The morphological features of the mediopatellar and lateral folds of the developing knee joint: a fetus cadaveric study

Abstract

The aim of the study was to evaluate the morphological features of the mediopatellar and lateral folds in fetal knees in the absence of any exposure to certain stress factors such as exercise or trauma. The study was performed in the knee joints of 15 fetuses (6 males, 9 females) obtained as spontaneous abortion material at 20-34 weeks of gestation. The mediopatellar and lateral folds of the fetuses were classified into eight subgroups according to the following morphological features: A- Absence of folds; B- Short vertical band; C- Long vertical band; D- Narrow horizontal band; E- Broad horizontal band; F- Horizontal band accompanied by a vertical band; G- Horizontal band without a vertical band; H- Fenestrated band. The synovial membrane, covering the infrapatellar fat pad and forming the alar folds, extended upwards and formed the medial and lateral horizontal folds that covered the inferior part of the posterior aspect of the patella. These horizontal folds were thicker in the lower parts (close to their insertions) and became thinner towards the free ends. The horizontal band of the mediopatellar fold was observed in all cases, with an accompanying vertical band in 76.7% of the cases. A horizontally located lateral fold was absent in both knees of one fetus. The frequency of a horizontally located lateral fold was 93.3% and a vertical fold was accompanying in only 28.6% of these cases. It is of note that the horizontal band of the mediopatellar fold observed in all specimens has never been defined in previous classifications. In 10% of the knees, the vertically located part of the mediopatellar fold presented as a large band extending upward and being squeezed between the articular surface of the patella and the medial condyle of the femur. The lateral fold was observed as a large band in 10% of the knees. Another observation was that the higher level the vertical band of the mediopatellar and lateral folds began, the wider the horizontal band was, occupying more place in the patellofemoral space. It was remarkable that the frequencies of the vertically located parts of the lateral and mediopatellar folds in fetuses were higher than those reported for the adults in the literature. Our findings suggest that the resorption process of the mesenchymal tissue, particularly in the lateral part, continues until adulthood and causes age-dependent alterations in the formation of intra-articular folds. The synovial folds occupy more space between the patella and femur in the early stages of life than seen in adults. This may be a more frequent cause of unexplained knee pain in children than expected.