Knee menisci help to provide optimal knee function and stability through load-sharing, stress distribution, and shock absorption. The meniscus is known to increase the contact area and decrease peak contact pressure in the tibiofemoral joint of the human knee1-4. A tear in the meniscus often causes mechanical symptoms of catching, locking, effusion, stiffness, and pain. When conservative nonoperative treatment fails, arthroscopy with partial medial meniscectomy is often performed for pain relief5,6. Partial meniscectomy is one of the most commonly performed orthopaedic procedures in the United States7. However, a partial meniscectomy is not completely benign. Several studies have revealed its negative effects on the knee joint4,8-10. Fairbank first noted an increased incidence of degenerative changes on knee radiographs after meniscectomy and questioned the sequela of meniscectomies9. Studies have examined the biomechanical sequela of sequential partial meniscectomies. Lee et al. showed that peak contact stresses increase proportionally to the amount of meniscus removed in their study of partial meniscectomies for vertical tears10. Bedi et al. showed that complete radial tears and partial meniscectomy result in decreased contact area and increased pressure4. However, there is limited information on what the effects of a horizontal cleavage tear (HCT) or partial leaf resection following an HCT have on tibiofemoral mechanics.
HCTs of the medial meniscus are common degenerative tears that often occur in late middle age11,12. An open meniscal repair technique was used by Sallé de Chou et al. on young patients, showing increased Lysholm and IKDC (International Knee Documentation Committee) scores on 2 to 10-year follow-up13. Pujol et al. saw similar results, but the success rate dropped significantly in patients >30 years old14. Arthroscopy with partial meniscectomy of either the inferior flap or both the inferior and superior flaps is a common surgical treatment for those who are not candidates for meniscal repair. It is unclear what the effects of these procedures are biomechanically on the knee joint. The following hypotheses were proposed: (1) HCT would result in a decrease in the contact area and an increase in peak contact pressure; (2) resection of the inferior leaf would decrease the contact area and increase peak contact pressure compared with the intact condition; (3) resection of both the inferior and superior leaves would decrease the contact area and increase peak contact pressure compared with the intact condition; (4) resection of both the inferior and superior leaves would decrease the contact area and increase peak contact pressure compared with the resection of the inferior leaf alone.
Materials and Methods
Fresh-frozen human cadaveric knees were thawed and inspected through a small arthrotomy for any signs of arthritis or meniscal or ligamentous damage. Preliminary data were obtained for 4 knees. Assuming the peak pressure change from the intact condition was 15% and the standard deviation was 14%, for paired comparison, 12 knees would give a power of 92.1%. Twelve fresh-frozen cadaveric knees without cartilage damage (6 male donors and 6 female donors; average age of 52 years [range, 22 to 73 years]) were selected for testing. The knees were stripped of all surrounding musculature as well as the patella, while preserving the posterior meniscocapsular attachment along with the supportive ligaments (Fig. 1). A standard paramedian longitudinal incision was made anteriorly to gain exposure of the joint, and the soft tissue surrounding the joint was elevated subperiosteally with a metal elevator to expose the femur and the tibia while preserving the meniscus along with the anterior cruciate ligament (ACL), the posterior cruciate ligament (PCL), the medial collateral ligament (MCL), and the lateral collateral ligament (LCL). A submeniscal arthrotomy was performed anteriorly and posteriorly to allow sensors to be inserted to capture the test results. An oblique osteotomy of the medial femoral condyle was performed by cutting from the posterior aspect of the condyle anteriorly using a saw blade in a similar technique to that reported by Martens et al.15. The osteotomy allowed access to the meniscus while preserving the ACL, PCL, MCL, and LCL, and was rigidly fixed using 2 screws placed perpendicular to the osteotomy for testing. The femur and tibia were cut 15 cm distal to the joint line to fit into the testing jig. A 6.5-mm suspensory rod was inserted through the transepicondylar axis to secure the knee in the testing jig and allow flexion and extension. The tibia was secured using an aluminum cylinder with multiple screws fixing the tibia rigidly from multiple radial directions and at multiple superior-inferior levels.
Each knee underwent testing using a custom mechanical testing jig with a linear actuator for loading the tibiofemoral compartments axially (Fig. 2). The load was applied through 2 threaded rods 12.7 mm in diameter, 1 on the medial and 1 on the lateral side of the knee, transmitting the axial load to the transepicondylar rod (Fig. 2). The threaded rods could be adjusted in the anteroposterior and superior-inferior directions to apply balanced load to the medial and lateral sides of the transepicondylar rod and to the femur. The aluminum cylinder holding the tibia was placed inside a matching flange, allowing the tibia to rotate about its long axis freely during loading. The flange was held rigidly in a vise, which was mounted on an x-y table, allowing the tibia to move freely in the anteroposterior and mediolateral directions during the axial loading. The free rotation and translations of the tibia in the horizontal plane avoided excessive tibial constraints during axial loading to ensure physiological loading during each test.
