Upper limb injuries in mixed martial arts

ABSTRACT Objective Mixed-Martial-Arts(MMA) is a worldwide growing sport that incorporates different fighting styles and disciplines and is often associated with the Ultimate Fighting Championship(UFC) . The aim of this study is to explore the patterns and trends of upper limb injuries in MMA. Methods Ringside physician reports of the UFC fights between 2016 and 2019(inclusive) were extracted and screened from the Nevada State Athletic Commission(NSAC). The following variables were included: sex, weight division, injury mechanism, injury type, injury location, and type of finish. Injury rates were calculated and expressed per 100 athletic exposures (AE). An independent t-test, a one way analysis of variance(ANOVA), and a Joinpoint regression analysis were conducted to explore any significant differences or trends among variables. P-values<0.05 were considered significant(95% CI). Results A total of 81 upper limb injuries in 408 fights were recorded between 2016 and 2019. The injury rate was 9.9 injuries per 100 athletic-exposures(AE). Striking opponents was the most common mechanism of injury(p < 0.001). The hand was the most commonly injured location with an injury rate of 6.61 per 100AE(p < 0.001). Females had a higher upper limb injury rate than their male counterparts, but the difference failed to reach significance(p = 0.454). Similarly, no significant differences existed between rates of different types of injures. Matches ending with decision had the highest number of upper limb injuries with a rate of 12.6 per 100AE; however, no significant difference was determined between the rates of different ways of finish(p = 0.115). The strawweight(20.5 per 100AE), female flyweight(19.2 per 100AE), and male flyweight(13.8 per 100AE) divisions had the highest upper limb injury rates. Conclusion The hand was the most commonly injured upper limb location in MMA, and ‘striking opponent’ was the most common injury mechanism. Increasing padding in gloves and implementing medical examinations during bouts can help reduce injury rates.


Introduction
Multiple fighting styles and disciplines are incorporated in Mixed Martial Arts (MMA), a full-contact combat sport that was first introduced in North America in the early 1990s [1,2].Fighting styles can involve strikes, submissions, takedowns, and clinching.Competition can end by way of knockout (KO), technical knockout (TKO), submission, or decision [3].The sport was criticized early on by multiple political and medical parties for the lack of decent protective strategies and the lack of regulations [4][5][6].That being said, it has evolved substantially over the past several years with the introduction of guidelines designed to improve organization, judging, refereeing and most importantly, athlete safety [1][2][3].Accordingly, the sport became increasingly popular, and is now one of the most followed and supported sports in the world [7].Multiple fighting promotions arose due to the sport's evolution; nevertheless, the brand 'Ultimate Fighting Championship (UFC)' remains the leading MMA promotion in the world [8].
Despite worldwide acceptance and recognition, MMA remains a violent sport with a high risk of debilitating injuries [9,10].The upper limb is especially vulnerable to damage, due to the high involvement of striking in the sport, and the deleterious effects of some submission techniques on the joints of the upper extremity [2,3].These different injuries can occur in multiple positions and can involve different anatomical locations within the upper limb, with different variables and predictors.There is a paucity of literature on upper limb injuries in MMA.Existing studies in the literature often discuss general MMA injury profiles, with a main focus on traumatic head injuries [8,[10][11][12].For example, Rainey et al and Ngai et al explored injuries in professional and amateur MMA athletes and presented injury profiles with respect to general anatomical locations and injury types [8,11].Fares et al explored the general profile of MMA injuries, and later extensively studied head injuries in the sport [9,10].Thomas and Thomas conducted a systematic review of MMA injuries and similarly reported on studies that involve general injury patterns in MMA, without extensively focusing on the upper limb [12].Some studies, on the other hand, explored potential variables like sex and weight divisions, and how these can act as predictors to match outcome and fighting style [9,13,14].It is important to understand the patterns and trends of upper limb injuries in MMA, and to discover potential injury predictors like sex or weight divisions.This is essential in order to facilitate diagnosis, establish causative factors, and extrapolate possible preventive strategies.Accordingly, the aim of this study is to provide an epidemiological analysis of upper limb injuries in MMA, by exploring the patterns and trends of these injuries in the UFC from 2016 till 2019.

