The Function of the Hip Capsular Ligaments: A Quantitative Report

Transcription

1 The Function of the Hip Capsular Ligaments: A Quantitative Report Hal D. Martin, DO Adam Savage, B.S. Brett A. Braly Ian J. Palmer, Ph.D. Douglas P. Beall, M.D. Bryan Kelley, M.D.

2 Abstract Purpose: To analyze the anatomy and quantitative contributions of the hip capsular ligaments. Methods: The stabilizing roles of the medial and lateral arms of the iliofemoral ligament, pubofemoral ligament, and ischiofemoral ligament are examined in 12 matched pairs of fresh frozen cadaveric hips 6 male and 6 female hips. The motion at the hip joint was measured in internal and external rotation through ranges of motion from 30 degrees flexion to 10 degrees extension along a neutral swing path. The motion was standardized via frame stabilization and motion tracking. Results: There is a clear and consistent ligamentous pattern within the hip corresponding to a distinct function and contribution to internal and external rotation. Upon releasing the ischiofemoral ligament, the greatest gain in range of motion was that of internal rotation. The largest increase of motion by releasing the pubofemoral ligament was observed in external rotation, especially during extension. The release of the medial and lateral arms of the iliofemoral ligament each gave the greatest increase of motion in external rotation, with the lateral arm release providing more range of motion in flexion and in a neutral position. The lateral arm release also demonstrated significant motion increase in internal rotation, primarily in extension. Conclusions: The ischiofemoral ligament controls internal rotation in flexion and extension. The lateral arm of the iliofemoral ligament has dual control of external rotation in flexion and both internal and external rotation in extension. The pubofemoral ligament controls external rotation in extension with contribution from the medial and lateral arms of the iliofemoral ligament. Together, these findings can have significant clinical applications. Clinical Relevance: When abnormal muscular and osseous pathology can be eliminated as a cause of instability or restrictive range of motion, the understanding of the independent functions of the hip ligaments will aid in defining accurate assessment, nonsurgical, and arthroscopic treatment techniques. 2

3 Keywords: Hip; ligaments; flexion; extension; internal rotation; external rotation Introduction The hip is a unique joint that possesses both mobility and stability because of its anatomic configuration [1]. A portion of the hip s stability may be attributed to the strong, dense articular capsule of the hip. The capsule has a cylindrical sleeve-like shape and proximally inserts both anteriorly and posteriorly along the periphery of the acetabulum outside the labrum. Distally, the capsule attaches to the femur anteriorly along the intertrochanteric line, but posteriorly has an arched free border that only partially covers the femoral neck. Most of the fibers are longitudinally oriented, except for the circular fibers of the zona orbicularis located posteriorly and inferiorly [2,3]. Together, these osseous and ligamentous structures and the musculotendonous components help to characterize and constrain the dynamic movements of the hip [4]. It is known that peak contact forces are two to three times the body weight in level walking, well over seven times during stair climbing, and over eight times during stumbling [5,6]. The hip is, therefore, not only important in the transfer of weight and energy between the appendicular and axial skeleton, but is crucial in the execution of lower-limb motion such as walking, running, jumping, and kicking [1,7]. Despite its importance in everyday maneuvers, the hip is less understood than other large joints such as the shoulder and the knee. The hip joint s stability and range of motion may be compromised in many ways. Traumatic dislocation of the hip joint is uncommon due to the strength and stability of the joint but the hip may be dislocated posteriorly when the hip is flexed, adducted, and medially rotated during a traumatic even such as a motor vehicle accident. Anterior dislocations may result from a violent injury that forces the hip into extension, abduction, and lateral rotation [8]. Children are most susceptible to dislocation due to their shallow acetabulum [4,9]. Congenital dislocation of the hip is much more common [8,10]. Ten to 24% of athletic 3

