Kinematic analysis of the agility total ankle during gait

In Vivo Total Ankle Arthroplasty Kinematic Evaluation: A Prospective Radiostereometric Analysis

Ankle osteoarthritis (OA) represents a significant social burden and is one of the main causes of chronic disability in a rapidly growing part of the world's population. Total ankle arthroplasty (TAA) has become increasingly popular despite the poor results obtained with the first dedicated designs. The purpose of this paper was to evaluate the ankle kinematics, in vivo and under weight-bearing conditions, of a TAA through a dynamic model-based radiostereometric analysis (MB-RSA). The clinical evaluation was performed by administering the American Orthopaedic Foot and Ankle Society ankle-hindfoot score and Short Form-36 questionnaires. The kinematic evaluation was conducted through MB-RSA during the execution of an open kinetic chain and a closed kinetic chain motor task. Double radiographic images of the ankle joint were processed using dedicated software to obtain a 3D reconstruction of the ankle prosthetic components' motion. Eighteen patients (five females) completed the clinical and instrumental preoperative and postoperative evaluations (age 59.1 ± 10.3). All clinical scores showed a marked improvement (p < 0.005). During the closed kinetic chain motor tasks, the ankle showed a total range of motion (ROM) in dorsi-plantarflexion of 19.84°. The parameters in varus-valgus were recorded. Physiological motion can be achieved in TAA, characterized by a wide range of motion and coupling of movements on the three planes. The results of the present work may help to understand the real movement of a widespread TAA model and possibly to improve future designs and instrumentation.

Gait Kinetic and Kinematic Changes in Chronic Low Back Pain Patients and the Effect of Manual Therapy: A Randomized Controlled Trial

Patients with chronic back pain as a result of degenerated disc disease, besides pain, also present with impaired gait. The purpose of the article was to evaluate kinetic and kinematic characteristics during gait analysis in patients with chronic low back pain as a result of degenerated disc disease, before and after the application of physiotherapy, including manual therapy techniques. Seventy-five patients suffering from chronic low back pain were randomly divided into 3 groups of 25 each. Each group received five sessions (one per week) of interventions with the first group receiving manual therapy treatment, the second a sham treatment and the third, classic physiotherapy (stretching exercises, TENS and massage). The effectiveness of each treatment was evaluated using an optoelectronic system for recording and analysis of gait (kinetic and kinematic data). Patients overall showed an impaired gait pattern with a difference in kinetic and kinematic data between the left and the right side. Following the application of the above-named interventions, only the group that received manual therapy showed a tendency towards symmetry between the right and left side. In patients suffering from chronic low back pain as a result of degenerated disc disease, the application of five manual therapy sessions seems to produce a tendency towards symmetry in gait.

Damage patterns in polyethylene fixed bearings of retrieved total ankle replacements

INTRODUCTION

Poor long-term outcomes continue to hinder the universal adoption of total ankle replacements (TAR) for end stage arthritis. In the present study, polyethylene inserts of TARs retrieved at revision surgery were analyzed for burnishing, scratching, mechanical damage, pitting, and embedded particles.

METHODS

Fourteen retrieved polyethylene inserts from a fixed bearing total ankle replacement design currently in clinical use were analyzed. Duration of time in vivo was between 11.5 months and 120.1 months. Three investigators independently graded each articular surface in quadrants for five features of damage: burnishing, scratching, mechanical damage, pitting, and embedded particles.

RESULTS

No correlation was found for burnishing between the anterior and posterior aspects (p = 0.47); however, scratching and pitting were significantly higher on the posterior aspect compared to the anterior aspect (p < 0.03). There was a high correlation between burnishing and in vivo duration of the implant (anterior: R = 0.67, p = 0.01, posterior: R = 0.68, p = 0.01).

