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Prevalence of Cam-Type Morphology in Elite Ice Hockey Players Frantz Lerebours, William Robertson, Brian Neri, Brian Schulz, Thomas Youm and Orr Limpisvasti Am J Sports Med published online January 28, 2016 DOI: 10.1177/0363546515624671 The online version of this article can be found at: http://ajs.sagepub.com/content/early/2016/01/28/0363546515624671
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Prevalence of Cam-Type Morphology in Elite Ice Hockey Players Frantz Lerebours,* MD, William Robertson,yz MD, Brian Neri,§|| MD, Brian Schulz,*{ MD, Thomas Youm,# MD, and Orr Limpisvasti,*{** MD Investigation performed at Kerlan Jobe Orthopaedic Clinic, Los Angeles, California, USA Background: Femoroacetabular impingement (FAI) has been increasingly recognized as a cause of hip pain in athletes at all levels of competition, specifically ice hockey players. Purpose/Hypothesis: The purpose of this study was to define the prevalence of cam and pincer radiographic deformity in elite ice hockey players. The hypothesis was that elite hockey players will have a higher prevalence of radiographic hip abnormalities compared with the general population. Study Design: Cross-sectional study; Level of evidence, 3. Methods: Anteroposterior and frog-leg lateral radiographs on 137 elite ice hockey players were prospectively obtained during the 2014-2015 preseason entrance examinations. Study participants included National Hockey League roster players as well as the respective farm team members. Demographic data were collected, including age, position, shooting side, and any history of hip pain or hip surgery. Patients with a history of hip surgery were excluded from the analysis. A single sports medicine fellowship– trained orthopaedic surgeon used standard radiographic measurements to assess for the radiographic presence of cam or pincer deformity. Radiographs with an alpha angle 55° on a frog-leg lateral view were defined as cam-positive. Each participant underwent a preseason physical examination with an assessment of hip range of motion and impingement testing. Results: A total of 130 elite ice hockey players were included in the analysis; 180 (69.4%) hips met radiographic criteria for camtype deformity. The prevalence in right and left hips was 89 (69.5%) and 91 (70.0%), respectively; 70 (60.8%) players demonstrated bilateral involvement. Hips with cam deformity had a mean alpha angle of 67.7° 6 8.3° on the right and 68.9° 6 9.0° on the left. Of the patients with alpha angles 55°, 5.6% (5/89) had a positive anterior impingement test of the right hip, while 11% (10/91) had positive anterior impingement test of the left. Players with radiologic cam deformity had a statistically significant deficit in external rotation of the right hip, as well as in both internal and external rotation of the left hip, compared with those with normal alpha angles. When assessing for crossover sign, 64 of 107 (59.8%) had a positive radiographic finding. Forty-one players (38.3%) had evidence of a crossover sign of the right hip and 42 (39.3%) of the left. When comparing position players, goalies had the highest prevalence of cam-type deformity (93.8%) and the least acetabular coverage. Conclusion: The study data suggest that elite ice hockey players have a significantly higher prevalence of radiographic cam deformity in comparison to what has been reported for the general population. Keywords: femoroacetabular impingement; ice hockey; FAI; elite athletes
to cam FAI. Ayeni et al3 used magnetic resonance imaging (MRI) to evaluate the presence of radiographic FAI in elite ice hockey players and compare it with a control group of nonathletes. They found the odds of having cam impingement are 2.5 times greater in athletes participating in elite ice hockey than in nonathletes with similar demographics. However, despite the high prevalence of radiographic hip abnormalities in hockey players, many remain asymptomatic. Silvis et al31 evaluated the prevalence of abnormal MRI findings in asymptomatic collegiate ice hockey players and found acetabular labral tears in 56% of participants. These authors emphasized caution when interpreting MRI scans, as they have the potential to detect lesions that are not temporally correlated with self-reported measures of pain or disability. Although the cause of FAI is unknown, it has been postulated that the cam deformity is a normal physiologic
Hip and groin injuries are extremely common in ice hockey players, with a reported incidence of 19.87 injuries per 100 players at the elite level.11 Femoroacetabular impingement (FAI) has been increasingly recognized as a cause of hip pain in athletes at all levels of competition.14 Numerous studies have found an increased prevalence of FAI in competitive athletes.3,14,26,30 Philippon et al26 looked at the prevalence of FAI in youth ice hockey players and found a significant correlation between age and elevated alpha angles associated with cam FAI that was not found in skier-matched controls. They concluded that properties inherent to ice hockey likely enhanced the development of a bony overgrowth adjacent to the femoral neck, leading The American Journal of Sports Medicine, Vol. XX, No. X DOI: 10.1177/0363546515624671 Ó 2016 The Author(s)
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response to loading forces.21 High-level sports activity during the growth years is associated with an increased risk for the development of cam lesions.5,19 Repetitive microtrauma to the proximal femoral physis leads to reactive bone formation, resulting in an abnormal contour of the femoral head-neck junction.26 Many postulate that developmental factors related to activity and hip positioning during sports place patients at risk for developing FAI. In the past decade, the treatment of intra-articular hip disorders has drastically increased. This increasing trend is a result of the technological advances in hip arthroscopy, improved diagnostic imaging and interpretation,24 an improved understanding of intra-articular hip disorders, and an increased emphasis on hip arthroscopy in residency and fellowship training programs.18 Despite the increased proficiency in the diagnosis and treatment of FAI, the natural history of patients with FAI is largely unknown. Numerous studies have demonstrated radiographic findings of FAI in asymptomatic populations.13-16 The literature suggests that the overall incidence of radiographic FAI in an asymptomatic population is approximately 15%.13-16 To our knowledge, no study has defined the prevalence of radiographic abnormalities in elite ice hockey players. The purpose of this study was to establish normative data to confirm the prevalence of radiographic deformities of the hip in elite ice hockey players.
METHODS Institutional review board approval and informed consent from participants were obtained for this study. Data were obtained during the 2014-2015 preseason entrance examinations. The participants included all potential roster members of 3 National Hockey League (NHL) professional teams. The NHL athlete is considered at the highest level of performance. Each NHL team has a farm team in the American Hockey League (AHL), and players frequently move up or down during the course of a season. The participants in our study included NHL roster players as well as the respective farm team members. All participants with prior hip surgery were excluded from the study. Each patient underwent a demographic assessment and screening radiography, including anteroposterior (AP) pelvis and frog-leg lateral views of both hips. The demographic assessment included age, player position, history of hip pain, history of hip surgery, and shooting side. In addition, each participant underwent a preseason physical
examination with an assessment of hip range of motion (ROM) as well impingement testing by 3 of the authors (B.N., O.L., W.R.) who work for the respective organizations. Hip flexion, abduction, and adduction were assessed in the supine position with the use of a goniometer. Hip internal rotation, external rotation, and extension were measured with the patient prone. Anterior and posterior impingement testing was performed on all participants. An anterior impingement test was performed by first passively flexing the hip to 90° and then applying an adduction and internal rotation moment to the hip. Posteroinferior impingement testing was performed by extending and externally rotating the hip with the patient lying at the edge of the examination table in the supine position. A test was considered positive if any of the provocative testing maneuvers elicited groin pain. Radiographs were performed by 3 separate radiology technicians at the respective team professional arenas. All images were evaluated by a single board-certified, fellowship-trained orthopaedic surgeon to determine adequacy of the studies as well as the radiographic characteristics. Anteroposterior pelvic images were deemed adequate if the coccyx was centered over, and approximately 3 cm above, the pubic symphysis, with the obturator foramen neutrally rotated. The frog-leg lateral views were considered acceptable if there was clear visualization of the anterior and posterior head-neck junctions. Cam lesions were defined as positive if there was an alpha angle 55° on frog-lateral views. Alpha angles were measured on the frog-leg lateral view by using a radiographic computer goniometer (Impax PACS Imagining System; Afga Healthcare Corp). The alpha angle was measured using a digital circular template, drawing a best-fit circle surrounding the femoral head, thus using its center to serve as the angle’s vertex. Lines were drawn from the vertex down the center of the femoral neck and to the point where the best-fit circle deviates from the anterior femoral neck. The angle formed by these lines is defined as the alpha angle (Figure 1). On an appropriately obtained AP pelvis radiograph, the crossover sign is seen when there is an overlap between the lines tracing the anterior and posterior acetabular walls. This crossover sign represents anterior overcoverage of the acetabulum and served as the criterion for positive pincer deformity for this study. We measured the lateral centeredge angle (LCEA) and defined an abnormality as an angle \25°. The center-edge angle is the angle formed by a line drawn from the center of the femoral head to the outer edge of the acetabular roof and a vertical line drawn through the center of the femoral head (Figure 2).
