Knee Effusion-Synovitis Is Not Associated With Self-Reported Knee Pain in Division I Female Athletes

Abstract

Background:

Recent research indicates a potential link between effusion-synovitis and knee pain in athletes. This study investigates the association of knee effusion-synovitis with self-reported knee pain in elite female athletes, leveraging ultrasound imaging for effusion-synovitis assessment.

Hypothesis:

Presence of knee effusion-synovitis is associated with increased self-reported knee pain in Division I female athletes.

Study Design:

Cross-sectional study.

Level of Evidence:

Level 3.

Methods:

A total of 53 NCAA Division I female athletes underwent bilateral knee ultrasound to identify effusion-synovitis. The Knee Injury and Osteoarthritis Outcome Survey (KOOS) Pain subscale assessed knee pain. A 1-way analysis of variance compared KOOS pain, symptoms, activities during daily living (ADL), and quality of life (QoL) scores across groups with no, unilateral, and bilateral effusion-synovitis.

Results:

Among the athletes, 49.1% showed no effusion-synovitis, 26.4% had unilateral, and 24.5% had bilateral effusion-synovitis. There were no differences in self-reported pain scores (F = 0.027; P = 0.97), ADL (F = 0.256; P = 0.78), or QoL (F = 0.120; P = 0.88) between any groups. In addition, the frequency of effusion-synovitis was as follows: for the right limb, Grade 0 = 35 (66%), Grade 1 = 15 (28%), Grade 2 = 1 (2%), and Grade 3 = 2 (4%); for the left limb, Grade 0 = 31 (58%), Grade 1 = 19 (36%), Grade 2 = 3 (6%), and Grade 3 = 0 (0%).

Conclusion:

The presence of effusion-synovitis, irrespective of being unilateral or bilateral, was not associated with self-reported knee pain in elite female athletes. This suggests that lower grades of effusion-synovitis may not significantly impact knee pain.

Clinical Relevance:

The findings of this study challenge existing assumptions about the impact of effusion-synovitis on knee pain in athletes, contributing to the nuanced understanding of knee joint health in sports medicine.

Pain is a complex and subjective experience that encompasses both emotional and sensory aspects, resulting in an unpleasant sensation that varies among individual people. ¹⁸ In sport athletes, knee pain is common and is positively associated with the type, amount, and duration of sport participation. ¹⁰ In the context of assessing knee pain among athletes with varying skill levels, the severity of knee pain does not relate to the athlete skill level. ³ Among athletes of higher skill level, and specifically in elite youth basketball players, pain has been reported in as many as 55% of all players, although ranges of self-reported knee pain vary across all sports. ¹³ In addition, due to repetitive stress placed on the sport-specific muscles and joints, female athletes who specialize in a single sport exhibit a higher risk of experiencing knee pain than multisport athletes. ²⁸ This repetitive stress due to athletic participation can lead to inflammation in the joint, subsequently impacting the sensation of pain in these athletes. ²² However, there is a lack of information regarding the relative number of female athletes that are experiencing pain due to inflammation in the knee.

Knee inflammation and the associated effusion-synovitis may contribute to the pain that is experienced. ² Effusion-synovitis refers to inflammation in the synovial membrane, which can result in an excess of synovial fluid in the joint. When examining effusion-synovitis in the knee, the resulting accumulation of fluid can be found between the prefemoral fat pad and the suprapatellar fat pad.^8,33 Previous studies have found a positive association between knee effusion-synovitis and knee pain. ²⁹ However, these studies often categorized participants based on the presence or absence of knee pain, limiting the overall relationship between knee pain and effusion-synovitis by not considering the severity of pain. Also, effusion-synovitis can emerge for various reasons, including bone marrow lesions or osteoarthritis, potentially contributing to the perception of knee pain. ³⁷ Recent work suggests that engaging in both anaerobic and aerobic training activities, such as dancing, running, and weightlifting, may elevate the likelihood of developing effusion-synovitis in the knee.^30-32 As a consequence, when considering the training regimens typically employed by elite athletes, monitoring effusion-synovitis could offer valuable insights into their overall knee health and wellbeing. However, among an elite athletic population, there is a limited understanding of the correlation between knee effusion-synovitis and knee pain.

