Dynamic Postural Stability after Cartilage Repair in the Knee

1. INTRODUCTION

It is no surprise to state that neuromuscular control is essential to maintaining balance as well as producing desired movements. The neuromuscular system is comprised of a variety of sensorimotor units and the central integration and processing of various components provide for overall functional joint stability and control of movements [1]. Stability and balance are based on inputs from a host of afferents that provide input to the central nervous system, which then affects muscle control to maintain postural stability [2]. This is all done unconsciously, yet if there is a deficit in proprioceptive input, the neuromuscular pathways can be impacted, potentially leading to the development of risk factors that may contribute to injury [3].

Among the tissues in the knee joint, mechanoreceptors have been previously documented in detail [4, 5], with peripheral receptors (mechanoreceptors) being found within joints, ligaments, tendons, muscles, and skin [6]. It has been stated that this afferent system controls motion with a high degree of regulation against internal and external disturbances and maintains joint stability [7]. However, there is little understanding of the role, if any, that articular cartilage may play in proprioception. There has been some indication that chondrocytes may contain mechanoreceptors [8], while an earlier article had proposed a chondrocyte mechanoreceptor model [9]. More recently, Donnell et al. (2019) stated that subchondral bone may provide ingrowth of sensory nerves into the articular cartilage [10].

However, there has been little research into articular cartilage's role in neuromuscular control and joint stability. Dynamic postural stability (DPS) has already been documented to be affected by a variety of lower extremity injuries [11-14]. However, very little data has been presented, which has assessed DPS regarding chondral lesions. Unfortunately, articular cartilage has a very limited capacity for intrinsic repair [15]. Full-thickness cartilage lesions may be associated with significant pain and impaired function, and if left untreated, these defects will fill with biomechanically incompetent fibrous tissue, eventually leading to premature osteoarthritis [16]. While it is generally recognized that symptomatic articular cartilage defects ought to be restored, these lesions remain a difficult medical problem to treat [17]. As a result, cartilage defects, with their associated degenerative changes, maybe a major source of disability and present a significant socioeconomic burden [18].

A recent paper investigated the proprioceptive function of patients with isolated articular cartilage lesions of the knee [19]. The authors reported that patients with isolated articular cartilage lesions of the knee demonstrated a significant proprioceptive deficit as compared to a control cohort with normal knees. These authors further hypothesized that a proprioceptive deficit may lead to altered gait, with the resultant unphysiological joint loading, thereby leading to degenerative changes within the joint [19]. As a treatment for chondral lesions, a variety of surgical techniques have been developed that aim to restore the articular surface and tissue specific integrity, thereby restoring joint function and preventing progressive joint degeneration [17, 20]. Among these techniques, our clinic uses a one-stage procedure in which a bone marrow stimulation procedure is enhanced by covering the treated site with porcine-derived collagen I/III membrane. This procedure, known as autologous matrix induced chondrogenesis (AMIC), has already been shown to result in positive outcomes [21-23].

While the patient reported outcomes measures (PROM) have been encouraging, it would add to our knowledge base if there was an objective assessment of biomechanics following treatment. To this end, we sought to evaluate the proprioceptive function of patients who had undergone AMIC by assessing their dynamic postural stability (DPS) using the untreated knee as a control.

2. METHODS

2.4. Statistical Analysis

Statistical analysis was conducted with Graph Pad Prism 7 (Graph Pad Software, San Diego, USA). With regard to the SEBT, a t-test was used for the comparison of index limbs to control. In order to evaluate any relationship between Lysholm scores and SEBT results, the Pearson product moment test was used for the correlation analysis. Level of significance was set at p <0.05.

3. RESULTS

3.3. Star Excursion Balance Test

The mean of the normalized composite reach distance of the index limbs was 91.14 ± 8.88cm versus 92.82 ± 8.86cm for the control limbs. Statistical analysis of the SEBT revealed no significant differences in the normalized composite reach distance of index limbs compared to contralateral limbs (p = 0.479), which was also independent of gender overall (p= 0.543), as depicted in Fig. (2). The bilateral difference in the anterior reach distance exhibited a mean of 3.89 ± 3.3 cm, which was likewise independent of gender (Fig. 3). There was no relationship between Lysholm scores and the SEBT (p = 0.1, r² = 0.009), as shown in Fig. (4).

