Ligamentum Teres

(ligamentum capitis femoris)

Ligamentum incognitum

ligamentum capitis femoris, круглая связка, νεῦρον, ligamentum teres, связка головки бедренной кости, ligament of head of femur, גִּיד, oberschenkelknochenkopfband, nervum, ligament rond, στρογγύλων συνδέσμων, interarticular ligament, [mt], ligamenti teretis, жила состава бедра, ligamenta cartilaginea, 大腿骨頭靭帯, suspensory ligament, лигаментумъ ротундумъ, sinew, neruum femoris, ligamentum internum, ligamentum rotundum acetabuli, triangular ligament of the hip joint, round ligament, ligamentum suspensorium pelvis, собственная связка бедра, ligamento redondo, więzadło głowy kości udowej, spannader

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ON THE ROLE OF THE LIGAMENTUM CAPITIS FEMORIS

IN THE MAINTENANCE OF DIFFERENT TYPES OF ERECT POSTURE

S. V. Arkhipov

Polessk Central District Hospital, Polessk, Kaliningrad oblast, 238630 Russia

Received September 27, 2006

 

Abstract —New experimental and clinical data on the function of the ligamentum capitis femoris (LCF) and its participation in maintaining an erect posture were obtained. It was established that this anatomical element is involved in constraining the hip joint adduction and may fix the joint in the frontal plane, turning it into an analogue of a second-class lever. In both unstrained one-support and asymmetrical two-support orthostatic postures, when the LCF is stretched and the abductor muscle group is exerted, a load equal to the body weight is evenly distributed between the upper and lower hemispheres of the caput femoris. In addition, the LCF function increases the steadiness of the erect posture and unloads the muscle apparatus.

DOI: 10.1134/S036211970801012X

INTRODUCTION

 

The ligamentum capitis femoris (LCF) is an integral anatomical element of the human body [1, 2]. It is located in the hip joint (HJ), connecting the thigh and hip bones [3], in a special osteochondrous cavity composed of the acetabular fossa and notch on one side and the articular surface of the caput femoris (CF) on the other side. The normal LCF length is about 2.5 cm [4], so that its visualization is possible only with modern tools [5–7]. We found one of the first reliable mentions of the LCF in Vesalius’s Epitome […] (1543) [8]. In the Russian literature, the earliest description of the LCF was given by Naranovich (1850) [9].

 

The function of the LCF has not been unambiguously determined [6] and is subject to controversy. Tonkov wrote that the LCF function “… is not perfectly clear; in any case, its mechanical significance is not so great” [4]. However, according to Neverov and Shil’nikov, it plays an important role in HJ biomechanics [10], while Vorob’ev claimed that its “biomechanical function” is of importance only under certain conditions [11]. On the other hand, Pirogov compared the LCF to “a steel spring on which the pelvis is suspended from the caput” [12]. Gerdy and Savory [13] advanced a similar opinion, the former author noting that the LCF is exerted in the erect posture. Ivanitskii, when touching on the role of the LCF in maintaining an erect posture, wrote [14], “[…] in an asymmetrical posture, with the pelvis tilted, the ligamentum capitis femoris on the side of the supporting, usually straightened, leg is stretched to reinforce the hip joint” [14].

 

Four main types of erect posture are known (Fig. 1). A horizontal position of the pelvis and equal loading of both inferior limbs straightened in the knee joints characterize a two-support symmetrical orthostatic position. With a two-support asymmetrical orthostatic posiposition (asymmetrical standing, or an at ease posture), one of the legs is straightened while the other is bent at the knee joint and HJ, the pelvis deviating from the horizontal plane [14, 15]. One-support orthostatic positions are usually subdivided into “strong” and “weak” postures [16]. In our opinion, it is more apposite to call them “strained” and “unstrained,” respectively. The strained one-support position is characterized by a horizontal position of the pelvis, while its inclination to the side opposite the support, with less exertion of the muscles of the supporting leg, is characteristic of the unstrained posture.

