Knee Surg Sports Traumatol Arthrosc DOI 10.1007/s00167-013-2777-4
HIP
Herniation pits as a radiographic indicator of pincer-type femoroacetabular impingement in symptomatic patients Hyung-Min Ji • Ji-Hoon Baek • Kyoung-Woon Kim Ji-Woong Yoon • Yong-Chan Ha
•
Received: 18 May 2013 / Accepted: 11 November 2013 Ó Springer-Verlag Berlin Heidelberg 2013
Abstract Purpose The role of herniation pits as a radiographic indicator is still debated. This case–control study was to determine (1) the prevalence and sizes of herniation pits and (2) the relationship between herniation pits and femoral and acetabular bony morphology consistent with femoroacetabular impingement. Methods This comparative study was performed on 151 patients (151 hips; median patient age 46 years; range 16–73 years) with mechanical symptoms, who underwent multi-detector computed tomography (MDCT) arthrography (the symptomatic group), and an age-, gender-, site (left or right)-, and time (at diagnosis)-matched group of control patients that underwent multi-detector computed tomography due to an ureter stone (the asymptomatic group). Two orthopaedic surgeons reviewed images to evaluate the prevalence, sizes of herniation pits, and relationship with morphological abnormality. Results The prevalences of herniation pits in symptomatic and asymptomatic groups were 23.8 % (36/151) and 3.3 % (5/151), respectively (OR 9.14, 95 % CI 3.47–24.30; p \ 0.001). Herniation pits were found to be significantly associated with pincer-type abnormality (p = 0.034), especially central acetabular retroversion (p \ 0.001).
H.-M. Ji Department of Orthopedic Surgery, Ajou University School of Medicine, Suwon, Gyeonggi-do, South Korea J.-H. Baek K.-W. Kim J.-W. Yoon Y.-C. Ha (&) Department of Orthopaedic Surgery, Chung-Ang University College of Medicine, 224-1 Heukseok-dong, Dongjak-ku, Seoul 156-755, South Korea e-mail: [email protected]
Conclusions This study shows that the prevalence of herniation pits is higher in symptomatic patients with femoroacetabular impingement, and herniation pits are associated with central acetabular retroversion. Furthermore, herniation pits were also found to be a useful predictor of pincer-type femoroacetabular impingement. Level of evidence III. Keywords Acetabular retroversion Femoroacetabular impingement Herniation pit Pincer-type abnormality
Introduction Herniation pits (HPs) of the femoral neck were first described in 1982 by Pitt et al. [17]. Recently, several studies have reported high prevalences of HPs in patients with femoroacetabular impingement (FAI) and that HPs are a radiographic indicator of FAI [2, 11, 15, 19]. However, clinical implications of HPs are still disputed [9, 13, 17]. Some studies have concluded that HPs are normal variations and that an incidental finding of HPs is not related to the presence of FAI [9, 13, 17]. Therefore, a case-control study was designed in patients with mechanical symptoms, such as, groin pain, clicking, locking, and giving way, which are well known to be related to FAI [16]. The purpose of this study was to determine differences between patients with and without mechanical symptoms in terms of the prevalences and sizes of HPs and to determine the nature of the relation between HPs and femoral and acetabular morphology consistent with femoroacetabular impingement.
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Imaging protocols
head–neck junction to minimize the likelihood of damage to the acetabular labrum or articular cartilage, and 10–12 ml of mixed meglumine ioxitalamate–saline solution (13 ml meglumine ioxitalamate (Telebrix 30 Meglumine; Guerbet, Aulnay-sous-Bois, France) in 7 ml of normal saline) was injected. CT scans were obtained using a 16-channel (Mx 8000 IDT, Philips Medical Systems, Best, Netherlands) or a 64-channel multidetector CT system (Brilliance 64, Philips Medical Systems, Best, Netherlands) using the following standard acquisition protocols. For 16-channel MDCT: rotation speed 0.75 s per rotation, 240 mAs, 120 kVp, collimation 2.5 mm, field of view at acquisition 15 cm, slice thickness 1.0 mm, and slice increment 0.5 mm (50 % section overlap). For 64-channel MDCT: rotation speed 0.75 s per rotation, 300 mAs, 140 kVp, collimation 0.625 mm, field of view at acquisition 30 cm, slice thickness 0.67 mm, and slice increment of 0.33 mm (50 % section overlap). This high-resolution isotropic CT volume allowed image reformation in any desired plane without degrading image quality. Routinely, coronal, sagittal, and oblique axial images (parallel to the femoral neck axis) were reconstructed using Rapidia 2.8 workstation (INFINITT healthcare, Seoul, Korea) after axial scanning.
CT arthrography
CT reformations in the control group
Under fluoroscopic observation in the supine position, a 22-gauge needle was inserted just below the femoral head at the head and neck junction such that the needle tip was placed inside the affected hip joint at the femoral
Raw data from abdominal and pelvic CT scans, performed on a 16-channel (Mx 8000 IDT, Philips Medical Systems, Best, Netherlands) or 64-channel multi-detector CT system (Brilliance 64, Philips Medical Systems, Best, Netherlands) using standard acquisition protocols, were reformatted using a bone algorithm, as follows: (1) Orthogonal axial plane through the pelvic and hip joints; (2) Oblique coronal and axial planes along the plane of the femoral neck for each hip; (3) Transparent three-dimensional rotational model of the whole pelvis (simulating a pelvic radiograph), allowing anterior/posterior and lateral rotation; and (4) 360° rotational three-dimensional model along the axis through the centre of the femoral neck for each hip.
