The functional consequences of Generalized Joint Hypermobility: a cross-sectional study

An excessive range of motion, which is referred to as Generalized Joint Hypermobility, is present in in 2 to 57% of the child and adult population [1, 2]. It is assumed that GJH is an expression of laxity of connective tissue, due to genetic alterations in elastic fibers and thus affecting the structural integrity of connective tissue throughout the whole human organism [3]. This in turn, affects the function of multiple organs and structures that are comprised of connective tissue.

Connective tissue laxity is also a clinical feature of specific pathological entities like Ehlers-Danlos Syndrome, Marfan or Ostegenesis Imperfecta [3]. These hereditary diseases of connective tissue (HDCT) are rare and can have serious consequences in terms of disability and in some cases may even result in death. In recent years the genetic origin of collagen diseases has been explored [4–7], whereas also a subgroup of connective tissue disorders was identified. This subgroup of connective tissue disorders shares the typical, although less severe, clinical presentation, but lacks biological markers [8]. These disorders are often referred to as Hypermobility Syndrome (HMS) or Ehlers-Danlos Syndrome (hypermobile type) [9]. The exact prevalence is unknown, and estimates do vary [10].

Not all individuals with GJH are symptomatic, some even take advantage of GJH and excel in certain sports like gymnastics, martial arts or dancing [11, 12]. Others experience mild to severe musculoskeletal complaints [13], like joint pain in multiple joints [10], fatigue [13], diminished motor competence [14] and muscle weakness [15]. In a recent study by Scheper et al., GJH was also found to be independently associated with physical deconditioning, fatigue and psychological complaints in professional dancers who are considered to benefit from GJH in order to perform complex dance routines. These findings and other literature indicate that the consequences of GJH for performance remain poorly understood. If the assumption of connective tissue laxity is correct then GJH should also affect functional status, even in individuals who should excel in functional ability, like professional dancers.

Functional status is a multi-dimensional concept defined as a patient-oriented health outcome which contains aspects of individual daily functioning, including physical, psychological and social factors [16]. Functional status is often used as a primary outcome in a variety of study designs, whereas an operational definition is frequently lacking [17]. It can, however, be operationalized in both capacity and performance measures, where capacity refers to what a patient can do in a standardized environment, and performance to what a person does in daily life [18]. Although often reported by patients and clinicians, the evidence of impairments on functional status in symptomatic GJH is limited, as well as factors influencing functional status.

Weight bearing physical activities like standing, walking and participating in sports and leisure activities might be physically demanding in subjects with symptomatic GJH [19–22]. This is possibly due to the presence of pain, fatigue and reduced physical fitness that could negatively influence functional status [22–24]. However, how much these factors contribute to functional status remains unknown, as do the factors that would enable professional dancers to benefit from GJH instead of adding to functional disability.

Therefore, the aim of the present study was to investigate the association between GJH and functional status, in terms of capacity and performance. In addition the secondary objective was to explore the contribution of physical fitness and musculoskeletal complaints to this association.

Based on the presented data and after correction for confounders, GJH was associated with a decrease in functional status in terms of capacity, measured as walking distance and jumping capacity. No significant associations were found between GJH and a decrease in functional status in terms of performance (self-reported PAL). When regarding the capacity measures, both BMI and fatigue were found to be negative influencing factors on 6MWT. In contrast, increases in muscle strength and being a professional dancer were found to be positively associated with higher capacity of 6MWT and jump capacity.

The current sample consisted of young female adults recruited among healthcare students and a selected group of professional performing arts students (dancers). These two populations were found to differ on several clinical characteristics. First of all, dancers had significantly higher Beighton scores and lower scores on BMI, indicating that on average these subjects are slimmer and more flexible. An explanation for the observed difference can be found in the admission criteria for the professional dance education, where students with high flexibility and slim posture are more likely to be admitted. Despite the high flexibility and the significantly higher levels of fatigue of the included dancers, these individuals showed higher levels of physical capacity (6MWT, jumping capacity).

Besides the selection by flexibility and slender posture, dancers were admitted to the education when they excel in performing complex choreographs. We postulate that as result of the stringent selection criteria and training for professional dancers, they were able to perform better on all capacity measures, and especially on the jumping tests that also rely heavily on general gross motor competences. Previous studies on children and adults diagnosed with symptomatic forms of hypermobility have been found to have less motor control [14] and proprioception. Combined with a loss in physical fitness in terms of muscle strength and cardiovascular exercise capacity [15, 30], this may lead to functional decline in individuals with symptomatic hypermobility. However, in the current study the presence of GJH was independently associated with a lower physical capacity (both 6MWT and jumping capacity), even in physically well-trained professional dancers. This could imply that connective tissue laxity, in terms of GJH, is a risk factor for functional decline rather than the consequence of deconditioning [39].

