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Address correspondence to Sean B. Sequeira, M.D., Department of Orthopaedic Surgery, MedStar Union Memorial Hospital, 3333 North Calvert St., Suite 400, Baltimore, MD 21218, U.S.A.
The objective of this study was to examine the impact of progressive radial tears in the lateral meniscal root on the lateral compartment contact forces and joint surface area through a range of motion of knee and evaluate the role of the meniscofemoral ligament (MFL) in preventing adverse tibiofemoral joint forces.
Methods
Ten fresh frozen cadaveric knees were tested using 6 experimental conditions (0% lateral meniscal posterior root tear, 25% tear, 50% tear, 75% tear, 100% tear, 100% tear and resection of MFL) at five flexion angles (0°, 30°, 45°, 60°, and 90°) under 100-1,000-N axial load. Contact joint pressure and lateral compartment surface area were measured using Tekscan sensors. Statistical analysis, including descriptive, ANOVA, and post hoc Tukey analysis, was performed.
Results
Progressive radial tears of the lateral meniscal root were not associated with an increase in tibiofemoral contact pressure or decrease in lateral compartment surface area. Complete lateral root tear and resection of MFL were associated with increased joint contact pressure (P < .001) at knee flexion angles of 30, 45, 60, and 90° and decreased lateral compartment surface (P < .001) at all knee flexion angles area compared to complete lateral meniscectomy alone.
Conclusion
Isolated complete tears of lateral meniscus root and progressive radial tears of the lateral meniscus posterior root were not associated with any change to tibiofemoral contact forces. However, additional resection of the MFL increased contact pressure and decreased lateral compartment surface area.
Introduction
Posterior root tears of the lateral meniscus are a common injury, often occurring concomitantly with anterior cruciate ligament (ACL) tears. Biomechanically, the medial and lateral menisci serve as a cushion in the tibiofemoral joint to minimize tibiofemoral contact forces, which can ultimately lead to cartilage degeneration and early osteoarthritis.
Although the role of the medial meniscus in maintaining tibiofemoral joint pressure and the surface area has been extensively studied, the role of the lateral meniscus and meniscofemoral ligament has not been fully elucidated.
Tibiofemoral contact pressure and joint surface area have been recognized as important kinematic parameters, as increased contact pressure and decreased joint surface area have been linked to cartilage degeneration and progression of osteoarthritis.
Prior studies pertaining to the lateral meniscus suggest that inferior leaf resection at 0 and 60° of knee flexion were associated with decreased contact area and increased peak contact pressure.
There is conflict in the literature regarding the role of the meniscofemoral ligament (MFL) in the distribution of knee joint contact forces, particularly in the setting of progressive lateral meniscal root tears.
The MFL has been previously shown to stabilize the root of the lateral meniscus, and recent studies have suggested that extrusion of the lateral meniscus can occur when the MFL is compromised.
A study that evaluated 5 cadaveric knee joints found that resection of the MFL led to worsening tibiofemoral contact forces, underscoring its importance in preventing the progression of knee osteoarthritis.
Another study evaluated the MFL and posterior root of the lateral meniscus in a porcine model and concluded that the 2 structures are complementary for tibiofemoral loads.
Complementary function of the meniscofemoral ligament and lateral meniscus posterior root to stabilize the lateral meniscus posterior horn: A biomechanical study in a porcine knee model.
The role of the MFL when the root of the lateral meniscus is progressively compromised is poorly understood.
The purposes of this study are to examine the impact of progressive radial tears in the lateral meniscal root on the lateral compartment contact forces and joint surface area through a range of motion of knee. A secondary aim of this investigation was to evaluate the role of the meniscofemoral ligament (MFL) in preventing adverse tibiofemoral joint forces. It was hypothesized that progressive radial tears will not increase tibiofemoral contact forces and decrease surface area, although adverse tibiofemoral contacts would occur only in the presence of a transected MFL.
Materials and Methods
Ten fresh frozen cadaveric knees with intact menisci, cruciate anatomy, and MFLs were used. Specimens with meniscal damage or cartilage degeneration beyond Outerbridge I were excluded.
