Injury of the anterior cruciate ligament (ACL) is common, with an annual incidence of 81 per 100,000, and reconstructions numbering at 107,000 per year in the United States alone. (1
) ACL rupture has been associated with functional impairment secondary to joint instability, meniscal injury, and ultimately osteoarthritis (OA). (3
) The rate of OA following ACL injuries is controversial. Long term database studies evaluating soccer players following ACL injury showed the development of radiographic degenerative joint disease in injured knees to be 51 percent, while the rate of OA in the contralateral knee was only 8 percent. (6
) A recent review also estimated that 50 percent of patients developed OA 10 to 20 years following ACL injury. (7
) However, in contrast, a meta-analysis showed the rate of radiographic OA to be lower, especially in those patients with an isolated ACL tears (with no meniscal injury) who displayed a 0-13 percent prevalence of OA. (4
) Despite these findings, ACL reconstruction has not been shown to decrease the rate of OA despite the immediate improvements in stability. (4
Knee kinematics have been studied with a variety of modalities, including gait analysis, (8
) dual-plane fluoroscopy, (14
) stereoradiographic analysis, (16
) and magnetic resonance (MR) kinematics. (17
) In vivo analysis of tibiofemoral kinematics following ACL injury has shown differences between the ACL-injured and contralateral uninjured legs. (8
) In general, anterior-posterior (A-P) laxity of the knee has been considered largely restored following reconstruction. (10
) However, it has been suggested that the most popular surgical technique – the single bundle transtibial reconstruction, with either bone patellar tendon bone or hamstrings grafts – fails to restore normal kinematics, specifically with respect to rotational sability. (10
) The observed changes in knee joint motion are thought to modify loading patterns. And these changes in kinematics have been suggested as one of the significant factors contributing to post-traumatic OA development in ACL injured patients. (5
). Investigators have recommended that femoral drilling through anteromedial portal drilling may better restore rotational laxity, and thus, may have better outcomes. However, its effect on preventing OA development have yet to be determined.
It has proven difficult to show a direct relationship between changes in knee kinematics and the development of radiographic evidence of degenerative joint disease. This difficulty is largely a result of the relatively long time between injury and resultant morphological cartilage changes seen in OA. However, advancements in imaging technology such as quantitative magnetic resonance imaging (MRI) – T1ρ
quantification as well as delayed gadolinium enhanced MRI for cartilage (dGEMRIC) techniques – allow for the early detection of biochemical changes in the cartilage matrix associated with OA. (22
) Novel imaging techniques such as T1ρ
MRI coupled with MR kinematics may allow for analysis of tibiofemoral kinematics as well as early detection of cartilage matrix degeneration.
The purpose of our study was to explore the relationship between abnormal tibiofemoral kinematics following ACL reconstruction and early degeneration of the cartilage matrix, as measured by T1ρ relaxation times. Our hypotheses are threefold: 1) ACL reconstruction using a single bundle anteromedial drilling technique will not restore normal knee kinematics, particularly with respect to tibial rotation; 2) ACL-reconstructed knees will exhibit elevated T1ρ relaxation times in the medial compartment cartilage of the knee when compared to the contralateral knee; 3) Patients with abnormal knee kinematics, relative to the contralateral knee, will exhibit higher cartilage T1ρ relaxation times compared to those patients with restored tibiofemoral kinematics.