Materials and methods All patients were informed that their medical data could be used in a scientific study and provided consent. Between 2007 and 2010, 151 patients (151 hips) with a complaint of a mechanical symptom, such as groin pain, clicking, locking, or giving way, for minimum of 3 months and positive signs by physical examination, which included the impingement test, the log-roll test, and the FABER test, underwent multi-detector computed tomography (MDCT) arthrography. There were 68 men and 83 women of median age at time of diagnosis of 46 years (range 16–73 years) (Table 1). The 151 asymptomatic subjects were matched with the 151 symptomatic subjects for gender, age (within 1 year), site (right or left), time of CT examination (within 6 months), and type of CT (16 or 64 channel). In addition, body mass index and the University of California Los Angeles (UCLA) activity-level rating [1] were evaluated between the two groups (Table 1). The indications for the control group were pain due to a ureter stone and a diagnostic abdominal and pelvic CT scan. Controls reported no hip-related problems in reply to appropriate questions.
Table 1 Demographics of the symptomatic and asymptomatic groups Symptomatic group
Asymptomatic group
p value
Number
151
151
Gender (M/F)
68/83
68/83
n.s.
Age (year) (median ± SD)
46 ± 12.0
46 ± 12.0
n.s.
Body mass index (mean ± SD)
24.3 ± 3.1
24.2 ± 2.9
n.s.
UCLA activity
5.2 ± 2.1
4.8 ± 2.4
n.s.
Lateral CE (°) (mean ± SD)
35.6 ± 9.0
31.8 ± 7.6
\0.001
Cranial anteversion (°) (mean ± SD)
3.6 ± 7.9
7.4 ± 8.4
\0.001
Central anteversion (°) (mean ± SD)
10.5 ± 7.3
17.8 ± 6.1
\0.001
Alpha (°) (mean ± SD)
44.8 ± 8.9
40.1 ± 8.7
\0.001
SD standard deviation, UCLA the University of California Los Angeles, CE centre-edge
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Assessment of HP factors HPs were defined as cystic lesions in the femoral head beneath the anterior cortex of size C2 mm, as determined using the method devised by Panzer et al. [15]. To determine HP sizes, the largest observed lesions were used when sizes differed in axial, coronal, sagittal, and oblique axial planes. Furthermore, HPs were dichotomized by size for statistical analysis. HPs larger than the median value ([7.4 mm) were assigned to the large HP group and those of B7.4 mm to the small HP group.
Knee Surg Sports Traumatol Arthrosc
Fig. 1 Assessment parameters with MDCT arthrography (a) Lateral centre-edge angle (the angle formed by a vertical line and a line connecting the femoral head centre with the lateral edge of the acetabulum), (b) Alpha angle (the angle formed by the femoral neck axis and a line connecting the centre of the femoral head with the point of beginning asphericity), (c) Central acetabular version (the
angle made by a line connecting the anterior and posterior rims of the acetabulum and a line extending anteriorly from the posterior wall, perpendicular to the transverse plane of the pelvis, as measured at a point corresponding to the 3 o’clock position on the femoral head), and (d) Cranial acetabular version. (Acetabular version as measured at a point corresponding to the 1 o’clock position on the femoral head)
Assessments of radiological factors
versions were measured as described by Reynolds et al. [18], who classified acetabular versions as either cranial or central. Cranial acetabular version angles were measured at a point corresponding to the 1 o’clock position on the femoral head, and a measurement of\0° was considered to indicate retroversion [6, 18]. Central acetabular retroversion was measured at a point corresponding to the 3 o’clock position on the femoral head, and a measurement of \10° was considered to indicate retroversion [6, 18].
Alpha angle, lateral centre-edge angle, and cranial/central acetabular version were measured by MDCT (Fig. 1). Alpha angles were measured as described by Notzli et al. [14], and cam-type deformity was considered present for alpha angles of [50°[14]. Lateral centre-edge angles were measured as described by Wiberg [22], and overcoverage was defined as a centre-edge angle [39 [21]. Acetabular
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Assessment of clinical factors Relations between HPs and symptom duration and impingement test results were assessed. The design and protocol of this retrospective study were approved by the institutional review board of our hospital (IRB approval, Chung-Ang University Hospital, C2010120(416)).
cases among the 70 without structural bony abnormalities in the asymptomatic group. The presence of HPs was found to be significantly associated with the presence of pincertype abnormality (p = 0.034) and gender (p = 0.027) Table 2 Comparisons of prevalence and morphologic characteristics of HPs between the symptomatic and asymptomatic groups Symptomatic group (151 hips) Number (%)
Asymptomatic group (151 hips) Number (%)
p value
36/151 (23.8)
5/151 (3.3)
\0.001
Small (\7.4 mm)
17
3
n.s.
Large (C7.4 mm)
19
2
n.s.
Prevalence of FAI/TN
120/151 (79.4)
81/151 (53.6)
\0.001
Prevalence of HPs/FAI
28/120 (23.3)
3/81 (3.7)
\0.001
Cam
1/10
1/21
n.s.
Pincer Mixed
25/89 2/19
1/56 1/3
\0.001 n.s.
Statistical analysis Two blinded reviewers (KKW and HYC) independently reviewed the MDCTA scans of the 151 symptomatic patients on two separate occasions; there was no communication between the reviewers. MDCTA data were presented to reviewers in random order, and presentation orders were changed for repeat sessions. Interobserver and intraobserver reliabilities of the prevalences and sizes of HPs, and of the four measured radiological parameters (alpha angle, lateral centre-edge angle, central acetabular anteversion, and cranial acetabular anteversion) were assessed using correlation coefficients. Intraclass correlation coefficients were interpreted as follows: \0.20, slight agreement; 0.21–0.40, fair agreement; 0.41–0.60, moderate agreement; 0.61–0.80, substantial agreement; and [0.80, almost perfect agreement [12]. The v2 test was used to analyse categorical variables and the two sample t test to analyse numerical variables. All reported p values are two sided, and p values of \0.05 were deemed significant. Data were analysed using SPSS 16.0 (SPSS, Chicago, Illinois).
