Prevalence and Pain Distribution of Anterior Knee Pain in Collegiate Basketball Players

Basketball is a physically demanding sport, requiring repeated jumping, landing, and change-of-direction tasks.^1,2 These intense functional demands place a high load on structures of the anterior knee. Anterior knee pain (AKP) is prevalent in basketball players,³ and many clinical presentations of AKP occur in jumping athletes, including patellofemoral pain (PFP) and patellar tendinopathy.^4,5

Differential diagnosis of patellar tendinopathy and PFP is challenging, as no criterion standard diagnostic tests exist for either condition.^6,7 Previous research has often used tenderness on palpation and imaging abnormality^8,9 as diagnostic tests. However, tendon abnormality on imaging, tenderness on tendon palpation, or both can also be present in asymptomatic jumping athletes¹⁰ and athletes with either patellar tendinopathy and PFP.¹¹ These findings question the role of imaging and individual clinical tests in diagnosis, and as a result, multiple outcome measures have been recommended to assist in the diagnosis of both conditions.⁷ Given that imaging abnormality and tenderness on palpation are commonly reported inclusion criteria for patellar tendinopathy and PFP, prior results could have feasibly overstated the burden of either condition in elite basketball athletes.

A further limitation of our understanding of AKP conditions in elite basketball is the method used to record injury. Many injury-epidemiology studies in basketball have relied on time-loss measures for quantifying injury burden. Yet these measures may fail to capture overuse knee injuries, as a number of athletes with patellar tendinopathy or PFP continue to train and play while symptomatic. The Oslo Sports Trauma Research Centre developed an overuse injury questionnaire (OSTRC-Overuse Injury questionnaire [OSTRC-O]) to quantify non–time-loss injuries.¹² This questionnaire has subsequently been modified to quantify knee overuse injuries (OSTRC-Knee).

The OSTRC-Knee has been used in a basketball population to capture the burden of knee injuries¹³; the prevalence was higher than that based on time-loss measures alone. Given the utility of the OSTRC,¹⁴ research by Owoeye et al¹⁵ has informed the further adaptation as a non–time-loss measure specific to patellar tendinopathy (OSTRC-Patellar Tendinopathy Questionnaire [OSTRC-P]) using knee pain location as a critical component for diagnosis. The OSTRC questionnaires have been critical in identifying the burden of overuse injuries; however, these methods cannot be used to record the clinical presentations of knee pain.

Clinical presentations of knee pain can be captured using athlete-reported pain mapping.¹⁶ Pain mapping involves the use of images or diagrams as a reference for individuals to depict their pain by recording or selecting their pain location from predefined pain maps. This method captures information about the location and spread of pain rather than pain severity alone. Pain mapping has been used to describe clinical presentations in a variety of AKP conditions, including osteoarthritis,¹⁶ PFP,¹⁷ and patellar tendinopathy.¹⁸ In addition, athlete-reported pain locations have been found to be reliable.¹⁹

Pain mapping has been used as an adjunct in research examining the burden of patellar tendinopathy in elite basketball athletes,¹⁸ defining patellar tendinopathy as the selection of a focal, inferior pole pain map during a functional load test.¹⁸ This method showed a lower prevalence of patellar tendinopathy than reported in studies using alternative diagnostic criteria (including imaging and tenderness on palpation).¹⁸ In addition, the noted variability in knee pain locations warrants further investigation.

Due to the lack of criterion standard diagnostic tests, recent consensus statements for both patellar tendinopathy²⁰ and PFP⁶ have recommended a combination of functional clinical tests to assist in diagnosis. However, these clinical tests, including squatting, lunging, jumping, and activities of daily living,^6,20 may provoke both conditions, creating further challenges in differential diagnosis. Because clinical tests may provoke both patellar tendon pain and PFP, we may need to move away from whether the test was provocative (yes or no) and instead explore the features that differentiate clinical conditions; one useful measure may be the pain location during functional testing.

Therefore, the primary aim of our research was to describe the prevalence and location of AKP in Canadian basketball players using pain mapping. Given previous results of a high prevalence of patellar tendinopathy in basketball players, our secondary aim was to use 2 outcome measures to describe the prevalence of patellar tendinopathy in this cohort. The 2 measures were the OSTRC-P (a validated self-report measure for the diagnosis of patellar tendinopathy) and inferior pole pain with a functional loading test (pain mapping when completing the single-legged decline squat [SLDS]).

METHODS

Players older than 17 years of age who were currently playing basketball in the Canadian Inter-University Sport League and the Alberta Colleges Athletic Conference were invited to participate in this study. Data were collected at the same single time point at the start of the 2018–2019 competitive season, when training and practice games began for all teams. The research methods were approved by university ethics committees, and all players provided informed consent.