**Address correspondence to Orr Limpisvasti, MD, Kerlan Jobe Orthopaedic Clinic, 6801 Park Terrace, Los Angeles, CA 90045, USA (email: [email protected]). *Kerlan-Jobe Orthopaedic Clinic, Los Angeles, California, USA. y Department of Orthopaedic Surgery, University of Texas Southwestern Medical Center, Dallas, Texas, USA. z Dallas Stars, National Hockey League, Dallas, Texas, USA. § ProHealth Care Associates, Lake Success, New York, USA. || New York Islanders, National Hockey League, New York, New York, USA. { Anaheim Ducks, National Hockey League, Anaheim, California, USA. # Department of Orthopaedic Surgery, New York University Langone Medical Center, New York, New York, USA. The authors declared that they have no conflicts of interest in the authorship and publication of this contribution.
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Figure 1. The alpha angle was obtained by first drawing a best-fit circle surrounding the femoral head. The center of the circle served as the angle’s vertex. Lines were drawn from the vertex down the center of the femoral neck and to the point where the best-fit circle deviates from the anterior femoral neck. The angle formed by these lines was defined as the alpha angle.
Statistical Analysis Descriptive statistics were used in our data analysis. Statistical calculations were performed using SAS version 9.2 (SAS Institute). The Fisher exact test was used to examine the significance of the associations between positions and radiographic evidence of cam deformity. The independent-samples t test was used to compare numerical variables (shown as mean 6 SD) across 2 groups, and the Fisher exact test was used to compare categorical variables (shown as n [%]) across groups. The .05 significance level was used throughout.
RESULTS The mean age of the patients involved in our study was 24.35 6 4.30 years. A total of 137 patients underwent preseason physicals among the 3 teams participating in our study. Two patients were excluded because of incomplete demographic and physical examination data, and 5 patients had undergone prior hip surgery and were therefore excluded from our analysis, bringing the total number of elite ice hockey players included in our analysis to 130. Of these, 32 (24.6%) players reported having a history of hip pain. Radiographs with an alpha angle 55° on frogleg lateral views were defined as indicating cam-type deformity. The total number of hips that met radiographic criteria for having cam-type deformity was 180 of 260 (69.4%) (Table 1). The prevalence in right and left hips was 89 of 130 (68.5%) and 91 of 130 (70.0%), respectively. A total of 79 of 130 (60.8%) patients demonstrated evidence of bilateral cam-type deformity (Table 1). The percentage of players with a history of hip pain and an elevated alpha angle were 16.2% (21/130) and 18.5% (24/130) for right and left hips, respectively. Of the patients with alpha
Figure 2. The lateral center-edge angle is the angle formed by a vertical line drawn through the center of the femoral head and a line drawn from the center of the femoral head to the outer edge of the acetabular roof.
angles 55°, 5.6% (5/89) had a positive anterior impingement test of the right hip, while 11% (10/91) had positive anterior impingement test of the left (Table 1). Seven (5.4%) players in our cohort were found to have a history of hip pain, a positive anterior impingement test, and an elevated alpha angle in any hip. We performed a subanalysis looking at differences in ROM between patients with alpha angles 55° (group A) versus those with alpha angles \55° (group B). In contrast, internal rotation of the right hip showed no difference between those in groups A and B. External rotation of the right hip was significantly lower for players in group A (38.9° 6 9.1°) compared with those in group B (43.6° 6 8.1°) (P = .006) (Table 2). When looking at left hip ROM, group A demonstrated a statistically significant deficit of both internal and external rotation. Internal rotation of the left hip in group A was 29.1° 6 9.74°, compared with 32.7° 6 11.9° in group B (P = .046) (Table 3). External rotation was 39.7°6 9.2° and 44.0° 6 10.4° for groups A and B, respectively (P = .020) (Table 3). The mean alpha angles for cam-positive right and left hips were 67.7° 6 8.3° and 68.9° 6 9.0°, respectively (Table 1). The mean alpha angles for players without radiographic evidence of cam lesions were 49.9° 6 3.6° on the right and 49.6°6 3.9° on the left. There was no association between age and the prevalence of elevated alpha angles.
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TABLE 1 Patients With Radiographic Evidence of Cam Deformitya
Alpha angle 55° Alpha angle in patient with positive cam deformity, deg, mean 6 SD Positive anterior impingement test
Right Hip
Left Hip
Bilateral
68.5 (89/130) 67.7 6 8.3 5.6 (5/89)
70.0 (91/130) 68.9 6 9.0 11 (10/91)
60.8 (79/130)
a
Data are reported as % (n/total number assessed) unless otherwise indicated.
TABLE 2 Mean Right Hip Range of Motion Range of Motion, deg Flexion Abduction Adduction Internal rotation External rotation Extension
Group A (Alpha Angle 55°) 112.5 40.9 18.1 31.5 38.9 14.9
Group B (Alpha Angle \55°) 113.1 41.3 18.5 32.0 43.6 14.6
610.9 6 9.2 6 5.5 6 10.9 6 9.1 6 6.9
6 6 6 6 6 6
11.8 9.6 5.1 9.6 8.1 6.9
P Value .78 .84 .73 .80 .006a .81
a
Statistically significant difference between groups (P \ .05).
TABLE 3 Mean Left Hip Range of Motion Range of Motion, deg Flexion Abduction Adduction Internal rotation External rotation Extension
Group A (Alpha Angle 55°) 114.1 41.3 19.3 29.1 39.7 14.9
6 6 6 6 6 6
Group B (Alpha Angle \55°)
11.4 9.3 6.4 9.7 9.2 6.72
111.8 40.5 17.3 32.7 44.0 14.9
6 6 6 6 6 6
20.4 8.4 5.0 11.9 10.4 6.5
P Value .51 .62 .089 .046a .020a .96
a
Statistically significant difference between groups (P \ .05).
