- Email: [email protected]
In Vivo Hip Morphology and Kinematics in Elite Baseball Pitchers
In Vivo Hip Morphology and Kinematics in Elite Baseball Pitchers Eileen A. Crawford, M.D., David Whiteside, Ph.D., Jessica M. Deneweth, Ph.D., James R. Ross, M.D., Asheesh Bedi, M.D., and Grant C. Goulet, Ph.D.
Purpose: To compare passive and real-time active hip range of motion (ROM) in asymptomatic collegiate pitchers, to investigate whether differences in hip morphology and ROM exist between lead and trail hips, and to relate active hip ROM during the pitch to hip morphology and femoroacetabular impingement. Methods: Eleven collegiate baseball pitchers participated in kinematic testing that involved throwing four fastball pitches while wearing a full-body inertialbased motion-capture system. Passive flexion and rotation of each hip were measured using a goniometer. Nine pitchers also underwent a computed tomography (CT) pelvic scan, from which subject-specific computer models for each hip were created. Morphologic measurements were calculated from the models, and the models were tested for impingement during simulated pitching. Results: Hip flexion was the only passive ROM measurement showing a significant difference between the lead and trail hips (mean difference [MD], 4 ; P ¼ .027). During the pitching motion, within-individual differences were discovered between the lead and trail hips for flexion (MD, 34 ; P < .0001), extension (MD, 26 ; P < .0001), abduction (MD, 8 ; P ¼ .026), adduction (MD, 6 ; P ¼ .008), external rotation (MD, 20 ; P ¼ .001), and total arc of rotation (MD, 13 ; P ¼ .001). There were no significant differences in morphologic measures between the lead and trail hips. Dynamic CT modeling did not lead to bony impingement in any subject. Conclusions: Asymptomatic collegiate pitchers approach their extremes of passive hip rotation when executing a fastball pitch. No differences were found in passive hip ROM or morphology other than a small difference in passive hip flexion. Dynamic CT modeling did not show femoroacetabular impingement during the pitching motion. Clinical Relevance: Hip dysmorphology or poor pitching mechanics may lead to a high risk of bony impingement because pitchers have little reserve hip motion during the fastball pitch.
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roin and hip pain is experienced by a substantial proportion of athletes, with 23% of high-level male athletes reporting symptomatic hip pathology during the preceding year of training.1 With improvements in clinical diagnosis and imaging, a surprisingly high incidence of prearthritic hip deformity has been discovered in athletes. A recent study of elite soccer players reported radiographic evidence of femoroacetabular impingement (FAI) in the form of a cam or
From the Sports Medicine and Shoulder Service, Department of Orthopaedic Surgery (E.A.C., J.R.R., A.B.), and School of Kinesiology (D.W., J.M.D., G.C.G.), University of Michigan, Ann Arbor, Michigan; and Broward Orthopedic Specialists (J.R.R.), Fort Lauderdale, Florida, U.S.A. The authors report the following potential conflict of interest or source of funding: A.B. receives support from Smith & Nephew and A3 Surgical. Received February 9, 2015; accepted November 20, 2015. Address correspondence to Eileen A. Crawford, M.D., Bayhealth Orthopaedic Surgery, 655 Bay Rd, Ste F1, Dover, DE 19901, U.S.A. E-mail: [email protected] Ó 2016 by the Arthroscopy Association of North America 0749-8063/15123/$36.00 http://dx.doi.org/10.1016/j.arthro.2015.11.052
pincer lesion in 72% of the male and 50% of the female athletes.2 Another study reported that 89% of skeletally mature basketball players had an alpha angle greater than 55 , compared with 9% of non-athletes in the control group. Furthermore, hip internal rotation was significantly lower in the basketball players compared with the non-athletes, a difference that increased with age.3 Although it may be expected that athletes would have hip pain and injury from the significant physical demands of athletic competition, it is yet unclear why athletes would be more likely to have abnormal hip morphology and if unique athletic demands on each hip may predispose to symptoms. Theories focus on the adaptability of bone, particularly in the young athlete, to remodel in response to repetitive stresses.4,5 Athletes who specialize in a specific sport at a young age may be excessively subjecting their bones to repetitive activities characteristic of that sport.2,5 Morphologic adaptations may be accentuated in athletes who perform an asymmetrical activity using a dominant extremity6; for example, the dominant upper extremity of adolescent
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female tennis players shows higher bone mineral density than the nondominant upper extremity, and this difference is correlated with starting age of playing and training intensity.7,8 Similarly, baseball pitchers frequently execute an asymmetrical, high-force throwing motion during their athletic careers. The effects of repetitive throwing on the proximal humeral physis and the glenohumeral ligaments and capsule are well known,9,10 but with greater understanding of the kinetic chain, attention has turned to hip motion, lumbopelvic motion, and core musculature in pitchers as well. In the propulsive phase of the pitching motion, force is initially generated by the lower extremities before being transferred through the trunk and into the pitching arm to propel the ball.11,12 Abnormal loading mechanics of the trail limb and landing pattern of the lead limb during the pitching motion can cause hip maladaptations and inefficient energy transfer, requiring the trunk and upper extremities to generate more force to maintain ball velocity.11-13 Thus hip dysmorphology and consequential reduction in terminal hip range of motion (ROM) can result in impaired performance and injuries, not only to the hip but also to structures more distal in the kinetic chain.12,14 By gaining a better understanding of both normal and abnormal hip morphology and ROM in athletes, as well as the differences between dominant and nondominant extremities during specific athletic tasks, we can recognize at-risk athletes and develop prospective injury prevention strategies. Recent studies have examined passive and active hip ROM and side-to-side differences in baseball pitchers, with somewhat conflicting results.6,11,12,14 The objectives of this study were to compare passive and real-time active hip ROM in asymptomatic collegiate pitchers, to investigate whether differences in hip morphology and ROM exist between lead and trail hips, and to relate active hip ROM during the pitch to hip morphology and FAI. We hypothesized that active ROM during the pitch would approach the maximal passive ROM, particularly for lead hip flexion and bilateral hip internal rotation; hip morphology and ROM would differ between the lead and trail lower extremities; and active hip ROM in hips with abnormal morphology would exhibit bony impingement at terminal ROM.
training room, and kinematic testing was performed in the team’s indoor practice pitching facility. On arrival at the testing site, subjects gave written informed consent and completed a questionnaire regarding injury history. Each subject then dressed in a full-body inertial-based motion-capture system suit (Xsens MVN BIOMECH; Xsens, Enschede, Netherlands), which recorded at 120 Hz (Fig 1). The motion-tracking sensors (mass, 0.03 kg; dimensions, 0.038 0.053 0.021 m) were contained in the Lycra suit and additionally secured with athletic wrap around the lower legs, thighs, and throwing arm to minimize any movement artifacts during the pitch. The accuracy of this inertial-based motion-capture system has been validated against established electromagnetic and optoelectronic tracking systems for human movement.15,16 Passive ROM Testing Each subject was first examined in the training room for passive ROM. The subject was positioned supine on the examination table. The pelvis was secured to the examination table with a strap across the anterior superior iliac spine to prevent pelvic motion. The same
Methods Before commencement, this study received approval from the institutional review board. Eleven Division I collegiate baseball pitchers were recruited for participation in this study. Pitchers who reported previous hip surgery and those who were unable to complete standard pitching practice because of injuries were excluded. All testing occurred in the university baseball complex. Passive ROM testing was performed in the
Fig 1. Subject wearing full-body inertial-based motioncapture system suit during kinematic testing.