Study design
This is a descriptive epidemiological study.The Nevada State Athletic Commission (NSAC) website was screened for professional UFC fights that took place between January 1 st , 2016 and 31 st , December 2019 (inclusive) [15].Match scorecards were analyzed, along with reported athlete characteristics and outcomes.Ringside physician's reports were examined in order to assess upper limb injuries inflicted during fights.Match stats including the total number of strikes thrown and the number of minutes played were retrieved and recorded from the UFC's website (www.ufc.com),(ufcstats.com) and (www.sherdog.com),all of which are trusted websites in MMA media [16][17][18].Play-by-play analysis was examined through (www.sherdog.com)to determine the mechanism of injury [18].When the mechanism was not very evident, a video analysis was conducted, by which the author reviewed the fight meticulously to record all potentially relevant information, like mechanism of injury.While our main source of data and information was through the NSAC database, the play-by-play records and the conducted video analysis helped corroborate and confirm information in case it was missing or ambiguous.In addition, a thorough exploration of all subsequent reports in trusted MMA media outlets regarding the injured athletes was conducted in order to retrieve as many details about the injuries as possible.Our dataset can be made available upon request for scholarly/ research purposes.

Dataset collected
All sanctioned UFC fights were included, except for those that ended in 'No Contest' or 'Disqualification.'The generated dataset included sex, match result, fighting stance, rounds fought, weight division, way of finish, total number of strikes thrown, location, type, and mechanism of upper limb injury.UFC fights can end in a multitude of ways [3].A Knockout (KO) occurs when an athlete loses consciousness after sustaining blunt trauma from his/her opponent.A technical knockout (TKO) occurs when the sustained blunt trauma causes deterred mental status and inability to intelligently defend oneself, but without full loss of consciousness.A Submission occurs when an athlete physically (tapping) or verbally concedes due to an incapacitating grappling technique by his/her opponent.Finally, and if none of the described stoppages take place prior to the end of the fighting rounds, a panel of expert judges decide the winner, and the way of finish is deemed a Decision [3].

Definitions
Upper limb injuries were classified into six different anatomic locations: shoulder, arm, elbow, forearm, wrist, and hand.Furthermore, upper limb injuries were also classified according to type.'Fractures' were defined as any traumatic injury that resulted in a fracture as confirmed by postmatch imaging or by subsequent reports.'Contusions/ Bruises' were defined as any blunt traumatic injury that occurred with no reports of fractures via post-fight imaging or media reports.'Muscle/Ligament tears' were defined as injuries that resulted in strained/torn muscular damage or sprained/torn ligaments.Upper limb injuries that did not fall into these categories were termed 'Other.'The mechanism of injury was analyzed by evaluating play-by-play records, video analysis, match stats and subsequent media reports of the upper limb injury.The four main mechanisms of injury included 'striking opponent,' 'blocking strikes,' 'grappling,' 'overuse,' and 'others.'

Statistical analysis
Athletic exposures (AEs) were calculated by multiplying the total number of fights recorded in the study by the number of athletes involved in one fight (two) [9,19,20].Rates were then reported as number of injuries per 100 AE.
An independent t-test was conducted to assess for any statistically significant differences between upper limb injury rate of female and male athletes.A one-way analysis of variance (ANOVA) test was used when determining whether any statistically significant differences exist between upper limb injury rates of different types, locations, mechanisms, and ways of finish.If the difference was deemed significant, an appropriate post-hoc test was conducted to indicate which comparisons deemed a significant result, depending on whether the studied population was considered parametric or not (Games-Howell test vs Tukey's test).A JoinPoint regression analysis was conducted to explore the trends of upper limb injuries across different male weight divisions, with a minimum of 1 joinpoint on analysis.We considered P-value less than 0.05 (95% confidence interval (CI)) to be statistically significant.Statistical Package for the Social Sciences for Windows software version 25.0 (IBM SPSS, 2017) and JoinPoint regression analysis software tool were used to perform statistical analysis.