4 injuries in children are hip related, and 5% to 6% of adult sports injuries originate in the hip and pelvis [7,11]. External rotation of the hip in golf or martial arts tends to push the femoral head anteriorly and over time and may lead to focal anterior capsular laxity and stretching of the iliofemoral ligament. Subsequent joint instability and labral tears in the anterosuperior region of the acetabulum may follow. A labral tear leads to reduction in the joint seal that helps to hold the femoral head in place via negative pressure and increased translation of the femoral head may result. The increase of hip joint flexibility required by athletes involved in such sports as ballet, ice skating, or gymnastics may lead to generalized ligamentous laxity and result in symptoms of hip instability. Direct blows to the greater trochanter in sports such as football or hockey may lead to many injuries including isolated labral tears and chondral injuries. In addition to trauma, these athletes can suffer from overuse-type hip injuries [4]. An understanding of the structure and function of the hip capsular ligaments can be of potential value when engaged in the process of diagnosis and treatment of patients presenting with hip pain. Due to the difficulty in defining their exact structure and function [15], controversy and discrepancy surround the current structural descriptions and functional theories of the hip ligaments. In perhaps the most complete and in depth study of the hip, Fuss and Bacher anatomically describe the hip ligaments differently than every other source [16]. They describe the iliofemoral ligament as consisting of three bands, while all others depict two. They portray the ischiofemoral ligament as also consisting of three bands, one of which attaching to the lesser trochanter; whereas no other sources describe this structural anatomy. Similar discrepancies are found in the number of bands contributing to both the pubofemoral ligament and the ligamentum teres. And finally, some illustrate the orbicularis ligament as encircling the entire femoral neck, while others report only a posterior contribution [16-21,1-4,8,12-13]. There are at least as many incongruities concerning the function of these ligaments. Fuss and Bacher divide the function of their three iliofemoral bands into five categories, none of which coincides with 4

5 Crowninshield s restricting adduction [22]. Fuss and Bacher again divide the function of their three ischiofemoral bands into four categories, different than any other author [16,1-5,8,17,17,19-24].The contribution of the ligamentum teres is said to be minimal or no role whatsoever by most [4,8,10,13,16], but others believe it contributes significantly to the stabilization of the hip [12].These many inconsistencies only add to the uncertainty in treating hip-related pathologies. The lack of a clear and specific description of the function and anatomy of the hip capsular ligaments warranted the development of this investigational study. The purpose, therefore, is to provide a surgically and clinically useful description of the origin and insertion of each primary hip ligament for the direct analysis of percent contribution of each ligament in the control of internal and external rotation. It is hypothesized that the medial and lateral arms of the iliofemoral ligament, the pubofemoral ligament, and the ischiofemoral ligament each have a specialized restrictive function to internal and external rotation that is unique to the specific range of motion within a neutral swingpath. Methods Twelve fresh-frozen human cadaveric hips (avg. age 62 years) were dissected leaving the ligamentous structure of the pelvis and hips intact. Two were excluded from the study due to severe arthritis and artificial hardware. All musculature was removed to expose the underlying hip capsular ligaments. The ligaments that were found included the iliofemoral ligament, pubofemoral ligament, ischiofemoral ligament, ligamentum orbicularis, and the ligamentum teres femoris. All were cleaned and left in situ so that careful examination of their exact origin, insertion, and course could be defined and documented. Once the skeletonization was completed, radiographic and manual examinations were conducted of the hip, pelvis, and spine to ensure no occult pathological state existed. If any specimen showed signs of arthrosis or osseous pathology, as well as decreased mobility, signs of surgical interventions, or clearly 5

