Kinematics of a total arthroplasty of the ankle: comparison to normal ankle motion

Return to Sports and Activity After Total Ankle Arthroplasty and Arthrodesis: A Systematic Review

BACKGROUND

There is no consensus regarding participation in sports and recreational activities following total ankle replacement (TAR) and ankle arthrodesis (AA). This systematic review summarizes the evidence on return to sports and activity after operative management with either TAR or AA for ankle osteoarthritis (OA).

METHODS

A literature search of MEDLINE, EMBASE, CINAHL, and Cochrane Library databases was performed. Risk of bias of included studies was assessed using Methodological Index for Non-Randomized Studies (MINORS) criteria. Included studies reported sport and activity outcomes in patients undergoing TAR and AA, with primary outcomes being the percentage of sports participation and level of sports participation.

RESULTS

Twelve studies met inclusion criteria for analysis. There were 1270 ankle procedures, of which 923 TAR and 347 AA were performed. The mean reported patient age was 59.2 years and the mean BMI was 28 kg/m². The mean follow-up was 43 months. Fifty-four percent of patients were active in sports preoperatively compared with 63.7% postoperatively. The mean preoperative activity participation rate was 41% in the TAR cohort, but it improved to 59% after TAR, whereas the preoperative activity participation rate of 73% was similar to the postoperative rate of 70% in the AA cohort. The most common sports in the TAR and AA groups were swimming, hiking, cycling, and skiing.

CONCLUSION

Participation in sports activity was nearly 10% improved after operative management of ankle OA with TAR and remains high after AA. The existing literature demonstrated a large improvement in pre- to postoperative activity levels after TAR, with minimal change in activity after AA; however, AA patients were more active at baseline. The most frequent postoperative sports activities after operative management of ankle OA were swimming, hiking, cycling, and skiing. Participation in high-impact sports such as tennis, soccer, and running was consistently limited after surgery. This review of the literature will allow patients and foot and ankle surgeons to set evidence-based goals and establish realistic expectations for postoperative physical activity after TAR and AA.

LEVEL OF EVIDENCE

Level III, systematic review.

Motion at the Tibial and Polyethylene Component Interface in a Mobile-Bearing Total Ankle Replacement

BACKGROUND

Normal biomechanics of the ankle joint includes sagittal as well as axial rotation. Current understanding of mobile-bearing motion at the tibial-polyethylene interface in total ankle arthroplasty (TAA) is limited to anterior-posterior (AP) motion of the polyethylene component. The purpose of our study was to define the motion of the polyethylene component in relation to the tibial component in a mobile-bearing TAA in both the sagittal and axial planes in postoperative patients.

METHODS

Patients who were a minimum of 12 months postoperative from a third-generation mobile-bearing TAA were identified. AP images were saved at maximum internal and external rotation, and the lateral images were saved in maximum plantarflexion and dorsiflexion. Sagittal range of motion and AP translation of the polyethylene component were measured from the lateral images. Axial rotation was determined by measuring the relative position of the 2 wires within the polyethylene component on AP internal and external rotation imaging. This relationship was compared to a table developed from fluoroscopic images taken at standardized degrees of axial rotation of a nonimplanted polyethylene with the associated length relationship of the 2 imbedded wires. Sixteen patients were included in this investigation, 9 (56%) were male and average age was 68 (range, 49-80) years. Time from surgery averaged 25 (range, 12-38) months.

RESULTS

Total sagittal range of motion averaged 23±9 (range, 9-33) degrees. Axial motion for total internal and external rotation of the polyethylene component on the tibial component averaged 6±5 (range, 0-18) degrees. AP translation of the polyethylene component relative to the tibial component averaged 1±1 (range, 0-3) mm. There was no relationship between axial rotation or AP translation of the polyethylene component and ankle joint range of motion (P > .05).