 

In HJ biomechanics, it is commonly accepted that maintaining an orthostatic position in the frontal plane depends only on muscles [16–20]. The LCF is not mentioned as a functional component of the HJ, and its mechanical reaction is not considered in calculating CF loading.

 

The purpose of this study was to clarify the function of the LCF and its role in maintaining different types of erect posture.

 

EXPERIMENTAL 

 

In order to study the different types of erect posture, we selected 104 men with no HJ pathology aged from 18 to 24 years (18.9 years on average). At the first stage, each subject assumed a two-support symmetrical orthostatic position with equal loads on both inferior limbs. Then, the subject was asked to assume a two-support asymmetrical orthostatic position, with the left leg bent at the HJ and knee joint, the right one remaining straightened, and the pelvis tilted relative to the horizontal plane. Then, the subject assumed a strained onesupport orthostatic position with the weight on the right leg; this was followed by a transition to the unstrained position. In this position, we measured the value of hip adduction in the supporting HJ. In each type of erect posture, we recorded the position of the pelvis and the angular proportions in the large joints of the inferior limbs. In the one-support position, attention was paid to the degree of exertion of the muscles of the supporting leg and the general steadiness of the posture.

 

Fig.1

Fig. 1. Diagram of the main types of erect posture: (a) the two-support symmetrical orthostatic position; (b) the two support asymmetrical orthostatic position; (c) the unstrained one-support orthostatic position; (d) the strained onesupport orthostatic position.

 

At the second stage, we clarified the role of the ligament apparatus in constraining adduction of the hip and tilting of the pelvis and in fixing the HJ in an unstrained one-support position. The relationships between the positions of the pelvis and the supporting hip were reproduced in a prone position with completely relaxed muscles, which permitted us to exclude the influence of the weight of the body and muscles on functioning of the ligament apparatus of the HJ. The straightened, relaxed leg of the subject was elevated upwards as far as possible and shifted to the body midline up to the limit of the ligament stretching. Then, we measured the value of the hip adduction angle of the HJ. Quantitative data were analyzed using the Excel 97 software. The program calculated the mean, the standard deviation, the median, the mode, Student’s test, and the coefficient of correlation. The value of the adduction of the supporting hip in an unstrained onesupport orthostatic position was compared with that of the maximum adduction of the hip in a prone position, with maximum HJ extension and relaxed muscles.

 

In order to clarify the functions of the LCF and abductor muscle group, we constructed a plane mechanical model of the HJ containing analogues of the considered structures. It was based on an actual survey roentgenogram of the pelvis of a young man with no HJ pathology. The pelvis and the proximal part of the right femoral bone were drawn full size, separately, on a sheet of stiff cardboard and then cut out along the contour. The centers of the drawings of the acetabulum and LCF were conjoined or, in some cases, linked by a metal pin. A thin nylon thread 20 mm long linking the center of the drawing of the CF fossa with a point in the lower section of the drawing of the acetabular fossa was used as a model of the LCF. A thin rubber belt 1 mm in diameter was used as a model of the abductor muscle group. One of the ends was fastened to the upper edge of the drawing of the iliac crest, and the other, to the analogue of the greater trochanter. The properties of the model were studied both in the absence of the LCF and abductor muscle group models and in their presence in different combinations. We clarified the possible rotational and translational movements of the femoral part of the model in the frontal plane. The location of the loading regions in the acetabulum and CF, the direction of the reaction forces of the LCF and abductor muscle group analogues, and the direction of the resultant force at different phases of adduction were determined. We simulated equilibrium conditions for a pelvis moving in the frontal plane in the strained and unstrained one-support orthostatic positions (Figs. 2a, 2b).

