Anterior cruciate ligament reconstruction : subjective knee function, graft failure and revision surgery

Abstract

An anterior cruciate ligament (ACL) tear is a severe knee injury, which leads to increased knee laxity and often functional instability. An ACL reconstruction (ACLR) is generally recommended to patients who desire to return to pivoting sports. Surgery is also recommended in cases of persistent instability during activities of daily living. An ACL tear is commonly associated with meniscal and/or cartilage injuries. Patients with an ACL tear, especially if combined with cartilage and/ or meniscal injuries, have a high risk of developing knee osteoarthritis in the long term. One major problem after ACLR is the risk of graft failure and/or contralateral ACL injury. Revision and contralateral ACLR are relatively common in clinical practice. This thesis consists of five cohort studies with data obtained from our registry (Capio Artro Clinic, Stockholm, Sweden). The overall aims were to identify factors affecting objective and subjective outcomes after ACLR, the risk of associated (cartilage and meniscus) injuries and meniscus repair at the time of primary ACLR, as well as evaluating and comparing the subjective and objective outcomes of revision and contralateral ACLR with those of primary ACLR.

Study I evaluated risk factors for abnormal (KT-1000 STS > 5 mm) anteroposterior knee laxity after primary ACLR. A total of 5,462 patients were included. Younger (< 30 years) age, preoperative STS difference > 5 mm, medial meniscus resection and the use of an HT autograft over a BPTB autograft increased the odds of abnormal knee laxity 6 months after ACLR. Female gender, medial meniscus repair, lateral meniscus resection or repair did not affect the risk of having abnormal knee laxity after primary ACLR.

Study II compared knee laxity (KT-1000) and functional knee outcome (KOOS) between primary and revision ACLR. A total of 200 patients who underwent primary ACLR with an HT autograft followed by revision ACLR with a BPTB autograft were identified. Comparisons of knee laxity and functional knee outcome were based on a cohort of 118 and 73 patients respectively. Revision ACLR restored knee laxity to a level comparable with that of primary ACLR, but it resulted in a significantly inferior functional knee outcome.

In Study III, the primary aim was to evaluate the effect of delayed ACLR on cartilage injuries, meniscus injuries, meniscus repair and abnormal knee laxity at the time of primary ACLR. A second aim was to study the effect of other variables (age, gender, BMI) on the same outcomes. The study included 3,976 patients and established several associations between time from injury to surgery, patient characteristics, associated injuries, meniscus repair and knee laxity. The main findings were that a time from injury to surgery longer than 12 months increased the odds of cartilage and medial meniscus tears, whereas a time from injury to surgery longer than 6 months increased the odds of abnormal (STS > 5mm) knee laxity at the time of ACLR and reduced the chance of medial meniscus repair.

In Study IV the aims were: 1) to evaluate the rate of patients reporting a PASS 2 years after ACLR; 2) to determine a wide range of preoperative, intraoperative and postoperative factors that might affect the achievement of a PASS. Patients with a complete KOOS at 2 years were included (n = 2,335). A PASS on 4 KOOS subscales was reported by more than 60% of the patients. Among the non-modifiable factors, older age (≥ 30 years) and female gender were those that most affected (positively and negatively respectively) the chance of achieving a PASS. Among the modifiable factors, quadriceps strength and the SLH test performance 6 months after ACLR were those that most affected (increased) the chance of achieving a PASS.

Study V evaluated and compared the results of primary and contralateral ACLR in terms of knee laxity (KT-1000) and functional knee outcome (KOOS). A total of 326 patients with primary and contralateral ACLR were identified. A cohort of 226 patients for whom instrumented (KT-1000) laxity measurements were available and a cohort of 256 patients for whom KOOS values were available for both surgeries were included for analysis. The findings of the study showed that there were no significant differences between primary and contralateral ACLR with regard to the investigated outcomes. We therefore concluded that contralateral ACLR produces predictable results in terms of knee laxity and functional knee outcome, as they do not differ from those of primary ACLR.

In conclusion, several factors are associated with abnormal knee laxity (STS > 5 mm, graft failure) after ACLR. They are younger (< 30 years) age, preoperative STS > 5 mm, medial meniscus resection and the use of an HT autograft over a BPTB autograft. A time from injury to ACLR > 6 months is associated with a preoperative STS > 5 mm which is in turn an important risk factor for abnormal postoperative knee laxity. Delay in ACLR is also associated with increased odds of medial meniscus and cartilage injuries and a reduced likelihood of medial meniscus repair. Both ACL graft rupture and contralateral ACL tear are devastating events for the ACLR patient. However, even though both revision ACLR and contralateral ACLR restore knee laxity, revision ACLR is associated with a significantly inferior functional knee outcome compared with primary ACLR. On the other hand, contralateral ACLR produces a functional knee outcome comparable to that of primary ACLR. Finally, there are several factors associated with subjective knee outcome (2 years PASS) after primary ACLR. Older age (≥ 30 years) and female gender are the non-modifiable factors that most affect (positively and negatively respectively) the chance of achieving a PASS. Quadriceps strength and the SLH test performance 6 months after ACLR are the modifiable factors that most affect (increase) the chance of achieving a PASS. This highlights the fundamental role of rehabilitation after ACLR.