The Foot and Ankle Kinematics of a Simulated Progressive Collapsing Foot Deformity During Stance Phase: A Cadaveric Study

BACKGROUND

Progressive collapsing foot deformity (PCFD) is a complex pathology associated with tendon insufficiency, ligamentous failure, joint malalignment, and aberrant plantar force distribution. Existing knowledge of PCFD consists of static measurements, which provide information about structure but little about foot and ankle kinematics during gait. A model of PCFD was simulated in cadavers (sPCFD) to quantify the difference in joint kinematics and plantar pressure between the intact and sPCFD conditions during simulated stance phase of gait.

METHODS

In 12 cadaveric foot and ankle specimens, the sPCFD condition was created via sectioning of the spring ligament and the medial talonavicular joint capsule followed by cyclic axial compression. Specimens were then analyzed in intact and sPCFD conditions via a robotic gait simulator, using actuators to control the extrinsic tendons and a rotating force plate underneath the specimen to mimic the stance phase of walking. Force plate position and muscle forces were optimized using a fuzzy logic iterative process to converge and simulate in vivo ground reaction forces. An 8-camera motion capture system recorded the positions of markers fixed to bones, which were then used to calculate joint kinematics, and a plantar pressure mat collected pressure distribution data. Joint kinematics and plantar pressures were compared between intact and sPCFD conditions.

RESULTS

The sPCFD condition increased subtalar eversion in early, mid-, and late stance (P < .05), increased talonavicular abduction in mid- and late stance (P < .05), and increased ankle plantarflexion (P < .05), adduction (P < .05), and inversion (P < .05). The center of plantar pressure was significantly (P < .01) medialized in this model of sPCFD and simulated stance phase of gait.

DISCUSSION

Subtalar and talonavicular joint kinematics and plantar pressure distribution significantly changed with the sPCFD and in the directions expected from a PCFD foot. We also found that ankle joint kinematics changed with medial and plantar drift of the talar head, indicating abnormal talar rotation. Although comparison to an in vivo PCFD foot was not performed, this sPCFD model produced changes in foot kinematics and indicates that concomitant abnormal changes may occur at the ankle joint with PCFD.

CLINICAL RELEVANCE

This study describes the dynamic kinematic and plantar pressure changes in a cadaveric model of simulated progressive collapsing foot deformity during simulated stance phase.

Cadaveric Gait Simulation of the Effect of Subtalar Arthrodesis on Total Ankle Replacement Kinematics

BACKGROUND

Patients undergoing total ankle replacement (TAR) often have symptomatic adjacent joint arthritis and deformity. Subtalar arthrodesis can effectively address a degenerative and/or malaligned hindfoot, but there is concern that it places abnormal stresses on the TAR and adjacent joints of the foot, potentially leading to early TAR failure. This study hypothesized that ankle and talonavicular joint kinematics would be altered after subtalar arthrodesis in the setting of TAR.

METHODS

Thirteen mid-tibia cadaveric specimens with neutral alignment were tested in a robotic gait simulator. To simulate gait, each specimen was secured to a static mounting fixture about a 6-degree of freedom robotic platform, and a force plate moves relative to the stationary specimen based on standardized gait parameters. Specimens were tested sequentially in TAR and TAR with subtalar arthrodesis (TAR-ST_fuse). Kinematics and range of motion of the ankle and talonavicular joint were compared between TAR and TAR-ST_fuse.

RESULTS

There were significant differences in kinematics and range of motion between TAR and TAR-ST_fuse groups. At the ankle joint, TAR-ST_fuse had less internal rotation in early-mid stance (P < .05), with decreased range of motion in the sagittal (-2.7 degrees, P = .008) and axial (-1.8 degrees, P = .002) planes in early stance, and increased range of motion in the coronal plane in middle (+1.2 degrees, P < .001) and late (+2.5 degrees, P = .012) stance. At the talonavicular joint, there were significant differences in axial and coronal kinematics in early and late stance (P < .05). Subtalar arthrodesis resulted in significantly decreased talonavicular range of motion in all planes in early and late stance (P < .003).

CONCLUSION

In ankles implanted with the TAR design used in this study, kinematics of the ankle and talonavicular joint were found to be altered after subtalar arthrodesis. Aberrant motion may reflect altered contact mechanics at the prosthesis and increased stress at the bone-implant interface, and affect the progression of adjacent joint arthritis in the talonavicular joint.

CLINICAL RELEVANCE

These findings may provide a correlate to clinical studies that have cited hindfoot arthrodesis as a risk factor for TAR failure.

