BACKGROUND:The use of weightbearing images to diagnose foot and ankle injuries continues to offer hope for improved insight into pathologies, but weightbearing CT imaging has been limited by availability. The ability to apply force to the lower limb in a horizontal bore CT system may offer an adaptation to currently available imaging systems that provides access to weightbearing images without the acquisition of additional expensive imaging space or equipment.METHODS:In order to determine whether a horizontal CT system could produce the same results as a standing CT, 3 images of one foot from 10 subjects was obtained and standard measures were calculated. Each subject underwent a standing CT scan, a scan in a horizontal bore CT machine while the subject pressed against a pedal with spring resistance and a finally a scan with the foot placed on the pedal but without any pressure.RESULTS:No statistically significant difference between the standing and pedal-based CTs resulted. Navicular height and Meary angle (axial) were statistically different from nonweightbearing for both standing and horizontal systems. The horizontal results were statistically different from nonweightbearing in IM angle, talocalcaneal angle, and talonavicular coverage. No differences from nonweightbearing were found for either system in talar tilt, talocrural angle, or the lateral Meary angle.CONCLUSION:The results in this initial study of normal control subjects suggest that a pedal-based loading mechanism may adapt a horizontal-bore CT system for the acquisition of weightbearing images.CLINICAL RELEVANCE:The ability to acquire a weightbearing CT from a horizontal bore CT machine can make these images more available.

Background: Malposition of the sesamoids relative to the first metatarsal head may relate to intersesamoid crista underdevelopment or erosion. Using 3-dimensional models created from weightbearing CT (WBCT) scans, the current work examined crista volume and its relationship to first metatarsal pronation and sesamoid station. Methods: Thirty-eight hallux valgus (HV) patients and 10 normal subjects underwent weightbearing or simulated WBCT imaging. The crista was outlined by the inferior articular surface, and a line was drawn to connect the lowest point of each sulcus on either side of the intersesamoidal crista throughout the length of the crista. The volume was calculated. Sesamoid station and first metatarsal pronation were calculated from the 3D reconstructions. The mean crista volumes between HV and normal patients were statistically compared, as were the crista volume and pronation angle between sesamoid stations. Results: The mean crista volume in HV patients was 80.10 ± 35 mm3 and in normal subjects was 150.64 ± 24 mm3, which differed significantly between the 2 groups (P < .001). Mean crista volumes were found to be statistically significantly different between the sesamoid stations (P < .001) with decreasing crista volumes significantly and strongly correlated with increasing sesamoid station (r = −0.80, P < .001). There was no difference in the mean pronation angle between the 4 sesamoid stations (P = .37). The pronation angle was not associated with crista volume (P = .52). Conclusion: HV patients have lower mean crista volume than normal patients. Crista volume is correlated with sesamoid station. Pronation of the first metatarsal was not associated with crista volume. Clinical Relevance: Crista volume may offer an additional determinant for the severity of hallux valgus.

