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Home / Equine Research Bank / BMC Vet Res / The equine patellar ligaments and the infrapatellar fat pad ...
BMC veterinary research2023; 19(1); 20; doi: 10.1186/s12917-023-03579-3

The equine patellar ligaments and the infrapatellar fat pad – a microanatomical study.

Abstract: Interpretation of patellar ligament (PL) ultrasonography may be difficult, as hypoechoic or heterogenous echogenicity are common findings. Verifying suspected disease of equine PLs by histopathology is also problematic as descriptions of normal PL vascularity and histology are scarce. The current study describes the PL and infrapatellar fat pad (IFP) vascular pattern from computed tomography scans of barium perfused normal equine specimens (n = 8; age 10 days to 18 years), as well as routine histology to serve as a reference for future investigations into PL pathology and IFP disease. Results: The PLs received a bipolar blood supply. Vascular architecture consisted of numerous distinct longitudinal vessels with several horizontal connections, which branched into extensive latticeworks of smaller vessels throughout the ligaments. Several vascular connections between the PLs and the IFP were identified. One distinct longitudinal vessel was seen entering each of the IFP lobes at the distocranial aspect, branching extensively into lobar vascular networks which anastomosed by several horizontal branches at the mid portion of the IFP where the two lobes merge. Histologically, there were large variations in PL interfascicular endotenon thickness, vascularity and fatty infiltration; these parameters increased with age for the intermediate and medial PL. Areas of metaplastic tenocytes / chondroid metaplasia were identified in all investigated adult medial PLs; in 2/7 in the intermediate PL and in 4/7 in the lateral PL. The adult IFP consisted of white unilocular adipose tissue, organized in lobules separated by thin connective tissue septa increasing in thickness towards the periphery and the distocentral aspect. Conclusions: The equine PLs and IFP are highly vascularized structures with ample vascular connections suggestive of crosstalk. This, together with the large variation in PL endotenon thickness, vascularity and fatty infiltration, should be taken into consideration when assessing potential PL histopathology as these changes increase with age and are found in horses without clinical signs of stifle disease. Metaplastic tenocytes / chondroid metaplasia should be considered a normal finding throughout the medial PL and is not age dependent. The role of the equine IFP in stifle disease has yet to be elucidated.
© 2023. The Author(s).
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Publication Date: 2023-01-23 PubMed ID: 36691004PubMed Central: PMC9869593DOI: 10.1186/s12917-023-03579-3Google Scholar: Lookup
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Summary

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The study provides a detailed description of the vascular pattern of the equine patellar ligaments and infrapatellar fat pad, using computed tomography scans and routine histology. The findings are intended to serve as a reference for future research into diseases affecting these structures.

The Research

  • The authors of this study aimed to give a detailed description of the patellar ligament (PL) and infrapatellar fat pad (IFP) in horses, in order to aid further study into diseases affecting these structures.
  • This research utilised computed tomography (CT) scans and routine histology techniques on a range of specimens from horses of different ages.

Methodology

  • Eight equine specimens, ranging in age from 10 days to 18 years old, were subjected to CT scans after being perfused with barium to highlight the vascular structures.
  • The researchers then conducted a histological analysis to evaluate tissue structure and morphology.

Findings

  • The study found that the equine PLs receive a bipolar blood supply with numerous longitudinal and horizontal vessels, which create extensive networks throughout the ligaments.
  • There were also several vascular connections between the PLs and the IFP found. In the IFP, distinct longitudinal vessels entered each of the fat pad lobes, branching widely into lobar vascular networks.
  • Through histology, it was observed that there were large variations in PL interfascicular endotenon (a structure connecting various components of a ligament) thickness, vascularity, and fatty infiltration. All these parameters increased with age. Areas of metaplastic tenocytes, cells responsible for the generation of tendons, and chondroid metaplasia, the conversion of normal cells into cartilage cells, were found in all adult PLs.
  • The IFP consisted of white unilocular adipose tissue, organized into lobules separated by thin connective tissue, with its thickness increasing towards the peripheral areas.

Conclusions

  • The authors concluded that both the PLs and the IFP are highly vascularized (have a rich blood supply) structures and have several vascular connections that could be significant for the functionality of the respective structures.
  • However, these findings should be considered in context, as variations in PL endotenon thickness, vascularity, and fatty infiltration were found to increase with age and are prevalent even in horses without clinical signs of stifle disease.
  • Lastly, the exact role of the equine IFP in stifle disease (a condition affecting the horse’s knee) remains unclear and requires further investigation.

Cite This Article

APA
Fjordbakk CT, Marques-Smith P. (2023). The equine patellar ligaments and the infrapatellar fat pad – a microanatomical study. BMC Vet Res, 19(1), 20. https://doi.org/10.1186/s12917-023-03579-3

Publication

BMC veterinary research
ISSN: 1746-6148
NlmUniqueID: 101249759
Country: England
Language: English
Volume: 19
Issue: 1
Pages: 20
PII: 20

Researcher Affiliations

Fjordbakk, Cathrine Taule
  • Faculty of Veterinary Medicine, Department of Companion Animal Clinical Sciences, Norwegian University of Life Sciences, Equine Teaching Hospital, Oluf Thesens Vei 24, 1432, Ås, Norway. cathrine.fjordbakk@nmbu.no.
Marques-Smith, Patrick
  • Faculty of Veterinary Medicine, Department of Companion Animal Clinical Sciences, Norwegian University of Life Sciences, Equine Teaching Hospital, Oluf Thesens Vei 24, 1432, Ås, Norway.

MeSH Terms

  • Animals
  • Adipose Tissue / anatomy & histology
  • Adipose Tissue / diagnostic imaging
  • Horses / anatomy & histology
  • Knee Joint
  • Patella
  • Patellar Ligament / anatomy & histology
  • Patellar Ligament / blood supply
  • Patellar Ligament / diagnostic imaging
  • Stifle
  • Tomography, X-Ray Computed / veterinary

Grant Funding

  • H-18-47-393 / Swedish-Norwegian Foundation for Equine Research
  • H-18-47-393 / Swedish-Norwegian Foundation for Equine Research

Conflict of Interest Statement

There are no competing interests.

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Citations

This article has been cited 3 times.
  1. Hefferan SA, Blaker CL, Ashton DM, Little CB, Clarke EC. Structural Variations of Tendons: A Systematic Search and Narrative Review of Histological Differences Between Tendons, Tendon Regions, Sex, and Age. J Orthop Res 2025 May;43(5):994-1011.
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  2. Law E, Wright L, Uhlhorn M, Hernlund E, Nilemo C, Rhodin M. Hypoechoic ultrasonographic findings in the patellar ligaments are common in riding and trotting horses in training (116 cases). Vet Radiol Ultrasound 2025 Jan;66(1):e13446.
    doi: 10.1111/vru.13446pubmed: 39377554google scholar: lookup
  3. Schöpper H, Egerbacher M. Arterial Blood Supply of the Stifle Joint in Horses. Animals (Basel) 2024 Apr 24;14(9).
    doi: 10.3390/ani14091279pubmed: 38731283google scholar: lookup
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