Finite Element Modelling of Planus and Rectus Foot Types for the Study of First Metatarsophalangeal and First Metatarsocuneiform Joint Contact Mechanics

Evaluating the contact mechanics of human joints is an important element in understanding the pathomechanics of orthopaedic diseases. Although physical testing is essential in the evaluation process, reliable computational models can augment these experiments by non-invasive predictions of biomechanical or surgical variables. The objective of this study was to perform verification of a framework for developing a medial forefoot finite element. Verification was conducted by comparing computational predictions to experimental measurements of first metatarsophalangeal and first metatarsocuneiform joint contact mechanics. A custom-built force-controlled cadaveric test-rig was used to derive measurements of contact pressure, force, and area. A quasi-static finite element was developed and driven under the same boundary and loading conditions. Calibration of cartilage moduli and mesh sensitivity analyses were performed. Mean errors in contact pressures, forces, and areas were 24%, 4%, and 40% at the first metatarsophalangeal joint and 23%, 12%, and 19% at the first Metatarsocuneiform joint, respectively. Verification of a medial forefoot finite element model development framework was presented and found to be within 30% for contact pressure and contact force of both joints. This study presents a method to verify and simulate realistic physiological loading to investigate orthopaedic diseases of the medial forefoot.

Finite Element Analysis of Tibial Bone-Implant Load Transfer and Bone Strains with a Modern Fixed-bearing Total Ankle Replacement

Category:

Ankle Arthritis

Introduction/Purpose:

Loosening of the tibial component is the primary failure mode in total ankle arthroplasty (TAA). The mechanics of the tibial component loosening has not been fully elucidated. Clinically observed radiolucency and cyst formation in the periprosthetic bone may be associated with unfavorable load sharing at and adjacent to the tibial bone-implant interface contributory to implant loosening. However, no study has fully investigated the load transfer from the tibial component to the bone under multiaxial loads in the ankle. The objective of this study was to utilize subject-specific finite element (FE) models to investigate the load transfer through tibial bone-implant interface, as well as periprosthetic bone strains under simulated multiaxial loads.

Methods:

Bone-implant FE models were developed from CT datasets of three cadaveric specimens that underwent TAA using a modern fixed-bearing tibial implant (a cobalt-chrome tray with a polyethylene bearing, Salto Talaris, Integra LifeSciences). Implant placement was estimated from the post-operative CT scans. Bone was modeled as isotropic elastic material with inhomogeneous Young’s modulus (determined from CT Hounsfield units) and a uniform Poisson’s ratio of 0.3. The tibial tray (Young’s modulus: 200,000 MPa, Poisson’s ratio: 0.3) and the polyethylene bearing (Young’s modulus: 600 MPa, Poisson’s ratio: 0.4) were modeled as isotropic elastic. A 100-N compressive force, a 300-N anterior force, and a 3-Nm moment were applied to two literature based loading regions on the surface of the polyethylene bearing. The proximal tibia was fixed in all directions. The bone-implant contact was modeled as frictional with a coefficient of 0.7, whereas the polyethylene bearing was bonded to the tray.

Results:

Along the long axis of the tibia, load was transferred to the bone primarily through the flat bone-contacting base of the tibial tray and the cylindrical top of the keel, little amount of load was transferred to the bone between those two features (Fig. 1A). Low strain was observed in bone regions medial and lateral to the keel of the tibial tray, where bone cysts were often observed clinically (Fig. 1A). On average, approximated 70% of load was transferred through the anterior aspect of the tibial tray at the flat bone-contacting base, which corresponded to the relatively high bone strain adjacent to the implant edge in the anterior bone-implant interface (Fig. 1B).

Conclusion:

Our results demonstrated a two-step load transfer pattern along the long axis of the tibia, revealing regions with low bone strain peripheral to the keel indicative to stress shielding. Those regions were consistent with the locations of bone cysts observed clinically, which may be explained by the stress shielding associated remodeling of bone. These findings could also describe the mechanism of implant loosening and failure. Future studies may use our model to simulate more loading scenarios, as well as different implant placement and design, to identify means to optimize load transfer to the bone and prevent stress shielding.

