Keywords
knee joint - menstrual cycle - hormone, sex steroid - relaxin - athletes
Introduction
The most common injuries related to joints have been reported to involve the ankles
and the knees.[1] Knee injuries which occur during sports is mostly associated to sub-luxation or
dislocation.[2] A clear understanding on the injury pattern, the mechanisms underlying this injury
and the risk factors is crucial in exercise physiology and sports medicine which could
be related to gender, genetic and whole-body aerobic capacity.[3] Knee injuries undoubtedly affect the athlete performances that can prevent by increasing
the strength of the quadriceps muscle during isometric, eccentric contractions, and
concentric.[4] A remarkable number of non-traumatic injuries among women during sports over the
years has led to multiple studies being performed to better understand the underlying
mechanism involved.[5]
[6] Females are known to be more vulnerable than males toward knee injury.[7] In female, the occurrence was related to different phases of the menstrual cycle.[8] Several reports indicated that high incidence of non-contact knee injury happened
during the follicular phase of the cycle, while others reported that the incidence
is the highest at ovulation and in the luteal phase of the cycle.[9]
[10] These raised the possibility that female sex hormones could be involved in this
injury. The role of sex steroids on knee injury remains poorly understood and represent
an area for investigation.
Female were found has two to ten times greater risk of non-traumatic knee injury than
male.[11] The reason for this occurrence is unclear. Evidences have suggested that female
sex hormones may be involved as they could affect knee laxity and knee laxity increase
during the menstrual cycle.[12] Up-to-date, the reports with regards to sex steroids effect on knee laxity were
conflicting. Several studies indicated that female anterior knee laxity was highest
in follicular (pre-ovulatory) phase,[13] while others reported that laxity was the greatest in ovulatory,[12] and luteal phases.[14]
[15] There were studies which showed that no differences in knee laxity was observed
between phases of the menstrual cycle.[16] In addition to sex steroids, relaxin was also found to influence knee laxity where
high relaxin levels could contribute to increased knee laxity.[15]
While previous studies focused mainly on sex-steroid effect on ACL laxity,[6]
[17] changes in laxity of LCL and MCL under sex-steroid influence remain unknown. Furthermore,
the relationship between serum sex-steroids and relaxin levels with medial and lateral
knee laxities has never been identified. In view of this, our study aimed at investigating
changes in medial and lateral knee laxities in females particularly in athletes at
different phases of menstrual cycle. The relationship between laxities and serum sex-steroid
and relaxin levels will also be determined. We hypothesized that medial and lateral
laxities of the knee changes with phases of the menstrual cycle and increasing in
luteal phase, therefore contributed toward differences in the incidence of non-contact
knee injuries between menstrual phases. Meanwhile changes in non-female athletes will
also be investigated.
Methods
Subject's Recruitment
Forty six healthy females, 24 professional athletes (20.3 ± 1.28 years, 21.9 ± 2.6
BMI) with over 6–7 years experience of basketball, netball, footsul, swimming, and
handball national team members, and 22 non-athletes (21.7 ± 2.27 years, 22.2 ± 3.42
BMI) who were not on hormonal contraceptives and regular cycles for 3 consecutive
months volunteered to participate in this study. The inclusion criteria include no
history of knee surgery or history of injury or chronic pain in both lower extremities
for the past 1 year. Subjects were not on any specific medications. Amenorrheic, oligomenorrhoeic
and polymenorrhoeic subjects were excluded. We also excluded subjects who had undergone
surgery, leg trauma, as well as those who had no regular menstrual cycle. The participants
were informed detail of the study from the information sheet provided, and written
informed consent was also obtained. This study was registered (Medical Ethics Number
1010.90) and approved by the ethical review of the Medical Centre Board, University
Malaya. The methods were performed in accordance with the approved guidelines of institutional
Medical Centre Board ethics committee.