 

In order to study the functions of the LCF and abductor muscle group in more detail, we constructed a three-dimensional HJ model. We used a Thompson unipolar HJ endoprosthesis fixed on a ringlike base, with a small plate simulating the greater trochanter, as a femoral basal element. In accordance with the diameter of the CF analogue, a metal model of the acetabulum was made in the form of a thick-walled spherical shell having a shaped recess that simulated the acetabular fossa and notch. A plate simulating the iliac crest and a plate for suspending a load, a 1- to 3-kg dumbbell, were attached from the outside. The model contained an LCF analogue made from a nylon cord 5 mm in diameter. One end of this cord was tightly fixed to an opening made in the shaped recess of the acetabulum model, and the other, to the CF analogue. Both parts of the model were also linked to a dynamometer, whose spring simulated the function of the abductor muscle group; oil lubricated the friction node. The properties of the model were studied both in the absence of the LCF and abductor muscle group analogues and in their presence in different combinations. In some experiments, we changed the length of the abductor muscle group analogue, thereby modeling different degrees of its exertion. We determined the possible rotational and translational movements in the hinge of the model, their range, and constraints. We modeled equilibrium conditions for the pelvis moving in the frontal plane in the unstrained and strained types of one-support orthostatic position (Figs. 2c–2e) and clarified the location of the load region in the simulated CF. 

Fig.2

Fig. 2. Simulation of different types of one-support erect posture using a two-dimensional mechanical model of the hip joint: (a) the strained one-support orthostatic position; (b) the unstrained one-support orthostatic position; the analogue of the LCF is indicated with an arrow. Simulation of different types of one-support erect posture using a three-dimensional mechanical model of the hip joint: (c) the strained one-support orthostatic position; (d) the unstrained one-support orthostatic position with both the LCF and the analogue of the abductor muscle group stretched; (e) the same position with a relaxed abductor muscle group analogue.

 

RESULTS AND DISCUSSION

 

Analysis of the data obtained for healthy subjects permitted us to characterize the main features of the known orthostatic positions. In a two-support symmetrical orthostatic position, the pelvis was disposed horizontally; in the asymmetrical position, it was tilted toward the leg bent at the HJ and knee joint. The body was at rest with no prominent fluctuations in the frontal plane. The two-support asymmetrical orthostatic position has proved to be preferable for subjects as requiring a lesser effort of the muscles of the leg bent at the knee joint. In a strained one-support orthostatic position, the pelvis acquired a horizontal orientation. On a transition to the unstrained one-support orthostatic position, we observed adduction, extension, and outward rotation in the HJ. The pelvis shifted translationally toward the supporting leg, its nonsupporting half leaning downwards. The amount of tilt of the pelvis in the frontal plane was practically the same as that in a two-support asymmetrical orthostatic position (Fig. 1). Both unstrained and strained one-support orthostatic positions were equally steady, but a lesser exertion of the muscles of the supporting leg was characteristic of the unstrained position. We found the presence of muscle tone in the abductor muscle group. The mean angular value of the maximum adduction in the supporting HJ was 18.51±2.29°, with medians and modes equal to 19°. When the positions of the pelvis and the supporting hip characteristic of an unstrained one-support orthostatic position were reproduced in the prone posture, the mean angular value of the maximum HJ adduction was 19.09±2.52°, with the median and mode equal to 19°. Comparison of the adduction angles in the unstrained one-support orthostatic and recumbent postures showed that, at the individual level, the correlation of their values was 0.90 (p< 0.001) with no statistically significant differences in the mean values. Therefore, in the unstrained one-support orthostatic position, the adduction of the hip and closing of the HJ in the frontal plane are maximum, which occurs mainly at the expense of the ligaments with minimum participation of muscles.

