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Effect of attachment site and routing variations in split tendon transfer of tibialis posterior
Matthew F Moran1, James O Sanders, Neil A Sharkey
1Center for Locomotion Studies, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
Insights
Split tibialis posterior (TP) tendon transfers effectively reduce hindfoot inversion in children with cerebral palsy. However, routing the TP tendon through the interosseous membrane significantly impairs ankle function compared to other methods.
Area of Science:
- Orthopedic Surgery
- Pediatric Orthopedics
- Biomechanics
Background:
- Spastic equinovarus gait in cerebral palsy often requires surgical intervention.
- Split tibialis posterior (TP) tendon transfers aim to correct hindfoot inversion.
Purpose of the Study:
- To evaluate the biomechanical effectiveness of three split TP tendon transfer variations.
- To assess the impact of different tendon routing and attachment sites on TP muscle function.
Main Methods:
- Computed TP muscle moment arms before and after three surgical variations.
- Controlled for tendon tension to isolate the effects of surgical technique.
- Compared hindfoot inversion and ankle plantarflexion/dorsiflexion capabilities.
Main Results:
- All three split TP transfer variations significantly reduced hindfoot inversion.
- Interosseous membrane routing resulted in less inversion reduction than other methods.
- Interosseous membrane routing also diminished plantarflexion ability, unlike other variations.
Conclusions:
- Split TP tendon transfers are effective in correcting equinovarus in cerebral palsy.
- Interosseous membrane routing compromises ankle function and is less effective.
- Attachment site variation (proximal vs. distal peroneus brevis) had minimal impact on mechanical outcomes.
Abstract:
Spastic equinovarus is a condition that commonly affects the gait of children with cerebral palsy. Split tendon transfers of the tibialis posterior (TP) are often performed to eliminate the excessive hindfoot inversion present in equinovarus. TP muscle moment arms were computed before and after three variations of split TP tendon transfer to assess the effectiveness of each. The three surgeries tested were (1) the original split TP transfer to the distal peroneus brevis tendon routing behind the lateral malleolus; (2) an attachment variation in which the transferred tendon half was attached to the proximal peroneus brevis tendon rather than to the distal site; and (3) a routing variation in which the transferred tendon half was passed through a window in the interosseous membrane and attached to the distal peroneus brevis tendon. Tendon tension was controlled for in these experiments because improper tensioning is often cited as a reason for poor outcomes. All three surgeries significantly reduced the ability of TP to invert the hindfoot, thus eliminating a potential deforming force, but the reduction following interosseous routing was significantly less than that found for the other two transfer procedures. Routing through the interosseous membrane also reduced the ability of the TP to plantarflex the foot, but ankle actions were preserved following the other two surgeries. Routing through the interosseous membrane to an anterior attachment site resulted in a muscle with minimal potential to create or resist action about the ankle joint. Similar moment arms were measured when the attachment site on the peroneus brevis tendon was located either proximally or distally, suggesting that this choice does not appear to significantly affect the mechanical outcome.
