Tennis is a worldwide sport enjoyed by millions of individuals, with 200 nations having an affiliation with the International Tennis Federation.1 Young tennis players often focus on the sport at an early age to improve their skills, making them competitive in recruitment for college scholarships.2 Epidemiology studies have reported that lower extremity injuries are the most common in tennis (31% to 67%), followed by upper extremity injuries (20% to 49%).1,3–7 However, upper extremity injuries affect the tennis population with a greater time loss due to the manifestation of chronicity. Shoulder and elbow injuries are often studied in tennis because the epidemiological literature shows that these joints represent the highest frequency of injuries to the upper extremity.7 As such, documenting patient-perceived function to the shoulder and elbow should be included as part of a clinician's person-centered approach to health care through the implementation of patient-reported outcome measures (PROMs). Clinicians who implement a person-centered approach are incorporating a component of evidence-based medicine into clinical practice. According to evidence-based medicine principles, patient-oriented research yields data that are person-centered, which are meaningful for patient care.8 Incorporating person-centered care is essential in maintaining patient involvement and is fundamental to providing high-quality health care.8
A PROM is broadly defined as any report of the status of a patient's health condition that comes directly from the patient, without interpretation of the patient's response by a clinician or anyone else.9 Health care professionals implementing PROMs in routine practice may provide an effective and efficient way of evaluating and improving health-related outcomes.10 In addition to PROMs providing information on patient perception and quality of life, these measures allow clinicians to consider patient views. In most cases, patients welcome being involved in their own health journey, which may in itself have health benefits.11 There are many PROMs available for clinicians to measure a patient's self-perceived quality of life12,13; however, PROMs specific to sport are more limited.14,15 Collecting sport-specific functional PROM data specific to the shoulder and elbow may aid in injury detection, especially in those with a previous injury history,16 and allow clinicians to adopt a person-centered care approach to maintaining and promoting an athlete's health.8 The Kerlan-Jobe Orthopaedic Clinic (KJOC) Shoulder and Elbow questionnaire is a PROM that could be used within an overhead athletic population, such as a tennis player.15
The KJOC questionnaire was first introduced in 2010 by Alberta et al.,15 who showed the instrument to be valid and responsive in the evaluation of overhead athletes in multiple sports. To date, normative data of the KJOC questionnaire have been established with baseball, softball, cricket, and swimming populations.16–19 However, no study has sought to establish normative KJOC data in tennis players despite the repetitive stress that is placed on the shoulder and elbow during competition. Establishing normative data within a tennis population will provide clinicians with baseline scores that can be used to assess the performance and function of tennis players.
Normative KJOC data in tennis players may be useful for clinicians to understand how players perceive arm health during practice and competition. Therefore, the primary purpose of this study was to establish normative KJOC scores in college and junior tennis players. It was hypothesized that KJOC scores would be similar between male and female collegiate and junior level tennis players. The secondary purpose was to determine the validity of this instrument, more specifically whether the KJOC is able to discriminate between symptomatic and asymptomatic tennis players. It was hypothesized that the KJOC would be able to discriminate between symptomatic and asymptomatic tennis players.
Young competitive tennis players provided written informed consent (or assent with guardian consent, when applicable) to participate in this cross-sectional study, which was approved by Texas State University's Institutional Review Board. Players were considered eligible if they: (1) participated in tennis at least three times a week; (2) were between 10 and 24 years of age; (3) participated in tennis at the collegiate or junior level; and (4) could speak and read English. Junior players were recruited from a sample of convenience from one tennis academy and were eligible if they participated in at least one sectional, regional, or national tournament. Collegiate players were from National Collegiate Athletic Association Division I to III programs. Excluded from the study were players with a current lower extremity injury, previous surgeries within the past 3 months, or a diagnosed concussion within the past 3 months before the study. The mean ± standard deviation universal tennis ratings were 11.9 ± 2 and 8.8 ± 1.3 for male and female college tennis players, respectively. The average universal tennis ratings were 6.8 ± 2.4 and 5.2 ± 2.2 for male and female junior tennis players, respectively. The universal tennis rating is a global system that rates every tennis player regardless of age, gender, or nationality on a 16-point scale. Players rated between 1 and 4 are considered recreational, 5 to 12 competitive, and 13 to 16 professional.20
The KJOC questionnaire was completed by all eligible players at one time point during the competitive season. Junior players completed the KJOC questionnaire in September 2018 or June 2019 and lived in the state of Texas. All collegiate players completed the KJOC questionnaire during the Fall of 2018.
