Posterolateral ankle ligament injuries affect ankle stability: a finite element study

Syndesmosis dislocation and ankle ligament stress in the posterior malleolus fracture fixated - "in vitro analysis"

PURPOSE

The objectives of this study were to compare syndesmosis dislocation and ankle ligament stress after the fixation of the posterior malleolus fracture (PMF) with four different techniques by Finite Element Analysis (FEM).

METHODS

Four internal fixation techniques used for fixation of PMF were assessed by FEM: posterior one-third tubular 3.5 mm buttress plate (PP) with one screw (PP 1 screw), PP with two screws (PP 2 screws), two cannulated 3.5 mm lag screws in the anteroposterior (AP) direction (AP lag screws), and two posteroanterior (PA) cannulated 3.5 mm lag screws (PA lag screws). PMF with 30% fragment size was simulated through computational processing reconstructed from computed tomography (CT). The simulated loads of 700 N and 1200 N were applied to the proximal tibial end. The FEM evaluated the syndesmosis dislocation (mm) and stress values of the posterior tibiofibular ligament (PTFL) (in Kpa) and deltoid ligament (in Kpa) in the four mentioned subgroups.

RESULTS

We found that with a load of 700 N, syndesmosis dislocation varied from 6.5 to 7.9 mm, being the lowest and greatest for PA lag screw and PP 1 screw, respectively. In all groups was observed a greater dislocation in the syndesmosis at 1200 N of load. We observed that the stress values on the PTFL were lower for AP lag screws and PP 2 screws with 700 N and 1200 N, respectively. For both loads, PP 1 screw presented the greatest stress. Regarding the stress in the deltoid ligament, the AP lag screws presented the lowest stress for 700 N and PP 1 screw for 1200 N. For all fixation techniques, the syndesmosis displacement and ligament stresses were higher when 1200 N were imposed.

CONCLUSION

This study demonstrated that PMF fixed with lag screws presents greater stability in the distal tibiofibular syndesmosis and higher joint loadings promoted greater displacement and ligaments stress, regardless of the fixation technique. Besides, lower stress in the syndesmosis is accompanied by a greater load on the deltoid ligament.

Risk factors for chronic ankle instability after first episode of lateral ankle sprain: A retrospective analysis of 362 cases

BACKGROUND

Chronic ankle instability (CAI) is a common sequela following an acute lateral ankle sprain (LAS). To treat an acute LAS more effectively and efficiently, it is important to identify patients at substantial risk for developing CAI. This study identifies magnetic resonance imaging (MRI) manifestations for predicting CAI development after a first episode of LAS and explores appropriate clinical indications for ordering MRI scans for these patients.

METHODS

All patients with a first-episode LAS who received plain radiograph and MRI scanning within the first 2 weeks after LAS from December 1, 2017 to December 1, 2019 were identified. Data were collected using the Cumberland Ankle Instability Tool at final follow-up. Demographic and other related clinical variables, including age, sex, body mass index, and treatment were also recorded. Univariable and multivariable analyses were performed successively to identify risk factors for CAI after first-episode LAS.

RESULTS

A total 131 out of 362 patients with a mean follow-up of 3.0 ± 0.6 years (mean ± SD; 2.0-4.1 years) developed CAI after first-episode LAS. According to multivariable regression, development of CAI after first-episode LAS was associated with 5 prognostic factors: age (odds ratio (OR) = 0.96, 95% confidence interval (95%CI): 0.93-1.00, p = 0.032); body mass index (OR = 1.09, 95%CI: 1.02-1.17, p = 0.009); posterior talofibular ligament injury (OR = 2.17, 95%CI: 1.05-4.48, p = 0.035); large bone marrow lesion of the talus (OR = 2.69, 95%CI: 1.30-5.58, p = 0.008), and Grade 2 effusion of the tibiotalar joint (OR = 2.61, 95%CI: 1.39-4.89, p = 0.003). When patients had at least 1 positive clinical finding in the 10-m walk test, anterior drawer test, or inversion tilt test, they had a 90.2% sensitivity and 77.4% specificity in terms of detecting at least 1 prognostic factor by MRI.

CONCLUSION

MRI scanning is valuable in predicting CAI after first-episode LAS for those patients with at least 1 positive clinical finding in the 10-m walk test, anterior drawer test, and inversion tilt test. Further prospective and large-scale studies are necessary for validation.

