KNEE ARTICULAR CARTILAGE INJURIES IN THE NATIONAL FOOTBALL LEAGUE – EPIDEMIOLOGY AND TREATMENT APPROACH BY TEAM PHYSICIANS

Robert H. Brophy, MD, Scott A. Rodeo, MD, Ronnie P. Barnes, MA, ATC, John W. Powell, PhD, Russell F. Warren, MD

ABSTRACT

This study describes the epidemiology of knee articular cartilage injuries in the National Football League (NFL) and the typical treatment approach by NFL team physicians. All knee articular cartilage injuries in the league database from 1992 to 2006 were reviewed, and team physicians were surveyed about their treatment approach to these injuries. A total of 118 cases were identified, for an average of 8 per year, with a higher injury rate during games compared with practice. Approximately half of the injuries occurred in linemen, and the most common site of injury was the femoral condyle. Fortysix percent of these injuries were treated surgically, with slower return to play after surgery (124 versus 36 days, P < .01). Among team physicians, microfracture was the most popular treatment approach (43%), followed by debridement (31%) and nonoperative management (13%). More research is needed to compare longterm outcomes based on lesion size in these athletes.
[J Knee Surg. 2009;22:331-338.]

INTRODUCTION

The articular cartilage of the knee is at risk during participation in cutting and contact sports such as American football. Cartilage lesions can be difficult to treat in any athlete, and these lesions are particularly challenging in elite athletes facing the demands of professional football. However, there is little in the literature on the prevalence and treatment of cartilage lesions in professional American football players. Only a single published study, a case series on the results of microfracture, has focused on articular cartilage lesions of the knee in these athletes.(18) New treatments for articular cartilage are becoming available, and although there are some reports of using these techniques in athletes, (6,7,15) no results specific to American football players are available.

This study was designed to advance our understanding of knee articular cartilage injuries in professional American football athletes by examining how often these injuries occur, the type of treatment the athletes receive and when they return to play, and what factors influence the treatment for and outcome of these injuries. The purpose of this 2-part study was to determine the number, effect, and treatment of knee cartilage injuries among professional football players in the National Football League (NFL) and to outline the current treatment approach to these injuries by NFL team physicians.

MATERIALS AND METHODS

NFL Injury Database

After receiving institutional review board approval, the NFL injury database was reviewed for knee cartilage injuries from 1992 through 2006. An initial diagnosis and other required data are entered into this registry at the time of the injury by a certified athletic trainer for each NFL team. Evaluation of these athletes includes physical examination and imaging, usually radiographs and magnetic resonance imaging. Information on treatment rendered, number of missed games and practices, and a final diagnosis, if different from the initial diagnosis, is entered into the registry during the course of treatment and recovery. If an athlete returns to competition (practice or game) the following day, the time lost is recorded as zero days. If an athlete is injured near the end of the season, return to play is recorded as when the athlete is able to participate in football-related activities, such as weight training or off-season practice.

For this study, the following data were collected from the registry: type and location of cartilage injury; mechanism of injury and setting (ie, game or practice); associated injuries; player’s position, age, height, and weight; treatment (surgical versus nonsurgical); and time to return to play. Total athlete exposures in the NFL by game and practice during the study period were available from the registry to calculate the incidence of cartilage injury. Time to return to play was compared between different cohorts based on treatment, lesion location, player age, and player body mass index (BMI) using a t test or analysis of variance and post hoc Tukey t tests where indicated. Statistical analysis was performed using SPSS version 14.0 (SPSS, Chicago, Ill).

NFL Team Physicians Survey

A survey also was sent to NFL team physicians. The survey asked the head team physicians to rank the following variables in terms of importance (1 = most important and 5 = least important) when deciding how to treat an isolated acute, symptomatic, focal full-thickness cartilage lesion with no other degenerative changes, no other injuries, and normal alignment:

  • Lesion size.
  • Player age.
  • Affected compartment (ie, patellofemoral, medial, lateral).
  • Time of year that the injury occurred (ie, early season versus early off-season).
  • Player position.