Results The prevalences of HPs in symptomatic and asymptomatic groups were 23.8 % (36/151) and 3.3 % (5/151), respectively (OR 9.14, 95 % CI 3.47–24.30; p \ 0.001) (Table 2). One hundred and twenty of the 151 symptomatic hips (79.4 %) had a structural bony abnormality. Of 120 structural bony abnormalities in symptomatic groups, 28 HPs were found. One HP was found in 10 hips of the isolated cam type, 25 HPs were found in 89 hips of the isolated pincer type, and two HPs were found in 19 hips of the mixed type (Table 2). Eighty-one of the 151 asymptomatic hips (53.6 %) had a structural bony abnormality. Of 81 structural bony abnormalities in asymptomatic groups, 3 HPs were found. One HP was found in the 21 hips of the isolated cam type, and one HP was found in 56 hips of the isolated pincer type (Table 2). Herniation pits were found in six cases among the 31 without structural bony abnormalities in the symptomatic group and in three
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Prevalence of HPs/TN Size (mm)
TN total number (151 hips), HPs herniation pits, FAI femoroacetabular impingement
Table 3 Comparisons of structural abnormalities in hips with and without HPs
Number
HP group Number (%)
Non-HP group Number (%)
41 (13.2)
261 (86.8)
p value
Symptom (yes/no)
36/5
115/146
\0.001
Age (year) (mean ± SD)
46.8 ± 13.1
44.4 ± 11.7
n.s.
Gender (male/female)
25/16
111/150
0.027
Relation to FAI Cam
2
30
n.s.
Pincer
26
119
0.034
Mixed
3
22
n.s.
Normal or dysplasia
31 (75.6)
161 (61.7)
Overcoverage
10 (24.4)
100 (38.3)
Lateral centre-edge angle
n.s.
Cranial anteversion
n.s.
Retroversion
14 (34.1)
58 (22.2)
Normal
27 (65.9)
203 (77.8)
Retroversion
21 (51.2)
64 (24.5)
Normal
20 (48.8)
197 (75.5)
Normal
36 (87.8)
209 (80.1)
Abnormal
5 (12.2)
52 (19.9)
\0.001
Central anteversion
Alpha angle
n.s.
SD standard deviation, HPs herniation pits, FAI femoroacetabular impingement
Knee Surg Sports Traumatol Arthrosc
(Table 3). However, no significant intergroup difference was observed for the cam-type or mixed-type abnormality. Of the four radiographic indicators of FAI, only central acetabular retroversion showed significant difference between groups with and without HPs (p \ 0.001). Alpha angles, lateral centre-edge angles, and cranial acetabular retroversions were not significantly different between the two groups (Table 3). Sizes of HPs varied between 2.3 and 12 mm (median value 7.4 mm). Twenty of HPs were\7.4 mm, and 21 were [7.4 mm (Table 2). No significant differences were found between the groups of small HPs (2–7.4 mm) and large HPs (C7.4 mm) with respect to the all measurements, and also there are no statistical significance between clinical data and other variables. Intra- and inter-observer correlations for combinations of all measurements, except HP size, were found to be reproducible and reliable among observers (Table 4).
Discussions The most important finding of the present study was HPs as a radiographic indicator of pincer-type femoroacetabular Table 4 Interobserver and intraobserver reliabilities of radiographic parameters Measuring parameters
Interobserver reproducibility
Intraobserver repeatability
Prevalence of HPs
0.92
0.96
Size of HPs
0.57
0.75
Lateral centre-edge angle
0.90
0.95
Cranial anteversion
0.78
0.86
Central anteversion
0.79
0.90
Alpha angle
0.91
0.93
Labral tear
0.81
0.91
impingement in symptomatic patients. In spite of controversies in the role of herniation pits as a radiographic indicator, the findings of this study are consistent with those of previous studies in which HPs were identified an indicator of femoroacetabular impingement [2, 11, 20]. Although HPs are present in patients with cam and mixedtype impingement as well as in a small percentage of asymptomatic patients, HPs in this study were significantly prevalent in symptomatic patients with pincer-type impingements. In this case-control study, the prevalence of HPs (23.8 %) in the symptomatic group was greater than in the asymptomatic control group (3.3 %). Although Panzer et al. [15] reported the prevalence of herniation pit to be 42.5 % in the general population based on 200 CT scans, reports in normal populations from other studies have shown that herniation pits are incidentally found in 0–12 % of patients [5, 8–11]. Kim et al. [9] found 80 herniation pits among 4,491 patients (1.8 %) who underwent anteroposterior pelvic radiography. The reason of discrepancy of prevalence of herniation pits in general population might be related to the difference of study cohorts. However, only one observational study by Leunig et al. [11] has addressed symptomatic FAI and hips with developmental dysplasia (DD). They reported that 33 % of symptomatic FAI patients, but no DD hip, had HPs. However, the authors used a DD group as a control, which is not representative of the general population. Nevertheless, this finding suggests that HPs are significantly associated with clinical symptoms, such as groin pain, locking, giving way, and clicking. Considerable debate exists regarding the relationship between HPs and the morphologic characteristics of FAI. Although Leunig et al. [11] suggested that HPs might be a radiographic indicator of FAI, they did not suggest a specific type of FAI, such as the cam or pincer type. Panzer et al. [15] performed an observational study using 200 pelvic CT scans for the purpose of posttraumatic,
Fig. 2 Difficulty of measuring the size of herniation pits (a) herniation pits were measured to be 8.2 mm on axial plane (b) In the same patient, herniation pits were measured to be 14.8 mm on sagittal plane. There are difficulties in measuring the size consistently, because of septation or multiplicity of lesions. In our series, the largest lesion on each plane was used