6 detectable crepitations or deformities, then they were excluded from the study. All specimens were also radiographically checked for femoral and acetabular anteversion, cam and pincer lesions, and the center edge and neck-shaft angles were measured and the McKibbin s index was calculated [25-26]. The hips with abnormal McKibbin s index of greater than 60 or less than 20 were eliminated from this study to establish a foundation for the individual ligamentous restraint under normal osseous geometric conditions. Each specimen was then placed in a lateral position and two rods were positioned perpendicularly and drilled through the T12 or L1 vertebrate and set with Ilizarov osseous fixation (Figure 1). Figure 1. Ligament resection through the lateral aspect of the medial iliofemoral ligament. The dissection table apparatus is demonstrated showing the table mount; Illizarov frame; and the pelvic cadaver specimen. The setscrew was placed perpendicular to the femur to lock the intramedullary rod and to be used as a reference guide. The pelvis was also stabilized by fixing the iliac wing to a dissection stand and table mount (Figure 1). The femur was reamed and cut at midshaft. Intramedullary rod fixation of the distal femur was performed 6

7 and held in place by screwing a setscrew perpendicularly into the femur (Figure 1). The femoral rod was inserted through a vertical plane grid that was used to assess the hip joint s range of motion. Measurement marks representing specific angles of 10 degrees in extension, 0 degrees neutral, and 15 and 30 degrees in flexion were placed on the vertical plane grid. This range of motion correlates to that of the average walking step. For each femoral location along the swing path, the degrees of external and internal passive rotation were measured using a goniometer. A total of three independent measurements were made at each location. Any measurement greater than one standard deviation away from the mean was disregarded from the study and thus an additional measurement would be recorded in its place. Internal and external rotation measurements were taken with completely intact ligaments to serve as our baseline measurements. After these range of motion values were attained, sequential ligamentous cutting was performed. The hips were guided through the slotted grid for each ligamentous group and external and internal rotation angles were measured. The hip capsular ligaments were removed in the following order: 1) medial arm of the iliofemoral ligament, 2) lateral arm of the iliofemoral ligament, 3) pubofemoral ligament, and 4) ischiofemoral ligament. The medial arm of the iliofemoral ligament was cut at the base proximal to its insertion along the distal intertrochanteric line with care not to disturb any portion of the other ligaments (Figure 1). The lateral arm was cut at the twelve o clock position, proximal to its insertion at the anterior greater trochanteric ridge. The pubofemoral and ischiofemoral were cut in a similar manner as to include the entire ligament but nothing more. The ischiofemoral was cut posterior to twelve o clock proximal to its insertion. Finally a 2cm labrum resection was made at the one o clock position in a longitudinal fashion between the medial arm of the iliofemoral and the pubofemoral where the majority of all acetabular labral tears occur. 7

8 After all the external ligaments of the hip capsule were resected, clear examination of the ligamentum teres was performed. As with the other ligaments, a careful anatomical appearance was recorded. After all measurements were made, an ANOVA data analysis was performed on each specimen along with an independent variable analysis. Results Our first goal with this study was to anatomically describe the gross structure of the hip capsular ligaments. The medial arm of the iliofemoral was observed to originate between the AIIS and the iliac portion of the acetabular rim and transverse nearly vertically downward. Its insertion was consistently noted to be on a bump, or knob, located on the distal intertrochanteric line. The name of this structure was not found in our research. The lateral arm originates superior to the medial, closer to the AIIS, and traverses more horizontally along the neck of the femur, covering the orbicular ligamentous fibers running perpendicular to the lateral arm at its distal portion. The lateral arm of the iliofemoral ligament inserts on the anterior greater trochanteric crest (Figure 2a). Figure 2a. Line drawing of the left hip anterior ligaments. A) Intertrochanteric Knob, insertion of the iliofemoral ligament medial arm; B) Intertrochanteric Crest, insertion of the iliofemoral ligament lateral arm; C) Iliopectineal Eminence, medial to the insertion of the pubofemoral ligament; and the Orbicular ligament (Small black arrows). 8