A subgroup analysis using the Fisher exact test was performed based on position. The prevalence of right-sided cam FAI for goalies and centers approached statistical significance. Goalies (93.8%) were more likely to develop right-sided cam FAI, while centers (54.6%) were less likely (P = .076) (Table 4). The mean alpha angles for goalies were 66.38° 6 9.90° and 65.81° 6 11.54° for right and left hips, respectively (Table 4). An abnormal LCEA was observed in 11 of 130 (8.46%) right hips and 17 of 130 (13.08%) left hips. Goalies had the lowest mean LCEA, with the right and left hip measuring 27.6° 6 7.0° and 26.4° 6 7.07°, respectively. When evaluating for the presence of a crossover sign, we found that 64 of 107 (59.8%) had a positive radiographic finding. Forty-one players (38.3%) had evidence of a crossover sign of the right hip, and 42 (39.3%) players demonstrated a crossover on the left. Twenty-three patients were removed from our analysis because of inadequate radiograph projections due to asymmetry of the obturator foramen. When looking at patients with both an elevated alpha angle and positive crossover sign, 41 of 107 (54.7%) right hips and 42 of 107 (55.3%) left hips had concomitant morphologic variations.
DISCUSSION The exact cause of FAI is not completely understood. However, recent literature has shown an increased prevalence of FAI in competitive athletes, specifically those participating at a high level at an early age.3,14,26,30 Hip and groin injuries are among the most commonly reported complaints in ice hockey players.1,6 The most common morphologic variations about the hip that can result in dynamic hip impingement and subsequent loss of motion in athletes include femoral retroversion, acetabular retroversion, camtype deformity, and loss of femoral neck offset.4 These morphologic variations are extremely common in athletes, potentially due to developmental growth alterations that lead to nonphysiologic remodeling of the femoral head during repetitive high-impact and rotational loads on the physis. Recent studies have found the prevalence of cam deformity in the general population to be 14% in asymptomatic individuals.16 Men have been shown to have a higher prevalence of cam lesions than women (9.6%-24% vs 5%).15,16 Several studies have shown an increased prevalence of FAI in competitive athletes. Philippon et al26 found an increased prevalence of elevated alpha angles in youth
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TABLE 4 Subanalysis of Alpha Angle by Position Alpha Angle 55°, % Position Center (n = 33) Defenseman (n = 43) Goalie (n = 16) Left wing (n = 23) Right wing (n = 15)
Mean Alpha Angle, deg
Right Hip
Left Hip
Right Hip
Left Hip
54.6 69.8 93.8 65.2 73.3
66.7 65.1 81.3 78.3 66.7
58.9 61.9 66.4 62.4 65.1
60.1 61.8 65.8 67.7 63.5
ice hockey players. An interesting finding of the study was the linear correlation with age and elevated alpha angles, compared with age-matched controls.26 Gerhardt et al14 found an increased prevalence of cam FAI in elite soccer players. They found that 68% of men and 50% of women had radiographic evidence of cam FAI in their cohort. Similarly, our data found the prevalence of cam deformity to be 69.4%. Elite ice hockey players are more than 3 times more likely to develop cam deformity than the general population. There has been a reported genetic association with FAI.28 However, many believe the origin of cam FAI may result from subclinical microtrauma, due to a repetitive overuse phenomenon. It appears that there is something inherent to the mechanics of ice skating that places hockey players at risk for developing FAI. The biomechanics of ice skating, participation at an early age, on-ice exposure, style of play, and position may all play a role in the risk of developing FAI. Ng and Ellis21 highlighted that disruption of the physis through abnormal loading, biomechanics, vascularity, or trauma can have significant effects on the morphologic development of the hip. Siebenrock et al30 looked at growth plate deformity before and after physeal closure in basketball players and found that altered shape of the growth plate may precede a cam-type deformity in basketball athletes, suggesting a developmental abnormality. Their study suggested that the decreased head-neck offset associated with cam-type deformity was associated with epiphyseal extension rather than a reactive process.30 Despite the controversy in the origin of FAI, there is a consensus on the association that certain high-level sports increase the risk of developing FAI as an adult. Morphologic variations that can lead to dynamic hip impingement and subsequent loss of motion include femoral retroversion, cam-type deformity, loss of femoral offset, and acetabular retroversion.4 These morphologic variations result in restricted hip motion, which leads to compensatory increases in motion of the hemipelvis and lumbar spine to achieve functional range of motion for sport.10 A survey conducted by the NHL from 2006 to 2010 found that hockey goalies had a significantly higher rate of hip injuries per 1000 player game appearances in comparison to positional players.12 Our data suggest that goalies have a higher prevalence of cam deformity, but they also have a lower LCEA and less acetabular coverage. Are goalies without acetabular undercoverage selected out and therefore less likely to make it at the elite level? Or is this a protective mechanism, adapted during development as a result of high repetitive loads
and extreme ROM positions? Goalies place their hips at extremes of motion compared with position players, particularly during the ‘‘butterfly save.’’ During the butterfly save, a goalie maximally flexes and internally rotates his hips in order to place his lower extremity pads parallel to the ice. Ross et al29 used plain radiographs and computed tomography (CT) scans to characterize the radiographic deformity observed in consecutive series of butterfly goalies with symptomatic mechanical hip pain. They similarly found that acetabular dysplasia was more common among hockey goalies (29%) than among positional athletes (15%), with a mean lateral center-edge angle (LCEA) measuring 27.3°.29 Recognizing and understanding the structural characteristics in patients with acetabular dysplasia is imperative. An aggressive rim resection in patients with acetabular dysplasia can increase the risk of iatrogenic structural instability.33 Our data suggest that there are a significant number of asymptomatic elite hockey players with radiographic evidence of cam deformity. In our study, the prevalence of cam-type deformities in right and left hips was 89 of 130 (69.46%) and 91 of 130 (70.00%), respectively. Given the high prevalence of these morphologic FAI features in elite hockey players, it is important to keep in mind that an elevated alpha angle alone is not diagnostic of FAI. Instead, it is a clinical diagnosis based on history, symptom profile, and objective signs on physical examination. In a recent series, FAI was the diagnosis in 81% of professional hockey players requiring hip arthroscopy for painful hip conditions.27 It is apparent that there has been an increase in the number of hip arthroscopies being performed,9,18 but there are few reports on the incidence or demographics of patients undergoing these procedures in the United States.18 Long-term outcome studies are lacking and the natural history of operative versus nonoperative management is largely unknown. McCarthy et al17 reported 80% excellent results after hip arthroscopy in elite athletes with a mean follow-up of 23.6 months. Philippon et al25 reported that 93% (42/45) of professional athletes returned to professional competition after arthroscopic decompression of FAI at a mean of 1.6 years. A recognized limitation of our study was the use of plain radiographs to obtain our measurements. Although the Dunn view or frog-leg lateral radiographs7 have been identified as a reliable imaging projection for the measurement of femoral head asphericity using the alpha angle of Notzli et al,22 the multiplanar imaging provided by CT and MRI can better assess cam deformity and reduce the risk of
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underestimating the alpha angle. Computed tomography and MRI also offer the benefit of assessing femoral version. In the case of cam-type FAI, femoral anteversion can protect against a cam lesion entering the joint, whereas femoral retroversion can exacerbate the issue. We did not assess femoral version in this study, which could confound the relationships between pain and ROM in the setting of a given alpha angle. In addition, we recognize that the 45° Dunn view has become the more widely accepted view used in clinical practice. However, we concluded that using frog-leg lateral radiographs would show more consistency in adequacy given that our radiologist for the respective organizations performs this view on a regular basis. In addition, frog-leg laterals have been validated in numerous studies for diagnosing cam FAI.14 Nepple et al20 compared the Dunn view and frog-leg lateral view in assessing cam-type deformity using radiographic measurements and correlated them with CT scan findings. They concluded that the Dunn view was more sensitive at detecting cam lesions (71%81%), but the frog-leg lateral was more specific (91%100%). There is also a recognized limitation of diagnosing a pincer lesion using the crossover sign on standard AP radiographs. Obtaining consistency in symmetric AP radiographs was challenging, and we excluded 23 patients as a result of inadequate projections. Even after standardizing the radiographs based on rotation and the distance between the coccyx and pubic symphysis, subtle changes in tilt and rotation can significantly alter the presence of a crossover sign. Another limitation of our study was in our assessment of ROM. We used goniometer-based assessment, among 3 physicians, in the prone position. Nussbaumer et al23 evaluated the validity and reliability of goniometer-based measurements in hip ROM assessment in patients with FAI. They concluded that goniometer-based assessments conventionally used in orthopaedic clinical practice overestimate the majority of passive hip motion patterns by measuring intersegmental angles, such as thigh flexion on the trunk for hip flexion, rather than true hip ROM. In our study, we found a statistically significant loss of external rotation of the right hip in our cam-positive group. However, in patients with cam deformity, we would expect to see a loss of internal rotation, not external rotation. Perhaps if our measurements were performed in the ‘‘at-risk’’ position, with the patient supine with the hip flexed, our statistical comparisons would have been consistent with the ROM deficits seen in FAI. Another limitation of our study was that a single orthopaedic surgeon reviewed our radiographs, which limits the interobserver reliability of our radiographic findings. However, we believe the benefit of having a single surgeon review and interpret all films greatly outweighs any negatives. Last, preseason evaluation and player recall may affect reports of hip pain and positive provocative test results.
