Acetabular labral tears are a potential cause of hip pain.2,11,14 These tears are associated with trauma,12,18 classic hip dysplasia,6,15 Legg-Calve-Perthes disease,23 and osteoarthritis (OA).1 An association between more subtle structural abnormalities of the hip and labral tears has been reported.1,7,13,17 The current study is the first of which we are aware that evaluated the percentage of patients with acetabular labral tears who have a structural hip abnormality that can be detected on conventional radiographs with a comprehensive radiographic assessment.
MATERIALS AND METHODS
After appropriate institutional review board approval, a review of our institution’s surgical, computed tomography (CT), and magnetic resonance (MR) hip arthrogram reports from 1996 through 2002 was performed. Forty patients with labral tears were identified. In the review, patients were excluded who had classic hip dysplasia (Wiberg angle < 15, Tönnis angle > 15, and Lesquesne angle < 15), advanced OA (marked joint space loss), or a history of pelvic or femoral osteotomy. Nine additional patients were excluded. Two patients were excluded because the magnetic resonance imaging (MRI) scans were indeterminate for labral tears and the patients did not have surgery. Seven patients were excluded because they did not have available hip radiographs.
The labral tears were documented with CT arthrography, MR arthrography, and/or surgery as outlined in Table 1. The MRI scans available for review included high resolution, small FOV (18–22 cm) images acquired with or without intraarticular gadolinium. The examinations with intraarticular gadolinium typically included three planes (axial, sagittal, coronal) of T1-weighted images with fat saturation and one additional T2-weighted fast spin echo (FSE) image acquisition with fat saturation (axial or coronal). The MRI examinations done without gadolinium included multiplanar images (axial, coronal, and sagittal) with T1- and nonfat-saturated T2-weighted proton density images with the addition of an axial or coronal T2-weighted FSE image acquisition with fat saturation.
;)
Table 1: Method of Diagnosing Labral Tears
The MR and CT arthrograms were reviewed by two musculoskeletal radiologists to confirm the presence of a tear (KRK, DEW). Tears were defined as extension of contrast material into the labrum, detachment of the labrum from the acetabulum, or a combination of abnormal signal with abnormal thickening or abnormal morphologic features.3 Abnormal intrasubstance signal in a labrum with normal morphologic features, that did not extend to a surface, was not classified as a tear. The size and anatomic location of the tears were assessed relative to division of the labrum into four quadrants: anterosuperior, anteroinferior, posterosuperior, and posteroinferior.
The conventional radiographic review and radiographic measurements were made by consensus opinion of two musculoskeletal radiologists (KRK, DEW) and an orthopaedic surgeon (RTT). The radiographs were initially evaluated to determine if they were of adequate technical quality. We routinely obtain an AP view of the pelvis with the patient in the supine position, cross-table lateral, and standing false profile radiograph when evaluating young patients with symptomatic hip disorders. Symmetry of the trochanters was evaluated to ensure that the lower extremities were positioned appropriately in approximately 20° internal rotation for proper compensation for normal femoral neck anteversion and accurate assessment of projected neck-shaft angle. Projection of the coccyx approximately 1.0 cm above the superior aspect of the symphysis pubis was evaluated, because a position higher or lower indicates anterior or posterior tilt of the pelvis and affects the projected acetabular version. The obturator foramina were also evaluated for asymmetry that would indicate lateral rotation of the pelvis, which also alters the projected acetabular version. Cross-table lateral views were evaluated for proper patient positioning and the degree of magnification was noted. Radiographs that were determined to be of sufficient technical quality were evaluated for the presence of abnormal findings defined as Tönnis (horizontal toit externe) angle ≥ 15°; center-edge angle of Wiberg < 15°; retroversion of the acetabulum, crossover sign; neck-shaft angle < 120° or > 140°; incongruency between the femoral head and acetabulum; head-neck offset of < 7.2 mm on a cross-table lateral view of the hip; and the presence of osteophytes on the femoral head. The techniques that were used to assess the conventional radiographic parameters are shown in Figures 1–5.
Fig 1.:
An AP radiograph shows the method of measuring the Tönnis angle of the hip; the Tönnis angle is formed by the intersection of Lines 4 and 5.