CONCLUSION

To our knowledge, this is the first investigation to measure axial and sagittal motion of the polyethylene component at the tibial implant interface in patients following a mobile-bearing TAA. Based on outcome scores and range-of-motion measurements, we believe the patients in this study are a representative cross section of subjects compared to other TAA research results. The results from this investigation indicate the potential for a mobile-bearing TAA to fall within the parameters of normal polyaxial ankle motion. The multiplanar articulation in a mobile-bearing TAA may reduce excessively high peak pressures during the complex dynamic tibial and talar motion, which may have a positive influence on gait pattern, polyethylene wear, and implant longevity.

LEVEL OF EVIDENCE

Level IV, case series.

Effects of Ankle Arthrodesis on Biomechanical Performance of the Entire Foot

Background/Methodology

Ankle arthrodesis is one popular surgical treatment for ankle arthritis, chronic instability, and degenerative deformity. However, complications such as foot pain, joint arthritis, and bone fracture may cause patients to suffer other problems. Understanding the internal biomechanics of the foot is critical for assessing the effectiveness of ankle arthrodesis and provides a baseline for the surgical plan. This study aimed to understand the biomechanical effects of ankle arthrodesis on the entire foot and ankle using finite element analyses. A three-dimensional finite element model of the foot and ankle, involving 28 bones, 103 ligaments, the plantar fascia, major muscle groups, and encapsulated soft tissue, was developed and validated. The biomechanical performances of a normal foot and a foot with ankle arthrodesis were compared at three gait instants, first-peak, mid-stance, and second-peak.

Principal Findings/Conclusions

Changes in plantar pressure distribution, joint contact pressure and forces, von Mises stress on bone and foot deformation were predicted. Compared with those in the normal foot, the peak plantar pressure was increased and the center of pressure moved anteriorly in the foot with ankle arthrodesis. The talonavicular joint and joints of the first to third rays in the hind- and mid-foot bore the majority of the loading and sustained substantially increased loading after ankle arthrodesis. An average contact pressure of 2.14 MPa was predicted at the talonavicular joint after surgery and the maximum variation was shown to be 80% in joints of the first ray. The contact force and pressure of the subtalar joint decreased after surgery, indicating that arthritis at this joint was not necessarily a consequence of ankle arthrodesis but rather a progression of pre-existing degenerative changes. Von Mises stress in the second and third metatarsal bones at the second-peak instant increased to 52 MPa and 34 MPa, respectively, after surgery. These variations can provide indications for outcome assessment of ankle arthrodesis surgery.

Initial instability in total ankle replacement: a cadaveric biomechanical investigation of the STAR and agility prostheses

BACKGROUND

Design improvements have increased the success of total ankle replacement, providing patients with end-stage ankle arthritis a viable alternative to arthrodesis. However, revision rates are higher than those for hip and knee arthroplasty, with the most prevalent cause of failure being aseptic loosening. The objective of this study was to quantify and compare the relative bone-implant motion patterns in two well-known total ankle replacement designs.

METHODS

A custom-designed mechanical simulator applied compressive loads (up to 300 N) and bending moments (3 Nm) to six pairs of human cadaveric ankles implanted with total ankle replacements, inducing a natural range of motion about three orthogonal axes: plantar flexion-dorsiflexion, inversion-eversion, and internal-external rotation. The implants analyzed were the Agility and the STAR (Scandinavian Total Ankle Replacement). The relative bone-implant motions for each implant component were measured with use of an optical motion capture system.

RESULTS

The Agility typically exhibited greater relative motion than the STAR, with significant differences for the tibial component in inversion-eversion (p = 0.037) and for the talar component in internal-external rotation (p = 0.039). The magnitudes of the relative motions were affected by the loading direction and by compression. The motion magnitudes were quite large, with values exceeding 1000 μm for the Agility talar component in plantar flexion-dorsiflexion and in inversion-eversion.