Determination of Basal Body Temperature (BBT) and Phases Determination
The basal body temperature (BBT) was used to identify the ovulatory cycle which was
featured by a slight increase in core body temperature (∼0.5oC) during mid-cycle.[18] BBT was measured when the body was at rest. Based on BBT test, subject's individual
phases were determined. In determining BBT, rectal temperature (ADC ADTemp V Fast
Read Pen Type Digital thermometer, American Diagnostic, USA) was obtained. The temperature
was taken at 7 o'clock in the morning for 1 month duration. All subjects participated
in this study were found to have ovulatory cycle. The sample of BBT recorded is shown
in [Fig. 1].
Fig. 1 Basal body temperatures chart.
Body Composition Measurement by Bioelectrical Impedance Analysis (BIA)
BIA is a reliable and accessible method for screening body fat. The standing BIA device
(BC-418, Tanita Corp., Tokyo, Japan), with stainless-steel plates is used to measure
whole body and segmental impedance. Subjects stand without shoes on the base and hold
the handgrips with embedded electrodes; soles of both feet are in contact with the
electrode plates. They were weighed, and impedance was measured their total body water,
total protein, total mineral, skeletal muscle mass, body fat mass, body mass index,
waist hip ratio, fitness score (estimated fitness score based on total body condition)
and basal metabolic rate in athletes and non-athletes (no clicking on the machin whether
subject is an athlete or not). Measurements were performed in the morning before breakfast
(7:30–8:30 am) at the same day of sampling by the same examiner in all subjects. The participants
were told not to eat or drink before the measuremen. In the 24 hours prior to the
measurements they also did not consume any medications (including alcohol and caffeine)
or perform high intensity physical activity that could effect the results.
Blood Sample Collection and Serum Hormones Analyses
Blood samples were collected three times in a month: follicular phase, ovulatory phase,
and mid-luteal phase.[19] The three phases were determined by using a fertility chart and at the days stated,
blood samples were withdrawn via venepuncture. The blood was collected in a separator
tube (SST), allowed to clot at room temperature for 30 minutes. The clotted blood
was then centrifuge at 3000 g, 15 minutes. Serum samples were then aliquot and stored
at –20°C. Serum samples were analyzed in duplicate for relaxin concentration by using
specific human relaxin peptide enzyme-linked immunosorbent assay (ELISA) kit (CUSABIO
– USA, with detect range of 6.25 pg/ml-400 pg/ml. ELISA was performed according to
the manufacturer's guidelines. The absorbance for relaxin was determined by using
a microplate reader (iMark; Bio - Rad, Hercules, CA, USA) at a wavelength of 450 nm.
A set of standard serial dilutions of known concentrations of relxin were provided
by the manufacturer and were used to construct a standard curve to determine the hormone
levels (400, 200, 100, 50, 25, 12.5, 6.25, 0 pg/ml). Meanwhile, radioimmunoassay (RIA)
was used to determine serum levels of estrogen in pg/ml, progesterone in ng/ml and
testosterone Radioimmunoassay (RIA) was used to determine serum levels of estrogen
in pg/ml, and progesterone in ng/ml.
Knee Rotational Movement
Varus and valgus stress tests were applied to the knee to determine medial and lateral
laxities. Measurements were performed manually by using a orthopaedic goniometer (model:
MR0104 PVC material 180°), and repeated to confirm by using an custom-made electronic
chair which was designed based on described previously.[20] To establish reliability, examination was performed by two raters (a physical therapist
and a human movement scientist), both trained by a clinician, independently performed
measurements. The examiners were blinded to phase of subjects cycle. Subjects' both
knees were assessed for changes in varus/valgus angles. The test was accomplished
by fixing the knee at 0° and 20° of flexion. Ligament injuries have not observed the
presence of varus/valgus or axial load up to 20°.[21] In view of that the angle of 0° and 20° are chosen for this study. All procedures
were identical to those described in the clinical examination textbook,[22] and van der Esch et al.[20]
The varus/valgus measurements were conducted manually by using a orthopaedic goniometer.