 

Experiments with the plane and three-dimensional mechanical models showed that the LCF imposes constraints on the HJ adduction by limiting abduction, pronation and supination, and translational outward and upward CF movements, and also prevents dislocation. Stretching of the LCF is brought about by adducting the hip and inclining the pelvis to the nonsupporting side, which means that the HJ closes in the frontal plane, becoming an analogue of a second-class lever (Fig. 3a). In the absence of abductor muscle group exertion, the resultant force acting on the HJ is directed upwards, loading only the inner distal part of the CF (Figs. 2e, 3a). Our data confirm that exertion of the abductor muscle group increases abduction and constrains adduction of the hip. In cooperation with antagonists, it is capable of closing the HJ in the frontal plane in an arbitrary position. If the abductor muscle group is exerted without stretching of the LCF, the resultant force acting on the HJ is directed upwards, loading only the inner proximal part of the CF (Figs. 2c, 3c). The abductor muscle group cooperates with the LCF in constraining adduction. Its tightening can decrease the LCF stretching, and, vice versa, a stretched LCF decreases the load on the abductor muscle group (Figs. 2b, 2d, 3b).

 

It was established experimentally that the LCF is not subjected to stretching in a strained one-support orthostatic posture, while the abductor muscle group and its antagonists damp the HJ movements in the frontal plane (Figs. 2a, 2c). Here, the HJ is an analogue of a first-class lever, which means loading of the upper hemisphere of the CF. If we assume that the lever (L) of the body weight (P) exceeds threefold the lever (L1) of the abductor muscle group effort (F) (Fig. 3c), then the equilibrium condition for a strained type of one-support orthostatic position in the frontal plane is,

 

LP=L1F.

The force (F1) produced by the abductor muscle group will be three times greater than the body weight,

 

F=LP/L1= 3P.

 

Then, the resultant downward force (F1) acting on the CF is four times greater than the body weight:

 

F1=F+P= 4P.

 

Such heavy loads are normally brief, being observed in the case of the strained type of the one-support orthostatic position and during the transition from the twosupport orthostatic posture to the unstrained type of the one-support orthostatic position. In our opinion, the prolonged fixation of the HJ in the one-support orthostatic posture at the expense of only muscle exertion is inefficient, leading to LCF overloading and, therefore, to HJ pathology. The above calculations hold true even in the case of a severe LCF injury, e.g., after a cured traumatic hip dislocation and in HJ endoprostheses devoid of an LCF analogue.

 

Analysis of the experimental data and results of clinical examinations indicates that, in the unstrained one-support orthostatic posture, hip adduction and tilting of the pelvis toward nonsupporting side are constrained mainly by a stretching LCF (Figs. 2b, 2d, 2e), which agrees with the opinions of other authors [3, 14]. The pelvis, as stated by Pirogov, is “suspended” from the LCF [12]. The function of the abductor muscle group consists only of decreasing the LCF loading, which ensures the body’s equilibrium. The combination of stretching of the LCF and exertion of the abductor muscle group is optimal in terms of loading all HJ elements and maintaining the steadiness of the erect posture in the frontal plane. In this case, the proximal region of the LCF fixation is the center of rotation, while the HJ is an analogue of a first-class lever. If one assumes that the lever (L) of the body weight (P) is equal to the lever (L1) of the abductor muscle group effort ( F) (Fig. 3b), then the equilibrium condition in the frontal plane is as follows:

 

LP=L1F1,

 

the LCF reaction (F1) will be

F1=P+F= 2P.

 

Given this type of a one-support orthostatic posture, both the stretched LCF and the tightened abductor muscle group deviate from the vertical. The horizontal components of the reaction forces of the LCF and the abductor muscle group are summed, resulting in a horizontal force (F2) that uniformly presses the acetabulum to the CF. The mean angular deviation from the vertical of the force produced by the abductor muscle group is 21°[17]; the angular deviation of the LCF is, according to our data, about 50°. The calculations show that the amount of F2 pressing the pelvis to the CF is approximately equal to twice the weight of the body (1.96P), with the horizontal component of the LCF reaction force equal to 1.6P and the horizontal component of the abductor muscle group reaction force equal to 0.36P. The loads on the upper and lower CF hemispheres are approximately equivalent to the body weight without taking into account the mass of the supporting leg.

 

In an unstrained one-support orthostatic posture with little or no participation of the abductor muscle (Fig. 2d), the movement of the HJ in the frontal plane is that of a second-class lever analogue. If we assume that the lever (L) of the body weight (P) exceeds threefold the lever (L1) of the LCF reaction force (F1) (Fig. 3a), then the equilibrium condition of this kind of erect posture can be written as follows:

 

LкP=L1F1.

