ORIGINAL ARTICLES
Stabilization of Joint Forces of the Subtalar Complex via HyProCure Sinus Tarsi Stent
Michael E.Graham,DPM*
Rachit Parikh,MS*
Vijay Goel,PhD†
手工纸花Devdatt Mhatre,MS†
Aaron Matyas,MS†Background:The foot is the foundation of the body.The stability of the osous
hindfoot structure is crucial in bipedal locomotion.The subtalar joint is responsible for
conversion of the rotatory forces of the lower extremities and dictates the movements of
the midtarsal joints and the forefoot.In a hyperpronated foot,excessive abnormal
pronation results in partial to full obliteration of the sinus tarsi.The hypothesis is that the
茶话会活动方案HyProCure device will prevent obliteration of the sinus tarsi,thereby stabilizing the
subtalar joint complex and eliminating the excessive forces to the proximal and distal
musculoskeletal system that occur with every step.
网瘾
Methods:Five fresh-frozen human foot cadaver specimens that reprented pathologic
hindfoot and midfoot instability and partial to full obliteration of the sinus tarsi were
axially compresd to2,000N and internally rotated by158to produce maximum
pronation of the subtalar joint using a biaxial materials testing machine.The forces were
measured across the posterior and anterior talocalcaneal joint facets before and after
placement of the HyProCure stent.
Results:The subtalar joint stabilized after placement of the HyProCure sinus tarsi stent.
The mean61SD forces in the posterior talocalcaneal joint incread from795.886
向上英文106N to1,004.86672.41N(P,0.05,two-tailed paired t test).The mean6SD forces
at the anterior talocalcaneal joint decread from520.156127.18N to394.56673.83
N(P,0.05),shifting the contact area posteriorly.
纷至沓来的读音Conclusions:Placement of the HyProCure subtalar stabilization stent in a hyper-
pronated foot prevents excessive talar subluxation and assists in proper distribution of
the axial loads on the subtalar facet joints.(J Am Podiatr Med Assoc101(5):390-399,
2011)
Walking is the cond most common conscious function of the body next to breathing.It has been estimated that the average person takes8,000to 10,000steps per day.1,2The foot has to bear the weight and the inertial forces of the body above and the pressure from the ground below.A stable subtalar joint complex is crucial to provide support to the proximal osous structures and to allow the normal transfer of forces from the leg through the foot and onto the weightbearing surface.Instability of the normal axis of motion of the subtalar joint will result in excessive forces actin板报图案设计
g on the joints and soft tissues of the foot,leading to pathologic conditions distally,3-5‘‘wear and tear,’’and mal-alignment of the proximal musculoskeletal kinetic chain.4,6-8
Many previous investigations6,9-11have stated the importance of the subtalar joint in the biomechanics of the hindfoot.The subtalar joint assists in transferring the proximal forces from the body through the rest of the foot.The contact forces and the pressures between joint surfaces are the quantitative parameters that help detect the condi-tions that change the joint mechanics.11As Harris and Beath12stated,‘‘A strong foot is one in which the tarsal bones are so articulated with each other that the weight of the body is borne without appreciable movement between them.’’A weak foot
*Graham International Implant Institute,Macomb,MI.
†University of Toledo,Toledo,OH.
Corresponding author:Michael E.Graham,DPM,FACFAS, Graham International Implant Institute,16137Leone Dr, Macomb,MI48042.(E-mail:)
would indicate instability of the talus on the calcaneus,resulting in excessive joint motion. Abnormal excessive motion of the talus on the calcaneus during weightbearing leads to excessive pronatory m
otion of the foot.The talus rotates into a varus position,and the foot will compensate, resulting in hyperpronation.