CONCLUSIONS

The greater magnitudes of relative motion in the Agility suggest that primary instability of the implant may contribute to its higher clinically observed aseptic loosening rate. Future total ankle replacement designs will require better fixation to improve outcomes. The results underscore the need to conduct preclinical biomechanical assessments of relative motion patterns in ankle replacements.

CLINICAL RELEVANCE

Stable initial implant fixation will likely improve clinical outcomes of total ankle replacement.

Comparison of gait after total ankle arthroplasty and ankle arthrodesis

BACKGROUND

Prior studies reported improved gait after total ankle arthroplasty and better parameters of gait than those reported in earlier studies of patients after ankle arthrodesis. However, there are very limited data prospectively evaluating the effects on gait after ankle arthroplasty compared with ankle arthrodesis. Controversy remains regarding the relative advantages and disadvantages of these 2 treatments and especially the differences in function between them.

METHODS

We performed a prospective study involving 28 patients with posttraumatic and primary ankle osteoarthritis and a control group of 14 normal volunteers. We compared gait in 14 patients who had undergone ankle arthrodesis with the gait of 14 patients who had ankle arthroplasty preoperatively and at 1 year postoperatively. Three-dimensional gait analysis was performed with a 12-camera digital-motion capture system. Temporospatial measurements included stride length and cadence. The kinematic parameters that were measured included the sagittal plane range of motion of the ankle and the coronal plane range of motion of the ankle. Double force plates were used to collect kinetic parameters such as ankle coronal and plantar flexion-dorsiflexion moments and sagittal plane ankle power. Center of pressure (CoP) and its progression in gait cycle were calculated.

RESULTS

Baseline parameters showed comparability among the treatment and control groups. Temporospatial analysis, using time as the main effect, showed that compared with ankle arthrodesis, patients with total ankle arthroplasty had higher walking velocity attributable to both increases in stride length and cadence as well as more normalized first and second rockers of the gait cycle. Kinematic analysis, using time and intervention as the main effects, showed that patients who had ankle arthroplasty had better sagittal dorsiflexion (P = .001), whereas those undergoing ankle arthrodesis had better coronal plane eversion (P = .01). Neither ankle arthrodesis nor arthroplasty altered the CoP progression during stance phase. Total ankle arthroplasty produced a more symmetrical vertical ground reaction force curve, which was closer to that of the controls than was the curve of the ankle arthrodesis group.

CONCLUSIONS

Patients in both the arthrodesis and arthroplasty groups had significant improvements in various parameters of gait when compared with their own preoperative function. Neither group functioned as well as the normal control subjects. Neither group was superior in every parameter of gait at 1 year postoperatively. However, the data suggest that the major parameters of gait after ankle arthrodesis in deformed ankle arthritis are comparable to gait function after total ankle arthroplasty in nondeformed ankle arthritis.

LEVEL OF EVIDENCE

Level II, prospective comparative study.

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.

The in vitro reliability of the CODA MPX30 as the basis for a method of assessing the in vivo motion of the subtalar joint

BACKGROUND

The considerable variation in subtalar joint structure and function shown by studies indicates the importance of developing a noninvasive in vivo technique for assessing subtalar joint movement. This article reports the in vitro testing of the CODA MPX30, an active infrared marker motion analysis system. This work represents the first stage in the development of a noninvasive in vivo method for measuring subtalar joint motion during walking.

METHODS

The in vitro repeatability of the CODA MPX30 system's measurements of marker position, simple and intermarker set angles, was tested. Angular orientations of markers representing the position of the talus and the calcaneus were measured using a purpose-designed marker placement model.

RESULTS

Marker location measurements were shown to vary by less than 1.0 mm in all of the planes. The measurement of a 90° angle was also found to be repeatable in all of the planes, although measurements made in the yz plane were shown to be consistently inaccurate (mean, 92.47°). Estimation of segmental orientation was found to be repeatable. Estimations of marker set orientations were shown to increase in variability after a coordinate transform was performed (maximum SD, 1.14°).

