The Effect of Post-operative KT-1000 Score on Long-term Outcome in Anterior Cruciate Ligament Reconstruction

OBJECTIVES: Many long-term outcome studies have looked at risk factors for developing osteoarthritis after anterior cruciate ligament reconstruction (ACL). The purpose of this study was to evaluate the effect of post-operative graft laxity as measured by KT-1000 arthrometry on long-term clinical knee scores as well as the subsequent risk of additional knee surgery in transtibial ACL reconstructed patients. METHODS: Between 1992 and 1998, a cohort study of 171 consecutive patients undergoing transtibial bone-patellar tendon-bone ACL reconstruction was performed. Any patient with a history of prior ipsilateral or contralateral ACL reconstruction, menisectomy or cartilage restoration was excluded from this study. At 6, 12 and 24 months postoperatively, patients were evaluated by clinical examination, subjective and objective scoring systems, and KT-1000 arthrometry. Patients with a side to side difference of less than 3mm as measured by KT-1000 were considered ‘tight grafts’ and patients with a side to side difference of greater than 5mm were considered ‘loose’. At long-term follow-up patients completed subjective outcomes scores as well as questionnaires regarding their knee function. Differences within and between groups were analyzed. RESULTS: The study cohort comprised of eighty-five patients who met inclusion criteria; sixty-five ‘tight’ patients, and twenty ‘loose’ patients. 46 of 65 ‘tight’ patients (71%) and 15 of 20 ‘loose’ patients (75%) were available at long-term follow up (average 17 years; range 14.25 to 19.2). Lysholm scores improved significantly from pre-operative levels in both ‘tight’ and ‘loose’ reconstructions at both 2-year and long-term follow up; ‘tight’ grafts improved from 65.8 ± 20.0 to 93.8 ± 7.7, p<0.0001 and 90.4 ± 10.4, p<0.0001 at 2-year and long-term follow up respectively, whereas ‘loose’ grafts improved from 74.2 + 13.4 to 94.4 ± 6.7, p=0.0003 and 90.0 ± 13.5, p=0.01 respectively. In addition, Lysholm scores at 17-years did not differ significantly from 2-year post-operative scores in either group (‘tight’, p=0.10; ‘loose’, p=0.18). Moreover, at long-term follow-up, there was no significant difference between ‘tight’ or ‘loose’ reconstructions in any outcome measure; Lysholm p=0.85, Tegner p=0.77, KOOS p=0.96, and IKDC (subjective) p=0.42. Tegner activity scores did, however, deteriorate significantly within each group at 17-years when compared with 2-years’ scores (‘tight’, p=0.003; ‘loose’, p<0.01). With respect to number of additional surgical procedures required on the ACL reconstructed knee at 17 years, there was no difference between groups (24% ‘tight’, 7% loose; p=0.15). CONCLUSION: A side to side difference of greater than 5mm as measured by KT-1000 arthrometry has historically been considered a failure of ACL reconstruction. Our study suggests that a clinically loose post-operative result may not correlate with clinical failure at 17-year follow-up, and that transtibial ACL reconstruction still can provide excellent clinical results at long-term follow up.