Subtalar arthroereisis is a minimally invasive percutaneous procedure that eliminates excessive talar displacement and calcaneal eversion by placing a stabilization device in the sinus tarsi.This may be a viable treatment option compared with more aggressive surgical procedures,such as calcaneal osteotomy with or without bone grafts and arthrodesis of the talus to the calcaneus using Steinmann pins,staples,or cancellous screws. There is a long history of various designs and materials of subtalar stabilization devices.8,13-17 Limitations of subtalar arthroereisis have also been reviewed but are primarily due to the inrtion technique,material composition,anatomical posi-tion,sizing,and tolerability.17,18
The HyProCure(GraMedica,Macomb,Michigan) sinus tarsi stent was designed taking into consider-ation the limitations of the previous devices.This device is compod of titanium and will not fragment like predicate devices compod of medical-grade plastics.Titanium is stronger than bone and can withstand repetitive forces.The inrtion of this device follows the alignment of the sinus tarsi,that is,from anterior-distal-lateral to proximal-medial-posterior(Fig.1),compared with other designs that are inrted purely lateral to medial.8,17,18HyProCure is placed in both the sinus and c
analis portions of the sinus tarsi,whereas other devices are placed in the outer50%of the sinus tarsi.This stent goes deeper into the sinus tarsi as compared with the other devices.Owing to the inherent shape of the HyProCure device,the middle tapered portion of the device abuts the lateral part of the canalis tarsi to ensure proper placement and prevent overinrtion.Trial sizers are ud to determine the appropriate size to stabilize subtalar joint motion,which eliminates excessive motion while allowing the normal amount of pronation.
We conducted this study to analyze the contact forces on the subtalar joint facets as a result of inrtion of the HyProCure subtalar stabilization device.The contact forces of the posterior and anterior talocalcaneal joint facets before and after placement of the HyProCure device were measured using a weightbearing cadaver model by applying an axial load of2,000N on the tibia/fibula.A2,000-N force simulates four times the body weight when a person is standing on one leg.We did not measure the forces in the talonavicular,calcaneocuboid,and tibiotalar joints before and after HyProCure becau it would have compromid the stability of the osous structures to Chopart’s joint.To place the transducers into tho joints,tranction of the ligaments would have led to rious instability of the foot,compromising the integrity of the subtalar joint complex.Also,to ensure maximum pronation at the subtalar joint,the tibia/fibular gment was given an internal torque of08to
158until full obliteration of the sinus tarsi was visualized.It was hypothesized that after placing the device into the sinus tarsi there would be stabilization of the forces acting on the facets of the talocalcaneal articulation. As a result,the excessive talar motion would be eliminated and,hence,normal motion would be restored,preventing the destructive repetitive forc-es acting proximal and distal to the musculoskeletal chain with every step taken.
Materials and Methods
Five fresh-frozen human cadaveric adult foot specimens trancted20to30cm above the tibial plafond were ud.Four right-footed specimens and one left-footed specimen were ud to quantify the total forces transmitted in the subtalar joints and the translation of the contact area of forces with and without a HyProCure sinus tarsi stent in a flatfoot model.Before testing,each specimen was completely thawed at room temperature.All of the specimens exhibited the pathologic instability of the talus on the calcaneus and navicular bones, resulting in partial to full obliteration of the sinus tarsi.They were free of any condition(s)that would inhibit the range of motion of the subtalar joint complex.Each specimen was discted free of soft tissue at the proximal tibial andfibular gment. The proximal gment and forefoot werefixated in blocks of polymethylmethacrylate for mounting in the testingfixture(Fig.2).Care was taken so that no damage was done to the soft-tissue structures of t
he subtalar joint complex.A lateral incision was made over the sinus tarsi for inrtion of the HyProCure stent.The appropriate-sized HyProCure stent to allow the normal amount of pronation was deter-mined using HyProCure trial sizers.The capsular ligaments between the anterior and posterior talocalcaneal joints were compromid for inrtion of the Tekscan nsor(Tekscan Inc,South Boston, Massachutts)(Fig.3).We did not quantify the forces in the talonavicular and calcaneocuboidal
joints becau compromi of the ligaments for inrtion of the nsor might have caud more instability in the foot.It is assumed that most of the remaining forces pasd through the talonavicular and calcaneocuboidal joints and that minimal force was applied on the stent.
We measured facet joint loads in the articulating joints with the Tekscan nsor equipped with model 4000nsors.This thin,flexible nsor had two independent nsing elements.Each nsor was conditionedfive times at120%of the maximum load by loading it between machined aluminum plates covered with3-mm-thick foam in a rvohydraulic materials testing machine.The nsors were then calibrated by loading each one to20%and80%of the maximum expected load.I-Scan software(Tekscan Inc)was ud to record the calibration loads and determine the calibration curves using2-point calibration.The raw data from each measured trial were converted to the forces on the j
oints using I-Scan software.
