Jimmy J Chan¹, Christine S Williams^1*, Kevin K Chen¹, Christopher J Ball¹, Ettore Vulcano^1,2

¹Leni and Peter W. May Department of Orthopedic Surgery, Icahn School of Medicine at Mount Sinai, 5 E 98^th St, 9^th Fl, New York, NY 10029, USA
²Columbia University Division of Orthopedics at Mount Sinai Medical Center 4300 Alton Road, Miami Beach, FL 33140, USA

*Corresponding Author: Christine S Williams, Department of Orthopedic Surgery, Icahn School of Medicine at Mount Sinai, 1 Gustave L. Levy Place, New York, NY 10029 USA;
Email: [email protected]

Published Date: 15-07-2022

Copyright© 2022 by Williams CS, et al. All rights reserved. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Abstract

Objective: Patella instability injuries are often sports-related and occur in young athletes. These injuries severely impact the season and career trajectory of high-level competitors. This is the first large epidemiological study that evaluates these injury events in NCAA athletes.

Methods: Patellar instability injuries across 16 sports among NCAA men and women during the 2004-05 to 2013-14 academic years were analyzed using the NCAA Injury Surveillance Program (NCAA-ISP). Patellar instability injuries per 100,000 Athlete-Exposures (AEs), operative rate, annual injury and reinjury rates, in-season status (pre/regular/post-season) and time lost were compiled and calculated.

Results: A total of 11,778,265 Athlete-Exposures (AE) were identified and included. 380 patellar instability injuries were identified (Injury Rate IR = 3.23 per 100,000 AEs). 91 (23.95%) were severe injuries with a significantly higher time loss from play (40.5 days) and risk of operative management (50.55%). The most common sports during which a patellar instability event occurred were Women’s Gymnastics (IR=7.87), Soccer (IR=5.83), and Basketball (IR=4.34) and Men’s Wrestling (IR=5.44), Football (IR=4.84), and Soccer (IR=3.06). Male athletes had a statistically significant higher risk of season or career-ending injuries in all patellar instability injuries (3.20% vs 0.89%, p=0.0013). Severe injuries were more likely to result from contact mechanisms (58.24% vs 40.66%).

Conclusion: Patella instability injuries have a profound impact on the longevity and sustainability of a collegiate athletes’ career. The risk of recurrence once a patellar injury has occurred is significant and athletes often require surgery. While more female athletes sustained these injuries, male athletes were more likely to require operative management and sustain a season-ending injury.

Keywords                                          Patella Instability; Patella Dislocation; NCAA Injuries

Introduction

Patella instability injuries, which include subluxation or patellofemoral dislocation typically occur in young, active individuals and are often sports-related [1-13]. When high level collegiate athletes sustain these injuries it can be devastating and significantly alter career trajectory. A better understanding of which athletes are at risk for patella instability injury as well as the impact these injuries have on time loss from play, risk of recurrence, and operative vs non-operative treatment can help physician decision making.

The patellofemoral joint is a biomechanically complex articulation between the patella and the distal femoral condyles. Stability of the patellofemoral joint is dependent on patellar positioning within the trochlear groove as well as coordinated interaction between these osseous structures and both static and dynamic soft-tissue structures throughout the arc of knee motion [2,7,11,12]. The trochlear groove is a complex and unique concave sulcus at the distal aspect of the femur that provides an articular surface along which the patella can glide throughout knee flexion and extension [2]. As the knee progresses from full extension through early flexion, the soft tissue structures of the medial knee, including the Medial Patellofemoral Ligament (MPFL) and medial patellotibial ligament, provide the most stability because the patella is not fully engaged in the trochlear groove. Within the first 20 degrees of flexion the patella sits into the trochlear groove and should be correctly centered within the groove at 30 degrees of flexion [2,12-18]. Understandably, anatomic variants of the patella and/or trochlea can influence patella tracking and predispose an individual to a first-time patellar dislocation, which in turn increases the risk of recurrent instability events. These anatomic risk factors include trochlear dysplasia, patella alta, patellar tilt, and the Tibial Tuberosity to Trochlear Groove (TT-TG) distance [2,7,12,13,15].