CONCLUSIONS

The CODA MPX30 was shown to produce repeatable estimations of marker position. Levels of variation in segmental orientation estimates were shown to increase subsequent to coordinate transforms. The combination of the CODA MPX30 and an appropriate marker placement model offers the basis of an in vivo measurement strategy of subtalar joint movement, an important development in the understanding of the function of the joint during gait.

Analysis of joint laxity after total ankle arthroplasty: cadaver study

BACKGROUND

Clinical results of total ankle arthroplasty with early designs were disappointing. Recently-developed ankle prostheses have good mid-term results; however, limited information is available regarding effects of total ankle arthroplasty on ankle laxity.

METHODS

Eight cadaveric lower extremities were tested with a custom device which enabled measurement of multi-axial forces, moments, and displacement during applied axial, shear, and rotational loading. Tests consisted of anterior-posterior and medial-lateral translation and internal-external rotation of the talus relative to the tibia during axial loads on the tibia simulating body weight (700 N) and an unloaded condition (5 N). Tests were performed in neutral, dorsiflexion, and plantarflexion. Laxity was determined for the intact ankle, and following insertion of an unconstrained total ankle implant, comparing load-displacement curve.

FINDINGS

Laxity after total ankle arthroplasty did not approximate the normal ankle in most conditions tested. Displacement was significantly greater for total ankle arthroplasty in both posterior and lateral translation, and internal rotation, with 5 N axial loading, and anterior-posterior, medial-lateral translation, and internal-external rotation for 700 N axial loading. For the 700 N axial load condition, in the neutral ankle position, total anterior-posterior translation averaged 0.4 mm (SD 0.2 mm), but 6.0 mm (SD 1.5 mm) after total ankle arthroplasty (P<0.01). This study demonstrated more laxity in the replaced ankle than normal ankle for both unloaded and 700 N axially loaded conditions.

INTERPRETATION

These data indicate the increased responsibility of the ligaments for ankle laxity after total ankle arthroplasty and suggest the importance of meticulous ligament reconstruction with total ankle arthroplasty operations.

Proprioception after total ankle arthroplasty

BACKGROUND

Total ankle arthroplasty (TAA) is becoming an effective treatment for end-stage ankle arthritis. It is unknown if TAA alters the patient's ability to sense ankle joint position.

MATERIALS AND METHODS

Thirteen unilateral TAA patients with a minimum of 2-years followup completed proprioceptive testing of the TAA and the contralateral side. The task was to reproduce a given ankle angle using a joystick-driven device while the lower limb was obscured from view. Nine angles were tested, including two angles in dorsiflexion, three in plantarflexion, two in inversion, and two in eversion. A repeated-measures ANOVA was used to evaluate the results.

RESULTS

No statistically significant differences between the TAA ankle and the contralateral side were found.

CONCLUSION

TAA does not cause a change in proprioceptive abilities in arthritis patients when compared to the contralateral, unaffected side in a small sample of unilateral patients. Surgeons and rehabilitation professionals may use this information when designing rehabilitation plans following the insertion of a TAA.

Management of the varus arthritic ankle

Treatment of the arthritic varus ankle presents a significant surgical challenge. The recognition of the causes and associated deformities directs the treatment of the individual patient and optimizes functional outcome. Arthrodesis and total ankle replacement often will need to be augmented by corrective hind- and midfoot procedures and by careful soft tissue balancing. Often multiple procedures are required to achieve the desired result, and patients need to be advised that surgery may need to be staged.

Biomechanics of the ankle joint and clinical outcomes of total ankle replacement

Until the 1970s ankle arthrodesis was considered to be the "gold-standard" to treat arthritis. But the low fusion rate of ankle arthrodeses along with the inability to achieve normal range of motion led to the growing interest in the development of total ankle replacements. Though the short-term outcomes were good, their long-term outcomes were not as promising. To date, most models do not exactly mimic the anatomical functionality of a natural ankle joint. Therefore, research is being conducted worldwide to either enhance the existing models or develop new models while understanding the intricacies of the joint more precisely. This paper reviews the anatomical and biomechanical aspects of the ankle joint. Also, the evolution and comparison of clinical outcomes of various total ankle replacements are presented.

