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2025ArkhipovSV. Why Acetabular Labrum Repair May Be Ineffective

 

Original in Russian is available at the link: С.В. Архипова «Почему восстановление вертлужной губы может быть неэффективно?» (06.04.2025), below is a machine translation edited by a non-native speaker (version dated 06/04/2025).


Thematic Internet Journal
About round ligament of femur
April 2025

WHY ACETABULAR LABRUM REPAIR MAY BE INEFFECTIVE?: A NOTE ON THE MYSTERIOUS "DARK MATTER" OF THE HIP JOINT
S.V. Arkhipov, Independent Researcher, Joensuu, Finland

Abstract

Acetabular labrum repair and reconstruction do not prevent hip joint instability during gait and the development of osteoarthritis in the case of an elongated ligamentum capitis femoris. This conclusion is based on mathematical calculations and analysis of experiments conducted on a mechanical hip joint model.

Keywords: arthroscopy, hip joint, acetabular labrum, ligamentum capitis femoris, ligamentum teres, ligament of head of femur, reconstruction, repair


Introduction

Nearly 80% of primary hip arthroscopies involve labral repair (2019WestermannRW_RosneckJT). Reconstruction is the most common procedure for addressing labral pathology and during revision arthroscopy (2020MaldonadoDR_DombBG). Numerous support groups on Facebook exist for individuals who have undergone such treatments. Unfortunately, patient feedback is not always positive.

A cause of poor outcomes after labral surgery may lie in changes to the ligamentum capitis femoris (LCF). This strong internal ligament is an important stabilizer of the hip joint (2012CerezalL_Pérez-CarroL). However, as early as 1833, P.N. Gerdy, based on morphological studies, stated that the LCF could contribute to hip dislocation. We have verified and refined the opinion of the authoritative anatomist through experiments on a mechanical model of the hip joint.

It was found that tension of the LCF, with normal length and attachment locations, presses the acetabulum against the femoral head (2024aАрхиповСВ). Conversely, tension of an elongated LCF with peripherally displaced proximal attachment separates the acetabulum from the femoral head, provoking subluxation (2024bАрхиповСВ). This is due to a radical change in the direction of the horizontal force generated by the elongated LCF (Fig. 1).


Figure 1. Direction of horizontal force (Fhor) with normal (top) and elongated (bottom) LCF; left – mechanical model experiments, right – schematic diagrams (author’s illustrations).


The Hip Joint’s "Dark Matter"

It is widely accepted that during single-leg stance, the abductor muscle group prevents the pelvis, tilted downwards, from falling in the medial direction (1993BombelliR; 2012PauwelsF). A key role is played by the horizontal component of muscular effort, which presses the acetabulum against the femoral head (Fig. 2).

However, according to A.I. Kapandji (2009), the primary abductor muscles collectively generate a force (Fabd) equivalent to 28.5 kg (gluteus medius – 16 kg; gluteus minimus – 4.9 kg; tensor fasciae latae – 7.6 kg). If positioned at a 60º angle to the horizontal, their combined tension would produce a horizontal force (Fhor) of 14.25 kg, calculated as:

Fhor = Fabd × cos60º (1).


Figure 2. Diagram illustrating the compression effect of the acetabulum on the femoral head in a single-leg stance; Fhor – horizontal force, Fabd – abductor muscle group effort (adapted from 1965StrangeFGStC, with our additions).

Additional compression of the femoral head against the acetabulum arises from negative pressure during attempts to separate the joint. This is provided by the continuity of the acetabular synovial membrane, synovial fluid, and the labrum. Normally, this suction seal is equivalent to about 100 pounds or 45.36 kg (2025MortensenAJ_AokiSK). Thus, the muscles and labrum together generate a force equivalent to an average traction of 59.61 kg.

Assuming body mass of 58.7 kg, during single-leg stance, the mass to stabilize over the hip joint is 47.76 kg (2012PauwelsF). This suggests that the abductor muscles and labrum can counteract forces separating the femoral head and acetabulum when the pelvis tilts downward.

During walking, inertial forces act on body segments. The maximum dynamic force, equivalent to 24.35 kg, occurs in the 17th phase of the gait cycle (2012PauwelsF). Therefore, during the mid-stance phase of the gait cycle (single-leg stance), the separating load can reach 72.11 kg.


Figure 3. Pelvic tilt toward the non-supporting side (the norm) during single-leg stance – 4º (left), and mid-stance phase of the gait cycle – 3º (right) (from 2012АрхиповСВ, with additions).