Traumatic patella instability injuries most commonly occur in sporting activities and are often non-contact torsional injuries with the knee extended and foot externally rotated [19-26]. They can also occur during contact sports via a direct blow to the knee [21,26]. These injuries sustained in college athletes during a game can result in a profound impact on playtime and often requires operative management or a period of prolonged immobilization.

To date, there are no large epidemiological studies describing the incidence of traumatic patellar instability injuries in collegiate athletes in the United States. The purpose of this study is to provide an epidemiological overview of collegiate athletes who sustained patellar instability injury events. Specifically, the aim was to evaluate data from the National Collegiate Athletic Association Injury Surveillance Program (NCAA-ISP) to report on trends in demographics, injury patterns and to determine risk environments in this population. A greater understanding of the factors associated with increased risk of patella instability injuries in adult athletes may help elucidate prevention strategies and help the athlete and the physician to fully understand the impact these injuries have on the involved extremity including the significant risk of recurrence and arthritic changes as well as the impact on their athletic career.

Methods

An institutional review board exemption was granted for this study and the research review board of the NCAA approved this study. The NCAA Injury Surveillance Program (ISP) prospectively collects de-identified injury data for collegiate athletes. This study utilized two cohorts from NCAA-ISP, including 2004-05 to 2008-09 and 2009-10 to 2013-14. A complete methodology of NCAA-ISP data collection has also been described by Kerr, et al., [17].

Definitions

A reportable Athlete-Exposure (AE) is defined as one athlete participating in one NCAA-sanctioned practice or competition in which he or she was exposed to the possibility of an athletic injury regardless of the time associated with that participation [22].

In accordance with current literature that utilizes the NCAA-ISP database, a reportable injury is defined as any injury that (1) occurred during a team-sanctioned event, (2) required attention from an Athletic Trainer (AT) or a physician, and (3) resulted in restriction of the athlete’s participation in organized practice or competition for more than one day. We applied these inclusion criteria to the data from the 2004-05 through 2008-09 seasons. For the 2009-10 season and onward, non-time-loss injury data was collected and defined using the first two criteria as a reportable injury, but did not result in restricted play beyond the day of the injury or day 0.17 This information was not available prior to the 2009-10 season. For the 2009-10 through 2013-14 seasons both reportable injuries and non-time-loss injuries was included in the analysis. We identified patellar instability injuries by manually searching through the database by diagnosis. The diagnoses for patellar instability injuries included patella subluxation or dislocation. To enhance our analysis, we performed sub-classification on injuries deemed to be severe. In this study, severe injuries were defined as those injuries that were season or career ending, required surgical intervention, or resulted in >30 days’ time loss. A period of time loss >30 days was ultimately deemed to be severe in accordance with prior time loss intervals proposed by Kucera, et al., [19].

Operative injuries were defined as injuries which resulted in the athlete to undergo surgical intervention as treatment for the reported injury. Recurrence was defined as injuries that occurred in an athlete who had returned to play then suffered the same injury. Season-ending injury was defined as injury which rendered the athlete unable to return to their sport for the same academic year. This included both season-ending and career-ending injuries. Time loss was defined as days unable to participate in team-related activity in athletes who ended up returning to play in the same season (all season-ending injuries were excluded from calculation). Injury mechanism was divided into either contact or non-contact injuries. The definition of a contact injury mechanism included contact with another player, surface, equipment, or out-of-bound object; while non-contact mechanisms included gradual or overuse injuries or non-contact injuries. Season of play was defined as the segment of the year when the injury occurred, which can be preseason, regular season, or postseason.