Varus test is a stress force applied from medial side by adducting the ankle. Testing
the LCL was performed when the knee was flexed at 0° or 20° of flexion with the subjects
lying flat. One hand of the examiner was placed over the lateral joint line while
another hand held the lower leg firmly at the ankle. Meanwhile, valgus test is a stress
force applied on the lateral side by abducting the ankle. Stretching of MCL was performed
when the knee was at 0° or 20° of flexion. When performing this test, patient was
lying flat with one examiner's hand placed over the medial joint line and another
hand held the lower leg firmly. The diffrences of angle was recorded manually by using
an orthopaedic goniometer.
The varus/valgus measurements were reconducted by using an custom-made electronic
chair. Reliability ranging of intraclass correlation coefficient (ICC) test was performed
to detect minimal differences in varus and valgus deviations or high precision measurement
with high reproducibility. The reliability was conducted on ten subjects of athletes
and non athletes, with reliability an scores ranging of 0.95 and 0.93 (ICC) respectively.
The females participants were seated comfortably in the electronic chair with a back
support. The knee joint was fixed in 0° or 20° of flexion throughout the measurement.
The thigh, lower leg and ankle were fixed to the chair at 0° or 20° and medial, lateral,
internal, external rotational movements in leg were not possible. The subject's foot
and distal part were fastened using clamps at the ankle or distal part of the leg.
The lower leg and upper thigh were fastened to the device using a Velcro bandage.
A free moving arm was directly located under the tibiofemoral subject's joint as a
axis of rotation (middle of the popliteal fossa). To supply a steady moment to the
knee of 7.7 Nm, a deadweight was used which the weight was attached by a cord to the
freemoving arm. The cord was fastened 74cm from the axis of rotation of the arm. The
weight load was applied to both medially and laterally sides of the lower leg, resulted
in the knee joint varus/valgus measure. Raters were seated behind the subjects and
applied the load slowly to their lower leg by hand in a standardized manner. An attached
digital measurement system was recorded the end point of the varus/valgus rotaitional
movement during 5s. To avoid increasing of muscle tone resulting from pain during
the measurement, subjects were trained to relax report the onset of pain. Laxity movement
of the knee joint angle was calculated as the sum of the varus/valgus deviations in
degree.[23]
[24] The result of manual laxity tests was almost the same as for electronic chair of
the knee.
Statistical Analysis
All data were presented as mean ± standard deviation. Hormone levels and rotational
angles of each subject at different phases of the menstrual cycle were analyzed by
descriptive statistics. Levene's equality of variable assumption was applied and the
results revealed no significant differences among the observations. The means of these
observations were computed and used for data analysis. Two-way analysis of variance
(ANOVA) was used to compare between athletes and non-athletes groups. For variables
with normal distribution, Pearson correlation coefficient and for non-normal distributed
variable, Spearman correlation coefficient was applied. SPSS 18.0 were used in this
study and p < 0.05 was considered as statistically significant.