Ankle replacement versus arthrodesis: a comparative gait analysis study

BACKGROUND

The improving survivorship of ankle replacements is making this an increasingly popular option in the treatment of ankle arthritis, rather than the established option of ankle fusion. The potential benefits of restoring movement, improving gait and protecting adjacent joints are persuasive arguments in favor of replacing rather than fusing the ankle joint.

METHODS

Gait analysis was performed before and after ankle arthroplasty on 12 patients, and compared to 12 patients with a successful ankle arthrodesis and to a healthy control group of 12 people.

RESULTS

Important differences between the arthrodesis and ankle replacement groups were demonstrated although neither restored normal movement or walking speed. Ankle arthrodesis resulted in a faster gait with a longer step length compared to replacement, although the timing of gait demonstrated greater asymmetry. The ankle replacement group had greater movement at the ankle, a symmetrical timing of gait and restored ground reaction force pattern.

CONCLUSION

The improved timing of gait would support the observation of a reduction in limp with ankle replacement though the gait is significantly slower. Longer term results are necessary to determine whether the improved movement and force transmission persists with time and protects adjacent articulations.

Gait analysis in ankle osteoarthritis and total ankle replacement

BACKGROUND

Little information is available about gait changes in ankle osteoarthritis and total ankle replacement, and also about total ankle replacement patients' rehabilitation in the first year after surgery.

METHODS

Thirty subjects were included in this study: 15 unilateral post-traumatic ankle osteoarthritis patients and 15 age-/gender-matched control subjects. Patients were followed prospectively: preoperatively, at 3, 6, 9, and 12 months after total ankle replacement. The clinical-functional level was assessed by the American Orthopaedic Foot and Ankle Society ankle and the Short-Form-36 health survey score. 3D ankle-hindfoot kinematic-kinetic analysis was performed using a motion analysis and a two-plate force-platform system. Statistics included repeated measures analysis of variances, independent sample and paired Student's t-tests (significance alpha=0.05).

FINDINGS

Compared to normal subjects, ankle osteoarthritis caused significant reduction of the American Orthopaedic Foot and Ankle Society and Short-Form-36 score. In gait analysis, ankle osteoarthritis showed a significant deficiency in six of seven spatiotemporal variables, a decrease of the tri-planar ankle movement, a decrease of the second active maximal vertical and the maximal medial ground reaction force, a reduction of the sagittal and transverse ankle joint moments, a reduction of the ankle joint power. Three months after total ankle replacement surgery patients experienced a worsening of gait. At 12 months follow-up, all spatiotemporal variables were not different from the normal subjects (full rehabilitation); in six of 11 kinematic and kinetic variables there was a partial rehabilitation.

INTERPRETATION

This study provides data for the clinical-biomechanical understanding of the normal, arthritic, and total ankle replacement treated ankle during walking and the first year of rehabilitation.

[Anatomical and biomechanical aspects of total ankle replacement]

The success of total ankle replacement highly depends on how successfully the physiological kinematics are maintained or reconstructed. Normal kinematics of the ankle joint can be replicated by designing an implant that is as close as possible to the normal bony anatomy, aligning the ankle and balancing the ligaments. Mimicking normal kinematics and kinetics of a healthy ankle joint will consequently decrease damaging joint contact stress forces and stress forces on the surrounding soft tissue, which may cause wear, implant failure, and pain. This article summarizes the anatomical and biomechanical basics that are required in total ankle replacement.

J. Leonard Goldner Award 2006. Total ankle replacement in ankle osteoarthritis: an analysis of muscle rehabilitation

BACKGROUND

The aim of this prospective study was to determine muscle rehabilitation in total ankle replacement (TAR) for unilateral severe ankle osteoarthritis.