In addition, physicians were asked how they would treat the same injury pattern in a football player under a number of different conditions. The survey is shown in Table 1. ±

RESULTS

NFL Injury Database

A total of 118 cases of knee cartilage injury were identified in the NFL injury database from 1992 to 2006, for an average of 8 knee cartilage injuries per year. Mean age of the injured athletes was 26.8 ± 3.0 years. Mean height was 6’2″ ± 2.3″, mean weight was 247 ± 41 lb, and mean BMI was 31.7 ± 4.0. The most common injury mechanism was contact, accounting for 42% of injuries. Noncontact injuries occurred in 26% of cases; other injuries were either chronic injuries or occurred via a nonspecific mechanism.
Fifty-four percent of injuries occurred during practice, and 46% occurred during games. Although more injuries occurred during practice, the injury rate was more than 4 times higher in games compared with practice. The incidence per practice was 2.2 per 100,000 practice exposures compared with 11.4 per 100,000 game exposures. During the study period, the injury rate in practice remained fairly constant, but the injury rate per game increased (Figure). Defensive linemen comprised 21% of all injured athletes,
followed by linebackers (17%), offensive linemen (16%), and defensive secondary (14%).
Overall, the femoral condyle was the most common identified site of focal chondral injury, involved in 54% of injured athletes, followed by the patellofemoral joint (16%) and the tibial plateau (14%). The other athletes had either ostechondritis dissecans at an unidentified location (12%) or lesions in multiple compartments (3%).
Forty-six percent of the athletes were treated surgically (54 cases), and 54% (64 cases) were treated nonoperatively. Data on the specific type of surgical treatment (eg, debridement, microfracture) was not available in the league database.

On average, it took athletes 76.6 days to return to play after their injury. Return to play depended on whether the athletes needed surgical treatment; the average time to return to play in athletes treated nonoperatively was 36 days compared with 124 days for athletes who required surgery (P < .01). Among the athletes who did not require surgery, there was no difference in the time to return to play based on age or BMI (Table 2), or location of the lesion. The only significant finding by position was that running backs took significantly longer to recover after nonsurgical treatment of these lesions (112 days) compared with athletes in other positions (27 days) (P < .01). Among the athletes who required surgery, return to play for athletes with lesions on the femoral condyle took longer (135 days) than for those with lesions elsewhere (tibial plateau lesions, 88 days; patellofemoral joint lesions, 82 days) (P = .03) (Table 3). Athletes ≥ 30 years took longer to return to play (180 days) than athletes ,30 years (111 days) (P = .04) (Table 2). There were no significant differences in recovery time after surgery by position.

NFL Team Physicians Survey

Twenty-eight of 31 NFL team physicians (90%) completed the treatment survey. The most important factor among NFL team physicians for deciding treatment of an acute knee cartilage injury was lesion size. The next most important factors were the affected compartment and when the injury occurred (ie, early season versus early off-season). The least important factors were the athlete’s age and position. Overall, for all lesions under all conditions, microfracture was the most popular treatment approach (43.3%), followed by debridement (31.4%) and nonoperative management (13.2%). Mosaicplasty was the treatment of choice in 6% of the responses, whereas allograft was selected in 3.5% and cellular transplantation (eg, autologous chondrocyte implantation [ACI]) in 2.6%.
Lesion size affected treatment choice. Small lesions (1 cm²) were most likely to be treated by microfracture (43.8%), followed by debridement (30.2%) and nonoperative management (22.6%). Allografts and cellular transplantation were never selected as treatment for 1-cm lesions. Although large lesions (5 cm²) also were treated most often by microfracture (43.2%) and debridement (32.7%), only 3.7% were managed nonoperatively. Mosaicplasty was the third most common treatment approach (8.7%), followed by allograft (7.1%). Cellular transplantation was used more often than nonoperative management for these lesions (4.5%).

The involved knee compartment also affected treatment choice to the extent that patellofemoral lesions were treated differently than lesions of the medial or lateral femoral condyle. The treatment trends in the medial and lateral compartments were similar to the overall data and to each other. However, treatment in the patellofemoral compartment was significantly different, with debridement as the most popular treatment approach (49%), followed by microfracture (25.7%) and nonoperative management (22.4%). None of the team physicians treated patellofemoral lesions with cellular transplantation or allograft. Finally, player experience or position did not affect treatment choice in this survey.

