Improving
Postoperative Comfort and Increasing the Reliability of Hip Prostheses by
Supplementing with Artificial Ligaments: Proof of Concept and Prototype
Demonstration
The principle of operation of an experimental total hip endoprosthesis augmented with ligament analogs has been demonstrated in single-leg vertical stances and at the mid-stance phase of the single-support period of gait. The experiments were conducted on a specially designed mechatronic testing rig. The concept of the important role of the ligamentous apparatus is further illustrated by a set of demonstrative mechanical models. The data obtained from the experiments enabled the development of a prototype total hip endoprosthesis incorporating an analog of the ligamentum capitis femoris (LCF), exhibiting pronounced anti-dislocation properties. The use of ligament analogs is expected to substantially increase the reliability of total hip endoprostheses and improve postoperative patient comfort.
The problems associated with hip arthroplasty
are well-known: dislocation, gait disturbance, instability of
vertical posture, destabilization of components, wear of the friction pair, and
accumulation of wear debris (Figure 1). The black metal-polymer
paste generated by friction contaminates the intra-articular environment and
serves as a prerequisite for aseptic and septic inflammation. Confidence in the
reliability of the implant is undermined by the relatively high probability of
prosthesis dislocation. According to the literature, the dislocation rate in
the 1970s and 1980s reached 15% (1985BinnsM). Currently, in primary hip
arthroplasty, dislocations occur in 0.2–10% of cases, particularly frequently
following femoral neck fractures (1999FenderD_GreggP; 2005BerryDJ_HarmsenWS;
2006MeekRM_HowieCR; 2007PatelPD_FroimsonMI; 2008ParviziJ_SharkeyPF;
2014DargelJ_EyselP). In revision arthroplasty, dislocation rates
can reach 25–31% (1997HedlundhU_FredinH; 2007PatelPD_FroimsonMI; 2014DargelJ_EyselP). Over time, the probability of prosthesis dislocation steadily
increases, regardless of the surgical approach used or the meticulousness of
soft tissue closure (2004BerryDJ_HarmsenWS; 2006KwonMS_SalehKJ).
 |
| Figure 1. Illustrations of wear on the articulating surfaces of hip endoprostheses; left – hemiarthroplasty with polyethylene head; right – polyethylene liner of the acetabular component of a total endoprosthesis (author's observations). |
In our view, the primary cause of these adverse phenomena is the absence of a ligamentous apparatus analog in the design of artificial joints. In particular, without the ligamentum capitis femoris (LCF), the pressure exerted by the femoral head on the superior sector of the acetabular cavity increases significantly. This was noted as early as the 17th century and confirmed by authoritative researchers in subsequent centuries (1672GengaB; 1698CowperW; 1728WaltherAF; 1801BellJ; 1836WeberW_WeberE; 1845ArnoldF; 1856MeyerGH; 1857TurnerW; 1874SavoryWS). The significant role of the femoral head ligament in the biomechanics and stabilization of the hip joint was emphasized by authors of the 20th century (1969DeeR; 1976CrelinES; 1985ИваницкийМФ; 1993НеверовВА_ШильниковВА). Information substantiating the importance of the hip joint ligaments, especially the LCF, has been compiled by us within the framework of a Russian-English bibliographic project (https://roundligament.blogspot.com [En]; https://kruglayasvyazka.blogspot.com [Ru]). We suggest using the articles and quotations on these web resources as an additional literature review for this publication.
