The quadriceps insertion of the medial patellofemoral complex demonstrates the greatest anisometry through flexion

Abstract

PurposeA comprehensive understanding of the biomechanical properties of the medial patellofemoral complex (MPFC) is necessary when performing an MPFC reconstruction. How components of the MPFC change over the course of flexion can influence the surgeon’s choice of location for graft fixation along the extensor mechanism. The purpose of this study was to (1) determine native MPFC length changes throughout a 90° arc using an anatomically based attachment and using Schöttle’s point, and (2) compare native MPFC length changes with different MPFC attachment sites along the extensor mechanism. MethodsEight fresh‐frozen (n = 8), cadaveric knees were dissected of all soft tissue structures except the MPFC. The distance between the femoral footprint (identified through anatomical landmarks and Schottle’s point) and the MPFC was calculated at four attachment sites along the extensor mechanism [midpoint of the patella [MP], the center of the osseous footprint of the MPFC (FC), the superomedial corner of the patella at the quadriceps insertion (SM), and the proximal extent of the MPFC along the quadriceps tendon (QT)] at 0°, 20°, 40°, 60°, and 90° of flexion. ResultsLength changes were investigated between the MPFL femoral attachment site and the radiographic surrogate of the MPFL attachment site, Schottle’s Point (SP). Paired t tests at each of the four components showed no differences in length change from 0° to 90° when comparing SP to the anatomic MPFC insertion. MPFL length changes from 0° to 90° were greatest at the QT point (13.9 ± 3.0 mm) and smallest at the MP point (2.7 ± 4.4 mm). The FC and SM points had a length change of 6.6 ± 4.2 and 9.0 ± 3.8, respectively. Finally, when examining how the length of the MPFC components changed through flexion, the greatest differences were seen at QT where all comparisons were significant (p < 0.01) except when comparing 0° vs 20° (n.s.). ConclusionThe MPFC demonstrates the most significant length changes between 0° and 20° of flexion, while more isometric behavior was seen during 20°–90°. The attachment points along the extensor mechanism demonstrate different length behaviors, where the more proximal components of the MPFC display greater anisometry through the arc of motion. When performing a proximal MPFC reconstruction, surgeons should expect increased length changes compared to reconstructions utilizing distal attachment sites.

Why Determining the Native Length Change Pattern of Medial Patellofemoral Ligament Is Still a Challenge: State-of-the-Art Review of Potential Sources of Heterogeneity within Studies Evaluating Isometry of MPFL

“…However, different authors adopted different measures to properly mark them. For example, femoral attachment of MPFL was reported to be identified either by using Schöttle's point [25,27] or midway between adductor tubercle and medial epicondyle [14,23]. On the patellar attachment, authors reported identifying different insertions such as "at 20%, 40%, and 60% of the patellar length from the proximal tip" [22] or "20% (point 20), 30% (point 30), 40% (point 40), 50% (point 50), and 60% (point 60) from the superior pole of the patella" [25].…”

“…From 10 original articles included in this review, nine studies identified multiple fibers of MPFL for assessment of length change [7,14,21,22,[24][25][26][27][28] and one study assessed only a single fiber [23]. Various femoral and patellar attachments were analyzed, as specified in Table 2.…”

“…Nine studies performed measurements in 3D [14,[21][22][23][24][25][26][27][28]; however, only in four was MPFL measured with respect to its convexity [7,14,24,25]. CT was utilized in four studies [14,22,24,25], caliper in two studies [21,27], MRI in one study [7], suture in one study [23], and other measurement methods in two studies [26,28]. Only five out of 10 studies reported precision of measurements [14,21,23,24,27].…”

“…CT was utilized in four studies [14,22,24,25], caliper in two studies [21,27], MRI in one study [7], suture in one study [23], and other measurement methods in two studies [26,28]. Only five out of 10 studies reported precision of measurements [14,21,23,24,27]. Within included review articles, just one study investigated whether the methodology of identification of measured fibers had an impact on observed MPFL length change pattern [29].…”

“…While it is not clear whether demographics influence biomechanics of MPFL, it was reported to influence the biomechanics of other ligaments, potentially making it important to precisely report number, age, and sex of patients/cadavers [16,20]. Within original studies included in this review, all 10 articles reported number of patients/cadavers [7,14,[21][22][23][24][25][26][27][28]; however, only seven studies specified the age of patients/cadavers [7,14,[22][23][24][25][26], and also seven studies reported the sex of patients/cadavers [7,14,[21][22][23][24][25]. Within included review articles, only one of them investigated number of patients/cadavers and their age as potential factors influencing MPFL length change pattern [16].…”