The specimen preparation began with soft tissue dissection of the cadaveric knee. All muscles and tendons were removed and patellectomy was performed, taking care to preserve the collateral ligaments, cruciate ligaments, and menisci. Resin was used to pot the sample, which subsequently hardened overnight. An oscillating saw was used to create a lateral femoral condylar osteotomy, which allowed access to the lateral meniscus posterior root (Fig 1). Osteotomy has been previously reported to have no effect on the tibiofemoral load-bearing characteristics of the knee.
A standard knee pressure sensor device (Tekscan 4011) was placed underneath between the medial and lateral meniscus and the tibial plateau and was secured with two double-loaded Arthrex suture anchors to the anterior and posterior tibia. Calibration of the sensor device was performed, according to manufacturer’s recommendation.
Fig 1TekScan sensor placed following lateral condylar osteotomy to gauge tibiofemoral contact pressures in anticipation for various testing conditions.
The knee was mounted onto a Mini Bionix load frame using a 6° of freedom fixture (Fig 2). When the axial load was applied during testing, the load frame and fixture facilitated multiplanar rotation, replicating native knee arc of motion. Furthermore, this custom construct-ensured forces were directed axially and eliminated stress riser or shear in the construct, minimizing the potential effect of any extraneous forces on the system. The apparatus also neutralized the effects of coronal malalignment of the knee (Fig 3) and facilitated testing states in various degrees of knee flexion. The first reading taken was with the intact meniscus in 0° of flexion. Further readings for intact meniscus were taken in flexion angle of 30°, 45°, 60° and 90° of flexion. Progressive tears in the lateral meniscus were created until the lateral meniscus was completely torn. Finally, the MFL was resected with a concomitant complete tear of the lateral meniscus.
Fig 2Demonstrated of mounted specimen to prevent coronal malalignment and evaluate testing conditions in various degrees of knee flexion.
Fig 3Final mounted specimen with TekScan sensors in place with combined apparatus to appropriately control various forces to evaluate tibiofemoral contact forces.
The lateral meniscus posterior root attachment site was identified. The menisco-capsular junction was identified and served as the posterior boundary for the radial tear sectioning. A #15 scalpel was used to generate the radial tears 6 mm from the posterior root insertion. Successive sectioning was based upon the overall width of the native medial meniscus and was confirmed visually by two observers. Next meniscus sectioning was performed to 50%, and readings were taken again for various flexion angles as mentioned before. The sectioning was further carried to 75%, 100%, and 100% with resection of meniscofemoral ligament. The MFL was sectioned at its attachment with the meniscus. The final resection group was performed after complete meniscectomy, indicating that the full lateral meniscus had been excised. The medial meniscus was left undisturbed throughout lateral meniscus sectioning, resection of MFL, and subsequent testing.
Biomechanical Testing
The knees were loaded from 100 to 1000 N of compressive force along the tibial axis to simulate the force on the knee during normal ambulation at 5 different flexion angles of 0°, 30°, 45°, 60°, and 90°. Data were collected at a rate of 10 readings per second. A TekScan contact pressure map was generated for the lateral compartments of each knee following constant force application (Fig 4). Each knee was successively taken through axial load testing, and data were collected at each degree of knee flexion. Joint pressure and surface area were measured in the lateral compartment at flexion angles from 0 to 90°. A priori power analysis determined that 10 specimens would provide greater than 99% power to detect a statistically significant difference in peak contact pressure and joint surface area. Using a significance level of .01 and Bonferroni accounting of 5 major cross-comparisons to obtain an effect size of d = 1.33 performed similar to Geeslin et al., 10 specimens were required to achieve an appropriate power.
One-way repeated measures ANOVA with post hoc Tukey analysis was used to evaluate statistical significance. A P value ≤.05 was considered significant. Statistical analysis was performed using R statistical software package, RStudio (version 1.4.1717-3; Boston, MA).
Results
Eight male and two female cadavers were included. The average age was 77.2 (range: 58-94) years. At a flexion angle of 30° and 45°, progressive radial tear of the root of the lateral meniscus was associated with a gradual increase in tibiofemoral joint pressure (Table 1 and 2), although this relationship was not linear. Furthermore, resection of the MFL in tandem with complete root tear was associated with higher tibiofemoral joint pressure when compared to a complete root tear in isolation for 0°, 30°, 45°, 60°, and 90° of knee flexion (Tables 1 and 2). There were no significant differences in tibiofemoral joint pressure with progressive radial tearing of the root of the lateral meniscus at flexion angles 0°, 60°, and 90°.