 

Fig.3

Fig. 3. Diagrams of different types of erect posture, with acting forces indicated: (a) the unstrained one-support orthostatic position, the hip joint fixed only by the LCF without participation of the abductor muscle group; (b) the unstrained one-support orthostatic position with both the LCF and the analogue of the abductor muscle group stretched; (c) the strained one-support orthostatic position with a nonstretched LCF; (d) the two-support symmetrical orthostatic position with both LCFs loose; (e) the two-support asymmetrical orthostatic position with a stretched left LCF. Simplified schemes below the diagrams illustrate the pelvis equilibrium patterns in the frontal plane; mgm - is the m. gluteus medius, and load patterns for the CF are indicated by thin arrows (see the text for details).

 

Therefore, the LCF reaction (F1) is equal to three times the weight of the body:

 

 F1 = LP/L1 = 3P,

 

 The resultant upward force (F2) acting on the CF is equal to two times the weight of the body:

 

 F2 = F1 P = 2P.

 

 F1 and P have opposite signs, as the forces equilibrating the pelvis have opposite directions.

 

In the two-support symmetrical orthostatic position, the pelvis–lower limbs system is an analogue of a hinged frame. If the legs are evenly loaded, the resultant force acts predominantly on the upper hemisphere of both CFs. Without muscle exertion being taken into account, each of them is under a load equal to one half of the body weight located above the HJ level. The abductor and adductor muscles, without the participation of the LCF (Fig. 3d), bring about fixation of the HJ in the frontal plane.

 

In a two-support asymmetrical orthostatic position, the lower limb girdle is also an analogue of a hinged frame, the pelvis being tilted in the frontal plane. On the side of the straightened leg, provided that the LCF stretching and the abductor muscle group tightening are in equilibrium, the load on the CF is evenly distributed, as in the case of an unstrained one-support orthostatic position.

 

Thus, both its upper and lower hemispheres are subjected to a load equal to one-fourth of the body weight located above the HJ. On the side of the bent leg, the LCF is not stretched, and so the CF is under downward pressure equal to one half of the body weight (Fig. 3e). The pelvis is fixed in the frontal plane by means of the abductor muscle group and its antagonists and on the side of the extended leg by means of the LCF. The twosupport asymmetrical orthostatic position is optimal with respect to the distribution of load between both HJs and the muscles.

 

CONCLUSIONS

 

1. We established experimentally that the LCF constrains adduction and lateral and cranial CF displacement and can close the HJ in the frontal plane, which is equivalent to the transformation of this structure into an analogue of a second-class lever.

 

2. The unstrained type of the one-support orthostatic position, when frontal closure of the HJ is only at the expense of the LCF, provides complete unloading of the abductor muscle group. In this case, the resultant load on the CF has an upward direction, being approximately equal to twice the body weight. This load is evenly distributed between the upper and lower CF hemispheres by a combination of tightening of the abductor muscle group and stretching of the LCF.

 

3. LCF stretching does not occur in a strained type of the one-support orthostatic position. The HJ is damped in the frontal plane by exertion of the abductor muscle group and its antagonists, the resultant load on the CF having a downward direction and being approximately equal to four times the body weight.

 

4. In the two-support symmetrical orthostatic position, provided that the legs are evenly loaded, the resultant force acts predominantly on the upper hemispheres of both CFs, each of these carrying one half of the body weight located above the HJ level.

 

5. In the two-support asymmetrical orthostatic position, the resultant force, which is equal to one half of the body weight, acts, on the side of the bent leg, on the upper hemisphere of the CF, while on the side of the straightened leg, the load on the CF is evenly distributed between the upper and lower hemispheres and is equal to one-fourth of the body weight located above the HJ level.