In a healthy individual standing on one leg and mid-stance phase of the gait cycle, the pelvis tilts downward (Fig. 3). Common sense and our calculations suggest that dislocation should occur during walking. An additional force of at least 12.5 kg is needed to reinforce the joint. Thus, we conclude that labral repair (reconstruction) ensures hip stability in a single-leg stance but not during walking. This implies the existence of an anatomical structure or effect generating the missing force.

Normal-Length LCF

Our experiments with the mechanical model revealed the presence of a lateral force, which, among other things, prevents dislocation when standing on one leg. This is generated by the tension of LCF oriented upward and outward. This structure resembles the mysterious "dark matter" of cosmology (2022Chadha-DayF_MarshDJ). Opinions on it, as well as on the LCF, are conflicting. The function of the LCF in the natural joint remains poorly understood and debated. The role of the LCF is primarily assessed through anatomical specimens, models, calculations, and reasoning.

Under the weight of a body supported on one leg, the LCF tenses, generating a reaction force (Fr), or elastic force, equal in magnitude to the acting body weight (m) if vertically aligned, and decreasing with deviation:

Fr = mg × cosα (2).

For a body mass of 47.76 kg at rest and an LCF angled 20º from the vertical, the reaction force is 440.27 N. The horizontal component (Fhor) is calculated as:

Fhor = Fr × sin20º (3).

Directed laterally (Fig. 1a), it equals 150.57 N, or 15.35 kg. Combined with muscle contraction and the labrum’s effect of suction seal, this increases the potential compressive force in the hip join to 74.96 kg during single-leg stance.

During walking, centrifugal force (Fc) further affects the LCF. It depends on the speed of movement (v), the acting mass of the body (m) and the length of the LCF (L):

Fc = mg × v2 / Llcf (4).

With parameters of 47.76 kg, LCF length of 0.025 m, which moves at a speed of 0.04 m/s, centrifugal force equals 29.98 N, or approximately 3.05 kg. Thus, in the mid-stance phase of the gait cycle, with the LCF at a 20º angle (open downward and medially), the reaction force reaches 470.25 N, with a lateral horizontal component of 160.82 N, or 16.39 kg (Eq. 3). In a healthy individual, the tensed LCF, muscles, and labrum can resist a joint-separating traction of 76.00 kg, explaining why a 72.11 kg load during walking does not cause dislocation with a normal LCF.

LCF reaction force is directed upward, countering body weight that reducing pressure on the femoral head. This is supported by mechanical model experiments (2024cАрхиповСВ) and a simplified equation for pelvic equilibrium in the frontal plane during single-leg stance:

0 = mgL + FabdL1 - FrL2 (5),

where L is the lever arm of body weight (mg), L1 is the lever arm of the abductor muscle group (Fabd), and L2 is the LCF reaction force arm (Fr).

Our experiments showed that the acetabular labrum has minimal influence on torsional moments in the frontal plane (2024dАрхиповСВ, Fig. 4). Its retaining function is more relevant to translational motion of the femoral head. The stabilizing role of the acetabular labrum is greatest in preventing the outward (laterally downward) translational movement of the femoral head with a fixed pelvis, or inward acetabular displacement (medially upward) with a fixed femur.


Figure 4. Experiments on a mechanical model: changing of the abductor muscle analog effort in the absence of an acetabular labrum analogue (left) and the presence of an acetabular labrum analogue (right); a 2 kg load is suspended from the acetabulum model (photos by the author).

Elongated LCF

In mechanical model experiments, elongation of the LCF was simulated by shifting the proximal attachment outward (2024bАрхиповСВ). In the real hip joint, this corresponds to a partial avulsion of the proximal end of the LCF. Post-transformation of our mechanical model, the LCF analog adopted an opposite orientation, with its axis tilted upward and inward. Tension of the LCF in this position caused medial displacement of the acetabular model (Fig. 1b).

For a tensioned LCF inclined at 20º (angle open downwards and laterally), in a single-leg stance with a 47.76 kg mass, the reaction force reaches 440.27 N (Eq. 2). Its horizontal component (Fhor), directed medially, is 150.57 N, or 15.35 kg (Eq. 3). This force tends to displace the acetabulum off the femoral head. In a natural hip joint, there will be a tendency to dislocation. It is prevented by: the abductor muscle group and the acetabular labrum, which provides a suction seal. The listed structures are normally effective with an average traction of 59.61 kg. At the same time, the horizontal component of the reaction force of the tensioned LCF will reduce the threshold of resistance to dislocation to 44.26 kg. The obtained value is less than the effective body weight in a single-support pose of 47.76 kg (2012PauwelsF).