HIP KINEMATICS IN ELITE BASEBALL PITCHERS
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order before each pitch. Only the data from the four designated fastball pitches were used for this study; the data for the remaining pitches were used for a separate study. The kinematic data collected from the suit were transmitted directly to the accompanying computer software (Xsens). The ROM data extracted from the kinematic testing included maximal hip flexion, extension, adduction, abduction, internal rotation, and external rotation during the pitching motion (wind-up to follow-through). Total arc of rotational motion was calculated as the sum of internal and external rotation.
Fig 2. Passive range-of-motion testing was completed with the subject resting supine and the pelvis secured to the examination table. One study team member positioned the extremity while another took measurements with a goniometer.
study team member (J.M.D.) measured the passive ROM of each hip using a goniometer while the hip was positioned at the terminal end of motion for each position by one of two other study team members (E.A.C., D.W.) (Fig 2). Each hip was tested for flexion, internal rotation in extension, external rotation in extension, internal rotation in 90 of flexion, and external rotation in 90 of flexion. For rotational testing in extension, the knees were flexed over the end of the examination table and the pelvis remained secured to the table. Total arc of motion was calculated as the sum of internal and external rotation in 90 of knee flexion. The arm of the goniometer was aligned with the diaphysis of the femur for hip flexion measurements and with the diaphysis of the tibia for rotational measurements. Each measurement was performed three times, and the mean standard deviation of the recorded values was calculated. Kinematic Testing After passive ROM testing, subjects proceeded to the pitching mound for kinematic testing. Before data collection, each subject was asked to replicate the standard game-day warm-up, which generally involved whole-body stretches and throwing progression. All pitches were performed on a regulation National Collegiate Athletic Association pitching mound and directed to a catcher positioned at regulation distance (60 ft 6 in) from the pitcher’s rubber. Pitchers threw a total of 16 pitches, 4 each of fastball, curveball, slider, and change-up pitches, assigned to the pitcher in random
Morphologic Testing Nine of the 11 pitchers also consented to highresolution computed tomography (CT) scans of the pelvis and distal femur. Two subjects declined to consent to the CT scan for unsolicited reasons, so they were excluded from this portion of the study. All CT scans were performed at the same hospital using a standardized, low-dose CT protocol previously described for characterizing hip bony morphology.17 This CT protocol involves 0.625-mm slice-thickness reconstruction of 2.5-mm slices and includes an algorithm designed by GE Healthcare (Waukesha, WI) to further reduce the radiation dose by 20%, resulting in a 2.85-mSv dose to the hip and a 0.075-mSv dose to the knee. By use of computer-assisted modeling of the three-dimensional reconstructions (DYONICS PLAN; Smith & Nephew, Andover, MA), subject-specific dynamic models of the bony anatomy of the lead and trail hips for each subject were created. The software calculated the following morphologic measurements from each model: femoral neck version, femoral neck-shaft angle, alpha angle at all positions along the clock face, acetabular version, and lateral center-edge angle. The models were moved through the ROM to determine maximal passive hip flexion, internal rotation in 90 of flexion, and internal rotation combined with 90 of flexion and 15 of adduction (FADIR position). The unique ROM requirements during a pitch, as determined for each individual from the kinematic testing, were subsequently used to determine if bony impingement (contact between the acetabulum and the femoral head-neck junction) occurred in the CT model during a simulated pitch for that subject. This bony impingement could occur from a focal region of abnormal femoral head-neck offset contacting the acetabular rim (camtype impingement) or from focal or global acetabular overcoverage contacting a normal femoral head-neck junction (pincer-type impingement). Statistical Analysis Statistical analysis was performed with SPSS software (version 10.0; SPSS, Chicago, IL). Means and standard deviations were calculated for the overall study group
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Table 1. Passive ROM for Lead and Trail Hips for All Subjects Mean Passive ROM (N ¼ 11) Flexion, IR in 0 of extension, ER in 0 of extension, IR in 90 of flexion, ER in 90 of flexion, Total arc of rotation in extension, Total arc of rotation in flexion,
Lead Hip 114 8 29 6 25 7 33 7 32 8 54 10
Trail Hip 118 8 29 3 23 5 31 6 32 5 52 7
P Value .027* .796 .217 .307 .927 .126
66 11
63 8
.431
NOTE. Data are presented at mean standard deviation. ER, external rotation; IR, internal rotation; ROM, range of motion. *Statistically significant.
for passive ROM parameters, active ROM parameters, and morphologic data for the lead and trail hips. Comparisons between the lead and trail hips were performed using a two-tailed paired t test and presented with mean differences (MDs) and effect sizes (d) to aid interpretation. In accordance with Cohen’s scale,18 effect sizes were considered either small (<0.2), medium (0.5), or large (>0.8). The level of significance for all statistical analyses was set at P .05.