Fig 2.:
An AP radiograph shows the method of measuring the center-edge angle of the hip; the center-edge angle is formed by the intersection of Lines 4 and 5.
Fig 3.:
A–B. (A) An AP radiograph of the pelvis shows normal anteversion of the acetabula bilaterally. The posterior acetabular rims are marked with a solid line and anterior acetabular rims are marked with dashed lines. (B) Retroverted acetabula bilaterally can be seen with crossing of the anterior acetabular rims (dashed lines) over the posterior acetabular rims (solid lines) on the AP radiograph of the pelvis.
Fig 4.:
An AP radiograph shows the method of measuring the femoral neck-shaft angle of the hip. The neck-shaft angle is formed by the intersection of Lines 2 and 3.
Fig 5.:
The method of measuring the anterior femoral head-neck offset using a cross-table lateral view of the hip is shown. The head and neck of the femur are outlined with a white dashed line. The anterior head-neck offset is the distance between Lines 2 and 3, taking into account a correction factor for magnification.
The Tönnis angle was determined by identifying the sourcil (Fig 1). Sourcil, meaning eyebrow, is the sclerotic, weightbearing portion of the superior acetabulum. The medial and lateral extent of the sourcil was identified and marked (Line 1). A horizontal line was then drawn along the inferior aspect of the ischial tuberosities (Line 2). After localization of the center of the femoral head (Line 3), a line parallel to Line 2 was drawn through the center of the femoral head (Line 4). A line was drawn through the medial and lateral aspects of the sourcil and connected to the horizontal Line 4 (Line 5). The intersection of Lines 4 and 5 form the Tönnis angle, which normally measures < 10°.25
The center-edge angle of Wiberg (Fig 2) was determined by drawing a horizontal line along the inferior aspect of the ischial tuberosities (Line 1). After localization of the center of the femoral head (Line 2), a second line parallel to Line 1 was drawn through the center of the femoral head (Line 3). A line perpendicular to Line 3 was drawn through the center of the femoral head (Line 4). A line was drawn from the center of the femoral head to the lateral aspect of the acetabulum (Line 5). The angle formed by the intersection of Lines 5 and 4 is the center-edge angle of Wiberg. The center-edge angle is normally > 25° with 20°–25° considered borderline.5
Acetabular version can be quantified accurately with cross-sectional imaging. However, a qualitative assessment, based on the relationship between the anterior and posterior walls of the acetabulum, can be obtained from AP radiographs of the pelvis (Fig 3). A line is drawn along the posterior acetabular rim (Fig 3, solid lines). The posterior rim usually can be identified by extending a line from the ischial tuberosity superiorly and laterally along the posterior wall to the region of the roof of the acetabulum. A line then was drawn along the anterior acetabular rim (Fig 3, dashed lines). The anterior wall of the acetabulum usually can be identified by extending a line from the region of the acetabular teardrop superolaterally along the margin of the acetabular rim to the roof superolaterally. If the lines do not cross, the acetabulum is anteverted (Fig 3A). If the lines do cross, the acetabulum is retroverted (Fig 3B). The acetabulum normally is anteverted 15°–20°.21,25
Femoral neck-shaft angle (Fig 4) was determined by identifying the center of the femoral head (Line 1). A line was drawn through the center of the femoral head, parallel to the femoral neck (Line 2). A line was drawn through the center of the long axis of the femoral shaft (Line 3). The angle formed by Lines 2 and 3 is the femoral neck-shaft angle. The normal femoral neck-shaft-angle is 125°–135°.8 Coxa vara is defined by a measurement < 125° and coxa valga by an angle > 140°.
Congruency was measured using templates to evaluate the relative match of the curvature of the femoral head and acetabulum. A discrepancy of the radius of curvature > 2 mm was considered to represent incongruency.
Anterior femoral head-neck offset (Fig 5) was determined on the cross-table lateral view of the hip. A line was drawn through the center of the long-axis of the femoral neck (Line 1). A parallel line was drawn through the anterior most aspect of the femoral neck (Line 2) and another parallel line was drawn along the anterior aspect of the femoral head (Line 3). The distance between Lines 2 and 3 (taking into account magnification on the film) is the anterior femoral head-neck offset. Normal anterior femoral head-neck offset is 11.6 mm. The definition for an abnormal offset in the current study was 7.2 mm and is two standard deviations below normal.7
A summary of published normal measurements and the definition for abnormal measurements used in this study are presented in Table 2. All findings reported as abnormal in this study were at, or typically exceeded, published limits of normal and abnormal measurements.