Table 1The Association Between Progressive Radial Tears of the Lateral Meniscal Root and Resection of the MFL and Contact Pressure Across Various Knee Flexion Angles
Flexion Angle
Pressure with progressive increasing tear
Intact
50%
75%
100%
100% + MFL
P-value
0
1156.7±213.3
1105±160.5
1098.7±168.8
1059.9±204.5
1127.2±162.7
NS
30
1070.4±292.0
1069.5±294.8
1099.4±273.6
1098.8±250.7
1197±243.6
0.04
45
1127.8±251.5
1089.4±255.4
1073.1±231.2
1086.4±244
1377.3±445.5
0.02
60
1175.2±294.6
1130.4±333.7
1137.6±273.1
1139.8±238.0
1134.2±398.6
NS
90
1046.0±182.9
1028.8±228.6
1052.7±245.5
1081.7±389.3
1291.5±389.2
NS
NOTE. Boldface indicates statistical significance (P < .05). Various knee flexion angles is expressed as newton per millimeter squared.
Table 2Post Hoc Tukey Analysis of the Association Between Progressive Radial Tears of the Lateral Meniscal Root and Resection of the MFL and Contact Pressure Across Various Knee Flexion Angles
At all flexion angles, progressive radial tear of the root of the lateral meniscus was associated with a decrease in tibiofemoral lateral contact surface area (P = .001), found in Tables 3 and 4. Moreover, resection of the MFL in conjunction with a complete root tear was associated with a decrease in tibiofemoral lateral contact surface area compared to a complete root tear in silo at all flexion angles.
Table 3The Association Between Progressive Radial Tears of the Lateral Meniscal Root and Resection of the MFL and Lateral Joint Surface Area Across Various Knee Flexion Angles
Flexion Angle
Lateral Contact Surface Area With Progressive Increasing Tear
Table 4Post Hoc Tukey Analysis Between the Association Between Progressive Radial Tears of the Lateral Meniscal Root and Resection of the MFL and Lateral Joint Surface Area Across Various Knee Flexion Angles
In the present study, progressive radial tears of the root of the lateral meniscus were not associated with increased tibiofemoral contact pressure and decreased tibiofemoral lateral joint surface area. Moreover, resection of the MFL in tandem with complete meniscectomy was associated with increased tibiofemoral contact pressure and decreased tibiofemoral lateral joint surface area than when compared to complete meniscectomy alone. The authors are not aware of any previous studies that have evaluated the relationship between progressive tears of the lateral meniscus posterior root on tibiofemoral contact pressure and surface area. These findings provide insight into the role of the lateral meniscus posterior root and the MFL in preventing early chondral wear.
These findings suggest that progressive tears of the lateral meniscus did not produce increased tibiofemoral contact pressure or decrease in lateral joint surface area, which is consistent with the literature to date. A finite element analysis by Bao et al. demonstrated that a lateral meniscectomy alone does not adversely worsen tibiofemoral contact forces in isolation.
Similarly, a cadaveric study of 10 porcine knees found that despite the presence of a lateral meniscal root tear, there was no adverse effect on tibiofemoral contact pressure.
They further postulated that the biomechanical consequences of the knee and adverse tibiofemoral contact forces are dependent upon the integrity of the MFL. Finally, cadaveric studies comparing posterior root avulsions of the lateral meniscus to an intact state found no difference in lateral compartment surface area or contact pressure, further corroborating the present study’s findings.
It is interesting to note that the tibiofemoral contact pressure was different across the various treatment conditions at knee flexion angles 30° and 45°, but were notably the same at all other knee flexion angles. Interestingly, Geeslin et al. also found that at knee flexion angle 45°, repair of the lateral meniscus posterior root was unable to restore tibiofemoral contact pressures to the intact level of pressure. Although there is currently no biomechanical explanation for this phenomenon, it is theorized that at this point of knee flexion, the posterior root is especially important in stabilization of tibial translation and tibiofemoral contact pressure at midflexion.
Although future studies will need to more comprehensively characterize this finding, the present study demonstrates the stabilizing effect of the lateral meniscus in early flexion angles. This finding requires further exploration in order to translate it into clinically meaningful and impactful patient care.
