Mechanical effects of immobilization on the Achilles' tendon.
OBJECTIVE
To measure the biomechanical effects of immobilization on the Achilles' tendon.


METHODS
Experimental, controlled study.


METHODS
Physiatry research laboratory.


METHODS
Twenty adult rabbits.


METHODS
One hindlimb immobilized in a cast for 4 weeks (n=10) or 8 weeks (n=10). The contralateral legs (n=20) served as controls.


METHODS
Cross-sectional Achilles' tendon area, mode of failure, mean failure load, and tendon stiffness.


RESULTS
The Achilles' tendon cross-sectional area did not change. Achilles' tendon-calcaneus units failed at insertion at 4 weeks and in controls. Calcaneus fracture was the most prevalent mode of failure at 8 weeks. The mean load to failure of both immobilized groups (4wk: 187.5+/-45.7N; 8wk: 162.6+/-39.3N) was significantly smaller than that of the control group (549.2+/-93.7N, both P<.005). The mean tendon stiffness of both immobilized groups (4wk: 64.6+/-24.8N/mm; 8wk: 53.9+/-19.9N/mm) was significantly lower than that of the control group (125.1+/-26.5N/mm, both P<.005).


CONCLUSIONS
Immobility for up to 8 weeks caused decreased stiffness but no atrophy or rupture of the Achilles' tendon, suggesting that immobility does not constitute a risk factor for Achilles' tendon midsubstance rupture. Clinically, graded reloading is required after immobilization to restore the tendon insertion and to reverse calcaneal disuse osteoporosis.
Matsumoto
Fujio
F
Bone and Joint Laboratory, University of Ottawa, Ottawa, ON, Canada.
Trudel
Guy
G
Uhthoff
Hans K
HK
Backman
David S
DS
D000125:Achilles Tendon / Q000293:injuries*; D000818:Animals; D001696:Biomechanical Phenomena; D002111:Calcaneus / Q000293:injuries; D002370:Casts, Surgical / Q000009:adverse effects; D004195:Disease Models, Animal; D005260:Female; D050723:Fractures, Bone / Q000209:etiology / Q000473:pathology / Q000517:prevention & control; D019417:Hindlimb Suspension / Q000009:adverse effects*; D010024:Osteoporosis / Q000209:etiology / Q000473:pathology / Q000517:prevention & control; D011817:Rabbits; D016059:Range of Motion, Articular; D012307:Risk Factors; D012421:Rupture; D013708:Tendon Injuries / Q000209:etiology / Q000473:pathology / Q000517:prevention & control; D013718:Tensile Strength; D013997:Time Factors; D016474:Weight-Bearing