Comment on ‘Quadriceps tendon malalignment is an independent anatomical deformity which is the primary abnormality associated with lateral facet patellofemoral joint osteoarthritis’

We have read the paper by Talbot et al. “Quadriceps tendon malalignment is an independent anatomical deformity which is the primary abnormality associated with lateral facet patellofemoral joint osteoarthritis” that appeared in the December 2023 issue of KSSTA [1].

We would like to congratulate the authors on their work describing this novel measurement and bringing to light the importance of quadriceps malalignment. We look forward to further works examining patellofemoral joint (PFJ) instability (PFJI) and pain (PFJP), along with optimising patellofemoral kinematics post total joint arthroplasty.

However, we think it is important to highlight in writing some of the potential concerns with this study, else the conclusions from the paper may go unchallenged with future literature.

The paper draws the conclusion that quadriceps tendon malalignment (QTA) is independent of bony morphology and the dominant predictor of lateral Patella femoral joint osteoarthritis (PFJOA).

In contrast, other papers have highlighted the trochlear dysplasia is the main aetiology of PFJOA [8, 10, 13].

Talbot et al. measured trochlear morphology using a number of methods and utilising multiple locations from proximal to distal along the trochlea. Trochlear dysplasia relates to the morphology in the most proximal portion of the trochlear, even in patients with high-grade trochlear dysplasia, the sulcus angle will normalise as you move distally along the trochlea [6].

We have concerns that their measurements for trochlear dysplasia involve measuring the trochlea at a positions too distal to correctly diagnose and quantify the trochlear dysplasia accurately.

There is no utilisation of the Dejour V2 classification for trochlear dysplasia, which is based on CT [5]. The Dejour V2 classification was of landmark importance because it highlighted importance of the supratrochlear spur. The supratrochlear spur is the anteriorization of the trochlea floor relative to the anterior femoral cortex. This has recently been proven in biomechanical literature to increase the patellofemoral joint reaction forces independent of the axial shape of the trochlea, via an anti-Maquet effect [4]. The decreased congruence of the patella with the dysplastic trochlea, due to changes to the trochlea morphology in the axial plan, has also been shown to increase PFJ pressures [14] and PFJOA [11], and has been the clinical rationale to treat trochlear dysplasia in patients with anterior knee pain [3, 7, 15]. In PFJ arthroplasty, success is influenced by the ability to reduce the trochlear offset with respect to the anterior femoral cortex [2], again highlighting the importance of trochlear bony anatomy to outcomes with respect to PFJ surgery for PFJOA. In trochlear dysplasia, there is also coronal plan malalignment of the trochlear sulcus with respect to the mechanical axis of the femur, emphasizing the importance of realigning the new sulcus of the PFJ arthroplasty to improve of patellar tracking [9].

The primary author circulates videos on social media and at scientific presentations [12] to describe how to measure the QTA, which clearly demonstrates high grade trochlea dysplasia, which is illustrative and reflective of the points made here.

Patellofemoral pathological is a complex interplay of bony, ligamentous, muscle and muscle balance. We advise the authors to pay attention to their measurements for trochlear dysplasia, to better investigate the association of trochlear dysplasia with PFJOA and QTA in their population. We fear that failure to do so will result in misinformation that the QTA is independent of trochlear bone morphology, when it potentially could be the cause of it.