METHOD

Fifteen patients were assessed before and after TAR in 3-month intervals up to 1 year. Clinically, the pain score, the American Orthopaedic Foot and Ankle Society (AOFAS) ankle score, ankle range of motion for dorsiflexion and plantarflexion (ROM DF/PF) and the calf circumference difference between the affected and contralateral healthy leg were measured. Radiographic assessment consisted of osteoarthritis grading abd evaluation of TAR loosening or migration. Biochemically, isometric maximal voluntary torque for ankle dorsiflexion and plantarflexion was measured simultaneously with surface electromyography (EMG; mean frequency and intensity) of the anterior tibial, medial gastrocnemius, soleus, and peroneus longus muscles. Data were compared to a group of 15 age-matched and gender-matched normal subjects.

RESULTS

From preoperative to 12 months after TAR, improvement was noted in pain scores (from 6.8 to 0.8 points), AOFAS ankle scores (33.7 to 93.3 points), and ROM DF/PF significantly (16.0 to 31.0 degrees). The difference in mean calf circumference between legs decreased not significantly from 2.1 cm to 1.7 cm. The mean DF torque (16.4 to 23.1 Nm) and PF torque (15.8 to 21.6 Nm) of the affected ankle increased significantly. Compared to the contralateral healthy side, the mean EMG intensity recovered.

CONCLUSION

TAR surgery improved muscle function (torque, EMG intensity) in osteoarthritic ankles. However, after 1 year, patients did not reach the level of the contralateral healthy leg, and the EMG frequency remained unchanged.

The Scandinavian total ankle replacement (STAR)

Ankle joint arthritis is a condition that affects many people. Initial conservative treatment includes nonsteroidal antiinflammatory drugs, soft bracing, and ankle foot orthosis. When conservative management fails, surgical intervention is often considered. Previously an ankle joint fusion has been considered the "gold standard" to treat disabling ankle joint arthritis because early total ankle joint replacements had unacceptably high complication rates. However, early and midterm data have demonstrated that the Scandinavian Total Ankle Replacement (STAR) or Agility Total Ankle may be a reasonable alternative to an ankle joint fusion.

[Muscle biomechanics in total ankle replacement]

The purpose of this orthopaedic-biomechanical study was to evaluate the muscle function in total ankle replacement (TAR) patients 1 year after surgery. Ten patients underwent a combined clinical and muscle biomechanical assessment prior to implantation and at the 1-year follow-up. Pain score, American Orthopaedic Foot and Ankle Society (AOFAS) ankle score, ankle range of motion (ROM), and calf circumference difference between the affected leg and contralateral healthy leg were assessed. Biomechanically, isometric maximal voluntary torque for ankle dorsiflexion and plantar flexion was measured simultaneously with surface electromyography of four lower leg muscles. At follow-up, a significant improvement of the pain score (from 6.7 to 0.8 points), AOFAS ankle score (from 35.6 to 92.3 points), and ROM could be shown. Not significantly, the mean calf circumference difference between legs decreased from 2.2 to 1.4 cm. However, a significant increase was seen in the mean dorsiflexion (from 17.0 to 25.8 Nm) and plantar flexion torque (15.7 to 24.6 Nm) of the TAR-treated ankle. The mean EMG frequency content of the affected lower leg at TAR follow-up was lower than in the muscles of the contralateral healthy side. In contrast, the mean EMG intensity at TAR follow-up in side-comparison was statistically the same for all muscles. Ankle OA patients have better muscle function with TAR than under the arthritic condition, but they do not reach the normal level of the contralateral healthy leg 1 year after surgery.