CONCLUSION

The higher concentration of posterior damage on these polyethylene inserts suggested that prosthesis-related (design) or surgeon-related (technique) factors might restrict the articulation of the implant. The resulting higher stresses in the posterior articular surfaces may have contributed to the failure of retrieved implants Keywords: Retrieval, Polyethylene Damage, Total Ankle Replacement.

A Systematic Review of Unsystematic Total Ankle Replacement Wear Evaluations

BACKGROUND

Numerous studies have reported the use of laboratory multistation joint simulators to successfully predict wear performance and functionality of hip and knee replacements. In contrast, few studies in the peer-reviewed literature have used joint simulation to quantify the wear performance and functionality of ankle replacements. We performed a systematic review of the literature on joint simulator studies that quantified polyethylene wear in total ankle arthroplasty. In addition to the quantified wear results, the load and motion parameters were identified and compared among the studies.

METHODS

A search was performed according to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines to identify articles reporting total ankle replacement polyethylene wear using joint simulators.

RESULTS

Nine studies that used joint simulators and 1 study that used a computer simulation were found. Although all studies used physiological multidirectional motions (i.e., internal/external rotation, plantar flexion/dorsiflexion, anterior/posterior translation), there was large variability among the studies in the magnitudes of these motions. Among these studies, mean non-cross-linked polyethylene wear ranged from 3.3 ± 0.4 to 25.8 ± 3.1 mm per million cycles. In contrast, mean highly cross-linked polyethylene wear ranged from 2.1 ± 0.3 to 3.3 ± 0.4 mm per million cycles. The wide distribution in wear rates was attributable to the highly inconsistent kinematic parameters and loads applied as well as differences in implant design and materials.

CONCLUSIONS

There is a severe lack of clinically applicable data on wear performance of total ankle replacements in the peer-reviewed literature. No universal set of kinematic load parameters has been established. Furthermore, only 2 of the published studies have validated their findings using independently derived data, such as retrieval analysis. These shortcomings make it difficult to compare findings as a function of design parameters and materials, or to draw clinically relevant conclusions from these simulations. More work is required to enhance the predictive capability of in vitro simulations of total ankle replacements.

CLINICAL RELEVANCE

The results of joint wear simulator studies may not accurately represent in vivo wear of total ankle replacements. Joint simulator studies should establish that they are accurately replicating in vivo wear, thus enabling use of their predictive capabilities for new materials and designs.

Finite element analysis of biomechanical effects of total ankle arthroplasty on the foot

Background

Total ankle arthroplasty is gaining popularity as an alternation to ankle arthrodesis for end-stage ankle arthritis. Owing to the complex anatomical characteristics of the ankle joint, total ankle arthroplasty has higher failure rates. Biomechanical exploration of the effects of total ankle arthroplasty on the foot and ankle is imperative for the precaution of postoperative complications. The objectives of this study are (1) to investigate the biomechanical differences of the foot and ankle between the foot with total ankle arthroplasty and the intact foot and (2) to investigate the performance of the three-component ankle prosthesis.

Methods

To understand the loading environment of the inner foot, comprehensive finite element models of an intact foot and a foot with total ankle arthroplasty were developed to simulate the stance phase of gait. Motion analysis on the model subject was conducted to obtain the boundary and loading conditions. The model was validated through comparison of plantar pressure and joint contact pressure between computational prediction and experimental measurement. A pressure mapping system was used to measure the plantar pressure during balanced standing and walking in the motion analysis experiment, and joint contact pressure at the talonavicular joint was measured in a cadaver foot.

Results

Plantar pressure, stress distribution in bones and implants and joint contact loading in the two models were compared, and motion of the prosthesis was analysed. Compared with the intact foot model, averaged contact pressure at the medial cuneonavicular joint increased by 67.4% at the second-peak instant. The maximum stress in the metatarsal bones increased by 19.8% and 31.3% at the mid-stance and second-peak instants, respectively. Force that was transmitted in three medial columns was 0.33, 0.53 and 1.15 times of body weight, respectively, at the first-peak, mid-stance and second-peak instants. The range of motion of the prosthetic ankle was constrained in the frontal plane. The lateral side of the prosthesis sustained higher loading than the medial side.