Magnetic resonance imaging (MRI) is commonly used to determine the level of severity of effusion-synovitis present in the knee. However, the high cost, need for extensive training, and limited clinical accessibility prevents the routine use of MRI for monitoring effusion-synovitis in athletes. ²⁵ In addition, although physical examinations, such as the sweep test, may be used to assess effusion-synovitis, these assessment techniques lack the sensitivity needed for valid detection.^16,17,34 Previous studies have highlighted ultrasound as a reliable and noninvasive tool to detect effusion-synovitis and as relatively inexpensive and accurate in comparison with MRI scans. ¹⁵ Furthermore, ultrasound-assessed synovitis has been linked strongly to constant knee pain in people with osteoarthritis, indicating that synovial inflammation plays a crucial role in chronic pain, even in earlier stages of the disease. ²⁴ Studies have shown that detecting effusion and synovial hypertrophy through ultrasonography is correlated strongly with knee pain in patients with both early and established symptoms, and it also predicts worsening knee pain over a 1-year period. ²⁹ However, these associations often become apparent only when the disease has progressed to more severe stages, indicating that ultrasonographic detection of these features is more common in advanced pathology. ²⁹ Conversely, traditional assessments have used a semiquantitative method to grade effusion-synovitis, providing a more practical and accessible approach for categorizing people experiencing this condition. ³⁶ Furthermore, similar works have demonstrated that the quantitative measurement of suprapatellar effusion via ultrasonography was associated significantly with knee pain and stiffness in people with radiographic knee osteoarthritis in addition to an emphasis that ultrasonographic features such as effusion and synovial thickening are linked to increased knee pain.^6,7 Ultrasound assessments coupled with a semiquantitative grading scale can evaluate effusion-synovitis based on joint capsule distention, in real time and without additional image analysis, which is essential to longitudinal monitoring of effusion-synovitis in athletes.^5,36

Although there has been progress in understanding the mechanisms underlying knee effusion-synovitis, the correlation between effusion-synovitis and self-reported knee pain experienced by female elite athletes remains unknown. Furthermore, ultrasound imaging may be more effective to monitor knee effusion-synovitis in this elite athletic population. Therefore, the current study aims to evaluate the association between ultrasound detected effusion-synovitis and self-reported knee pain and function in female Division I athletes. To evaluate self-reported knee pain in this population, we utilized the Pain subscale of the Knee Injury and Osteoarthritis Outcome Survey (KOOS). In addition, we included the Activities of Daily Living (ADL), Symptoms, Sports and Recreation, and Quality of Life (QoL) subscales with the intention of providing a comprehensive evaluation of the impact of knee conditions on athlete daily function and overall wellbeing. We hypothesize that self-reported knee pain is associated with ultrasound-detected effusion-synovitis in Division I female athletes.

Methods

Participants

A total of 53 NCAA Division I female athletes (height, 169.3 ± 6.7 cm; mass, 68.0 ± 9.3 kg; age, 19.0 ± 1.2 years; sport type: field hockey, 19; volleyball, 12; soccer, 22) were evaluated as part of a larger ongoing longitudinal study monitoring various outcomes in female collegiate athletes. We included athletes between the age of 18 and 25 years who were members of one of the university’s female athletic teams. We excluded athletes who were unable to participate in data collection due to occurrence of upper and/or lower extremity injury within the previous 4 weeks. This included lower extremity injuries such as ligamentous rupture (eg, anterior cruciate ligament rupture), sprain, or strain and upper extremity injuries such as concussion. At the request of each respective team coach, no results were shared with any athlete during the course of the study. In addition, all participants provided written consent and the current study was approved by the university’s institutional review board (IRB approval number, 00003754).