Category: Bunion Introduction/Purpose: The hallux valgus (HV) deformity results in progressive subluxation of the sesamoids from their position (station) under the plantar surface of the first metatarsal head. This subluxation may result in erosion of the crista that separates the sesamoid grooves due to contact with the tibial sesamoid during weightbearing. While previous work using weightbearing CT (WBCT) scans has suggested that tibial sesamoid position is associated with degenerative change of the sesamoid metatarsal joint (Katsui FAI), no studies have quantified the relationship between sesamoid metatarsal degenerative changes and sesamoid subluxation. The purpose of the current investigation is to examine the relationship of the volume of the crista to first metatarsal pronation and sesamoid station, using three-dimensional models of patients' deformities created from WBCT scans. Methods: Thirty-nine HV patients and nine normal subjects underwent weightbearing or simulated weightbearing CT (WBCT) imaging. Crista volume was determined using a line drawn to connect the nadir of each sulcus on either side of the intersesamoidal crista for the length of the crista (Figure 1). The Mann-Whitney U test was used to compare mean crista volume between HV and normal patients. WBCT scans were used to establish sesamoid position using a four-stage scale (Kim FAI 2015) and quantify first metatarsal pronation using 3D reconstructions as previously described (Campbell FAI 2018). Single-factor analysis of variance (ANOVA) tests were used to compared the crista volume and pronation angle between the four sesamoid stations. A linear regression was performed to determine whether crista volume was associated with the pronation angle. Spearman's rank coefficient (r) was used to test the relationship of the sesamoid station against the crista volume and pronation angle. Results: The mean crista volume in HV patients was 80.10 mm 3 +- 35 mm 3 and in normal subjects was 150.64 mm 3 +- 24 mm 3 , which differed significantly between the two groups (P<0.001). Mean crista volumes were found to be statistically significantly different between the sesamoid stations (P<0.001) with decreasing crista volumes significantly and strongly correlated with increasing sesamoid station (r = -0.80, P<0.001). The mean standard deviation values of the crista volume by sesamoid station were 154.4 mm 3 +- 18.7 mm3 for station zero, 98.19 mm3 +- 26.9 mm 3 for station one, 78.45 mm 3 +- 30.1 mm 3 for station two, and 44.77 mm 3 +- 13.5 mm 3 for station three. There was no difference in the mean pronation angle between the four sesamoid stations (P=0.37). Additionally, no statistically significant relationship was found between sesamoid station and pronation angle. The pronation angle was not associated with crista volume (P=0.52). Conclusion: Our study found that HV patients have significantly lower mean crista volumes compared to normal patients. Crista volume was strongly correlated with sesamoid subluxation/station, suggesting that tibial sesamoid subluxation results in erosion of the crista. In contrast, the pronation deformity was not associated with crista volume demonstrating that the degenerative changes of the sesamoid metatarsal are not related to the rotational deformity of the first metatarsal. This supports the hypothesis that tibial sesamoid subluxation may result in osteoarthritis of the sesamoid metatarsal joint and may be an overlooked source of pain in HV.

BACKGROUND:The purpose of this study was to determine if a postoperative decrease in first metatarsal pronation on 3-dimensional imaging was associated with changes in patient-reported outcomes as measured by the Patient-Reported Outcomes Measurement Information System (PROMIS) physical function, pain interference, and pain intensity domains or recurrence rates in patients with hallux valgus (HV) who undergo a first tarsometatarsal fusion (modified Lapidus procedure).METHODS:Thirty-nine consecutive HV patients who met the inclusion criteria and underwent a modified Lapidus procedure had preoperative and ≥2-year postoperative PROMIS scores and had first metatarsal pronation measured on preoperative and at least 5-month postoperative weightbearing CT scans were included. Multivariable regression analyses were used to investigate differences in the change in PROMIS domains preoperatively and 2 years postoperatively between patients with "no change/increased first metatarsal pronation" and "decreased first metatarsal pronation." A log-binomial regression analysis was performed to identify if a decrease in first metatarsal pronation was associated with recurrence of the HV deformity.RESULTS:The decreased first metatarsal pronation group had a significantly greater improvement in the PROMIS physical function scale by 7.2 points (P = .007) compared with the no change/increased first metatarsal pronation group. Recurrence rates were significantly lower in the decreased first metatarsal pronation group when compared to the no change/increased first metatarsal pronation group (risk ratio 0.25, P = .025).CONCLUSION:Detailed review of this limited cohort of patients who underwent a modified Lapidus procedure suggests that the rotational component of the HV deformity may play an important role in outcomes and recurrence rates following the modified Lapidus procedure.LEVEL OF EVIDENCE:Level III, retrospective cohort study.

INTRODUCTION:In hallux valgus (HV), first metatarsal pronation is increasingly recognized as an important aspect of the deformity. The purpose of this study was to compare pronation in HV patients determined from the shape of the lateral head of the first metatarsal on AP weightbearing radiographs with pronation calculated from weightbearing CT (WBCT) scans. METHODS:Patients were included in this study if they had preoperative and 5-month postoperative WBCT scans and corresponding weightbearing AP radiographs of the affected foot. Pronation of the first metatarsal on WBCT scans was measured using a 3D CAD model and the alpha angle and categorized into four groups on radiographs. Association between pronation groups on radiographs and WBCT scans was determined using Spearman correlation coefficients (rs) and by comparing mean WBCT pronation of the first metatarsal between plain radiograph pronation groups. RESULTS:Agreement between the two observers' pronation on radiographs was good (k = 0.634) and moderate (k = 0.501), respectively. There was no correlation between radiographic pronation and the 3D CAD model (rs < 0.15). Preoperatively, there was weak correlation between the alpha angle and the radiographic pronation groups (rs = 0.371, P = 0.048) although this relationship did not hold postoperatively (rs = 0.330, P = 0.081). There was no difference in mean pronation calculated on WBCT scans between the plain radiographic groups. CONCLUSION:Pronation of the first metatarsal measured on weightbearing AP radiographs had moderate interobserver agreement and was only weakly associated with pronation measured from WBCT scans. These results suggest that first metatarsal pronation measured on weightbearing radiographs is not a substitute for pronation measured on WBCT scans. LEVEL OF EVIDENCE:III, retrospective cohort study.