Conclusion

Total ankle arthroplasty resulted in great increase of contact pressure at the medial cuneonavicular joint, making it sustain the highest contact pressure among all joints in the foot. The motion of the prosthesis was constrained in the frontal plane, and asymmetric loading was distributed in the bearing component of the ankle prosthesis in the mediolateral direction.

The translational potential of this article

Biomechanical variations resulted from total ankle arthroplasty may contribute to negative postoperative outcomes. The exploration of the biomechanical performance in this study might benefit the surgeons in the determination of surgical protocols to avoid complications. The analysis of the performance of the ankle prosthesis could enhance the knowledge of prosthetic design.

Comparison of Multisegmental Foot and Ankle Motion Between Total Ankle Replacement and Ankle Arthrodesis in Adults

BACKGROUND

Total ankle replacement (TAR) and ankle arthrodesis (AA) are usually performed for severe ankle arthritis. We compared postoperative foot segmental motion during gait in patients treated with TAR and AA.

METHODS

Gait analysis was performed in 17 and 7 patients undergoing TAR and AA, respectively. Subjects were evaluated using a 3-dimensional multisegmental foot model with 15 markers. Temporal gait parameters were calculated. The maximum and minimum values and the differences in hallux, forefoot, hindfoot, and arch in 3 planes (sagittal, coronal, transverse) were compared between the 2 groups. One hundred healthy adults were evaluated as a control.

RESULTS

Gait speed was faster in the TAR ( P = .028). On analysis of foot and ankle segmental motion, the range of hindfoot sagittal motion was significantly greater in the TAR (15.1 vs 10.2 degrees in AA; P = .004). The main component of motion increase was hindfoot dorsiflexion (12.3 and 8.6 degrees). The range of forefoot sagittal motion was greater in the TAR (9.3 vs 5.8 degrees in AA; P = .004). Maximum ankle power in the TAR (1.16) was significantly higher than 0.32 in AA; P = .008). However, the range of hindfoot and forefoot sagittal motion was decreased in both TAR and AA compared with the control group ( P = .000).

CONCLUSION

Although biomechanical results of TAR and AA were not similar to those in the normal controls, joint motions in the TAR more closely matched normal values. Treatment decision making should involve considerations of the effect of surgery on the adjacent joints.

LEVEL OF EVIDENCE

Level III, case-control study.

Force-controlled dynamic wear testing of total ankle replacements

Currently, our knowledge of wear performance in total ankle replacements is limited. The aim of this study is to develop a scenario for force-controlled testing and wear testing of total ankle replacements. A force-controlled wear test was developed: based on cadaver measurements, the passive stabilization (ligaments and soft tissue) of the ankle joint was characterized and a restraint model for ankle stabilization was developed. Kinematics and kinetics acting at the replaced ankle joint were defined based on literature data and gait analysis. Afterwards, force-controlled wear testing was carried out on a mobile, three-component, total ankle replacement design. Wear was assessed gravimetrically and wear particles were analyzed. Wear testing resulted in a mean wear rate of 18.2±1.4mm(3)/10(6) cycles. Wear particles showed a mean size of 0.23μm with an aspect ratio of 1.61±0.96 and a roundness of 0.62±0.14. Wear testing of total ankle replacement shows that a relevant wear mass is generated with wear particles in a biologically relevant size range. The developed wear test provides a basis for future wear testing of total ankle replacements.

Prospective study of the effect on gait of a two-component total ankle replacement

BACKGROUND

The purpose of this study was to evaluate the functional outcome as measured by prospective gait analysis of patients undergoing total ankle arthroplasty using a 2-component Salto Talaris total ankle prostheses with a fixed polyethylene bearing.