Ultrasound Image Acquisition of Effusion-Synovitis

Before ultrasound assessment, participants were nonweightbearing for a minimum of 30 minutes. Participants were supine with their leg positioned into 20° to 30° of knee flexion supported by a bolster positioned under their knee. Ultrasound images were collected with a GE LOGIQ P9 R3 ultrasound system and L3-12-RS wideband linear array probe (GE Healthcare). ¹¹ Based on a previously published standardized imaging protocol, ³⁶ we acquired 2 bilateral longitudinal images of the suprapatellar recess inline with the quadriceps tendon at its proximal insertion on the patella (Figure 1).

Figure 1.

Acquisition of knee ultrasound images. (a) Suprapatellar longitudinal scan: probe position, distal femur and patella; participant position, supine 30° flexion. (b) Example image of suprapatellar longitudinal scan with effusion. (c) Example image of suprapatellar scan without effusion. 1, proximal pole of the patella; 2, quadriceps tendon; 3, femur; 4, effusion-synovitis; PFF, prefemoral fat pad; SPF, suprapatellar fat pad.

Grading Knee Effusion on Ultrasound Images

A single reader graded the presence of knee effusion using a previously published semiquantitative scoring atlas. ³⁶ Effusion was identified as an abnormally hypoechoic (ie, dark) area deep to the quadriceps tendon and located between the suprapatellar fat pad and prefemoral fat pad. Knee effusion was characterized as: 0, no joint capsular distension; 1, joint capsular distension parallel to the bone or the presence of a small hypoechoic/anechoic region beneath the joint capsule; 2, joint capsular distension or a joint capsule elevated parallel to the joint area; 3, convex or bulging joint capsular distension or a strong convex distension of the joint. ⁵ Previous studies have found that this technique demonstrates excellent reliability for assessing knee effusion-synovitis. ¹⁹ For this study, we categorized the athletes into 1 of 3 groups: those absent of effusion-synovitis, those with effusion-synovitis unilaterally, and those with effusion-synovitis bilaterally.

Quantifying Knee Pain

During the ultrasound assessment, the athletes used a laptop to complete the KOOS to evaluate their self-reported knee-related health status, including symptoms, pain, ADL, sports and recreational activities, and QoL. The KOOS consists of 5 subscales - pain, symptoms, ADL, sport and recreation (Sport/Rec), and QoL - each containing Likert scale questions with responses ranging from 0 to 4, where higher scores indicate fewer difficulties or symptoms. Each subscale was converted to a score from 0 to 100, with 100 indicating no patient-reported disability within the respective subscale.^26,27

Statistical Analysis

Means and standard deviations were calculated for the descriptive characteristics (ie, height, mass, age) of the sample population. Participants were categorized into their respective groups: no effusion-synovitis, unilateral effusion-synovitis, or bilateral effusion-synovitis. During the assessment, athletes were evaluated for effusion-synovitis in the affected limb or limbs; however, the severity grade was not considered in the criteria for grouping them as having unilateral or bilateral effusion-synovitis. Due to the possibility of nonparametric data, a Shapiro-Wilks test for normality were used and found all KOOS subscales to be non-normally distributed. Therefore, a nonparametric Kruskal-Wallis Test was used to compare the differences in KOOS pain, ADL, symptoms, Sport/Rec, and QoL scores between the 3 groups. If significant differences were found, a least significant difference (LSD) post hoc test was used to determine where specific differences were between the groups. Statistical analysis was performed using SPSS statistical software Version 28.01 (SPSS Inc). All data were considered statistically significant at P ≤ 0.05. ⁴

Results

Table 1 highlights the demographics of the 53 Division I female athletes (19 field hockey, 22 soccer, 12 volleyball) included in this study. Of the 53 athletes, 6 (11%) had a history of anterior cruciate ligament reconstruction (ACLR). At the time of assessment, 26 (49.1%) athletes did not have effusion-synovitis, 14 (26.4%) athletes were found to have unilateral effusion-synovitis, and 13 (24.5%) were found to have bilateral effusion-synovitis. Table 2 provides an extensive breakdown of the prevalence and grade of effusion-synovitis across both limbs and sport. There were no differences in self-reported pain (H = 0.515; P = 0.77), ADL (H = 0.049; P = 0.98), symptoms (H = 0.146; P = 0.56), Sport/Rec (H = 0.043; P = 0.98), and QoL (H = 0.256; P = 0.56) scores (Table 3).