Instability of the First Ray and Hallux Valgus in Patients with Adult Acquired Flatfoot Deformity (AAFD)

Category:

Bunion

Introduction/Purpose:

Longitudinal arch collapse and first ray instability represent landmarks for adult acquired flatfoot deformity (AAFD), and have been linked to the development and progression of hallux valgus (HV). Radiographic evaluation of first ray instability is usually marked by increased angulation between the first and second metatarsals. The 1-2 intermetatarsal angle (IMA) is also an important aspect in the staging of HV deformity. Weightbearing CT imaging (WBCT) provides three-dimensional evaluation of dynamic deformities such as AAFD and HV. The purpose of this study was to assess the correlation between hallux valgus severity and foot collapse indicators using WBCT measurements, in patients with AAFD. We hypothesized that a flattening of the longitudinal arch, increased hindfoot valgus and forefoot abduction would correlate with greater IMA and HV angles.

Methods:

In this retrospective comparative study, 108 patients with stage II AAFD, 36 men and 72 women, with a mean age of 54.4 (range, 20-78) years, had their WBCTs evaluated by 2 blinded and independent board-certified foot and ankle orthopedic surgeons. The readers assessed multiple variables related to the severity of the hallux valgus and flatfoot deformities including: 1-2 intermetarsal angle, hallux valgus angle, talocalcaneal angle in the axial plane, talus-first metatarsal angle in the axial and sagittal planes, hindfoot alignment angle, hindfoot moment arm, navicular- and medial cuneiform-floor distance and the talonavicular uncoverage angle. Intra- and interobserver reliability were calculated by Pearson or Spearman’s correlation and intraclass correlation coefficient, respectively. A multiple regression analysis was used to evaluate the correlation between the variables indicative of AAFD and the severity of HV. P-values less than 0.05 were considered significant.

Results:

The intra- and interobserver reliability ranged from (0.65-0.99). Means and standard deviations for IM and HV angles were 11.3°±3.7° and 17.6°±13.4°, respectively. These angles significantly correlated with each other (p<0.0001). Most of the AAFD measurements evaluated were significantly associated with either increased IM or HV angles. IM angle correlated with increased talocalcaneal (26.0°±10.3°, p<0.0001), talus-first metatarsal (19.0°±13.6°, p=0.0001), and hindfoot alignment angles (22.3°±12.9°, p= 0.0049). HV angle correlated with medial cuneiform-floor distance (15.1mm±5.5 mm, p=0.0183), talus-first metatarsal angle in the axial plane (p=0.0004) and sagittal plane (15.7°±8.8°, p=0.0351), talonavicular uncoverage angle (17.8°±13.9°, p=0.0035). Hindfoot moment arm and navicular-floor distance were the only AAFD measurements that did not correlate with IM or HV angles.

Conclusion:

To the best of our knowledge this is the first study to confirm the association between AAFD, first ray instability and hallux valgus deformity using WBCT images. Our study results demonstrated that stage II flatfoot patients indeed have increased intermetatarsal and hallux valgus angles. Measurements traditionally used for staging the severity of AAFD showed significant positive correlation with increased IM or HV angles. Even though cause and effect cannot be determined with certainty, foot and ankle surgeons should consider these findings during evaluation and surgical planning of patients with AAFD.

Weightbearing CT and MRI findings of Stage II Flatfoot Deformity

Category:

Hindfoot

Introduction/Purpose:

Adult acquired flatfoot deformity (AAFD) is characterized by concurrent bony deformities, tendinous and ligamentous insufficiencies. Weightbearing CT (WBCT) is a new imaging technique that allows excellent evaluation of the relative three-dimensional positioning of the tarsal bones in dynamic deformities such as AAFD. MRI, on the other hand, provides an accurate evaluation of soft tissue integrity in the unloaded foot. The objective of this study was to evaluate the correlation between bone deformity and soft tissue insufficiency in patients with stage II AAFD, using WBCT and MR images. We hypothesized that a significant correlation would be found between WBCT measurements of increased longitudinal arch collapse, hindfoot valgus, peritalar subluxation and forefoot abduction, with MRI findings demonstrating degree of involvement of ligaments and posterior tibial tendon (PTT).

Methods:

This retrospective comparative study included 55 patients (56 feet) with stage II AAFD, 20 men and 35 women, mean age of 52.5 (range, 20 to 78) years. Multiple WBCT and MRI variables related to the severity of the deformity were evaluated by four blinded and independent readers (two radiologists and two foot and ankle surgeons), including: arch collapse (navicular-floor distance and forefoot arch angle), hindfoot alignment angle (HAA), forefoot abduction (talonavicular uncoverage angle), subtalar joint subluxation, sinus tarsi and subfibular impingement, and soft tissue insufficiency (posterior tibial tendon, spring and talocalcaneal ligaments). Tendinous and ligamentous involvement on MRI were graded from zero (normal) to four (complete tear). Intra- and interobserver reliabilities were assessed by Pearson/Spearman’s and intraclass correlation coefficient, respectively. A multiple regression analysis was used to evaluate the relationship between bone alignment (WBCT variables) and soft tissue injury (MRI variables). P-values of less than 0.05 were considered significant.