METHODS

Twenty-one patients with severe ankle arthritis who underwent unilateral total ankle arthroplasty using a 2-component Salto Talaris device with a fixed polyethylene bearing were studied prospectively. Mean age was 69 years in 16 female and 5 male patients, and mean follow-up was 37.2 (range, 24-50) months. Three-dimensional gait analysis was performed using a 12-camera digital-motion capture system preoperatively and repeated at a minimum of 2 years postoperatively. Temporospatial measurements included velocity, cadence, step length, and support times. Measured kinematic parameters included sagittal plane range of motion of the ankle, knee, and hip. Kinetic parameters included sagittal plane ankle power and ankle plantarflexion moment.

RESULTS

There was significant improvement in temporospatial parameters, including step length (P = .014) and walking velocity, which increased from 0.9 to 1 m/s (P = .01). Kinematic results showed sagittal plane range of motion of the ankle increased significantly from a mean of 15.8 degrees preoperatively to 20.6 degrees (P = .00005) postoperatively with the increase occurring primarily in dorsiflexion. Kinetic results showed ankle peak power increased from a mean of 0.7 Nm/kg to 1.1 Nm/kg (P = .004).

CONCLUSIONS

A prospective study of gait in patients undergoing total ankle arthroplasty using a 2-component Salto Talaris device with a fixed polyethylene bearing showed, at midterm follow-up, significant improvements in multiple parameters of gait when compared to the patients' own preoperative function.

LEVEL OF EVIDENCE

Level IV, prospective case series.

Biomechanics of the normal and arthritic ankle joint

Understanding biomechanics of the normal and arthritic ankle joint can aid in analysis of an underlying clinical problem and provide a strategic basis for a more optimal management. The challenge to the clinician and the biomechanist is that the mechanical complexity of the ankle joint still clouds current understanding. This article provides an overview of current understanding of functional ankle anatomy, how this function can be altered in the degenerated ankle, and how surgical intervention further affects foot and ankle biomechanics. The focus is on how altered loading of neighboring joints in the midfoot and hindfoot may induce postoperative joint remodeling and can manifest in secondary clinical problems.

A functional outcome study comparing total ankle arthroplasty (TAA) subjects with pain to subjects with absent level of pain by means of videofluoroscopy

BACKGROUND

Total ankle arthroplasty (TAA) subjects often suffer pain on the anteromedial side of their ankle joint. Whether this prevalent pain is caused by a changed motion pattern of the TAA is unclear. Therefore, this study assessed the kinematic differences in the motion of the TAA components during gait, comparing TAA subjects with elevated versus absent levels of pain.

METHODS

Eleven TAA subjects (5 with pain vs. 6 without pain), all with unilateral Mobility™ TAA and at least two years post-operation, were recruited and stratified based on standard clinical assessed patient data. The 3D motion of the TAA was assessed by means of videofluoroscopy during level, uphill and downhill walking.

RESULTS

The hypothesis that the pain group shows a different kinematic motion pattern than the no pain group could not be confirmed.

CONCLUSIONS

The same kinematic motion pattern causes pain in some patients, but not in others. Further investigation concerning ligament stresses is needed.

Three-dimensional kinematics of an unconstrained ankle arthroplasty: a preliminary in vivo videofluoroscopic feasibility study

BACKGROUND

Understanding the functionality of total ankle arthroplasties (TAA) requires thorough knowledge of the kinematics during activities of daily life. Videofluoroscopy enables the in vivo measurement of the 3D kinematics of implant components more accurately than by means of skin marker tracking. The aim of the present preliminary study was to quantify the 3D kinematics of a TAA during the stance phase of level and slope walking using single plane videofluoroscopy.

METHODS

The experimental set up consisted of a videofluoroscopy system (BV Pulsera, Philips Medical Systems, Switzerland, 25 Hz, 1 ms shutter time) integrated in a walkway, allowing the assessment of free level gait, uphill, downhill and cross-slope walking. 2D/3D registration was performed using the CAD models of the TAA. In a preliminary feasibility study, the presented method was applied on four patients with successful unilateral TAA (Mobility™ Total Ankle, DePuy) with good outcomes.

