Patellofemoral Anatomy and Its Surgical Implications

Proximal Medial Patellar Complex

As our understanding of medial patellofemoral anatomy continues to grow, the implications for surgical reconstruction have evolved. Whereas earlier reports focused on reconstruction of the medial patellofemoral ligament (MPFL) as the primary treatment for lateral patellar instability, more recent anatomical descriptions have noted additional fibres that extend proximal to the patella, leading to the development of new reconstruction techniques. Additional reports have focused on the significance of the fibres that are distal to the MPFL and contribute to the lateral restraint of the patella in knee flexion.

These anatomical studies have led to several new terms that are used to describe and classify the medial patellar stabilisers that include the MPFL. The proximal medial restraints are the MPFL and medial quadriceps tendon femoral ligament (MQTFL), which some authors also refer to in a combined fashion as the proximal medial patellofemoral complex (MPFC) because of the variability of the fibres at their attachment on the extensor mechanism.

The MPFL has traditionally been described as an extension of fibres from the medial femur to the medial border of the patella, in a broad, fan-shaped attachment spanning 14 to 41 mm. ^{, ,} The ligament is thin, reported to be 0.44 ± 0.19 mm in one study, running in layer 2 of the knee, deep to the vastus medialis obliquus, while remaining superficial (extraarticular) in relation to the capsule. Additional proximal fibres of the MPFL extending to the quadriceps tendon have been highlighted by authors who have performed dissections using an intraarticular approach. Fulkerson termed these fibres as the MQTFL, describing the attachment point as distinct from the MPFL fibres that insert on the patella ( Fig. 26.1 ). Tanaka described the broad attachment to both structures as part of a single complex, showing in a cadaveric study of 28 knees that 57% ± 20% of the fibres attached to the patella, whereas the remainder of the fibres attached to the quadriceps tendon. The author also noted significant variability between the location of the attachments that may account for some of these differing descriptions, with some knees having all fibres attaching to the patella and others having all fibres attaching solely to the quadriceps tendon.

The biomechanics of the proximal structures to date have focused on the MPFL; the MPFL is agreeably the primary stabiliser resisting lateral patellar translation, contributing approximately 50% to 60% in early knee flexion. ^{, ,} The literature also supports that the MPFL is injured in nearly all acute traumatic dislocations, with the patella insertion primarily involved in isolation or combination in the paediatric population. The biomechanics and injury pattern of the MQTFL portion of the proximal medial structures continue to be defined.

Surgical Correlation for Proximal MPFC Patellar Attachment Sites

The broad attachment of the fibres on the extensor mechanism allows for several options in terms of reconstruction. The proximal extent of the MPFC has been described to be 14.6 mm proximal to the superior pole of the patella, with the distal extent inserting 26.7 mm distal to the superior pole, indicating that anatomical reconstruction should maintain the fixation points on the extensor mechanism within these areas.

Kang et al. described two functional bundles within this complex, including the superior oblique bundle attaching to the proximal patella and the quadriceps tendon and the inferior straight bundle extending to the patella. The differential lengths of the proximal and distal fibres are reported to be 2 to 7 mm, ^, which suggest varying isometric functions between the two. This supports the concept of a 2019 report on a double bundle reconstruction technique that includes concurrent reconstruction of both MPFL and MQTFL fibres. In a two-arm MPFL surgical construct in a patient with a small patella or short articular length, the distal arm of the MPFL graft should not be positioned lower than 50% of the articular surface length. Therefore positioning one arm to the proximal patella and the superior arm to the quadriceps tendon would potentially be a better surgical construct ( Fig. 26.2 ).

Alternatively, understanding the midpoint of the anterior attachment can serve as a guide in the setting of reconstruction with single-stranded grafts. The midpoint of the MPFC at its anterior attachment has been reported to be reproducibly identified at the junction of the medial border of the quadriceps tendon and the articular surface of the patella in a cadaveric study. This point has also been shown to correlate radiographically with a location that is 19% of the patellar articular distance from the superior articular pole, which may be helpful when using fluoroscopic guidance to identify the midpoint of its patellar attachment.