The first unipolar hip endoprosthesis with an analog of the LCF was described in 1954 by L.L. Pellet (1956PelletLL; Figure 2). In 1984, G.E. Dudko performed the first implantation of an original unipolar artificial joint equipped with an analog of the LCF (1990DudkoGE). In 1994, we proposed our own designs of total and subtotal hip replacements, with integrated external and internal ligaments (1996ArkhipovSV(a); 1996ArkhipovSV(b); Figure 3). Alongside theoretical developments, substantial evidence supporting the viability of the concept has been provided by experimental methods. Our initial experiments on hip joint models with ligament analogs were first described in 2004 (2004Архипов-БалтийскийСВ). In 2008, we clarified our concept regarding the role of the LCF in maintaining vertical postures (2008ArkhipovSV). In a dissertation-based experimental-clinical study defended in 2013, we demonstrated the significant role of pathology of the LCF in the pathogenesis of hip osteoarthritis (2012АрхиповСВ). In 2019, the results of a pilot experimental study examining the role of the LCF using an electromechanical model—which became the precursor to an endoprosthesis with artificial ligaments—were published (2019ArkhipovSV_SkvortsovDV). A review of patented endoprosthesis designs incorporating the LCF was prepared by us in 2021 (2021ArkhipovSV_SkvortsovDV). An expanded critical analysis of all known designs of this type and a synthesis of current information on the topic were completed in 2025 (2025АрхиповСВ, Parts 1–3).
 |
| Figure 2. Femoral endoprosthesis proposed in 1954 by L.L. Pellet (fragment of illustration from 1956PelletLL; image rotated clockwise). |
Our own
research has convinced us of the benefits of hip arthroplasty incorporating a
ligamentous apparatus. We believe that in this symphony, the lead violin is
played by the LCF. In 2025, the importance of this structure was confirmed by several
studies of various designs. Experiments have shown that an artificial joint
with a LCF accurately
replicates the motions of the human hip joint (2025TengJ_RenL). Finite element
analysis has helped confirm the role of the LCF as a rotational stabilizer in the
frontal and transverse planes (2025ZhangY_MartinRL). Experimental evidence has
been obtained demonstrating unloading of the superior acetabular region upon
tensioning of the LCF (2025ChenJH_AcklandD). The use of an analog of the LCF in the joint of a zoomorphic robot
has also been described (2025ItoH_SuzumoriK). This has provided new impetus to
our development of hip endoprostheses with ligament analogs, initiated in 1994
(Figure 3).
%D0%90%D1%80%D1%85%D0%B8%D0%BF%D0%BE%D0%B2%D0%A1%D0%92(invention).jpg) |
| Figure 3. Artificial hip joint designed by S.V. Arkhipov (illustration from invention application No. 94040447 dated 04.11.1994); designations: A – lateral view of the artificial joint with attached artificial ligaments; B – longitudinal section of the artificial joint; C – cross-section of the acetabular component (from 1996ArkhipovSV(b), with altered figures arrangement). |
Here, we briefly describe the main results of testing an experimental total hip endoprosthesis with ligament analogs, as well as a prototype total hip endoprosthesis incorporating an analog of the LCF. The foundation of the presented work consists of our clinical studies, review of specialized literature, and experiments on mechanical models (for details, see the corresponding section of the website kruglayasvyazka.blogspot.com).
For the
present study, we fabricated an experimental total hip endoprosthesis augmented
with ligament analogs. The base was a unipolar hip endoprosthesis developed in
1950 by F. Thompson (1952ThompsonFR; 1983WaggonerWH). The polished hollow head
of the design had a diameter of 54 mm. An elliptically shaped neck connected to
a stem 108 mm long with a maximum thickness of 10 mm. Two through transverse
holes were drilled in the stem for attachment elements. A through hole 6 mm in
diameter was drilled in the center of the medial sector of the head, directed
toward the neck (Figure 4).
 |
| Figure 4. Subtotal endoprosthesis designed by F.R. Thompson in our modification; the arrow indicates the hole in the medial part of the head, a photograph of the product label is placed next to it. |
The
acetabular component was machined from stainless steel. It consisted of a 1/2
portion of a thick-walled spherical shell with an outer diameter of 70 mm. At
the shell apex, a cylindrical rod 55 mm long and 15 mm in diameter was
integrally machined. Three through transverse holes 6 mm in diameter were
drilled in the rod for attachment. The inner spherical surface, 54 mm in
diameter, was machined to provide a sliding fit for the spherical head model.