Background: There is no consensus in the foot and ankle literature regarding how to measure pronation of the first metatarsal in patients with hallux valgus. The primary purpose of this study was to compare 2 previously published methods for measuring pronation of the first metatarsal and a novel 3-dimensional measurement of pronation to determine if different measurements of pronation are associated with each other. Methods: Thirty patients who underwent a modified Lapidus procedure for their hallux valgus deformity were included in this study. Pronation of the first metatarsal was measured on weightbearing computed tomography (WBCT) scans using the α angle with reference to the floor, a 3-dimensional computer-aided design (3D CAD) calculation with reference to the second metatarsal, and a novel method, called the triplanar angle of pronation (TAP), that included references to both the floor (floor TAP) and base of the second metatarsal (second TAP). Pearson’s correlation coefficients were used to determine if the 3 calculated angles of pronation correlated to each other. Results: Preoperative and postoperative α angle and 3D CAD had no correlation with each other ( r = 0.094, P = .626 and r = 0.076, P = .694, respectively). Preoperative and postoperative second TAP and 3D CAD also had no correlation ( r = 0.095, P = .624 and r = 0.320, P = .09, respectively). However, preoperative and postoperative floor TAP and α angle were found to have moderate correlations ( r = 0.595, P = .001 and r = 0.501, P = .005, respectively). Conclusion: The calculation of first metatarsal pronation is affected by the reference and technique used, and further work is needed to establish a consistent measurement for the foot and ankle community. Level of Evidence: Level III, retrospective cohort study.

Background: Hallux valgus (HV) is a triplanar deformity of the first ray including pronation of the first metatarsal with subluxation of the sesamoids. The purpose of this study was to investigate if a first tarsometatarsal fusion (modified Lapidus technique), without preoperative knowledge of pronation measured on weightbearing computed tomographic (CT) scans, changed pronation of the first metatarsal and determine if reduction of the sesamoids was correlated with changes in first metatarsal pronation. Methods: Thirty-one feet in 31 patients with HV who underwent a modified Lapidus procedure had preoperative and at least 5-month postoperative weightbearing CT scans and radiographs. Differences in preoperative and postoperative pronation of the first metatarsal using a 3-dimensional computer-aided design, HV angle, and intermetatarsal angle (IMA) were calculated using Wilcoxon signed-rank tests. After dividing patients into groups based on sesamoid station, Kruskal-Wallis H tests were used to compare first metatarsal pronation between the groups. Results: The mean preoperative and postoperative pronation of the first metatarsal was 29.0 degrees (range 15.8-51.1, SD 8.7) and 20.2 degrees (range 10.4-32.6, SD 5.4), respectively, which was a mean change in pronation of the first ray of −8.8 degrees ( P < .001). There was no difference in pronation of the first ray when stratified by postoperative sesamoid position ( P > .250). The average preoperative and postoperative IMA was 16.7 degrees (SD 3.2) and 8.8 degrees (SD 2.8), which demonstrated a significant change ( P < .001). Conclusions: The modified Lapidus procedure was an effective tool to change pronation of the first ray. Reduction of the sesamoids was not associated with postoperative first metatarsal pronation. Level of Evidence: Level IV, case series.