Table 2: Comparison of Measurements Defined as Abnormal versus Published Normal Values
The percentage of patients with an abnormal finding and the 95% confidence intervals were calculated. When applicable, the average of abnormal findings and the abnormal range are presented to describe the degree to which the findings were abnormal (Table 3).
Table 3: Results of Radiographic Assessment of Hips for Structural Abnormalities
RESULTS
The majority of patients with labral tears had structural abnormalities that were identifiable on conventional radiographs. Thirty-one labral tears were identified in 31 patients (21 men and 10 women). The average age of the patients was 39.9 years with a range of 18–77 years. Ten patients had a retroverted acetabulum, 16 had coxa valga, two had an abnormal Tönnis angle, 11 had an abnormal femoral head-neck offset, and two had incongruent hips (Table 3). Four of 31 patients (13%) had no detectable radiographic abnormalities. Fourteen patients had osteophytes of the femoral head anterolaterally near the head-neck junction. Thirteen of these patients also had a radiographic structural abnormality of the hip. Version of the acetabulum on three patients was thought to be indeterminate and therefore results in this category were calculated for 28 patients. Cross-table lateral radiographs were not obtained in four patients and therefore, femoral head-neck offset could be determined only for 27 patients. Eighty-seven percent of patients (27 of 31 patients) with labral tears had a structural hip abnormality that was detectable on conventional radiographs (Table 4). Furthermore, 35% of patients (11 of 31 patients) had more than one abnormality. Of these patients, 10 had two abnormal findings and one patient had three structural abnormalities.
Table 4: Percentage of Patients with Labral Tears of the Hip with Structural Abnormalities
The MR and CT arthrographs were obtained for 22 of the 31 patients with labral tears. Assessment of these arthrographs revealed that 95% of the tears involved the anterosuperior quadrant of the labrum (Table 5). Additionally, 68% of the tears involved more than one quadrant of the labrum. Only one tear involved the posteroinferior quadrant exclusively.
Table 5: Anatomic Location of Labral Tears
DISCUSSION
Acetabular labral tears are increasingly recognized as a potential cause of hip pain.2,11,14 This increased awareness has led to greater use of arthroscopy and radiographic techniques for diagnosis. These tears are associated with trauma,12,18 classic hip dysplasia,6,15 Legg-Calve-Perthes disease,23 and OA.1 An association between more subtle structural abnormalities of the hip and labral tears has been reported.1,7,13,17
The early detection of tears is aided when the diagnosis is suspected clinically. The diagnosis can be made with MR arthrography, which has been advocated by several authors as the preferred method for initial diagnosis because of its high sensitivity and specificity for labral tears.4,11,16,19,20 In certain populations, predisposing factors are known to cause labral tears, and therefore the diagnosis is routinely considered. This seems to be true of classic hip dysplasia, in which the association between pathologic labral lesions and dysplasia is estimated to be as much as 30%, and of OA in the elderly in whom degeneration and tearing of the labrum are relatively common.15
In certain populations, the diagnosis of a labral tear may easily go unrecognized as the source of hip pain, particularly in younger patients who do not have classic dysplasia and often do not recall a specific traumatic event in association with the onset of symptoms.11 This population is largely reflected in the current study in which patients with classic dysplasia and advanced OA were excluded and the average patient age was 39.9 years. This is further reflected in the data, which showed only two incongruent hips, no hips with abnormal Wiberg angles, and only two hips with mildly abnormal Tönnis angles. The diagnosis of labral tear in this population is particularly important as debridement or repair or both often is done, whereas this is less common in patients with classic dysplasia or advanced OA.
To our knowledge, this is the first study to document that the majority of patients in this population with labral tears have a structural hip abnormality detectable (some subtle) with conventional radiographs. Overall, 87% of patients with labral tears had at least one underlying structural abnormality. The most common abnormalities were a retroverted acetabulum (36%), an abnormally small anterior femoral head-neck offset (41%), and coxa valga (52%).