Results The mean age of the subjects at the time of the study was 20.4 years (SD, 1.6 years). The mean height of the subjects was 191.4 cm (SD, 6.0 cm), and the mean weight was 92.9 kg (SD, 8.0 kg). There were 8 righthanded pitchers and 3 left-handed pitchers; all 11 used a standard over-arm action. Descriptive statistics for passive ROM are reported in Table 1. When the lead and trail hips within subjects were compared, hip flexion was the only passive ROM measurement that showed a significant difference (MD, 4 ; P ¼ .027, d ¼ 0.78). Table 2 reports the means and standard deviations for requisite motion during the pitch. Several statistically Table 2. Active ROM for Lead and Trail Hips for All Subjects Mean Active ROM (N ¼ 11) Flexion, Extension, Abduction, Adduction, Internal rotation, External rotation, Total arc of rotation,
Lead Hip 84 14 13 3 38 8 17 6 33 10
Trail Hip 50 11 38 5 46 6 11 5 26 11
P Value .001 .001 .026 .008 .064
13 5
33 11
.001
46 8
59 10
.001
NOTE. Data are presented at mean standard deviation. ROM, range of motion.
significant within-individual differences were discovered in the requisite ROM between the lead and trail hips: flexion (MD, 34 ; P < .0001, d ¼ 2.16), extension (MD, 26 ; P < .0001, d ¼ 5.46), abduction (MD, 8 ; P ¼ .026, d ¼ 0.79), adduction (MD, 6 ; P ¼ .008, d ¼ 1.00), external rotation (MD, 20 ; P ¼ .001, d ¼ 1.46), and total arc of rotation (MD, 13 ; P ¼ .001, d ¼ 1.31). Although internal rotation was not significantly different between the lead and trail hips, it did display a medium to large effect size (d ¼ 0.63). The mean values for the CT morphology parameters are reported in Table 3. These values exclude the two subjects who did not consent to CT scans. The mean maximal alpha angle was located at 1:30 on the clock face. There were no significant differences in morphologic measures between the trail and lead legs when compared within individuals. Dynamic CT modeling using the maximal ROM parameters during the pitching motion did not lead to bony impingement in any of the subjects.
Discussion The results of this study show that active hip rotation required for the fastball pitchdspecifically, internal rotation of the lead hip and external rotation of the trail hipdapproaches terminal passive hip rotation in asymptomatic collegiate pitchers. Pitchers generate acceleration from the wind-up and stride phases of the pitching sequence,19,20 where hip and pelvic motion plays an important role. During the wind-up, the lead hip flexes, adducts, and internally rotates, thereby placing it at risk of anterior-superior impingement. As the pitcher moves into the stride phase, the pelvis and trunk accelerate forward while the trail hip extends, abducts, and externally rotates. With this motion, the Table 3. CT Morphology Parameters for Lead and Trail Hips for All Subjects With CT Scans CT Morphology Parameter (n ¼ 9) Femoral version, Femoral neck-shaft angle, Maximum alpha angle, Maximum acetabular anteversion, Lateral center-edge angle, Simulated maximum hip flexion, Simulated maximum IR in 90 of flexion, Simulated maximum IR in FADIR,
Lead Hip 21 12 133 4
Trail Hip 20 12 133 3
P Value .868 .791
58 8 17 4
59 7 17 3
.637 > .99
32 6
30 7
.154
117 13
119 13
.137
34 21
37 20
.259
24 20
27 20
.311
NOTE. Data are presented at mean standard deviation. CT, computed tomography; FADIR, flexioneadductioneinternal rotation position; IR, internal rotation.
HIP KINEMATICS IN ELITE BASEBALL PITCHERS
trail hip is at risk of anterior rotational instability.13,14 The lead hip also abducts and externally rotates during the stride; however, the follow-through involves flexion, adduction, and internal rotation at the hip, providing another opportunity for anterior-superior impingement.13,14 The pitchers in this study approached their passive rotational limits during the fastball pitch, suggesting an absence of any reserve motion and a high risk of bony impingement with any pathomorphology of the hip or poor pitching mechanics and pelvic control. The lead and trail legs have distinct roles and motion sequences in the baseball pitch. The significant differences and effect sizes in maximal requisite ROM parameters between the lead and trail legs reported in this study corroborate this observation. This finding is important to keep in mind when one is considering surgical treatment of FAI in baseball athletes, because a successful clinical outcome is often predicated on an improvement in ROM that allows the athlete to
Fig 3. Hip angles of lead (upper) and trail (lower) legs throughout phases of pitching motion. The curves represent the means of all subjects.
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complete a specific task. The fact that internal rotation differences did not reach statistical significance may indicate that motion in that direction is high for both hips, albeit at separate phases of the pitching motion (Fig 3). The effect size of 0.63 does suggest that there may be a clinically meaningful difference in active internal rotation between the lead and trail hips with greater motion in the lead hip, even though the difference did not quite reach statistical significance. Despite the asymmetrical nature of the pitching motion, the data in this study show that hip flexion is the only passive ROM parameter that exhibits a statistically significant difference between the lead and trail hips of an individual pitcher. This difference in mean hip flexion for the lead and trail hips is only 4 , which may not be a clinically significant difference. In addition, the various radiographic measures of osseous hip morphology did not show any differences between the lead and trail hips of an individual pitcher. Several recent studies have examined hip ROM for the lead and
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trail lower extremities in baseball pitchers, with somewhat conflicting results. Ellenbecker et al.6 found no significant differences between the lead and trail hips in passive or active ROM for 101 professional baseball pitchers. Active ROM in their study, however, was measured on the examination table rather than during an in vivo functional task, such as the pitching motion used herein. The authors did report that 42% of pitchers had a difference of at least 10 of external rotation between the lead and trail hips, although this finding was not statistically significant.6 In contrast, Robb et al.11 studied passive ROM in 19 professional baseball pitchers and reported that the lead hip had significantly less internal rotation, external rotation, and adduction than the trail hip. They suggested that differences in measurement technique between their study and that of Ellenbecker et al. may have accounted for their contrary findings. Additional studies have supported the finding that the lead and trail hips in baseball pitchers show symmetrical passive ROM, although differences exist among pitchers and position players at the same level of competition.12,14 However, from an FAI perspective, it is somewhat difficult to derive any direct clinical or practical applications from this body of work because researchers have failed to appraise ROM during the task in which impingement is expected to occurdpitching. By quantifying bilateral hip ROM in the pitching motion, our study provides a framework for clinicians and coaches to better understand the hip mechanics that characterize a sportspecific movement. This study is also unique in examining CT-based, three-dimensional bony morphology of both hips in these athletes and correlating with the observed passive and active ROM. There were no morphologic differences between the lead and trail hips, offering little support for the theory that the repetitive and asymmetrical stress of the pitching motion may distinctly and asymmetrically affect hip morphology. However, the data show some interesting characteristics of the hips in collegiate pitchers. The mean femoral anteversion of 20.4 is high compared with the normal range in the general population of 8 to 10 .21,22 Increased femoral anteversion allows for additional internal rotation of the hip before bony contact occurs, which may be a favorable trait in pitchers because they approach terminal passive internal rotation during the pitch. Of course, increased femoral anteversion also means that bony contact occurs sooner in external rotation. Acetabular anteversion is on the lower end of the normal range23 in these pitchers, which would temper the effect of increased femoral anteversion. Finally, cam morphology was observed frequently in these pitchers (Fig 4). The mean maximal alpha angle was 58 , with five pitchers (56%) having a maximal alpha angle greater than 55 in both hips and one pitcher (11%) having a maximal alpha angle greater
Fig 4. Computed tomography image of one subject showing bilateral cam deformities (arrows).
