Anterior knee pain in runners after a half-marathon race

Abstract

Background

Anterior knee pain has been associated with sports activity, especially long-distance running and endurance sports. It is important to determine the incidence of anterior knee pain (AKP) in runners after a half-marathon race and identify possible risk factors associated.

Methods

Cross-sectional study where runners from a half marathon race were randomly invited to participate. Participants were recruited at the race kit pickup site the day before the race. Eligible participants completed a survey regarding demographic information, running experience and training details. An orthopedic surgeon performed a physical examination and recorded the medical history. At the finish line, the participants were evaluated again for possible new injuries.

Results

A total of 205 runners were included in the study, with a 98.5% follow-up rate (n = 203). 24% of runners had an injury at the end of the race (n = 49). Anterior knee pain was the most frequent injury (n = 12), followed by iliotibial band syndrome (n = 10), muscle cramps (n = 7) and hamstring tears (n = 4). Anterior knee pain had a statistically significant association with insufficient stretching of the hamstrings (p = 0.048) and finishing the race in more than 2 h (p = 0.014).

Conclusions

Anterior knee pain was the most frequent new injury in the half-marathon runners after the competition. Spending more than 2 h to finish the race and stretching the hamstrings by less than 70° in the supine position were risk factors for anterior knee pain.

1. Introduction

Anterior knee pain (AKP), also known as patellofemoral pain syndrome or runner's knee, is a common musculoskeletal condition characterized by diffuse retropatellar or peripatellar pain that is aggravated by loading the knee in flexion during activities such as running, stair descending or squatting.^1,2 AKP is considered one of the most common causes of knee pain affecting all age groups, mainly between 16 and 25 years old, but AKP is more prevalent in the physically active population.³ AKP accounts for 11–17% of all knee pain visits to the ambulatory clinic and has an incidence of 15–33/1000 patients per year.^4,5 There is no definitive clinical test to diagnose it; the best available test is the anterior knee pain test performed during a squatting maneuver, which has an 80% positive predictive value for anterior knee pain.^6,7

Both amateur and professional athletes are at high risk for this kind of syndrome. AKP contributes to 5.4% of all sports injuries in athletes,² with long-distance runners being the main group of athletes at high risk for developing AKP.⁸ There are risk factors that have been associated with anterior knee pain, such as the female sex, insufficient stretching of the lower limb muscles and a slow step rate during running.⁸ It is important to understand the factors associated with anterior knee pain in runners because running has become more popular since it is a component of a healthy lifestyle,⁹ can be practiced individually, and requires minimal logistics and little equipment to carry out.¹⁰

There are few studies on injuries during races. In the Westfield Sydney to Melbourne run in 1990, musculoskeletal injuries were evaluated during the ultramarathon, and patellofemoral pain syndrome accounted for 15.6% of the injuries; however, ankle injuries were the most frequent (30%).¹¹ Similar outcomes were observed after the ultramarathon in Nottingham in August 1982, where ankle injuries were the most frequent (50%) injuries.¹² In 1993, during the Auckland Citibank marathon, risk factors for injuries and other health problems were evaluated immediately after participation in the marathon, and anterior kneel pain was found to be the most frequent injury (25%).¹³

Understanding the incidence of AKP and associated risk factors will allow the development of targeted treatments and ways to avoid recurrence.⁸ This study aimed to determine the incidence of anterior knee pain in runners after a half-marathon race and identify possible risk factors for anterior knee pain. The hypothesis was that anterior knee pain would be the most frequent injury un runners after the race.

2. Methods

2.1. Study design and participants

This is a cross-sectional study conducted during the 2016 Cali half-marathon race. This study was approved and supervised by the Ethical Committee in Biomedical Research of Fundación Valle del Lili. There was no patient and public involvement in the design, or conduct, or reporting, or dissemination plans of the research. Participants were recruited randomly the day before the race at the race kit pickup site, which every runner had to visit. All runners of the 21.1 km distance were eligible. After receiving information and addressing any doubts the potential participants might have had, the eligible participants signed a written consent form and completed a survey regarding demographic information, running experience and training information. Afterwards, an orthopedic surgeon (JPM-C) conducted a physical examination and recorded the medical history.

A tent was set up at the finish line, and the participants were instructed to arrive at the tent as soon as they completed the race for a physical examination and assessment of their new injuries (the main outcome of the study). These injuries were compared with the findings of the previous assessment. Attendance to the second assessment was encouraged by providing a comfortable space to rest with a selection of beverages and fruits. The race time of each runner was recorded. In addition, 10 different people actively searched for the enrolled participants at the finish line and showed the participants the way to the tent. The participants were identified with a green bracelet. If a participant did not show up at the tent, they were contacted by phone on the next day and asked about possible injuries; if an injury was suspected, they were scheduled to be seen during the next 2 days.