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orthopaedic, internal, urological, and neurological diagnoses and identified HPs in 85 of the 200 patients. Furthermore, they reported that alpha angle was significantly larger (by 10 %) in those with HPs. Recently, Kim et al. [9] evaluated 80 HPs using pelvic anteroposterior radiographs and concluded that HPs are not a radiographic indicator of FAI but simply an incidental finding. However, our findings show that HPs seem to be related to pincer-type impingement. Most HPs (63.4 %, 26/41) in the present study were found in hips with pincer-type impingement, especially those hips with central acetabular retroversion, which is more consistent with the proposed flexion-induced pressure mechanism. Based on case reports of rapid HP growth in a ballerina and avid jogger [4], we hypothesized that a relation exists between HP size and symptoms of FAI, but no significance was found in this study. This finding might be due to the difficulty of measuring the size consistently, because of septation or multiplicity of lesion (Fig. 2). This study has several limitations that require consideration. First, the results of this study are difficult to compare directly with those of other studies, because different methods were used to measure parameters and different diagnostic criteria were used. However, the prevalences of HPs in the symptomatic and asymptomatic groups tend to agree with previously published values. Second, it can be difficult to distinguish HPs from other lesions, such as osteoid osteoma and intramedullary lipoma. Although images were closely reviewed in accord with previously mentioned criteria, the possibility of misidentification remains. Third, this was a retrospective matched case–control study, and selection bias might have been introduced when we chose members of the asymptomatic group. Nevertheless, we believe that control selection did not diminish our finding that herniation pits are closely related to symptomatic FAI, especially in cases with central acetabular retroversion. Fourth, in the present study of the 120 symptomatic hips with a structural bony abnormality, 74.2 % were of the isolated pincer type, 6.6 % had an isolated cam-type abnormality, and 12.6 % showed combined cam–pincer impingement. However, cam and pincer impingements are known to occur rarely in isolation. In one epidemiological study of 149 hips with impingement, 17 % had isolated cam impingement, 10 % had isolated pincer impingement, and 72 % had combined cam–pincer impingement [3]. These differences between studies could be due to the differences in the methods used for subject selection, the applied diagnostic criteria, gender, ethnicity, or the age of study subjects [7]. Finally, our definition of cranial retroversion (less than 0°) was not validated. Jamali et al. defined acetabular retroversion based on a radiographic crossover sign. A positive crossover sign was 96 % sensitive to cranial acetabular anteversion of \4 degrees [6]. In this study, we used the
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parameter of \0 degrees of anteversion, which may have decreased the prevalence of cranial retroversion. Despite these limitations, we were able to document the prevalence of HPs to be higher in symptomatic patients than in asymptomatic individuals.
Conclusion This study shows that the prevalence of herniation pits is higher in symptomatic patients with femoroacetabular impingement and that HPs are significantly associated with central acetabular retroversion, which is a useful radiographic indicator of pincer-type FAI. We believe that these findings increase our understanding on morphological characteristics of HPs. Conflict of interest The authors did not receive any outside funding or grants in support of their research for or preparation of this work. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, division, centre, clinical practice, or other charitable or non-profit organization with which the authors, or a member of their immediate families, are affiliated or associated.
References 1. Amstutz HC, Thomas BJ, Jinnah R, Kim W, Grogan T, Yale C (1984) Treatment of primary osteoarthritis of the hip. A comparison of total joint and surface replacement arthroplasty. J Bone Joint Surg Am 66(2):228–241 2. Beall DP, Sweet CF, Martin HD, Lastine CL, Grayson DE, Ly JQ, Fish JR (2005) Imaging findings of femoroacetabular impingement syndrome. Skeletal Radiol 34(11):691–701 3. Beck M, Kalhor M, Leunig M, Ganz R (2005) Hip morphology influences the pattern of damage to the acetabular cartilage: femoroacetabular impingement as a cause of early osteoarthritis of the hip. J Bone Joint Surg Br 87(7):1012–1018 4. Crabbe JP, Martel W, Matthews LS (1992) Rapid growth of femoral herniation pit. AJR Am J Roentgenol 159(5):1038–1040 5. Hong SJ, Shon WY, Lee CY, Myung JS, Kang CH, Kim BH (2010) Imaging findings of femoroacetabular impingement syndrome: focusing on mixed-type impingement. Clin Imaging 34(2):116–120 6. Jamali AA, Mladenov K, Meyer DC, Martinez A, Beck M, Ganz R, Leunig M (2007) Anteroposterior pelvic radiographs to assess acetabular retroversion: high validity of the ‘‘cross-over-sign’’. J Orthop Res 25(6):758–765 7. Karachalios T, Karantanas AH, Malizos K (2007) Hip osteoarthritis: what the radiologist wants to know. Eur J Radiol 63(1):36–48 8. Kassarjian A, Yoon LS, Belzile E, Connolly SA, Millis MB, Palmer WE (2005) Triad of MR arthrographic findings in patients with cam-type femoroacetabular impingement. Radiology 236(2):588–592 9. Kim JA, Park JS, Jin W, Ryu K (2011) Herniation pits in the femoral neck: a radiographic indicator of femoroacetabular impingement? Skeletal Radiol 40(2):167–172