The acetabular component wall thickness was 8 mm. Seven blind threaded M3 holes
were made in the end face of its outer rim at the 2, 4, 5, 7, 8, 10, and 12
o'clock positions. A shaped recess resembling a tennis racket was machined
inside the spherical shell. This shaped recess consisted of a central circular depression
(fossa) and a groove. The groove extended to the rim of the cup, with its long
axis oriented toward 6 o'clock. The described shaped recess was intended to
simulate the acetabular fossa and acetabular notch (Figure 5).
 |
| Figure 5. Acetabular component of the experimental total hip endoprosthesis; view of the inner cavity reproducing the acetabular fossa and acetabular notch; a polymer cable imitating the LCF is inserted into one of the through holes. |
The
diameter of the central part of the shaped recess was 30 mm, the width of the
longitudinal groove was 10 mm, and its length was 30 mm. The depth of the
shaped recess did not exceed 5 mm in any area. The width of the contact surface
of the spherical shell, which served as an analog of the lunate surface of the
acetabulum, was 25 mm. The central angle of the fossa of the component was 70°,
and the maximum cavity depth was 33 mm. Several through holes were drilled in
the shaped recess of the spherical shell for attachment of the analog of the LCF. Flexible steel cables 1.5 mm in
diameter with a polymer coating were used as artificial ligaments for the
experimental total hip endoprosthesis (Figure 6). The femoral and acetabular
components were externally connected by four flexible elements: superior,
inferior, anterior, and posterior. These reproduced the external hip ligaments:
ischiofemoral ligament, pubofemoral ligament, and the two portions of the
iliofemoral ligament. Their orientation, attachment, and length approximately
corresponded to the natural analogs.
 |
| Figure 6. Flexible elements made of 1.5 mm diameter steel cable used to reproduce the ligaments of the experimental total hip endoprosthesis. |
The LCF was reproduced using a flexible
steel wire cable 1.5 mm in diameter with a polymer coating. The distal end of
the ligament analog was passed through the through hole in the spherical head
and secured with a screw clamp to the stem. The proximal end of the ligament
analog was inserted into a hole in the shaped recess of the acetabular
component located at the boundary between the fossa and the longitudinal
groove. The acetabular component was then placed onto the spherical head
lubricated with household machine oil per TU 1-15-691-77. Thereafter, the
analog of the LCF was tensioned and secured with a screw clamp on the exterior of the
acetabular component. The length of the ligament analog located inside the
joint of the experimental endoprosthesis was selected to prevent damage to the
distal end of the flexible element during movements (Figure 7).
 |
| Figure 7. View of the acetabular component and femoral head of the experimental total hip endoprosthesis; the principle of their connection by the analog of the LCF is shown. |
A
mechatronic testing rig was designed to test the experimental total hip
endoprosthesis with artificial ligaments. The femoral component was fixed in a
position natural for the weight-bearing femur at the upper part of a mechanical
analog of the lower limb. The latter was represented by a 30 mm diameter metal
tube, the lower part of which was connected via a ball joint to a horizontal
massive platform measuring 100 × 80 cm. Four guy lines with turnbuckles were
used to maintain and adjust the position of the lower limb analog (Figure 8).
 |
| Figure 8. Testing rig for the experimental total hip endoprosthesis with ligament analogs, prior to installation of mechatronic components; ligament analogs are not secured, and the pelvic analog is held by a spring dynamometer simulating the action of the abductor muscle group. |
The
acetabular component was fixed in a pelvic analog assembled from perforated
plates and M6 threaded fasteners. The size of the pelvic analog approximately
corresponded to the dimensions of an adult human pelvis. The dimensions of the
pelvic analog approximated those of an adult human pelvis and were based on an
anteroposterior pelvic radiograph of a healthy 27-year-old male. The acetabular
component was positioned in a standard orientation: 45° of lateral inclination
and 25° of anteversion in the horizontal plane. A spring dynamometer with
adjustable length was used to hold the pelvic analog at rest during the
preliminary stage. The weight of the pelvic analog without additional equipment
did not exceed two kilograms. The position of the overall center of mass of the
pelvic analog was adjusted so that its projection coincided with the ball joint
at the lower part of the lower limb analog. The total height of the testing rig
was approximately 90 cm.