Results
Body Composition Analyses
Differences between body composition in athletes and non-athletes at different phases
of the menstrual cycle are shown in [Table 1]. The average total body water, total protein, total mineral, skeletal muscle mass,
body fat mass, body mass index, waist hip ratio, fitness score and basal metabolic
rate in athletes and non-athletes were presented. Measurement was performed three
times and average values were entered as a final measurement. Levene's equality of
variable assumption stated that there were no significant difference between these
variables.[25]
Table 1
|
Variables
|
Athletes
Mean ± SD
|
Non-Athletes
Mean ± SD
|
|
Age (years)
|
20.3 ± 1.28
|
21.7 ± 2.27
|
|
Height (cm)
|
163 ± 2.75
|
158.5 ± 5.28
|
|
Weight (kg)
|
|
- Follicular phase
|
58 ± 7.93
|
56.5 ± 9.96
|
|
- Ovulatory phase
|
57.5 ± 7.75
|
55.7 ± 9.99
|
|
- Luteal phase
|
58 ± 7.93
|
56.1 ± 10
|
|
Total Body Water (kg)
|
|
- Follicular phase *
|
30.8 ± 2.42
|
27 ± 3.19
|
|
- Ovulatory phase *
|
30.4 ± 2.33
|
27 ± 3.1
|
|
- Luteal phase*
|
30.6 ± 2.45
|
27.1 ± 3.2
|
|
Total Protein (kg)
|
|
- Follicular phase *
|
7.18 ± 0.75
|
8.24 ± 0.66
|
|
- Ovulatory phase *
|
7.21 ± 0.81
|
8.24 ± 0.66
|
|
- Luteal phase*
|
7.21 ± 0.85
|
8.22 ± 0.65
|
|
Total Mineral (kg)
|
|
- Follicular phase *
|
3.08 ± 0.25
|
2.73 ± 0.32
|
|
- Ovulatory phase *
|
3.03 ± 0.26
|
2.69 ± 0.3
|
|
- Luteal phase*
|
3.05 ± 0.27
|
2.71 ± 0.33
|
|
Skeletal Muscle Mass (kg)
|
|
- Follicular phase *
|
23 ± 2.05
|
19.7 ± 2.55
|
|
- Ovulatory phase *
|
22.7 ± 2.02
|
19.7 ± 2.47
|
|
- Luteal phase*
|
22.8 ± 1.91
|
19.8 ± 2.58
|
|
Body Fat Mass (kg)
|
|
- Follicular phase *
|
15.7 ± 5.34 (26.7%)
|
19.1 ± 7.02(33.4%)
|
|
- Ovulatory phase *
|
15.9 ± 5.44 (26.7%)
|
19 ± 7.34 (33%)
|
|
- Luteal phase*
|
16.1 ± 5.5 (27.3%)
|
19 ± 7.06 (33%)
|
|
Body Mass Index (kg/m2)
|
|
- Follicular phase
|
21.9 ± 2.55
|
22.2 ± 3.37
|
|
- Ovulatory phase
|
21.8 ± 2.59
|
22.2 ± 3.51
|
|
- Luteal phase
|
22 ± 2.67
|
22.2 ± 3.39
|
|
Waist Hip Ratio*
|
0.82 ± 0.04
|
0.84 ± 0.06
|
|
Fitness Score (points)*
|
75.1 ± 2.93
|
69.3 ± 5.51
|
|
Basal Metabolic Rate (kcal)
|
|
- Follicular phase *
|
1284 ± 75.8
|
1160 ± 96.6
|
|
- Ovulatory phase *
|
1272 ± 75
|
1167 ± 90.9
|
|
- Luteal phase*
|
1275 ± 77.2
|
1170 ± 94.7
|
Our findings indicated that mean weight of athletes were higher than non-athletes
however the differences were not statistically significant. The weight was higher
in luteal and menstruation phases as compared with follicular phase. Athletes in general
had higher total body water as compared with nonathletes. However, there were no significant
differences in total body water between menstrual cycle phases. Meanwhile, total protein
estimate was significantly higher in non-athletes as compared with athletes (p < 0.05) and no significant difference was noted between phases of the menstrual cycle.
Total mineral content in athletes was significantly higher than non-athletes and in
both groups, total mineral content was highest in menstruation phase of the cycle.
Skeletal muscle mass was higher in athletes as compared with non-athletes (p < 0.05) and no significant difference was noted between phases of the menstrual cycle.
Body fat mass was higher in nonathletes than athletes (p < 0.05) and no significant difference was noted between phases of the menstrual cycle.
Body mass index was slightly lower in athletes than non-athletes with no significant
difference was noted between the two groups. Waist hip ratio was significantly lower
in athletes than non-athletes, while fitness score index was significantly higher
in athletes than non-athletes (p < 0.05). Finally, athletes have higher basal metabolic rate (BMR) than non-athletes,
however no significant difference in BMR was noted between phases of the menstrual
cycle.
