SLR - February 2016 - Ali Ghorbanifarajzadeh

Title: Comparison of Proximal and Distal Oblique Second Metatarsal Osteotomies with Varying Achilles Tendon Tension: Biomechanical Study in a Cadaver Model

Reference: Aydogan U, Moore B, Andrews SH, Roush EP, Kunselman AR, Lewis GS. Comparison of Proximal and Distal Oblique Second Metatarsal Osteotomies with Varying Achilles Tendon Tension: Biomechanical Study in a Cadaver Model. J Bone Joint Surg Am. 2015 Dec 2: 97(23): 1945-51.

Scientific Literature Review

Reviewed By: Ali Ghorbanifarajzadeh, DPM
Residency Program: Aventura Hospital and Medical Center

Podiatric Relevance: Metatarsalgia is a common problem amongst podiatric surgeons on a daily basis. One source of pain may be from overload of the plantar pressure of the Second metatarsal. This increased plantar pressure may lead to pain and development of ulcerations that in diabetics may result in amputation. In the diabetic population, contractures of the Achilles tendon may lead to increased peak plantar pressures which may further contribute to ulcerations and put limbs at risk. The goal of this biomechanical study was to find the optimal surgery to reduce pressure under the second metatarsal head using varying osteotomies (including classic distal oblique, modified distal oblique, and proximal oblique metatarsal) of the second metatarsal with varying Achilles tendon tensioning.

Methods: Twelve matched fresh frozen cadaver feet from six donors were obtained without any evidence of previous surgical procedures performed or any deformity related to arthritis. Left and right feet from each donor were randomly assigned to distal oblique (classic followed by modified distal) group (n=6) or proximal oblique group (n=6). The classic distal oblique osteotomy was performed with a microsagittal saw parallel to the floor through the dorsal one-third of the metatarsal head 2 mm distal to the articular surface and translated proximally 3 mm. The osteotomy site was fixed with a 2.4 mm cannulated screw. The modified distal oblique was performed with a parallel resection of 3 mm of bone, equal to the amount of translation of the metatarsal head creating 5 mm total of dorsal translation (including 2 x 1 mm saw thickness) using the same screw hole following the classic distal procedure to secure fragments. The proximal oblique osteotomy was performed with a microsagittal saw with a 3 mm dorsally based wedge resected at 45° angle starting 1 cm distal to the metatarsal base and proceeded proximal to distal, which was then fixed with a 2.4 mm cannulated screw. Specimens were loaded with 0, 300, and 600 N of Achilles tendon tension and a fixed 400 N ground reactive force using a servohydraulic machine. Average and peak pressures of the first, second, and third metatarsals were measured.

Results: Prior to osteotomies being performed, average plantar pressure under 300 N of Achilles tendon force measured 53.3, 58.0, and 49.5 kPa under the first, second, and third metatarsals, respectively. Peak pressures measured 111.7, 100.8, and 90.0 kPa, respectively. Proximal oblique osteotomy significantly decreased average pressure under the second metatarsal by 19.4 kPa at 300 N of force (p < 0.001) and 29.7 at 600 N of force (p < 0.017) while increasing average and peak pressures under the first metatarsal at 300 N of force. Decreased pressure under the third metatarsal was observed but not statistically significant. The modified distal oblique osteotomy significantly decreased average pressure by 20.2 kPa under the second metatarsal under 600 N of force (p = 0.044) but pressure decrease was not found to be significant under 300 N of force (p = 0.17). The classic distal oblique osteotomy had small effects on plantar pressure that were not found to be significant. No significant differences were observed in other contact areas.  

Conclusions: The study demonstrated how the proximal oblique osteotomy was the most effective in reducing plantar pressure under the second metatarsal and also shifted load to the first metatarsal head. The modified distal oblique osteotomy resulted in decreased average pressure under the second metatarsal head and may be used in a different mechanism in the treatment of metatarsalgia in an attempt to shift pressure more posterior or to decrease stress at the metatarsophalangeal joints (over the classic procedure). Proximal oblique osteotomies may result in less complications such as joint stiffness and floating toe (result of plantarflexion of the metatarsal head in the distal oblique osteotomy) as the procedure is performed through an extra-articular approach. The proximal oblique osteotomy is more technically challenging and requires more offloading after surgery in order to heal after surgery. The limitations of the study include small testing size of six matched pairs of cadaver feet, and only testing the foot in a static, flat position. Future testing could involve the foot in a heel rise as increased Achilles tendon force (600 N) would lead to increased plantar pressures anteriorly and diminished pressures at the heel. The study provides another set of options in an attempt to treat patients for metatarsalgia depending on how one would like to decrease plantar pressures under the second metatarsal over the classic distal oblique osteotomy. 

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