CONCLUSION FAI surgery has evolved rapidly and at a pace far quicker than our understanding about the natural history and epidemiologic characteristics of the condition.2,8,32 Despite the
high prevalence of radiographic abnormalities in our study, a large number of patients were asymptomatic. This study further emphasizes that FAI is a clinical diagnosis, and imaging abnormalities alone are not sufficient in making the diagnosis. A preventative screening program for elite ice hockey players at the start of their professional careers may potentially identify patients with clinical characteristics and radiographic hip deformity that may place them at a higher risk for injury. Interventions aimed at adapting to their functional ROM and reducing the frequency of impingement can then be implemented. REFERENCES 1. Agel J, Dompier TP, Dick R, Marshall SW. Descriptive epidemiology of collegiate men’s ice hockey injuries: National Collegiate Athletic Association Injury Surveillance System, 1988-1989 through 20032004. J Athl Train. 2007;42(2):241-248. 2. Allen D, Beaule PE, Ramadan O, Doucette S. Prevalence of associated deformities and hip pain in patients with cam-type femoroacetabular impingement. J Bone Joint Surg Br. 2009;91(5):589594. 3. Ayeni OR, Banga K, Bhandari M, et al. Femoroacetabular impingement in elite ice hockey players. Knee Surg Sports Traumatol Arthrosc. 2014;22(4):920-925. 4. Bedi A, Dolan M, Leunig M, Kelly BT. Static and dynamic mechanical causes of hip pain. Arthroscopy. 2011;27(2):235-251. 5. Bizzini M, Notzli HP, Maffiuletti NA. Femoroacetabular impingement in professional ice hockey players: a case series of 5 athletes after open surgical decompression of the hip. Am J Sports Med. 2007;35(11):1955-1959. 6. Brown RA, Mascia A, Kinnear DG, Lacroix V, Feldman L, Mulder DS. An 18-year review of sports groin injuries in the elite hockey player: clinical presentation, new diagnostic imaging, treatment, and results. Clin J Sport Med. 2008;18(3):221-226. 7. Clohisy JC, Nunley RM, Otto RJ, Schoenecker PL. The frog-leg lateral radiograph accurately visualized hip cam impingement abnormalities. Clin Orthop Relat Res. 2007;462:115-121. 8. Clohisy JC, St John LC, Schutz AL. Surgical treatment of femoroacetabular impingement: a systematic review of the literature. Clin Orthop Relat Res. 2010;468(2):555-564. 9. Colvin AC, Harrast J, Harner C. Trends in hip arthroscopy. J Bone Joint Surg Am. 2012;94(4):e23. 10. Draovitch P, Edelstein J, Kelly BT. The layer concept: utilization in determining the pain generators, pathology and how structure determines treatment. Curr Rev Musculoskelet Med. 2012;5(1):1-8. 11. Emery CA, Meeuwisse WH, Powell JW. Groin and abdominal strain injuries in the National Hockey League. Clin J Sport Med. 1999;9(3):151-156. 12. Epstein DM, McHugh M, Yorio M, Neri B. Intra-articular hip injuries in National Hockey League players: a descriptive epidemiological study. Am J Sports Med. 2013;41(2):343-348. 13. Ganz R, Leunig M, Leunig-Ganz K, Harris WH. The etiology of osteoarthritis of the hip: an integrated mechanical concept. Clin Orthop Relat Res. 2008;466(2):264-272. 14. Gerhardt MB, Romero AA, Silvers HJ, Harris DJ, Watanabe D, Mandelbaum BR. The prevalence of radiographic hip abnormalities in elite soccer players. Am J Sports Med. 2012;40(3):584-588. 15. Gosvig KK, Jacobsen S, Sonne-Holm S, Gebuhr P. The prevalence of cam-type deformity of the hip joint: a survey of 4151 subjects of the Copenhagen Osteoarthritis Study. Acta Radiol. 2008;49(4): 436-441. 16. Hack K, Di Primio G, Rakhra K, Beaule´ PE. Prevalence of cam-type femoroacetabular impingement morphology in asymptomatic volunteers. J Bone Joint Surg Am. 2010;92(14):2436-2444.
