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Am J Sports Med. 2012 Aug;40(8):1772-80. doi: 10.1177/0363546512449618. Epub 2012 Jun 19.

Effect of calcium phosphate-hybridized tendon graft in anterior cruciate ligament reconstruction: a randomized controlled trial.

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  • 1Department of Orthopaedic Surgery, Ibaraki Prefectural University of Health Sciences, Ami-machi, Inashiki-gun, Japan.



The authors developed a novel technique to improve tendon-bone healing by hybridizing calcium phosphate (CaP) with a tendon graft using an alternating soaking process.


Anterior cruciate ligament (ACL) reconstruction using the CaP-hybridized tendon graft would have a better clinical outcome and reduce the percentage of bone tunnel enlargement compared with a conventional method because of the enhanced anchoring between the tendon graft and the bone.


Randomized controlled trial; Level of evidence, 1.


Patients (N = 64) with unilateral ACL rupture underwent arthroscopically assisted single-bundle ACL reconstruction using a 4-strand semitendinosus tendon or 4-strand semitendinosus and gracilis tendons with EndoButton femoral fixation and screw washer tibial fixation. These patients were equally randomized to undergo the CaP (n = 32) or conventional (n = 32) method using a transtibial tunnel approach according to the closed envelope method. In the CaP group, the tendon graft was hybridized with the CaP at both ends of the graft. One surgeon performed all reconstructions without knowing which graft was prepared. Patients' backgrounds regarding age at surgery, gender, period before surgery, and associated meniscal injuries were similar in the 2 groups. All patients followed the same postoperative protocol. At 1 and 2 years after surgery, they were evaluated with the manual knee laxity test, KT-1000 arthrometry, International Knee Documentation Committee (IKDC) examination form, Tegner scale, and Lysholm scale. Also, 1 year postoperatively, bone tunnel enlargement was analyzed using computed tomography, intensity of the tendon graft by magnetic resonance imaging (MRI), and tendon graft appearance by arthroscopic examination. All the examinations were performed blindly.


All patients underwent a minimum 2-year follow-up. KT-1000 arthrometry data indicated statistically significant decreased average anterior tibial translation in the CaP group compared with the conventional method group: 1.0 ± 2.0 mm versus 1.9 ± 1.6 mm (P < .05), respectively, at 1 year; 1.6 ± 2.1 mm versus 2.6 ± 2.4 mm (P < .05), respectively, at 2 years. The Lysholm score was higher in the CaP group than in the conventional method group at 2 years (96.9 ± 4.3 vs 91.7 ± 13.3, P < .05). The CaP-hybridized tendon graft reduced the percentage of bone tunnel enlargement of the anteroposterior diameter at the main joint aperture site 1 year postoperatively (femoral side: 15.5% ± 13.4% vs 22.1% ± 16.4%, P < .05; tibial side: 19.3% ± 17.1% vs 26.1% ± 13.7%, P < .05). The results of the pivot-shift test, IKDC grade, and Tegner score; the intensity of the tendon graft (MRI); and arthroscopic appearance were not significantly different at both follow-up periods in the 2 groups.


The CaP-hybridized tendon graft improved anterior knee stability and Lysholm scores at the 2-year follow-up and improved anterior knee stability and reduced the percentage of bone tunnel enlargement in both tunnels at the 1-year follow-up compared with the conventional method for single-bundle ACL reconstruction. However, longer follow-up is needed to investigate the appearance of any increased instability.

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