Abstract
Purpose
To compare Radiostereometric Analysis (RSA) and subjective outcomes of Total Knee Arthroplasty (TKA) and Total Ankle Arthroplasty (TAA).
Method
Twenty-five patients were recruited to receive TKA (Zimmer, NexGen LPS Trabecular Metal Monoblock) and 20 patients were recruited to receive TAA (DePuy, Mobility). The tibial component of the TKA and the tibial component of the TAA were followed for two years with RSA with exams postoperatively at six, 12 and 24 months. At two years, inducible displacement RSA at the knee and ankle was also performed. RSA outcomes measured were translations in the anterior-posterior, medial-lateral and distal-proximal directions of both implants. SF-36 outcome questionnaires were completed preoperatively and at each RSA follow-up with the outcome being the mental component score (MCS) and physical component score (PCS). Analysis of variance statistical testing was used to compare RSA outcomes and subjective outcomes.
Results
Preoperatively there were no differences in age, BMI, SF-36 MCS or SF-36 PCS between the TKA and TAA patients. At six, 12 and 24 months the TKA group had significantly higher SF-36 PCS scores (p=0.006, p=0.002 and p=0.004 respectively. There were no differences at any time point in SF-36 MCS. Longitudinal RSA results showed that the TAA tibial component moved further into the bone at all follow-ups (p=0.000 at all time points). The TAA also migrated more anteriorly compared with the TKA, although this only became significant at 12 and 24 months (p=0.013, p=0.05). RSA inducible displacement showed that the TAA had greater inducible displacement into the bone than the TKA (p=0.015).
Conclusion
The subjective data show that TAA and TKA both improve the symptoms of patients. However, the subjective results of the TAA have not achieved the high standard set by TKA.
The RSA data suggest that the TAA is stabilizing within the bone. However, the higher longitudinal migrations and inducible displacements seen in the TAA suggest that the interface may not be as robust as in the TKA. This may partially be explained by the much smaller surface area available to distribute the loads at the ankle resulting in higher stresses and migrations.
The 3rd generation of TAA has recently been reintroduced as a treatment option for severe arthritis of the ankle. Previous generations of TAA have been unsuccessful with high failure rates. It is unclear if the current generation of TAA will be more successful in the long term. Comparisons between these arthroplasty procedures with high precision measures such as RSA can provide insight into whether TAA has achieved the same level of success as TKA. Although there are no comparable migration thresholds for TAA as TKA, this study suggests that TAA may not achieve as robust an interface with the bone as TKA.
The results of the current generation of TAA are promising. However, TAA still has room for improvement to achieve the same outstanding results as TKA.