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17. McCarthy J, Barsoum W, Puri L, Lee J, Murphy S, Cooke P. The role of hip arthroscopy in the elite athlete. Clin Orthop Relat Res. 2003;406:71-74. 18. Montgomery SR, Ngo SS, Hobson T, et al. Trends and demographics in hip arthroscopy in the United States. Arthroscopy. 2013;29(4):661-665. 19. Murray RO, Duncan C. Athletic activity in adolescence as an etiological factor in degenerative hip disease. J Bone Joint Surg Br. 1971;53(3):406-419. 20. Nepple JJ, Martel JM, Kim YJ, Zaltz I, Clohisy JC. Do plain radiographs correlate with CT for imaging of cam-type femoroacetabular impingement? Clin Orthop Relat Res. 2012;470:3313-3320. 21. Ng VY, Ellis TJ. More than just a bump: cam-type femoroacetabular impingement and the evolution of the femoral neck. Hip Int. 2011;21(1):1-8. 22. Notzli HP, Wyss TF, Stoeklin CH, Schmid MR, Treiber K, Hodler J. The contour of the femoral head-neck junction as a predictor for anterior impingement. J Bone Joint Surg Br. 2002;84:556-560. 23. Nussbaumer S, Leunig M, Glatthorn JF, Stauffacher S, Gerber H, Maffiuletti NA. Validity and test-retest reliability of manual goniometers for measuring passive hip range of motion in femoroacetabular impingement patients. BMC Musculoskelet Disord. 2010;11:194. 24. Perdikakis E, Karachalios T, Katonis P, Karantanas A. Comparison of MR-arthrography and MDCT-arthrography for detection of labral and articular cartilage hip pathology. Skeletal Radiol. 2011;40(11):14411447. 25. Philippon M, Schenker M, Briggs K, Kuppersmith D. Femoroacetabular impingement in 45 professional athletes: associated pathologies
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and return to sport following arthroscopic decompression. Knee Surg Sport Traumatol Arthrosc. 2007;15(7):908-914. Philippon MJ, Ho CP, Briggs KK, Stull J, LaPrade RF. Prevalence of increased alpha angles as a measure of cam-type femoroacetabular impingement in youth ice hockey players. Am J Sports Med. 2013;41(6):1357-1362. Philippon MJ, Schenker ML. Arthroscopy for the treatment of femoroacetabular impingement in the athlete. Clin Sports Med. 2006; 25(2):299-308. Pollard TCB, Villar RN, Norton MR, et al. Genetic influences in the aetiology of femoroacetabular impingement: a sibling study. J Bone Joint Surg Br. 2010;92(2):209-216. Ross JR, Bedi A, Stone RM, Sibilsky Enselman E, Kelly BT, Larson CM. Characterization of symptomatic hip impingement in butterfly ice hockey goalies. Arthroscopy. 2015;31(4):635-642. Siebenrock KA, Behning A, Mamisch TC, Schwab JM. Growth plate alteration precedes cam-type deformity in elite basketball players hip. Clin Orthop Relat Res. 2013;471(4):1084-1091. Silvis ML, Mosher TJ, Smetana BS, et al. High prevalence of pelvic and hip magnetic resonance imaging findings in asymptomatic collegiate and professional hockey players. Am J Sports Med. 2011;39(4):715-721. Wall PDH, Fernandez M, Griffin DR, Foster NE. Nonoperative treatment for femoroacetabular impingement: a systematic review of the literature. PMR. 2013;5(5):418-426. Weber AE, Jacobson JA, Bedi A. A review of imaging modalities for the hip. Curr Rev Musculoskelet Med. 2013;6(3):226-234.
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Prevalence of Cam-Type Morphology in Elite Ice Hockey Players Frantz Lerebours, William Robertson, Brian Neri, Brian Schulz, Thomas Youm and Orr Limpisvasti Am J Sports Med published online January 28, 2016 DOI: 10.1177/0363546515624671 The online version of this article can be found at: http://ajs.sagepub.com/content/early/2016/01/28/0363546515624671
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Prevalence of Cam-Type Morphology in Elite Ice Hockey Players Frantz Lerebours,* MD, William Robertson,yz MD, Brian Neri,§|| MD, Brian Schulz,*{ MD, Thomas Youm,# MD, and Orr Limpisvasti,*{** MD Investigation performed at Kerlan Jobe Orthopaedic Clinic, Los Angeles, California, USA Background: Femoroacetabular impingement (FAI) has been increasingly recognized as a cause of hip pain in athletes at all levels of competition, specifically ice hockey players. Purpose/Hypothesis: The purpose of this study was to define the prevalence of cam and pincer radiographic deformity in elite ice hockey players. The hypothesis was that elite hockey players will have a higher prevalence of radiographic hip abnormalities compared with the general population. Study Design: Cross-sectional study; Level of evidence, 3. Methods: Anteroposterior and frog-leg lateral radiographs on 137 elite ice hockey players were prospectively obtained during the 2014-2015 preseason entrance examinations. Study participants included National Hockey League roster players as well as the respective farm team members. Demographic data were collected, including age, position, shooting side, and any history of hip pain or hip surgery. Patients with a history of hip surgery were excluded from the analysis. A single sports medicine fellowship– trained orthopaedic surgeon used standard radiographic measurements to assess for the radiographic presence of cam or pincer deformity. Radiographs with an alpha angle 55° on a frog-leg lateral view were defined as cam-positive. Each participant underwent a preseason physical examination with an assessment of hip range of motion and impingement testing. Results: A total of 130 elite ice hockey players were included in the analysis; 180 (69.4%) hips met radiographic criteria for camtype deformity. The prevalence in right and left hips was 89 (69.5%) and 91 (70.0%), respectively; 70 (60.8%) players demonstrated bilateral involvement. Hips with cam deformity had a mean alpha angle of 67.7° 6 8.3° on the right and 68.9° 6 9.0° on the left. Of the patients with alpha angles 55°, 5.6% (5/89) had a positive anterior impingement test of the right hip, while 11% (10/91) had positive anterior impingement test of the left. Players with radiologic cam deformity had a statistically significant deficit in external rotation of the right hip, as well as in both internal and external rotation of the left hip, compared with those with normal alpha angles. When assessing for crossover sign, 64 of 107 (59.8%) had a positive radiographic finding. Forty-one players (38.3%) had evidence of a crossover sign of the right hip and 42 (39.3%) of the left. When comparing position players, goalies had the highest prevalence of cam-type deformity (93.8%) and the least acetabular coverage. Conclusion: The study data suggest that elite ice hockey players have a significantly higher prevalence of radiographic cam deformity in comparison to what has been reported for the general population. Keywords: femoroacetabular impingement; ice hockey; FAI; elite athletes
to cam FAI. Ayeni et al3 used magnetic resonance imaging (MRI) to evaluate the presence of radiographic FAI in elite ice hockey players and compare it with a control group of nonathletes. They found the odds of having cam impingement are 2.5 times greater in athletes participating in elite ice hockey than in nonathletes with similar demographics. However, despite the high prevalence of radiographic hip abnormalities in hockey players, many remain asymptomatic. Silvis et al31 evaluated the prevalence of abnormal MRI findings in asymptomatic collegiate ice hockey players and found acetabular labral tears in 56% of participants. These authors emphasized caution when interpreting MRI scans, as they have the potential to detect lesions that are not temporally correlated with self-reported measures of pain or disability. Although the cause of FAI is unknown, it has been postulated that the cam deformity is a normal physiologic
Hip and groin injuries are extremely common in ice hockey players, with a reported incidence of 19.87 injuries per 100 players at the elite level.11 Femoroacetabular impingement (FAI) has been increasingly recognized as a cause of hip pain in athletes at all levels of competition.14 Numerous studies have found an increased prevalence of FAI in competitive athletes.3,14,26,30 Philippon et al26 looked at the prevalence of FAI in youth ice hockey players and found a significant correlation between age and elevated alpha angles associated with cam FAI that was not found in skier-matched controls. They concluded that properties inherent to ice hockey likely enhanced the development of a bony overgrowth adjacent to the femoral neck, leading The American Journal of Sports Medicine, Vol. XX, No. X DOI: 10.1177/0363546515624671 Ó 2016 The Author(s)
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response to loading forces.21 High-level sports activity during the growth years is associated with an increased risk for the development of cam lesions.5,19 Repetitive microtrauma to the proximal femoral physis leads to reactive bone formation, resulting in an abnormal contour of the femoral head-neck junction.26 Many postulate that developmental factors related to activity and hip positioning during sports place patients at risk for developing FAI. In the past decade, the treatment of intra-articular hip disorders has drastically increased. This increasing trend is a result of the technological advances in hip arthroscopy, improved diagnostic imaging and interpretation,24 an improved understanding of intra-articular hip disorders, and an increased emphasis on hip arthroscopy in residency and fellowship training programs.18 Despite the increased proficiency in the diagnosis and treatment of FAI, the natural history of patients with FAI is largely unknown. Numerous studies have demonstrated radiographic findings of FAI in asymptomatic populations.13-16 The literature suggests that the overall incidence of radiographic FAI in an asymptomatic population is approximately 15%.13-16 To our knowledge, no study has defined the prevalence of radiographic abnormalities in elite ice hockey players. The purpose of this study was to establish normative data to confirm the prevalence of radiographic deformities of the hip in elite ice hockey players.
