EDS: Less Strength and Worse Proprioception

The association between muscle strength and activity limitations in patients with the hypermobility type of Ehlers–Danlos syndrome: the impact of proprioception: Disability and Rehabilitation: Vol 0, No 0 – 24 Jun 2016 – free full-text article

The patients diagnosed with Ehlers–Danlos Syndrome Hypermobility Type (EDS-HT) are characterized by pain, proprioceptive inacuity, muscle weakness, potentially leading to activity limitations.

In EDS-HT, a direct relationship between muscle strength, proprioception and activity limitations has never been studied.

The objective of the study was to establish the association between muscle strength and activity limitations and the impact of proprioception on this association in EDS-HT patients.  

Methods

Twenty-four EDS-HT patients were compared with 24 controls. Activity limitations were quantified by Health Assessment Questionnaire (HAQ), Six-Minute Walk test (6MWT) and 30-s chair-rise test (30CRT).

Muscle strength was quantified by handheld dynamometry. Proprioception was quantified by movement detection paradigm.

In analyses, the association between muscle strength and activity limitations was controlled for proprioception and confounders.

Results

Muscle strength was found to be associated with activity limitations, however, proprioceptive inacuity confounded this association.

Conclusions:

Muscle strength is associated with activity limitations in EDS-HT patients. Joint proprioception is of influence on this association and should be considered in the development of new treatment strategies for patients with EDS-HT.

Implications for rehabilitation

Reducing activity limitations by enhancing muscle strength is frequently applied in the treatment of EDS-HT patients. Although evidence regarding treatment efficacy is scarce, the current paper confirms the rationality that muscle strength is an important factor in the occurrence of activity limitations in EDS-HT patients.

Although muscle strength is the most dominant factor that is associated with activity limitations, this association is confounded by proprioception.

In contrast to common belief proprioception was not directly associated with activity limitations but confounded this association.

Controlling muscle strength on the bases of proprioceptive input may be more important for reducing activity limitations than just enhancing sheer muscle strength.

Full article continues:

Patients diagnosed with Ehlers–Danlos syndrome, are characterized by an altered structural integrity of connective tissue resulting in frailty and multi-systemic manifestations like

  • orthostatic intolerance
  • organ dysfunction
  • and joint instability
  • hyper-elastic skin

The phenotype of EDS-HT is heterogeneous, in which the severity of complaints varies from mild to severe

Pain and fatigue are highly prevalent in EDS-HT patients. Pain is present in multiple joints over a period of >3 months is one of the diagnostic criteria

Pain has several causes and can appear by minimal provocation and is frequently the result of biomechanical overload

Pain and fatigue, combined with multi-systemic dysfunction, may cause severe limitations in daily activities. 

EDS-HT patients often perceive limitations during (stair)walking, self-care, transfers, sports and household activities.

In addition, these individuals show an higher dependency on assistive devices.

The underlying mechanisms of the musculoskeletal complaints and functional decline remain unknown

In EDS-HT patients, an important aim of rehabilitation is to reduce activity limitations by increasing muscle strength and enhancing motor control. However, the evidence to support this rationality is scarce.

Muscle strength might be an important determinant of activity limitations, however, a direct relationship between muscle strength and activity limitations in EDS-HT has never been demonstrated.

Muscle weakness and atrophy have frequently been observed in both non-symptomatic (e.g. dancers) and symptomatic forms of GJH

In these studies, muscle weakness was found to be associated with pain and fatigue.

The association between activity limitations and muscle strength might also be influenced by biomechanical factors, such as joint proprioception.

Proprioception provides the brain with positional and motion sense through mechanoreceptors localized within joint-capsules, muscles and tendons.

Neural inputs derived from proprioceptive sensors are hypothesized to be crucial for the recruitment of motor units in relation to task requirements.

It has been shown that proprioception of the knee is reduced in EDS-HT patients however, the impact of proprioception on the association between muscle strength and activity limitations in EDS-HT is unknown.

Therefore, the aim of the study was to establish the association between muscle strength and activity limitations controlled for proprioception, pain and fatigue in EDS-HT patients.

Results

  • The mean age of the population was 40 years (SD: 10, range: 21–57).
  • In EDS-HT patients (n = 24), duration of pain in years (mean (SD)) was 24(12) and the duration of soft tissue injuries (mean years (SD)) was 23(13).
  • Fatigue was present in 92% of the EDS-HT patients (mean years (SD): 14(11).
  • Gastro-intestinal complaints were present in 80% of the EDS-HT patients (mean years (SD): 14(14).

Time since diagnosis (mean years (SD) was 8.2(7.8).

