New Suture Method for Radial Tears of the Meniscus

Materials and Methods

We tested 40 fresh human lateral menisci from patients who underwent total knee arthroplasty (TKA) because of varus knee osteoarthritis. The TKA procedure included excising the meniscus in its entirety as close as possible to the capsular tissue. All the menisci in our study were from the lateral compartment and had no macroscopic signs of meniscal tear or degeneration, such as fibrillation or fragmentation.

The cross-suture group (group A) contained 20 menisci from 20 patients (17 women, 3 men) with a mean age of 75.9 years (range, 68-84 years). The double horizontal suture group (group B) contained 20 menisci from 20 patients (17 women, 3 men) with a mean age of 75.7 years (range, 70-84 years). The study was approved by the ethics committee of the university. All patients were informed of the purpose of the study and gave their written consent. After being harvested during the surgical procedure, the menisci were kept in saline solution and tested within 24 hours. We practiced each of the suture techniques in 5 menisci before starting the study to ensure consistency in the suture techniques. For all 40 menisci, we used a No. 15 scalpel to create a complete radial tear from the meniscal center to the rim in the middle third of the meniscus, in the process completely transecting the meniscus at the junction of the body and the posterior horn of the meniscus.

Suture Techniques

All menisci were repaired with the same suture material (2-0 Prolene, Ethicon Inc, Johnson & Johnson, Somerville, New Jersey), which consists of 2 straight suture needles at both ends of the thread. In each group, we oriented the 4 points of the suture as follows: 2 points 5 mm from the meniscal rim and 5 mm from the tear, and the other 2 points 10 mm from the meniscal rim and 5 mm from the tear (Figure 1).

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Figure 1.

Group A: (1) Cross-suture technique. (2) Suturing cross over the 4 points: 2 points 5 mm from the meniscal rim and 5 mm from the tear, and the other 2 points 10 mm from the meniscal rim and 5 mm from the tear. Group B: (1) Double horizontal suture technique. (2) Suturing parallel to the 4 points: 2 points 5 mm from the meniscal rim and 5 mm from the tear, and the other 2 points 10 mm from the meniscal rim and 5 mm from the tear.

In the cross-suture group (group A), we repaired the meniscal tear by suturing 2 stitches that crossed over each other at the tear (Figure 1). We repaired the menisci in group B by the standard double horizontal suture technique with parallel sutures 5 mm and 10 mm from the meniscal rim (Figure 1). All sutures in both groups were secured by 3 knots at the lateral edge of the menisci.

Cyclic Load Testing

We loaded the specimens onto a universal testing machine and clamped the peripheral sections of the repaired meniscus with custom-made tissue clamps (Figure 2). Furthermore, we stitched baseball sutures through both ends of the meniscus using 4-0 Ethibond (Ethicon Inc, Johnson & Johnson) and securely fastened them to the clamps to prevent slippage. We performed a pilot study in 5 menisci of each suture technique to ensure that no rotation or slippage occurred between the meniscus-clamp interfaces during the procedure.

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Figure 2.

Two custom-made tissue clamps hold the specimen in place during cyclic load testing.

Testing was performed at room temperature, and samples were kept moist using normal saline to prevent desiccation. The specimens were cyclically preconditioned between 5 and 30 N at 1 Hz for 500 cycles at a displacement rate of 5 mm/min in accordance with the testing conditions that other researchers have described in previous studies.^4,8,20

Results

Ultimate Failure Load

The cross-suture technique specimens had a significantly higher failure load than did the double horizontal suture technique specimens (P < .05) (Table 1).

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Table 1

Ultimate Failure Load, Stiffness, and Displacement of Meniscal Repair Devices After 500 Cyclic Loading Between 5 and 30 N

	Ultimate Failure Load, N	Stiffness, N/mm	Displacement 1, a mm	Displacement 2, b mm
Cross-suture	78.96 ± 19.27	8.01 ± 1.54	5.74 ± 1.84	10.31 ± 3.56
Double horizontal suture	68.16 ± 12.92	6.46 ± 1.12	8.56 ± 2.39	10.77 ± 2.31

a

Displacement 1: displacement after cyclic load testing.

b

Displacement 2: displacement after load-to-failure test.

Discussion

Radial tears of the menisci are relatively common. Magee et al ²³ reported a 14% incidence of radial tears among 200 patients who underwent arthroscopy. Among these cases, the most frequent location was the midbody of the lateral meniscus.

Preserving meniscal anatomic structures whenever possible is important. Collagen fibrils in the main portion of the meniscus are oriented in a circular direction that transforms joint stress on the meniscus into circular stress. ³⁰ Because radial tears extending to the meniscal rim that completely transect the collagen fibrils lead to loss of hoop strain, the goal for repairing complete radial tears is to restore the hoop strain.

