Prepatellar quadriceps continuation: MRI of cadavers with gross anatomic and histologic correlation.

OBJECTIVE: The "prepatellar quadriceps continuation" is the appropriate designation for the deepest soft-tissue layer that lies anterior to the patella, related to the deep rectus femoris tendinous fibers. The purpose of this study was to define and investigate the prepatellar quadriceps continuation and its relationship with the patella in cadavers using MRI and gross anatomic and histologic analyses.
MATERIALS AND METHODS: MRI of 12 fresh-frozen knee specimens was performed using T1-weighted sequences in the axial and sagittal planes. Specimens were then sectioned in 3-mm-thick slices to correspond precisely with the MR images. Histologic analysis was performed in two specimens. The MR images were compared with findings seen on anatomic sectioning and histology. In addition, the layered organization of the patellar tendon was analyzed in 29 embalmed knee specimens obtained from human cadavers of both sexes.
RESULTS: The normal prepatellar quadriceps continuation was seen as a band of low signal intensity in the MR images. This structure could not be differentiated easily from the low signal intensity of the patellar cortical bone. The sagittal plane was the most optimal plane for visualization of the attachment site of this continuation to the patella. Gross anatomic dissections revealed that at the proximal pole of the patella, the quadriceps tendon was formed by the rectus femoris and vastus intermedius muscles. The entire quadriceps tendon had an average thickness of 8.54 mm in this region. The thickness of the quadriceps tendon fibers extending over the anterior patellar surface measured, on average, 0.68 mm, and the average thickness of those fibers inserting into the proximal patellar pole was 7.87 mm. Histologic analysis showed that the attachment site of the prepatellar quadriceps continuation was formed by the distal extension of the deep longitudinal fibers of the rectus femoris tendon. At the border zone between the tendons and the patella, the tendinous fibers gradually were transformed into fibrocartilage. This so-called chondroapophyseal type of attachment was found to cover the entire anterior surface of the patella. The average thickness of the fibrocartilage at the insertion of the quadriceps tendon, patellar tendon, and prepatellar quadriceps continuation measured 0.136, 0.023, and 0.004 mm, respectively.
CONCLUSION: The prepatellar quadriceps continuation is formed by fibers of the rectus femoris tendon and connects the quadriceps and patellar tendons. All tendons are attached through formation of a chondroapophyseal zone and are therefore transformed into a seam of fibrocartilage. Based on these anatomic features, separation of the prepatellar quadriceps continuation from the patella in the absence of more extensive abnormalities of the quadriceps mechanism is plausible.