In radial meniscal tears, disruption of peripheral circumferential fibers results in loss of meniscal function, including load transmission and shock absorption.1–4 Several clinical studies have reported that untreated radial meniscal tears rapidly develop osteoarthritic changes in the knee joint.5,6 In addition, recent biomechanical studies have shown that a complete radial meniscal tear or meniscectomy following a radial tear significantly increased knee joint contact pressure compared with that following repair of a radial meniscal tear.7,8 These findings emphasize the importance of repairing radial meniscal tears.
Although radial meniscal tears pass through a poorly vascularized central zone with relatively low healing potential, various methods have been developed to repair these tears with good clinical outcomes. Yoo et al9 reported healing of radial meniscal tears following all-inside vertical suturing using suture hooks. Ra et al10 also reported satisfactory outcomes using an inside-out horizontal suture technique. Nevertheless, incomplete healing in the central zone of radial meniscal tears remains a challenging problem.11
For successful healing and appropriate rehabilitation in the repair of radial meniscal tears, sufficient suture strength through the tear surface as well as biological enhancement is essential. In previous biomechanical studies on the repair of radial meniscal tears, vertical sutures and cross sutures showed superior mechanical properties than horizontal sutures.12,13 Moreover, in a study by Herbort et al,14 double horizontal sutures demonstrated significantly increased strength compared with single horizontal sutures. However, the biomechanical properties of vertical, cross, and horizontal sutures have not been compared simultaneously, especially in a double suture technique. In addition, the suture strength of each technique, especially in the central zone of radial tears, has not been investigated previously.
The purpose of this study was to compare the biomechanical properties of double all-inside vertical sutures, inside-out cross sutures, and double inside-out horizontal sutures in the repair of radial meniscal tears. To evaluate the suture strength of each technique in the central and peripheral zones separately, gap configuration analysis was used. The authors hypothesized that double all-inside vertical sutures would show superior biomechanical properties than inside-out cross sutures and double inside-out horizontal sutures, especially in the central zone.
Materials and Methods
This study used 60 matched and paired (medial and lateral) fresh-frozen porcine menisci. An a priori power analysis was performed with the assumption that a 0.5-mm gap distance was significant, with a standard deviation of 0.6 mm based on the pilot test, and that 20 menisci were sufficient for all parameters (alpha=0.05, beta=0.8). Animals (mean age, 24±2 weeks) were obtained from a local butcher; within 12 hours of death, the menisci were dissected free, leaving the peripheral capsular structure intact, and the menisci were stored at −24°C. Menisci were thawed at room temperature for 5 hours before testing. Double all-inside vertical, inside-out cross, and double inside-out horizontal suture techniques for repair of radial meniscal tears were compared, and 10 matched and paired medial and lateral menisci were allocated into each group. Anatomical variables of porcine menisci were compared among the 3 test groups, and there were no significant differences in all parameters (Table 1).
Anatomical Data of Porcine Menisci
In all 3 groups, the menisci were resected longitudinally to the circumferential fiber in the exact center of the midhorn using a no. 11 blade, and a complete radial tear was created from the peripheral margin to the meniscocapsular junction. Although the meniscocapsular junction usually is preserved in radial meniscal tears, except in extensive radial tears with a large defect, capsular tissue routinely was resected to eliminate the bias generated by the remaining joint capsule. All suturing was performed with a double-arm needle and 2-0 braided polyester with ultra-high-molecular-weight polyethylene suture (FiberWire; Arthrex, Naples, Florida).
As in the study by Matsubara et al,12 4 entry points using 2 sutures were created at identical positions in all 3 groups: 5 mm from the meniscocapsular junction and 5 mm from the tear margin, and 10 mm from the meniscocapsular junction and 5 mm from the tear margin. In the vertical suture group, 2 all-inside vertical sutures were tied with 3 square knots on the superior surface of the meniscus. In the cross suture group, 2 sutures that crossed over each other at the tear surface were tied with 3 square knots on the lateral capsular surface. In the horizontal suture group, 2 inside-out horizontal sutures were tied with 3 square knots on the lateral capsular surface (Figure 1).
Meniscus repair construct for double all-inside vertical (A), inside-out cross (B), and double inside-out horizontal (C) sutures.
Biomechanical testing was performed using a universal testing machine, and tensile load was applied perpendicular to the radial tear, simulating a worst-case scenario (Figure 2A). To prevent slippage and deformation of the specimens, custom-made clamps with spikes and holes were used (Figure 2B). After specimen-engaged clamps were mounted in the testing machine, a preload of 2 N was applied, and preconditioning was performed with 500 loading cycles of 5 to 30 N at 1 Hz, as described previously.15–17 After completion of the cyclic loading test, specimens underwent load-to-failure testing at a rate of 5 mm/min until failure.
