The preoperative flexion tear gap affects postoperative meniscus stability after pullout repair for medial meniscus posterior root tear

Abstract

Background: We investigated whether the preoperative flexion tear gap (FTG) observed in open magnetic resonance imaging (MRI) affects meniscus stability after medial meniscus (MM) posterior root (MMPR) repairs. Furthermore, time-correlated MRI findings from MMPR tear occurrence were evaluated.

Methods: This retrospective observational study included 54 patients (mean age, 64.6 years; 13 males and 41 females) who underwent pullout repair for radial degenerative MMPR tear. Meniscus stability (scored 0-4 points) was assessed using a semi-quantitative arthroscopic scoring system during second-look arthroscopy 1 year postoperatively. The FTG was evaluated on preoperative axial MRI at 90° knee flexion. Other MRI measurements included MM extrusion (MME) at 10° knee flexion, MM posterior extrusion (MMPE) at 90° knee flexion, and MM posteromedial extrusion (MMpmE) at 90° knee flexion preoperatively and 1 year postoperatively. The correlation between the arthroscopic stability score and MRI findings was investigated. A receiver-operating characteristic curve was calculated to predict a good meniscus healing score (3-4 points). The correlation between the FTG and patient demographics, including time from injury to MRI, was analyzed.

Results: At 1 year postoperatively, MME increased by 1.1 mm, while MMpmE and MMPE decreased by 0.4 mm and 1.0 mm, respectively. The meniscus stability score was negatively correlated with the preoperative FTG (r = -0.61, p < 0.01). The time from injury to MRI was significantly correlated with the preoperative FTG. The receiver-operating characteristic curve identified an FTG cut-off value of 8.7 mm for predicting good postoperative stability, with sensitivity and specificity of 67% and 85%, respectively.

Conclusions: FTG evaluated with open MRI at 90° knee flexion was associated with time from injury and affected meniscus stability following pullout repair. MMPR tears should be treated in the early phase to increase meniscus healing stability.

Keywords: Distance; Medial meniscus; Posterior root tear; Pullout repair; Second-look arthroscopy.

Fig. 1

Illustration of four suture configurations. a Two simple stitches. b Two simple stitches with an additional posteromedial pullout. c Two cinch stitches. d Two cinch stitches with an additional posterior anchoring. MFC medial femoral condyle, PCL posterior cruciate ligament

Fig. 2

Arthroscopic meniscus stability test of the bridging tissue using probing. a Two-point stability; lift on probing at both 20° and 60° knee flexion. b Three-point stability; lift on probing at 20° but not at 60° knee flexion. c Four-point stability; no lift on probing at either 20° or 60° knee flexion

Fig. 3

Magnetic resonance imaging measurement of the flexion tear gap (FTG). Image overlay of two axial magnetic resonance images of the knee flexed at 90° shows the FTG. The FTG was measured as the distance between the medial meniscus (MM) posterior root (MMPR) insertion (center of the white circle) and the tip of the tear stump (triangle)

Fig. 4

Measurements and reference lines in three-dimensional (3D)-reconstructed MRI of the right knee. MRI images at 10° (a, b) and 90° (c, d) knee flexion. A 3D-reconstructed medial meniscus (MM) from above the tibial plateau with the purple area representing the protruding portion from the tibia (e). a. Medial meniscus extrusion (MME) measured from the tibial edge (dashed line) to the outer edge (line) of the meniscus in the midcoronal plane, excluding osteophytes. b. Root tear gap was sometimes not obvious. c. Medial meniscus posteromedial extrusion (MMpmE) measured from the tibial edge (dashed line) to the outer edge of the meniscus (line), approximately 4 mm anterior to the posterior edge of the tibial plateau. d. Medial meniscus posterior extrusion (MMPE) measured from the tibial edge (dashed line) to the outer edge of the meniscus (line). e. Reference lines for a–d. MRI magnetic resonance imaging

Fig. 5

Receiver-operating characteristic curve of the flexion tear gap (FTG) predicting good stability (3, 4 points) The cut-off value of the FTG for good stability was 8.7 mm, with a sensitivity and specificity of 66.7% and 84.6%, respectively. AUC area under the curve, CI confidence interval

Fig. 6

Regression lines of the time-dependent changes in preoperative magnetic resonance imaging (MRI) findings a. Moderate correlation between the flexion tear gap (FTG) and time from injury to MRI (R² = 0.12). b. Moderate correlation between medial meniscus posteromedial extrusion (MMpmE) and time from injury to MRI (R.² = 0.12) c. No correlation between medial meniscus posterior extrusion (MMPE) and time from injury to MRI (R²=0.01)

Fig. 7

Illustration of time-correlated changes in preoperative magnetic resonance imaging findings with the knee flexed at 90° above the tibial plateau. MM medial meniscus, MMpmE medial meniscus posteromedial extrusion, MMPE medial meniscus posterior extrusion, FTG flexion tear gap