**4. Discussion**

The aim of this study was to investigate the effectiveness of MI practice as adjunct intervention to routine physical therapy in patients after TKA on measures of physical function and pain.

A current umbrella review with a meta-analysis showed a positive effect of MI on physical function in general (small cES = 0.55), strength (moderate ES = 0.85), timedup and go test (small ES = 0.49), self-reported physical function (small ES = 0.34), and pain intensity reduction (moderate ES = 0.67) in TKA patients. Given that both fixed and random meta-analysis models showed similar results, these findings can be interpreted as robust.

There are several review articles aimed to investigate the effects of psychological interventions on physical function measures in the apparently healthy [19, 20] and diseased populations [10, 11, 21, 22]. However, these investigations substantially differed in the primary aims, the population included and measures of interests, which consequently resulted in the overall methodology adopted. For example, Paravlic et al. [19] investigated the effects of MI practice on the measures of maximal strength in the healthy adults. Authors found positive effects of MI practice on maximal strength, favoring isometric imagined muscle actions over dynamic muscle actions, whereas a combination of MI with physical practice was found equally effective as physical practice alone [19]. In other reviews, authors investigated the effects of various cognitive strategies in athletes sustaining anterior cruciate injuries (ACL) [21], TKA and total hip arthroplasty patients [9, 22] or TKA patients in isolation [10, 11]. These studies were looking at different measures of interest such as functional mobility [9, 21, 23], balance [9–11, 23], maximal strength [10, 11, 19] or pain intensity [10, 11] and found equivocal results. Therefore, the current study with a rigorous methodological approach showed robust and positive findings supporting MI practice intervention use in rehabilitation of TKA patients when physical function and pain are primary rehabilitation goals.

Ample evidence suggests that the mechanism underlying effectiveness of imagined contractions relies on both neurophysiological and psychological factors [19, 24, 25]. There is an evidence that imagined movements are functionally equivalent to the physically executed movements in terms of intention, planning, execution duration and task difficulty [25, 26]. The present study found a positive effect of MI on maximal strength and other measures of physical function that are more complex in nature, such as walking and dynamic balance (assessed by TUG test). TUG test is a

complex test that evaluates a several motor-related domains such as lower body strength (e.g. getting up from the chair), walking speed (e.g. walking from the chair to the first turning point at a distance of 4.5 m), agility (turning around a cone), and dynamic balance (e.g. all these tasks together). Paravlic et al. showed a positive transfer from simple MI task that focused only on strength to more complex motor tasks mentioned above. The authors also showed that strength improvements following MI practice in TKA patients were significantly and positively correlated with preto-post-intervention changes in patients' kineasthetic (high, r = 0.741) and internal (moderate, r = 0.623) ability to imagine given tasks. This supports previous findings in the literature that the effects of MI depend on the individual's ability to imagine a particular task as well as the MI type and MI perspective used by the subject [27]. It is suggested that someone who cannot visualize a given task will not benefit from the MI practice [27]. However, Paravlic et al. demonstrated that MI ability can be improved by the MI practice intervention exposure, providing those unfamiliar with MI with new knowledge about how to begin using MI and benefit from it.

In addition to improving physical function, this study showed a positive effect of MI on pain reduction in TKA patients. This finding is consistent with a recent review by Benjamin et al. [28], which showed that MI as adjunctive therapy is superior to standard physical therapy alone in terms of pain reduction and ROM improvements in patients with chronic musculoskeletal conditions. In contrast, the authors found no differences in efficacy between MI and routine therapies acute pain is considered. Because centrally driven mechanisms (e.g. neuroplastic changes and central sensations) [29] predominate in chronic pain, in contrast to acute pain conditions that are driven by peripheral factors (e.g. structural impairment at a peripheral site) [30], the efficacy of MI can be explained by the modulation of cortical areas associated with pain-related cortical reorganization, such as the primary somatosensory cortex, the anterior cingulate cortex and the insula [31]. Although the subsequent mechanisms behind the efficacy of MI in chronic pain are still controversial, MI actually allows activation of motor cortex without overt movement execution [19, 25], sending a motor-related cortical potential via efferents and consequently uncoupling movement from pain perception [28, 31]. Even preliminary data indicate that the MI practice may not be more effective than routine therapy alone, given its mechanism, it could serve to prevent further exacerbation of symptoms and avoid chronic pain events [28].

Considering MI practice programming, only one review with meta-analysis examined a MI practice dose–response relationship, suggesting that effects of cognitive training on outcomes in TKA patients were predicted by the total number of training sessions per study [9]. A recent review by Paravlic suggested recommendations for MI rehabilitation practice in the home setting [32]. In brief, there are some steps that should be followed to benefit from MI practice: (a) patients' imagery ability must be assessed to inform the therapist which MI perspective and which MI type should be used; (b) it is recommended to provide patients with audio instructions to follow during practice sessions [33]; (c) at the beginning of MI practice therapist should propose simple motor task that is easy to perform by patient and (d) the following motor imagery variables were associated with strength improvement: a training period of 4 weeks, a training frequency of three sessions per week, a training volume of two to three sets, 25 repetitions per set and a single session duration of 15 minutes [19]. While the latter recommendations were compiled from the published literature, the original studies aimed at investigating the effects of different MI practice volumes (training duration, weekly frequency, number of imagined contractions per set, and per single session) are justified.

*Motor Imagery as Adjunct Therapy for Rehabilitation of Total Knee Arthroplasty Patients… DOI: http://dx.doi.org/10.5772/intechopen.106388*