Additionally, this study demonstrated that a complete resection of the lateral meniscus posterior root, in addition to resection of the MFL, was associated with an increase in tibiofemoral contact pressure and decrease in lateral joint surface area. These findings imply that the MFL is a critical structure in the prevention of adverse tibiofemoral biomechanics and progression of cartilage degeneration. The MFL has been implicated in the reduction of intra-articular pressure of the lateral compartment of the knee and may help to disperse hoop stresses to the femur.
Other studies have also found that a tear of the lateral meniscus posterior root only adversely impacts tibiofemoral contact forces when in the presence of an MFL tear.
This study’s biomechanical findings provide support for previous radiologic and biomechanical studies, which have suggested that the MFL exerts a stabilizing force on the root of the lateral meniscus.
This study’s biomechanical findings also correlate with the results of clinical studies that have evaluated lateral meniscal root tears. Shelbourne et al. concluded that there was no difference in long-term outcomes of patients with lateral meniscus posterior root tears that were left unaddressed during anterior cruciate ligament reconstruction (ACLR) compared to patients who underwent isolated ACLR without a concomitant lateral meniscal root tear.
Similar studies by the MOON group and Lee et al. also showed that lateral meniscus posterior root tears left in situ at the time of ACL reconstruction did not require reoperation at a minimum 6-year follow-up and had comparable clinical outcomes to isolated ACL injuries.
Clinical, radiological, and morphological evaluations of posterior horn tears of the lateral meniscus left in situ during anterior cruciate ligament reconstruction.
These clinical studies provide credence to this study’s findings, which failed to show significant increase in peak joint contact pressure or reduction in joint surface area with isolated complete tears of the lateral meniscus. Interestingly, there are no studies that specifically evaluate clinical or functional outcomes of patients with MFL resection. Further clinical studies are needed to determine the impact of a lateral meniscal root tear in combination with MFL injury on functional outcome scores.
Clinically, the findings of this study have important ramifications for surgical decision-making. By demonstrating that an isolated lateral meniscal root tear does not adversely change the contact pressure or surface area of the knee, the present study’s findings suggest that it may be reasonable to pursue nonoperative management in some patients with these isolated injuries. Furthermore, it is important to note that the posterior root of the lateral meniscus has a complete blood supply, thereby enhancing the healing potential of the root should a tear occur.
However, if a patient with a lateral meniscus posterior root tear demonstrates radiologic findings suggestive of concomitant MFL injury, the results of the present study and others suggest that operative treatment may be indicated to ameliorate the risk of cartilage degeneration.
However, these results require additional corroboration to translate to a clinical setting, since these results were performed at time 0. Furthermore, since the present study did not evaluate the posterior lateral root tear as a condition in isolation, we cannot comment as to whether that condition is associated with a secondary rupture of the MFL.
Limitations
This study does have limitations. Although the present study conformed to standard practice for a cadaveric laboratory study, it may not accurately reflect the biomechanical forces in a patient’s knee in the clinical setting. Moreover, the present study only evaluated static forces and likely does not accurately mimic the stresses a native knee experiences during rehabilitation and/or physical therapy. Furthermore, lateral meniscus root tears often occur concomitantly with an ACL tear—since the present study did not include a cadaveric specimen(s) with an ACL tear, the present findings may be limited when applying these results in a clinical setting. Meticulous evaluation of change in location of peak contact pressure was also not examined in this study, which may have important implications for cartilage thickness and, therefore, limit the generalizability of this study’s findings. Finally, this study only included axial loads to evaluate the impact of lateral meniscus and MFL on tibiofemoral contact forces and area—additional work should include rotational and combined forces to comprehensively understand how forces across the knee impact knee biomechanics.
Conclusion
Isolated complete tears of lateral meniscus root and progressive radial tears of the lateral meniscus posterior root were not associated with any change to tibiofemoral contact forces. However, additional resection of the MFL increased contact pressure and decreased lateral compartment surface area.
Complementary function of the meniscofemoral ligament and lateral meniscus posterior root to stabilize the lateral meniscus posterior horn: A biomechanical study in a porcine knee model.
Clinical, radiological, and morphological evaluations of posterior horn tears of the lateral meniscus left in situ during anterior cruciate ligament reconstruction.
The authors report the following potential conflicts of interest or sources of funding: H.P.G. reports editorial board membership in Arthroscopy. J.D. reports board or committee membership in AOSSM and research support from Zimmer. Full ICMJE author disclosure forms are available for this article online, as supplementary material.
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