The testing
rig was supplemented with analogs of the gluteus medius muscle and short
external rotator hip muscles (Figure 9).
 |
| Figure 9. Testing rig for the experimental total hip endoprosthesis with ligament analogs; the pelvic analog is equipped mechatronic components connected to a personal computer, and additional load. |
The gluteus
medius analog was intended to simulate the action of the hip abductor muscle
group complex. The short hip muscle analog reproduced the average direction of
force produced by these muscles during thigh supination. The muscle analogs
were made from flexible metal cables connected to rotary digital DC
servomotors. A programmable platform based on an Arduino board powered by a
battery was assembled for control. The flexible metal cables of the muscle
analogs were attached to the lower limb analog, while the controlling
servomotors were fixed inside the pelvic analog. Approximate force measurements
were obtained using a spring dynamometer with a maximum load of 10 kg and a
resolution of 0.1 kg incorporated into the gluteus medius analog. A movable 1
kg load was attached superiorly and posteriorly to the pelvic analog to adjust
the position of the overall center of mass (Figure 10).
 |
| Figure 10. Top view of the pelvic analog and mechatronic components of the testing rig for the experimental total hip endoprosthesis with ligament analogs. |
The testing
rig was used to verify the fundamental feasibility of adequate functioning of
the experimental total hip endoprosthesis with ligament analogs. In the first
series of experiments, we reproduced the two main types of single-leg stance.
The "tense" type is characterized by a horizontal pelvic position,
while the "relaxed" type features pelvic tilt toward the
non-weight-bearing leg (Figure 11).
 |
| Figure 11. Schematic representation of the main types of single-leg stance; left – relaxed single-leg orthostatic posture; right – tense single-leg orthostatic posture (from 2008ArkhipovSV). |
In the
second series of experiments, pelvic motion in the mid-stance phase of the
single-support period of gait was reproduced. In both series, the additional
load on the pelvic analog was fixed in a position corresponding to the location
of the overall center of mass in single-leg stance and during the
single-support phase of gait. Available data from examinations of healthy
subjects using optical motion capture systems served as a reference. During
testing of the experimental endoprosthesis, changes in the readings of the dynamometer
of the gluteus medius muscle analog were recorded. Attention was also paid to
the degree of tension in both the external ligament analogs and the analog of
the LCF. Pelvic
analog displacements during reproduction of motions in the mid-stance phase of
the single-support period were recorded using a video camera.
Direct
observation of changes in the position of the ligament analog was impossible.
To gain insight into its movements during experiments, we fabricated a series of
demonstrative models. A planar pelvic model with hip joints was made from
plywood. Flexible nylon elements served as ligament of the analogs of the LCF, while rubber cords were used as
gluteus medius analogs. A three-dimensional "pelvis–femur" mock-up
was assembled from anatomical bone models produced by Synbone company. The
mock-up was supplemented with polymer articular surfaces and a nylon cord
analog of the LCF. A through hole was made in the projection of the acetabular fossa for
visualization of the ligament analog.
We analyzed
the interaction between muscle analogs and ligament analogs of the experimental
total hip endoprosthesis during simulation of vertical postures and walking.
Optimal attachment points and lengths of the artificial ligaments were
determined. Based on the experimental results, we fabricated a prototype total
hip endoprosthesis with a LCF analog. Preliminary testing was performed to identify specific positive
and negative properties. Since direct observation of the ligament analog within
the prototype was not feasible, an additional demonstrative mechanical hip
joint model was constructed. This model was based on a commercially available
hemiarthroplasty prosthesis, complemented by a custom-machined acetabular
component with a through-hole in the fossa region and a polymer cord
reproducing the LCF. A modified spring dynamometer was used to stabilise the femoral and
pelvic components of the model.