Background: Charcot-Marie-Tooth (CMT) disease is a hereditary motor-sensory neuropathy that is often associated with a cavovarus foot deformity. Limited evidence exists for the orthopedic management of these patients. Our goal was to develop consensus guidelines based upon the clinical experiences and practices of an expert group of foot and ankle surgeons. Methods: Thirteen experienced, board-certified orthopedic foot and ankle surgeons and a neurologist specializing in CMT disease convened at a 1-day meeting. The group discussed clinical and surgical considerations based upon existing literature and individual experience. After extensive debate, conclusion statements were deemed “consensus” if 85% of the group were in agreement and “unanimous” if 100% were in support. Conclusions: The group defined consensus terminology, agreed upon standardized templates for history and physical examination, and recommended a comprehensive approach to surgery. Early in the course of the disease, an orthopedic foot and ankle surgeon should be part of the care team. This consensus statement by a team of experienced orthopedic foot and ankle surgeons provides a comprehensive approach to the management of CMT cavovarus deformity. Level of Evidence: Level V, expert opinion.

BACKGROUND::The current work sought to quantify pronation of the first metatarsal relative to the second metatarsal and of the proximal phalanx of the great toe relative to the first metatarsal.METHODS::Three-dimensional models were reconstructed from weightbearing computed tomography (CT) images (10 hallux valgus, 10 normal). The orientations of bones related to hallux valgus (HV) (ie, the phalanx, first and second metatarsals) were determined from coordinate systems established by selecting landmarks. After determining the hallux valgus and intermetatarsal angles, additional calculations geometrically determined the 3-dimensional (3D) angles using the aeronautical system of yaw-pitch-roll. The 3D geometrically determined angles were compared to the conventional plain radiographic angles.RESULTS::HV measurements taken with CT and 3D computer-aided design (3DCAD) geometric methods were the same as measurements taken from plain radiographs (P > .05). The average pronation of the first metatarsal relative to the second metatarsal was 8.2 degrees greater in the hallux valgus group (27.3 degrees) than in the normal group (19.1 degrees) (P = .044). A regression analysis of pronation vs intermetatarsal angle (IMA) was not found to be significant. There was also no correlation between pronation of the great toe and first metatarsal in the HV group.CONCLUSIONS::The pronation angle of the first metatarsal relative to the second metatarsal between normal and hallux valgus patients was larger in HV patients but was not well correlated with the IMA.CLINICAL RELEVANCE::The findings of this study indicate that pronation may need to be considered in the operative correction of hallux valgus for restoration of normal anatomy.

Tarsal coalitions, while relatively uncommon, are typically identified in adult patients during an evaluation for ankle instability, sinus tarsus pain, and/or pes planovalgus. The true incidence of tarsal coalition is unknown with estimates ranging from 1% to 12% of the overall population. The most common area of involvement of the subtalar joint is the middle facet, and heightened awareness should be present in adult patients with limited motion of the subtalar joint. Standard radiographic imaging, to include a Harris heel view, is recommended initially, although computerized tomography scan and MRI are often necessary to confirm the diagnosis.

To consistentlyand successfully treat musculoskeletal problems, the orthopedic surgeon must make a proper diagnosis that includes an understanding of the etiology and all structural components of a deformity, choose the proper surgical procedure from an often numerous list of possible treatment options, and properly perform the procedure chosen. References that describe over 120 surgical procedures that have been published for the correction of bunion deformities either means that the foot and ankle community has an intimate understanding of a very complex and heterogeneous deformity and has determined that this vast number of procedures is necessary to deal with this diversity or that we simply do not understand, or have significant misconceptions of, the etiology and source of patient complaints with bunions and that we widely differ in our interpretation of the physical examination findings and radiographic evaluation. This, in turn, has allowed us to devise so many surgical procedures with each attempting to address our own individual concepts of bunion deformities. The assessment and treatment of bunion deformities has traditionally been based on an analysis of the correction of radiographic angular abnormalities or measurement of patient satisfaction after a given surgical procedure. Most papers even try to comment on etiology that use the word "multifactorial" when describing how bunions form and progress. Rather than focus on a surgical procedure to fix radiographic angular abnormalities, I have developed an algorithm to correct bunion deformities that is based on suspected etiology that is being more carefully investigated in ongoing research.

