SLR - June 2014 - Tee Adeleke

Biomechanical Assessment of Flexible Flatfoot Correction

Reference: Zanoli D,  Glisson R,  Nunley J,  Easley M. Biomechanical Assessment of Flexible Flatfoot Correction. Journal of Bone and Joint Surgery. March 2014; 96:e45(1-8).

Scientific Literature Review

Reviewed By: Tee Adeleke, DPM
Residency Program: Western Pennsylvania Hospital, Pittsburgh, PA

Podiatric Relevance: Flexible flatfoot deformity is a common podiatric problem in which multiple surgical techniques can be utilized to achieve correction. This class of deformity is typically amenable to joint sparing techniques focused on using hindfoot osteotomies and soft tissue reconstruction to correct for posterior tibial tendon (PTT) elongation, hindfoot valgus, forefoot abduction, and arch collapse. This article aims to address the paucity of biomechanical studies evaluating the effects of these joint-sparing surgical techniques. The authors in this article present objective findings of the effects of hindfoot osteotomies and soft tissue reconstructions used to correct stage 2B (flexible) flatfoot deformity in advanced cadaveric models.

Methods: Ten (eight male / two female) fresh frozen cadaveric limbs sectioned at the midpoint of the tibia were obtained and underwent advanced preparation for pre-conditioning and flattening. The proximal ends of extrinsic tendons were sutured to plastic rings to provide secure tensile load applications points. Steel rods were inserted in the medullary canal in a fashion to obtain and maintain a neutral flexion position. Electronic clinometers measured angular position in reference to their vertical plane position and were attached to pre-inserted half pins. Clinometers were attached to the talus and first metatarsal measuring the inclination of talus to the first metatarsal in the sagittal plane. Other clinometers were attached to the talus and the navicular measuring their inclination in the coronal plane. These angles would be used to document degree of flattening. A sophisticated system of pulleys, cables, and weights (powered by a hydraulic motorcycle jack) were used in applying 50 percent of physiologic stance-phase loading as well as 50 percent of physiologic axial load to extrinsic tendons including the Achilles. Preconditioning of the limbs was performed using cyclical tibial axial load along with constant caudally-directed tendon loads. Bone alignment under load was measured and used as a reference to quantify the amount of flattening induced and the correction achieved per surgical technique used. Flattening was achieved by sectioning ligaments, including part of the spring ligament, and applying axial load between 808 and 1780 N (numbers calculated after preconditioning) for 1000 cycles. Extrinsic tendons except for the PT (to mimic insufficiency) were loaded. Surgical procedures were divided into six groups consisting of: Lateral column lengthening (1), medial displacement calcaneal osteotomy with flexor digitorum longus transfer (2), medial displacement calcaneal osteotomy with flexor digitorum longus transfer and lateral column lengthening (3), treatment #3 with pants over vest spring ligament repair (4), treatment #3 with spring ligament repair using distal PTT stump (5), treatment #3 with suture and anchor spring ligament repair (6). The respective procedures were performed in standard fashion. A series of post-operative cyclical loads was used to measure significant differences in loss of correction among the six operative techniques.

Results: Pre-correction flattening mimicked moderate flatfoot deformity with mean longitudinal arch flattening of 8.3 degrees and mean talus-navicular angle change of 6.0 degrees. These two angular dimensions were used in comparing the six surgical techniques. Variance analysis showed that initial correction achieved by treatments 1, 3, 4, 5 and 6 significantly exceeded correction of treatment 2. Treatment 2 was also significantly inferior when it came to coronal talar-navicular and sagittal talar – first metatarsal angle correction. In terms of reflattening resistance, treatments 1, 3, 4, 5 and 6 were once again superior to treatment 2 in maintaining their correction significantly with treatment 2 completely losing correction at load cycle 1000. The article showed that spring ligament augmentation only gave slight resistance to loss of correction, however non-significant, and did not provide significant further correction. No significant difference was seen among treatments 1, 3, 4, 5 and 6.

Conclusions: Treatment modalities involving lateral column lengthening demonstrated evidence to be significantly superior in obtaining and maintaining correction. The use of electronic clinometric technology demonstrated to be instrumental in attaining desired physiologic static and dynamic loading, which has been a limiting factor in previous laboratory models. A draw back of this technology is the inability to assess forefoot abduction since the clinometers only monitor angles in vertical planes. The authors acknowledged study limitations consisting of: failure to incorporate ligamentous healing and tendon transfers into their model along with the failure to fully mimic physiologic stance-phase loading despite marked improvements. Although previous studies advocate spring ligament repair in flatfoot reconstruction, the authors in this study showed that it does not add further correction beyond that of osseous procedures. The sophisticated flatfoot model introduced in this article is one that lends itself to future refinement to include transverse planar analysis for future studies.

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