METHODS Institutional review board approval and informed consent from participants were obtained for this study. Data were obtained during the 2014-2015 preseason entrance examinations. The participants included all potential roster members of 3 National Hockey League (NHL) professional teams. The NHL athlete is considered at the highest level of performance. Each NHL team has a farm team in the American Hockey League (AHL), and players frequently move up or down during the course of a season. The participants in our study included NHL roster players as well as the respective farm team members. All participants with prior hip surgery were excluded from the study. Each patient underwent a demographic assessment and screening radiography, including anteroposterior (AP) pelvis and frog-leg lateral views of both hips. The demographic assessment included age, player position, history of hip pain, history of hip surgery, and shooting side. In addition, each participant underwent a preseason physical
examination with an assessment of hip range of motion (ROM) as well impingement testing by 3 of the authors (B.N., O.L., W.R.) who work for the respective organizations. Hip flexion, abduction, and adduction were assessed in the supine position with the use of a goniometer. Hip internal rotation, external rotation, and extension were measured with the patient prone. Anterior and posterior impingement testing was performed on all participants. An anterior impingement test was performed by first passively flexing the hip to 90° and then applying an adduction and internal rotation moment to the hip. Posteroinferior impingement testing was performed by extending and externally rotating the hip with the patient lying at the edge of the examination table in the supine position. A test was considered positive if any of the provocative testing maneuvers elicited groin pain. Radiographs were performed by 3 separate radiology technicians at the respective team professional arenas. All images were evaluated by a single board-certified, fellowship-trained orthopaedic surgeon to determine adequacy of the studies as well as the radiographic characteristics. Anteroposterior pelvic images were deemed adequate if the coccyx was centered over, and approximately 3 cm above, the pubic symphysis, with the obturator foramen neutrally rotated. The frog-leg lateral views were considered acceptable if there was clear visualization of the anterior and posterior head-neck junctions. Cam lesions were defined as positive if there was an alpha angle 55° on frog-lateral views. Alpha angles were measured on the frog-leg lateral view by using a radiographic computer goniometer (Impax PACS Imagining System; Afga Healthcare Corp). The alpha angle was measured using a digital circular template, drawing a best-fit circle surrounding the femoral head, thus using its center to serve as the angle’s vertex. Lines were drawn from the vertex down the center of the femoral neck and to the point where the best-fit circle deviates from the anterior femoral neck. The angle formed by these lines is defined as the alpha angle (Figure 1). On an appropriately obtained AP pelvis radiograph, the crossover sign is seen when there is an overlap between the lines tracing the anterior and posterior acetabular walls. This crossover sign represents anterior overcoverage of the acetabulum and served as the criterion for positive pincer deformity for this study. We measured the lateral centeredge angle (LCEA) and defined an abnormality as an angle \25°. The center-edge angle is the angle formed by a line drawn from the center of the femoral head to the outer edge of the acetabular roof and a vertical line drawn through the center of the femoral head (Figure 2).
**Address correspondence to Orr Limpisvasti, MD, Kerlan Jobe Orthopaedic Clinic, 6801 Park Terrace, Los Angeles, CA 90045, USA (email: [email protected]). *Kerlan-Jobe Orthopaedic Clinic, Los Angeles, California, USA. y Department of Orthopaedic Surgery, University of Texas Southwestern Medical Center, Dallas, Texas, USA. z Dallas Stars, National Hockey League, Dallas, Texas, USA. § ProHealth Care Associates, Lake Success, New York, USA. || New York Islanders, National Hockey League, New York, New York, USA. { Anaheim Ducks, National Hockey League, Anaheim, California, USA. # Department of Orthopaedic Surgery, New York University Langone Medical Center, New York, New York, USA. The authors declared that they have no conflicts of interest in the authorship and publication of this contribution.
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Figure 1. The alpha angle was obtained by first drawing a best-fit circle surrounding the femoral head. The center of the circle served as the angle’s vertex. Lines were drawn from the vertex down the center of the femoral neck and to the point where the best-fit circle deviates from the anterior femoral neck. The angle formed by these lines was defined as the alpha angle.
Statistical Analysis Descriptive statistics were used in our data analysis. Statistical calculations were performed using SAS version 9.2 (SAS Institute). The Fisher exact test was used to examine the significance of the associations between positions and radiographic evidence of cam deformity. The independent-samples t test was used to compare numerical variables (shown as mean 6 SD) across 2 groups, and the Fisher exact test was used to compare categorical variables (shown as n [%]) across groups. The .05 significance level was used throughout.
RESULTS The mean age of the patients involved in our study was 24.35 6 4.30 years. A total of 137 patients underwent preseason physicals among the 3 teams participating in our study. Two patients were excluded because of incomplete demographic and physical examination data, and 5 patients had undergone prior hip surgery and were therefore excluded from our analysis, bringing the total number of elite ice hockey players included in our analysis to 130. Of these, 32 (24.6%) players reported having a history of hip pain. Radiographs with an alpha angle 55° on frogleg lateral views were defined as indicating cam-type deformity. The total number of hips that met radiographic criteria for having cam-type deformity was 180 of 260 (69.4%) (Table 1). The prevalence in right and left hips was 89 of 130 (68.5%) and 91 of 130 (70.0%), respectively. A total of 79 of 130 (60.8%) patients demonstrated evidence of bilateral cam-type deformity (Table 1). The percentage of players with a history of hip pain and an elevated alpha angle were 16.2% (21/130) and 18.5% (24/130) for right and left hips, respectively. Of the patients with alpha
Figure 2. The lateral center-edge angle is the angle formed by a vertical line drawn through the center of the femoral head and a line drawn from the center of the femoral head to the outer edge of the acetabular roof.
angles 55°, 5.6% (5/89) had a positive anterior impingement test of the right hip, while 11% (10/91) had positive anterior impingement test of the left (Table 1). Seven (5.4%) players in our cohort were found to have a history of hip pain, a positive anterior impingement test, and an elevated alpha angle in any hip. We performed a subanalysis looking at differences in ROM between patients with alpha angles 55° (group A) versus those with alpha angles \55° (group B). In contrast, internal rotation of the right hip showed no difference between those in groups A and B. External rotation of the right hip was significantly lower for players in group A (38.9° 6 9.1°) compared with those in group B (43.6° 6 8.1°) (P = .006) (Table 2). When looking at left hip ROM, group A demonstrated a statistically significant deficit of both internal and external rotation. Internal rotation of the left hip in group A was 29.1° 6 9.74°, compared with 32.7° 6 11.9° in group B (P = .046) (Table 3). External rotation was 39.7°6 9.2° and 44.0° 6 10.4° for groups A and B, respectively (P = .020) (Table 3). The mean alpha angles for cam-positive right and left hips were 67.7° 6 8.3° and 68.9° 6 9.0°, respectively (Table 1). The mean alpha angles for players without radiographic evidence of cam lesions were 49.9° 6 3.6° on the right and 49.6°6 3.9° on the left. There was no association between age and the prevalence of elevated alpha angles.
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TABLE 1 Patients With Radiographic Evidence of Cam Deformitya
Alpha angle 55° Alpha angle in patient with positive cam deformity, deg, mean 6 SD Positive anterior impingement test
Right Hip
Left Hip
Bilateral
68.5 (89/130) 67.7 6 8.3 5.6 (5/89)
70.0 (91/130) 68.9 6 9.0 11 (10/91)
60.8 (79/130)
a
Data are reported as % (n/total number assessed) unless otherwise indicated.