9 The pubofemoral ligament was noted to resemble a sling, running inferior to the medial arm of the iliofemoral ligament, medial and inferior to the iliopectineal eminence, originating at the pubic portion of the acetabular rim and the obturator crest of the pubic bone and attaching distally to the femoral neck. Fibers from the pubofemoral ligament blend with the medial arm of the iliofemoral ligament. The sling of the pubofemoral ligament was also noted to wrap inferiorly around the neck of the femur and insert inferior to the ischiofemoral along the posterior intertrochanteric crest. The ischiofemoral ligament originates at the ischial portion of the acetabular rim and crosses the hip capsule in two horizontal bands. The superior band spirals superolaterally, arching across the femoral neck to blend with the zona orbicularis fibers and inserts medial to the anterosuperior base of the greater trochanter. The inferior band inserts more posterior, medial to the base of the greater trochanter along the posterior intertrochanteric crest (Figure 2b). Figure 2b. Line drawing of the left hip posterior ligaments. A) Insertion of the superior band of the ischiofemoral ligament, which is anterior to the midaxis of the greater trochanter; B) Inferior band of the ischiofemoral ligament; C) Point at which the Zona Orbicularis blends with the ischiofemoral ligament; D) Origin of the lateral arm of the iliofemoral ligament; Sling of pubofemoral ligament and inferior orbicular ligament (black arrow). When the hip is in internal rotation (Table 1, 2, Figure 3) and the medial arm of the iliofemoral ligament was severed, no notable change was observed. However, when the lateral arm of the iliofemoral was cut, 9

10 an increase of 5 degrees was seen in all positions except 30 degrees flexion. Similar to the medial arm, when the pubofemoral ligament was ressected, no significant change was noted. When the ischiofemoral ligament was cut, the amount of internal rotation allowed doubled throughout the entire swing path of the femur. Therefore, the ischiofemoral ligament was observed to be the most significant restrictor of internal rotation. Of note, the lateral arm of the iliofemoral ligament is also a principle contributor to the hip s stability in internal rotation. Furthermore, its contribution increases as femur moves from flexion to extension along a neutral swing path. Thus, the lateral arm limits internal rotation most in extension. Figure 3. Summary of internal rotation of hip ligaments through ranges of motion from 30 degrees flexion to 10 degrees extension along a neutral swing path. The greatest increase in internal rotation was seen after transection of the ischiofemoral ligament (far right segment of the graph). The amount of internal rotation doubled after this ligament was destabilized. The lateral arm of the iliofemoral ligament was also noted to contribute to the stability of the hip in internal rotation (this contribution increases as the hip moves from flexion to extension). 10

11 The summary of external rotation (Table 1, 2, Figure 4) illustrates the contributions of both the medial and lateral arms of the iliofemoral ligament. The lateral arm was observed to have a greater contribution in all locations along the neutral swing path except for extension. A minimum increase of 7 degrees was noted with release of the lateral arm. No change was observed for the pubofemoral ligament along the entire neutral swing path concerning internal rotation. Similarly, no notable change was seen in external rotation when the pubofemoral ligament was removed, except for in extension. Without ligamentous restraints, the hip subluxed anteriorly at 48 degrees of external rotation. Additionally, with the anterior labrum transected, the stability of the hip in either internal or external rotation is severely diminished. Table 1: Average Internal and External Rotation Following Ligament Release 30 Flexion 15 Flexion 0 Neutral 10 Extension IR ER IR ER IR ER IR ER All Intact: Med Ilio: Lat Ilio: Pubo: Ischio: Values are in degrees of internal rotation (IR) and external rotation (ER) after the corresponding ligament was released. Figures 3 and 4 are visual representations of Table 1. Table 2: 95% Confidence Intervals for Mean Values 30 Flexion 15 Flexion 0 Neutral 10 Extension IR ER IR ER IR ER IR ER All Intact: Med Ilio: Lat Ilio: Pubo: Ischio: The 95% confidence intervals for the mean values given in Table 1. 11