Knee Joint Angles at Different Phases of the Menstrual Cycle
[Table 2] and [3] show the degree of knee angles at 0° and 20° flexion in varus and valgus stress
tests in athletes and non-athletes. In varus 0° and 20° of flexion tests, non-athletes
have higher knee angle as compared with athletes at all phases of the cycle. In both
groups, knee angle was the highest in the luteal phase, followed by follicular phase
and the lowest in the ovulatory phase. In valgus 0° and 20° of flexion tests, non-athletes
appear to have greater knee angle in all phases of the cycle as compared with athletes
(p < 0.05). The highest angle was noted in the luteal phase, followed by follicular
phase and ovulatory phase.
Table 2
|
Athletes
Mean(SD)
|
Non-Athletes
Mean (SD)
|
t value
|
P value
|
Effect size
|
|
Varus 0°
|
|
- Follicular phase
|
3.75 (1.13)
|
5.33(1.02)
|
4.63
|
<0.05
|
1.47
|
|
- Ovulatory phase
|
1.80 (0.43)
|
3.44(0.95)
|
7.00
|
<0.05
|
2.38
|
|
- Luteal phase
|
5.45 (1.01)
|
7.19(1.01)
|
5.46
|
<0.05
|
1.72
|
|
Valgus 0°
|
|
- Follicular phase
|
3.09 (1.21)
|
4.76(0.89)
|
4.99
|
<0.05
|
1.60
|
|
- Ovulatory phase
|
1.39 (0.51)
|
3.44(0.56)
|
12.09
|
<0.05
|
3.83
|
|
- Luteal phase
|
4.76 (1.32)
|
5.56(0.72)
|
2.37
|
<0.05
|
0.78
|
|
Varus 20°
|
|
- Follicular phase
|
11.48(1.21)
|
12.80(1.03)
|
3.74
|
<0.05
|
1.18
|
|
- Ovulatory phase
|
9.35(0.75)
|
10.95(0.72)
|
6.89
|
<0.05
|
2.18
|
|
- Luteal phase
|
14.25(1.18)
|
15.11(1.05)
|
2.44
|
<0.05
|
0.77
|
|
Valgus 20°
|
|
- Follicular phase
|
9.58(1.56)
|
11.71(1.51)
|
4.40
|
<0.05
|
1.39
|
|
- Ovulatory phase
|
7.63(1.00)
|
10.11(0.88)
|
8.36
|
<0.05
|
2.64
|
|
- Luteal phase
|
11.64(1.29)
|
12.98(1.79)
|
2.73
|
<0.05
|
0.87
|
Table 3
|
Athletes
Mean(SD)
|
Non-Athletes
Mean (SD)
|
|
Varus 0°
|
|
- Follicular phase
|
3.88 (1.57)
|
5.52(1.77)
|
|
- Ovulatory phase
|
1.49 (0.71)
|
4.01(1.53)
|
|
- Luteal phase
|
4.95 (1.32)
|
6.97(1.68)
|
|
Valgus 0°
|
|
- Follicular phase
|
3.22 (1.18)
|
4.64(0.52)
|
|
- Ovulatory phase
|
1.49 (1.32)
|
3.81(1.62)
|
|
- Luteal phase
|
4.69 (1.76)
|
6.03(1.25)
|
|
Varus 20°
|
|
- Follicular phase
|
10.81(3.02)
|
11.98(2.11)
|
|
- Ovulatory phase
|
9.73(2.41)
|
10.83(1.56)
|
|
- Luteal phase
|
13.55(3.12)
|
14.87(1.55)
|
|
Valgus 20°
|
|
- Follicular phase
|
9.85(1.56)
|
11.59(2.31)
|
|
- Ovulatory phase
|
7.71(2.07)
|
10.67(1.05)
|
|
- Luteal phase
|
12.02(2.14)
|
12.69(2.13)
|
Changes in Serum Sex-Steroids and Relaxin Levels at Different Phases of the Menstrual
Cycle
[Table 4] shows the values of serum sex-steroids and relaxin levels in athletes and non-athletes.
