Comparison of Extramedullary Versus Intramedullary Referencing for Tibial Component Alignment in Total Ankle Arthroplasty

SLR- January 2014- Scott Hoffman

Reference: Adams SB Jr, Demetracopoulos CA, Viens NA, DeOrio JK, Easley ME, Queen RM, Nunley JA 2nd, Foot Ankle Int.2013 Sep 16. [E-pub ahead of print].

 

Scientific Literature Review

Reviewed By: Scott M. Hoffman, DPM
Residency Program: St. John Hospital and Medical Center-Detroit, Michigan
 

Podiatric Relevance: Determination of the optimal component position in total ankle arthroplasty (TAA) and the effects that component malposition might have on long-termimplant survival are significant topics of interest to the foot and ankle surgeon. While the majority of TAA systems use extramedullary (EM) alignment guides for tibial component placement, at least one TAA system is available that uses IM referencing for alignment of the tibial component. In total knee arthroplasty (TKA), studies suggest that tibial component placement is more accurate within tramedullary referencing. Currently, there are no reports comparing these two alignment techniques with respect to the accuracy of tibial component alignment in TAA. The authors performed a retrospective study tocompare the accuracy of initial tibial component positioning between EM referencing and IM referencing techniques in patients who underwent TAA with fixed-bearing prostheses.

Methods: The medical records of 277 consecutive patients who underwent TAA with a fixed-bearing prosthesis between 7/2007 and 6/2010 were reviewed. All surgeries were performed by one of three surgeons using a similar operative technique. Exclusion criteria included history of tibial diaphyseal or pilon fracture, tibial deformity, or insufficient radiographs. This left a study population of 236 patients. Patients received either an Inbone (Wright Medical Technology Inc, Arlington, TN) or a Salto Talaris (Tornier, Edina, MN) prosthesis. The Salto Talaris used an EM referencing guide for tibial component placement while the Inbone used an IM reference drill to guide tibial component placement. Patients were divided into two groups based on the type of referencing used for component alignment (EM vs. IM). Post-operative radiographs were taken of all ankles in a standardized fashion and the coronal and sagittal implant angles were measured in all tibial components to the nearest 1/10 of a degree using a PACS system (General Electric Healthcare, UK). The absolute magnitude of the difference between the measured angle and surgeon-specific intended angle for each component was then calculated to determine the accuracy of alignment of each technique. The accuracy of alignment was compared between techniques using unpaired Student t tests. A two-way random effects model with single measures was used to determine Intraclass correlation coefficients for intrarater and interrater reliability. Intra-class correlation coefficients greater than .74 were graded as excellent. An alpha level of .05 was deemed statistically significant.
 

Results: two-hundred-thirty-six patients were included for statistical analysis (83 patients in the EM group and 153 patients in the IM group). Intraclass correlation coefficients demonstrated excellent interrater and intrarater reliability for coronal and sagittal implant angles. The accuracy of alignment for the EM group was within a mean of 1.5 ± 1.4 degrees in the coronal plane and 4.1 ± 2.9 degrees in the sagittal plane. The accuracy of alignment in the IM group was within a mean of 1.4 ± 1.1 degrees in the coronal plane and 2.5 ± 1.8 degrees in the sagittal plane. There was not a significant difference inaccuracy between the ignment referencing techniques with respect to the coronal plane alignment (P = .37). However, implants placed with the IM technique were found to be more accurate in sagittal alignment than implants placed with the EM technique (P< .001).

Conclusions: Both EM and IM referencing techniques provide good overall accuracy for tibial component placement in TAA in both the coronal and sagittal planes. Satisfactory alignment can be achieved with both techniques. The results demonstrate that there was not a statistically significant difference in the accuracy of tibial component positioning in the coronal plane when comparing EM and IM referencing techniques. However, the IM referencing technique demonstrated significantly improved accuracy of tibial component placement in the sagittal plane. The clinical significance of the mean difference in accuracy between the two techniques, 1.6 degrees, remains unclear.  Thus, no absolute recommendations can be made for one technique over the other.  Further studies are needed to determine the optimal component position in TAA and the effects that component malposition might have on long-term implant survival.