Universal testing machine with tissue clamps (A). Custom-made clamp with 5 spikes and spike holes used to prevent slippage and deformation of specimens (B).
Throughout the biomechanical testing, load and displacement were recorded in the test machine program, and a load-displacement curve was generated. Failure load was defined as loss of suture integrity indicated by the first peak on the displacement curve. Stiffness also was calculated from the linear region of the load-displacement curve. Mode of failure was determined by observing failed tissue or suture material. All experiments were performed in a constant humidity room, and the meniscus was moisturized to prevent change of biomechanical properties.
Gap Configuration Analysis
Gap configuration analysis was performed to compare suture strength in the peripheral-central zone (Figure 3). First, the meniscus was divided longitudinally into 2 equal parts (central and peripheral zones). A central gap and a peripheral gap were defined as the distance between superior and inferior tear margins at the exact midpoint of the central and peripheral zones, respectively. Total gap was defined as the change in distance between the 2 tissue clamps.
Gap configuration analysis. Central and peripheral gap were measured separately at the exact midpoint of the central and peripheral zones to evaluate suture strength. Total gap was defined as the change in distance between 2 tissue clamps.
After a 500-cycle loading test, digital photographs were obtained (LUMIX G DMC-GX7; Panasonic, Tokyo, Japan) at the same location in all measurements. ImageJ software (National Institutes of Health, Bethesda, Maryland) was used for measurements of central and peripheral gaps on the digital photographs. A 10-mm diameter hexagonal bolt in the clamp was used for calibration of measured distance. Two independent examiners measured the central and peripheral gaps twice at a time interval of 1 week. Total gap was calculated automatically on the testing machine as the distance between the 2 tissue clamps. This study did not involve human participants or living animals.
Statistical analysis was conducted using SPSS version 18.0 software (SPSS Inc, Chicago, Illinois), and P<.05 was considered significant. Data for all parameters showed a normal distribution. Analysis of variance was used to analyze continuous variables. When significant differences were obtained with analysis of variance, t test was used to determine intergroup significance. Interrater and intrarater reliability were evaluated with the intraclass correlation coefficient (ICC), and the ICC value was greater than 0.8 for all parameters.
Gap Configuration Analysis
After 500 loading cycles, double vertical sutures showed significantly lower total and central gap displacement than cross and double horizontal sutures (P<.05) (Table 2). However, there was no significant difference in peripheral gap within each group (P=.53). Cross and double horizontal sutures were more vulnerable to central gap formation than double vertical sutures. As a result, double vertical sutures showed a trapezoidal gap configuration, whereas cross and double horizontal sutures showed a triangular gap configuration (Figure 4).
Gap Configuration and Displacement After 500 Cycles Between 5 and 30 N
Configuration of gap after 500 loading cycles. Double all-inside vertical sutures (A) had a trapezoidal gap configuration whereas inside-out cross (B) and double inside-out horizontal (C) sutures had a triangular gap. Significantly increased medial gap with cross and horizontal sutures and a similar peripheral gap among the 3 techniques resulted in different gap configurations.
Ultimate Failure Load and Stiffness
Ultimate failure load was significantly higher in the double vertical suture group compared with the cross and double horizontal suture groups (P<.05) (Table 3). Stiffness of suture construct also was significantly higher in the double vertical suture group compared with the cross and double horizontal suture groups. There was no difference in ultimate failure load and stiffness between the cross and double horizontal suture groups.
Ultimate Failure Load, Stiffness, and Mode of Failure
In the double vertical suture group, 11 tissue failures and 9 suture failures were observed. In the cross suture group, 12 tissue failures and 8 suture failures were observed. In the double horizontal suture groups, 10 tissue failures and 10 suture failures were observed.
The most important finding of this study was that double all-inside vertical sutures showed superior mechanical strength compared with double inside-out horizontal and cross sutures, especially in the central zone of a radial tear. Double inside-out horizontal and cross sutures were more vulnerable to central zone displacement under cyclic loading compared with double all-inside vertical sutures in gap configuration analysis. However, there was no difference in peripheral gaps among these 3 suture techniques.
During the pilot test, different gap configurations (trapezoidal for vertical sutures, and triangular for cross and horizontal sutures) were observed. Previous biomechanical studies on meniscal repair evaluated suture strength under cyclic loading with the displacement of 2 tissue clamps.12,18 However, this measurement can have limitations for evaluating the suture strength in central or peripheral zones separately.
In the current study, gap configuration analysis that measured central, peripheral, and total gaps separately was used to evaluate suture strength in the central peripheral zone. Significantly increased central gap in the cross and double horizontal suture techniques can be explained by suture passage on the tear surface of each technique (Figure 5). In the double vertical suture technique, the central stitch passed the central zone of the radial tear, resulting in improved suture strength in the central zone. However, in the cross and double horizontal suture techniques, the sutures did not pass or passed only the superior portion of the central zone. Instead, two stitches passed the midportion of the peripheral zone on the tear surface and cerclaged the peripheral zone, resulting in no difference in peripheral gap formation.