Functional Testing

Single-Leg Decline Squat

The SLDS was used as a knee pain-provocation test as it preferentially loads the anterior knee.²¹ Instructions were consistent for all players. Participants stood on a 25° board in a standard position (back toward the wall) and squatted on each leg to a range that provoked pain or to 90° of knee flexion if they had no pain. Participants recorded a pain score on a numeric rating scale (NRS) from 0 to 10 when performing the SLDS, with 0 being no pain. Pain with provocation testing was defined as a score >0 on the NRS during the SLDS.

Pain Mapping

A player who reported pain >0 on the NRS during the SLDS was asked to indicate the pain location using a predefined pain map of the knee area.¹⁸ Pain mapping has been used to research knee arthritis,¹⁶ Australian football players,¹⁹ and more recently, knee pain in an elite basketball cohort.¹⁸ Players were prompted to select 1 or more images (Figure 2) that corresponded with their pain location from 9 pain maps that have been used in earlier investigations.¹⁸

Pain location was dichotomized a priori into focal and diffuse pain groups. Diffuse pain was defined as pain maps A, B, C, D, E, or I or >1 pain map location. Focal pain was defined as pain maps F, G, or H. For comparison with the OSTRC-P, the diagnosis of patellar tendinopathy using pain mapping was defined as the selection of the inferior pole of the patellar in isolation (pain map G; Figure 1).

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RESULTS

A total of 242 participants on 19 teams (of 38 invited teams, 50%) from the Canadian Inter-University Sport League and the Alberta Colleges Athletic Conference in Alberta, Canada (104 participants from 8 men's teams, 138 participants from 11 women's teams) were included in the study. A history of self-reported patellar tendinopathy was noted in 102 players (42%; Table 1). More men self-reported a history of patellar tendinopathy (63%) than women (26%; Table 1).

Table 1 Participant Demographics

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Self-Reported Knee Pain

Self-reported current knee pain (of any type) using the OSTRC-Knee was described by 101 players (43%). Men reported a higher prevalence of knee pain (n = 49, 48%) than women (n = 52, 38%). Participants with and those without knee pain reported similar numbers of training sessions and games per week (Table 2).

Table 2 Players Who Reported Knee Pain Compared With Those Who Did Not (n = 235)

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Comparison of the Prevalence of Patellar Tendinopathy

Using Pain Mapping

When patellar tendinopathy was classified as focal, inferior pole pain during the SLDS (pain map G), the overall prevalence was 10.3% (n = 25; unilateral = 22, bilateral = 3) of the entire cohort (n = 242). Prevalence was similar in the left (n = 17, 7.0%) and right knees (n = 11, 4.5%). Men noted a higher prevalence of focal, inferior pole pain in the left knee only (Table 3).

Table 3 Prevalence of Patellar Tendinopathy

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Using the OSTRC-P Score

Using the OSTRC-P score to identify the prevalence of patellar tendinopathy, we found an overall prevalence of 8.7% (n = 21; unilateral = 13, bilateral = 8): 6.6% (n = 16) on the right, and 5.4% (n = 13) on the left. Using the OSTRC-P score for classifying patellar tendinopathy, we observed similar prevalence in men and women (Table 3).

DISCUSSION

Anterior knee pain was common in Canadian basketball players when tested clinically using a pain-provocation test (SLDS) or a patient-reported outcome measure. Almost one-half of the players in this study described AKP when completing the SLDS; however, their pain locations were variable, indicating that the test was provocative but not specific. The SLDS is commonly used in patellar tendinopathy research²¹ but clearly provokes variable presentations of AKP. Capturing the presence of pain dichotomously (yes or no) fails to exclude diffuse AKP presentations such as PFP.

Few players reported localized, inferior pole pain during the SLDS or when using a self-reported, validated outcome measure (OSTRC-P). Findings from these 2 outcome measures suggested that patellar tendinopathy accounted for very few AKP presentations in this jumping cohort, which contrasts with the high prevalence demonstrated in both basketball and volleyball athletes.^22,23

The lower prevalence of patellar tendinopathy our cohort displayed may be related to how patellar tendinopathy has been diagnosed in research. Earlier authors who studied basketball players have used criteria such as tenderness on tendon palpation²² or a previous diagnosis²³ to classify patellar tendinopathy. However, a combination of functional clinical tests has been recommended to replace the diagnostic criteria (imaging and palpation) used in prior studies.^7,20 These methods may have overdiagnosed patellar tendinopathy in jumping athletes and not accounted for variability in clinical presentations.