Where the pelvis is tilted medially, this condition results in subluxation, which inevitably stretches the joint capsule and external ligaments, causing discomfort or pain. Relief is achieved by tilting the pelvis upward and laterally. Arthroscopic evidence confirms that in early hip osteoarthritis, the LCF is often damaged, dystrophically altered, or absent (1998ByrdJW; 2001МалаховаСО; 2004ОрлецкийАК_ОгаревЕВ; 2006RuhmannO_BohnsackM).

Patients with LCF pathology intuitively raise the pelvis, lean their torso, or extend an arm toward the affected side during single-leg stance or mid-stance phase of the gait cycle. Our data show that in individuals without hip pathology, pelvic tilt downward in single-leg stance is 5.8±2.4º; in stage 1 coxarthrosis, it is 2.3±1.9º; and in stages 2-3, it tilts upward by 4.6±2.5º. Of the 82 examined individuals with osteoarthritis of the hip joint, 78 had a pelvic tilt to the non-supporting side in the mid-stance phase of the step that was less than the norm of 2.2±1.7°. Excessive arm abduction and its imbalance were observed in 79 cases, with spinal deviation toward the supporting side averaging 7.1±3.1º (vs. 1.9±2.0º normal) across all coxarthrosis stages (2012,2023АрхиповСВ).

Lateral pelvic tilt eliminates subluxation risk, including by relaxing the LCF. However, compensatory disruption of posture and gait has detrimental effects on the musculoskeletal system. Without an adequately functioning LCF, which is an additional flexible support for the body, the average daily pressure on the upper segment of the femoral head increases (Eq. 5). In adults, this provokes: subluxation, formation of intraosseous cysts, abrasion of cartilage or so-called "aseptic necrosis" of the femoral head, which always end in osteoarthritis (Fig. 5).


Figure 5. Femoral head removed during hip replacement for osteoarthritis, with cartilage wear zone indicated (from 2012АрхиповСВ , with additions).


In our view, elongated LCF in children may, beyond subluxation, lead to coxa magna or Legg-Calvé-Perthes disease.

Conclusion

Calculations highlight the LCF’s critical role in hip joint stabilization. Partial proximal detachment LCF with elongation promote subluxation during single-leg stance. To solve this problem, restoration of the normal length of the LCF and proximal attachment is required. Without this, surgical treatment of the acetabular labrum injury is ineffective, since isolated labral repair does not prevent instability during walking and osteoarthritis.

References

Bombelli R. Structure and function in normal and abnormal hip: how to rescue mechanically jeopardized hip. 3-rd. ed., rev. and enl. p. Berlin, Heidelberg, New York: Springer Verlag, 1993. link.springer.com

Byrd JW. Operative hip arthroscopy. New York: Thieme, 1998. chamblinbookmine.com

Cerezal L, Arnaiz J, Canga A, Piedra T, Altónaga JR, Munafo R, Pérez-Carro L. Emerging topics on the hip: ligamentum teres and hip microinstability. European journal of radiology. 2012;81(12)3745-54. artroscopiaycadera.es

Chadha-Day F, Ellis J, Marsh DJ. Axion dark matter: What is it and why now?. Science advances. 2022;8(8)eabj3618. pmc.ncbi.nlm.nih.gov

Gerdy PN. Physiologie médicale, didactique et critique. T. 1. Paris: Librairie de Crochard, 1833. books.google

Maldonado DR, Glein RM, Domb BG. Arthroscopic acetabular labral reconstruction: a review. Journal of hip preservation surgery. 20207(4)611-20. academic.oup.com

Mortensen AJ, Johnson BT, Featherall J, Mills MK, Metz AK, Froerer DL, Aoki SK. Increased Labral Height is Associated with Greater Distractive Stability of the Hip: An In Vivo Analysis. Arthroscopy: The Journal of Arthroscopic & Related Surgery. 27 March 2025.    sciencedirect.com

Pauwels F. Biomechanics of the locomotor apparatus: contributions on the functional anatomy of the locomotor apparatus. Berline [etc.], Springer Science & Business Media, 2012. books.google

Ruhmann O, Borner C, von Lewinski G, Bohnsack M. Ligamentum teres. Orthopade. 2006;35(1)59-66.  link.springer.com

Strange FGStC. The hip. London: William Heinemann Medical, 1965. amazon.co.uk

Westermann RW, Day MA, Duchman KR, Glass NA, Lynch TS, Rosneck JT. Trends in hip arthroscopic labral repair: an American Board of Orthopaedic Surgery Database Study. Arthroscopy: The Journal of Arthroscopic & Related Surgery. 2019;35(5)1413-9. arthroscopyjournal.org