The potted specimen was mounted in a
biaxial
Figure2.The specimen is mounted on a materials testing machine to simulate compression of2,000N
and maximum internal rotation of158to the tibia/fibula.PMMA indicates知无不言言无不尽
polymethylmethacrylate.
Figure1.Placement of the HyProCure stent in alignment with the sinus tarsi and abutting the lateral p
art of the canalis tarsi.
rvohydraulic materials testing machine (Instron DynaMight 8841;Instron,Canton,Massachutts)equipped with a calibrated 5.0-kN load cell,and it was loaded under compression using a load control procedure.The foot was axially loaded through the axis of the tibia/fibula with a compressive force of 2,000N at the rate of 1200N/min and then was rotated internally by 158to produce pronation of the subtalar joint.The proximal gment was rotated at 58/min.The forces in the joint were measured by inrting the nsor at the anterior talocalcaneal and posterior talocalcaneal joint facets after com-promising the capsular ligaments.The forces on the joints were recorded one at a time.The analysis involved measuring the forces in the joints before and after placement of the HyProCure sinus tarsi stent.The size of the sinus tarsi stent ud depended mainly on the foot specimen.An appro-
priate stent from sizes 6,7,and 8was lected,depending on the geometry of the sinus tarsi of the specimen.The forces on the joints were quantified using I-Scan software.
Statistical Analysis
The forces on the posterior and anterior talocalca-neal joints were analyzed using I-Scan software b
efore and after inrtion of the HyProCure stent.The average force on each specimen over the entire loading period and the mean (SD)for all of the specimens were computed.Statistical analysis of the biomechanical data was performed by the two-tailed paired t test using Minitab software (Minitab Inc,State College,Pennsylvania).Values are expresd as mean 6SD.A P ,0.05was considered
significant.
Figure 3.A,The Tekscan nsor 4000placed between the posterior talocalcaneal joint and placement of the HyProCure stent between the sinus tarsi.B,Inrtion of the nsor between the anterior talocalcaneal joint with the HyProCure stent in the sinus tarsi.
Results
The loading pattern for the posterior talocalcaneal joint showed a decrea in joint forces after a particular peak force for all five specimens,indicat-ing a loss of stability (Fig.4).The average forces acting on the posterior joint are shown in Figure 5.The contact forces shifted in an anteromedial direction.However,with inrtion of the device,the articular contact area and,hence,the contact forces were maintained on the posterior facet (Fig.6).The mean 61SD force on the
posterior
Figure 4.The forces in the posterior talocalcaneal joint for the five specimens when the tiba/fibula was loaded with a compressive force of 2,000N and internally rotated by 158to simulate pronation of the foot.
talocalcaneal joint for the five specimens after the load application was 795.886106N (Fig.7).However,after inrtion of the stent,the mean 61SD force on the posterior talocalcaneal joint incread to 1,004.86672.41N (P ,0.05).
From Figures 8and 9we can state that with the applied load,the contact forces shifted anteriorly to the anterior articulating surfaces.The contact area also shifted in the anteromedial direction (Fig.10).The mean 61SD force without the stent on the
anterior talocalcaneal joint was 520.156127.18N.However,as a result of inrtion of the stent,the hindfoot was stabilized,and the mean 61SD force on the anterior talocalcaneal joint decread to 394.56673.83N (P ,0.05).The remaining forces must,therefore,pass through the talonavicular and calcaneocuboidal joints and on the stent.Thus,the stent did not allow excessive medial deviation of the talus,thereby decreasing the contact forces on the anterior articulating surfaces,and,conquentl和服穿法
y,the forces in the foot were distributed more evenly.
Figure 5.The average forces on the posterior talocalcaneal joint during the loading period for the five
specimens.
Figure 6.The contact area for the posterior talocalcaneal joint.A,There is a shift in the contact area a
nteromedially without the stent as the foot goes into maximum pronation.B,With inrtion of the stent,the contact area shifts back posteriorly.
Figure 7.The mean SD forces on the posterior and anterior talocalcaneal joints.