No previous investigators who examined knee pain in basketball players have provided player-reported pain locations. Pain mapping has been used in PFP research^17,24 and showed variability in clinical presentations. Capturing athlete-reported pain locations enabled us to highlight the variations in knee pain presentations and may add value when describing clinical presentations in future studies.

We found a higher prevalence of knee pain reported using the OSTRC-Knee compared with studies using time-loss measures alone.^25,26 This result supports previous research¹⁴ using non–time-loss methods of injury surveillance. A higher prevalence of non–time-loss knee pain suggests that many players continued to participate fully in basketball trainings and games. Furthermore, knee pain conditions may have been underreported and underrepresented in previous epidemiologic studies and league registries that use a missed-games definition of injury.

Data from our study indicated either variability in the pain location of patients with patellar tendinopathy or a high prevalence of other causes of knee pain, such as PFP, in this cohort. The low prevalence of patellar tendinopathy identified by the OSTRC-P supports the latter. Patellofemoral pain is an umbrella term that captures different pathoanatomical contributors to pain⁶ and as a result may present in variable or diffuse pain locations. In contrast, patellar tendinopathy is commonly localized to the inferior pole of the patella.²¹ Although pain mapping is not diagnostic in nature, the low prevalence of pain reported at the inferior pole of the patellar suggests that patellar tendinopathy prevalence was low.

Men reported a higher prevalence of inferior pole pain than women but on the left side only. Diffuse pain presentations were similar between men and women. Although earlier authors²⁷ identified PFP as more common in women, few have described PFP in an athletic population. Despite this, our results support those of Boling et al,²⁸ who demonstrated similar prevalence of PFP diagnosed with functional testing between sexes in a highly trained population. The prevalence of PFP may be higher than previously stated in both male and female athletes.

The increased prevalence of left-sided inferior pole pain in men is a novel finding and has not been noted in previous research. The differences in left and right limb prevalence may be related to lower limb use in functional tasks. Population data suggest that right-handedness is more common and that the jumping load on the contralateral lower limb may be increased in basketball players. To our knowledge, we are the first to describe knee pain locations for both limbs in a basketball population; however, we did not collect data on handedness and leg dominance. Further studies are needed to examine the difference between the left and right limbs.

Although it is challenging to compare prevalence across different studies due to variability in training loads and participant characteristics, prior researchers²⁹ using both time-loss, and non–time-loss measures determined that knee injuries contributed to a significant injury burden at the elite level.

Pain mapping captured variable knee pain presentations that may be missed by traditional methods of injury surveillance. This finding reinforces the challenges of using these methods to capture the prevalence of specific conditions. Given that no single diagnostic test exists for AKP conditions,^6,7,20 pain mapping may provide a useful adjunct to injury surveillance or when a combination of clinical tests is not feasible. Recording pain location may also allow clinicians to determine whether research findings can be applied to their patients. To reduce research waste, we must improve our transparency with respect to the clinical presentations of participants, regardless of the pathoanatomical diagnosis.

This study is the first to use the OSTRC-Knee and pain mapping in a large sample of elite male and female basketball players to examine the location and burden of knee pain (irrespective of a specific diagnosis). Fifty percent of the eligible teams participated, suggesting that the findings are likely to be representative of the cohort. However, these collegiate players had a younger average age than those in other elite competitions worldwide. Therefore, differences in training load and participant age may limit the transferability of results between other elite basketball leagues.

The small number of athletes who reported focal, inferior pole pain and patellar tendinopathy diagnosed using the OSTRC-P is itself an interesting finding and contrasts with previous results. Ironically, due to the small number of participants with focal, inferior pole pain in this jumping cohort, we were unable to compare the diagnostic ability of the OSTRC-P and pain mapping. Future investigators should continue to include descriptions of pain locations during provocative tests to examine whether the knee pain prevalence and clinical presentations vary across a basketball season.

CONCLUSIONS

The SLDS test is a provocative test for the anterior knee, and almost one-half of the cohort described pain with this test. Most participants depicted pain in a diffuse distribution commonly associated with PFP. Few players reported pain at the inferior pole of the patella during the SLDS, and a small number of players reported patellar tendinopathy based on the OSTRC-P score. These findings suggest that patellar tendinopathy was not a primary knee pain presentation in this elite jumping cohort, contrasting previous research. Our results reinforce that clinical tests can provoke multiple clinical presentations of knee pain and highlight that the pain location, rather than the presence of pain alone, must be captured to classify participants for research and inform clinical practice.