Suture passage at the radial meniscal tear surface. Double all-inside vertical sutures (A) crossed the midpoint of the central zone. Inside-out cross (B) and double inside-out horizontal (C) sutures did not pass or passed only the superior point of the central zone.
In load-to-failure testing, the maximum failure load for double vertical sutures was significantly higher than for double horizontal and cross sutures. Similarly, Beamer et al13 reported vertical sutures provided superior strength compared with horizontal sutures in meniscal repair of radial tears using a single suture technique. These results may be related to the microarchitecture of collagen fibrils in the meniscus. In the central two thirds of a normal meniscus, collagen fibrils are arranged predominantly in radial fashion.4,19 Compared with horizontal and cross sutures, vertical sutures can capture meniscal tissue more perpendicular to the radial fibers, resulting in increased resistance to tensile forces. On the other hand, the current study found no difference between double horizontal and cross sutures, which is contrary to the findings of Matsubara et al,12 who reported superior strength of cross sutures compared with horizontal sutures for patients with radial meniscal tears. The discrepancy between these studies may be caused by the difference in materials (porcine vs human meniscus). To compare the superiority of strength between cross and horizontal sutures, further study with a larger number of nondegenerative human menisci is needed.
The results of gap configuration analysis can provide a reasonable rationale for the establishment of appropriate rehabilitation protocols. Kawai et al20 reported maximum strength against tensile force following meniscal repair reached 80% after approximately 3 months in a canine model. Therefore, early rehabilitation with knee flexion or partial weight bearing should be determined according to the suture strength of each technique. However, basic or clinical studies on rehabilitation following meniscal repair of radial tears are limited. The current study compared the mechanical strength of different techniques in the central-peripheral zone, and the findings can help establish appropriate rehabilitation protocols for the type of repair. A slower rehabilitation protocol may be necessary for patients treated with a horizontal or cross suture technique compared with patients treated with a vertical suture technique to avoid lax or incomplete healing of the meniscus. Moreover, if technically feasible, additional all-inside vertical sutures in the central zone can provide greater stable suture integrity for a more rapid progression of rehabilitation.
This study has several limitations. First, porcine menisci were used as an alternative to human nondegenerative menisci. Porcine menisci are thicker and denser than human menisci,21 and the different tissue properties may affect the biomechanical results. However, there was no difference in size parameters including diameter, width, height, and laterality among the 3 study groups. Moreover, porcine menisci have been used as an alternative to human menisci in previous biomechanical studies.15–18,22–25 Therefore, a comparison of suture strength might not be affected significantly by this difference.
Another limitation is that the test was performed under uniaxial tensile force perpendicular to the radial tear. Mechanical stress on the meniscus during natural knee motion is composed of multidirectional tensile, shear, and compressive forces. Although this experimental setting was designed for the evaluation of a worst-case scenario, it cannot entirely reflect natural knee motion, especially in weight-bearing conditions. Nevertheless, most comparative biomechanical studies of meniscal repair technique have used similar experimental settings, assuming that biomechanical results in a worst-case scenario can represent relative suture strength in other complex knee motions. Therefore, this limitation should be considered when the results of this study are applied to real knee motions. Also, additional biomechanical testing under shear force or development of equipment that can measure displacement and failure load under simulation of actual knee motion should be considered to overcome this limitation.
Finally, this was a biomechanical time-zero study performed immediately after meniscal repair. In clinical practice, flexion of the knee joint or partial weight bearing is not permitted for at least 3 to 6 weeks after repair of a radial meniscal tear. The temporal discrepancy between the test and practical rehabilitation can affect suture strength. However, 3 to 6 weeks are not sufficient for stable meniscal healing according to Kawai et al.20 Therefore, the result of a time-zero study can provide meaningful information for the establishment of appropriate rehabilitation protocols. Further biomechanical study combined with an in vivo animal study during a different postoperative period is required for clarification.
Double vertical sutures showed superior mechanical properties compared with cross and double horizontal sutures in the repair of radial meniscal tears, especially in the central zone. These biomechanical properties should be considered in determining appropriate rehabilitation protocols for each suture technique.
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Anatomical Data of Porcine Menisci
|Meniscal Dimension||Mean±SD, mm||P|
|Vertical Suture Group (n=20)||Cross Suture Group (n=20)||Horizontal Suture Group (n=20)|
Gap Configuration and Displacement After 500 Cycles Between 5 and 30 Na
|Suture Group||Gap Configuration||Mean±SD, mm|
|Central Gap||Peripheral Gap||Total Gap|
Ultimate Failure Load, Stiffness, and Mode of Failure
|Ultimate Failure Load, N||Stiffness, N/mm||Mode of Failure, Tissue:Suture|