Anatomical Footprint of the Tibialis Anterior Tendon: Surgical Implications for Foot and Ankle Reconstruction

SLR - September 2017 - Meghan Hurley

Scientific Literature Review

Reviewed By: Meghan Hurley, DPM 
Residency Program: North Colorado Medical Center Podiatric Medicine and Surgery, Greeley, CO

Podiatric Relevance: As foot and ankle specialists, our anatomic understanding of the osseous and soft-tissue structures within the distal lower extremity should exceed our various medical counterparts. Comprehension of normal and abnormal anatomic variants allows us to better prepare for surgical procedures and potential complications. The tibialis anterior tendon (TAT) has recently surfaced as a more prominent topic of discussion partly due to the increasing popularity of first TMTJ fusion for correction of a bunion deformity. Analysis of the TAT footprint and its variations was the driving force behind this study with the hopes that further research would aid in performing anatomical reconstruction and assist in elucidation of established fundamentals for tendon harvest.

Methods: Anatomic analysis of TAT insertion on 41 cadaveric lower-leg specimens with the average age of 85.2 years. Sharp excision was performed removing all soft-tissue structures aside from the TAT. The bony insertion “footprint” of the TAT was marked with ink and meticulously documented. Midfoot bones were disarticulated to allow for detailed analysis. The Musial classification system was utilized to assist in determining whether the bony area of insertion on medial cuneiform or first metatarsal base has more surface area involvement.
 
Results: Type I insertion consisting of equal medial cuneiform and first metatarsal base insertion was discovered on 48.8 percent of subjects. Type I was further broken down into Ia (wide, wide) and Ib (narrow, narrow) bony footprints. The majority (41.5 percent) of Type I patients resulted in Ib subtype. All but one of the remaining cadaveric limbs displayed Type II insertion consisting of wide attachment on the medial cuneiform and narrow footprint of the first metatarsal. The medial cuneiform mean width of insertion was 6.7 mm compared to 4.6 mm on first metatarsal. The mean length of both insertions was approximately 14.0 mm. The footprint location on medial surface of both bones was documented in 70.7 percent of cases. Most commonly found insertional shape of TAT was crescentic (75.6 percent) on the first metatarsal base and ovate (58.5 percent) on the medial cuneiform.

Conclusions: Close inspection of the insertional anatomy of ligamentous and tendinous structures provides valuable surgical insight, especially for situations that would require relocation or reattachment of powerful muscles, such as the tibialis anterior. Anatomic reconstruction of the natural course and biomechanical lever arm of the TAT assures the best possible outcome for restoration of ankle dorsiflexion and forefoot supination. This study found that more than half of cadaveric subjects presented with equal distribution of the TAT on both the first metatarsal and medial cuneiform bones. All but one of the remaining patients had an overwhelming display of wide medial cuneiform distribution with narrow first metatarsal base footprint. The increasing popularity of the plantar plating technique for first TMTJ fusion often involves the TAT insertion and may necessitate partial detachment to avoid impingement.

Approximately thirty percent of patients, according to this study, have medial-plantar TAT insertions. Knowledge concerning anatomic distribution could assist in determining whether adjunctive anchors or alternative ORIF procedures should be considered for bunion correction.