Although multiple case reports regarding the repair of radial meniscal tears have been published,^{9,12,16,27,28,35} few biomechanical studies have been performed on radial tear repairs. Herbort et al ¹⁶ conducted a biomechanical study analyzing the outcomes of complete radial meniscal tears that were repaired at different distances from the meniscal rim and tear edges with different numbers of sutures. Their analysis found that double horizontal suture techniques closer to the meniscal rim had stronger structural properties than single suture techniques on tears more distant from the meniscal rim.

However, uncertainty persists as to whether employing double horizontal suture techniques to repair complete radial tears can actually provide sufficient fixation strength to withstand physiological cyclic loading in vivo. Bedi et al ⁶ performed a cadaveric study and reported that partial meniscectomy led to further increase in contact pressure transmitted to the medial tibial plateau under physiological loads. Furthermore, double horizontal suture repair of a 90% tear did not restore the location of the pressure peak compared with the intact knee. Their measurements of the magnitude and location of peak contact pressure did not show any differences between a radial tear and the double horizontal suture repair. These findings suggest that menisci repaired by the double horizontal suture technique cannot play a role in load distribution because of gap formation under physiological loads. Therefore, we hypothesized that the cross-suture could achieve superior primary stability compared with the double horizontal suture.

The primary stability of meniscal repair for a complete radial tear is a key factor in determining success of the repair. To reduce the risk of suture rupture or tissue failure, we focused on the orientation of the sutures relative to the meniscal tear and particularly the relationship between the orientation of the sutures and the orientation of the collagen fibers. For example, several studies that have examined repair techniques for longitudinal meniscal tears have determined that the vertical suture technique provides superior ultimate strength over the horizontal suture technique, findings that have contributed to establishing vertical suturing as the gold standard for longitudinal meniscal fixation.^3,5,15,19

Similarly, it is suggested that the superiority of the cross-suture technique in the ultimate failure load and stiffness derives from the ability to capture a greater proportion of the semicircular-oriented meniscal collagen fibers because the direction of the sutures is oblique to the meniscal collagen fibers rather than parallel to the fibers, as is the case with the double horizontal technique.

Displacement after 500 cyclic loading was significantly smaller in the cross-suture technique than that in the double horizontal suture technique. These results suggest that cross-suturing reduces the likelihood of a subsequent “cheese-cut” tissue failure.

Cyclic loading protocols are thought to more closely imitate the usual loads to which the repaired menisci are subjected in vivo. In our study, we used a protocol similar to what previous researchers have used in their meniscus studies: 500 cycles between 5 and 50 N. Biomechanical testing was performed using a slow loading rate to simulate the stresses to which the meniscus might be subjected during early postoperative rehabilitation exercises and activities of daily living such as slow-speed walking, stair climbing or descending, and squatting. The loading range was selected to simulate known medial meniscal loads during the application of forces equivalent to a clinical examination under both ACL-intact and ACL-deficient conditions. ²⁹ However, pretest experiments in our laboratory found that setting the upper limit at 50 N led to very high rates of failure, making meaningful comparisons of study groups difficult. We therefore confined our testing of the study specimens to 500 cycles between 5 and 30 N.

Our study was limited by our decision to use human lateral menisci, taken from patients who received TKA. As a result, these human lateral menisci differed to some degree from each other with respect to degenerative changes, shape, thickness, and stiffness despite our efforts to select cases in which the cartilage and meniscus were well preserved in the lateral compartment. Before our human study, we tested porcine menisci, but their smaller size and greater thickness compared with human menisci made it difficult to load porcine menisci onto our cyclic testing machine. To our knowledge, our study is the first biomechanical study examining repair techniques for radial meniscal tears using fresh human menisci. Indeed, because previous studies have often used porcine or cadaveric menisci, one of the aims of our study was to collect data on fresh human menisci.

Another limitation to our study was that we used a nonphysiological method of loading. Our setup was a “worst case scenario” test, whereby the load is applied parallel to the axis of meniscal sutures and perpendicular to the tears. The real in vivo forces might be more complex, but the real forces are still unknown. We considered the main affecting force is the tensile force in radial tears and minimized the disruptive factors, such as shearing forces. The cross-suture group still had an average displacement of 5 mm after cyclic loading, which would not be conducive to clinical healing. However, we proved that the cross-suture technique could get more superior stability than the double horizontal suture technique in vitro. After this, the clinical relevance of this biomechanical study is important. Clinical and animal studies with appropriate controls are recommended to validate our findings in vivo and to determine the biological sequelae of the cross-suture technique under clinical conditions. Nonetheless, the significant improvement in biomechanical properties that we observed in conjunction with the minor modification in the technique of reorienting the sutures from parallel to cross still should provide encouragement for surgeons to consider utilizing the cross-suture technique in their clinical practice. In fact, this technique does not require any significant modification from the horizontal double suture in the arthroscopic surgical maneuvers.

Conclusion

Our study findings indicate that cross-suturing significantly improves the structural properties of complete radial meniscal repairs and appears to improve primary stability of the repaired meniscus compared with double horizontal suture techniques. Our new method for repairing radial tears could be a promising solution in both young and active patients.