liana da Silva, Antônio C. Rocha-Barbosa, Andressa N. Ferreira-Cardoso, Marina R. Carneiro, Daniel C. Resende, Mariana B. Reis, Fernando A. Monteiro
Background
The femorotibiopatellar joint, commonly known as the knee joint, plays a pivotal role in locomotion. In Myrmecophaga tridactyla (giant anteater), a large and terrestrial xenarthran, this joint supports unique locomotor adaptations such as knuckle-walking and digging. Despite its functional significance, detailed anatomical and functional knowledge of the joint remains limited. This study aims to describe the joint using an integrative multimodal approach to better understand its morphology, function, and potential evolutionary implications.
Methods
The researchers employed a combination of dissection, osteological analysis, computed tomography (CT), magnetic resonance imaging (MRI), and histological examination to analyze the knee joints of 11 specimens (both sexes). They documented the bony morphology, soft tissue structures, synovial components, and histoarchitecture of the articular cartilage and menisci. Comparative insights were drawn using available literature on other mammals.
Results
The femorotibiopatellar joint in M. tridactyla exhibits a combination of typical mammalian features and unique specializations. Notable structures included robust cruciate ligaments, a thick meniscus, and a highly congruent femoral-tibial articulation. The patella showed a marked medial positioning. Histological analysis revealed a well-developed layered structure of articular cartilage and fibrocartilaginous menisci. CT and MRI confirmed structural details, such as bone contours and ligament insertions, without notable pathologies. These adaptations are consistent with weight-bearing and mechanical stress associated with knuckle-walking and digging behaviors.
Limitations
The sample size was limited, and some specimens were from captivity, potentially affecting anatomical integrity. Additionally, while imaging techniques enhanced visualization, dynamic studies (e.g., gait analysis) were not conducted, limiting direct functional inference.
Conclusions
The giant anteater's femorotibiopatellar joint combines structural robustness with specific morphological adaptations aligned with its unique locomotor and foraging behaviors. This multimodal study provides foundational knowledge that contributes to both functional anatomy and conservation-focused veterinary care, while also offering comparative insight into xenarthran evolution and biomechanics.
Myrmecophaga tridactyla, radiographs (A and B) and arthrographies (C and D) of the stifle joint. A, C: caudocranial view. (A) left SJ.
1: medial condyle of the femur; 2: lateral condyle of the femur; 3: medial condyle of the tibia; 4: lateral condyle of the tibia; 5: patella; 6: intercondylar
eminences of the tibia; 7: sesamoid bone of the popliteus muscle; 8: head of the fibula; : joint space. (B) left SJ. 1: overlapping femoral condyles; 2:
overlapping tibial condyles; 3: overlapping intercondylar eminences; 4: patella; 5: sesamoid bone of the popliteus muscle; 6: head of the fibula; : joint
space (topography of the infrapatellar fat body); Arrowhead: topography of the patellar ligament. (C) right SJ. 1: suprapatellar recess; 2: patella; 3:
lateral recess; 3’: medial recess; 4: point of insertion of the joint capsule into the extensor sulcus of the tibia; 5: head of the fibula; arrow: joint space
(topography of cruciate ligaments); Arrowhead: lateral meniscus; Filled arrow: medial meniscus; : point of contrast leakage. (D) right SJ. 1:
overlapping femoral condyles; 2: suprapatellar recess; 3: overlapping intercondylar eminences; 4: patella; 5: head of the fibula; : joint space
(topography of the infrapatellar fat body); Arrowhead: caudal recess
How did we do?
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