Our findings indicate that the highest estrogen level was observed in the ovulatory
phase in both groups whereby there were no significant differences between athletes
and non-athletes. Meanwhile, progesterone levels were the highest in luteal phase
with athletes having a significantly lower level than non-athletes (p < 0.05). Similarly, progesterone level was also higher in non-athletes as compared
with athletes at follicular phase, although this level was ∼12 times lower than in
the luteal phase of the cycle. No significant difference in progesterone level was
observed in the ovulatory phase between the two groups.
Table 4
|
Athletes
Mean(SD)
|
Non-Athletes
Mean(SD)
|
t value
|
P value
|
Effect size
|
|
Estrogen (pg/ml)
|
|
- Follicular phase
|
170.20(39.86)
|
197.65(71.97)
|
1.49
|
>0.05
|
0.50
|
|
- Ovulatory phase
|
507.35(161.52)
|
492.30(276.96)
|
0.21
|
>0.05
|
0.07
|
|
- Luteal phase
|
439.50(150.54)
|
409.45(163.89)
|
0.60
|
>0.05
|
0.19
|
|
Progesterone (ng/ml)
|
|
- Follicular phase
|
2.28(1.00)
|
4.19(2.53)
|
3.14
|
<0.05**
|
1.08
|
|
- Ovulatory phase
|
1.80(1.24)
|
1.74(0.60)
|
0.20
|
>0.05
|
0.07
|
|
- Luteal phase
|
24.74(11.34)
|
31.33(8.09)
|
2.12
|
<0.05**
|
0.68
|
|
Testosterone (ng/ml)
|
|
- Follicular phase
|
0.82(0.38)
|
1.24(0.47)
|
3.08
|
<0.05**
|
0.99
|
|
- Ovulatory phase
|
1.21(0.54)
|
1.39(0.48)
|
1.12
|
>0.05
|
0.36
|
|
- Luteal phase
|
1.22(0.61)
|
1.37(0.63)
|
0.76
|
>0.05
|
0.24
|
|
Relaxin (pg/ml)
|
|
- Follicular phase
|
2.10(0.56)
|
1.69(1.27)
|
1.33
|
>0.05
|
0.45
|
|
- Ovulatory phase
|
1.38(0.87)
|
0.34(0.45)
|
4.73
|
<0.05**
|
1.58
|
|
- Luteal phase
|
15.58(5.36)
|
10.35(2.96)
|
3.82
|
<0.05**
|
1.26
|
Meanwhile, the levels of testosterone, which were lower than estrogen and progesterone,
were found to be higher in non-athletes than athletes. In non-athletes, testosterone
levels were the highest in ovulatory phase followed by luteal phase. The lowest testosterone
levels were noted in athletes at follicular phase. Serum levels of relaxin were highest
in athletes as compared with non-athletes, in particular during the ovulatory and
luteal phases of the cycle. No significant differences in relaxin levels were noted
during the follicular phase between the two groups.
Correlations between Sex-Steroids and Relaxin Levels with Knee Joint Angles
[Table 5], [6] and [7] show correlation between sex-steroid levels and knee joint angles in athlete and
nonathlete females. In general, strong correlations were observed between progesterone
and relaxin levels with knee joint angles in both varus and valgus tests (0° and 20°
of flexion), in athletes and non-athletes. The highest correlations between serum
levels of progesterone and relaxin with knee angles were observed in varus test at
20° of flexion in both athletes and non-athletes.