Results:

We found overall good to excellent intra (range, 0.83-0.99) and interobserver reliability (range, 0.71-0.97) for WBCT measurements and MRI readings. Spring ligament superomedial component involvement was the only finding to correlate with medial column collapse and decreased navicular-floor distance (p=0.03). Superomedial spring ligament and PTT degeneration were also significantly correlated with increased HAA (p<0.01). Involvement of the talocalcaneal interosseous ligament significantly correlated with increased forefoot abduction as measured by the talonavicular uncoverage angle. Spring ligament degeneration, of both superomedial and inferior components, and talocalcaneal interosseous ligaments significantly correlated to subtalar joint subluxation (p<0.001). Involvement of the talocalcaneal interosseous ligament was the only one to significantly correlate to the presence of subfibular impingement (p=0.02). Degeneration of the PTT was significantly associated with sinus tarsi impingement (p=0.04).

Conclusion:

This study is the first to evaluate correlation between bone, tendinous and ligamentous involvement in AAFD patients, using WBCT and MR images. Our results demonstrated that progressive bone deformity in WBCT is significantly correlated to MRI involvement of the PTT and other important restraints such as the spring and talocalcaneal ligaments. The implications are that WBCT can predict ligamentous injuries and that MRI can predict dynamic bone deformity in AAFD patients. Furthermore, the correlation of bone and soft tissue involvement could impact surgical planning of flatfoot patients, decreasing thresholds for additional soft tissue procedures such as a spring ligament reconstruction.

Influence of Tibial Component Position on Altered Kinematics Following Total Ankle Arthroplasty During Simulated Gait

Category:

Ankle Arthritis

Introduction/Purpose:

Correct positioning of total ankle arthroplasty (TAA) implants has been associated with superior clinical outcomes. Furthermore, biomechanical studies have demonstrated that poor alignment of the components may lead to early component wear, compromising the longevity of the prosthesis. Malpositioning of TAA implants affects ligament engagement patterns and joint contact mechanics, possibly leading to altered joint kinematics. However, the correlation between implant position and ankle joint motion is still unclear. The objective of this study was to assess the effect of tibial component position on ankle kinematics following TAA during simulated gait.

Methods:

Eight mid-tibia cadaveric specimens were utilized in this IRB approved study. The stance phase of gait was simulated both pre- and post-TAA in each specimen using a six-degree of freedom robotic platform. Ground reaction forces and tibial kinematic from in vivo data were replicated while physiologic tendon force profiles were applied to each extrinsic ankle tendons by linear actuators instrumented. Ankle kinematics was measured from reflective markers attached to bones via surgical pins. TAAs were completed using a common fixed-bearing total ankle system following the manufacturer recommended protocol (Salto Talaris, Integra LifeSciences). Using reconstructed CT data, 3D tibial component position relative to a standard ankle joint reference was characterized (Figure 1A). The effect of tibial component position on absolute differences in ankle kinematics (pre – post TAA) was assessed using linear regression with a level of significance set to p = 0.05.

Results:

Differences in ankle joint kinematics were only identified in the transverse plane, where internal talar rotation was significantly increased following TAA compared to the native condition (Figure 1B). The medial position of TAA tibial components was found to be positively associated with increased internal talar rotation (Figure 1C; β = 1.861 degrees/mm, R2 = 0.72, p = 0.008). No other measurements of tibial component position (anterior-posterior/inferior-superior position, sagittal/frontal/transverse plane angle) were found to be significantly associated with altered ankle kinematics following TAA (All β < 0.1 and p > 0.05).

Conclusion:

This study suggests that medial positioning of the tibial implant affects ankle kinematics. During operative procedures the tibial component is usually positioned in order to preserve bone stock of the medial and lateral malleolus. However, little attention is given to the position of the implant in relation to the center of the tibial axis. This finding could have clinical implications for techniques implemented during surgical procedures and for the development of new instrumentation systems.

Ankle and Hindfoot Kinematics of a Next Generation Total Ankle Replacement During Simulated Gait

Category:

Ankle Arthritis

Introduction/Purpose:

Total ankle arthroplasty (TAA) has developed as a viable treatment option for end-stage ankle arthritis. The primary benefit proposed with TAA is that allows for maintained motion of the ankle and hindfoot joint compared to the alternative option of an ankle arthrodesis. Consequently, recent TAA systems have focused on designs that advance kinematic function. Cadaveric gait simulation is a valuable tool for investigating the direct effects of surgical procedures and devices on foot and ankle biomechanics. The objective of this study was to assess whether a next generation TAA system permits normal ankle and hindfoot kinematics using cadaveric gait simulation.