RESULTS

Isolated 3D TAA kinematics was quantified with a rotational and translational error of 0.2 degrees and 0.4 mm in plane and 1.3 degrees and 2.1 mm out of plane. In the feasibility study it was found that only minor limitations occurred in sagittal plane motion. Any restrictions were caused by a limitation in dorsiflexion, whereas plantarflexion was for all gait conditions sufficiently provided. Transverse and frontal plane rotation was marginal, the main rotation occurred around the talar construction axis itself.

CONCLUSION

The presented method enabled accurate estimation of the 3D TAA kinematics in vivo, without being limited by skin movement artifacts and isolated from subtalar motion. Since the available amount of dorsiflexion is the crucial factor to allow unrestrictive gait, walking uphill is an appropriate motion task to challenge and evaluate the performance of the TAA.

CLINICAL RELEVANCE

The presented method has the potential to identify specific kinematic patterns and thereby help clinicians and implant developers to evaluate current designs and future design modifications.

In vivo kinematics and articular surface congruency of total ankle arthroplasty during gait

Relatively high rates of loosening and implant failure have been reported after total ankle arthroplasty. Abnormal kinematics and incongruency of the articular surface may cause increased contact pressure and rotational torque applied to the implant, leading to loosening and implant failure. We measured in vivo kinematics of two-component total ankle arthroplasty (TNK ankle), and assessed congruency of the articular surface during the stance phase of gait. Eighteen ankles of 15 patients with a mean age of 75±6 years (mean±standard deviation) and follow-up of 44±38 months were enrolled. Lateral fluoroscopic images were taken during the stance phase of gait. 3D-2D model-image registration was performed using the fluoroscopic image and the implant models, and three-dimensional kinematics of the implant and incongruency of the articular surface were determined. The mean ranges of motion were 11.1±4.6°, 0.8±0.4°, and 2.6±1.5° for dorsi-/plantarflexion, inversion/eversion, and internal/external rotation, respectively. At least one type of incongruency of the articular surface occurred in eight of 18 ankles, including anterior hinging in one ankle, medial or lateral lift off in four ankles, and excessive axial rotation in five ankles. Among the four ankles in which lift off occurred during gait, only one ankle showed lift off in the static weightbearing radiograph. Our observations will provide useful data against which kinematics of other implant designs, such as three-component total ankle arthroplasty, can be compared. Our results also showed that evaluation of lift off in the standard weightbearing radiograph may not predict its occurrence during gait.

Kinematics of the three components of a total ankle replacement: in vivo fluoroscopic analysis

BACKGROUND

Careful kinematic analysis of ankle joints with newly developed prostheses should be carried out to assess the actual performance in vivo. This study analyzed the pattern of motion of the three components of a ligament-compatible ankle replacement, developed to replicate normal joint kinematics.

MATERIALS AND METHODS

Twelve patients treated with this design were analyzed at 6, 12, and 24 months followup. A series of images were acquired by videofluoroscopy at extremes of the range of motion, and during flexion/extension against gravity and stair-climbing/descending. Three-dimensional positions and orientations of the tibial and talar metal components and of the polyethylene mobile-bearing were obtained from the images by a standard shape-matching procedure. Motion between the three components was calculated and descriptively analyzed.

RESULTS

Large tibiotalar joint mobility of the replaced ankle was observed in all three anatomical planes, particularly in the sagittal. In flexion/extension against gravity, the mean range of flexion was 17.6, 17.7, and 16.2 degrees, respectively, over the three followups. The inclination angle of the mean axis of joint rotation was 3.7 degrees down and lateral in the frontal plane and 4.7 degrees posterior and lateral in the transverse plane, similar to those in the normal ankle. The corresponding antero-posterior translation of the meniscal-bearing with respect to the tibia was 3.3, 3.3, and 3.2 mm, with statistically significant correlation with joint flexion.