Demographics
Total screening involved 412 UFC matches.Four of these matches were excluded from our study because they ended in a Disqualification or a No-Contest.Accordingly, the final dataset included 408 UFC matches involving 816 athletes (710 males and 106 females).A total of 445 injuries were reported across all weight divisions, during our studied period (2016-2019).Of the matches included in our study, 53 (13%) involved female athletes and 355 (87%) involved male athletes.The total injury rate was 55 injuries per 100AE (Table 1).Upper limb injuries constituted 81 injuries (18.2%) with an injury rate of 9.9 per 100 AE (Table 1).These injuries occurred in 71 athletes (57 Males and 14 females) during 75 fights, with six fights resulting in more than one upper limb injury.There were evidence of recurrence in seven injuries (8.6%).
Athletes who sustained upper limb injuries had an average record of 12 wins and 3 losses.They competed for an average of 12 minutes and 52 seconds (range: 36 seconds -25 minutes) and landed an average of 69 strikes using all limbs (range: 4-185 strikes) per fight.Out of the 71 injured athletes, 53 (75%) adopted an Orthodox stance, 11 (15%) adopted a Southpaw stance, and 7(10%) adopted a Switch stance.All athletes were seen and assessed by a ringside physician and underwent a post-fight medical evaluation, which included proper diagnostic imaging studies.X-rays were used in the diagnosis of 50 upper limb injuries (62%), whereas magnetic imaging resonance (MRI) was used in 8 injuries (10%).Around 48 upper limb injuries (59%) were reported on a winning athlete, 31 (38%) were reported on a losing athlete, and 2 (3%) were reported on an athlete whose fight resulted in a draw.
Accordingly, ANOVA analysis showed significant differences between the different injury mechanisms in our study (p < 0.001; Effect size: 0.863).'Striking opponent' caused a significantly higher number of upper limb injuries when compared to 'overuse' (p < 0.001; CI [5.22,14.28

Upper limb injury: anatomic location
The hand was the most commonly injured location in the upper limb, with 54 injuries (67%) and an injury rate of 6.61 per 100AE (Table 2).The shoulder followed with 9 injuries (11%) and an injury rate of 1.1 per 100 AE.Seven injuries (9%) involved the elbow, while 6 injuries (7%) involved the forearm.The wrist recorded 4 injuries (5%) and only one injury (1%) was attributed to the arm location.Injury rates of different upper limb anatomic locations can be seen in Table 2.
When assessing for statistical significance, ANOVA showed significant differences between the injury rates of different upper limb locations (p < 0.001; Effect size:0.822).The hand was injured significantly moe often than the shoulder  3).

Upper limb injury: type
Contusion/bruise was the most common type of upper limb injury with 32 injuries (39.5%), and an injury rate of 3.9 per 100AE (Table 2).Muscle/ligament tears followed with 20 injuries (25%), and an injury rate of 2.4 per 100 AE (Table 2).
Fractures constituted 15 injuries (18.5%) and an injury rate of 1.9 per 100 AE (Table 2).Upper limb injuries of other types constituted 14 injuries (17%) and an injury rate of 1.7 per 100AE (Table 2).There were no statistically significant differences between the different types of upper limb injuries (p = 0.173; Effect size: 0.330).
When exploring the different types of injuries across various upper limb anatomic locations, contusions/bruises were the most common type of upper limb injuries in the hand and wrist, with 28 (52%) and 2 (50%) injuries, respectively (Table 4).Fractures were the most common type of injury in the forearm with four injuries (66.7%).Muscle/ligament tears were the most common type of injury in the elbow and shoulder with 4 (57%) and 8 (89%) injuries, respectively.In addition, the only arm injury was attributed to a muscle tear (100%).The distribution of the upper limb injury types according to anatomic location can be seen in Table 4.

Sex
Male athletes sustained 65 upper limb injuries (80%), with an injury rate of 9.2 per 100AE, while female athletes sustained 16 injuries (20%), and an injury rate of 15.1 per 100AE.While the difference is notably high, it was not deemed significant upon analysis (p = 0.454; Mean Difference: 8.875; Effect size: 1).
With respect to mechanism of injury, anatomical location and injury type, distribution of upper limb injuries was similar in both male and female athletes (Figure 2).'Striking opponent' was the most common mechanism of injury in both sexes, contributing to 65% of upper limb injuries in males, and 50% of upper limb injuries in females.Similarly, the hand was the most commonly injured anatomical location in the upper limb, with a rate of 10.38 per 100AE in females and a rate of 6 per 100AE in males.Moreover, contusion/bruise was the most common type of upper limb injuries encountered, with a rate of 21.88 per 100AE in females, and a rate of 3.52 per 100AE in males (Figure 2).