Biomechanical Sequelae of Syndesmosis Injury and Repair

This review characterizes fibula mechanics in the context of syndesmosis injury and repair. Through detailed understanding of fibula kinematics (the study of motion) and kinetics (the study of forces that cause motion), the full complexity of fibula motion can be appreciated. Although the magnitudes of fibula rotation and translation are inherently small, even slight alterations of fibula position or movement can substantially impact force propagation through the ankle and hindfoot joints. Accordingly, implications for clinical care are discussed.

Diagnostic value of the posterior talofibular ligament area for chronic lateral ankle instability

An injured posterior talofibular ligament (PTFL) is one of the reasons for chronic lateral ankle instability (CLAI). Previous researches have demonstrated that the PTFL thickness (PTFLT) is associated with chronic ligament injuries. However, ligament hypertrophy is different from ligament thickness. Thus, we created the PTFL cross-sectional area (PTFLCSA) as a diagnostic image parameter to assess the hypertrophy of the whole PTFL. We assumed that the PTFLCSA is a key morphological diagnostic parameter in CLAI. PTFL data were obtained from 15 subjects with CLAI and from 16 normal individuals. The T1-weighted axial ankle-MR (A-MR) images were acquired at the level of PTFL. We measured the PTFLT and PTFLCSA at the posterior aspect of the ankle using our imaging analysis program. The PTFLT was measured as the thickness between point of anterior and posterior fiber of PTFL. The PTFLCSA was calculated as the whole cross-sectional PTFL area. The average PTFLT was 3.43 ± 0.52 mm in the healthy group and 4.89 ± 0.80 mm in the CLAI group. The mean PTFLCSA was 41.06 ± 12.18 mm 2 in the healthy group and 80.41 ± 19.14 mm 2 in the CLAI group. CLAI patients had significantly greater PTFLT ( P < .001) and PTFLCSA ( P < .001) than the healthy group. A receiver operating characteristic curve analysis demonstrated that the optimal cutoff score of the PTFLT was 4.19 mm, with 93.3% sensitivity, 93.7% specificity, and an area under the curve of 0.97. The most suitable cutoff value of the PTFLCSA was 61.15 mm 2 , with 93.3% sensitivity, 100% specificity, and area under the curve of 0.99. Even though the PTFLT and PTFLCSA were both significantly associated with CLAI, the PTFLCSA was a more exact morphological measurement parameter.

Effect of coronal fracture angle on the stability of screw fixation in medial malleolar fractures: A finite element analysis

Malleolar screw fixation is the most widely used treatment method for medial malleolar (MM) fractures. Here, although buttress plate fixation is advocated for vertical MM fractures, the angular discrimination between oblique and vertical MM fractures is still not fully understood. The purpose of this study is to test the adequacy of screw fixation in MM fractures with different angles and determination of a ‘critical fracture angle’ to guide surgeons in the decision-making for screw fixation for MM fractures by utilizing an advanced engineering simulation approach. In addition to loading of the healthy tibia structure, various cases of the MM fracture double screw fixation (14 simulation scenarios in total with fracture angles between 30° and 90°, in 5° increments) were considered in this research and their static loading conditions just after fixation operation were simulated through nonlinear (geometric and contact nonlinearity) finite element analysis (FEA). Patient-specific computed tomography scan data, parametric three-dimensional solid modelling and finite element method (FEM) based engineering codes were employed in order to simulate the fixation scenarios. Visual and numerical outputs for the deformation and stress distributions, separation and sliding behaviours of the MM fracture fragments of various screw fixations were clearly exhibited through FEA results. Minimum and maximum separation distances (gap) of 3.75 and 150.34 µm between fracture fragments at fracture angles of 30° and 90° were calculated respectively against minimum and maximum sliding distances of 25.87 and 41.37 µm between fracture fragments at fracture angles of 90° and 35°, respectively. The FEA results revealed that while the separation distance was increasing, the sliding distance was decreasing and there were no distinct differences in sliding distances in the scenarios from fracture angles of 30°–90°. The limitations and errors in a FEA study are inevitable, however, it was interpreted that the FEA scenarios were setup in this study by utilizing acceptable assumptions providing logical outputs under pre-defined boundary conditions. Finally, the fracture healing threshold for separation and/or sliding distance between fracture fragments was assigned as 100 µm by referring to previous literature and it was concluded that the screws fixed perpendicular to the fracture in a MM fracture with more than 70° angle with the tibial plafond results in a significant articular separation (>100 µm) during single-leg stand. Below this critical angle of 70°, two screws provide sufficient fixation.