All included EDS-HT patients fulfilled the Ville-Franche criteria (n = 24: 100%) and thus the diagnosis of EDS-HT was confirmed.

When regarding the main diagnostic criteria:

  • GJH (Beighton ≥5) was present in 17 subjects (71%),
  • Hyper-elastic skin was present in all the subjects (n = 24: 100%).

When regarding the minor criteria:

  • in all subjects recurring joint dislocations and chronic pain (>3 months) were present (n = 24: 100%) and
  • in 10 subjects a positive family history was present (42%).

EDS-HT patients showed

  • significant higher skin laxity (ΔD: +15.9%, p = 0.032),
  • higher BMI (ΔD: +16.5%, p<0.0001),
  • lower muscle strength (ΔD: −20.2%, p<0.0001) and
  • poorer proprioception, in terms of higher errors in movement detection
  • Low muscle strength was correlated with poor proprioception (r = −0.58, p < 0.0001) pain (r = −0.57, p = <0.0001) and fatigue

Discussion

Muscle strength was found to be associated with activity limitations in EDS-HT patients.

This finding is important, despite the prevalent use of muscle strength enhancement in clinical practice aiming at reducing activity limitations, the scientific ground for such rationale is lacking.

Proprioception confounded the association between muscle strength and the HAQ and the 30CRT, but not the association between muscle strength and 6 MWT.

These results indicate that proprioception is of influence on the associations between muscle strength and activity limitations, but this influence is not consistent.

These findings support evidence for the core assumption that treatment based on muscle strengthening and increasing proprioception acuity might be effective. 

Although the present study provides supporting evidence for the usage of muscle strength training as a treatment modality, it also raises questions that should be addressed before strength training can be implemented into practice

Muscle strength in EDS-HT patients was lower than healthy controls.

The difference in muscle strength can be explained by the difference in connective tissue, the main clinical characteristic of EDS-HT patients.

In these patients more elastic and potentially more fragile connective tissue is present, which is expressed in GJH and a hyper-extensible skin.

Previous research has shown that the presence of GJH is an independent factor associated with muscle weakness, not only in subjects with symptomatic forms of GJH but also in healthy professional dancers.

It can be hypothesized that muscle weakness is not only the result of deconditioning, but is partially caused by the inefficient force transfer through muscle fibers due to altered structural integrity of connective tissue

If this hypothesis is true, it could have consequences for the trainability of muscle strength in EDS-HT patients

We found that poor proprioception is associated with an increase in activity limitations. Poor proprioception has frequently been reported in EDS-HT patients and has been postulated to be an important factor in activity limitations

Our results indicate that poor proprioception, especially during activities that require controlling discrete joint motion (knee flexion), has an influence on muscle strength

It has been shown that the function of proprioception is not limited to providing the brain with coordinates of joint positions, but also plays an important role in the coordination of muscle force in relation to the required movements

Our results might indicate that proprioception is especially important for coordinating muscle force rather than controlling joint angular momentum.

Transferring these results into clinical practice, it can be speculated that learning to control the required muscle force is more important than just increasing raw muscle power

Possible reasons for poor proprioception are part of discussion

One possible reason is that proprioceptive signals are based on inadequate mechanical forces generated from lax joint-capsules and muscle tissue

In EDS-HT patients this would result in an increased activation threshold, due to altered mechanical properties of connective tissue, and resulting in decreased proprioceptive feedback

Another possible reason could be muscle atrophy. Muscle atrophy has been found to result in a reduction of proprioceptive sensor density in osteoarthritis patients.

Although a reduced sensor density has not been demonstrated in EDS-HT, the presence of muscle atrophy has indeed been shown in EDS-HT patients

Therefore, the prevention of muscle atrophy by muscle training could also protect against poor proprioception.

Pain and fatigue were found to be independently associated with activity limitations.

It is postulated that the origin of pain in EDS-HT patients can be found in micro-fractures within joint surfaces and muscle structures, which leads to activity limitations and in turn to further muscle weakness

Overuse could potentially activate nociceptive receptors which could inhibit motor unit recruitment and further add to muscle weakness

In addition, pain and poor proprioception were also found to be correlated.

EDS-HT patients were found to have lower pain thresholds which could also be a factor that may lead to activity avoidance. The presence of secondary hyperalgesia and proprioceptive inacuity could also indicate neurologically oriented mechanism that affects sensory modalities

Regarding fatigue, muscle weakness could result in additional effort during functional activities which may in turn lead to inefficient energy consumption.

Conclusion

Muscle strength is associated with activity limitations in EDS-HT patients.

Proprioception is of influence on this association and should be considered in the development of treatment strategies aiming to reduce activity limitation in EDS-HT patients.

 

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