Discussion

Injuries to the articular cartilage of the knee can be difficult to treat, particularly in athletes playing contact, pivoting sports such as American football. However, few studies have been published on knee articular cartilage injuries in professional American football players.(18) Our review of the NFL injury database demonstrates injuries to the articular cartilage of the knee were associated with a prolonged recovery period for NFL athletes. Athletes faced a higher risk for these injuries during games, although the total number of injuries was greater in the practice setting. Overall, these injuries resulted in an average recovery time of 2.5 months. When surgery was necessary, the average recovery time increased to 4 months, and certain athletes faced an average recovery time of
more than 5 months after surgery. Injuries involving the femoral condyle required a longer recovery time than injuries involving the patellofemoral joint or tibial plateau; older and heavier athletes often took longer to recover after surgery.
Although the league database did not have any information on the type of surgical treatment, the results of our survey provide a comprehensive overview of the current treatment approach to these injuries by NFL team physicians. Lesion size was the most important factor for team physicians when deciding appropriate treatment for these lesions. In the responses to specific scenarios, physicians indicated lesion size clearly made a difference in their treatment approach. Larger lesions were much more likely to be treated surgically, and newer surgical techniques such as mosaicplasty, allograft transplantation, and cellular transplantation were more likely to be used. Lesion size has been described as an important variable in planning for treatment of articular cartilage lesions in the knee,(1,19) and a previous biomechanical study demonstrated that articular cartilage defects ≥10 mm result in stress concentration around the rim of the defect.(8) Unfortunately, the league database does not collect data on the size of articular cartilage lesions.
The involved compartment also is an important variable to consider. This was ranked as the second most important variable by the NFL team physicians. Lesions in the patellofemoral joint were more likely to be treated with debridement and less likely to be treated with microfracture than condylar lesions. Based on the league data, femoral condyle lesions required a longer recovery period after surgery compared with tibial plateau or patellofemoral injuries. The shorter recovery period for tibial plateau or patellofemoral lesions may be due in part to these lesions being treated with simple debridement, which allows a more rapid recovery, rather than a reconstructive procedure such as microfracture.
Interestingly, the team physicians did not consider player age to be as important, even though previous studies have demonstrated age is related to outcome after cartilage surgery.(9,10,15,17) Age may not be considered an important factor because the majority of NFL athletes are relatively young (<40 years). Team physicians did not alter their treatment approach in fifth-year veterans as opposed to first-year players, nor did they change treatment in linemen compared with other positions. However, the results of our analysis of NFL cartilage injuries suggest player age may affect outcome, even in this relatively young patient population.
According to the NFL team physician survey, the time of year when the injury occurred was an important variable. However, we could not find any evidence of this from the injury database. Time of year when an injury occurred was not related to the probability of receiving surgical treatment, nor was it related to return to play.
Return to play after surgery probably was determined as much by the treatment performed as it was by the location of the defect. For example, an athlete who underwent microfracture would not be allowed to return for at least 6 months regardless of lesion size or location. Therefore, the fact that players with patella lesions returned to play more quickly may be attributed to physician preference for debridement, independent of the location of the lesion. Again, the limitations of the database prevented any direct analysis of this potential treatment effect.
The higher incidence of knee articular cartilage injuries during games compared with practices is similar to other knee injuries. A study of anterior cruciate ligament injuries in the NFL reported more injuries during games than during practices.(3) This also has been demonstrated at the collegiate level by a number of studies.(4,16) The higher injury rate during games is logical given the higher intensity level and speed of play compared with practices.(4)
Historically, treatment options for these injuries were limited. In recent years, more sophisticated treatment options aimed at restoring articular cartilage have become available. Microfracture was one of the relatively early surgical treatments, and it has been shown to have some success with these lesions in professional American football athletes. In one study on the results of microfracture for full-thickness chondral lesions in NFL players,(18) 19 of 25 players (76%) returned to play the following season and 9 of 25 players (36%) continued to play at average follow-up of 4.5 years (range, 2-13 years). Fourteen of the 25 players were linemen, although the study did not report results by position. Another study on high-impact athletics after microfracture found only 3 of 9 football players returned to their sport after this surgery.13 This may be related to player size, as a higher BMI (specifically, BMI >30) has been shown to be associated with worse outcomes after microfracture.(12) This may be particularly relevant for linemen, who had the highest BMI in a recent study of one NFL team (BMI of 37.1 ± 1.9 for offensive line versus BMI of 34.6 ± 1.4 for defensive line).(11)