Table 5
|
0 o
|
20 o
|
|
varus
|
valgus
|
varus
|
valgus
|
|
Estrogen
- Pearson
|
-0.15
|
-0.17
|
-0.09
|
-0.14
|
|
Progesterone
- Spearman
|
0.70**
|
0.62**
|
0.76**
|
0.62**
|
|
Testosterone
- Pearson
|
0.07
|
0.12
|
0.12
|
0.07
|
|
Relaxin
- Spearman
|
0.58**
|
0.50**
|
0.65**
|
0.47**
|
Table 6
|
0 o
|
20 o
|
|
varus
|
valgus
|
varus
|
valgus
|
|
Estrogen
- Pearson
|
-0.13
|
-0.15
|
-0.04
|
-0.14
|
|
Progesterone
- Spearman
|
0.66**
|
0.58**
|
0.70**
|
0.59**
|
|
Testosterone
- Pearson
|
0.05
|
0.03
|
0.06
|
-0.06
|
|
Relaxin
- Spearman
|
0.69**
|
0.65**
|
0.74**
|
0.64**
|
Table 7
|
0 o
|
20 o
|
|
varus
|
valgus
|
varus
|
valgus
|
|
Estrogen
- Pearson
|
-0.17
|
-0.26*
|
-0.13
|
-0.17
|
|
Progesterone
- Spearman
|
0.72**
|
0.65**
|
0.80**
|
0.60**
|
|
Testosterone
- Pearson
|
-0.10
|
0.01
|
0.01
|
0.00
|
|
Relaxin
- Spearman
|
0.81**
|
0.73**
|
0.80**
|
0.62**
|
Discussion
The major findings from this study are (i) athletes have lesser degree of medial and
lateral knee laxities as compared with non-athletes, (ii) both athletes and non-athletes
have greatest medial and lateral knee laxities in luteal phase of the cycle (iii)
progesterone and relaxin levels in both athletes and non-athletes were highest in
luteal phase whereas estrogen levels were highest in ovulatory phase (iv) progesterone
levels in luteal and follicular phases were lower in athletes as compared with nonathletes
and (v) strong correlation was observed between serum progesterone and relaxin levels
with medial and lateral knee laxities (both varus and valgus at 0 and 20°) in both
athletes and non-athletes. Other findings are the athletes have higher total body
water, total mineral content, skeletal muscle mass, fitness score and BMR as compared
with non-athletes. The total protein content, body fat mass and waist to hip ratio
in athletes were however lower than non-athletes.
We have found that medial and lateral knee laxities were highest in the luteal phase
which correlate with highest serum progesterone and relaxin levels. The highest medial
and lateral laxities could predispose to knee instabilities, therefore increasing
the risk of knee dislocation and non-contact knee injuries for example ligament and
menisceal tear. Previous reports have revealed that anterior laxity of the knee increases
with increasing progesterone levels.[26] Higher incidences of ACL tear and non-contact knee injury were reported in the post-ovulatory
or luteal phases where progesterone levels were high.[8]
Recently, anterior laxity and valgus movement of the knee were reported to correlate
with blood progesterone levels.[27] In animal for example rats, increased in collateral ligament laxities has been reported
higher at diestrus and proestrus phases correlated with the high serum progesterone
levels.[28] Evidence has suggested that progesterone influence on knee laxities could be due
to increased collagen breakdown as the serum levels of biomarkers for collagen degradation
were high in early luteal phase of menstrual cycle as reported in eumenorrhoeic women,[29] Our findings in athletes which indicate increased knee laxity in the luteal phase,
that correlates with the high serum progesterone levels are in agreement with the
finding by Heitz et al,[30] who reported that a significant increase in ACL laxity occur at peak progesterone
levels in physically active women.