In the
first series of experiments, the experimental total hip endoprosthesis with
ligament analogs was tested in single-leg vertical stances. Initially, the
tense type of stance with a horizontal pelvic position was reproduced on the
testing rig (Figures 11, 12).
 |
| Figure 12. Approximate relationship between the femur and pelvis in a tense single-leg stance reproduced using the “pelvis–femur” mock-up. The inset in the lower right shows a view through the opening in the acetabular fossa of the pelvic model, revealing a slack analog of the LCF. |
To maintain
the horizontal position of the pelvic analog on the testing rig, shortening of
the gluteus medius analog was required. This simulated contraction of the
muscle, as confirmed by the dynamometer readings (Figure 13).
 |
| Figure 13. Reproduction of a tense single-leg stance on the testing rig; the pelvic analog is maintained in a horizontal position by the force generated by the gluteus medius analog (see text for details). |
The gluteus
medius analog acted only in the frontal plane, preventing medial tilt of the
pelvic analog. In the joint of the experimental total hip endoprosthesis with
ligament analogs, a position close to the midpoint between abduction and
adduction was achieved. In the sagittal plane, the pelvic analog tended to
rotate backward relative to the horizontal axis, primarily under the influence
of the additional load. Resistance to backward tilting of the pelvic analog was
provided by tension in the pubofemoral ligament analog. The other ligament
analogs remained slack. Relaxation of the LCF analog was determined by sagging of
the portion exiting the acetabular component.
It is
normal for the LCF to be slack in positions other than maximum adduction in the hip joint.
This is clearly demonstrated by the planar pelvic model with hip joints
equipped with LCF analogs (Figure 14).
 |
| Figure 14. Planar pelvic model with hip joints; reproduction of the midpoint position between abduction and adduction in both hip joints; right – overall view of the model; left – view of the right hip joint with a relaxed analog of the LCF. |
It was
noted that, in addition to backward tilt of the pelvic analog in the sagittal
plane, it automatically rotated backward in the horizontal plane. This
reproduced supination in the joint of the experimental total hip endoprosthesis
with ligament analogs. Limitation of horizontal rotation of the pelvic analog
was provided by tension in the pubofemoral ligament analog. Maintenance of
pelvic stability did not require activation of the analog of the short external
rotator muscles of the hip.
The
experiment demonstrated that, to ensure stability in the tense single-leg
stance on a total hip endoprosthesis with ligament analogs, the force from the
abductor muscle group and tension the pubofemoral ligament analog will be
necessary and sufficient. In this posture, such an endoprosthesis offers no
advantages over existing designs.
Next, the
relaxed type of stance with pelvic tilt was reproduced on the testing rig
(Figure 11). Studies on hip joint biomechanics generally do not differentiate
between tense and relaxed single-leg vertical postures. However, they differ
not only externally but also in the functioning of the hip ligaments. In the relaxed
single-leg stance, adduction of the femur results in at least tensioning of the
LCF analog. This
is clearly demonstrated on the "pelvis–femur" mock-up (Figure 15).
 |
| Figure 15. Approximate relationship between the femur and pelvis in the relaxed single-leg stance reproduced on the "pelvis–femur" mock-up; the inset at bottom right shows a view of the hole in the acetabular fossa of the pelvic model, through which the tensioned analog of the LCF is visible. |
When
reproducing the relaxed stance type on the testing rig, the pelvic analog
tilted medially in the frontal plane. To shift the pelvic analog from the
horizontal position, elongation of the gluteus medius analog was required. This
simulated relaxation of the muscle, as confirmed by dynamometer readings. Force
in the gluteus medius analog system decreased to zero. Nevertheless, the pelvic
analog was in a position of stable equilibrium. In the joint of the
experimental total hip endoprosthesis with ligament analogs, a position
corresponding to femoral adduction was achieved. Further medial tilt of the
pelvic analog was prevented solely by the tensioned ligament analogs (Figure
16).
 |
| Figure 16. Reproduction of the relaxed single-leg stance on the testing rig; the pelvic analog with a 5° medial tilt is held by tensioned ligament analogs (details in text). |
The
tensioned ligament analogs also limited backward deviation of the pelvic analog
in the sagittal plane caused by the additional load. It was noted that the
pelvic analog automatically rotated forward in the horizontal plane. This
reproduced pronation in the endoprosthesis joint. Simultaneously, moderate
elongation of the short external rotator analog occurred. Limitation of forward
horizontal rotation of the pelvic analog was due to combined tension in the
ligament analogs.