Knee Surg Sports Traumatol Arthrosc 10. Laborie LB, Lehmann TG, Engesaeter IO, Eastwood DM, Engesaeter LB, Rosendahl K (2011) Prevalence of radiographic findings thought to be associated with femoroacetabular impingement in a population-based cohort of 2081 healthy young adults. Radiology 260(2):494–502 11. Leunig M, Beck M, Kalhor M, Kim YJ, Werlen S, Ganz R (2005) Fibrocystic changes at anterosuperior femoral neck: prevalence in hips with femoroacetabular impingement. Radiology 236(1): 237–246 12. Montgomery AA, Graham A, Evans PH, Fahey T (2002) Interrater agreement in the scoring of abstracts submitted to a primary care research conference. BMC Health Serv Res 2(1):8 13. Nokes SR, Vogler JB, Spritzer CE, Martinez S, Herfkens RJ (1989) Herniation pits of the femoral neck: appearance at MR imaging. Radiology 172(1):231–234 14. Notzli HP, Wyss TF, Stoecklin CH, Schmid MR, Treiber K, Hodler J (2002) The contour of the femoral head-neck junction as a predictor for the risk of anterior impingement. J Bone Joint Surg Br 84(4):556–560 15. Panzer S, Augat P, Esch U (2008) CT assessment of herniation pits: prevalence, characteristics, and potential association with
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morphological predictors of femoroacetabular impingement. Eur Radiol 18(9):1869–1875 Petersilge CA, Haque MA, Petersilge WJ, Lewin JS, Lieberman JM, Buly R (1996) Acetabular labral tears: evaluation with MR arthrography. Radiology 200(1):231–235 Pitt MJ, Graham AR, Shipman JH, Birkby W (1982) Herniation pit of the femoral neck. AJR Am J Roentgenol 138(6):1115–1121 Reynolds D, Lucas J, Klaue K (1999) Retroversion of the acetabulum. A cause of hip pain. J Bone Joint Surg Br 81(2):281–288 Tannast M, Siebenrock KA, Anderson SE (2007) Femoroacetabular impingement: radiographic diagnosis–what the radiologist should know. AJR Am J Roentgenol 188(6):1540–1552 Tannast M, Siebenrock KA, Anderson SE (2008) Femoroacetabular impingement: radiographic diagnosis–what the radiologist should know. Radiologia 50(4):271–284 Tonnis D, Heinecke A (1999) Acetabular and femoral anteversion: relationship with osteoarthritis of the hip. J Bone Joint Surg Am 81(12):1747–1770 Wiberg G (1939) Studies on dysplastic acetabula and congenital subluxation of the hip joint. Acta Chir Scand 83:1–135
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HIP
Herniation pits as a radiographic indicator of pincer-type femoroacetabular impingement in symptomatic patients Hyung-Min Ji • Ji-Hoon Baek • Kyoung-Woon Kim Ji-Woong Yoon • Yong-Chan Ha
•
Received: 18 May 2013 / Accepted: 11 November 2013 Ó Springer-Verlag Berlin Heidelberg 2013
Abstract Purpose The role of herniation pits as a radiographic indicator is still debated. This case–control study was to determine (1) the prevalence and sizes of herniation pits and (2) the relationship between herniation pits and femoral and acetabular bony morphology consistent with femoroacetabular impingement. Methods This comparative study was performed on 151 patients (151 hips; median patient age 46 years; range 16–73 years) with mechanical symptoms, who underwent multi-detector computed tomography (MDCT) arthrography (the symptomatic group), and an age-, gender-, site (left or right)-, and time (at diagnosis)-matched group of control patients that underwent multi-detector computed tomography due to an ureter stone (the asymptomatic group). Two orthopaedic surgeons reviewed images to evaluate the prevalence, sizes of herniation pits, and relationship with morphological abnormality. Results The prevalences of herniation pits in symptomatic and asymptomatic groups were 23.8 % (36/151) and 3.3 % (5/151), respectively (OR 9.14, 95 % CI 3.47–24.30; p \ 0.001). Herniation pits were found to be significantly associated with pincer-type abnormality (p = 0.034), especially central acetabular retroversion (p \ 0.001).
H.-M. Ji Department of Orthopedic Surgery, Ajou University School of Medicine, Suwon, Gyeonggi-do, South Korea J.-H. Baek K.-W. Kim J.-W. Yoon Y.-C. Ha (&) Department of Orthopaedic Surgery, Chung-Ang University College of Medicine, 224-1 Heukseok-dong, Dongjak-ku, Seoul 156-755, South Korea e-mail: [email protected]
Conclusions This study shows that the prevalence of herniation pits is higher in symptomatic patients with femoroacetabular impingement, and herniation pits are associated with central acetabular retroversion. Furthermore, herniation pits were also found to be a useful predictor of pincer-type femoroacetabular impingement. Level of evidence III. Keywords Acetabular retroversion Femoroacetabular impingement Herniation pit Pincer-type abnormality
Introduction Herniation pits (HPs) of the femoral neck were first described in 1982 by Pitt et al. [17]. Recently, several studies have reported high prevalences of HPs in patients with femoroacetabular impingement (FAI) and that HPs are a radiographic indicator of FAI [2, 11, 15, 19]. However, clinical implications of HPs are still disputed [9, 13, 17]. Some studies have concluded that HPs are normal variations and that an incidental finding of HPs is not related to the presence of FAI [9, 13, 17]. Therefore, a case-control study was designed in patients with mechanical symptoms, such as, groin pain, clicking, locking, and giving way, which are well known to be related to FAI [16]. The purpose of this study was to determine differences between patients with and without mechanical symptoms in terms of the prevalences and sizes of HPs and to determine the nature of the relation between HPs and femoral and acetabular morphology consistent with femoroacetabular impingement.