12 Figure 4. Summary of external rotation of hip ligaments through ranges of motion from 30 degrees flexion to 10 degrees extension along a neutral swing path. Notice the slope of line increases (representing more external rotation) as each ligament is subtracted. The graph illustrates the contribution of the iliofemoral ligament and is the main limiter of external rotation in flexion. The lateral arm has a greater contribution than the medial arm in all locations except for in extension. The pubofemoral ligament also has an important contribution in extension and is the main restrictor in extension. The ischiofemoral ligament s contribution to the stability of the hip in internal rotation is clearly seen (Table 3, Figure 5). Also observed here is the lateral arm of the iliofemoral ligament s restriction to internal and external rotation in extension. The greatest inhibitor to external rotation in extension appears to be the medial arm of the iliofemoral ligament. The pubofemoral ligament s main restriction is external rotation in extension. It should be noted that as the femur moves from flexion to extension, the potential range of motion to be gained increases greatly suggesting that the hip rests in a looser state when in flexion. 12

13 Table 3: Percent Change in Internal and External Rotation Following Ligament Release 30 Flexion 15 Flexion 0 Neutral 10 Extension IR ER IR ER IR ER IR ER All Intact: Med Ilio: Lat Ilio: Pubo: Ischio: The amount of change observed after each ligament removal was of special interest in analyzing the data. Figure 5 provides the visual compliment of Table 3. (Note: each percent change was calculated in reference to the previous range of motion. Ex: An increase from 10 to 18 degrees represents an 80% change.) Figure 5. Summary of the amount of change observed after each ligament removal. Note the contribution to hip stability by the ischiofemoral ligament (Ischio) in internal rotation (IR). Both the lateral arm (Lat Ilio) and the medial arm (Med Ilio) of the iliofemoral ligament provided restriction to IR in extension. The Lat Ilio also provides a major contribution to external rotation (ER). The primary restrictor of ER in extension is the Med Ilio. The pubofemoral ligament (Pubo) has the overall least amount of change, however its greatest contribution is to restrict ER in extension. This graph also illustrates a greater degree of laxity when the hip is in flexion as the percent change of all of the ligaments is less in flexion. 13

14 The contribution of each ligament s removal towards the total range of motion was also determined (Table 4, Figure 6). The greatest contribution to internal rotation in all degrees of flexion and extension was the ishiofemoral ligament, accounting for more than 60% contribution. An additional 12 30% contribution to internal rotation was determined to be the lateral arm of the iliofemoral ligament. For external rotation in all degrees of flexion and extension, both the lateral and medial arms of the iliofemoral ligament accounted for over 50% contribution. The pubofemoral ligament provided very little contribution (less than 5%) to internal rotation. However, the percent contribution of the pubofemoral ligament to external rotation increased to 10 20% from 30 flexion to neutral and provided its greatest contribution of 34% to external rotation in extension. Table 4: Percent Contribution of Each Ligament to Internal and External Rotation 30 Flexion 15 Flexion 0 Neutral 10 Extension IR ER IR ER IR ER IR ER All Intact: Med Ilio: Lat Ilio: Pubo: Ischio: The percent contribution of each ligament with the visual compliment in Figure 6. The authors believed this data also needed to be analyzed in order to counter any misleading data given by the percent change. Ex) An increase from 2 to 6 degrees was represented by a 200% change in the previous method; however, concerning the total contribution to the range of motion, this 4 degrees is of minor weight. 14

15 Figure 6. Summary of the contribution of each ligament s removal towards the total range of motion. The graph illustrates that the ischiofemoral ligament (Ischio) shows the greatest contribution to restriction of internal rotation (IR) with the lateral arm of the iliofemoral ligament (Lat Ilio) being the second most important contributor. The iliofemoral ligament, both the medial arm (Med Ilio) and the Lat Ilio together, provide more than half the contribution to external rotation (ER) on all degrees of flexion and extension. The contribution by the pubofemoral ligament (Pubo) to IR is very small, however its greatest contribution is to ER, particularly in extension. Discussion In order to develop a surgically and clinically useful description of the hip capsular ligaments the origin and insertion of four major ligaments were defined in ten human cadaveric hips. The iliofemoral ligament was found to consist of two bands, the medial arm and a lateral arm. The medial arm originates between the AIIS and the iliac portion of the acetabular rim and the lateral arm originates superior to the medial arm, closer to the AIIS. Insertion of the medial arm was determined to be on a bump, or knob, structure located on the distal intertrochanteric line. Insertion of the lateral arm was determined to be on the anterior greater trochanteric crest. The pubofemoral ligament origin was determined to be at the pubic portion of the acetabular rim and the obturator crest of the pubic bone. The pubofemoral ligament resembled a sling which wrapped inferiorly around the femoral neck and blended with the medial arm of 15