The peak axial load of 800 N was chosen because this represents the full body load during single-leg standing and provided consistent load on our testing jig without compromising the integrity of the femoral osteotomy. A knee-pressure sensor (model 4000; Tekscan) was used to measure the tibiofemoral contact area and contact pressure (Fig. 2). The sensor was calibrated between every 2 consecutive experimental conditions to a load of 800 N. The protocol was partially based on that of previous related studies16,17, with modification to allow additional degrees of freedom to ensure proper loading and pressure measurement.
Meniscal Testing Conditions
The prepared human cadaveric knees were tested under 10 conditions while being kept moist with saline solution during testing. Each knee underwent testing of 5 serial conditions of posterior medial meniscectomy (intact meniscus, HCT, repaired HCT, inferior leaf resection, and resection of both leaves), each with the knee at 2 flexion angles (0° and 60°) under the 800-N axial load. The 0° and 60° knee flexion angles were chosen because they are representative knee positions in the extended and flexed positions18. Knee flexion was checked with use of a goniometer.
Testing Condition 1
The intact meniscus was tested.
Testing Condition 2
Using a number-11 blade, an HCT was created 1 cm away from the medial root and extending to the root’s attachment to the MCL, creating a 100% HCT in the posterior third of the meniscus (Fig. 3-A).
Testing Condition 3
The HCT was repaired with 2-0 high-strength polyethylene suture (FiberWire; Arthrex) with an open inside-out meniscal repair technique using 2 vertical mattress stitches 8 mm apart (Fig. 3-B).
Testing Condition 4
The inferior leaf was resected using an arthroscopic biter toward the capsule with the peripheral rim left intact, similar to an arthroscopic resection of the inferior leaf. The inferior leaf was resected first in keeping with standard clinical practice (Fig. 3-C).
Testing Condition 5
Following the testing of the specimens, the superior leaf was then resected with a number-11 blade at the edge, leaving behind a rim at the meniscocapsular junction, creating the equivalent of a subtotal posterior meniscectomy (Fig. 3-D).
Statistical analyses were performed using SPSS Statistics (version 22; IBM), with p < 0.05 as the level of significance. A 2-way analysis of variance (ANOVA) with repeated measures was used to analyze the peak pressure and contact area across the 2 knee positions and 5 meniscal testing conditions. The contact pressure and contact area were compared with the measurements for the intact meniscal condition for each specimen. One-way ANOVA with repeated measures was used to compare the effects of the meniscal conditions at each of the knee flexion angles. Post-hoc analysis with Bonferroni correction was used in subsequent multiple comparisons among the meniscal testing conditions.
ANOVA showed that there were significant effects of the knee flexion angle (p < 0.001) and the meniscal testing condition on contact pressure (p = 0.001). Similarly, there were also significant effects of the knee flexion angle (p = 0.004) and the meniscal testing condition (p < 0.001) on contact area.
At 0° of knee flexion, HCT demonstrated a mean (and standard deviation) 94.0% ± 6.0% of the normalized contact area and 115.4% ± 19.4% of the normalized peak contact pressure compared with the intact meniscus; these differences between the HCT and intact conditions were not significant (p = 0.069 for contact area and p = 0.499 for contact pressure). At 60° of flexion, HCT demonstrated a mean 95.0% ± 11.7% of the normalized contact area and 106.3% ± 12.4% of the peak contact pressure compared with the intact meniscus; these differences were not significant (p > 0.05).
Repair of the horizontal tear resulted in a mean 93.5% ± 6.9% of the normalized contact area at 0° of flexion but 100.4% ± 6.2% restoration of the contact area at 60° of flexion (Fig. 4). Repair resulted in a mean peak contact pressure of 113.9% ± 15.4% at 0° flexion and 120.2% ± 15.9% at 60° of flexion compared with the intact meniscus (Fig. 5). Differences in the contact area and peak contact pressure between the intact and repaired meniscal conditions were not significant (p > 0.05).
