Summary

This study demonstrated that the MPFC is one ligamentous complex, without structural separation or histologic variation between the MPFL and MQTFL fibers.

Abstract

The medial patellofemoral complex (MPFC) is known as the primary static restraint to lateral patellar translation. Previously referred to as the medial patellofemoral ligament (MPFL), more recent studies have highlighted the proximal attachment of the ligament to the quadriceps tendon, termed the medial quadriceps tendon femoral ligament (MQTFL) fibers. Despite the common origin of the ligaments on the femur, no studies have demonstrated the histologic relationships between the MPFL and MQTFL fibers. Therefore, the purpose of this study was to describe and compare the histologic appearance of the MPFL and MQTFL fibers to better understand its role in patellar stability.

Cadaveric knees were dissected using a lateral parapatellar approach, where the extensor mechanism was reflected to reveal an articular sided view of the medial patellofemoral joint. The synovium (Layer 3) was removed to reveal the MPFC fibers. On the extensor mechanism, the fibers attaching to the patella were defined as the MPFL fibers, and those attaching to the quadriceps were labeled as the MQTFL fibers. The percentage of fibers attaching to the patella (MPFL) was calculated. The proximal and distal margins of the MPFC were marked with ink, and the midsection of the ligament was removed en bloc and prepared in formalin solution and a paraffin block. Masson trichrome stains were used for determination of tissue micromorphology, and the specimen were evaluated for raphe, septae, or other indications of separation between the MPFL and MQTFL fibers. The morphology and distribution of collagen fibers, vascular structures were compared between the MPFL and MQTFL fibers.

Five cadaveric knees were included in this study, with a mean age of 72±12 years. The femoral attachment was 15.1±4.1mm in length, while the extensor mechanism attachment was 41.5±10.3mm. All knees were found to have attachments to both the patella and quadriceps tendon, with 45.0±22.4% of fibers attaching to the patella, and the remainder attaching to the quadriceps tendon. Along the entire length of the MPFC, continuous, parallel and densely packed collagen bundles were identified that spanned the entire ligament. No major raphe or septae was noted between the fibers, indicating that this was a single ligamentous structure. Throughout the ligament, a substantial presence of blood vessels was identified. When comparing the MPFL vs MQTFL fibers, no gross differences in the distribution or morphology of the collagen fibers was noted. Additionally no appreciable differences between the distribution or morphology of the vascular structures were identified.

This study demonstrated that the MPFC is one ligamentous complex, without structural separation or histologic variation between the MPFL and MQTFL fibers. Vascular structures such as arterioles were identified throughout the complex. Further studies are needed to understand the role of differentiating between the MPFL and MQTFL fibers from a biomechanical and clinical perspective to optimize reconstruction techniques in the surgical treatment of patellar instability.