Laboratory cultures are the main scientific input into the decision-making process that determines the course of treatment for suspected orthopedic infections, just as they constitute the mainstay of the diagnosis of infections in other medical specialties. This situation is archaic because culture techniques were virtually abandoned in Environmental Microbiology (Hugenholtz et al. 1998) many years ago, following the conclusion that <1% of the bacteria in any natural ecosystem can be recovered by standard cultural methods. Medical Microbiology has clung to culture techniques because they detect the bacteria that cause acute infections, with reasonable sensitivity and accuracy, but the time has come to examine both their sensitivity and their accuracy for the detection and identification of bacteria in chronic biofilm infections (Costerton et al. 1999).

To consistentlyand successfully treat musculoskeletal problems, the orthopedic surgeon must make a proper diagnosis that includes an understanding of the etiology and all structural components of a deformity, choose the proper surgical procedure from an often numerous list of possible treatment options, and properly perform the procedure chosen. References that describe over 120 surgical procedures that have been published for the correction of bunion deformities either means that the foot and ankle community has an intimate understanding of a very complex and heterogeneous deformity and has determined that this vast number of procedures is necessary to deal with this diversity or that we simply do not understand, or have significant misconceptions of, the etiology and source of patient complaints with bunions and that we widely differ in our interpretation of the physical examination findings and radiographic evaluation. This, in turn, has allowed us to devise so many surgical procedures with each attempting to address our own individual concepts of bunion deformities. The assessment and treatment of bunion deformities has traditionally been based on an analysis of the correction of radiographic angular abnormalities or measurement of patient satisfaction after a given surgical procedure. Most papers even try to comment on etiology that use the word “multifactorial” when describing how bunions form and progress. Rather than focus on a surgical procedure to fix radiographic angular abnormalities, I have developed an algorithm to correct bunion deformities that is based on suspected etiology that is being more carefully investigated in ongoing research.

Bacterial biofilms have been observed in many prosthesis-related infections, and this mode of growth renders the infection both difficult to treat and especially difficult to detect and diagnose using standard culture methods. We (1) tested a novel coupled PCR-mass spectrometric (PCR-MS) assay (the Ibis T5000) on an ankle arthroplasty that was culture negative on preoperative aspiration and then (2) confirmed that the Ibis assay had in fact detected a viable multispecies biofilm by further micrographic and molecular examinations, including confocal microscopy using Live/Dead stain, bacterial FISH, and reverse-transcriptase-PCR (RT-PCR) assay for bacterial mRNA. The Ibis technology detected Staphylococcus aureus, Staphylococcus epidermidis, and the methicillin resistance gene mecA in soft tissues associated with the explanted hardware. Viable S. aureus were confirmed using RT-PCR, and viable cocci in the biofilm configuration were detected microscopically on both tissue and hardware. Species-specific bacterial FISH confirmed a polymicrobial biofilm containing S. aureus. A novel culture method recovered S. aureus and S. epidermidis (both methicillin resistant) from the tibial metal component. These observations suggest that molecular methods, particularly the new Ibis methodology, may be a useful adjunct to routine cultures in the detection of biofilm bacteria in prosthetic joint infection.

BACKGROUND:The successful treatment of chronic mid-substance Achilles tendinopathy remains elusive. Approximately 25% to 50% of patients fail conservative treatment modalities. Scientific evidence has supported the use of platelet rich plasma (PRP) in the tendon healing process, however despite initial promise there is a paucity of clinical data to validate a role for PRP in the treatment of tendon disorders including chronic midsubstance Achilles tendinopathy.METHODS:As an alternative to operative treatment, our practice offers patients with chronic midsubstance Achilles tendinopathy intratendinous injection of PRP. We retrospectively reviewed all patients treated for Achilles tendinopathy with PRP injection over a 2-year period. Baseline and post injection functional scores including the Foot and Ankle Ability Measure (FAAM), Foot and Ankle Ability Measure - Sports (FAAMS), and the Short Form health survey (SF-8) were examined. Patients also underwent post-injection magnetic resonance imaging (MRI), which were compared to available pre-injection MRI data.RESULTS:Ten patients were identified for this study. Pre- and postinjection functional outcome scores were available for eight of ten patients. The average SF-8 score improved from 24.9 to 30.0, the average FAAM score improved from 55.4 to 65.8, and the average FAAMS score improved from 14.8 to 17.4. Complete MRI data was available for six patients. Only one in six Achilles tendons demonstrated qualitative MRI improvement post-injection.CONCLUSION:Patients who received PRP injection demonstrated modest improvement in functional outcome measures, however MRI appearance of diseased Achilles tendons remained largely unchanged following PRP injection.

