Weight-bearing recommendations after first metatarsophalangeal joint arthrodesis fixation: a biomechanical comparison.
BACKGROUND
This study sought to determine whether several metatarsophalangeal (MTP) fusion techniques require complete immobilization or if some level of weight-bearing could be recommended after surgery. A comparison of synthetic composite to actual bone was included in order to examine the validity of the testing conditions.


METHODS
Four MTP fusion modalities were tested in synthetic composite bone models: unlocked plating, locked plating, crossed lag screws, and an unlocked plate with a single lag screw. Stiffness was calculated and then used to find the two most rigid constructs; the load to failure was recorded. Stiffness and load to failure testing for the two more rigid constructs in paired cadaveric bones were followed.


RESULTS
The unlocked plate plus screw and crossed screw constructs were stiffest (p < 0.008). Loads to failure of the unlocked plate plus screw and crossed screws in synthetic bone were 131 and 101 N, respectively and in cadaveric bone were 154 and 94 N, respectively, which are less than the estimated 25% body weight required at the MTP joint. The plate plus screws were statistically more stiff than crossed screws (p = 0.008), but there was no statistical difference between synthetic and cadaveric bone in load to failure (p = 0.296).


CONCLUSIONS
The plate plus screw offered the greatest stiffness; the failure test showed that no construct could withstand weight-bearing as tolerated; and, synthetic composite models of the MTP joint did not provide the consistent results in stiffness and failure.
Department of Mechanical Engineering and Material Science, University of Pittsburgh, 3700 O'Hara Street, Pittsburgh, PA, 15261, USA. brc57@pitt.edu.
Bradley
B
Campbell
Department of Mechanical Engineering and Material Science, University of Pittsburgh, 3700 O'Hara Street, Pittsburgh, PA, 15261, USA.
Patrick
P
Schimoler
Department of Orthopaedic Surgery, Orthopaedic Biomechanics Laboratory, Allegheny General Hospital, 320 E. North Ave, Pittsburgh, PA, 15212, USA.
Sudhir
S
Belagaje
Department of Mechanical Engineering and Material Science, University of Pittsburgh, 3700 O'Hara Street, Pittsburgh, PA, 15261, USA.|Department of Orthopaedic Surgery, Orthopaedic Biomechanics Laboratory, Allegheny General Hospital, 320 E. North Ave, Pittsburgh, PA, 15212, USA.|Department of Bioengineering, University of Pittsburgh, 3700 O'Hara Street, Pittsburgh, PA, 15261, USA.
M C
MC
Miller
Orthopaedic Practices, Pittsburgh, PA, 15261, USA.
S F
SF
Conti
D000368:Aged; D000369:Aged, 80 and over; D001174:Arthrodesis / Q000295:instrumentation* / Q000379:methods; D001696:Biomechanical Phenomena / Q000502:physiology*; D001860:Bone Plates; D001863:Bone Screws; D005260:Female; D006801:Humans; D008297:Male; D008683:Metatarsophalangeal Joint / Q000502:physiology* / Q000601:surgery*; D008875:Middle Aged; D016474:Weight-Bearing / Q000502:physiology*
Foot; Fusion; Hallux rigidus; Metatarsal; Weight-bearing