than 55 in one hip. This finding supports previous reports of a high incidence of radiographic signs of FAI in soccer and basketball athletes.2,3 The cam morphology was not found to be clinically relevant for these subjects, however, because the cam lesion did not impinge on the acetabulum during simulated ROM. Similarly, markers of pincer morphologydacetabular version and lateral center-edge angledwere not so abnormal as to cause bony impingement during the pitching motion. Hip dysmorphology does not necessarily result in bony impingement, even with extreme motions such as pitching, and therefore can be asymptomatic. Although further studies are necessary, the results suggest that whereas repetitive microtrauma at the end ranges of motion may occur in throwing athletes with FAI, the specific combination of motion that results in FAI (i.e., simultaneous maximal flexion and maximal internal rotation) is not necessarily required for pitching. The etiology of FAI in these athletes may reflect unique forces of the developing physis but may not be the consequence of repetitive microtrauma to the head-neck junction and/or acetabular chondrolabral complex. CT-based hip models simulating the pitch did not show bony impingement at the extremes of motion in our group of pitchers. This discrepancy highlights the concept that FAI, and the development of symptomatic FAI, is more than just a consequence of abnormal bony morphology. As Byrd and Jones24 discussed, FAI is a morphologic variant that does not cause hip pain but rather predisposes individuals to the development of intra-articular hip pathology. The labrum, hip capsule, and surrounding musculature all affect hip ROM and mechanics, including the distribution of forces in the hip joint.25 FAI is a dynamic process involving abnormal compressive and shear forces within the hip joint.26 The CT model used in this study does not take into account the forces acting on the hip as it moves through the ROM of the pitch. Future studies that incorporate the mechanical forces within the hip during
HIP KINEMATICS IN ELITE BASEBALL PITCHERS
athletic activities will greatly add to our understanding of why symptoms develop in some athletes with FAI morphology but not in others. Limitations The limitations of this study include the small sample size and differences in how active and passive ROM values were expressed. The paucity of statistically significant differences between the lead and trail hips may be a result of the study being underpowered. However, elite athletic populations are always relatively small by nature of the availability and accessibility of this group, and our results regarding passive ROM are consistent with most of the similar studies referenced earlier, even with different techniques for measuring ROM.6,12,14 Future research on morphologic characteristics will help determine if the similarities between the lead and trail hips found in this study will bear out in larger groups and different types of athletes. When comparing active and passive ROM in this study, one should note that the hip postures are similar but not equivalent. Passive hip rotation was measured in either 0 of hip extension or 90 of hip flexion because the examiner can be more consistent when taking measurements in orthogonal planes. In contrast, the maximal active hip rotation was measured by the sensors in the motioncapture suit and thus could occur in any degree of hip flexion or extension. Despite this difference, the data may be most clinically useful in this format because clinicians tend to measure ROM on physical examination in a similar manner. In addition, because subjects were supine for passive ROM measurements, variations in lumbar lordosis could affect hip ROM measurements, even with the pelvis stabilized. Although Reichenbach et al.27 found the seated position to be more precise for measuring hip ROM, it had a strong correlation with measurements in the supine position. The precision of our supine technique may be better than that reported in the article by Reichenbach et al. because we stabilized the pelvis against the examination table with a strap, which was not done in their technique.
Conclusions Asymptomatic collegiate pitchers approach their extremes of passive hip rotation when executing a fastball pitch. No differences were found in passive hip ROM or morphology other than a small difference in passive hip flexion. Dynamic CT modeling did not show FAI during the pitching motion.
References 1. Jonasson P, Halldin K, Karlsson J, et al. Prevalence of joint-related pain in the extremities and spine in five groups of top athletes. Knee Surg Sports Traumatol Arthrosc 2011;19:1540-1546.
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2. 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;40:584-588. 3. Siebenrock KA, Ferner F, Noble PC, Santore RF, Werlen S, Mamisch TC. The cam-type deformity of the proximal femur arises in childhood in response to vigorous sporting activity. Clin Orthop Relat Res 2011;469:3229-3240. 4. Ferry B, Duclos M, Burt L, et al. Bone geometry and strength adaptations to physical constraints inherent in different sports: Comparison between elite female soccer players and swimmers. J Bone Miner Metab 2011;29:342-351. 5. Maffulli N. Intensive training in young athletes. The orthopaedic surgeon’s viewpoint. Sports Med 1990;9: 229-243. 6. Ellenbecker TS, Ellenbecker GA, Roetert EP, Silva RT, Keuter G, Sperling F. Descriptive profile of hip rotation range of motion in elite tennis players and professional baseball pitchers. Am J Sports Med 2007;35:1371-1376. 7. Haapasalo H, Kannus P, Sievanen H, et al. Effect of longterm unilateral activity on bone mineral density of female junior tennis players. J Bone Miner Res 1998;13:310-319. 8. Kannus P, Haapasalo H, Sankelo M, et al. Effect of starting age of physical activity on bone mass in the dominant arm of tennis and squash players. Ann Intern Med 1995;123:27-31. 9. Carson WG Jr, Gasser SI. Little Leaguer’s shoulder. A report of 23 cases. Am J Sports Med 1998;26:575-580. 10. Bigliani LU, Codd TP, Connor PM, Levine WN, Littlefield MA, Hershon SJ. Shoulder motion and laxity in the professional baseball player. Am J Sports Med 1997;25: 609-613. 11. Robb AJ, Fleisig G, Wilk K, Macrina L, Bolt B, Pajaczkowski J. Passive ranges of motion of the hips and their relationship with pitching biomechanics and ball velocity in professional baseball pitchers. Am J Sports Med 2010;38:2487-2493. 12. Laudner KG, Moore SD, Sipes RC, Meister K. Functional hip characteristics of baseball pitchers and position players. Am J Sports Med 2010;38:383-387. 13. Klingenstein GG, Martin R, Kivlan B, Kelly BT. Hip injuries in the overhead athlete. Clin Orthop Relat Res 2012;470:1579-1585. 14. Sauers EL, Huxel Bliven KC, Johnson MP, Falsone S, Walters S. Hip and glenohumeral rotational range of motion in healthy professional baseball pitchers and position players. Am J Sports Med 2014;42:430-436. 15. Saber-Sheikh K, Bryant EC, Glazzard C, Hamel A, Lee RY. Feasibility of using inertial sensors to assess human movement. Man Ther 2010;15:122-125. 16. Ferrari A, Cutti AG, Garofalo P, et al. First in vivo assessment of “Outwalk”: A novel protocol for clinical gait analysis based on inertial and magnetic sensors. Med Biol Eng Comput 2010;48:1-15. 17. Milone MT, Bedi A, Poultsides L, et al. Novel CT-based threedimensional software improves the characterization of cam morphology. Clin Orthop Relat Res 2013;471:2484-2491. 18. Cohen J. Statistical power analysis for the behavioral sciences. Hillsdale, NJ: L. Erlbaum Associates, 1988. 19. Pappas AM, Zawacki RM, Sullivan TJ. Biomechanics of baseball pitching. A preliminary report. Am J Sports Med 1985;13:216-222.