From the current data we can conclude that in females, muscle strength is a promoting factor in regard to functional status in terms of 6MWT, and furthermore, ascribes the potential benefit of strength training for improved capacity. However, due to the design of the study, the current study lacks methodological strength to prove such an assumption. Besides muscle weakness, reduced cardiovascular exercise tolerance has also been reported in literature in both symptomatic [30] and non-symptomatic GJH [11]. This was not included in the current analysis, however most functional activities do not require maximum exercise tolerance like effort, and even more so, most individuals rarely engage in sustained maximum cardiovascular efforts. When looking at the levels of muscle strength and functional capacity in dancers classified with GJH, these were considerably higher in comparison to non-dancers with GJH. Higher levels of physical fitness and motor competence could explain this difference and may be the result of training which is in line with current literature [40].

Pain intensity was not found to be a factor of influence on 6MWT. This could be related to the low intensity and stable, cyclic nature of walking like in the 6MWT. Pain intensity, which was a negatively influencing factor on SQH, might have been a more important factor in more dynamic activities like SQH, exerting more forces on joint surfaces, especially in movements requiring axial rotational forces.

According to the multivariate analyses, GJH had a negative contribution in all capacity variables. The presence of GJH, which could be the result of abnormal connective tissue laxity, may result in higher demands on active joint stabilization mechanisms [41, 42]. In combination with proprioceptive inaccuracy, during highly coordinative tasks like walking, demanding adaptive strategies like co-contraction or prolonged activation of certain muscle groups are required to stabilize joints during these activities [43]. Further, higher energy demands may be required, which could lead to fatigue [44]. In our data next to GJH, fatigue was also a negative contributor to the walking distance supporting this theory.

We found a profound difference between performance and capacity, which could be explained by the use of questionnaires which are based on subjective experience and recall. The lack of association in performance could be the result of estimation bias due to recall. In addition capacity measures are only able to reflect activity impairments partially as they do not account for environmental factors. The presence of recall bias could be avoided, while accounting for environmental factors, by the use of objective performance measures like 3d accelerometry. Although not possible in the current study due to time constraints, this would be recommended for future studies.

When interpreting the presented results, the following limitations should be considered. Firstly, the included population was selected from healthcare students, who may attend more to issues of healthy living when compared to the general population, as well as professional dance students, who have highly demanding physical routines in their daily life. In addition, the current included population was limited to only females due to the lack of available male dancers at time of inclusion. This limits the generalizability of these results to the general population. Still, these results do illustrate that biomechanical factors like GJH have direct consequences for functional status, however the magnitude of that effect could differ between populations, with this group being a high risk population. Secondly, the used outcomes of functional status are not dance specific, due to the issues of comparability between dancers and non-dancers. The effect of GJH on dancing itself might differ and should be investigated. Still, both walking and jumping are also applicable to dancers and could indicate that also GJH can have profound effects on dancing and might even be larger due to the high demands on joint stability during dancing. Currently the use of the Beighton score in order to determine GJH is highly debated. Although the Beighton score is still considered to be the “gold standard” for classifying GJH, aspects of its operationalization and the validity of the cut-off values are still in need of further research and a revision of the way GJH is determined is needed [40]. Thirdly, environmental and psychological factors were not incorporated in the current study. Social status, peer pressure, kinesiophobia and (pain) coping strategies could explain the discrepancies between the performance and capacity measures of functional status [45]. However, this is beyond the scope of the current paper but could prove to be a vital area of future research in order to fully understand the interaction between functional status and the human organism in its own individual context. Such knowledge is critical in order to develop effective treatment modalities that are able to diminish activity impairments for subjects diagnosed with symptomatic forms of GJH. It may also be important for treatment of other musculoskeletal diseases. Finally, based on the study design these results offer no causative evidence, therefore, these observations need to be replicated in longitudinal observational studies incorporating individuals with both symptomatic and non-symptomatic GJH.

We conclude, that GJH in females was associated with a decrease in functional status in terms of capacity, measured as walking distance and jumping capacity.

GJH is a factor to consider when assessing functional status in terms of walking and jumping capacity, possibly due to altered joint biomechanics, compromised by structural integrity of connective tissue. Incorporating the assessment of musculoskeletal complaints (pain), fatigue, and muscle strength could provide additional clinically relevant information. However, the role of connective tissue laxity, expressed by GJH, for functional status is still poorly understood.