16 the iliofemoral ligament. Insertion of the pubofemoral ligament was along the posterior intertrochanteric crest, inferior to the ischiofemoral ligament. The ischiofemoral ligament originated at the ischial portion of the acetabular rim and was noted to contain two horizontal bands, the superior band and inferior band. The superior band arched across the femoral neck blending with the fibers of the zona orbicularis and inserted medial to the anterosuperior base of the greater trochanter. Insertion of the inferior band was more posterior, medial to the base of the greater trochanter along the posterior intertrochanteric crest. The ischiofemoral ligament was noted to be the most significant restrictor of internal rotation. This accurately correlates with the qualitative description given by many others [1,2,8,16,17,20, 21]. Concerning external rotation, our findings also agree with past qualitative descriptions concerning the contributions of both the medial and lateral arms of the iliofemoral ligament [ 2,16,20,24]. It was also observed that the hip naturally internally rotates 20 degrees in extension. The removal of these four major ligaments of the hip revealed that the greatest gains in internal and external range of motion occur in extension. This affirms that the hip rests in a looser state when in flexion and is, therefore, at a greater risk for injury when in this position [2]. The quantitative contributions of the hip capsular ligaments have yet to be analyzed. This study quantitatively describes the stabilizing roles of the medial and lateral arms of the iliofemoral ligament, pubofemoral ligament, and ischiofemoral ligament in internal and external rotation of the hip through range of motion from 30 degrees flexion to 10 degrees extension which is the range of motion involved in normal activities. Since a quantitative report has yet to be done on the hip capsular ligaments, our approach was based off the recent work seen in the shoulder [27]. 16

17 The clinical applications regarding the loss of rotation, both internal and external, are found with many pathologic conditions existing in the hip. The separation of osseous, musculotendinous, and ligamentous causes are important to prescribing proper diagnosis and treatment strategies. Understanding of the ligamentous contribution in minimally invasive techniques may assist in more favorable outcomes. A clear dialectic of both function and anatomy will produce the opportunity for advancing understanding of the capsular plication, thermal caspulorraphy, capsulotomy, or therapy to reestablish more normal ranges of motion for improved kinematic motion. Leaving the lateral arm loosely closed in both arthroscopic and open surgery for femoral acetabular impingement aids in establishing a more normal range of motion when loss of internal rotation is found. The limitations of this study include analysis of 4 degrees of freedom and the ligament cutting order. Future studies should assess the bony geometry in relationship to ligamentous contribution to comprehensively appreciate the synergy existing between both the acetabulum and proximal femur in 6 degrees of freedom. Random removal of the ligaments would distinctly verify that our results were independent of cutting sequence however we intentionally removed the ligaments in a distinct order to give a greater power analysis. Lastly, based on our observation with all ligaments cut, a defined function of the teres was noted. Therefore, future studies include the function of the ligamentum teres with random cutting order and 6 degrees of freedom. Conclusion The ischiofemoral ligament controls internal rotation in flexion and extension. The lateral arm of the iliofemoral ligament has dual control of external rotation in flexion and both internal and external rotation in extension. The pubofemoral ligament controls external rotation in extension with contribution from the 17