Players had the option to complete the KJOC questionnaire (comprising visual analog scale [VAS] questions) using the traditional pen and paper method or Qualtrics, an online survey-based software (Qualtrics, Provo, UT). Completing a digital VAS has been shown to be similar to completing a traditional VAS via paper.21 The Qualtrics KJOC questionnaire was identical to the traditional pen and paper KJOC survey. The KJOC questionnaire comprises two sections.15 Section 1 included 10 questions related to demographic information and questions on current and past injury status related to the arm, level of competition, and current playing status. Playing status was grouped into one of three categories: playing without arm pain, playing with arm pain, or not playing because of arm pain. Section 2 included 10 questions in which players used a VAS to rate their level of perceived function during sport. The questions pertain to shoulder and elbow function, athletic performance, and social relationships related to performance.
Players using the traditional method marked a 100-mm VAS, and the location of each mark was measured to the nearest millimeter.15 Players who completed the questionnaire via Qualtrics were instructed to slide an interactive bar on a 100-mm VAS. The average of the 10 questions was calculated to determine a final KJOC score, with a possible range of 0 to 100 points. Scores closest to 100 represent perfect function. On average, players completed the KJOC questionnaire in 5 minutes.
To establish normative KJOC scores in male and female junior and collegiate level tennis players, a descriptive analysis was used including both mean ± standard deviation and median (interquartile range). The Shapiro–Wilk test was used to assess the distribution of the data given that previous studies have reported negatively skewed KJOC scores.15,22,23 The final KJOC score (main dependent variable) distribution was negatively skewed (Shapiro–Wilk test, P < .001). An assumption for using general linear models is normality of the sampling distribution of means; however, the analysis of variance is not sensitive to moderate deviations from normality; simulation studies using a variety of non-normal distributions show that the false-positive rate is not affected much by this violation of the assumption.24–26 Additionally, the data were negatively skewed (−1.9), and a reference of substantial departure from normality is an absolute skew value greater than 2.27 Therefore, a 2 × 2 analysis of variance was used to investigate differences in KJOC scores across sex (male vs female) and level of play (junior vs collegiate). Given the skewed sample data, median and interquartile ranges were reported along with means and standard deviations.
To determine whether the KJOC questionnaire could discriminate between symptomatic and asymptomatic tennis players, a Kruskal–Wallis test was used. The Kruskal–Wallis test is a non-parametric version of a one-way analysis of variance. Asymptomatic players were categorized into the playing without arm pain group and symptomatic players were categorized into the playing with arm pain and not playing because of arm pain groups. All data were analyzed using Statistical Package SPSS software (version 22; IBM Corporation, Armonk, NY). A P value of less than .05 was considered significant for all statistical analyses.
A total of 178 players completed the KJOC questionnaire (102 collegiate, 76 junior). Six of the 102 collegiate surveys were incomplete and were excluded from the study. Of the 96 collegiate participants, 73% were Division I, 24% were Division II, and 3% were Division III. Seventy-six junior tennis players completed the survey. The mean age was 14 ± 2 years for junior participants and 20 ± 1 years for collegiate participants. Descriptive data for the KJOC questionnaire across independent variables are presented in Table 1. There was no interaction between sex and level of play in KJOC scores for these tennis players (P = .17). Regardless of level of play, females scored higher (92 ± 10) on the KJOC questionnaire than males (87 ± 16) did (P = .02). The main effect for level of play was not significant (P = .45). Descriptive data of final scores for each KJOC question are reported in Table 2. There were 146 asymptomatic players and 26 symptomatic players (playing with arm pain). No player who completed the KJOC questionnaire was not playing because of arm pain. The KJOC questionnaire was able to discriminate between those who were asymptomatic (median = 95, interquartile range = 49) and symptomatic (median = 76, interquartile range = 67) (P < .01).
