The extensor hallucis longus tendon as the distal reference point in total knee arthroplasty and tibial alignment

The aim of this study was to compare the effects on tibial alignment of the use of the extensor hallucis longus (EHL) tendon with the use of the 2nd metatarsal as a reference in total knee arthroplasty (TKA) using the extramedullary technique.

The study evaluated 100 postoperative radiographs of 79 patients who underwent primary TKA between 2004 and 2008. Patients were grouped according to the distal anatomical landmark used during surgery. There were 36 patients (mean age: 68.3 years, range: 56 to 82 years) in the EHL-referenced (ERT) group and 43 patients (mean age: 70.2 years, range: 54 to 78 years) in the 2nd metatarsal-referenced (MRT) group. There were 47 components in the ERT group and 53 in the MRT group. Frontal alignments of the tibial components were measured. Angles of 90±2° were accepted as the normal boundaries while those above that value were labeled as 'varus' and those below as 'valgus'.

Average frontal alignment was 88.57° in the MRT group and 89.17° in the ERT group. The number of tibial components in the normal range was significantly higher (p=0.017) and the number of varus-oriented components significantly lower (p=0.024) in the ERT group. There were no significant differences in valgus-oriented outliers between groups (p=1.000).

The use of the EHL tendon as a reference improves coronal tibial alignment. The EHL is a reliable anatomical landmark to use with extramedullary guide systems.