Accuracy of Patient-Specific Instruments for Supramalleolar Osteotomies

Supramalleolar osteotomy (SMO) enables deformity correction of the distal tibia, but the procedure remains technically demanding. Patient-specific instruments (PSIs) have the potential to mitigate the technical drawbacks associated with SMO that are performed free-hand, but their accuracy has not been investigated. Therefore, we aimed to perform a pre- vs post-operative comparison to assess the accuracy of PSI in the setting of SMO correction.

Eighteen patients (mean age = 47 ± 13.5 years) who underwent SMO with a PSI were prospectively recruited in a pre-post comparative study design. Inclusion criteria were correction of supramalleolar ankle varus or valgus deformity by a closing wedge SMO. Exclusion criteria consisted of biplanar SMO that required associated free-hand osteotomies. Clinical outcomes were collected by the American Orthopaedic Foot & Ankle Society (AOFAS), European Foot and Ankle Society (EFAS), and visual analogue scale (VAS) scores. Apart from the standard weightbearing radiographs, a weightbearing CT was performed to generate corresponding 3-dimensional (3D) bone models and measure the lateral distal tibia angle (LDTA) as main radiographic parameter.

The pre-operative radiographic parameters of the tibia joint alignment in patients with ankle varus (n = 12) deformity (LDTA_var = 96.5° ± 4.5°) and valgus (n = 6) deformity (LDTA_valg = 82.4° ± 2.5°) improved significantly relative to their post-operative equivalents (LDTA_var = 90.2° ± 3.2°); LDTA_valg = 90.9° ± 0.8°; P < .05). The pre-operative clinical outcome scores (AOFAS = 52.7 ± 22.9, EFAS = 15.1° ± 7.91°, VAS = 5 [2-8]) improved significantly relative to their post-operative equivalents (AOFAS = 75.5 ± 19.6; EFAS = 19° ± 7.6°; VAS = 3 [0-8]; P < .05). The mean simulated correction differed from the mean post-operative achieved correction within 1° (mean = 0.4°; range 0.1°-0.8°).

This study demonstrated an accurate correction of distal tibia deformities by SMO using PSIs. The achieved post-operative correction differed within the range of 1° from the pre-operatively simulated correction. This indicates that PSIs provide a precise execution of the pre-operative planning. Future studies should assess the added value of performing an SMO with PSI compared with former free-hand techniques towards clinical and radiographical outcomes.