Data Collection

The NCAA-ISP collected voluntary, self-reported data across a total of 25 sports. The following men’s sports were included: Basketball, Baseball, Cross Country, Football, Ice Hockey, Lacrosse, Soccer, Swimming/Diving, Tennis, Outdoor Track, Indoor Track, Wrestling. The following women’s sports were included: Basketball, Cross Country, Field Hockey, Gymnastics, Ice Hockey, Lacrosse, Soccer, Softball, Swimming/Diving, Tennis, Outdoor Track, Indoor Track, and Volleyball.

The injury data was collected as injuries occurred or reported to the athletic training staff. The detailed history and physical findings of the injury was documented by individual Athletic Trainers (ATs) based upon their personal judgement. ATs had the ability to review and update the data as necessary over the course of a season. De-identified data was then exported manually by participating ATs (2004-05 to 2008-09) or extracted from the electronic medical record of participating ATs by a Common Data Element (CDE, 2009-10 to 2013-14) [10]. As per NCAA-ISP protocol, all exported data was passed through an automated verification process to assure quality and accuracy. Final confirmed data was then entered into the aggregate research dataset. With a formal request from our institutional research team, the NCAA-ISP granted access and permission to use the de-identified information from the dataset for this analysis.

Statistical Analysis

The Incidence Rate (IR) of patellar instability injuries, defined as the number of injuries per 100,000 AEs, and percentages were calculated. The overall rate, gender rate (male or female), individual sports rate (25 teams), and annual injury trend were reported. Rate of operative injury, recurrence, injury mechanism, season of play, season-ending injury, and time loss were determined based on total counts of injuries.

The distribution of injuries and resulting time loss were examined over the period of study. We used a Poisson regression model in which the injuries are the outcome with the offset of AEs to estimate the incidence rate along with the corresponding 95% Confidence Interval (CI) for the count data [14]. The same model was used to estimate the IR by including sex/contact as an independent variable. The proportion of subgroup injury was provided along with the corresponding permutation 95% CI. The point estimate as well as the robust 95% CI for the ratio of the male/contact injury proportion vs. the female/non-contact injury proportion was obtained using the Generalized Estimating Equation (GEE) model with Poisson distribution to control for mild violation of the Poisson distribution assumption [3]. Time loss was summarized as median and the Interquartile Range (IQR) due to a skewed distribution. The analyses were performed using SAS â Version 9.4. Copyright ã (2019) SAS Institute Inc. SAS and all other SAS Institute Inc. product or service names are registered trademarks or trademarks of SAS Institute Inc., Car, NC, USA.

Results

A total of 11,778,265 AEs, including 4,345,128 (36.89%) female AEs and 7,433,137 (63.11%) male AEs were identified for inclusion in this study. Overall, 380 patella instability injuries were reported in 25 NCAA sports from 2004-05 to 2013-14 academic years, resulting in an overall IR of 3.23 per 100,000 AEs (Table 1-4). The injury rate was higher in females (IR=3.34) compared to male athletes (IR=3.16). For female athletes, patella instability injuries occurred most frequently in the following sports: Gymnastics (IR=7.87), Soccer (IR=5.83), and Basketball (IR=4.34). For male athletes, patella instability injuries were most frequently seen in Wrestling (IR=5.44), Football (IR=4.84), and Soccer (IR=3.06). There was a decreasing trend of patella instability injuries from 2004-05 (IR=4.24) to 2012-13 (IR=1.93), with an increase in events during the 2013-14 season (IR=2.27).

Severe injuries presented a significant proportion of patella instability injuries. For all injuries, 12.11% required operative treatment with 27.63% of these cases recurrent injuries. 14.21% of injuries were season or career ending, and the median time loss was 8 days for non-season ending injuries. 57.63% of injuries occurred by contact mechanism and 41.58% were non-contact mechanisms.

There were 91 severe patella instability injuries (23.95%), resulting in an overall IR of 0.77. The injury rate was comparable between female (IR=0.78) and male (IR=0.77) athletes. For female athletes, severe injury most commonly occurred in Gymnastics (IR=4.92], Basketball (IR=1.53), and Volleyball (IR=0.89). For male athletes, severe injuries most commonly occurred in Tennis (IR=1.51), Football (IR=1.47), and Wrestling (IR=0.78).