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.

This manuscript offers current information regarding the examination, conservative treatment, and surgical treatment for individuals with posttraumatic arthritis. Although inflammatory and osteoarthritis can occur, posttraumatic arthritis is the most common form of arthritis to affect the ankle. Posttraumatic ankle arthritis occurs in a generally younger, active population. It is radiographically characterized by an asymmetrical degenerative process and may be associated with a history of trauma, instability, and/or lower extremity malalignment. When choosing between conservative/nonoperative versus surgical intervention, the extent of subchondral bone exposed and the time over which the arthritis has developed are factors that should be considered. The role and effectiveness for conservative treatment, such as medication, patient education, shoe modification, bracing, stretching, mobilization, strengthening, and symptom management, needs to be further determined. Surgical procedures for posttraumatic ankle arthritis can include distraction arthroplasty, arthrodesis, or total ankle arthroplasty. Unlike the relatively new procedure of distraction arthroplasty, the outcomes for arthrodesis have been well defined. Arthrodesis generally has a good outcome, but its limitations have been recognized. These limitations include the extended time required to achieve fusion, potential for nonunion, arthritis developing in adjacent joints, leg length discrepancy, malalignment, chronic edema, symptoms due to the hardware, stress fractures, and continued pain. While first generation total ankle arthroplasty led to poor results, advancements in prosthetic design and surgical technique have revived optimism regarding total ankle arthroplasty as an alternative to arthrodesis. The key for the future of total ankle arthroplasty may not be related to the development of newer ankle components but rather in refining the criteria to determine who would best benefit from joint replacement versus fusion.

Purpose of review: Ankle arthritis has been an area of clinical and research interest in recent years, with much emphasis having been placed on the development and improvement of second-generation total ankle replacement. This review article examines the important advances in the treatment of ankle arthritis during the last year. Recent findings: The post-traumatic etiology of most ankle arthritis has direct implications on treatment options. Ankle arthrodesis remains the gold standard for the treatment of ankle arthritis. As ankle replacement outcomes improve, surgeons have found a renewed interest for this procedure and it has emerged as a viable alternative to arthrodesis. Despite this enthusiasm, ankle replacement still holds several challenges that need to be addressed by the orthopaedic community. Other emerging techniques have also received some interest, including ankle distraction, viscosupplementation and fresh allograft transplantation. Summary: Treatment options for ankle arthritis continue to expand. A modern approach to the treatment of ankle arthritis needs to consider all of these alternatives while remaining prudent in response to the enthusiasm of investigators and industry.

BACKGROUND:With the increasing use of total ankle prostheses, kinematic analysis of these implants is important to our understanding of their specific biomechanics. Fluoroscopic analysis as used in this study has distinct advantages over previous experimental approaches and allows kinematic determination in vivo of dynamic weightbearing motions.METHODS:Ten patients with unilateral Agility (Depuy, A Johnson & Johnson Company, Warsaw, IN) total ankle replacements were tested using video fluoroscopy in weightbearing dynamic gait conditions. Their prosthetic ankle and normal ankle kinematics were then analyzed by computer with two-dimensional and three-dimensional model-fitting techniques.RESULTS:All of the total ankle prostheses in this study demonstrated less than 3.5 mm of posterior-to-anterior translation from heel strike to toe-off. In comparison, more variability was seen in posterior-to-anterior motion of the normal contralateral ankles, with three ankles translating more than 6 mm. When inversion and eversion and internal and external rotation of the ankle were measured, wide variations were seen among patients.CONCLUSIONS:While the relative incongruence theoretically decreases the shear stresses transmitted to the bone-prosthesis interface, it does allow more inversion-eversion and rotational freedom that can lead to edge loading and higher contact stresses. Despite good medium-term results having been published for this prosthesis, polyethylene wear and osteolysis have been observed. Further studies looking at the effect of the inversion and eversion and rotational freedom on polyethylene wear and prosthesis survival will assist in our understanding of the factors leading to successful outcome of total ankle prostheses.