The Effect of Hindfoot Stiffness on Osteolysis in Total Ankle Arthroplasty Robert Flavin, MD, Scott Coleman, James Brodsky, MD Baylor University Medical Center
The Effect of Hindfoot Stiffness on Osteolysis in Total Ankle Arthroplasty Robert Flavin My Disclosure is in the Final AOFAS Program Book, I have no potential conflicts with this presentation
Introduction Osteolysis or Aseptic Loosening is the commonest adverse event in all Total Joint Arthroplasty implants. Extensive literature has been published in relation to other major joints, i.e. Hip and Knee. However with survivorship ratings between 84-95% at 10 years for Total Ankle Arthroplasty implants, there is still little knowledge relating to the cause of this relatively low survivorship.
Aims To develop a generic osteolysis scoring system for Total Ankle Arthroplasty (Total Ankle Osteolysis Score, TAOS) Using the TAOS to determine which dependent and independent factors influenced early Osteolysis.
Materials & Methods We performed a prospective study analyzing the effect of gait parameters, demographic and tibial component alignment on the TAOS. We assessed three groups of patients with a mean follow up of greater than 8 years. The cohort of patients was divided into the groups based on hindfoot motion both clinically and by gait analysis. The Asymptomatic group comprised of 9 patients. 15 patients were in the Stiff Subtalar Motion group based on clinical assessment and less than 4 arc of Coronal ROM on gait analysis and Morrey grade 2 subtalar arthritis on the lateral foot radiograph. The third group, the Hindfoot Fusion Group, comprised of 9 patients, this group included all patients who underwent a Subtalar joint fusion ± a Talonavicular joint or Calcaneocuboid joint fusion prior to the implantation of the STAR. The mean follow up time was 8.5 years (7.7 9.1 years) for all groups.
TAOS G3 >100% G2 >50% G1 <50% G1 <50% G2 >50% G3 >100% The TAOS is the summation of the scores in each section depending on the Grade/depth of osteolysis on an AP and Lateral Radiograph. G1 = 1 point, G2 = 2 points, G3 = 3 points. Talar Subsidence is 12 points
Results Association between pre-op factors and osteolytic score Pre-operative factors Age at surgery (years, mean / sd) 0.096 0.160 0.373 Gender (male, n / %) -0.775-0.047 0.795 Univariable models Multivariable model * Coef. Beta P>t Coef. Beta P>t Weight (kg / sd) -0.217-0.452 0.009-0.151-0.316 0.026 Diagnosis (n/%) Group Posttraumatic OA ref. ref. ref. Primary OA 2.836 0.151 0.375 1.574 0.084 0.488 Rheumatoid Arthritis 7.636 0.438 0.014 5.799 0.333 0.017 Assymptomatic Stiff subtalar joint 10.31 1 0.763 0.000 9.320 0.680 0.000 Hindfoot Pathology 5.889 0.390 0.029 2.590 0.171 0.261 * Adjusted R-squared for the model as a whole was 0.58, F(5, 26)= 9.69, p<0.001 Beta stands for the Beta Coefficient which is used to compare the weighted influence of factors. Age and Gender have little influence on the osteolysis score, interestingly weight had a negative impact on the score (higher the patients weight the lower the osteolysis score). RA and stiff subtalar motion have the greatest impact of the osteolysis score
Results Multivariable association between pre-op factors, coronal angle and osteolytic score Variables Coef. Beta P>t lower 95% CI upper Weight (kg / sd) -0.108-0.226 0.100-0.239 0.022 Diagnosis (n/%) Posttraumatic OA ref. ref. ref. ref. ref. Primary OA 1.847 0.099 0.387-2.475 6.169 Rheumatoid Arthritis 5.486 0.315 0.017 1.084 9.887 Group Asymptomatic ref. ref. ref. ref. ref. Stiff Subtalar joint 11.227 0.820 0.000 7.069 15.385 Hindfoot Fusion Group 3.555 0.235 0.112-0.889 8.000 Change in coronal angle -0.291-0.278 0.041-0.570-0.013 * Adjusted R-squared for the model as a whole was 0.64, F(6, 25)= 9.98, p<0.001 If we just analyze the weight, diagnosis, hindfoot motion and coronal angle of implantation, we can demonstrate that a diagnosis of RA, Stiff Subtalar Motion and hindfoot fusion have the greatest impact on osteolysis, however these factors still account for only 64% of the influence. Weight has a negative impact and the change in coronal angle of implantation also has a negative impact as long as the angle is directed to 0 implantation angle error.
Discussion Both Independent and Dependent Multi-factorial relationship with osteolysis Strong impact of RA and loss of Hindfoot Motion. Importance of coronal angle correction with a negative impact on osteolysis. Weight had a negative impact, possibly due to lower activity levels. Gait parameters, demographic and tibial component alignment only accounted for 64% of the impact, therefore other factors have an important influence, i.e. activity levels.
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