Type of finish
Matches ending via decision witnessed the highest number of upper limb injuries with 48 injuries (59%), and an injury rate of 12.6 per 100AE.Those ending via TKO/KO followed with 24 injuries (30%), and an injury rate of 8.6 per 100AE.Matches ending via submission had the lowest number of upper limb injuries with 9 injuries (11%), and an injury rate of 5.7 per 100AE.While matches ending via decision had a notably higher upper limb injury rate when compared to other ways of finishes, statistical analysis via ANOVA test failed to produce significance (p = 0.115; Effect size: 0.381).
With respect to anatomical location, the hand was notably the most injured upper limb location amongst the three ways of finish comprising: 79% of upper limb injuries in fights ending via TKO/KO, 65% of injuries in fights ending via decision, and 44% of fights ending in submission.The elbow, nonetheless, followed closely in fights ending via submission, comprising 33% of upper limb injuries.The distribution of upper limb injuries according to anatomic location across the three different ways of finish can be seen in Table 5.With respect to injury type, muscle/ligament tears were the most common among matches ending in submission, comprising 67% of upper limb injuries.Contusion/bruise were the most common upper limb injury type in matches ending via TKO/KO or decision, contributing to 50% and 37.5% of injuries respectively (Table 6).

Weight division
Generally, upper limb injuries were more commonly seen among the lighter weight divisions.For females, the strawweight division had the highest rate of upper limb injuries (20.5 per 100AE), followed by the female flyweight division (19.2 per 100AE) and the female bantamweight division (6.25 per 100AE).There was no upper limb injuries reported in female featherweight athletes.For males, the male flyweight division had the highest injury rate at 13.8 per 100AE.The light heavyweight and middleweight divisions followed at 10.7 and 10.2 injuries per 100AE respectively.The lowest injury rate among male weight divisions was recorded in the lightweight division at 5.8 injuries per 100AE.
The trends of upper limb injuries were studied across male weight divisions only, due to the small sample size across female athletes.And even though the regression analysis software was able to detect one joinpoint and 2 distinct slopes, there was no significant trends visible between weight division and upper limb injury rates in our study (Figure 3).The first slope exhibited a decrease in rates of upper limb injuries (slope = −0.25),and was noted between flyweight division (125 lbs) and featherweight division (145 lbs).The second slope exhibited a subtle increase in rates of upper limb injuries (slope = 0.03) and was noted between lightweight division (155 lbs) and heavyweight division (265 lbs).