An abnormally small anterior femoral head-neck offset and decreased acetabular anteversion have been associated with femoroacetabular impingement.7,10,22 Both conditions can result in a relatively narrow distance between the femoral neck and acetabulum. Impaction between the femoral neck and the anterosuperior labrum and rim of the acetabulum occurs with hip flexion in these patients. Repetitive impaction can lead to damage to the labrum, eventual OA, and pain.7,10,13
The location of the labral tears support the concept of anterior femoroacetabular impingement and anterior acetabular deficiency as predominant mechanisms for their development. Twenty-one of the 22 patients (95%) with MR and CT arthrographs had involvement of the anterosuperior labrum. Twenty-seven percent of these patients had tears isolated to this region and 68% had tears involving at least one other quadrant. The preferential involvement of the anterosuperior labrum is compatible with impingement as a contributing mechanism for development of the tears. There is a strong possibility that many tears started in this region and then extended to involve other quadrants. Furthermore, the patient who did not have involvement of the anterosuperior labrum had an isolated tear of the posteroinferior labrum. Additional review of the records showed that this patient did not have a structural abnormality of the hip and that clinically the tear was thought to be the result of recent trauma.
Tears involving the anterosuperior labrum also indicate anterior acetabular deficiency that is associated with coxa valga. Coxa valga typically is seen in patients with dysplasia. Acetabular involvement typically results in a deficiency in acetabular coverage of the femoral head anteriorly and laterally. This deficiency may predispose the labrum to abnormal stress which eventually could lead to a tear.
The association between labral tears and structural abnormalities raises the issue of how best to treat these patients. It seems that if an underlying bony abnormality of the hip is predisposing patients to labral tears, debridement of the labrum alone may provide some relief, but this relief may be incomplete or temporary as the underlying condition remains. In fact, many labral tears may be a result of structural hip changes and a precursor to arthritic changes.
Early detection of these abnormalities is important in treatment and may be important in terms of prognosis. Early treatment may prevent or significantly delay pain and debility.9,10 Tönnis and Heinecke recommended correction of reduced acetabular anteversion with acetabular osteotomy to decrease pain and prevent early OA.25 In addition, Siebenrock et al22 reported a decrease in pain and functional disability in their study of young adult patients with symptomatic femoroacetabular impingement attributable to acetabular retroversion treated with periacetabular osteotomy. The success of periacetabular osteotomy in classic dysplastic hips has been shown to be highly dependent on the severity of OA at the time of surgery. Trousdale et al26 reported excellent or good results for 32 of 33 patients with periacetabular osteotomies with low-grade preoperative OA, whereas many patients with high-grade OA continued to have pain and disability. It may be that similar results would be found by surgically correcting more subtle abnormalities, but this has not been proven.
Surgical procedures including femoral osteotomy, periacetabular osteotomy, and femoral recontouring have been done to correct these various structural abnormalities. Currently, however, there are insufficient outcome data to advocate specific treatments for these milder structural abnormalities. It also is uncertain how much a role conservative treatment should play. Obviously the lifestyle of the patient plays a role in the development, symptoms, and options for treatment. Patients who participate in activities that require significant, repetitive hip flexion (ballet dancers, hurdlers, gymnasts) may be at higher risk and may require more aggressive modification of activity or treatment.
Our study has some limitations. We do not have a matched control group without labral lesions. This fact does not diminish the message that labral tears are uncommonly seen in the absence of structural problems.
The results of this study showed that there is a significant association between acetabular labral tears and structural abnormalities of the hip. Furthermore, many of the structural abnormalities can be identified on conventional radiographs. However, they can be subtle and may not be recognized. The three abnormalities most commonly seen in patients in this study, small anterior femoral head-neck offset, coxa valga, and retroversion of the acetabulum, have been implicated in predisposing patients to labral tears. Familiarity with these structural abnormalities is important for early detection and diagnosis which may impact development of an optimal treatment plan.
Acknowledgment
We thank Dirk Larson for assistance in statistical analysis in this study.
References
1. Altenberg A: Acetabular labrum tears: A cause of hip pain and degenerative arthritis. South Med J 70:174–175, 1977.
2. Cotton A, Boutry N, Demondion X, et al: Acetabular labrum: MRI in asymptomatic volunteers. J Comput Assist Tomogr 22:1–7, 1998.