2.2. Data collection

The data included sociodemographic information and clinical characteristics such as weight, height, body mass index (BMI), the number of previous half-marathons finished, the number of years of running experience, whether the participant stretched, injuries in the last 6 months and recent injuries (last month). In the physical examination, the stretching statuses for the quadriceps, hamstrings, gastrocnemius and iliotibial band were assessed. Any injuries found during the physical examination were recorded. The race time and the presence of new injuries were evaluated at the finish-line tent. This information was registered in the exclusive database of BD Clinic®.

2.3. Stretching assessment

The stretching statuses of four groups of muscles were evaluated.

The rectus femoris muscle was assessed with the participant in a prone position, the knee in maximum flexion, and the participant trying to touch the heel and the buttock, as in Ely's test. We measured the distance between the heel and buttock in centimeters.

The hamstrings were assessed with the participant in the supine position, as in a straight leg raise test, and the hip was flexed to its maximum point with the knee in complete extension. We measured the maximum angle between the stretcher and the leg, with the knee in full extension. This process is shown in Fig. 1.

Fig. 1.

Hamstrings stretching assessment with the participant in the supine position, as in a straight leg raise test, the hip is flexed to its maximum point with the knee in complete extension. We measured the maximum angle between the stretcher and the leg.

The gastrocnemius was assessed with the hip flexed to 45° and the knee in full extension; the degree of plantar flexion of the foot was measured, considering three grades of stretching deficits: low, medium and severe.

The iliotibial band was assessed with the hip flexed to 45°, the knee in full extension, and one leg crossed over the other leg, with three grades of stretching deficit: low, medium and severe. Fig. 2 shows this assessment.

Fig. 2.

Iliotibial band stretching assessment with the hip flexed to 45°, the knee in full extension, and one leg crossed over the other leg, with three grades of stretching deficit: low (30–45°, between yellow and blue lines), medium (45–60°, between red and yellow lines) and severe (≥60°, red line).

2.4. Statistical analysis

Stata 12.0 was used for statistical analysis. Sample size was by convenience with the maximum recruitment of runners as possible. Descriptive statistics were used to calculate the incidence of anterior knee pain and other injuries and to present the demographic characteristics of runners. During the analysis, the t-test, the χ² test and Fisher's exact test were used to evaluate the associations between possible risk factors and AKP, and p values ≤ 0.05 were considered statistically significant.

3. Results

3.1. Participants and follow-up

There were 2200 runners registered for the race, and 205 runners (9.3%) were included in the study and underwent the first assessment. Ninety-two percent of the study population (n = 189) finished the race, and 77.1% completed the postrun assessment on the same day (n = 158). During the following three days, the follow-up rate increased to 98.5% (n = 202). Fig. 3, shows the STROBE flow diagram for participants included.

Fig. 3.

STROBE flow diagram for participants included in the study.

3.2. Baseline characteristics

The mean age of the participants was 38.5 years old, and there was a male majority (67%). Seventy-four percent of the participants stretched before or after running; however, 64% had insufficient stretching of the hamstrings, and 39% had insufficient stretching of the gastrocnemius. Most of the participants (78%) had previously run a half marathon, with a mean of 5.8 competitions. The average number of years of running experience the participants had was 7.4 years. Thirty-one percent reported having had a running-related injury within the past 6 months, and 18% had one within the last month. Table 1 shows the baseline characteristics of the participants. The analysis did not demonstrate a statistically significant association between injuries and these variables.

Table 1.

Baseline characteristics of the 2016 half-marathon runners in XXX.

Variable	N = 205
Age, mean (SD)	38,5 (11)
Weight (kg), mean (IQR)	68 (60–76)
Height (cm) (IQR)	170 (165–175)
BMI, mean (IQR)	23,5 (21,6–25,6)
Sex (male), n (%)	131 (67)
Number of previous marathons, mean (SD)	5,84 (±11)
Weekly km, mean (SD)	36,3 (±23)
Number of years of running experience, mean (SD)	7,42 (±8)
Participants who stretch, n (%)	151 (74)
Injuries within the last 6 months, n (%)	63 (31)
Recent injuries, n (%)	36 (18)
Finishers, n (%)	189 (92)
Participants with new injuries, n (%)	49 (24%)

3.3. Injuries during the race

The incidence of injuries during the half marathon was 24% (n = 49). Anterior knee pain (n = 12) was the most frequent injury, followed by iliotibial band syndrome (n = 10), muscle cramps (n = 7) and hamstring tears (n = 4). The injuries incurred during the race can be seen in Table 2. The overall incidence of anterior knee pain among all runners was 5.9%; the combined prevalence and incidence of anterior knee pain was 14% among the runners (n = 29). There was a nonsignificant trend showing more injuries in the women than in the men, OR: 1.51 (IC 95%: 0.73–3.14), p = 0.27. The risk factors associated with anterior knee pain during the race were insufficient stretching of the hamstrings (p = 0.048) and finishing the race within more than 2 h (p = 0.014). In this study, there was no association between running experience and injuries, nor between previous injuries and new injuries.