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Imaging protocols
head–neck junction to minimize the likelihood of damage to the acetabular labrum or articular cartilage, and 10–12 ml of mixed meglumine ioxitalamate–saline solution (13 ml meglumine ioxitalamate (Telebrix 30 Meglumine; Guerbet, Aulnay-sous-Bois, France) in 7 ml of normal saline) was injected. CT scans were obtained using a 16-channel (Mx 8000 IDT, Philips Medical Systems, Best, Netherlands) or a 64-channel multidetector CT system (Brilliance 64, Philips Medical Systems, Best, Netherlands) using the following standard acquisition protocols. For 16-channel MDCT: rotation speed 0.75 s per rotation, 240 mAs, 120 kVp, collimation 2.5 mm, field of view at acquisition 15 cm, slice thickness 1.0 mm, and slice increment 0.5 mm (50 % section overlap). For 64-channel MDCT: rotation speed 0.75 s per rotation, 300 mAs, 140 kVp, collimation 0.625 mm, field of view at acquisition 30 cm, slice thickness 0.67 mm, and slice increment of 0.33 mm (50 % section overlap). This high-resolution isotropic CT volume allowed image reformation in any desired plane without degrading image quality. Routinely, coronal, sagittal, and oblique axial images (parallel to the femoral neck axis) were reconstructed using Rapidia 2.8 workstation (INFINITT healthcare, Seoul, Korea) after axial scanning.
CT arthrography
CT reformations in the control group
Under fluoroscopic observation in the supine position, a 22-gauge needle was inserted just below the femoral head at the head and neck junction such that the needle tip was placed inside the affected hip joint at the femoral
Raw data from abdominal and pelvic CT scans, performed on a 16-channel (Mx 8000 IDT, Philips Medical Systems, Best, Netherlands) or 64-channel multi-detector CT system (Brilliance 64, Philips Medical Systems, Best, Netherlands) using standard acquisition protocols, were reformatted using a bone algorithm, as follows: (1) Orthogonal axial plane through the pelvic and hip joints; (2) Oblique coronal and axial planes along the plane of the femoral neck for each hip; (3) Transparent three-dimensional rotational model of the whole pelvis (simulating a pelvic radiograph), allowing anterior/posterior and lateral rotation; and (4) 360° rotational three-dimensional model along the axis through the centre of the femoral neck for each hip.
Materials and methods All patients were informed that their medical data could be used in a scientific study and provided consent. Between 2007 and 2010, 151 patients (151 hips) with a complaint of a mechanical symptom, such as groin pain, clicking, locking, or giving way, for minimum of 3 months and positive signs by physical examination, which included the impingement test, the log-roll test, and the FABER test, underwent multi-detector computed tomography (MDCT) arthrography. There were 68 men and 83 women of median age at time of diagnosis of 46 years (range 16–73 years) (Table 1). The 151 asymptomatic subjects were matched with the 151 symptomatic subjects for gender, age (within 1 year), site (right or left), time of CT examination (within 6 months), and type of CT (16 or 64 channel). In addition, body mass index and the University of California Los Angeles (UCLA) activity-level rating [1] were evaluated between the two groups (Table 1). The indications for the control group were pain due to a ureter stone and a diagnostic abdominal and pelvic CT scan. Controls reported no hip-related problems in reply to appropriate questions.
Table 1 Demographics of the symptomatic and asymptomatic groups Symptomatic group
Asymptomatic group
p value
Number
151
151
Gender (M/F)
68/83
68/83
n.s.
Age (year) (median ± SD)
46 ± 12.0
46 ± 12.0
n.s.
Body mass index (mean ± SD)
24.3 ± 3.1
24.2 ± 2.9
n.s.
UCLA activity
5.2 ± 2.1
4.8 ± 2.4
n.s.
Lateral CE (°) (mean ± SD)
35.6 ± 9.0
31.8 ± 7.6
\0.001
Cranial anteversion (°) (mean ± SD)
3.6 ± 7.9
7.4 ± 8.4
\0.001
Central anteversion (°) (mean ± SD)
10.5 ± 7.3
17.8 ± 6.1
\0.001
Alpha (°) (mean ± SD)
44.8 ± 8.9
40.1 ± 8.7
\0.001
SD standard deviation, UCLA the University of California Los Angeles, CE centre-edge
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Assessment of HP factors HPs were defined as cystic lesions in the femoral head beneath the anterior cortex of size C2 mm, as determined using the method devised by Panzer et al. [15]. To determine HP sizes, the largest observed lesions were used when sizes differed in axial, coronal, sagittal, and oblique axial planes. Furthermore, HPs were dichotomized by size for statistical analysis. HPs larger than the median value ([7.4 mm) were assigned to the large HP group and those of B7.4 mm to the small HP group.
Knee Surg Sports Traumatol Arthrosc
Fig. 1 Assessment parameters with MDCT arthrography (a) Lateral centre-edge angle (the angle formed by a vertical line and a line connecting the femoral head centre with the lateral edge of the acetabulum), (b) Alpha angle (the angle formed by the femoral neck axis and a line connecting the centre of the femoral head with the point of beginning asphericity), (c) Central acetabular version (the
angle made by a line connecting the anterior and posterior rims of the acetabulum and a line extending anteriorly from the posterior wall, perpendicular to the transverse plane of the pelvis, as measured at a point corresponding to the 3 o’clock position on the femoral head), and (d) Cranial acetabular version. (Acetabular version as measured at a point corresponding to the 1 o’clock position on the femoral head)
Assessments of radiological factors
versions were measured as described by Reynolds et al. [18], who classified acetabular versions as either cranial or central. Cranial acetabular version angles were measured at a point corresponding to the 1 o’clock position on the femoral head, and a measurement of\0° was considered to indicate retroversion [6, 18]. Central acetabular retroversion was measured at a point corresponding to the 3 o’clock position on the femoral head, and a measurement of \10° was considered to indicate retroversion [6, 18].