KJOC Scores (mm) Across Different Categories of Junior and Collegiate Tennis Players
Individual KJOC Scores (mm) for Each VAS Question for Junior and Collegiate Tennis Players
The KJOC questionnaire was designed to evaluate the function and performance of the shoulder and elbow in overhead athletes. Most research pertaining to the KJOC questionnaire has been conducted among baseball players.22,28; however, the original validation study did include five tennis players.15 Our study is the first to provide normative KJOC scores in a tennis population. Our hypotheses were partially supported because symptomatic players scored on average 19 points lower compared to asymptomatic players; however, males reported lower KJOC scores when compared to their female counterparts. One potential explanation for the sex differences could be that of the 90 males there were 15 symptomatic males who scored on average 15 points lower on the KJOC questionnaire compared to 11 of 82 symptomatic females. Although sex differences were present in our study, the clinical meaningfulness of a 5-point spread should be interpreted with caution. In fact, the only study to our knowledge that has compared male and female KJOC scores was by Wymore and Fronek,18 in which these authors reported no difference between male and females.
The data presented in this study are similar to other normative studies investigating the KJOC questionnaire. Alberta et al.15 reported a mean KJOC score for overhead athletes (multiple sports) playing without arm pain as 94 and 61 for athletes playing with arm pain. The mean KJOC scores for both levels of play presented in this study are also similar to asymptomatic baseball and swimming athletes.22,28 Professional baseball players undergoing ulnar collateral ligament reconstruction and who were still competing with arm pain on average 38 months following surgery reported scores of 73.22 Overhead athletes 1 year after superior labral tear anterior to posterior repair playing with arm pain reported KJOC scores ranging from 51 to 81 and averaging 65.29 The tennis players in this study playing with arm pain reported similar scores and none underwent any past ulnar collateral ligament or labral surgery at the time of survey completion. This is concerning because these athletes are playing with a level of perceived arm disability and pain that is similar to athletes who have undergone surgical interventions followed by extensive rehabilitation. Finally, 13 (8%) tennis players reported that they were currently injured; however, none of these players associated themselves with not playing due to arm pain. Consequently, it is not uncommon to see players at the junior and college level playing while injured or with arm pain.
This study has some limitations to consider in interpreting the results. The junior sample size was nearly 20% lower than the collegiate sample size due to the challenges that come with parental consent. In addition to this sample size, the researchers were only able to collect junior data from the state of Texas; therefore, generalizability must be interpreted with caution. Although there was no geographical restriction on college participants within the United States, it should be noted that the distribution of KJOC data was not evenly distributed between Division I, II, and III institutions. The sample comprises mainly National Collegiate Athletic Association Division I athletes. Further research should include more junior players from other regions in the United States similar to the collegiate sample in this study. Sample size was not calculated prior to data collection; however, the sample was comparable to similar studies, and post-hoc power analyses (G*power 3.1) indicate very high power (0.99) given P = .05, b > .8, and d = 0.4.18,22 Future research should include expanding the KJOC questionnaire to other tennis populations (eg, high school players and recreational players with different Universal Tennis Ratings). Another limitation includes the subjective nature of the KJOC questionnaire. The results of this questionnaire depended on unbiased and honest responses from the participants. To combat this limitation, the research team assured all participants that all results were anonymous and only the research team had access to player names. Participants from our study had two options for survey completion; however, both forms of the KJOC questionnaire were the same regardless of delivery. Further validation between asymptomatic and symptomatic players is still warranted, because the sample size for symptomatic players was limited. Future research is under way to determine whether KJOC scores change throughout the course of a season in these competitive tennis players.