CONCLUSION

Physiological motion can be achieved in ligament-compatible ankle joint replacements. The considerable antero-posterior bearing-to-tibial motion and its coupling with flexion support the main original claims of this design.

Changes in gait following the Scandinavian Total Ankle Replacement

BACKGROUND

There is a resurgence of popularity with regard to total ankle arthroplasty, although there are limited data documenting the effect of total ankle arthroplasty on ankle joint motion, gait, or ankle function. The purpose of this study was to perform a prospective evaluation of the effect of the Scandinavian Total Ankle Replacement on gait.

METHODS

We prospectively studied fifty consecutive patients with advanced ankle arthritis who underwent unilateral total ankle arthroplasty with the Scandinavian Total Ankle Replacement ankle prosthesis. Three-dimensional gait analysis was performed with use of a twelve-camera digital-motion capture system. Kinetic parameters were collected with use of two force plates. Temporal-spatial measurements included stride length and cadence. The kinematic parameters that were measured included the sagittal plane range of motion of the ankle, knee, and hip. The kinetic parameters that were studied included ankle plantar flexion-dorsiflexion moment and sagittal plane ankle power. The mean period of follow-up was forty-nine months (range, twenty-four to 108 months).

RESULTS

Temporal-spatial analysis showed that walking velocity increased as a function of increases in both cadence and stride length, and to significant levels for each. Kinematic analysis showed that ankle range of motion increased from a mean of 14.2° to 17.9° (p < 0.001), with the increase coming from increased plantar flexion. Increased motion was also measured at the hip and knee. Significant increases were found in ankle power (from 0.69 to 1.00 W/kg [p < 0.001]) and ankle plantar flexion moment (from 0.88 to 1.09 Nm/kg [p < 0.001]).

CONCLUSIONS

This study demonstrated that, at the time of intermediate-term follow-up and in comparison with the effects of ankle arthrodesis on gait as reported in previous studies, total ankle arthroplasty was associated with a more normal ankle function and a more normal gait, both kinetically and in terms of temporal-spatial parameters. More importantly, the study demonstrated marked improvement in multiple, objective parameters of gait following total ankle arthroplasty as compared with the patient's own preoperative function. The long-term maintenance of the gait improvements will require further study.

Effect of ankle flexion angle on axial alignment of total ankle replacement

BACKGROUND

The Salto Talaris Anatomic® (Tornier) total ankle replacement (TAR) has found widespread use in the United States and features rotationally mobile trial components that auto-align the final components, which themselves are rotationally fixed and highly congruent. Based on recent work on prosthetic and native ankle kinematics, we investigated the influence of the ankle flexion angle at the time of final component preparation on the axial alignment of the Salto Talaris TAR.

MATERIALS AND METHODS

Following a power analysis based on a clinically meaningful difference of five degrees, eight fresh-frozen cadaveric thigh-to-foot specimens underwent installation of trial components using the Salto Talaris TAR system. Specimens were cycled from maximal dorsiflexion (DF) to plantarflexion (PF), as called for in the surgical technique guide, and drilling for the final component was carried out in both five degrees of DF and 15 degrees of PF using separate drill holes. These were compared with a reference drill hole previously placed along the axis of distal tibial cutting guide. Data were analyzed to determine whether components prepared in DF differed from those prepared in PF with respect to median (and variance) rotation.

RESULTS

We found no significant difference in median axial alignment (p = 0.139) or in variances between the two groups (p=0.937).

CONCLUSION

The ankle flexion angle at the time of final component preparation did not significantly alter the axial alignment of the Salto Talaris TAR.

CLINICAL RELEVANCE

Therefore, the rotational alignment of the tibial component is determined by the tibial bone cuts and will not auto-align to the rotation of the talar component.