Discussion
In our study, upper limb injuries constituted 18.2% of injuries in MMA with a reported rate of 9.9 injuries per 100AE.Other studies in the literature reported similar data in MMA with percentages of upper limb injuries ranging between 11.8-22.8%[8,12,21,22].Striking opponent was the most common mechanism of injury, the hand was the most commonly injured anatomic location, and contusion/bruise was the most common type of injury.In addition, upper limb injuries were more common amongst lower weight divisions.
Our study showed that the significant majority of upper limb injuries in MMA were self-inflicted via striking, and this would further explain why the hand was the most commonly injured location.Even though the sport of MMA allows striking using the elbow and the forearm, the hand (fist) remains the most frequently used part of the upper limb for striking [23].The minimal padding in MMA gloves (4-6 ounces) contributes to this finding, as it provides little protection to the hand and compromises its safety during the fight [24].In addition, athletes are often encouraged to engage in striking during MMA bouts, as striking is often considered more appealing to the audience when compared to prolonged grappling exchanges [25].This, along with the adrenaline rush exhibited by the athletes during the fight, may allow them to throw as much strikes as possible, ignoring any acquired injuries [26].As a result, higher injury rates -mainly to the body part that is engaging in the act of striking -are expected to occur.
There was no significant difference between the different types of upper limb injuries in our study.Blunt traumatic injuries like contusion/bruises and fractures were inevitable, considering the high emphasis of striking in MMA in order to attain an explosive finish [9,25].MMA rules allow athletes to strike using different parts of the upper limb [3].As a result, injuries included multiple elbow and forearm contusions and fractures.Muscle/ligament tears were also prevalent.MMA bouts often involve very high aerobic and anaerobic stress from the athletes [27].The incorporation of different fighting styles, along with excessive physiological demands implicated by an MMA competition predispose many athletes to overuse and strain injuries [28].In addition, different grappling techniques and explosive maneuvers exhibited in the sport can compromise the integrity of ligaments and muscles in different joints, and this predisposes these structures to tears and sprains [29,30].Such was the case with several shoulder and elbow injuries in our study.
A higher rate of upper limb injuries was exhibited among the lighter weight divisions.While the trends presented did not reach significance, commenting on the pattern seen is founded, as the lack of significance may have been caused by the relatively small sample size.This result falls in accordance with our finding that female athletes -who compete at lower weight divisions-had a noticeably higher upper limb injury rate than their male counterparts.The strawweight division, which recorded the highest rate of upper limb injuries is exclusive for female athletes.A previous study has shown that lighter weight divisions have lower rates of TKO/ KO finishes, most likely due to the greater knockout power found in heavier athletes [10,[31][32][33][34]. Thus, the extended fighting time allows for more strikes to take place, and as a result, increases the chance of injury.This supports our finding that fights ending with decision, where more time exists to exchange strikes, had higher rates of upper limb injuries than other ways of finish.Fights ending with submission, on the other hand, had low upper limb injury rates, mainly due to the nature of that finish, which allows athletes to communicate their withdrawal from the contest before serious injury occurs.Nevertheless, submissions had a noticeably high percentage of elbow injuries, attributed to techniques (e.g. the armbar) that compromise the stability of joints [22].
The rate of upper limb injuries in our study was higher than those reported in other combat sports like boxing (18.7 per 1000 fight participation), judo (1.34 per 100 AE), and wrestling (2.55 per 1000AE) (32)(33)(34).Multiple factors may contribute to this finding, like the aggressive nature of this sport, the ability to incorporate different strikes (using fist, forearm, or elbow) in different positions (standing, ground, clinch), and the minimal padding in MMA gloves when compared to that of other combat sports [3,24].
Many studies evaluating injuries in MMA focus on head injuries, and their sequelae [1,10,35].Nevertheless, the high rate of upper limb injuries in this sport, their debilitating nature, and the subsequent long resultant lay-offs that can substantially alter an athlete's career plans, emphasizethe need for preventive policies and measures.Padding in MMA gloves is notoriously minimal when compared to other combat sports like boxing [24].Increasing padding in MMA gloves can help decrease the risk of blunt traumatic injuries to the athletes' hands.Educating referees on the mechanisms, types, and presentations of certain upper limb injuries in the sport can allow for earlier interventions that can prevent injury exacerbation.This can be especially useful in the setting of submission techniques.Medical evaluations and physical examinations should be performed on athletes prior to, after, and during MMA bouts to ensure athlete safety and to avoid additional damage to already sustained injuries.And finally, additional research is warranted to better understand the epidemiology and biomechanics of upper limb injuries in MMA.
To our knowledge, this study is the first to comprehensively explore upper limb injuries in the sport of MMA.Nevertheless, several limitations exist.We are limited by the retrospective nature of this study, and as a result, we were not able to include some variables that were relevant to our study, like return to play or more specific anatomical locations.In addition, some of our data (injury mechanisms and types) was collected through play-byplay and video analyses, or through prominent MMA media articles and reports, and this may introduce human error.

Conclusion
A high rate of upper limb injuries is observed in MMA.Our study showed that the hand was the anatomic location with highest rate of injury and that striking was the most common mechanism of injury.Types of upper limb injuries were various, and these included fractures, contusions, and muscle/ligament tears.Lower weight divisions exhibited higher upper limb injury rates.
The worldwide growth and fame of MMA necessitates increased awareness regarding the high injury rates exhibited in the sport.Upper limb injuries in MMA can be very debilitating and can predispose its practitioners to chronic disabilities and long layoffs.Proposed interventions that can help reduce these injuries can include increasing padding in MMA gloves, educating referees on the different mechanisms and types of upper limb injuries, and emphasizing the need for medical and physical evaluations prior, during and after MMA bouts.Future research can help improve our understanding of the biomechanics that govern upper limb injuries in the sport.It can also identify additional limiting factors to extrapolate better protective strategies and ensure athlete safety.

Disclosure statement
We, the authors of this manuscript, declare that we have no conflicts of interest and no funding sources.

Figure 2 .
Figure 2. Distribution of the percentage of upper limb injuries in male and female athletes, by mechanism of injury, anatomical location, and injury type.

Table 1 .
Distribution of total injuries and upper limb injuries, and their respective percentages according to different weight divisions (2016-2019).
Figure 1.Distribution of Upper Limb injuries by mechanism.

Table 4 .
Number and percentage of different types of upper limb injuries across the different upper limb anatomical locations.