Roofplasty requirements in vitro for different tibial hole placements in anterior cruciate ligament reconstruction

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Abstract
In this study we sought both to quantify the forces that result in anterior cruciate ligament graft impingement and the amount of roofplasty necessary to prevent it. The perpendicular force of the intercondylar roof against an anterior cruciate ligament graft was meas ured in seven fresh-frozen cadaveric knees. Two tibial hole placements were evaluated: an anterior/eccentric hole (26.6% ± 3.1% of the sagittal depth) and a cus tomized hole aligned 4 to 5 mm posterior and parallel to the slope of the intercondylar roof in the extended knee (42.0% ± 2.6% of the sagittal depth). A transducer that measured the contact force with the graft was implanted in the roof. An extensive roofplasty was performed so that the sensor would bear all of the roof force. Graft tension was also measured. Extension moments were applied to 20 N-m with a six degree of freedom load application system. Load cycles were repeated with the roof force sensor backed out in 0.8 mm increments. The sensor backout represented a corresponding amount of bone removal in a roofplasty. The flexion angle at roof-graft contact was consist ently greater using the anterior tibial hole than the customized one. This held true for all increments of sensor backout. With the anterior hole, the roof sensor (no backout) contacted the graft at 12.8° ± 6.7° of flexion, whereas the customized hole resulted in con tact at 4.1° ± 4.2° ( P = 0.020). With zero impingement defined as no contact between the roof and the graft throughout the range of motion, the anterior hole re quired 4.6 ± 1.0 mm of roof removal, and the custom ized hole required 1.3 ± 1.1 mm of roof removal ( P ≤ 0.0001).

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