Evaluation of ligament laxity during pregnancy

Abstract

Objective

Pregnancy-related changes in ligament laxity have been shown to be associated with various disorders such as back pain or pelvic floor disorders. The purpose of this study was to assess laxity changes during pregnancy by confronting different methods in order to suggest a simple clinical tool helping to prevent the aforementioned problems.

Design

Seventeen pregnant women were evaluated at the first, second and third trimesters as cases and 16 non-pregnant women participated as controls. Ligamentous laxity was measured using an extensometer for the metacarpophalangeal joint of the index, a fingertip to floor test and a sit and reach test to assess hip and lumbar flexibility and the Beighton score. Statistical analysis included independent samples t-tests, analysis of variance and Pearson correlation coefficients.

Results

Laxity of the metacarpophalangeal joint increased by 11% from the first to the second trimester of pregnancy and stabilized until delivery. The Beighton score was significantly higher in the second trimester of pregnancy (p < 0.05). The flexibility of the hip and lumbar vertebra showed a significant increase of the distance measured between the foot soles and the middle fingers at third trimester (p < 0.05). A moderate correlation was observed between the results given by the extensometer and the Beighton score in both the cases and the control group at first trimester (r = 0.60, p < 0.05) but none was found for the two hip and lumbar flexibility tests.

Conclusion

Laxity reached its maximum at the second trimester. The combination of an objective measurement by the extensometer and a global evaluation of the laxity by the Beighton’ score for example may be useful for a daily assessment of laxity. However, the chosen clinical tests don’t seem appropriate to be used alone in pregnant women

Introduction

Pregnancy is a unique physiological condition that induces large morphologic changes (e.g. weight and posture) and also modifications of intrinsic parameters like ligamentous laxity [1]. The ligamentous laxity is at its maximum in early childhood after this, it decreases rapidly until adulthood [2]. However, in the female population, this gradual decline may be suspended and even reversed during pregnancy. In this regard, some authors explain that some hormones such as relaxine, progesterone or oestradiol which levels increase during pregnancy modify the ligament structure [[3], [4], [5]]. These hormonal changes result in physiological relaxation of the ligaments in the pelvic joints in order to enhance the passage of the baby through the birth canal [6]. This loosening would enable the pelvic joint to become more flexible but, as a counterpart, would also affect the pelvic joint and the spine responses to mechanical load. Some authors hypothesize indeed that these modifications of pelvic joint and spine responses favor pelvic dysfunctions and the occurrence of pain in this body region [7,8]. During pregnancy, hormonal changes affect not only ligaments in the pelvic joints but more generally collagen of connective tissues [9] and therefore ligaments and tendons in general (e.g., hand [10], wrist [11]). The observations concerning pelvic and spine joints are then extendable to the human body joints in general such as increased laxity may be related to various musculoskeletal disorders and increased pain in various joints of the body during pregnancy [12,13]. In the aforementioned studies investigating the relation between ligament laxity and disorders during pregnancy, the evolution of ligament laxity hasn’t been assessed throughout pregnancy. Nevertheless, early detection of its increase would be of particular interest in order to develop prevention of various disorders appearing with pregnancy.

In the literature, there is then a wide variety of in vivo laxity assessment devices and methods. The first type of methods try to assess directly the lengthening of a ligament after applying a specific force using medical imaging [14] or knee ligament arthrometers [15,16]. This methods allow measurement of small laxity changes with an accuracy up to 0.1 mm [17] but is quite expensive for a clinical follow up and requires some technical expertise. Moreover, not many ligaments can be isolated.

The second category of devices proposes to evaluate indirectly the ligament laxity through the measurement of articular mobility [1,7,8,11] even though articular mobility results from the mechanical behavior of various ligaments, tendons and capsules [18]. Typically, these systems, such as the extensometer of Jobbins [19], measure the amplitude reached by a joint of the pregnant woman for a specific torque applied on this joint. Such devices are portable, easy to use, affordable, atraumatic and reliable [1]. The main drawback is that the proposed devices measure flexibility in upper limb joint. Now, upper joints are affected by pregnancy-related changes in laxity but less involved in pathology.

The third category of methods would be clinical tests that estimate joint flexibility. The Beighton score [20] is the most commonly used test to assess the overall ligamentous laxity. It is a nine-point score evaluating laxity in the upper and lower limbs and lumbar and hip flexibility with a score ≥4/9 required to conclude a generalized hyper joint mobility. The reliability and reproducibility of this score was suggested as good to excellent in screening for generalized joint laxity in females [21] and children [22] and has already been used in pregnant women [1,23]. Calguneri and colleagues observed no significant difference in Beighton scores between the third trimester and postpartum [1]. Van Dongen and colleagues used the Beighton scale to study the generalized laxity in pregnant South African women [23]. They showed that hypermobility in this women is low (only 4.9% of the 509 pregnant women), decreasing with age, but not increasing during pregnancy. However, the main limit of the Beighton score would be the computation of the score based on the sum of one and zeros corresponding to the ability to reach or not specific joint postures.

In the literature, other more targeted clinical tests have been suggested to evaluate the lower back flexibility such as the “fingertip to floor test” [24] or the “sit and reach test” [25]. These tests have been intensively used in epidemiologic studies [26] and sport sciences [27]. They are easy to administer and require minimal skills training [26]. To the best of our knowledge, they have never been used to assess joint laxity in pregnant women. Conversely to the Beighton score, the performance corresponds to a distance, which is continuous measure. As such, they could be more sensitive to small changes in joint laxity and then present a good alternative to assess joint laxity throughout pregnancy. The “fingertip to floor test” is a little bit easier to spread than the “sit and reach test”. During the “fingertip to floor test”, the distance is indeed measured between the fingertip and the floor. During the “sit and reach test”, the distance is measured between the fingertip and a box. One has then to have an adequate box to be able to perform this test. However, a doubt remains about the ability for pregnant women to realize the “fingertip to floor test” at the end of pregnancy. The morphologic changes in terms of abdominal circumference, weight, and modification of the center of gravity position might indeed obstruct the ability to bend forwards as required by the “fingertip to floor test”.

In this study, we conducted a longitudinal monitoring of ligament laxity at a wide range of joints in pregnant women by combining an objective measure, the extensometer, that has been proven to be efficient to detect small changes in ligament laxity [1,19], and simple clinical tests. The aims of this study were to determine how laxity during pregnancy evolves and to propose a simple clinical methodology that could be used in daily practice helping to prevent pathologies associated with increase in laxity. An objective quantification of laxity could allow us to carry out further studies for a better understanding of the origins of back pain and pelvic floor disorders during pregnancy.