patient specific modeling of stage ii flatfoot deformity ... specific modeling of stage ii flatfoot...
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Patient Specific Modeling of Stage II Flatfoot Deformity Before
& After Surgery
EM Spratley, EA Matheis, RA Adelaar, CW Hayes, JS Wayne Richmond, Virginia
AOFAS Summer Meeting
June 20-23rd, 2012
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Patient Specific Modeling of Stage II Flatfoot
Deformity Before & After Surgery
E. Meade Spratley, M.S.
My disclosure is in the Final AOFAS Program Book. I have a potential conflict with this presentation due to:
CW Hayes: “Board member/ committee appointments for a society” JS Wayne: “Other financial or material support from a company or supplier; “Board member/ committee appointments for a society” RS Adelaar: “Board member/ committee appointments for a society”
DISCLOSURES
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Introduction • Adult Acquired Flatfoot Deformity (AAFD)
– Chronic & degenerative disease characterized by loss of normal arch function – Often secondary to PTT dysfunction – Causes static stretching of medial support structures of the arch, namely:
o spring, talocalcaneal interosseous, fibers of the anterior deltoid, & long /short plantar ligaments
– Presents clinically as a drop in medial longitudinal arch, forefoot abduction, & hindfoot valgus as well as significant pain & dysfunction
• Competing surgical treatments should be tailored to the individual patient’s
presentation
Objective Develop and validate a patient specific computational model to describe
foot/ankle function preoperatively and predict outcome of surgical correction
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Study Design & Imaging • With IRB approval, lower leg & foot of a 64yo ♀ imaged with MRI & X-ray
– Pre-Op:
1. 1.5T MRI using a T2 SPGR fat-saturated sequence, yielding 0.7mm3-isovolumetric scan
2. Weight-bearing single-leg X-rays in the ML & oblique AP planes; Hindfoot photos
– Post-Op: 1. Weight-bearing single-leg X-rays in the ML & oblique AP planes; Hindfoot photos
• All bony tissue was isolated and extrapolated from the MRI scans, then triangulated to yield accurate patient-specific anatomy
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Model Setup & Testing
Ligament of Interest Grade† Stiffness Attenuation
SuperoMedial Spring 1 25.0% InferoMedial Spring 0 0.0% Anterior Deltoid 1 25.0% Posterior Deltoid 0 0.0% Deep Deltoid 0 0.0% TaloCalcaneal Interosseous 0 0.0% Plantar Fascia 1 25.0%
• Full body weight axial load • All ligaments of the foot & ankle
included as tensile vectors • Muscle loading included as ratios of
body weight according to Thordarson et al.6 • Achilles = 50% BW • FHL = 10% BW • FDL = 6% BW
• Specific ligaments associated with AAFD were evaluated through MRI by CWH† & graded according to a scale of attenuation proposed by Deland et al1-3
.
BW 148lbs
Achilles 74lbs
FHL 15lbs
FDL 9lbs
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Surgical Treatment & Post-Op Modeling
1. PTT augmentation by FHL transfer through bony tunnel in the navicular
2. 5mm Medializing Calcaneal Osteotomy
(MCO or ‘Slide’ Osteotomy) Fixed with cancellous screw
FHL
5mm
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Validation Against Patient Radiographs • 6 angular measures used to
evaluate AAFD recorded for pre- & post-Op – ML (θ1- θ3)
1. calcaneal pitch (ML-CP) 2. talo-1st metatarsal (ML-T1MT) 3. talocalcaneal angle (ML-TC)
– Oblique AP (θ4, θ5) 4. talo-1st metatarsal angle (AP-T1MT) 5. talo-navicular coverage (AP-TN)
– Hindfoot (θ6) 6. PA hindfoot valgus (PA-HFV)
• Model compared to patient
data as well as AAFD population averages
– Coughlin & Kaz7 – Krans et al.8 – Murley et al.9
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Results: Model to Patient Comparisons
• Pre-Op – All but 1 angle within 5º
• Post-Op – all measures within <5°
---------------------------------------
• Patient angles within 6.5º of
published AAFD averages7-9
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Conclusions • A patient-specific flatfoot model was faithfully recreated in silica • Foot and ankle biomechanical function was dictated solely by:
– 3D articular anatomy – Ligaments – Muscle loading – & Body weight
• Model predictions of joint angles were very similar to patient radiographs & correctly predicted changes due to surgical treatment
Future Work • Future investigations can be used to assess changes in biomechanical
factors such as articular contact force / location or ligament strain as a means of predicting future patient outcome
• Additionally, these models could investigate new devices or surgeries in order to better tailor patient treatment
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References
1. Deland JT, de Asla RJ, Sung IH, Ernberg LA, and Potter HG, 2005, “Posterior tibial tendon insufficiency: which ligaments are involved?,” Foot Ankle Int, 26(6), pp. 427-435.
2. Blackman AJ, Blevins JJ, Sangeorzan BJ, and Ledoux WR, 2009, “Cadaveric flatfoot model: Ligament attenuation and Achilles tendon overpull,” J Ortho Res, 27(12), pp. 1547-1554.
3. Kitaoka HB, Ahn TK, Luo ZP, and An KN, 1997, “Stability of the arch of the foot,” Foot Ankle Int, 18(10), pp. 644-648.
4. Iaquinto JM, and Wayne JS, 2011, “Effects of surgical correction for the treatment of adult acquired flatfoot deformity: A computational investigation,” J Ortho Res, 29(7), pp. 1047-1054.
5. Spratley EM, and Wayne JS, 2010, “Computational Model of the Human Elbow and Forearm: Application to Complex Varus Instability,” Ann Biomed Eng, 39(3), pp. 1084-1091.
6. Thordarson DB, Schmotzer H, Chon J, and Peters J, 1995, “Dynamic support of the human longitudinal arch. A biomechanical evaluation,” Clin Orthop Relat Res, (316), pp. 165-172.
7. Coughlin MJ, and Kaz A, 2009, “Correlation of Harris mats, physical exam, pictures, and radiographic measurements in adult flatfoot deformity,” Foot Ankle Int, 30(7), pp. 604-612.
8. Krans A van der, Louwerens JWK, and Anderson P, 2006, “Adult acquired flexible flatfoot, treated by calcaneo-cuboid distraction arthrodesis, posterior tibial tendon augmentation, and percutaneous Achilles tendon lengthening: A prospective outcome study of 20 patients,” Acta Orthop, 77(1), pp. 156-163.
9. Murley GS, Menz HB, and Landorf KB, 2009, “A protocol for classifying normal- and flat-arched foot posture for research studies using clinical and radiographic measurements,” J Foot Ankle Res, 2, p. 22.
10. Thomas J, Kunkel M, Lopez R, and Sparks D, 2006, “Radiographic Values of the Adult Foot in a Standardized Population,” J Foot Ankle Surg, 45, pp. 3-12.