Overall, there was a decreasing trend in the rate of severe patella instability injuries over the 10-year study period with an uptick in injury events in 2007-08 (IR=1.01) and 2009-10 (IR=1.59). 50.6% of severe injuries required operative treatment and 37.45 were recurrent injuries. A large majority (59.3%) of severe injuries were season or career ending and the median time loss was 40.5 days. Consistent with all patella instability injuries, those that were categorized as severe were mostly contact mechanism injuries (58.2%).

Supplemental Table S1 present data examining the effect of gender on outcomes of patella instability injuries. There was a significantly higher risk of operative treatment seen in male athletes (2.01%) compared to female athletes (0.44%) for all patella instability injuries (p=.0063). For severe patella instability injuries, male athletes were at greater risk for requiring operative treatment when compared to female athletes, but this was not statistically significant (56.14% vs. 41.18%, p=0.19). Male athletes had a higher risk of season-ending injuries for all patella instability injuries (3.2% vs. 0.89%, p=0.0013). Similarly, male athletes had a higher risk of season-ending injuries for severe patella instability injuries compared to female counterparts but this was not statistically significant (64.9% vs. 50%, p=0.13).

Supplemental Table S2 demonstrates association of injury mechanism and outcomes of patella instability injuries. In both the patella instability injury and severe patella instability injury groups, no significant difference was noted between contact and non-contact injury groups in reference to operative risk, recurrence rate, season-ending injuries and median time loss.

Table 1: Baseline characteristics of all patella instability injuries.

Table 2: Baseline characteristics for severe patella instability injuries.

Table 3: Injury mechanism comparison for all patella instability injuries.

Table 4: Injury mechanism comparison for severe patella instability injuries.

Discussion

To date, this is the first large epidemiologic study that evaluates patella instability injury events in NCAA collegiate athletes in the United States. In this study we aimed to identify the incidence, risk factors, and the setting in which patella instability injuries take place. With a better understanding of the athletes at risk, we can help healthcare providers predict these injuries and implement preventative measures.

Over a ten-year period and across 25 NCAA sports, a total of 380 patella instability injuries were reported (IR=3.23) with a higher injury rate seen in females compared to males (IR=3.34 vs. 3.16, respectively).  Historically, the literature reported patella instability injuries to occur predominantly in females [6,16,20,21,23]. Dysplastic features such as increased Q angle, patella alta, and femoral anteversion are more prevalent in females and predispose to patellofemoral conditions such as patellofemoral pain syndrome and recurrent patellar instability9. However, more recent studies have shown no difference in sex predisposition and even a predominance of males [5,24,25]. The majority of this literature includes a study cohort comparable to the general population and an age group that includes pediatric, adolescent and adults. Comparatively, our study evaluates a much targeted population of high level collegiate adult athletes, which has not been published before.

Interestingly, while our study found that females had a higher injury rate, males were more likely to require operative management and more likely to sustain a season-ending injury. This may suggest that the injuries sustained in the female cohort may be chronic recurrent instability events that continued to be managed nonoperatively throughout the course of the season without significant time loss. A large majority of all patella instability injuries were a result of contact mechanisms (57.63%) and may have been sustained by male athletes given the fact that the injuries in the male cohort mostly occurred while playing football, wrestling, and soccer compared to the female cohort that sustained injuries mostly during gymnastics, basketball, and soccer. This may account for the higher rate of operative treatment and thus, injuries that are characterized as season-ending in male athletes.