Comparison of Fixation Techniques in Oblique and Biplanar Chevron Medial Malleolar Osteotomies; a Finite Element Analysis

This study aimed to evaluate different fixation techniques and implants in oblique and biplanar chevron medial malleolar osteotomies using finite element analysis. Both oblique and biplanar chevron osteotomy models were created, and each osteotomy was fixed with 2 different screws (3.5 mm cortical screw and 4.0 mm malleolar screw) in 2 different configurations; (1) 2 perpendicular screws, and (2) an additional third transverse screw. Nine simulation scenarios were set up, including 8 osteotomy fixations and the intact ankle. A bodyweight of 810.44 N vertical loading was applied to simulate a single leg stand on a fixed ankle. Sliding, separation, frictional stress, contact pressures between the fragments were analyzed. Maximum sliding (58.347µm) was seen in oblique osteotomy fixed with 2 malleolar screws, and the minimum sliding (17.272 µm) was seen in chevron osteotomy fixed with 3 cortical screws. The maximum separation was seen in chevron osteotomy fixed with 2 malleolar screws, and the minimum separation was seen in oblique osteotomy fixed with 3 cortical screws. Maximum contact pressure and the frictional stress at the osteotomy plane were obtained in chevron osteotomy fixed with 3 cortical screws. The closest value to normal tibiotalar contact pressures was obtained in chevron osteotomy fixed with 3 cortical screws. This study revealed that cortical screws provided better stability compared to malleolar screws in each tested osteotomy and fixation configuration. The insertion of the third transverse screw decreased both sliding and separation. Biplanar chevron osteotomy fixed with 3 cortical screws was the most stable model.

A new finite element model of intra-articular impacted fragment in posterior malleolar fractures: A technical note

Intra-articular impacted fragment (IAIF) was considered as the articular surface fragment resulting from impact and compressive forces. Malreduction of IAIF in posterior malleolar fractures was associated with the cause of talus subluxation and long-term arthritis. The effect of IAIF on ankle pressure and stress has not been studied, and it's difficult to do this in cadaver bone. So we established IAIF defect finite element model in posterior malleolar fractures and explored the effect of IAIF defect in ankle joint. We also discussed the relation between IAIF defect and post-traumatic arthritis.

Cartilage Matrix Changes in Hindfoot Joints in Chronic Ankle Instability Patients After Anatomic Repair Using T2-Mapping: Initial Experience With 3-Year Follow-Up

BACKGROUND

Anatomic repair is widely accepted as the primary surgical treatment for chronic lateral ankle instability (CLAI). T2-mapping is a powerful tool for quantitative assessment of biochemical changes in cartilage matrix.

PURPOSE

To longitudinally evaluate cartilage matrix changes in the hindfoot joints of CLAI patients before and after anatomic repair by using T2-mapping with magnetic resonance imaging (MRI).

STUDY TYPE

Prospective.

SUBJECTS

Thirty-two CLAI patients (males/females = 20/12) and 21 healthy controls (males/females = 13/7).

FIELD STRENGTH/SEQUENCE

3 T; sagittal multi-echo spin-echo technique (T2-mapping), coronal, sagittal, and axial spin-echo PD-FS, and sagittal T1WI sequences.

ASSESSMENT

MRI examinations were performed in CLAI patients at baseline (prior to surgery) and 3 years after anatomic repair and in healthy controls. On T2-maps, the hindfoot joints were segmented into 16 cartilage subregions. The T2 value of each subregion was measured. All patients were evaluated with the American Orthopedic Foot and Ankle Society (AOFAS) scale at baseline and after surgery.

STATISTICAL TESTS

Analysis of variance (ANOVA) and Student's t-test were used. The differences corresponding to P < 0.05 were considered statistically significant.

RESULTS

At baseline, the T2 values in most cartilage subregions of talar dome and medial posterior subtalar joint (pSTJ) were higher in CLAI patients than in healthy controls. After surgery, only the T2 value of anteriomedial talar dome decreased from that at baseline (31.11 ± 3.88 msec vs. 34.27 ± 5.30 msec). The T2 values of other subregions with elevated T2 values remained higher than healthy controls. There were no significant differences in T2 values in the midtarsal joints between CLAI patients and healthy controls (P = 0.262, 0.104, 0.169, 0.103). Postoperatively, the patients' AOFAS scores improved significantly from 67.81 to 89.13.

DATA CONCLUSION

CLAI patients exhibited elevated T2 values in most subregions of talar dome and medial pSTJ. After anatomic repair, although the patients exhibited good clinical outcomes, the elevated T2 values could not be fully recovered.