TABLE 2 Mean Right Hip Range of Motion Range of Motion, deg Flexion Abduction Adduction Internal rotation External rotation Extension
Group A (Alpha Angle 55°) 112.5 40.9 18.1 31.5 38.9 14.9
Group B (Alpha Angle \55°) 113.1 41.3 18.5 32.0 43.6 14.6
610.9 6 9.2 6 5.5 6 10.9 6 9.1 6 6.9
6 6 6 6 6 6
11.8 9.6 5.1 9.6 8.1 6.9
P Value .78 .84 .73 .80 .006a .81
a
Statistically significant difference between groups (P \ .05).
TABLE 3 Mean Left Hip Range of Motion Range of Motion, deg Flexion Abduction Adduction Internal rotation External rotation Extension
Group A (Alpha Angle 55°) 114.1 41.3 19.3 29.1 39.7 14.9
6 6 6 6 6 6
Group B (Alpha Angle \55°)
11.4 9.3 6.4 9.7 9.2 6.72
111.8 40.5 17.3 32.7 44.0 14.9
6 6 6 6 6 6
20.4 8.4 5.0 11.9 10.4 6.5
P Value .51 .62 .089 .046a .020a .96
a
Statistically significant difference between groups (P \ .05).
A subgroup analysis using the Fisher exact test was performed based on position. The prevalence of right-sided cam FAI for goalies and centers approached statistical significance. Goalies (93.8%) were more likely to develop right-sided cam FAI, while centers (54.6%) were less likely (P = .076) (Table 4). The mean alpha angles for goalies were 66.38° 6 9.90° and 65.81° 6 11.54° for right and left hips, respectively (Table 4). An abnormal LCEA was observed in 11 of 130 (8.46%) right hips and 17 of 130 (13.08%) left hips. Goalies had the lowest mean LCEA, with the right and left hip measuring 27.6° 6 7.0° and 26.4° 6 7.07°, respectively. When evaluating for the presence of a crossover sign, we found that 64 of 107 (59.8%) had a positive radiographic finding. Forty-one players (38.3%) had evidence of a crossover sign of the right hip, and 42 (39.3%) players demonstrated a crossover on the left. Twenty-three patients were removed from our analysis because of inadequate radiograph projections due to asymmetry of the obturator foramen. When looking at patients with both an elevated alpha angle and positive crossover sign, 41 of 107 (54.7%) right hips and 42 of 107 (55.3%) left hips had concomitant morphologic variations.
DISCUSSION The exact cause of FAI is not completely understood. However, recent literature has shown an increased prevalence of FAI in competitive athletes, specifically those participating at a high level at an early age.3,14,26,30 Hip and groin injuries are among the most commonly reported complaints in ice hockey players.1,6 The most common morphologic variations about the hip that can result in dynamic hip impingement and subsequent loss of motion in athletes include femoral retroversion, acetabular retroversion, camtype deformity, and loss of femoral neck offset.4 These morphologic variations are extremely common in athletes, potentially due to developmental growth alterations that lead to nonphysiologic remodeling of the femoral head during repetitive high-impact and rotational loads on the physis. Recent studies have found the prevalence of cam deformity in the general population to be 14% in asymptomatic individuals.16 Men have been shown to have a higher prevalence of cam lesions than women (9.6%-24% vs 5%).15,16 Several studies have shown an increased prevalence of FAI in competitive athletes. Philippon et al26 found an increased prevalence of elevated alpha angles in youth
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TABLE 4 Subanalysis of Alpha Angle by Position Alpha Angle 55°, % Position Center (n = 33) Defenseman (n = 43) Goalie (n = 16) Left wing (n = 23) Right wing (n = 15)
Mean Alpha Angle, deg
Right Hip
Left Hip
Right Hip
Left Hip
54.6 69.8 93.8 65.2 73.3
66.7 65.1 81.3 78.3 66.7
58.9 61.9 66.4 62.4 65.1
60.1 61.8 65.8 67.7 63.5
ice hockey players. An interesting finding of the study was the linear correlation with age and elevated alpha angles, compared with age-matched controls.26 Gerhardt et al14 found an increased prevalence of cam FAI in elite soccer players. They found that 68% of men and 50% of women had radiographic evidence of cam FAI in their cohort. Similarly, our data found the prevalence of cam deformity to be 69.4%. Elite ice hockey players are more than 3 times more likely to develop cam deformity than the general population. There has been a reported genetic association with FAI.28 However, many believe the origin of cam FAI may result from subclinical microtrauma, due to a repetitive overuse phenomenon. It appears that there is something inherent to the mechanics of ice skating that places hockey players at risk for developing FAI. The biomechanics of ice skating, participation at an early age, on-ice exposure, style of play, and position may all play a role in the risk of developing FAI. Ng and Ellis21 highlighted that disruption of the physis through abnormal loading, biomechanics, vascularity, or trauma can have significant effects on the morphologic development of the hip. Siebenrock et al30 looked at growth plate deformity before and after physeal closure in basketball players and found that altered shape of the growth plate may precede a cam-type deformity in basketball athletes, suggesting a developmental abnormality. Their study suggested that the decreased head-neck offset associated with cam-type deformity was associated with epiphyseal extension rather than a reactive process.30 Despite the controversy in the origin of FAI, there is a consensus on the association that certain high-level sports increase the risk of developing FAI as an adult. Morphologic variations that can lead to dynamic hip impingement and subsequent loss of motion include femoral retroversion, cam-type deformity, loss of femoral offset, and acetabular retroversion.4 These morphologic variations result in restricted hip motion, which leads to compensatory increases in motion of the hemipelvis and lumbar spine to achieve functional range of motion for sport.10 A survey conducted by the NHL from 2006 to 2010 found that hockey goalies had a significantly higher rate of hip injuries per 1000 player game appearances in comparison to positional players.12 Our data suggest that goalies have a higher prevalence of cam deformity, but they also have a lower LCEA and less acetabular coverage. Are goalies without acetabular undercoverage selected out and therefore less likely to make it at the elite level? Or is this a protective mechanism, adapted during development as a result of high repetitive loads
and extreme ROM positions? Goalies place their hips at extremes of motion compared with position players, particularly during the ‘‘butterfly save.’’ During the butterfly save, a goalie maximally flexes and internally rotates his hips in order to place his lower extremity pads parallel to the ice. Ross et al29 used plain radiographs and computed tomography (CT) scans to characterize the radiographic deformity observed in consecutive series of butterfly goalies with symptomatic mechanical hip pain. They similarly found that acetabular dysplasia was more common among hockey goalies (29%) than among positional athletes (15%), with a mean lateral center-edge angle (LCEA) measuring 27.3°.29 Recognizing and understanding the structural characteristics in patients with acetabular dysplasia is imperative. An aggressive rim resection in patients with acetabular dysplasia can increase the risk of iatrogenic structural instability.33 Our data suggest that there are a significant number of asymptomatic elite hockey players with radiographic evidence of cam deformity. In our study, the prevalence of cam-type deformities in right and left hips was 89 of 130 (69.46%) and 91 of 130 (70.00%), respectively. Given the high prevalence of these morphologic FAI features in elite hockey players, it is important to keep in mind that an elevated alpha angle alone is not diagnostic of FAI. Instead, it is a clinical diagnosis based on history, symptom profile, and objective signs on physical examination. In a recent series, FAI was the diagnosis in 81% of professional hockey players requiring hip arthroscopy for painful hip conditions.27 It is apparent that there has been an increase in the number of hip arthroscopies being performed,9,18 but there are few reports on the incidence or demographics of patients undergoing these procedures in the United States.18 Long-term outcome studies are lacking and the natural history of operative versus nonoperative management is largely unknown. McCarthy et al17 reported 80% excellent results after hip arthroscopy in elite athletes with a mean follow-up of 23.6 months. Philippon et al25 reported that 93% (42/45) of professional athletes returned to professional competition after arthroscopic decompression of FAI at a mean of 1.6 years. A recognized limitation of our study was the use of plain radiographs to obtain our measurements. Although the Dunn view or frog-leg lateral radiographs7 have been identified as a reliable imaging projection for the measurement of femoral head asphericity using the alpha angle of Notzli et al,22 the multiplanar imaging provided by CT and MRI can better assess cam deformity and reduce the risk of