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20. Dillman CJ, Fleisig GS, Andrews JR. Biomechanics of pitching with emphasis upon shoulder kinematics. J Orthop Sports Phys Ther 1993;18:402-408. 21. Koerner JD, Patel NM, Yoon RS, Sirkin MS, Reilly MC, Liporace FA. Femoral version of the general population: Does “normal” vary by gender or ethnicity? J Orthop Trauma 2013;27:308-311. 22. Audenaert EA, Peeters I, Vigneron L, Baelde N, Pattyn C. Hip morphological characteristics and range of internal rotation in femoroacetabular impingement. Am J Sports Med 2012;40:1329-1336. 23. Stem ES, O’Connor MI, Kransdorf MJ, Crook J. Computed tomography analysis of acetabular anteversion and abduction. Skeletal Radiol 2006;35:385-389.
24. Byrd JW, Jones KS. Arthroscopic management of femoroacetabular impingement: Minimum 2-year follow-up. Arthroscopy 2011;27:1379-1388. 25. Ejnisman L, Philippon MJ, Lertwanich P. Acetabular labral tears: Diagnosis, repair, and a method for labral reconstruction. Clin Sports Med 2011;30:317-329. 26. Bedi A, Dolan M, Magennis E, Lipman J, Buly R, Kelly BT. Computer-assisted modeling of osseous impingement and resection in femoroacetabular impingement. Arthroscopy 2012;28:204-210. 27. Reichenbach S, Juni P, Nuesch E, Frey F, Ganz R, Leunig M. An examination chair to measure internal rotation of the hip in routine settings: A validation study. Osteoarthritis Cartilage 2010;18:365-371.
Purpose: To compare passive and real-time active hip range of motion (ROM) in asymptomatic collegiate pitchers, to investigate whether differences in hip morphology and ROM exist between lead and trail hips, and to relate active hip ROM during the pitch to hip morphology and femoroacetabular impingement. Methods: Eleven collegiate baseball pitchers participated in kinematic testing that involved throwing four fastball pitches while wearing a full-body inertialbased motion-capture system. Passive flexion and rotation of each hip were measured using a goniometer. Nine pitchers also underwent a computed tomography (CT) pelvic scan, from which subject-specific computer models for each hip were created. Morphologic measurements were calculated from the models, and the models were tested for impingement during simulated pitching. Results: Hip flexion was the only passive ROM measurement showing a significant difference between the lead and trail hips (mean difference [MD], 4 ; P ¼ .027). During the pitching motion, within-individual differences were discovered between the lead and trail hips for flexion (MD, 34 ; P < .0001), extension (MD, 26 ; P < .0001), abduction (MD, 8 ; P ¼ .026), adduction (MD, 6 ; P ¼ .008), external rotation (MD, 20 ; P ¼ .001), and total arc of rotation (MD, 13 ; P ¼ .001). There were no significant differences in morphologic measures between the lead and trail hips. Dynamic CT modeling did not lead to bony impingement in any subject. Conclusions: Asymptomatic collegiate pitchers approach their extremes of passive hip rotation when executing a fastball pitch. No differences were found in passive hip ROM or morphology other than a small difference in passive hip flexion. Dynamic CT modeling did not show femoroacetabular impingement during the pitching motion. Clinical Relevance: Hip dysmorphology or poor pitching mechanics may lead to a high risk of bony impingement because pitchers have little reserve hip motion during the fastball pitch.
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roin and hip pain is experienced by a substantial proportion of athletes, with 23% of high-level male athletes reporting symptomatic hip pathology during the preceding year of training.1 With improvements in clinical diagnosis and imaging, a surprisingly high incidence of prearthritic hip deformity has been discovered in athletes. A recent study of elite soccer players reported radiographic evidence of femoroacetabular impingement (FAI) in the form of a cam or
From the Sports Medicine and Shoulder Service, Department of Orthopaedic Surgery (E.A.C., J.R.R., A.B.), and School of Kinesiology (D.W., J.M.D., G.C.G.), University of Michigan, Ann Arbor, Michigan; and Broward Orthopedic Specialists (J.R.R.), Fort Lauderdale, Florida, U.S.A. The authors report the following potential conflict of interest or source of funding: A.B. receives support from Smith & Nephew and A3 Surgical. Received February 9, 2015; accepted November 20, 2015. Address correspondence to Eileen A. Crawford, M.D., Bayhealth Orthopaedic Surgery, 655 Bay Rd, Ste F1, Dover, DE 19901, U.S.A. E-mail: [email protected] Ó 2016 by the Arthroscopy Association of North America 0749-8063/15123/$36.00 http://dx.doi.org/10.1016/j.arthro.2015.11.052
pincer lesion in 72% of the male and 50% of the female athletes.2 Another study reported that 89% of skeletally mature basketball players had an alpha angle greater than 55 , compared with 9% of non-athletes in the control group. Furthermore, hip internal rotation was significantly lower in the basketball players compared with the non-athletes, a difference that increased with age.3 Although it may be expected that athletes would have hip pain and injury from the significant physical demands of athletic competition, it is yet unclear why athletes would be more likely to have abnormal hip morphology and if unique athletic demands on each hip may predispose to symptoms. Theories focus on the adaptability of bone, particularly in the young athlete, to remodel in response to repetitive stresses.4,5 Athletes who specialize in a specific sport at a young age may be excessively subjecting their bones to repetitive activities characteristic of that sport.2,5 Morphologic adaptations may be accentuated in athletes who perform an asymmetrical activity using a dominant extremity6; for example, the dominant upper extremity of adolescent
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female tennis players shows higher bone mineral density than the nondominant upper extremity, and this difference is correlated with starting age of playing and training intensity.7,8 Similarly, baseball pitchers frequently execute an asymmetrical, high-force throwing motion during their athletic careers. The effects of repetitive throwing on the proximal humeral physis and the glenohumeral ligaments and capsule are well known,9,10 but with greater understanding of the kinetic chain, attention has turned to hip motion, lumbopelvic motion, and core musculature in pitchers as well. In the propulsive phase of the pitching motion, force is initially generated by the lower extremities before being transferred through the trunk and into the pitching arm to propel the ball.11,12 Abnormal loading mechanics of the trail limb and landing pattern of the lead limb during the pitching motion can cause hip maladaptations and inefficient energy transfer, requiring the trunk and upper extremities to generate more force to maintain ball velocity.11-13 Thus hip dysmorphology and consequential reduction in terminal hip range of motion (ROM) can result in impaired performance and injuries, not only to the hip but also to structures more distal in the kinetic chain.12,14 By gaining a better understanding of both normal and abnormal hip morphology and ROM in athletes, as well as the differences between dominant and nondominant extremities during specific athletic tasks, we can recognize at-risk athletes and develop prospective injury prevention strategies. Recent studies have examined passive and active hip ROM and side-to-side differences in baseball pitchers, with somewhat conflicting results.6,11,12,14 The objectives of this study were to compare passive and real-time active hip ROM in asymptomatic collegiate pitchers, to investigate whether differences in hip morphology and ROM exist between lead and trail hips, and to relate active hip ROM during the pitch to hip morphology and FAI. We hypothesized that active ROM during the pitch would approach the maximal passive ROM, particularly for lead hip flexion and bilateral hip internal rotation; hip morphology and ROM would differ between the lead and trail lower extremities; and active hip ROM in hips with abnormal morphology would exhibit bony impingement at terminal ROM.