Table 1.

Physical characteristics of participants

	All (n = 53)	No Effusion-Synovitis (n = 26)	Unilateral (n = 14)	Bilateral (n = 13)
Height, cm	169.3 ± 6.7	168.8 ± 6.1	169.2 ± 7.9	170.5 ± 6.8
Mass, kg	68.0 ± 9.4	68.1 ± 9.5	66.0 ± 9.1	69.8 ± 9.9
Age, y	19.0 ± 1.2	20.2 ± 1.4	19.6 ± 0.9	19.6 ± 1.2
ACLR, n (%)	6 (11)	2 (4)	2 (4)	2 (4)
KOOS pain score	93.2 ± 9.5	93.5 ± 10.2	93.0 ± 9.0	92.8 ± 9.0

All values are represented as means ± SD or percentages of the effusion-synovitis groups. ACLR, anterior cruciate ligament reconstruction; KOOS, knee injury and osteoarthritis outcomes score.

Table 2.

Grades of effusion-synovitis between sports

	All Sports	Field-Hockey	Volleyball	Soccer
	N = 53	N = 19	N = 12	N = 22
Effusion-synovitis right limb
No effusion-synovitis	35 (66.0)	12 (63.2)	8 (66.6)	15 (68.2)
Grade 1	15 (28.3)	6 (31.6)	3 (25.0)	6 (27.3)
Grade 2	1 (1.8)	0 (0.0)	0 (0.0)	1 (4.5)
Grade 3	2 (3.8)	1 (5.3)	1 (8.3	0 (0.0)
Effusion-synovitis left limb
No effusion-synovitis	31 (58.5)	12 (63.2)	6 (50.0)	13 (59.1)
Grade 1	19 (35.8)	6 (31.6)	5 (41.7)	8 (36.4)
Grade 2	3 (5.7)	1 (5.3)	1 (5.3)	1 (5.3)
Grade 3	0 (0.0)	0 (0.0)	0 (0.0)	0 (0.0)
Effusion-synovitis both limbs
No effusion-synovitis	26 (49.1)	10 (52.6)	5 (41.7)	11 (50.0)
Unilateral	14 (26.4)	4 (21.1)	4 (33.3)	6 (27.3)
Bilateral	13 (24.5)	5 (26.3)	3 (25.0)	5 (22.7)

Distributions in n (%) of effusion-synovitis and pain in the right and left limbs, in addition to unilateral, bilateral and no effusion-synovitis present.

Table 3.

KOOS outcome scores between effusion-synovitis groups

	H Value	No Effusion-Synovitis	Unilateral Effusion-Synovitis	Bilateral Effusion-Synovitis
Pain	H = 0.515 (P = 0.77)	93.5 ± 10.2	93.0 ± 9.0	92.8 ± 9.0
ADL	H = 0.049 (P = 0.98)	97.7 ± 5.1	97.0 ± 4.5	97.4 ± 4.3
Symptoms	H = 1.146 (P = 0.56)	70.7 ± 12.7	73.4 ± 19.9	73.4 ± 15.3
Sport/Rec	H = 0.043 (P = 0.98)	91.0 ± 13.7	91.2 ± 11.4	88.8 ± 17.0
QoL	H = 0.256 (P = 0.56)	89.4 ± 14.6	92.4 ± 10.5	89.4 ± 13.1

KOOS outcomes between groups are categorized by the presence of effusion-synovitis across all KOOS subscales. Survey data are reported as means ± SD. ADL, activities of daily living; KOOS, Knee Injury and Osteoarthritis Outcome Survey; Sport/Rec, sports and recreation; QoL, quality of life.

