A comprehensive in vivo kinematic, quantitative MRI and functional evaluation following ACL reconstruction — A comparison between mini-two incision and anteromedial portal femoral tunnel drilling

Highlights

• Imaging-based evaluation of two methods of anatomic ACL reconstruction

• Retrospective study of two age and gender-matched groups

• A side-to-side difference in tibial position was observed in the MT group.

• Medial tibial cartilage degenerative changes were observed in the MT group.

Abstract

Background

Multiple techniques are used for femoral tunnel drilling in ACL reconstruction, including the Mini-two Incision Method (MT) and Anteromedial Portal Technique (AM). Both techniques allow for independent placement of the femoral tunnel, though there are no reports comparing kinematics and cartilage health after these reconstructions. We hypothesized that both techniques would result in the restoration of normal knee kinematics and show no evidence of early cartilage degeneration.

Methods

A total of 20 patients were evaluated one year after ACL reconstruction, including 10 patients after MT and 10 patients after AM. MR-imaging was acquired bilaterally with the knee loaded in extension and flexion to evaluate the kinematics of the reconstructed knee compared with the normal knee. Quantitative cartilage imaging was obtained and compared with 10 matched control subjects. The Marx Activity Rating Scale and KOOS survey were administered.

Results

The tibia was positioned significantly more anteriorly in extension and flexion relative to the contralateral knee for the MT group. The tibial position in the AM group was not significantly different from the patient's contralateral knee. T₁ρ values in the central-medial tibia were significantly elevated in the MT group compared with the Control group. KOOS Symptom scores were significantly better for the MT group compared with the AM group.

Conclusions

We have observed in vivo differences in knee kinematics and early cartilage degeneration between patients following MT and AM ACL reconstructions. Both techniques allow for anatomic ACL reconstruction, though the MT group shows significant early differences compared with the patient's normal knee.

Level of evidence

Level III — retrospective comparative study

Introduction

Anterior cruciate ligament (ACL) tears are one of the most common knee ligament injuries that require surgical reconstruction [1]. The development of post-traumatic medial compartment arthritis is well-documented regardless of treatment, with several studies reporting increased rates of degenerative changes after ACL reconstruction [2], [3], [4], [5], [6]. There has been an increased emphasis on utilizing new methods to position the femoral tunnel in order to improve the current trend of achieving less than satisfactory mid-term and long-term results after ACL reconstruction.

The Anteromedial Portal Technique (AM) has gained popularity as it allows for all-inside placement of the femoral tunnel, independent of tibial tunnel placement. Potential pitfalls still remain with this method [7]. The tunnel length and orientation are dependent on the flexion angle of the knee at the time of drilling, and the knee must be hyperflexed past 100° of flexion to achieve an acceptable tunnel position and length, which frequently limits optimal visualization of the femoral ACL footprint while drilling [8]. There is also a risk of lateral cortex disruption while placing the femoral tunnel, since the endpoint of reaming is not well-defined [7]. A short femoral tunnel and damage to the articular cartilage are other potential downsides [7], [9].

A Mini-two Incision Technique (MT) has been developed to allow for a more reliable placement of the femoral tunnel [7]. The MT utilizes a one to two centimeters incision over the lateral femur to limit trauma to the soft tissue and iliotibial band [7]. The femoral tunnel is then drilled from the inside–out with a retrograde drill under arthroscopic visualization, which can lead to a reliable and anatomic position of the femoral tunnel [7]. Ultimate tunnel length is calculated prior to drilling, and a cadaveric study has shown that the tunnel created with this method is on average significantly longer than the tunnel drilled through the anteromedial portal [9]. This procedure is performed with the knee at 90° of flexion, which allows for improved identification of anatomic landmarks.

Advanced imaging methodologies can provide an early assessment of knee function through information on progressive cartilage degradation and abnormal kinematics. In particular, the T1ρ relaxation time, which describes spin–lattice relaxation in a rotating spatial frame, can provide detailed information on the extracellular matrix of cartilage [10]. This parameter reflects the proteoglycan content of cartilage and can detect early changes in the cartilage matrix prior to the development of radiographic abnormalities [11]. Kinematic MR imaging reconstructs static images in different positions to understand the complex rotational and translational movements of the knee [12], [13]. Accelerated medial compartment degenerative changes are commonly encountered after ACL injury, and quantitative MR imaging provides a focused assessment of abnormalities.

The purpose of this study is to evaluate MR-based in vivo kinematics, early cartilage degeneration, as measured by T₁ρ values, and patient reported outcomes between the MT reconstruction and the AM reconstruction. We hypothesized that both the MT and AM reconstructions would restore normal knee kinematics and produce similar patient reported outcomes. The primary outcome was a dynamic anterior tibial translation. Additionally, we hypothesized that both surgical techniques would lead to similar cartilage health as compared with healthy control patients.