Synovial folds of the hip

Synovial folds or plicae of the hip are vestigial structures within the hip joint and include labral and ligamental plicae as well as the femoral retinacula.

Gross anatomy

The following synovial folds, plicae or retinacula have been described in the hip joint ^1-5:

• femoral neck plicae or retinacula of Weitbrecht ^2,3
  • originate in the trochanter area
  • insert near the edge of the articular surface of the femoral head
  • anterior retinaculum
    • variably present
    • courses anterior to the femoral neck approximately in a 3 o’clock position
    • originates from the intertrochanteric line
  • medial retinaculum, neck plica, pectinofoveal fold or Amantini’s fold ^2-5:
    • runs inferior to the femoral neck
    • originates at the superior base of the lesser trochanter from the joint capsule (~75%) or the femur (~25%)
    • strongest and most mobile retinaculum
  • lateral retinaculum: 
    • runs superiorly from the media greater trochanteric base to the superior articular surface
• ligamental plica
  • runs parallel to the ligamentum teres
  • originates from the acetabular fossa
• labral plicae
  • interposed between the labrum and joint capsule

Function

The retinacula of Weitbrecht in particular the lateral retinaculum are considered to have an important role in the vascular supply of the femoral head ^1,2.

Histology

Histologically the retinacula consist of fatty tissue with bands of collagen and elastic fibers surrounded by synovium and a significant number of arteries within the stroma ².

Variant anatomy

The labral plicae are found in 80-90% of hip joints. The anterior retinaculum of Weitbrecht is absent in up to 60% of individuals ^1,2.

Radiographic features

MRI

On MRI the retinacula of Weitbrecht and the other synovial folds of the hip appear as hypointense bands surrounded by synovial fluid.

Signal characteristics

• T1: isointense
• T2: low signal intensity
• PDFS/T2FS: low signal intensity

CT/MR arthrography

On CT arthrography they can be seen as bands within the joint space.

The pectinofoveal fold or medial retinaculum of Weitbrecht can be visualized in up to 95% of individuals and displays a variable appearance with smooth or irregular contours ^3-5. Labral and ligamental plicae were visualized in up to 76% and 78% of MR arthrographies ^4,5.

Radiological report

The usage of the term ‘plica’ within the radiological report has been discouraged in particular for the pectinofoveal fold because symptomatic hip plicae represent a very rare condition ^1,4.

History and etymology

The synovial retinacula of the hip were first described by the German anatomist Josias Weitbrecht in 1742 ^1-3.

Labral plicae were first described by Z. Fu et al. in 1991 ^3,6.

Clinical importance

The degree of injury to the retinacula correlates with the displacement of femoral neck fractures ¹.

Intrinsic pathologies or clinical symptoms associated with plicae of the hip are rare and include pain, effusion and audible clicks. They have been described for the labral plica. The femoral neck plicae and ligament plica of the hip are considered to be unlikely symptomatic ^1,5.

Related pathology

• impingement
• chronic inflammation
• hip joint effusion