In this study, serum relaxin levels were found to correlate with knee laxity. The
serum level of relaxin were highest in luteal phase parallel with the increased in
serum progesterone levels. This was consistent with a report in female athletes where
the level of serum relaxin positively correlates with serum level of progesterone.[31] In athletes, serum level of relaxin during ovulatory and luteal phase was ∼4.0 and
1.5 times higher respectively as compared with nonathletes. In athletes, serum relaxin
levels were highest in the luteal phase (15.58 ± 5.36pg/ml) suggesting that relaxin
might influence medial and lateral knee laxities. Therefore, increased in serum relaxin
level could contribute to increased medial and lateral knee laxities as observed in
athletes and non-athletes during the luteal phase of the cycle. Our findings were
supported by a study by Dragoo et al.,[32] (2011) who reported that serum relaxin levels strongly correlates with the incidence
of ACL tear in elite collegiate female athletes. Meanwhile, in animal studies, relaxin
administration to guinea pigs resulted in increased ACL laxity.[32] The increase in laxity could be due to several factors which include up-regulation
of matrix metalloproteases (MMPs),[33] that cause increased collagen breakdown.[34] In addition, progesterone could also enhance relaxin action via up-regulating the
expression of relaxin receptor isoforms RXFP1 and RXFP2 in knee collateral ligaments
and patellar tendon of rats.[35] Relaxin receptor was also expressed in ACL of rodents,[36] and carpometacarpal joints of humans.[37]
In this study, no significant difference was observed in estrogen and testosterone
levels between athletes and non-athletes in both luteal and ovulatory phases of the
menstrual cycle. In athletes, serum testosterone level was slightly lower in the follicular
phase. Although serum estrogen levels were highest in ovulatory phase, laxity appeared
to be the lowest. Therefore, we concluded that high estrogen level may not be responsible
for the increase in medial and lateral knee laxities. Our findings were in contrast
with several other reports which indicate that high serum estrogen levels were responsible
for the increased in incidence of non-contact knee injury during ovulatory phase[12]
[38]
[39] The differences between our findings and others were unclear. Meanwhile, lower knee
laxity in ovulatory phase suggested that high estrogen levels could decrease the risk
of non-contact knee injury which was in contrast to high serum progesterone levels
which caused the opposite effect. Our findings supported those of Wojtys et al,[8] who reported that significantly fewer non-traumatic knee injuries was observed in
follicular phase as compared with post-ovulatory phase. Alternatively, lower risk
of non-traumatic knee injury in the ovulatory phase may be due to lower serum progesterone
and relaxin levels.
In this study, testosterone may not have influence on medial and lateral knee laxities
as no positive correlation were observed between serum testosterone level and knee
parameters. We have found that no significant difference in serum testosterone levels
was noted between athlete and non-athlete in ovulatory and luteal phases of the menstrual
cycle. A recent finding by O'Leary et al.,[40] reported that prolonged aerobic exercise in women with normal menstrual cycle could
induce a short-term elevation of plasma testosterone level. This effect however was
not observed in our study, meanwhile reported that testosterone effect on knee laxity
could be masked by the effect of estrogen and progesterone.
In conclusion, we have demonstrated that changes in medial and lateral knee laxities
in athletes and non-athletes differ with menstrual cycle phases. We have shown that
serum sex-hormones, in particular progesterone have strong positive correlation with
medial and lateral knee laxities. Wiertsema et al,[41] reported that clinical test for example Lachman is reliable in determining the anterior–posterior
laxity of ACL. Arthrometer could be used to determine anterior tibio-femoral movement
however this device has limited application when measuring the medial and lateral
knee laxities. The observed decreased in knee laxity in athletes could be due to greater
muscular control as athletes have greater muscle mass, fitness level, and differences
in the biomechanical properties in the ligament due to difference in loading.[42] The greater muscle mass would contribute toward greater tone which resists knee
joint movement. The higher medial and lateral knee laxities in non-athletes especially
in luteal phase suggest that this group are more susceptible toward non-traumatic
injury involving the knee.
Conclusion
The findings from this study is importance to the field of sports physiology and medicine
as it could provide the basis underlying increased incidence of non-traumatic knee
injury observed in females during the luteal phase of menstrual cycle. In view of
this, precautions are needed to reduce the risk of non-traumatic knee injury in female
athletes during this cycle phase.