In addition
to the external ligament analogs, tension in the LCF analog was recorded. This was
observed by tension in the portion of the element exiting the acetabular
component. Direct observation of tension in the LCF analog within the tested
experimental total endoprosthesis was not possible. Visualization of the
behavior of the ligament analog during femoral adduction is available on the
demonstrative planar pelvic model. On it, we reproduced the relaxed single-leg
vertical posture, in which the LCF is tensioned in the weight-bearing hip joint (Figure 17).
 |
| Figure 17. Planar pelvic model with hip joints; reproduction of the relaxed single-leg vertical posture with adduction in one hip joint and abduction in the other; right – overall view of the model; left – view of the right hip joint with a tensioned analog of the LCF. |
 |
| Figure 18. View of the inferior hemisphere of the femoral head component of the electromechanical hip joint model with ligament analogs; left – before the start of experimental studies; right – after completion of the series of experiments, with signs of wear appearing. |
Following
spontaneous tensioning of the ligament analogs in the experimental total hip
endoprosthesis, the pelvic analog remained in a stable position. It could not
be tilted downward medially, rotated backward in the sagittal plane, or displaced
forward in the horizontal plane. Reverse movements were performed virtually
unimpeded.
The experiment demonstrated that, to ensure stability in a relaxed single-leg stance supported by a total hip endoprosthesis with ligament analogs, the reaction forces of the ligaments—provided sufficient strength—are necessary and sufficient. Теоретически, для поддержания стабильности таза нет необходимости напрягать среднюю ягодичную мышцу, а также короткие мышцы бедра, которые обеспечивают наружное вращение бедра. In the relaxed single-leg posture, muscles are primarily needed to maintain balance and proportional ligament tension. A total hip endoprosthesis with ligament analogs will offer several advantages over existing designs. It will allow reduction of load on the abductor muscle group in the relaxed single-leg stance, decrease pressure from the superior sector of the acetabular component on the prosthetic head, and enhances overall body stability through pelvic stabilisation achieved by combined ligament tension.
At the
final stage of experiments on the testing rig, pelvic motion during the
mid-stance phase of the single-support period of gait was reproduced. During
this phase, the pelvis moves along an arc from superior to inferior and to
anterior while simultaneously tilting forward in the sagittal plane (Figure
19).
 |
| Figure 19. Fragment of a report from an optical motion analysis system examining normal human gait patterns; graphs illustrate pelvic motion in three planes; left – pelvic motion in the sagittal plane; center – pelvic motion in the frontal plane; right – pelvic motion in the horizontal plane; designations: green curve – angle change of the left pelvic half; red curve – angle change of the right pelvic half; black curve – average statistical angle change of the pelvis (norm according to program developers); vertical red and green lines mark the corresponding gait periods (report generated by C-Motion software; data kindly provided by O. Kudryashov, National Rehabilitation Center “Vaivari”, Latvia). |
In the
natural hip joint, mid-stance involves adduction from abduction and supination
from pronation, accompanied by continuous extension. These patterns were
observed in our analysis of video recordings of gait in healthy subjects
examined as part of a dissertation study (2012АрхиповСВ). It was noted that, normally, during the
single-support phase, adduction of the femur and medial pelvic tilt occur
(Figure 20). This position resembles the relaxed single-leg stance.
 |
| Figure 20. Frame from a normal gait kinogram; mid-stance phase of the single-support period (from 2012АрхиповСВ; yellow line added to indicate the magnitude of pelvic tilt toward the non-weight-bearing side). |
Data
obtained previously were taken into account during experiments on the testing
rig. At the first stage, we reproduced the pelvic position characteristic of
the beginning of mid-stance. The pelvic analog was rotated backward in the
horizontal plane and elevated above the support plane in the frontal plane. The
achieved position was fixed by shortening the gluteus medius analog and the
short external rotator analog. Force appeared in the gluteus medius analog
system, as confirmed by deflection of the dynamometer needle.