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underestimating the alpha angle. Computed tomography and MRI also offer the benefit of assessing femoral version. In the case of cam-type FAI, femoral anteversion can protect against a cam lesion entering the joint, whereas femoral retroversion can exacerbate the issue. We did not assess femoral version in this study, which could confound the relationships between pain and ROM in the setting of a given alpha angle. In addition, we recognize that the 45° Dunn view has become the more widely accepted view used in clinical practice. However, we concluded that using frog-leg lateral radiographs would show more consistency in adequacy given that our radiologist for the respective organizations performs this view on a regular basis. In addition, frog-leg laterals have been validated in numerous studies for diagnosing cam FAI.14 Nepple et al20 compared the Dunn view and frog-leg lateral view in assessing cam-type deformity using radiographic measurements and correlated them with CT scan findings. They concluded that the Dunn view was more sensitive at detecting cam lesions (71%81%), but the frog-leg lateral was more specific (91%100%). There is also a recognized limitation of diagnosing a pincer lesion using the crossover sign on standard AP radiographs. Obtaining consistency in symmetric AP radiographs was challenging, and we excluded 23 patients as a result of inadequate projections. Even after standardizing the radiographs based on rotation and the distance between the coccyx and pubic symphysis, subtle changes in tilt and rotation can significantly alter the presence of a crossover sign. Another limitation of our study was in our assessment of ROM. We used goniometer-based assessment, among 3 physicians, in the prone position. Nussbaumer et al23 evaluated the validity and reliability of goniometer-based measurements in hip ROM assessment in patients with FAI. They concluded that goniometer-based assessments conventionally used in orthopaedic clinical practice overestimate the majority of passive hip motion patterns by measuring intersegmental angles, such as thigh flexion on the trunk for hip flexion, rather than true hip ROM. In our study, we found a statistically significant loss of external rotation of the right hip in our cam-positive group. However, in patients with cam deformity, we would expect to see a loss of internal rotation, not external rotation. Perhaps if our measurements were performed in the ‘‘at-risk’’ position, with the patient supine with the hip flexed, our statistical comparisons would have been consistent with the ROM deficits seen in FAI. Another limitation of our study was that a single orthopaedic surgeon reviewed our radiographs, which limits the interobserver reliability of our radiographic findings. However, we believe the benefit of having a single surgeon review and interpret all films greatly outweighs any negatives. Last, preseason evaluation and player recall may affect reports of hip pain and positive provocative test results.
CONCLUSION FAI surgery has evolved rapidly and at a pace far quicker than our understanding about the natural history and epidemiologic characteristics of the condition.2,8,32 Despite the
high prevalence of radiographic abnormalities in our study, a large number of patients were asymptomatic. This study further emphasizes that FAI is a clinical diagnosis, and imaging abnormalities alone are not sufficient in making the diagnosis. A preventative screening program for elite ice hockey players at the start of their professional careers may potentially identify patients with clinical characteristics and radiographic hip deformity that may place them at a higher risk for injury. Interventions aimed at adapting to their functional ROM and reducing the frequency of impingement can then be implemented. REFERENCES 1. Agel J, Dompier TP, Dick R, Marshall SW. Descriptive epidemiology of collegiate men’s ice hockey injuries: National Collegiate Athletic Association Injury Surveillance System, 1988-1989 through 20032004. J Athl Train. 2007;42(2):241-248. 2. Allen D, Beaule PE, Ramadan O, Doucette S. Prevalence of associated deformities and hip pain in patients with cam-type femoroacetabular impingement. J Bone Joint Surg Br. 2009;91(5):589594. 3. Ayeni OR, Banga K, Bhandari M, et al. Femoroacetabular impingement in elite ice hockey players. Knee Surg Sports Traumatol Arthrosc. 2014;22(4):920-925. 4. Bedi A, Dolan M, Leunig M, Kelly BT. Static and dynamic mechanical causes of hip pain. Arthroscopy. 2011;27(2):235-251. 5. Bizzini M, Notzli HP, Maffiuletti NA. Femoroacetabular impingement in professional ice hockey players: a case series of 5 athletes after open surgical decompression of the hip. Am J Sports Med. 2007;35(11):1955-1959. 6. Brown RA, Mascia A, Kinnear DG, Lacroix V, Feldman L, Mulder DS. An 18-year review of sports groin injuries in the elite hockey player: clinical presentation, new diagnostic imaging, treatment, and results. Clin J Sport Med. 2008;18(3):221-226. 7. Clohisy JC, Nunley RM, Otto RJ, Schoenecker PL. The frog-leg lateral radiograph accurately visualized hip cam impingement abnormalities. Clin Orthop Relat Res. 2007;462:115-121. 8. Clohisy JC, St John LC, Schutz AL. Surgical treatment of femoroacetabular impingement: a systematic review of the literature. Clin Orthop Relat Res. 2010;468(2):555-564. 9. Colvin AC, Harrast J, Harner C. Trends in hip arthroscopy. J Bone Joint Surg Am. 2012;94(4):e23. 10. Draovitch P, Edelstein J, Kelly BT. The layer concept: utilization in determining the pain generators, pathology and how structure determines treatment. Curr Rev Musculoskelet Med. 2012;5(1):1-8. 11. Emery CA, Meeuwisse WH, Powell JW. Groin and abdominal strain injuries in the National Hockey League. Clin J Sport Med. 1999;9(3):151-156. 12. Epstein DM, McHugh M, Yorio M, Neri B. Intra-articular hip injuries in National Hockey League players: a descriptive epidemiological study. Am J Sports Med. 2013;41(2):343-348. 13. Ganz R, Leunig M, Leunig-Ganz K, Harris WH. The etiology of osteoarthritis of the hip: an integrated mechanical concept. Clin Orthop Relat Res. 2008;466(2):264-272. 14. Gerhardt MB, Romero AA, Silvers HJ, Harris DJ, Watanabe D, Mandelbaum BR. The prevalence of radiographic hip abnormalities in elite soccer players. Am J Sports Med. 2012;40(3):584-588. 15. Gosvig KK, Jacobsen S, Sonne-Holm S, Gebuhr P. The prevalence of cam-type deformity of the hip joint: a survey of 4151 subjects of the Copenhagen Osteoarthritis Study. Acta Radiol. 2008;49(4): 436-441. 16. Hack K, Di Primio G, Rakhra K, Beaule´ PE. Prevalence of cam-type femoroacetabular impingement morphology in asymptomatic volunteers. J Bone Joint Surg Am. 2010;92(14):2436-2444.
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