Finite element analysis of a total ankle replacement during the stance phase of gait

Total ankle replacement (TAR) designs have still several important issues to be addressed before the treatment becomes fully acceptable clinically. Very little is known about the performance, in terms of the contact pressures and kinematics of TAR when subjected to daily activities such as level gait. For this purpose, an explicit finite element model of a novel 3-component TAR was developed, which incorporated a previously validated mechanical model of the ankle ligament apparatus. The intermediate mobile polyethylene meniscal bearing was modelled as an elastic-plastic continuum while the articulating surfaces of the tibial and talar metal components as rigid bodies. Overall kinematics, contact pressures and ligament forces were analysed during passive, i.e. virtually unloaded, and active, i.e. stance phase of gait, conditions. Simulation of passive motion predicted similar kinematics as reported previously in an analytical four-bar linkage model. The meniscal bearing was observed to move 5.6 mm posteriorly during the simulated stance and the corresponding antero-posterior displacement of the talar component was 8.3 mm. The predicted pattern and the amount (10.6 degrees ) of internal-external rotation of the ankle complex were found to be in good agreement with corresponding in vivo measurements on normal ankles. A peak contact pressure of 16.8 MPa was observed, with majority of contact pressures below 10 MPa. For most ligaments, reaction forces remain within corresponding physiological ranges. A first realistic representation of the biomechanical behaviour of the human ankle when replaced by prosthetic joints is provided. The applied methodology can potentially be applied to other TAR designs.

Tissue engineered ceramic artificial joint--ex vivo osteogenic differentiation of patient mesenchymal cells on total ankle joints for treatment of osteoarthritis

Total joint arthroplasty is the common treatment of severe cases of osteoarthritis. However, complications involving failure of the bone-prosthesis interface are significant, especially in ankle arthroplasty. To prevent this complication, we attempted a tissue engineering approach using the mesenchymal cells of the patient. We collected a small amount of fresh bone marrow cells from the patient's iliac crest and expanded the number of mesenchymal cells. We then applied the mesenchymal cells to a ceramic ankle prosthesis and cultured them to form an osteoblasts/bone matrix on the prosthesis. We used tissue engineered prostheses on three patients suffering from ankle arthritis and followed their progress for at least 2 years. Follow-up X-ray examinations revealed early radiodense appearance (bone formation) around the cell-seeded areas of the prostheses about 2 months after the operation after which a stable host bone-prosthesis interface was established. All patients showed high clinical scores after the operation and did not exhibit inflammatory reactions. These preliminary results indicate that the tissue engineering approach using autologous cultured marrow mesenchymal cells might prevent aseptic loosening of the total ankle arthroplasty.

Biomechanics of and research challenges in uncemented total ankle replacement

Only limited data are available currently on the clinical performance of uncemented total ankle replacements. Even so, various complications, notably loosening and/or migration of the talar and/or tibial components, already have been seen. Nonetheless, the current consensus is that, in all likelihood, uncemented total ankle prostheses will continue to be implanted in some patients. Therefore, it is important that future designers of this prosthesis be conversant with all the requirements that a design must fulfill, be aware of the various features of second-generation designs that were introduced to address problems seen in implanted cemented first-generation replacement designs, be knowledgeable about the in vivo performance, to date, of uncemented second-generation total ankle replacement designs and how features of a design may impact its performance, and be cognizant of the gaps and/or controversies in the literature and the extent to which they could be addressed through focused research. All of these four aspects, which have been treated inadequately in the literature, are treated in detail in the current review, with the hope that the review will serve as a primer for those involved in designing the next generation of uncemented total ankle replacements. Thirteen design requirements, including kinematics, kinetics, and stability aspects, are described. Various features of three second-generation designs are described. For three second-generation designs, the relationship between their estimated in vivo performance and the extent of joint resurfacing needed to implant them is presented. Among the seven future research areas discussed are design, fabrication, and validation of an ankle simulator, and development of a set of standardized biomechanical tests.