Discussion

The primary aim of this study was to evaluate the association between ultrasound detected effusion-synovitis and presence of self-reported knee pain in female Division I athletes. Our findings revealed no significant association between the presence of knee effusion-synovitis and self-reported knee pain when specifically examining the KOOS pain subscale. Furthermore, no significant relationships were observed between knee effusion-synovitis and the other KOOS subscales, including ADL, symptoms, Sport/Rec, and QoL, suggesting that knee effusion-synovitis may be independent of various self-reported functional abilities and overall wellbeing in this population. Among our sample, 26 athletes were absent of effusion-synovitis, while 14 were found to have unilateral effusion-synovitis, and 13 were found to have bilateral effusion-synovitis. Moreover, this study utilized a more novel method to evaluate effusion-synovitis ultrasound imaging and clinically translatable grading scale for structural abnormalities in the knee.

Despite no significant association between the prevalence of knee effusion-synovitis and self-reported knee pain, a substantial proportion of athletes (51%) in this study exhibited effusion-synovitis in ≥1 knee. While effusion-synovitis is common after acute knee injury or in those with chronic musculoskeletal conditions (eg, osteoarthritis), ¹² it is unclear why there is such a high prevalence of effusion-synovitis in our sample of elite athletes who have medical clearance for full physical activity. Recent studies have explored a potential explanation resulting from the rigorous training loads that athletes experience and potential underlying microtrauma to the knee, thus causing an inflammatory response. ²¹ However, in our data, athletic season timing may have affected our results due to the inclusion of teams at various stages of their seasons. Further research is needed to understand effusion-synovitis prevalence and characteristics in athletes across different training cycles. Controlling for confounders such as sport position, training load, previous injury, and season phase in future studies may provide more insight into factors influencing effusion-synovitis in competitive athletes. The lack of association could be attributed to the relatively low-grade effusion-synovitis observed in this cohort. Among the 27 athletes experiencing knee effusion-synovitis, only 6 (~22%) were experiencing grades >1, which may not be substantial enough to trigger pain reporting. Another possible explanation for the high prevalence of Grade 1 effusion without a corresponding increase in knee pain could be that Grade 1 effusion reflects a normal, transient inflammatory response to the athlete training regimes. Inflammation is a key component of the body’s repair and adaptation processes postexercise, and a mild effusion may indicate that the body is in a natural repair mode rather than signaling a pathological condition. It is possible that a higher-grade effusion-synovitis, which leads to more joint capsule distention due to increased fluid, might surpass the pain threshold due to the more severe inflammatory response and establish a stronger association with pain. However, further studies involving people with higher grades of effusion-synovitis are needed to determine whether there is a distinct threshold of effusion-synovitis severity that correlates significantly with self-reported pain.

Whereas knee effusion-synovitis contributes to knee pain in older adults, ³⁵ the association in our sample of Division I female athletes could relate to sport participation factors, especially competition level and type. The lack of significant findings may be attributed to the overall absence of knee pain in this population, which could be due to their high pain tolerance, effective conditioning, or injury prevention strategies commonly implemented in elite athletic programs. Previous research indicates that athletes may under-report pain due to athletic-specific factors such as external pressures from coaches and teammates or important upcoming athletic events. ²⁰ Furthermore, athletes who train routinely for their sport demonstrate increased pain tolerance when compared with nonathletes and untrained people. ²³ Changes in pain tolerance among this population are proposed to result from repetitive exposure to low intensity pain which may alter central pain processing. ⁹ In addition, strength-based sports are associated with reduced pain sensitivity. ¹ Therefore, sport-specific influences, including type, competition level, and pain perception changes, may have impacted perceived or self-reported knee pain in the collegiate field hockey, soccer, and volleyball athletes included in this study. Further research controlling for sport type and including subjective pain tolerance measures could provide more insight into the complex relationship between knee effusion-synovitis and pain in competitive athletes.