 

REFERENCES

 

1. Kovanov, V.V. and Travin, A.A., Khirurgicheskaya anatomiya nizhnikh konechnostei (Surgical Anatomy of the Lower Limbs), Moscow, 1963.

2. Sinel’nikov, R.D., Atlas anatomii cheloveka (Atlas of Human Anatomy), Moscow: Meditsina, 1972, vol. 1.

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4. Tonkov, V., Anatomiya cheloveka: Obshchaya chast': Sistema organov dvizheniya (Human Anatomy: The General Part: The System of Locomotory Organs), Leningrad: Medgiz, 1946.

5. Orletskij, A.K., Malakhova, S.O., Morozov, A.K., and Ogaryov, Ye.V. Artroscopicheskaya chirurgia tazobedrennogo sustava (Arthroscopic Surgery of the Hip Joint), Moscow, 2004.

6. Byrd, J.W., Operative Hip Arthroscopy, New York: Thieme, 1998.

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9. Gayevskaya, L.I., Topographic Anatomical Features of the Ligament Apparatus in the Hip Joint and Their Significance for the Clinical Picture, Cand. Sci. (Med.) Dissertation, Leningrad, 1954.

10. Neverov, V.A. and Shil’nikov, V.A., Sposob fornirovaniya iskusstvennoj golovki bedra pri endoprotezirovanii (Method of Formation of an Artificial Ligamentum Capitis Femoris in Endoprosthetics), Vestn. Khir., 1993, no. 7-12, p. 81.

11. Vorob’ev, N.A., Svyazka golovki bedra i yeye prakticheskoye znachenuye (The Ligamentum Capitis Femoris and Its Practical Importance), in Voprosy travmatologii i ortopedii (Problems of Traumatology and Orthopedics), Kiev, 1962, p. 174.

12. Yurchak, V.F., and Yevtushenko, V.A., Morphological Features of the Fetal Hip Joint in the Second Half of Pregnancy, Ortoped. Travmatol, 1972, no. 1, p. 26.

13. Nikolaev, L.N., The Role of the Orbicular Ligament in the Hip Joint, Med. Zh., 1922, vol. 3, no. 1-2, p. 10.

14. Ivanitskii, M.F., Anatomiya cheloveka s osnovami dinamicheskoy i sportivnoy morfologii: Uchebnik dlya institutov fizicheskoy kultury (Human Anatomy with Essentials of Dynamic and Sports Morphology: A Textbook for Colleges of Physical Education), Leningrad: Fizkultura i Sport, 1985.

15. Nedrigailova, O.V. Essentials of Locomotorium Biomechanics in Health and Disease, in Mnogotomnoye rukovodstvo po ortopedii i travmatologii (A Multivolume Guide on Orthopedics and Traumatology), Moscow: Meditsina, 1967, vol. 1. p. 169.

16. Belen’kij, V.E., Some Problems in Hip Joint Biomechanics, Cand. Sci. (Med.) Dissertation, Moscow, 1962.

17. Shapovalov, V.M., Shatrov, N.P., Tikhilolv, R.M., et al., The Load Pattern in the Hip Joint in Acetabular Dysplasia and Caput Femoris Osteonecrosis, Travmatol. Ortoped. Ross., 1998, no. 3. p. 22.

18. Yanson, H.A., Biomekhanika nizhnei konechnosti cheloveka (Biomechanics of the Human Lower Limb), Riga: Zinatne, 1975.

19. Bombelli, R., Structure and Function in Normal and Abnormal Hip: How to Rescue Mechanically Jeopardized Hip, Berlin: Springer, 1993.

20. Pauwels, F., Gesammelte Abhandlung zur funktionellen Anatomie des Bewegungsapparates, Berlin: Springer, 1965.

 


ISSN 0362-1197, Human Physiology, 2008, Vol. 34, No. 1, pp. 79–85. © Pleiades Publishing, Inc., 2008.Original Russian Text © S.V. Arkhipov, 2008, published in Fiziologiya Cheloveka, 2008, Vol. 34, No. 1, pp. 89–95.

 

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