Pelvic analog motion was initiated by activating the servomotors. They simultaneously elongated the gluteus medius analog and the short external rotator analog (see video recording).
Dynamic tests on the mechatronic testing rig. The principle of operation of the experimental total hip endoprosthesis with ligament analogs is demonstrated during the mid-stance phase of the single-support period of gait.
In the joint of the tested experimental total hip endoprosthesis, adduction, supination, and flexion were observed. The pelvic analog spontaneously rotated forward in the horizontal plane, tilted downward medially in the frontal plane, and tilted forward in the sagittal plane. Pelvic analog displacement occurred under the force of gravity. Reduction in servomotor force ensured smooth motion of the pelvic analog but did not generate it.
When testing the experimental total hip endoprosthesis with ligament analogs, no tendency toward dislocation in the joint was noted, either in static positions or during gait simulation. When reproducing the relaxed vertical stance type and mid-stance of the single-support phase when walking, the anti-dislocation effect was produced by the resultant force generated by tension of the LCF analog (Figure 21).
 |
| Figure 21. Schematic representation of the joint of a total endoprosthesis with a LCF analog during adduction of the weight-bearing femur; designations: 1 – femoral head component; 2 – femoral neck component; 3 – acetabular component; 4 – LCF analog; green arrow indicates the reaction force of the ligament analog; red arrow indicates the resultant force pressing the acetabular component against the prosthetic head. |
Reproduction
of pelvic motions in mid-stance on the testing rig demonstrated that they can
occur spontaneously. It is sufficient for the gluteus medius and short external
rotators to function in a yielding mode. Predictable pelvic rotation and
forward translation of the overall center of mass are achieved through
sequential tensioning of the external ligament analogs and the LCF analog.
Thus, a
total hip endoprosthesis with ligament analogs will have significant advantages
over known designs. It will allow: reduction of load on the abductor muscle
group during walking, preservation of the natural gait stereotype, and
elimination of dislocation during femoral adduction. Given the features of load
distribution across the articulating surfaces of an endoprosthesis with ligament
analogs, a low rate of wear in the superior regions of the head and acetabular
component is expected. This, in turn, will reduce the amount of wear debris and
thereby decrease the likelihood of aseptic and septic inflammation.
Analysis of the testing results of the total hip endoprosthesis with ligament analogs on the rig indicated the feasibility of fabricating a prototype of similar design. Available femoral and acetabular components of total endoprostheses were used as the basis. We machined a special polymer annular liner for the acetabular component. The distal end of the LCF analog, made from a polymer cable, was attached to the head. The opposite end of the ligament analog was attached to the acetabular component shell. The length of the ligament analog was adjusted to prevent impingement in the joint at the intended adduction angle.
Manual
testing of the assembled prototype endoprosthesis revealed that the amplitude
of rotation in the horizontal plane (pronation and supination) as well as
abduction in the frontal plane was determined by the size of the opening in the
acetabular liner. Rotation in the sagittal plane forward and backward (flexion
and extension) up to 180° was unrestricted. During simulated adduction in the
prototype total hip endoprosthesis joint with a LCF analog, the femoral head component
was clearly pressed against the acetabular liner (Figure 22).
 |
| Figure 22. Prototype total hip endoprosthesis with a LCF analog; left – overall view of the acetabular component secured in a clamp; right – view of the endoprosthesis demonstrating spontaneous pressing of the femoral head component against the acetabular liner, preventing joint dislocation. |
The force
preventing dislocation appeared during simulated adduction. In the
endoprosthesis fixed in a stand, the anti-dislocation effect was due to the
resultant force arising from the combination of the reaction force of the
tensioned ligament analog and gravity, which tended to rotate the femoral
component toward the vertical line. A similar but less pronounced effect
occurred during simulated extreme supination and pronation with concurrent
moderate adduction. Abduction in the total hip replacement prototype relaxed
the femoral head ligament analog and unlocked the joint. The femoral head
component freely displaced laterally by the length of the ligament analog. A
similar phenomenon was observed when the acetabular component fixed in the
stand was tilted laterally (Figure 23).