Functional evaluation of the Scandinavian Total Ankle Replacement

The purpose of this study was to evaluate the function of the ankle joint during walking before and after Scandinavian Total Ankle Replacement (STAR). Nine patients (six males and three females) with an average age of 65 years, scheduled for unilateral total ankle replacement for osteoarthritis and rheumatoid arthritis, were evaluated both preoperatively and postoperatively in a gait analysis laboratory. Arthroplasty patients showed reduced range of motion at the ankle compared to normal controls. Postoperative arthroplasty subjects had significantly improved external ankle dorsiflexion moment, the moment that affects the plantarflexor muscles, when compared to their preoperative status. The moment in arthroplasty patients was increased, indicating improved function of the ankle joint.

Challenges in total ankle arthroplasty

In the past, total ankle arthroplasty was largely abandoned due to poor survivorship most often caused by loss of bone support. High complication rates were also reported. Despite this, there is renewed interest in ankle arthroplasty and encouraging results are seen in survivorship with midterm follow-up. The procedure, however, remains more challenging than total hip or total knee arthroplasty. With the limited soft tissue envelope, wound problems are not uncommon. Forces at the ankle are very large and yet the surface area for prosthetic support is small. Therefore, fixation can be more difficult. The strongest bone can be eccentric at the distal tibia. The tibial prosthesis can, therefore, tend to settle into the softer bone often laterally. Polyethylene needs to be sufficiently thick to maintain its integrity but that requires a larger bone resection, which weakens bone support. Polyethylene failure or wear leads to the majority of failures in hip and knee arthroplasty. There is a need for further basic science research in total ankle arthroplasty. The lessons learned from other arthroplasty should be considered in ankle arthroplasty design.

Transverse plane motion at the ankle joint

The ankle is often considered to have little or no capacity to move in the transverse plane. This is clear in the persistent concept that it is the role of the subtalar joint to accommodate the transverse plane motion of the leg while the foot remains in a fixed transverse plane position on the floor. We present data from noninvasive in vivo study of the ankle subtalar complex during standing internal and external rotation of the leg and study of the ankle subtalar complex during walking. These data reinforce the results of cadaver study and invasive in vivo study of the ankle/subtalar complex. We suggest that the ankle is capable of considerable movement in the transverse plane (generally greater than 15 degrees) and that its role in the mechanism that allows the foot to remain in a fixed transverse plane position on the floor while the leg rotates in the transverse plane, is not simply the transfer of the transverse plane moment to the subtalar joint, but is accommodation of some of the necessary movement.

Total ankle arthroplasty: a historical perspective

The ideal total ankle prosthesis has yet to be determined, but much has been learned from early experiences in ankle arthroplasty. Modern implants are typically more respectful of anatomic concerns, have found a happy medium of constraint, and have found novel approaches to decrease interface stress. Biologic fixation has improved on cemented results. Surgical techniques and understanding of wound healing and ligamentous deficiency have advanced. Current series still have varied results, and longer-term follow-up is needed. Despite this, some modern ankle replacements represent significant progress, with improved results and survival challenging those of arthrodesis. Further, benefits of preserved motion and avoidance of foot arthritis outstrip this traditional "gold standard." Today, tempered enthusiasm for the future of total ankle arthroplasty is again apparent. A diverse, international effort is underway to create a lasting joint implant. Building on the lessons of the past, different investigators in different countries, using markedly different prostheses, continue to work toward this goal.

Preoperative considerations in ankle replacement surgery

Total ankle arthroplasty continues to evolve as a viable treatment option for end-stage ankle arthritis. Proper patient selection is a critical aspect of promoting a successful result. Acceptable results have been reported in older, low-demand, nonobese patients who have osteoarthritis or rheumatoid arthritis. A significant percentage of patients with end-stage ankle arthritis, however, are younger patients with posttraumatic arthritis. Considerable controversy surrounds the use of ankle replacement in younger, more physically active patients and in those with significant deformity in the ankle or hindfoot. These patients should be approached cautiously because the risks and complications are still significant. More studies must be completed and further developments must be made to maximize the longevity and functional results of total ankle arthroplasty in future designs and applications.