It would be of value to determine a prior history of patellar instability and discern variations related to sex and age. While this information was not available for this study, it would be interesting to determine predisposing factors and family history of high-level athletes who sustain patellar instability injuries. Previous studies showed a positive family history ranging from 13-28% in individuals with current patellar instability [4,8,22] Many believe that it is uncommon to sustain a purely traumatic patellar instability injury, that there is likely a congenital deficit or predisposing anatomic abnormality that puts these individuals at risk [5,16]. This study shows that 27.63% of all patella instability injuries are cases of recurrence but it is unknown if recurrent injuries occurred more frequently in men versus women or the age at which the first injury event took place. It is commonly reported that the age at which the first instability event takes place is predictive of risk of recurrence. Cash, et al., demonstrated that patients aged 11 to 14 years old had a 60% incidence of redislocation after the initial injury and those 15 to 18 years old only had a 33% incidence of redislocation. Patients who were older than 28 did not experience any redislocation events [5]. Further investigations into a cohort similar to this to determine family history, previous injury and age of previous injury, as well as examination of the non-injured knee to determine the anatomy and elucidate any abnormality that would put the patient at risk for patellar instability injuries would be worthwhile. With this information, athletes can undergo careful physical examinations with attention to musculoskeletal abnormalities of the knee and be preselected to participate in physical therapy and supervised exercises that athletes typically undergo after sustaining the initial injury. This can have a profound impact on the longevity and sustainability of a collegiate athletes’ career.

The limitations of this study include that it is a database study in which data was coded by volunteer athletic trainers and team physicians without central guidelines and the data is five years old. Thus, variables with subjective elements, including coding for injury diagnoses, may have differed depending on who entered the data. Similarly, patella subluxations or dislocations that reduce spontaneously may not have been noticed and not coded for appropriately. One study specifically noted that spontaneous patella reductions make careful examination extremely important to diagnosing and treating dislocation events [5]. However, the NCAA-ISP has rigorous data monitoring and a quality control system to limit bias and misdiagnosis. In addition, we grouped severe injuries including season ending injuries and career ending injuries which may differ from how other surgeons may define severe injuries. If the injury occurred at the end of the season or the end of a players’ collegiate career, the injury may be incorrectly grouped as severe injury and we may have overestimated the rate of these injuries. Finally, our definition of contact injury can differ from others’ definition of contact mechanism injury. We defined contact injury as one where physical contact was made, whether to another athlete or an object in the field of play, and based our grouping on this definition.

Conflict of Interest

The authors declare no conflict of interest.