training room, and kinematic testing was performed in the team’s indoor practice pitching facility. On arrival at the testing site, subjects gave written informed consent and completed a questionnaire regarding injury history. Each subject then dressed in a full-body inertial-based motion-capture system suit (Xsens MVN BIOMECH; Xsens, Enschede, Netherlands), which recorded at 120 Hz (Fig 1). The motion-tracking sensors (mass, 0.03 kg; dimensions, 0.038 0.053 0.021 m) were contained in the Lycra suit and additionally secured with athletic wrap around the lower legs, thighs, and throwing arm to minimize any movement artifacts during the pitch. The accuracy of this inertial-based motion-capture system has been validated against established electromagnetic and optoelectronic tracking systems for human movement.15,16 Passive ROM Testing Each subject was first examined in the training room for passive ROM. The subject was positioned supine on the examination table. The pelvis was secured to the examination table with a strap across the anterior superior iliac spine to prevent pelvic motion. The same
Methods Before commencement, this study received approval from the institutional review board. Eleven Division I collegiate baseball pitchers were recruited for participation in this study. Pitchers who reported previous hip surgery and those who were unable to complete standard pitching practice because of injuries were excluded. All testing occurred in the university baseball complex. Passive ROM testing was performed in the
Fig 1. Subject wearing full-body inertial-based motioncapture system suit during kinematic testing.
HIP KINEMATICS IN ELITE BASEBALL PITCHERS
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order before each pitch. Only the data from the four designated fastball pitches were used for this study; the data for the remaining pitches were used for a separate study. The kinematic data collected from the suit were transmitted directly to the accompanying computer software (Xsens). The ROM data extracted from the kinematic testing included maximal hip flexion, extension, adduction, abduction, internal rotation, and external rotation during the pitching motion (wind-up to follow-through). Total arc of rotational motion was calculated as the sum of internal and external rotation.
Fig 2. Passive range-of-motion testing was completed with the subject resting supine and the pelvis secured to the examination table. One study team member positioned the extremity while another took measurements with a goniometer.
study team member (J.M.D.) measured the passive ROM of each hip using a goniometer while the hip was positioned at the terminal end of motion for each position by one of two other study team members (E.A.C., D.W.) (Fig 2). Each hip was tested for flexion, internal rotation in extension, external rotation in extension, internal rotation in 90 of flexion, and external rotation in 90 of flexion. For rotational testing in extension, the knees were flexed over the end of the examination table and the pelvis remained secured to the table. Total arc of motion was calculated as the sum of internal and external rotation in 90 of knee flexion. The arm of the goniometer was aligned with the diaphysis of the femur for hip flexion measurements and with the diaphysis of the tibia for rotational measurements. Each measurement was performed three times, and the mean standard deviation of the recorded values was calculated. Kinematic Testing After passive ROM testing, subjects proceeded to the pitching mound for kinematic testing. Before data collection, each subject was asked to replicate the standard game-day warm-up, which generally involved whole-body stretches and throwing progression. All pitches were performed on a regulation National Collegiate Athletic Association pitching mound and directed to a catcher positioned at regulation distance (60 ft 6 in) from the pitcher’s rubber. Pitchers threw a total of 16 pitches, 4 each of fastball, curveball, slider, and change-up pitches, assigned to the pitcher in random
Morphologic Testing Nine of the 11 pitchers also consented to highresolution computed tomography (CT) scans of the pelvis and distal femur. Two subjects declined to consent to the CT scan for unsolicited reasons, so they were excluded from this portion of the study. All CT scans were performed at the same hospital using a standardized, low-dose CT protocol previously described for characterizing hip bony morphology.17 This CT protocol involves 0.625-mm slice-thickness reconstruction of 2.5-mm slices and includes an algorithm designed by GE Healthcare (Waukesha, WI) to further reduce the radiation dose by 20%, resulting in a 2.85-mSv dose to the hip and a 0.075-mSv dose to the knee. By use of computer-assisted modeling of the three-dimensional reconstructions (DYONICS PLAN; Smith & Nephew, Andover, MA), subject-specific dynamic models of the bony anatomy of the lead and trail hips for each subject were created. The software calculated the following morphologic measurements from each model: femoral neck version, femoral neck-shaft angle, alpha angle at all positions along the clock face, acetabular version, and lateral center-edge angle. The models were moved through the ROM to determine maximal passive hip flexion, internal rotation in 90 of flexion, and internal rotation combined with 90 of flexion and 15 of adduction (FADIR position). The unique ROM requirements during a pitch, as determined for each individual from the kinematic testing, were subsequently used to determine if bony impingement (contact between the acetabulum and the femoral head-neck junction) occurred in the CT model during a simulated pitch for that subject. This bony impingement could occur from a focal region of abnormal femoral head-neck offset contacting the acetabular rim (camtype impingement) or from focal or global acetabular overcoverage contacting a normal femoral head-neck junction (pincer-type impingement). Statistical Analysis Statistical analysis was performed with SPSS software (version 10.0; SPSS, Chicago, IL). Means and standard deviations were calculated for the overall study group
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Table 1. Passive ROM for Lead and Trail Hips for All Subjects Mean Passive ROM (N ¼ 11) Flexion, IR in 0 of extension, ER in 0 of extension, IR in 90 of flexion, ER in 90 of flexion, Total arc of rotation in extension, Total arc of rotation in flexion,
Lead Hip 114 8 29 6 25 7 33 7 32 8 54 10
Trail Hip 118 8 29 3 23 5 31 6 32 5 52 7
P Value .027* .796 .217 .307 .927 .126
66 11
63 8
.431
NOTE. Data are presented at mean standard deviation. ER, external rotation; IR, internal rotation; ROM, range of motion. *Statistically significant.