3. Czerny C, Hofmann S, Neuhold A, et al: Lesions of the acetabular labrum: Accuracy and MR imaging and MR arthrography in detection and staging. Radiology 200:225–230, 1996.
4. Czerny C, Hofmann S, Urgan M, et al: MR arthrography of the adult acetabular capsular-labral complex: Correlation with surgery and anatomy. Am J Roentgenol 173:345–349, 1999.
5. Delaunay S, Dussault RG, Kaplan PA, Alford BA: Radiographic measurements of dysplastic adult hips. Skeletal Radiol 26:75–81, 1997.
6. Dorrell JH, Catterall A: The torn acetabular labrum. J Bone Joint Surg 68B:400–403, 1986.
7. Eijeer H, Leunig M, Mahomed N, Ganz R: Cross-table lateral radiographs for screening of anterior femoral head-neck offset in patients with femoro-acetabular impingement. Hip Int 11:37–41, 2001.
8. Fitzgerald RH: Acetabular labral tears. Clin Orthop 311:60–68, 1995.
9. Ganz R, Gill TJ, Gautier E, et al: Surgical dislocation of the adult hip: A technique with full access to the femoral head and acetabulum without the risk of avascular necrosis. J Bone Joint Surg 83B:1119–1124, 2001.
10. Ganz R, Parvizi J, Beck M, et al: Femoroacetabular impingement: A cause for osteoarthritis of the hip. Clin Orthop 417:112–120, 2003.
11. Hickman JM, Peters CL: Hip pain in the young adult: Diagnosis and treatment of disorders of the acetabular labrum and acetabular dysplasia. Am J Orthop 30:459–467, 2001.
12. Ikeda T, Awasya C, Suzuki S, et al: Torn acetabular labrum in young patients, arthroscopic diagnosis and management. J Bone Joint Surg 70A:13–16, 1988.
13. Ito K, Minka II MA, Leunig M, Werlen S, Ganz R: Femoroacetabular impingement and the cam-effect. J Bone Joint Surg 83B:171–176, 2001.
14. Kim YT, Azuma H: The nerve endings of the acetabular labrum. Clin Orthop 320:176–181, 1995.
15. Klaue K, Durnin CW, Ganz R: The acetabular rim syndrome. J Bone Joint Surg 73B:423–429, 1991.
16. Lequesne Par M: Coxometrie: Mesure des angles fondamentaux de la hanche radiographique de l’ adulte par un raporteur combine. Rev Rhum 30:479–485, 1963.
17. Menke W, Schmitz B, Schild H, Koper C: Transversal skelettachsen der unteren extremitat bei coxarthrose. Z Orthop Ihre Grenzgeb 129:25–29, 1991.
18. Patterson I: The torn acetabular labrum. J Bone Joint Surg 39:306–309, 1957.
19. Petersilge CA: Chronic adult hip pain: MR arthrography of the hip. Radiographics 20:43–52, 2000.
20. Petersilge CA: MR arthrography for evaluation of the acetabular labrum. Skeletal Radiol 30:423–430, 2001.
21. Reynolds D, Lucas J, Klaue K: Retroversion of the acetabulum: A cause of hip pain. J Bone Joint Surg 81B:281–288, 1999.
22. Siebenrock KA, Schoeniger R, Ganz R: Anterior femoro-acetabular impingement due to acetabular retroversion: Treatment with periacetabular osteotomy. J Bone Joint Surg 85A:278–286, 2003.
23. Suzuki S, Kasahara Y, Seto Y, et al: Arthroscopy in 19 patients with Perthes’ disease. Acta Orthop Scand 65:581–584, 1994.
24. Tönnis D: Normal values of the hip joint for the evaluation of x-rays in children and adults. Clin Orthop 119:39–47, 1976.
25. Tönnis D, Heinecke A: Acetabular and femoral anteversion: Relationship with osteoarthritis of the hip. J Bone Joint Surg 81A:1747–1770, 1999.
26. Trousdale RT, Ekkernkamp A, Ganz R, Wallrichs SL: Periacetabular and intertrochanteric osteotomy for the treatment of osteoarthritis in dysplastic hips. J Bone Joint Surg 77A:73–85, 1995.
27. Wiberg G: Studies on dysplastic acetabula and congenital subluxation of the hip joint. Acta Chir Scand 83:1–135, 1939.