References

1. Atkin DM, Fithian DC, Marangi KS, Stone ML, Dobson BE, Mendelsohn C. Characteristics of patients with primary acute lateral patellar dislocation and their recovery within the first 6 months of injury. Am J Sports Med. 2000;28(4):472-9.
2. Bollier M, Fulkerson JP. The role of trochlear dysplasia in patellofemoral instability. J Am Acad Orthop Surg. 2011;19:8-16.
3. Cameron, AC and Trivedi, PK, Regression Analysis of Count Data. 2^nd Ed Econometric Society. Cambridge University Press. 2013.
4. Carter, C and Sweetnam, R, Recurrent dislocation of the patella and of the shoulder. Their association with familial joint laxity. J Bone Joint Surg Br. 1960;42-r:721-7.
5. Cash JD, Hughston JC. Treatment of acute patellar dislocation. Am J Sports Med. 1988;16:244-9.
6. Cofield RH, Bryan RS. Acute dislocation of the patella: results of conservative treatment. J Trauma. 1977;17:526-31.
7. Colvin, AC and West, RV, Patellar instability. J Bone Joint Surg Am. 2008;90:2751-62.
8. Crosby EB and Insall J. Recurrent dislocation of the patella. Relation of treatment to osteoarthritis. J Bone Joint Surg Am. 1976;58:9-13.
9. Dejour H, Walch G, Nove-Josserand L, Guier C. Factors of patellar instability: an anatomic radiographic study. Knee Surg Sports Traumatol Arthrosc. 1994;2:19-26.
10. DiStefano LJ. The first decade of web-based sports injury surveillance: descriptive epidemiology of injuries in us high school girls’ soccer (2005-2006 Through 2013-2014) and National Collegiate Athletic Association Women’s Soccer (2004-2005 Through 2013-2014). J Athl Train. 2018;53:880-92.
11. Feller JA, Amis AA, Andrish JT, Arendt EA, Erasmus PJ, Powers CM. Surgical biomechanics of the patellofemoral joint. Arthroscopy. 2007;23:542-53.
12. Fithian DC, Nomura E, Arendt E. Anatomy of patellar dislocation. Operative Techniques in Sports Medicine. 2001;9:102-11.
13. Fithian DC. Epidemiology and natural history of acute patellar dislocation. Am J Sports Med. 2004;32:1114-21.
14. Fleiss JL, Levin B, Paik MC. Statistical Methods for Rates and Proportions. 3^rd John Wiley & Sons, Inc. 2003.
15. Frings J, Balcarek P, Tscholl P, Liebensteiner M, Dirisamer F, Koenen, P. Conservative versus surgical treatment for primary patellar dislocation. Dtsch Arztebl Int. 2020;117:279-86.
16. Jensen CM, Roosen JU. Acute traumatic dislocations of the patella. J Trauma. 1985;25:160-2.
17. Kerr ZY, Dompier TP, Snook EM, Marshall SW, Klossner D, Hainline B, et al., National collegiate athletic association injury surveillance system: review of methods for 2004-2005 through 2013-2014 data collection. J Athl Train. 2014;49:552-60.
18. Krych, AJ. Functional testing and return to sport following stabilization surgery for recurrent lateral patellar instability in competitive athletes. Knee Surg Sports Traumatol Arthrosc. 2018;26:711-8.
19. Kucera KL, Marshall SW, Bell DR, DiStefano MJ, Goerger CP, Oyama S. Validity of soccer injury data from the National Collegiate Athletic Association’s Injury Surveillance System. J Athl Train. 2011;46:489-99.
20. Larsen E, Lauridsen F. Conservative treatment of patellar dislocations. Influence of evident factors on the tendency to redislocation and the therapeutic result. Clin Orthop Relat Res. 1982:131-6.
21. Mäenpää H, Lehto MU. Surgery in acute patellar dislocation-evaluation of the effect of injury mechanism and family occurrence on the outcome of treatment. Br J Sports Med. 1995;29:239-41.
22. Rechel JA, Yard EE, Comstock RD. An epidemiologic comparison of high school sports injuries sustained in practice and competition. J Athl Train. 2008;43:197-204.
23. Rorabeck CH, Bobechko WP. Acute dislocation of the patella with osteochondral fracture: a review of eighteen cases. J Bone Joint Surg Br. 1976;58:237-40.
24. Scuderi G, Cuomo F, Scott WN. Lateral release and proximal realignment for patellar subluxation and dislocation. A long-term follow-up. J Bone Joint Surg Am. 1988;70:856-61.
25. Waterman BR, Belmont PJ Jr., Owens BD. Patellar dislocation in the United States: role of sex, age, race, and athletic participation. J Knee Surg. 2012;25:51-7.
26. Wolfe S, Varacallo M, Thomas JD, Carroll JJ, Kahwaji CI, Patellar Instability, in StatPearls. Publishing Copyright © 2021, StatPearls Publishing LLC: Treasure Island (FL).

Supplementary Files

Table S1: Gender comparison for all patella instability injuries.

Table S2: Gender comparisons for severe patella instability injuries.

Article Type

Data Article

Publication History

Received Date: 14-06-2022 
Accepted Date: 08-07-2022
Published Date: 15-07-2022

Copyright© 2022 by Williams CS, et al. All rights reserved. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Citation: Williams CS, et al. Epidemiology of Patella Instability Injuries in Collegiate Level Athletes in the United States. J Ortho Sci Res. 2022;3(2):1-19.

Table 1: Baseline characteristics of all patella instability injuries.

Table 2: Baseline characteristics for severe patella instability injuries.

Table 3: Injury mechanism comparison for all patella instability injuries.

Table 4: Injury mechanism comparison for severe patella instability injuries.

Table S1: Gender comparison for all patella instability injuries.

Table S2: Gender comparisons for severe patella instability injuries.