Alpha angle, lateral centre-edge angle, and cranial/central acetabular version were measured by MDCT (Fig. 1). Alpha angles were measured as described by Notzli et al. [14], and cam-type deformity was considered present for alpha angles of [50°[14]. Lateral centre-edge angles were measured as described by Wiberg [22], and overcoverage was defined as a centre-edge angle [39 [21]. Acetabular
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Assessment of clinical factors Relations between HPs and symptom duration and impingement test results were assessed. The design and protocol of this retrospective study were approved by the institutional review board of our hospital (IRB approval, Chung-Ang University Hospital, C2010120(416)).
cases among the 70 without structural bony abnormalities in the asymptomatic group. The presence of HPs was found to be significantly associated with the presence of pincertype abnormality (p = 0.034) and gender (p = 0.027) Table 2 Comparisons of prevalence and morphologic characteristics of HPs between the symptomatic and asymptomatic groups Symptomatic group (151 hips) Number (%)
Asymptomatic group (151 hips) Number (%)
p value
36/151 (23.8)
5/151 (3.3)
\0.001
Small (\7.4 mm)
17
3
n.s.
Large (C7.4 mm)
19
2
n.s.
Prevalence of FAI/TN
120/151 (79.4)
81/151 (53.6)
\0.001
Prevalence of HPs/FAI
28/120 (23.3)
3/81 (3.7)
\0.001
Cam
1/10
1/21
n.s.
Pincer Mixed
25/89 2/19
1/56 1/3
\0.001 n.s.
Statistical analysis Two blinded reviewers (KKW and HYC) independently reviewed the MDCTA scans of the 151 symptomatic patients on two separate occasions; there was no communication between the reviewers. MDCTA data were presented to reviewers in random order, and presentation orders were changed for repeat sessions. Interobserver and intraobserver reliabilities of the prevalences and sizes of HPs, and of the four measured radiological parameters (alpha angle, lateral centre-edge angle, central acetabular anteversion, and cranial acetabular anteversion) were assessed using correlation coefficients. Intraclass correlation coefficients were interpreted as follows: \0.20, slight agreement; 0.21–0.40, fair agreement; 0.41–0.60, moderate agreement; 0.61–0.80, substantial agreement; and [0.80, almost perfect agreement [12]. The v2 test was used to analyse categorical variables and the two sample t test to analyse numerical variables. All reported p values are two sided, and p values of \0.05 were deemed significant. Data were analysed using SPSS 16.0 (SPSS, Chicago, Illinois).
Results The prevalences of HPs in symptomatic and asymptomatic groups were 23.8 % (36/151) and 3.3 % (5/151), respectively (OR 9.14, 95 % CI 3.47–24.30; p \ 0.001) (Table 2). One hundred and twenty of the 151 symptomatic hips (79.4 %) had a structural bony abnormality. Of 120 structural bony abnormalities in symptomatic groups, 28 HPs were found. One HP was found in 10 hips of the isolated cam type, 25 HPs were found in 89 hips of the isolated pincer type, and two HPs were found in 19 hips of the mixed type (Table 2). Eighty-one of the 151 asymptomatic hips (53.6 %) had a structural bony abnormality. Of 81 structural bony abnormalities in asymptomatic groups, 3 HPs were found. One HP was found in the 21 hips of the isolated cam type, and one HP was found in 56 hips of the isolated pincer type (Table 2). Herniation pits were found in six cases among the 31 without structural bony abnormalities in the symptomatic group and in three
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Prevalence of HPs/TN Size (mm)
TN total number (151 hips), HPs herniation pits, FAI femoroacetabular impingement
Table 3 Comparisons of structural abnormalities in hips with and without HPs
Number
HP group Number (%)
Non-HP group Number (%)
41 (13.2)
261 (86.8)
p value
Symptom (yes/no)
36/5
115/146
\0.001
Age (year) (mean ± SD)
46.8 ± 13.1
44.4 ± 11.7
n.s.
Gender (male/female)
25/16
111/150
0.027
Relation to FAI Cam
2
30
n.s.
Pincer
26
119
0.034
Mixed
3
22
n.s.
Normal or dysplasia
31 (75.6)
161 (61.7)
Overcoverage
10 (24.4)
100 (38.3)
Lateral centre-edge angle
n.s.
Cranial anteversion
n.s.
Retroversion
14 (34.1)
58 (22.2)
Normal
27 (65.9)
203 (77.8)
Retroversion
21 (51.2)
64 (24.5)
Normal
20 (48.8)
197 (75.5)
Normal
36 (87.8)
209 (80.1)
Abnormal
5 (12.2)
52 (19.9)
\0.001
Central anteversion
Alpha angle
n.s.
SD standard deviation, HPs herniation pits, FAI femoroacetabular impingement
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(Table 3). However, no significant intergroup difference was observed for the cam-type or mixed-type abnormality. Of the four radiographic indicators of FAI, only central acetabular retroversion showed significant difference between groups with and without HPs (p \ 0.001). Alpha angles, lateral centre-edge angles, and cranial acetabular retroversions were not significantly different between the two groups (Table 3). Sizes of HPs varied between 2.3 and 12 mm (median value 7.4 mm). Twenty of HPs were\7.4 mm, and 21 were [7.4 mm (Table 2). No significant differences were found between the groups of small HPs (2–7.4 mm) and large HPs (C7.4 mm) with respect to the all measurements, and also there are no statistical significance between clinical data and other variables. Intra- and inter-observer correlations for combinations of all measurements, except HP size, were found to be reproducible and reliable among observers (Table 4).
