Serial magnetic resonance imaging of hamstring anterior cruciate ligament autografts during the first year of implantation

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Abstract
A prospective, observational study was performed to document the serial changes in the magnetic resonance signal of devascularized, hamstring ACL autografts dur ing the 1 st year of implantation. Twenty-one ACL deficient knees (14 chronic, 7 acute) were reconstructed. Instability developed in five knees within the first 6 months of graft implantation (24%). Magnetic resonance examinations were performed at 1, 6, 12, 24, 36, and >48 weeks postoperatively (rep etition time 1500, echo delay time = 50). A total of 104 scans were reviewed (average, five per knee). The ACL graft was divided into four unequal size zones for analysis. The proximal, middle, and distal thirds of the intraarticular portion of the graft and the portion of the graft within the tibial tunnel were independently an alyzed. The magnetic resonance signal in each portion of the graft was graded on a scale with (I) being a normal signal, (II) >50% of the total volume of the graft having a normal signal, (III) <50% of the graft having a normal signal, and (IV) 100% of the graft having an increased signal. The increased magnetic resonance signal of the ACL graft was observed to be regionalized and confined to the distal two-thirds of the intraarticular portion of the graft. The portion of the graft exiting the femoral tunnel and within the tibial tunnel retained a normal magnetic resonance signal. The increases in magnetic resonance graft signal were time-dependent, became well estab lished by 3 months, and remained unchanged at 1 year. The clinical outcome could not be predicted based on the magnetic resonance signal of the graft.