Other studies of microfracture in athletes have demonstrated similar results. In a cohort of 53 athletes, including 26 at the professional level, 80% were still active in strenuous sports after 2 years of follow-up; however, this decreased to 55% after 6 years of follow-up.(5) In another study of more than 230 athletes, including 48 elite athletes, 77% of the elite athletes returned to competition, with 71% participating at a level equal to or better than their preinjury level.(2) In another cohort of 38 athletes, including 1 at the professional level and 19 at a competitive level, only 44% returned to sport.(13) Return to sport improved to 67% if patients underwent surgery within 12 months of symptoms and to 86% if microfracture was the primary surgical treatment. Of note, this was a slightly older cohort, with a mean age of 38 years.
There are no published outcomes for newer surgical treatments such as mosaicplasty and ACI in professional American football athletes. Some studies have looked at outcomes for these procedures in cohorts of athletes from a variety of sports. One study of mosaicplasty in 52 athletes reported 100% good and excellent Hospital for Special Surgery knee scores at average follow-up of 26 months.(9) However, only 63% of athletes returned to full competition. Return to play was dependent on age, with 90% of athletes <30 years returning to full competition compared with only 23% of athletes ≥ 30 years. In another study, Gudas et al6 found mosaicplasty superior to microfracture for a young, athletic cohort. Mosaicplasty led to better clinical outcomes, better histology, and a higher rate of return to play. Patients < 30 years did better clinically, compared with older patients treated with mosaicplasty. This study also found significantly worse results among athletes treated with microfracture who had lesions >2 cm² but no difference
in outcome based on lesion size among patients treated with mosaicplasty.
Several studies have reported on the results of ACI in athletes. In a study of 20 adolescent athletes, only 60% returned to the same level of competition.(14) All of these athletes had undergone ≥ 1 previous surgical treatment, and athletes with >12 months of symptoms prior to ACI had a worse return to sport (33%). Another study of ACI in 45 soccer athletes reported an overall return rate of 33% to the same level of competition, although 83% of highlevel soccer players returned to competition.(15)
Several treatment algorithms for articular cartilage injuries of the knee have been proposed in the literature, although these are not based on strong evidence.(1,19) Lesion size, primary or secondary treatment, and patient demand have been proposed as key variables when selecting appropriate treatment for these lesions. Based on our survey, most NFL team physicians agreed that lesion size is a relevant variable in selecting optimal treatment. Based on our findings from the injury database, the location of the lesion in the knee influences recovery after surgery and may be useful to include in these treatment algorithms as well. Finally, patient age and BMI merit discrete consideration, although they both contribute to the overall assessment of patient demand.
The limitations of this retrospective study include the lack of data on lesion size, lesion depth, and the surgical technique used for treatment. This is particularly true in athletes treated nonoperatively, because without arthroscopy to provide a definitive diagnosis, there may be considerable error in the data. In these cases, the diagnosis was based on magnetic resonance imaging in conjunction with the history and physical examination. A prospective investigation with more complete information would provide a more precise description of these injuries, their effect on the athletes, and the results of treatment.
In this study, the definition of return to play was slightly different between the regular season and the offseason. During the season, return to practice or games qualified as return to play, whereas during the off-season, return to football-related activity such as weight training was considered return to play. Overall, this probably has a negligible effect on the data because the athletes may get back to weight training sooner than competition, but they are not followed as closely during the off-season as they are during the regular season.
Another major weakness is the lack of data on the long-term results of treatment, in particular how long athletes were able to compete after returning from theirarticular cartilage injury. Palliative treatments such as debridement obviously allow a quicker return to play but may have a relatively short treatment effect. In addition, our survey focused on acute defects and did not allow for previous treatments. Prior procedures are probably an important factor in selecting a surgical technique, but they were beyond the scope of this investigation.
Nevertheless, this is the first comprehensive study of knee articular cartilage injuries in the NFL. The epidemiologic information and treatment guidance suggested by the team physicians provide important insight into the prevailing opinions and treatment algorithms used by physicians caring for these elite athletes. This information provides valuable insight into the effect and management of knee articular cartilage injury in American football players. Although the demands of other sports differ to varying degrees, this information may apply to other sports that involve running, cutting, and contact (eg, soccer). The NFL injury database should consider collecting information on the size of articular cartilage lesions as well as the type of surgery that athletes received for these injuries. This would facilitate longer-term follow-up studies including imaging to provide objective evaluation of structural and architectural improvements in treated lesions. Future investigation studying the results of specific surgical treatments for these injuries then could be used to generate an evidence-based treatment protocol in these athletes.