Despite this study highlighting the high prevalence of effusion-synovitis in this population and the lack of association between effusion-synovitis and self-reported knee pain, there are some limitations that should be discussed. This study utilized the widely accepted semiquantitative scoring method for grading knee effusion-synovitis on ultrasound images, offering a clinically accessible and rapid approach for long-term monitoring. However, a quantitative assessment measuring the cross-sectional area of the effusion-synovitis could offer more detailed information. Previous research has shown that quantitative measures of the suprapatellar pouch cross-sectional area are associated with more precise assessments of knee inflammation.^6,14 Including both semiquantitative and quantitative measures in future studies could enhance understanding of the relationship between effusion-synovitis and knee pain, even though our cohort exhibited minimal pain symptoms. In addition, only the suprapatellar region was evaluated, which may have excluded some with effusion-synovitis in other knee areas. Our pain analysis encompassed self-reported knee pain during a given week, which may have introduced potential issues with specificity and recall bias in these athletes. Including participants that were injury-free for a minimum of 4 weeks may have captured residual pain from previous injury; a longer pain-free period could be required in future studies. Further, we included ACLR as a benchmark for previous knee injury due to restrictions in gathering an encompassing history of lower extremity injury; however, future studies should evaluate incidences of self-reported knee pain and effusion-synovitis and when controlling a history of lower extremity injuries. Finally, the high athletic workload of our sample likely contributed to the high effusion-synovitis prevalence observed, but more information is needed to know whether the amount of workload is the cause of the effusion-synovitis. We acknowledge the inability to conduct a subgroup analysis of grade 1 versus grades 2 to 3 effusion-synovitis scores due to our sample size, and would like to identify how various grades may have more of an effect on outcome scores. Going forward, quantitative effusion-synovitis measures, multiregion knee evaluations, recent pain measures, longer injury-free periods, and controlling for workload could provide further insights into connections between knee effusion-synovitis and pain in competitive athletes.

The key clinical takeaway from this study is that knee effusion-synovitis and self-reported knee pain may be disconnected in elite female athletes. Despite no association found between effusion-synovitis presence and pain reports, over half the athletes exhibited some degree of subclinical knee inflammation. This surprising structural symptom disconnect indicates that clinicians should evaluate both objective pathology and subjective symptoms when assessing joint health in competitive athletes. The high prevalence of asymptomatic effusion-synovitis also suggests a need for ongoing surveillance and management of training loads to avoid excessive inflammation that could precipitate long-term issues like osteoarthritis. Furthermore, the lack of pain reporting with mild inflammation presents an obstacle for early clinical detection. The conditioned pain tolerance of elite athletes likely raises their threshold for perceiving and vocalizing joint pain. Therefore, direct imaging techniques such as ultrasound are vital to identify pathology that may be “silent” in stoic athletic populations. However, more research is needed on whether severe effusion-synovitis relates to pain in a dose-response manner. Overall, these findings reveal subtleties in the link between structural knee abnormalities and patient-reported pain in athletes.

Limitations

This study has several limitations that should be considered. The cross-sectional design limits our ability to infer causality between knee effusion-synovitis and self-reported knee pain, and the absence of longitudinal data restricts understanding of how changes in effusion-synovitis over time may influence pain. The semiquantitative grading scale used to assess effusion-synovitis may not fully capture the severity of inflammation, and a quantitative measurement, such as cross-sectional area assessment, could offer more detailed insights. In addition, the study assessed only the suprapatellar region for effusion-synovitis, potentially missing effusion in other knee areas. Self-reported knee pain may be subject to recall bias, and, whereas participants were required to be injury-free for 4 weeks, residual pain from previous injuries could have influenced pain reporting. Furthermore, the mild nature of the effusion-synovitis observed in this cohort, with only 22% of athletes experiencing grades >1, may not have been severe enough to elicit significant pain. Finally, the lack of data on training loads, sport position, previous injuries, and season phase prevents control for these potential confounders. Future research with larger sample sizes, longitudinal designs, more precise quantification methods, and comprehensive control for confounding factors is needed to clarify the relationship between effusion-synovitis and self-reported knee pain in elite athletes.

Conclusion

Our findings show no significant relationship between knee effusion-synovitis and self-reported knee pain in Division I female athletes. In addition, no clear patterns emerged between those who did or did not report knee pain or effusion-synovitis, implying knee effusion may be independent of reported pain in this healthy elite female cohort. However, the notable effusion-synovitis prevalence warrants further investigation. While knee effusion-synovitis appears unrelated to self-reported knee pain in this sample, the high prevalence highlights the need for ongoing research to inform physical training practices that optimize joint health in competitive athletes.