4. DISCUSSION

To the best of our knowledge, this has been the first study reporting results regarding the bilateral difference in DPS following cartilage repair procedures in the knee. Our results indicate that DPS is bilaterally comparable following AMIC for the repair of chondral lesions. Until now, most studies reporting the outcome after cartilage repair have focused on functional outcome measures by established clinical outcome scores [27] and/or MRI scans [28]. The results of the functional outcome scores in our series have shown positive outcomes after the index procedure, which agrees with our previously reported results in midterm follow up [23]. The PROMs that we have reported are consistent with previously published data, in which a significant decrease in pain, as assessed by VAS, was noted in several studies following AMIC, with follow-up even in the longer term [23, 27]. With regard to PROMs, the Lysholm scale has been validated as a patient-administered instrument to measure the domains of symptoms and complaints in daily activities [29], and our results are in agreement with the literature, where the Lysholm improved significantly, relative to baseline, following AMIC procedure [30, 31]. In contrast to the Lysholm score, the KOOS score holds 42 items in five separately scored subscales [32]. The statistically and clinically significant improvement in KOOS that we noted is also in agreement with the results that were published in a recent meta-analysis [31].

While the results of all PROMs that we used are consistent with published literature concerning the repair of the chondral and osteochondral lesions in the knee, there is also a need to assess more objective measures with regard to the patient’s outcomes.

One aspect of motor function that may be important, especially as it relates to injury recurrence, is dynamic postural stability (DPS). The Star Excursion Balance Test (SEBT) was therefore selected to evaluate motor control strategies during a standardized motor task, as it functions as an index of DPS and has been frequently used to study motor control [26, 33] and shows excellent inter- and intra-rater reliability [34]. We noted no difference in SEBT measures when compared between operated and contralateral knees, which indicates that patients had achieved normal DPS. This may be relevant to the possibility of reinjury. Previous data have indicated that DPS may be predictive of ACL injuries [35], while other researchers have stated that a deficit in postural stability could be a risk factor in ankle sprains [36]. However, we cannot be sure whether the return to normal DPS is attributable to the surgical technique employed in these patients, their rehabilitation programme or even their baseline status.

The somatosensory system is essential to provide feedback for postural control and, subsequently, DPS [37]. As it pertains to cartilage lesions of the knee, it has been recently reported that articular cartilage lesions have a major influence on knee proprioception [19]. In that study, patients with confirmed articular cartilage lesions showed significantly worse scores in unilateral postural stabilometry than uninjured controls. As a notable point, the patients even exhibited a decreased proprioceptive control of the unaffected knee. This differs from our results but may be due to their patients being pre-operative, while ours were ≥3 years post-operative. As we did not have pre-operative DPS results, it would be purely speculative to state whether our patients regained DPS; however, this may be a clinically relevant topic for future study.

Among our patient cohort, we did not see a difference in the composite reach distance or the anterior reach distance when we compared the index versus the contralateral knees. It had been previously reported, among a prospective cohort, that patients who exhibited an anterior right/left reach distance difference greater than 4 cm were 2.5 times more likely to sustain a lower extremity injury, while those with a composite reach distance of less than 94.0% of their limb length were 6.5 times more likely to have a lower extremity injury [14]. As a cohort, the mean side-to-side difference was 3.8 cm, while some patients exceeded this threshold, as depicted in Fig. (3). Likewise, it was reported that a composite reach index of less than 94% leg length was associated with an elevated risk of re-injury [14], and while there were several of our patients who met this criterion, none had reported a re-injury at the time of follow-up.

The principal drawback to our research is that we did not have values for DPS prior to surgery. Another limitation to this study is the extent to which the findings can be generalized beyond the cases studied. The number here is too limited for broad generalization, however, this be seen as a fruitful avenue for future research under the same theme.

CONCLUSION

Our data represents, to the best of our knowledge, the first study reporting results of dynamic postural stability following cartilage repair in the knee. These results show that besides a positive clinical outcome, the AMIC technique enables normal dynamic postural stability when compared to the contralateral, unoperated limbs.

REFERENCES