Intermediate term outcome of the agility total ankle arthroplasty

BACKGROUND

Although ankle arthrodesis provides pain relief and improved function, newer generation total ankle arthroplasty designs, with improved kinematic properties, have emerged and showed encouraging results. The purpose of this study was to review the intermediate term outcome of the Agility Total Ankle Arthroplasty prosthesis.

MATERIALS AND METHODS

A retrospective review was performed on 28 total ankle arthroplasty procedures performed over a period of 5 years. The American Orthopedic Foot and Ankle Society (AOFAS) questionnaire was used for evaluation. Pre-existing medical and surgical conditions that could potentially affect outcome were recorded. The mean age at surgery was 68.5 years with 39% males and 61% females.

RESULTS

The mean AOFAS Ankle-Hindfoot score improved significantly from 34.9 to 76.4 (p < 0.001). Pain relief was the main factor in improving the score followed by improved function. Complications varied from delayed wound healing, wound infection, painful hardware, iatrogenic malleolar fracture and arterial injury, to patients requiring free flap coverage. Despite the high rate of complications, which were successfully treated, most patients were satisfied at the last followup.

CONCLUSION

Total ankle arthroplasty using the Agility Total Ankle Arthroplasty prosthesis has clinically encouraging outcomes; however the high complication rate should prompt surgeons to carefully select patients for this procedure.

Analysis of retrieved agility total ankle arthroplasty systems

BACKGROUND

First generation total ankle arthroplasty (TAA) systems showed high rates of failure. The Agility (DePuy, Warsaw, IN) TAA system, a second generation design, had improved outcomes; however, implant failure due to loosening of the metallic components persisted. The purpose of this study was to analyze the damage modes and radiographic mode(s) of failure observed in retrieved Agility TAA.

MATERIALS AND METHODS

Ten devices were collected and each component was analyzed for common damage modes using microscopy. Clinical damage was analyzed with postoperative implant and preoperative revision procedure radiographs.

RESULTS

Analyses revealed damage/wear to retrieved components, including abrasion, dishing, and pitting. These third-body wear particles may be a precursor to wear debris induced osteolysis which could cause component loosening. Seven TAA systems were removed due to loosening or subsidence, suggesting component damage/wear may lead to clinically observed component loosening. Retrieval analysis indicated the polyethylene experiences edge loading, resulting in increased contact stresses to polyethylene in the primary articulation region and wear.

CONCLUSION

Since poor clinical outcomes have been associated with component instability and osteolysis, analyzing retrieved components wear and damage may be an important step toward improving implant design, thereby decreasing wear debris induced osteolysis and improving clinical outcomes.

The effects of total ankle replacement on gait disability: analysis of energetic and mechanical variables

PURPOSE

The goal was to evaluate the effect of total ankle replacement (TAR) on gait in terms of mechanical and energetic variables.

METHODS

An observational, prospective study was undertaken in 20 patients before and approximately 7 months after unilateral mobile-bearing TAR. The clinical-functional level was assessed according to the American Orthopaedic Foot and Ankle Society 'AOFAS'. An instrumented motion analysis was used to assess spatiotemporal parameters, ankle kinematics, mechanical work, and electromyographic activity. Energy expenditure was analyzed using an ergospirometer.

RESULTS

AOFAS score improved 1.5 times. The speed was also significantly improved. In order to limit the influence of speed and to highlight the effect of the surgery, all variables were normalized by z-score to isolate the effect of TAR. With normalized z-score, spatiotemporal parameters and ankle amplitude instance were significantly improved. The vertical center of mass displacement was significantly improved, showing a less flat-walking pattern, and decreasing energy expenditure. Our results show that TAR has a beneficial effect on locomotor function.

CONCLUSIONS

Many studies have shown that improved clinical outcomes can be expected with the new generation of prostheses and this was as confirmed by our study. However, no previous study has investigated the effect of TAR on the functional limitations of gait as represented by mechanical and energetic variables.