Архипов СВ(a). Моделирование взаимодействия LCF нормальной длины и отводящей группы мышц. О круглой связке бедра. 09.06.2024. kruglayasvyazka.blogspot.com 

Архипов СВ(b). Моделирование взаимодействия удлиненной LCF и отводящей группы мышц. О круглой связке бедра. 09.06.2024. kruglayasvyazka.blogspot.com

Архипов СВ(c). Моделирование взаимодействия LCF нормальной длины и отводящей группы мышц. О круглой связке бедра. 09.06.2024 kruglayasvyazka.blogspot.com

Архипов СВ(d). Моделирование взаимодействия LCF, вертлужной губы и отводящей группы мышц. О круглой связке бедра. 12.06.2024. kruglayasvyazka.blogspot.com

Архипов СВ. Роль связки головки бедренной кости в патогенезе коксартроза: дис. … канд. мед. наук. Москва, 2012.  medical-diss.com  ,  kruglayasvyazka.blogspot.com

Архипов СВСвязка головки бедренной кости: функция и роль в патогенезе коксартроза; 2-ое изд., испр. и доп. Йоэнсуу: Издание Автора, 2023. books.google

Малахова СО. Артроскопия тазобедренного сустава (клинико-экспериментальное исследование): Дисс. … канд. мед. наук. Москва, 2001.  cito-priorov.ru

Орлецкий АК, Малахова СО, Морозов АК, Огарев ЕВ. Артроскопическая хирургия тазобедренного сустава. Под редакадС.П. Миронова. Москва, 2004. kingmed.info 


Reviews

First reviewer

Grok, Artificial Intelligence, Developed by xAI.

Review ofthe Article by S.V. Arkhipov "Why Restoration of the Acetabular Labrum MayBe Ineffective?: A Note on the Mysterious 'Dark Matter' of the Hip Joint".

Second reviewer (after revision of the article)

ChatGPT, a language model trained to assist with text analysis and editing OpenAI, 2025.

ScientificReview and Critical Commentary On the Article: “Why Acetabular Labrum RepairMay Be Ineffective: A Note on the Mysterious ‘Dark Matter’ in the Hip Joint”. Author:S.V. Arkhipov.



Address correspondence to Arkhipov Sergey, M.D., E-mail: archipovsv@gmail.com

 

Cite:

Online version:

Arkhipov SV. Why Acetabular Labrum Repair May Be Ineffective: A Note on the Mysterious ‘Dark Matter’ in the Hip Joint. About round ligament of femur. April 7, 2025. https://roundligament.blogspot.com/2025/04/2025arkhipovsv-why-acetabular-labrum.html

PDF version:

Arkhipov SV. Why Acetabular Labrum Repair May Be Ineffective: A Note on the Mysterious ‘Dark Matter’ in the Hip Joint. About round ligament of femur. April 7, 2025; 1-6. DOI: 10.13140/RG.2.2.26370.59842 , researchgate.net  ,  Google Drive


© 2025 Arkhipov S.V. This is an open access article under the CC BY-NC-ND license  (https://creativecommons.org/licenses/by-nc-nd/4.0/)

 

Additions

No.


History of the article:

First publications in the online magazine:

[Ru] Архипов СВ. Почему восстановление вертлужной губы может быть неэффективно?: Заметка о таинственной «темной материи» в тазобедренном суставе. О круглой связке бедра. 06.04.2025. https://kruglayasvyazka.blogspot.com/2025/04/2025.html


PDF version:

[Ru] Архипов СВ. Почему восстановление вертлужной губы может быть неэффективно?: Заметка о таинственной «темной материи» в тазобедренном суставе. О круглой связке бедра. 06.04.2025; 1-7.  DOI: 10.13140/RG.2.2.14659.31520 , researchgate.netGoogle Drive

[En] Arkhipov SV. Why Acetabular Labrum Repair May Be Ineffective: A Note on the Mysterious ‘Dark Matter’ in the Hip Joint. About round ligament of femur. April 7, 2025; 1-6. DOI: 10.13140/RG.2.2.26370.59842 , researchgate.net  ,  Google Drive


                                                                     

NB! Fair practice / use: copied for the purposes of criticism, review, comment, research and private study in accordance with Copyright Laws of the US: 17 U.S.C. §107; Copyright Law of the EU: Dir. 2001/29/EC, art.5/3a,d; Copyright Law of the RU: ГК РФ ст.1274/1.1-2,7




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