 |
| Figure 23. Prototype total hip endoprosthesis with a LCF analog; left – overall view of the acetabular component secured in a clamp and tilted laterally; right – external and top view of the endoprosthesis showing spontaneous downward displacement of the femoral head component out of the acetabular component. |
In the
absence of a force pressing the prosthetic head against the acetabular liner,
dislocation occurred. The femoral head component spontaneously displaced
outward and downward, suspended only by the tensioned ligament analog.
Accordingly, under specially created conditions, the anti-dislocation effect of
the prototype was neutralized.
In the
fabricated prototype, the LCF analog was enclosed by the acetabular component shell, preventing
observation of flexible element movement during articulations. To visualize
changes in the position of the ligament analog in the endoprosthesis, we
designed a special demonstrative mechanical hip joint model. Its main feature
was a through hole in the acetabular component (Figure 24).
 |
| Figure 24. Demonstrative mechanical hip joint model with a hole in the acetabular component; right – overall view; left – view of the hole in the acetabular component and the LCF analog. |
During
simulated adduction in the model, the ligament analog tended to assume a
vertical position. During reproduced pronation and supination, the proximal end
of the ligament analog displaced forward or backward, respectively. During
translational lateral displacement of the femoral head, the ligament analog
tended to assume a horizontal position. Similar movements should be expected in
a real total endoprosthesis with a LCF analog.
On the
mechatronic testing rig, we demonstrated the general operating principle of the
experimental total hip endoprosthesis augmented with ligament analogs in
single-leg vertical stances and during the mid-stance phase of the single-support
period of gait. The data obtained from the experiments enabled the fabrication
of a prototype total hip endoprosthesis incorporating an analog of the LCF.
The testing
results showed that incorporating ligament analogs into the design can increase
the reliability of the total hip endoprosthesis and improve postoperative
patient comfort. Specifically, reliability will be enhanced through: reduced
risk of dislocation, decreased wear rate of the articulating pair, reduced accumulation
of wear debris, and lowered risk of aseptic and septic inflammation. Patient
comfort will be improved by: minimizing the risk of dislocation in the early
postoperative period, reducing load on the abductor muscle group, restoring
natural gait, and increasing body stability in the relaxed vertical posture and
during walking.
The
prototype total hip endoprosthesis with a LCF analog exhibited pronounced
anti-dislocation properties. Such an artificial joint could serve as a foundation
for a series of implants intended for laboratory testing and animal
experiments. The clinical implementation of a total hip endoprosthesis
incorporating at least a LCF analog appears to be a promising direction. Arthroplasty using such
implants, while preserving the external ligaments, would allow elimination of
postoperative dislocation, extension of trouble-free service life, and
improvement of patient gait.
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Author of the article
Arkhipov S.V. – Independent Researcher, MD, PhD, Orthopedic Surgeon, Medical Writer, Joensuu, Finland.
Correspondence: Sergey Arkhipov, email: archipovsv @ gmail.com
Article history
December 28, 2025 - online version of the article published.
Suggested citation
Arkhipov SV. Improving Postoperative Comfort and Increasing the Reliability of Hip Prostheses by Supplementing with Artificial Ligaments: Proof of Concept and Prototype Demonstration. About Round Ligament of Femur. December 28, 2025. https://roundligament.blogspot.com/2025/12/improving-postoperative-comfort.html DOI: 10.13140/RG.2.2.15175.15524
Note
Translation
of the article: Архипов СВ. Улучшение
послеоперационного комфорта и повышение надежности тазобедренного протеза путем
дополнения искусственными связками: Демонстрация концепции и прототип. О
круглой связке бедра. 28.12.2025.
Keywords
ligamentum capitis femoris, ligamentum teres, ligament of head of femur, endoprosthesis, prosthesis, complication, dislocation of a hip joint prosthesis
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