Discussions The most important finding of the present study was HPs as a radiographic indicator of pincer-type femoroacetabular Table 4 Interobserver and intraobserver reliabilities of radiographic parameters Measuring parameters
Interobserver reproducibility
Intraobserver repeatability
Prevalence of HPs
0.92
0.96
Size of HPs
0.57
0.75
Lateral centre-edge angle
0.90
0.95
Cranial anteversion
0.78
0.86
Central anteversion
0.79
0.90
Alpha angle
0.91
0.93
Labral tear
0.81
0.91
impingement in symptomatic patients. In spite of controversies in the role of herniation pits as a radiographic indicator, the findings of this study are consistent with those of previous studies in which HPs were identified an indicator of femoroacetabular impingement [2, 11, 20]. Although HPs are present in patients with cam and mixedtype impingement as well as in a small percentage of asymptomatic patients, HPs in this study were significantly prevalent in symptomatic patients with pincer-type impingements. In this case-control study, the prevalence of HPs (23.8 %) in the symptomatic group was greater than in the asymptomatic control group (3.3 %). Although Panzer et al. [15] reported the prevalence of herniation pit to be 42.5 % in the general population based on 200 CT scans, reports in normal populations from other studies have shown that herniation pits are incidentally found in 0–12 % of patients [5, 8–11]. Kim et al. [9] found 80 herniation pits among 4,491 patients (1.8 %) who underwent anteroposterior pelvic radiography. The reason of discrepancy of prevalence of herniation pits in general population might be related to the difference of study cohorts. However, only one observational study by Leunig et al. [11] has addressed symptomatic FAI and hips with developmental dysplasia (DD). They reported that 33 % of symptomatic FAI patients, but no DD hip, had HPs. However, the authors used a DD group as a control, which is not representative of the general population. Nevertheless, this finding suggests that HPs are significantly associated with clinical symptoms, such as groin pain, locking, giving way, and clicking. Considerable debate exists regarding the relationship between HPs and the morphologic characteristics of FAI. Although Leunig et al. [11] suggested that HPs might be a radiographic indicator of FAI, they did not suggest a specific type of FAI, such as the cam or pincer type. Panzer et al. [15] performed an observational study using 200 pelvic CT scans for the purpose of posttraumatic,
Fig. 2 Difficulty of measuring the size of herniation pits (a) herniation pits were measured to be 8.2 mm on axial plane (b) In the same patient, herniation pits were measured to be 14.8 mm on sagittal plane. There are difficulties in measuring the size consistently, because of septation or multiplicity of lesions. In our series, the largest lesion on each plane was used
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orthopaedic, internal, urological, and neurological diagnoses and identified HPs in 85 of the 200 patients. Furthermore, they reported that alpha angle was significantly larger (by 10 %) in those with HPs. Recently, Kim et al. [9] evaluated 80 HPs using pelvic anteroposterior radiographs and concluded that HPs are not a radiographic indicator of FAI but simply an incidental finding. However, our findings show that HPs seem to be related to pincer-type impingement. Most HPs (63.4 %, 26/41) in the present study were found in hips with pincer-type impingement, especially those hips with central acetabular retroversion, which is more consistent with the proposed flexion-induced pressure mechanism. Based on case reports of rapid HP growth in a ballerina and avid jogger [4], we hypothesized that a relation exists between HP size and symptoms of FAI, but no significance was found in this study. This finding might be due to the difficulty of measuring the size consistently, because of septation or multiplicity of lesion (Fig. 2). This study has several limitations that require consideration. First, the results of this study are difficult to compare directly with those of other studies, because different methods were used to measure parameters and different diagnostic criteria were used. However, the prevalences of HPs in the symptomatic and asymptomatic groups tend to agree with previously published values. Second, it can be difficult to distinguish HPs from other lesions, such as osteoid osteoma and intramedullary lipoma. Although images were closely reviewed in accord with previously mentioned criteria, the possibility of misidentification remains. Third, this was a retrospective matched case–control study, and selection bias might have been introduced when we chose members of the asymptomatic group. Nevertheless, we believe that control selection did not diminish our finding that herniation pits are closely related to symptomatic FAI, especially in cases with central acetabular retroversion. Fourth, in the present study of the 120 symptomatic hips with a structural bony abnormality, 74.2 % were of the isolated pincer type, 6.6 % had an isolated cam-type abnormality, and 12.6 % showed combined cam–pincer impingement. However, cam and pincer impingements are known to occur rarely in isolation. In one epidemiological study of 149 hips with impingement, 17 % had isolated cam impingement, 10 % had isolated pincer impingement, and 72 % had combined cam–pincer impingement [3]. These differences between studies could be due to the differences in the methods used for subject selection, the applied diagnostic criteria, gender, ethnicity, or the age of study subjects [7]. Finally, our definition of cranial retroversion (less than 0°) was not validated. Jamali et al. defined acetabular retroversion based on a radiographic crossover sign. A positive crossover sign was 96 % sensitive to cranial acetabular anteversion of \4 degrees [6]. In this study, we used the
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parameter of \0 degrees of anteversion, which may have decreased the prevalence of cranial retroversion. Despite these limitations, we were able to document the prevalence of HPs to be higher in symptomatic patients than in asymptomatic individuals.
Conclusion This study shows that the prevalence of herniation pits is higher in symptomatic patients with femoroacetabular impingement and that HPs are significantly associated with central acetabular retroversion, which is a useful radiographic indicator of pincer-type FAI. We believe that these findings increase our understanding on morphological characteristics of HPs. Conflict of interest The authors did not receive any outside funding or grants in support of their research for or preparation of this work. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, division, centre, clinical practice, or other charitable or non-profit organization with which the authors, or a member of their immediate families, are affiliated or associated.
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