Is the contralateral limb a clinical and biomechanical reference to assess individuals with unilateral and bilateral patellofemoral pain? An intra and interlimb strategies and objective function analysis

Abstract

Objective function is one of the primary clinical outcomes on the treatment of patellofemoral pain (PFP). Previous studies have reported that individuals with PFP have compromised performance during clinical tests measuring objective function, such as the single leg hop test (SLHT). However, these findings are limited to analysis considering the comparison between painful (unilateral PFP) or most painful (bilateral PFP) limbs of individuals with PFP and the dominant or non-dominant limb of pain-free ones. This contrasts with the clinical practice, where objective function assessment using the SLHT is limited to the measure of the contralateral limb (i.e., pain-free or less painful limb) as a clinical reference, which may not be reliable when bilateral PFP is reported. In fact, individuals with unilateral PFP may present an interlimb asymmetry (i.e., limb symmetry index <90%) as their contralateral pain-free limb may have better performance, while those with bilateral PFP may present a misinterpreted interlimb symmetry (i.e., limb symmetry index >90%), that might indicate a compromised performance of both limbs. Such differences may suggest that assuming the contralateral limb as a normative value may not adequately assess objective function of individuals with unilateral and bilateral PFP during the SLHT. Furthermore, recent investigations have also raised some concerns regarding the poor accuracy of solely base the functional performance assessment on objective measures (i.e., hop distance in cm) as this analysis does not consider intra- and interlimb compensatory strategies that might be used to respond the demands of the task. Some compensatory strategies have already been identified in individuals with PFP and are proposed as attempts to reduce patellofemoral joint stress and avoid pain. However, these findings are also based on analyses investigating only the painful or most painful limbs of individuals with unilateral and bilateral PFP. It is possible that individuals with unilateral PFP may use interlimb compensatory strategies to reduce the demand on the painful limb, relying more demand on the pain-free one. On the other hand, individuals with bilateral PFP may rely on intralimb strategies to reduce the knees' contribution and re-distributes the demand to the ankle or hip joints. Such compensatory strategies may be reasonable in a short term, but their persistence use may favor bilateral consequences in those with unilateral PFP as well as ankle or hip injuries in those with bilateral PFP. Investigating intra and interlimb compensatory strategies in individuals with unilateral and bilateral PFP during landing of the SLHT may also suggest the needed to identify them in a clinical setting (e.g., using two-dimensional motion analysis) to further support the assessment of objective function and prevent their suboptimal identification. Therefore, this proposal has two aims: 1) to compare the performance of the painful or most painful, and contralateral limbs of individuals with bilateral and unilateral PFP during the SLHT, also comparing their performance with pain-free individuals; and 2) to compare intra and interlimb biomechanics during landing from SLHT in individuals with bilateral and unilateral PFP, and pain-free individuals. Female and male aged 18 to 35 years old, with and without PFP, will be recruited at Toledo-OH. Objective function will be assessed by the hop distance (in cm). Motion analysis during landing will be collected using a three-dimensional system synchronized with three force plates. The variables of interest will be: peak trunk and knee flexion angles, total energy absorption, hip, knee and ankle energy absorption contribution, intralimb hip to knee extensor moment and ankle to knee extensor moment, peak and loading rate of the vertical ground reaction force. General linear model using multivariate F statistics will be used to compare the variables of interest between groups and limbs.