Acknowledgment

The authors acknowledge the work of the NFL athletic trainers in maintaining the NFL database.

References

  1. Alford JW, Cole BJ. Cartilage restoration, II: Techniques, outcomes, and future directions. Am J Sports Med. 2005;33:443-460.
  2. Blevins FT, Steadman JR, Rodrigo JJ, Silliman J. Treatment of articular cartilage defects in athletes: An analysis of functional outcome and lesion appearance. Orthopedics. 1998;21:761-767.
  3. Bradley JP, Klimkiewicz JJ, Rytel MJ, Powell JW. Anterior cruciate ligament injuries in the National Football League: Epidemiology and current treatment trends among team physicians. Arthroscopy. 2002;18:502-509.
  4. Dick R, Ferrara MS, Agel J, et al. Descriptive epidemiology of collegiate men’s football injuries: National Collegiate Athletic Association Injury Surveillance System, 1988-1989 through 2003-2004. J Athl Train. 2007;42:221-233.
  5. Gobbi A, Nunag P, Malinowski K. Treatment of full thickness chondral lesions of the knee with microfracture in a group of athletes. Knee Surg Sports Traumatol Arthrosc. 2005;13:213-221.
  6. Gudas R, Kalesinskas RJ, Kimtys V, et al. A prospective randomized clinical study of mosaic osteochondral autologous transplantation versus microfracture for the treatment of osteochondral defects in the knee joint in young athletes. Arthroscopy. 2005;21:1066-1075.
  7. Gudas R, Stankevicius E, Monastyreckiene E, Pranys D, Kalesinskas RJ. Osteochondral autologous transplantation versus microfracture for the treatment of articular cartilage defects in the knee joint in athletes. Knee Surg Sports Traumatol Arthrosc. 2006;14:834-842.
  8. Guettler JH, Demetropoulos CK, Yang KH, Jurist KA. Osteochondral defects in the human knee: Influence of defect size on cartilage rim stress and load redistribution to surrounding cartilage. Am J Sports Med. 2004;32:1451-1458.
  9. Kish G, Modis L, Hangody L. Osteochondral mosaicplasty for the treatment of focal chondral and osteochondral lesions of the knee and talus in the athlete: Rationale, indications, techniques, and results. Clin Sports Med. 1999;18:45-66.
  10. Knutsen G, Engebretsen L, Ludvigsen TC, et al. Autologous chondrocyte implantation compared with microfracture in the knee: A randomized trial. J Bone Joint Surg Am. 2004;86:455-464.
  11. Kraemer WJ, Torine JC, Silvestre R, et al. Body size and composition of National Football League players. J Strength Cond Res. 2005;19:485-489.
  12. Mithoefer K, Williams RJ III, Warren RF, et al. The microfracture technique for the treatment of articular cartilage lesions in the knee: A prospective cohort study. J Bone Joint Surg Am. 2005;87:1911-1920.
  13. Mithoefer K, Williams RJ III, Warren RF, Wickiewicz TL, Marx RG. High-impact athletics after knee articular cartilage repair: A prospective evaluation of the microfracture technique. Am J Sports Med. 2006;34:1413-1418.
  14. Mithofer K, Minas T, Peterson L, Yeon H, Micheli LJ. Functional outcome of knee articular cartilage repair in adolescent athletes. Am J Sports Med. 2005;33:1147-1153.
  15. Mithofer K, Peterson L, Mandelbaum BR, Minas T. Articular cartilage repair in soccer players with autologous chondrocyte transplantation: Functional outcome and return to competition. Am J Sports Med. 2005;33:1639-1646.
  16. Powell JW. Pattern of knee injuries associated with college football 1975-1982. Athl Train J NATA. 1985;20:104-109.
  17. Steadman JR, Briggs KK, Rodrigo JJ, Kocher MS, Gill TJ, Rodkey WG. Outcomes of microfracture for traumatic chondral defects of the knee: Average 11-year follow-up. Arthroscopy. 2003;19:477-484.
  18. Steadman JR, Miller BS, Karas SG, Schlegel TF, Briggs KK, Hawkins RJ. The microfracture technique in the treatment of full-thickness chondral lesions of the knee in National Football League players. J Knee Surg. 2003;16:83-86.
  19. Williams RJ III, Brophy RH. Cartilage repair procedures: Clinical approach and decision making. Instr Course Lect. 2008;57:553-561.

ESTA É UMA REPRESENTAÇÃO FIEL DA PUBLICAÇÃO ACADÊMICA DE . ROBERT H. BROPHY. O ORIGINAL EM PDF PODE SER BAIXADO CLICANDO AQUI: Knee Articular Cartilage Injuries in the National Football League – Epidemiology and Treatment Approach by Team Physicians