18 medial and lateral arms of the iliofemoral ligament. Together, these findings can have significant clinical applications. References 1. Hughes PE, Hsu JC, Matava MJ. Hip anatomy and biomechanics in the athlete. Sports Medicine and Arthroscopy Review. Philadelphia: Lippincott Williams & Wilkins Inc., Wasielewski RC. The hip. The Adult Hip. J. J. Callaghan. Philadelphia: Lippincott-Raven Publishers, Stewart KJ, Edmonds-Wilson RH, Brand RA, Brown TD. Spatial distribution of hip capsule structural and material properties. Journal of Biomaechanics. 2002;35: Torry MR, Schenker ML, Martin H, Hogoboom D, Philippon MJ. Neuromuscular hip biomechanics and pathology in the athlete. Clinics in Sports Medicine.2006; 25: Crowninshield RD, Johnston RC, Andrews JG, Brand RA. A biomechanical investigation of the human hip. Journal of Biomechanics. 1978;11: Bergmann G, Graichen F, Rohlmann A. Hip joint contact forces during stumbling. Langenbecks Arch Surg. 2004;389: Braly BA, Beall DP, Martin HD. Clinical examination of the hip. Clinics in Sports Medicine. 2006;25: Moore KL, Dalley AE. Lower limb. Clinically Oriented Anatomy. 4 th edition. Moore KL, Dalley AE. Philadelphia: Lippincott Williams & Wilkins, Ralis Z, McKibbin B. Changes in shape of the human hip joint during its development and their relation to its stability. Journal of Bone and Joint Surgery.1973;55:

19 10. Brewster SF. The development of the ligament of the head of the femur. Clinical Anatomy. 1991;4: Boyd KT, Peirce NS, Batt ME. Common hip injuries in sports. Sports Med 1997;24: Rao J, Zhou YX, Villar RN. Injury to the ligamentum teres. Clinics in Sports Medicine. 2001;20: Erb RE. Current concepts in imaging the adult hip. Clinics in Sports Medicine. 2001;20: Spina AA. External coxa saltans (snapping hip) treated with active release techniques: a case report.25 May ng%20snapping%20hip%20syndrome.pdf 15. Buckwalter JA, Woo SLY. Age-related changes in ligaments and joint capsules: implications for participation in sports. Sports Medicine and Arthroscopy Review. 1996;4: Fuss FK, Bacher A. New aspects of the morphology and function of the human hip joint ligaments. American Journal of Anatomy. 1991;192: Hewitt J, Guilak F, Glisson R, Vail TP. The mechanical properties of the human hip capsule ligaments. Journal of Arthroplasty. 2002;17: Warwick R, Williams PL. Gray s Anatomy. 35 th British edition. Philadephia: W. B. Saunders, Daniel M, Iglic A, Kralj-Iglic V. The shape of acetabular cartilage optimizes hip contact stress distribution. Journal of Anatomy. 2005;207: Chung KW. Lower limb. Gross Anatomy. 5 th edition. Chung KW. Philadelphia: Lippincott Williams & Wilkins, Hewitt J, Guilak F, Glisson R, Vail TP. Regional material properties of the human hip 19

20 joint capsule ligaments. Journal of Orthopaedic Research. 2001;19: Crowninshield RD, Johnston RC, Brand RA, Pedersen DR. Pathologic ligamentous constraint of the hip. Clinical Orthopaedics and Related Research. 1983; 181: Vrahas MS, Brand RA, Brown TD, Andrews JG. Contribution of passive tissues to the intersegmental moments at the hip. Journal of Biomechanics.1990;23: Harding L, Barbe M, Shepard K, Marks A, Ajai R, Lardiere J, Sweringa H. Posterioranterior glide of the femoral head in the acetabulum: a cadaver study. Journal of Orthopaedic & Sports Physical Therapy. 2003;33: Tonnis D, Heinecke A. Acetabular and femoral anteversion: relationship with osteoarthritis of the hip. Journal of Bone and Joint Surgery. 1999;81: McKibbin, B. Anatomical factors in the stability of the hip joint in the newborn. Journal of Bone and Joint Surgery. 1970;52-B(1): Burkart A, Debski R. Anatomy and function of the glenohumeral ligaments in anterior shoulder instability. Clinical Orthopaedics and Related Research. 2002;400:

21 21