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The Effect of Cyclic Loading on Rotated Bone-Tendon-Bone Anterior Cruciate Ligament Graft Constructs

From the Section of Sports Medicine, Department of Orthopaedic Surgery, Rush Medical College, Rush University Medical Center, Chicago, Illinois

^* Address correspondence to Nadim Hallab, PhD, Rush University Medical Center, 1735 W Harrison, MC 107, Chicago, IL 60612 (e-mail: nhallab{at}rush.edu).

Background: Single-incision anterior cruciate ligament reconstruction with a bone–patellar tendon–bone construct is commonly performed with 180° rotation of the graft. It has been hypothesized that further rotation of the graft to 540° can effectively shorten the graft to address graft length–tunnel mismatch. Initial biomechanical failure characteristics of rotated constructs have been reported, but cyclic loading of tendons has not been performed.

Hypothesis: Graft rotation affects the biomechanical properties of the construct.

Study Design: Controlled laboratory study.

Methods: Thirty-five bone–patellar tendon–bone composite porcine right knee specimens were randomized into 3 groups and were externally rotated to 0°, 180°, or 540°. Each group was then cyclically loaded in an artificial synovial fluid medium between 50 and 250 N for 5000 cycles, loaded between 50 and 500 N for an additional 5000 cycles, and finally subjected to load-to-failure testing.

Results: Graft rotation shortened constructs by 1.7 ± 0.8 mm at 180° of rotation and 7.6 ± 2.0 mm at 540° of rotation (P < .01). There was a statistically significant increase in strain during cyclic loading at 540°. No significant differences in maximum load, yield stress, yield strain, or modulus of elasticity were detected in single-cycle load-to-failure testing after cyclic loading.

Conclusion: Rotation of bone–patellar tendon–bone constructs to 540° predictably shortens the effective graft length at the expense of increased strain with cyclic loading at stresses equivalent to walking and running.

Clinical Relevance: Although rotation to 540° potentially addresses graft length–tunnel mismatch, further clinical evaluation is required to evaluate the impact of increased strain on knee laxity and to determine the effects of physiologic loading of rotated bone–patellar tendon–bone constructs in vivo.

Key Words: anterior cruciate ligament (ACL) • bone–patellar tendon–bone (BPTB) • graft rotation • twist • biomechanics

This article has been cited by other articles:

				M. L. Busam, M. T. Provencher, and B. R. Bach Jr Complications of Anterior Cruciate Ligament Reconstruction With Bone-Patellar Tendon-Bone Constructs: Care and Prevention Am. J. Sports Med., February 1, 2008; 36(2): 379 - 394. [Abstract] [Full Text] [PDF]