for passive ROM parameters, active ROM parameters, and morphologic data for the lead and trail hips. Comparisons between the lead and trail hips were performed using a two-tailed paired t test and presented with mean differences (MDs) and effect sizes (d) to aid interpretation. In accordance with Cohen’s scale,18 effect sizes were considered either small (<0.2), medium (0.5), or large (>0.8). The level of significance for all statistical analyses was set at P .05.
Results The mean age of the subjects at the time of the study was 20.4 years (SD, 1.6 years). The mean height of the subjects was 191.4 cm (SD, 6.0 cm), and the mean weight was 92.9 kg (SD, 8.0 kg). There were 8 righthanded pitchers and 3 left-handed pitchers; all 11 used a standard over-arm action. Descriptive statistics for passive ROM are reported in Table 1. When the lead and trail hips within subjects were compared, hip flexion was the only passive ROM measurement that showed a significant difference (MD, 4 ; P ¼ .027, d ¼ 0.78). Table 2 reports the means and standard deviations for requisite motion during the pitch. Several statistically Table 2. Active ROM for Lead and Trail Hips for All Subjects Mean Active ROM (N ¼ 11) Flexion, Extension, Abduction, Adduction, Internal rotation, External rotation, Total arc of rotation,
Lead Hip 84 14 13 3 38 8 17 6 33 10
Trail Hip 50 11 38 5 46 6 11 5 26 11
P Value .001 .001 .026 .008 .064
13 5
33 11
.001
46 8
59 10
.001
NOTE. Data are presented at mean standard deviation. ROM, range of motion.
significant within-individual differences were discovered in the requisite ROM between the lead and trail hips: flexion (MD, 34 ; P < .0001, d ¼ 2.16), extension (MD, 26 ; P < .0001, d ¼ 5.46), abduction (MD, 8 ; P ¼ .026, d ¼ 0.79), adduction (MD, 6 ; P ¼ .008, d ¼ 1.00), external rotation (MD, 20 ; P ¼ .001, d ¼ 1.46), and total arc of rotation (MD, 13 ; P ¼ .001, d ¼ 1.31). Although internal rotation was not significantly different between the lead and trail hips, it did display a medium to large effect size (d ¼ 0.63). The mean values for the CT morphology parameters are reported in Table 3. These values exclude the two subjects who did not consent to CT scans. The mean maximal alpha angle was located at 1:30 on the clock face. There were no significant differences in morphologic measures between the trail and lead legs when compared within individuals. Dynamic CT modeling using the maximal ROM parameters during the pitching motion did not lead to bony impingement in any of the subjects.
Discussion The results of this study show that active hip rotation required for the fastball pitchdspecifically, internal rotation of the lead hip and external rotation of the trail hipdapproaches terminal passive hip rotation in asymptomatic collegiate pitchers. Pitchers generate acceleration from the wind-up and stride phases of the pitching sequence,19,20 where hip and pelvic motion plays an important role. During the wind-up, the lead hip flexes, adducts, and internally rotates, thereby placing it at risk of anterior-superior impingement. As the pitcher moves into the stride phase, the pelvis and trunk accelerate forward while the trail hip extends, abducts, and externally rotates. With this motion, the Table 3. CT Morphology Parameters for Lead and Trail Hips for All Subjects With CT Scans CT Morphology Parameter (n ¼ 9) Femoral version, Femoral neck-shaft angle, Maximum alpha angle, Maximum acetabular anteversion, Lateral center-edge angle, Simulated maximum hip flexion, Simulated maximum IR in 90 of flexion, Simulated maximum IR in FADIR,
Lead Hip 21 12 133 4
Trail Hip 20 12 133 3
P Value .868 .791
58 8 17 4
59 7 17 3
.637 > .99
32 6
30 7
.154
117 13
119 13
.137
34 21
37 20
.259
24 20
27 20
.311
NOTE. Data are presented at mean standard deviation. CT, computed tomography; FADIR, flexioneadductioneinternal rotation position; IR, internal rotation.
HIP KINEMATICS IN ELITE BASEBALL PITCHERS
trail hip is at risk of anterior rotational instability.13,14 The lead hip also abducts and externally rotates during the stride; however, the follow-through involves flexion, adduction, and internal rotation at the hip, providing another opportunity for anterior-superior impingement.13,14 The pitchers in this study approached their passive rotational limits during the fastball pitch, suggesting an absence of any reserve motion and a high risk of bony impingement with any pathomorphology of the hip or poor pitching mechanics and pelvic control. The lead and trail legs have distinct roles and motion sequences in the baseball pitch. The significant differences and effect sizes in maximal requisite ROM parameters between the lead and trail legs reported in this study corroborate this observation. This finding is important to keep in mind when one is considering surgical treatment of FAI in baseball athletes, because a successful clinical outcome is often predicated on an improvement in ROM that allows the athlete to
Fig 3. Hip angles of lead (upper) and trail (lower) legs throughout phases of pitching motion. The curves represent the means of all subjects.