Methods:

Ten mid-tibia cadaveric specimens were secured to a static mounting fixture relative a six-degree of freedom robotic platform to simulate gait in native-intact and TAA conditions. A force plate was moved relative to the stationary specimen through an inverse tibial kinematic path calculated from in vivo data while extrinsic tendons were actuated using physiologic loads (Figure 1A). Ankle and hindfoot kinematics were measured from reflective markers attached to bones via surgical pins. TAA was performed using a next generation, fixed bearing total ankle system by a fellowship trained foot and ankle surgeon using manufacturer described protocol (Cadence Total Ankle, Integra LifeSciences). Ankle and hindfoot joint kinematics were directly measured using the same kinematic inputs and muscle force as the intact condition. Non-parametric, bias-corrected bootstrapping was used to calculate 95% confidence intervals to compare motion between intact and total ankle replacement conditions.

Results:

Analyses revealed that no significant difference in average ankle or hindfoot joint kinematics were found between intact and TAA conditions (Figure 1B). This result was consistent in each the ankle, subtalar, and talonavicular joints, and in each plane of motion.

Conclusion:

This study found that normal kinematics were permitted on average by a next generation, fixed bearing TAA. This finding may indicate that improved functional outcomes following could be expected. However, increased variability and some characteristic differences in the paths of motion throughout stance were observed qualitatively. This report represents an initial analysis of preliminary data, future work will include further analyses and investigation on the influence of factors such as component position and alignment on outcomes. That said, the findings of this study are encouraging and may represent improved kinematic performance in new TAA designs.

The Function Axis of Rotation of the Ankle Joint during Simulated Gait

Category:

Ankle, Ankle Arthritis, Hindfoot

Introduction/Purpose:

Implant component positioning is considered as an important factor in function and longevity in total ankle arthroplasty (TAA). However, accurate and repeatable positioning remains a limitation with current techniques and instrumentation. In addition, further investigation is needed to objectively define the optimum component positioning. Cadaveric gait simulation is a valuable tool for investigating foot and ankle joint mechanics during functional tasks such as the stance phase of gait. The objective of this study was to investigate the functional axis of rotation of the native ankle joint during simulated gait.

Methods:

The stance phase of healthy gait was simulated with six mid-tibia cadaveric specimens using a previously validated device and methodology. A robotic platform reproduced tibial-ground kinematics by moving a force plate relative to the stationary specimen while physiologic loads were applied to the extrinsic tendons to actuate the foot. (Figure 1A). Ankle kinematics were measured from reflective markers attached to the tibia and talus via surgical pins. The helical axes of rotation of the talus with respect to the tibia was calculated during three portions of stance: initial plantarflexion during earlier-stance after heal strike, dorsiflexion during mid-stance, and final plantarflexion during late-stance. The position and orientation of these kinematic-defined axes of rotation were compared to the transmalleolar axis and reduced to its anteroposterior position and transverse plane angle (Figure 1B).

Results:

Analyses revealed that ankle joint functional axis of rotation varied from the anatomic reference throughout stance. The kinematic center of rotation was located 16.4 ± 5.8 mm, 16.5 ± 6.6 mm, and 15.6 ± 6.5 mm anterior to the transmalleolar axis during early-, mid- and late-portions of stance, respectively.

Conclusion:

This study revealed that the position of the flexion-extension axis varies greatly between specimens during simulated gait. While previous reports have suggested that the transmalleolar axis is an acceptable approximation for the ankle joint center, these findings suggest that further research in warranted to better describe the complex tibiotalar kinematics. This work may provide future insight to guide implant design and advance techniques, to better place articular constraints of a total ankle in the native center of rotation of the joint.

Inpatient social-cognitive skills training groups with conduct disordered and attention deficit disordered children

The impact of group treatment programs on the social skills and peer relations of psychiatrically hospitalized children with disruptive behavior disorders was evaluated. Children assigned to a social-cognitive skills training group (SCST; n = 36) were matched to children who participated in a social activity group (SA; n = 20). The results indicated significantly greater pre-post improvements for the SCST than the SA group in child-reported loneliness, staff sociometric ratings, role-play performances, and in vivo behavioral observations of individual social skills. Child diagnoses did not differentially effect treatment outcomes. The findings are discussed in the context of training, clinical, and methodological issues.