that, in a rabbit model, there is no connection between the lateral meniscus to the ACL as seen in humans (Proffen et al. 2012). However, supplemental fibers between the lateral meniscus and the ACL were too small to be identified in this study.
The lack of a posterior tibial attachment of the lateral meniscus makes the New Zealand white rabbit a difficult natural history model for lateral meniscal pathology. However, the similar attachments for the medial meniscus compared to the human knee make it a potentially viable model to investigate for medial compartment pathology. Meniscal root tears have been biomechanically reported to be equivalent to a subtotal meniscectomy (Allaire et al. 2008; LaPrade et al. 2014). Currently, an in vivo model of meniscal root tears has not been reported and the natural history of meniscal root tears is debated. Prior to embarking on animal model research which could assess the natural history of meniscal root tears on the development of ipsilateral knee compartment arthritis, it is essential to first define the anatomy of the meniscal root attachments to determine if this model is viable.
Because osteoarthritis is slow to develop in humans, the practicality of studying the natural history of the disease process in a timely fashion is limited. Therefore, animal models have been examined as potential tools in studying the progression of the disease and several authors have reported on the efficacy of an osteoarthritis rabbit model (Arzi et al. 2012; Langenskiold et al. 1979; Moskowitz et al. 1973; Hulth et al. 1970; Yoshioka et al. 1996; Aigner et al. 2010; Messner et al. 2001). However, the meniscal root anatomy of the rabbit stifle has not been quantitatively identified and the present study seeks to clarify the clinically relevant anatomical structures within this surrogate osteoarthritis model.
Quantitative anatomical references have become a valuable tool in the human knee joint, especially in a surgical setting. As researchers continue to search for the most relevant animal model of joint degeneration, the New Zealand white rabbit has shown promising results (Yan et al. 2014; Embree et al. 2015). Therefore, a quantitative anatomical examination of the rabbit’s meniscal anatomy would be important as a tool for validating any meniscal root sectioning procedure designed to examine the development of knee osteoarthritis in this in vivo model.
The authors recognize that this study has some limitations. First a possible bias was introduced by having all data collected by a single observer and performed once per specimen. This bias was limited by having all measurements recorded under the supervision of a board certified orthopaedic surgeon. Second, the specimen specifications including age, gender, and history were unavailable and, therefore, no conclusions could be drawn based on these parameters.
The anatomic quantification of the meniscal root attachments in New Zealand white rabbit stifles found that it was similar to the human knee. Particularly, both anterior meniscal roots and the posteromedial meniscal root attachment shared similarities to the human knee joint. Based upon the findings of this study, it is recommended that the rabbit stifle could serve as a model for the natural history of meniscal root tears and the development of osteoarthritis. Further anatomic investigation of the New Zealand white rabbit knee utilizing a variety of imaging modalities would allow for more detailed structural characterization and further validate its effectiveness as an in vivo model.
The results of this study provide a detailed quantitative and qualitative description of the anatomic bony and soft tissue structures of the rabbit stifle joint. Particularly, this study enhances previously existing literature regarding the relationships of the meniscal root attachments to landmarks that will be useful for future biomechanical, surgical, and in vitro studies utilizing the rabbit stifle joint as a translational model for human knee joint degenerative diseases.
anterior cruciate ligament
extensor digitorum longus groove
lateral anterior root attachment
ligament of Wrisberg
lateral tibial eminence
medial anterior root attachment
medial posterior root attachment
medial tibial eminence
posterior cruciate ligament
posterior meniscotibial ligament
The authors thank Grant Dornan, MSc and Travis Turnbull, PhD for their assistance with data analysis and Andy Evansen for his assistance with figure development. We have no direct conflict of interest surrounding this work. All devices were donated gratis, and the study was funded internally by the Steadman Philippon Research Institute.
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
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