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complete a specific task. The fact that internal rotation differences did not reach statistical significance may indicate that motion in that direction is high for both hips, albeit at separate phases of the pitching motion (Fig 3). The effect size of 0.63 does suggest that there may be a clinically meaningful difference in active internal rotation between the lead and trail hips with greater motion in the lead hip, even though the difference did not quite reach statistical significance. Despite the asymmetrical nature of the pitching motion, the data in this study show that hip flexion is the only passive ROM parameter that exhibits a statistically significant difference between the lead and trail hips of an individual pitcher. This difference in mean hip flexion for the lead and trail hips is only 4 , which may not be a clinically significant difference. In addition, the various radiographic measures of osseous hip morphology did not show any differences between the lead and trail hips of an individual pitcher. Several recent studies have examined hip ROM for the lead and
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trail lower extremities in baseball pitchers, with somewhat conflicting results. Ellenbecker et al.6 found no significant differences between the lead and trail hips in passive or active ROM for 101 professional baseball pitchers. Active ROM in their study, however, was measured on the examination table rather than during an in vivo functional task, such as the pitching motion used herein. The authors did report that 42% of pitchers had a difference of at least 10 of external rotation between the lead and trail hips, although this finding was not statistically significant.6 In contrast, Robb et al.11 studied passive ROM in 19 professional baseball pitchers and reported that the lead hip had significantly less internal rotation, external rotation, and adduction than the trail hip. They suggested that differences in measurement technique between their study and that of Ellenbecker et al. may have accounted for their contrary findings. Additional studies have supported the finding that the lead and trail hips in baseball pitchers show symmetrical passive ROM, although differences exist among pitchers and position players at the same level of competition.12,14 However, from an FAI perspective, it is somewhat difficult to derive any direct clinical or practical applications from this body of work because researchers have failed to appraise ROM during the task in which impingement is expected to occurdpitching. By quantifying bilateral hip ROM in the pitching motion, our study provides a framework for clinicians and coaches to better understand the hip mechanics that characterize a sportspecific movement. This study is also unique in examining CT-based, three-dimensional bony morphology of both hips in these athletes and correlating with the observed passive and active ROM. There were no morphologic differences between the lead and trail hips, offering little support for the theory that the repetitive and asymmetrical stress of the pitching motion may distinctly and asymmetrically affect hip morphology. However, the data show some interesting characteristics of the hips in collegiate pitchers. The mean femoral anteversion of 20.4 is high compared with the normal range in the general population of 8 to 10 .21,22 Increased femoral anteversion allows for additional internal rotation of the hip before bony contact occurs, which may be a favorable trait in pitchers because they approach terminal passive internal rotation during the pitch. Of course, increased femoral anteversion also means that bony contact occurs sooner in external rotation. Acetabular anteversion is on the lower end of the normal range23 in these pitchers, which would temper the effect of increased femoral anteversion. Finally, cam morphology was observed frequently in these pitchers (Fig 4). The mean maximal alpha angle was 58 , with five pitchers (56%) having a maximal alpha angle greater than 55 in both hips and one pitcher (11%) having a maximal alpha angle greater
Fig 4. Computed tomography image of one subject showing bilateral cam deformities (arrows).
than 55 in one hip. This finding supports previous reports of a high incidence of radiographic signs of FAI in soccer and basketball athletes.2,3 The cam morphology was not found to be clinically relevant for these subjects, however, because the cam lesion did not impinge on the acetabulum during simulated ROM. Similarly, markers of pincer morphologydacetabular version and lateral center-edge angledwere not so abnormal as to cause bony impingement during the pitching motion. Hip dysmorphology does not necessarily result in bony impingement, even with extreme motions such as pitching, and therefore can be asymptomatic. Although further studies are necessary, the results suggest that whereas repetitive microtrauma at the end ranges of motion may occur in throwing athletes with FAI, the specific combination of motion that results in FAI (i.e., simultaneous maximal flexion and maximal internal rotation) is not necessarily required for pitching. The etiology of FAI in these athletes may reflect unique forces of the developing physis but may not be the consequence of repetitive microtrauma to the head-neck junction and/or acetabular chondrolabral complex. CT-based hip models simulating the pitch did not show bony impingement at the extremes of motion in our group of pitchers. This discrepancy highlights the concept that FAI, and the development of symptomatic FAI, is more than just a consequence of abnormal bony morphology. As Byrd and Jones24 discussed, FAI is a morphologic variant that does not cause hip pain but rather predisposes individuals to the development of intra-articular hip pathology. The labrum, hip capsule, and surrounding musculature all affect hip ROM and mechanics, including the distribution of forces in the hip joint.25 FAI is a dynamic process involving abnormal compressive and shear forces within the hip joint.26 The CT model used in this study does not take into account the forces acting on the hip as it moves through the ROM of the pitch. Future studies that incorporate the mechanical forces within the hip during
HIP KINEMATICS IN ELITE BASEBALL PITCHERS
athletic activities will greatly add to our understanding of why symptoms develop in some athletes with FAI morphology but not in others. Limitations The limitations of this study include the small sample size and differences in how active and passive ROM values were expressed. The paucity of statistically significant differences between the lead and trail hips may be a result of the study being underpowered. However, elite athletic populations are always relatively small by nature of the availability and accessibility of this group, and our results regarding passive ROM are consistent with most of the similar studies referenced earlier, even with different techniques for measuring ROM.6,12,14 Future research on morphologic characteristics will help determine if the similarities between the lead and trail hips found in this study will bear out in larger groups and different types of athletes. When comparing active and passive ROM in this study, one should note that the hip postures are similar but not equivalent. Passive hip rotation was measured in either 0 of hip extension or 90 of hip flexion because the examiner can be more consistent when taking measurements in orthogonal planes. In contrast, the maximal active hip rotation was measured by the sensors in the motioncapture suit and thus could occur in any degree of hip flexion or extension. Despite this difference, the data may be most clinically useful in this format because clinicians tend to measure ROM on physical examination in a similar manner. In addition, because subjects were supine for passive ROM measurements, variations in lumbar lordosis could affect hip ROM measurements, even with the pelvis stabilized. Although Reichenbach et al.27 found the seated position to be more precise for measuring hip ROM, it had a strong correlation with measurements in the supine position. The precision of our supine technique may be better than that reported in the article by Reichenbach et al. because we stabilized the pelvis against the examination table with a strap, which was not done in their technique.
Conclusions Asymptomatic collegiate pitchers approach their extremes of passive hip rotation when executing a fastball pitch. No differences were found in passive hip ROM or morphology other than a small difference in passive hip flexion. Dynamic CT modeling did not show FAI during the pitching motion.
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24. Byrd JW, Jones KS. Arthroscopic management of femoroacetabular impingement: Minimum 2-year follow-up. Arthroscopy 2011;27:1379-1388. 25. Ejnisman L, Philippon MJ, Lertwanich P. Acetabular labral tears: Diagnosis, repair, and a method for labral reconstruction. Clin Sports Med 2011;30:317-329. 26. Bedi A, Dolan M, Magennis E, Lipman J, Buly R, Kelly BT. Computer-assisted modeling of osseous impingement and resection in femoroacetabular impingement. Arthroscopy 2012;28:204-210. 27. Reichenbach S, Juni P, Nuesch E, Frey F, Ganz R, Leunig M. An examination chair to measure internal rotation of the hip in routine settings: A validation study. Osteoarthritis Cartilage 2010;18:365-371.