LEVEL OF EVIDENCE

2 TECHNICAL EFFICACY STAGE: 4.

Effect of cartilage thickness mismatch in osteochondral grafting from knee to talus on articular contact pressures: A finite element analysis

Objectives

The aim of this study was to investigate the effect of cartilage thickness mismatch on tibiotalar articular contact pressure in osteochondral grafting from femoral condyles to medial talar dome using a finite element analysis (FEA).

Materials and methods

Flush-implanted osteochondral grafting was performed on the talar centromedial aspect of the dome using osteochondral plugs with two different cartilage thicknesses. One of the plugs had an equal cartilage thickness with the recipient talar cartilage and the second plug had a thicker cartilage representing a plug harvested from the knee. The ankle joint was loaded during a single-leg stance phase of gait. Tibiotalar contact pressure, frictional stress, equivalent stress (von Mises values), and deformation were analyzed.

Results

In both osteochondral grafting simulations, tibiotalar contact pressure, frictional stress, equivalent stress (von Mises values) on both tibial and talar cartilage surfaces were restored to near-normal values.

Conclusion

Cartilage thickness mismatch does not significantly change the tibiotalar contact biomechanics, when the graft is inserted flush with the talar cartilage surface.

Finite element analysis of the effect of sagittal angle on ankle joint stability in posterior malleolus fracture: A cohort study

OBJECTIVE

Aim of this study was to establish three-dimensional finite element model of the posterolateral-oblique type of posterior malleolus fracture with different sagittal angle and to explore the effect of sagittal angle on ankle joint stability.

METHODS

CT data of ankle were collected from a normal male volunteer.Established finite element model of the normal ankle and verified its reliability. Five posterior malleolus fracture models with different sagittal angles were established. Finite element analysis(FEA)was carried out to simulate the conditions of vertical loading in neutral position with a total weight of 600 N.Recorded the data and did statistical analyses.

RESULTS

(1) The contact area was 483.55 mm2 and the maximum contact stress was 3.793 MPa in the model of the normal ankle joint. (2) There was a positive correlation between the sagittal angle(SA)and the contact area(CA)(r = 0.925,P < 0.05). Regression equation was CA = 316.755 + 1.749* SA. The correlation between the sagittal angle and the maximum contact stress(MCS)was negative (r = -0.988,P < 0.01). Regression equation was MCS = 5.214-0.018*SA. There was a negative correlation between the sagittal angle of fracture and relative displacement(RD)(r = -0.950,P < 0.05). Regression equation was RD = 1.388-0.009*SA.

CONCLUSION

The greater the sagittal angle of fracture was, The more stable the ankle joint was. The sagittal angle of fracture could be used as a relative index to reflect ankle stability for posterior malleolus fracture.

Evaluation of the Talar Cartilage in Chronic Lateral Ankle Instability with Lateral Ligament Injury Using Biochemical T2* Mapping: Correlation with Clinical Symptoms

RATIONALE AND OBJECTIVES

This study aims to quantitatively compare T2* measurements of the talar cartilage between chronic lateral ankle instability (LAI) patients with lateral ligament injury and healthy volunteers, and to assess the association of T2* value with American Orthopedic Foot and Ankle Society (AOFAS) score.

MATERIALS AND METHODS

Nineteen consecutive patients with chronic LAI (LAI group) and 19 healthy individuals (control group) were enrolled. Biochemical magnetic resonance examination of the ankle was performed in all participants using three-dimensional gradient-echo T2* mapping. Total talar cartilage was divided into six subcompartments, including medial anterior (MA), central medial, medial posterior, lateral anterior, central lateral (LC), and lateral posterior regions. T2* values of respective cartilage areas were measured and compared between the two groups using Student t test. AOFAS scoring was performed for clinical evaluation. Then, the association of T2* value with AOFAS score was evaluated by Pearson correlation.

RESULTS

The T2* values of total talar cartilage, as well as MA and LC cartilage compartments, in the chronic LAI group were significantly higher than control values (P < .001, P = .039, and P = .014, respectively). Furthermore, the T2* value of MA in the chronic LAI group was negatively correlated with AOFAS score (r = -0.8089, P < .001).

CONCLUSIONS

Chronic LAI with lateral ligament injury may have a causal connection with early cartilage degeneration in the ankle joint, especially in MA and LC cartilage compartments, as assessed by quantitative T2* measurements. The clinical score correlates highly with T2* value of the MA cartilage compartment, indicating that MA may be the principal cartilage area conferring clinical symptoms.