Table 2.

New injuries developed during the race.

Type of injury	N = 49 n (%)
Anterior knee pain	12 (25)
Iliotibial band syndrome	10 (20)
Muscular cramps	7 (14)
Hamstrings tear	4 (8)
Periostitis (shin splints)	4 (8)
Lower back pain	3 (6)
Gastrosoleus tear	3 (6)
Plantar fascitis	2 (4)
Quadriceps tear	2 (4)
Adductors tear	1 (2)
Ankle sprain	1 (2)

4. Discussion

To our knowledge, this is the first prospective study evaluating musculoskeletal injuries sustained during a half-marathon race in runners. 24% of the runners were injured, with anterior knee pain being the most frequent type of injury. The factors that were found to be associated with the development of anterior knee pain were insufficient hamstring stretching and finishing the race within more than 2 h.

The incidence of anterior knee pain during the race was 5.9%, which seems low compared to that reported in one of the few studies concerning injuries during long-distance races, where the incidence of knee pain and stiffness after the race was 25.6%¹³; nevertheless, in the mentioned study, the participants were not evaluated by an orthopedic surgeon after the competition, the authors considered not only knee pain but also knee stiffness, and the symptoms were reported within the week after the race. In 1990, a study on running injuries during an ultramarathon that lasted 6 days was conducted; the authors found that ankle injuries were the most frequent type of injuries, followed by anterior knee pain; however, it is important to mention that this race took place on uneven ground, where ankle injuries tend to be more frequent, whereas knee injuries are more common on concrete surfaces.¹¹

Regarding the completion time, the runners who took more than 2 h to complete the race were at a significantly higher risk of developing anterior knee pain. Completing the race within less than 2 h seemed to be a protective factor for anterior knee pain, and this finding can be explained by the fact that for a given running distance, slow-speed running decreases knee joint loads per stride but conversely increases the cumulative load at the knee joint compared to running at fast speeds. The primary reason for the increase in cumulative load at slower speeds is the increase in the number of strides needed to cover the same distance; thus, running at slower speeds may increase the incidence of anterior knee pain.¹⁴ A study published in 2015 showed similar findings, concluding that muscle and patellofemoral joint forces change with step rate during running. A slow step rate increases patellofemoral contact and joint forces over time, predisposing individuals to anterior knee pain.¹⁵ Another explanation for this association might be that pain made runners go in a slower speed. In fact, a cross-sectional study can demonstrate de association between speed and incidence of AKP, but no causality can be established.

Insufficient hamstring stretching (less than 70°) was found to be a risk factor for developing anterior knee pain during the race. There are no recent studies that evaluated the mentioned association during a competition; however, some studies have presented statistically significant differences between insufficient stretching of the hamstrings and patellofemoral pain in athletes and nonanthletes.16, 17, 18 Improving the flexibility and strength of the lower limbs are part of the conservative treatment strategy for anterior knee pain.

Stretching before or after a competition was not a factor that influenced the incidence of anterior knee pain or any other injuries, as other studies have shown.^19,20 Although people may not be stretching efficiently when they stretch, it is difficult to measure the efficiency of stretching. We found that while 74% of the participants reported that they stretched, 64% still had stretching deficiency, showing that their stretching technique could be inappropriate.

Having an injury within the last 6 months did not increase the risk of new injuries; however, there are previous studies that show that it is in fact a risk factor.^21,22 Most likely, the sample size was not large enough to establish this association. The female sex has been associated with anterior knee pain,²³ although this study showed only a trend that women are more likely to develop patellofemoral pain than are men. In contrast, studies have shown that knee injuries are more frequent in female athletes than in male athletes, independent of the sport.^3,4,24,25

5. Limitations

The study evaluated most participants (77%) the day of the race, but some were assessed over the next three days. The runners may have developed anterior knee pain on the day after the race or some hours after the evaluation rather than at the moment that they finished the race and were seen for a physical examination (underestimation).

To measure stretching deficiency, we used cutoff points (in degrees for the hamstrings, in centimeters for the rectus femoris) and severity categories (mild, moderate and severe for the gastrocnemius & iliotibial band). However, there is probably no specific cutoff point that applies to every runner to avoid anterior knee pain because all individuals differ in terms of the capacity to gain strength and flexibility. Someone can feel truly stiff with 70° of flexibility in the hamstrings, while someone else can feel that they improved considerably when they can finally stretch their hamstrings to a 60° angle. These feelings depend on how long ago the person started stretching and how much he or she improved. Most likely, because of these inter-individual differences, in clinical practice, we could focus on personal goals instead of fixed cutoff points for everyone.

6. Conclusions

Anterior knee pain is the most frequent injury that occurs in half-marathon runners at the end of the competition. Spending more than 2 h to finish the race and not being able to stretch the hamstrings by 70°, regarding the angle between the leg and the stretcher in the supine position, were risk factors for anterior knee pain.