Implications for Clinical Practice
From a clinical implication standpoint, it is important to note that final KJOC scores averaged 90 within this sample of tennis players. As such, players who report scores substantially below this threshold should undergo an additional clinical evaluation that aims to assess arm health. This is especially important with KJOC scores below 73, which were significantly associated with arm pain in these players. Incorporating baseline and regular KJOC scores as part of the health care process in tennis players could be easily implemented and requires minimal time commitments from the player. Implementing the KJOC as a form of care in tennis players is one method clinicians can use to gain perspective on a player's self-reported shoulder and elbow health.
This study is the first to investigate KJOC scores in different level tennis players. The scores presented in this research can serve as important data for collegiate and junior level tennis populations. Health care professionals should consider distributing the KJOC questionnaire prior to the start of competition to see if players are functioning at full capacity. Despite the small sample of symptomatic players, the KJOC questionnaire is able to discriminate between asymptomatic and symptomatic players. Health care professionals should use the KJOC questionnaire to better understand the subjective function of an athlete's shoulder and elbow health.
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KJOC Scores (mm) Across Different Categories of Junior and Collegiate Tennis Playersa
|Characteristic||n (%)||Mean ± SD||Median (IQR)|
| Male||47 (62)||43 (45)||87 ± 16||88 ± 16||94 (20)||94 (17)|
| Female||29 (38)||53 (55)||95 ± 6||90 ± 12||96 (8)||94 (14)|
| Currently injured||5 (7)||8 (8)||67 ± 22||74 ± 13||79 (42)||70 (22)|
| Not currently injured||71 (93)||88 (92)||91 ± 13||91 ± 13||96 (14)||95 (13)|
| Playing with arm pain (symptomatic)||13 (17)||13 (14)||69 ± 20||78 ± 19||76 (35)||82 (27)|
| Playing without pain (asymptomatic)||63 (83)||83 (86)||94 ± 7||91 ± 12||96 (8)||95 (13)|
| Overall score||76 (100)||96 (100)||90 ± 14||89 ± 14||95 (14)||94 (15)|
Individual KJOC Scores (mm) for Each VAS Question for Junior and Collegiate Tennis Players
|Question||Junior Mean ± SD||Collegiate Mean ± SD||Junior Median (IQR)||Collegiate Median (IQR)|
|How difficult is it for you to get loose or warm prior to competition or practice?||80 ± 20||85 ± 21||85 (27)||94.5 (27)|
|How much pain do you experience in your shoulder or elbow?||87 ± 20||85 ± 23||98 (24)||98.5 (25)|
|How much weakness and/or fatigue (ie, loss of strength) do you experience in your shoulder or elbow?||88 ± 20||85 ± 21||98 (15)||99 (29)|
|How unstable does your shoulder or elbow feel during competition?||90 ± 20||87 ± 23||100 (10)||100 (18)|
|How much have arm problems affected your relationship with your coaches, management, and agents?||96 ± 11||96 ± 12||100 (1)||100 (1)|
|How much have you had to change your throwing motion, serve, stroke, etc. due to your arm?||89 ± 22||91 ± 16||100 (15)||100 (15)|
|How much has your velocity and/or power suffered due to your arm?||90 ± 20||89 ± 18||100 (9)||100 (15)|
|What limitation do you have in endurance in competition due to your arm?||91 ± 19||91 ± 16||100 (6)||100 (13)|
|How much has your control suffered due to your arm?||92 ± 17||91 ± 18||100 (7)||100 (9)|
|How much do you feel your arm affects your current level of competition in your sport (ie, is your arm holding you back from being at your full potential)?||93 ± 18||92 ± 15||100 (4)||100 (10)|