The common surgical treatment of inferior leaf resection resulted in significantly decreased contact area in the medial compartment compared with that of intact meniscus (to a mean 82.3% ± 9.9% of the intact condition at 0° of flexion, p = 0.001; and 81.8% ± 16.2% of the intact condition at 60° of flexion, p < 0.05) (Figs. 4 and 6), and increased peak contact pressure compared with intact meniscus (a mean 36.3% ± 26.2% increase at 0° of flexion, p = 0.015; and 43.2% ± 20.6% increase at 60° of flexion, p < 0.001) (Figs. 5 and 6). Further resection of the superior leaf resulted in marked reduction in contact area compared with the intact meniscus (to a mean 60.1% ± 12.9% of the intact condition at 0° of knee flexion, p < 0.001; and 49.7% ± 16.8% at 60° of knee flexion, p = 0.002) (Figs. 4 and 6) and substantially increased peak contact pressure (a mean 79.2% ± 48.3% increase at 0° of flexion, p = 0.043; and 74.9% ± 33.6% increase at 60° of flexion, p < 0.001) (Figs. 5 and 6). Superior leaf resection was found to demonstrate a significant change in contact area compared with inferior leaf resection at 0° and 60° of flexion (p < 0.001 and p = 0.002, respectively) as well as a significant change in peak contact pressure (p = 0.043 and p < 0.001, respectively). Representative pressure maps from an individual knee at each of the 10 testing conditions are shown in Figure 6.
The medial meniscus plays an important role in load-bearing in the knee. This study showed that cutting the inferior leaf or the superior and inferior leaves resulted in significant decreases in contact area and significant increases in peak contact pressure (Figs. 5 and 6) compared with the intact condition, allowing us to accept both hypotheses 2 and 3. Arno et al. showed a significant increase in contact pressure of 13% and a significant decrease in contact area of 6% with HCTs19. In our study, a similar trend was observed, but these changes between the intact and HCT conditions were not significant, so hypothesis 1 was rejected. Our study then investigated the typical treatment of these tears with arthroscopic partial leaf meniscectomy. The resection of meniscal tissue forming the inferior leaf of an HCT resulted in significantly decreased contact area and significantly increased contact pressure. This result is consistent with the findings of other studies showing that partial meniscectomies result in significant changes in contact area and pressures that irreversibly change the tibiofemoral mechanics1,20-22. When Ode et al. looked at radial tears in the lateral meniscus, they showed that partial meniscectomy significantly changed contact area and pressure as well18. In our study, the additional resection of the superior leaf resulted in further alteration of tibiofemoral mechanics, with a significant decrease in contact area and a significant increase in peak contact pressure, allowing us to accept hypothesis 4 (Fig. 6). In a clinical study, Kim et al. investigated common meniscal-tear treatments, 2 types of partial meniscectomy and subtotal meniscectomy23. At 5 years of follow-up, narrowing of the joint space was shown in all 3 states. The partial meniscectomy conditions showed about a 10% reduction in joint space, while subtotal meniscectomy showed a 24% reduction in joint space. When considering that joint-space narrowing is associated with articular cartilage degradation, which tends to be caused by elevated peak pressure, our results for the conditions of inferior leaf resection and resection of both leaves are consistent with the findings of Kim et al.
Haemer et al. studied the difference between inferior leaf resection and resection of both leaves, showing an additional 15% reduction in contact area and a 27% increase in contact pressure with double-leaf resection24. Brown et al. conducted a similar biomechanical study and also found a significant increase in peak pressure when both leaves were resected, but did not find a significant reduction in contact area, as seen in our study, and instead observed a trend of increasing contact area from the intact condition to the condition of double-leaf resection25. A main function of the meniscus is to increase the tibiofemoral contact area and to cushion and spread axial joint loading. Therefore, the resection of both leaves should result in decreased contact area. As noted above, this was also reported by Haemer et al.24. The discrepancies could be due to differences in the experimental setups and protocols. Our system allowed the tibia to slide freely in the mediolateral and anteroposterior directions and rotate axially, avoiding artificial constraints during axial compressive loading. Furthermore, our system allowed for the adjustment of loading between the medial and lateral compartments and in the anteroposterior direction (as indicated by the arrows in Figure 2). These biomechanical changes after meniscectomy may be why Faunø and Nielsen reported that 53% of knees that underwent partial meniscectomy went on to have evidence of osteoarthritic changes on radiographs at 8 years of follow-up, while only 27% of the untreated contralateral knees progressed26. In a long-term follow-up study, Andersson-Molina et al. confirmed the changes reported by Fairbank; changes and joint-space narrowing were seen in 33% of partial meniscectomy and 72% of total meniscectomy patients 14 years postoperatively9,21.
Multiple long-term studies have demonstrated that it is common to develop arthritis following partial meniscectomy12,27-29. Consideration should be given prior to resecting one or both of the leaves of an HCT of the meniscus. Repair may partially restore some of the biomechanical properties of the intact meniscus; however, due to the avascular degenerative nature of many horizontal tears, the healing potential is often low. Enhanced techniques such as the use of fibrin clots to repair horizontal tears are encouraging, demonstrating a significant increase in mean Lysholm score postoperatively with complete healing seen in 70% of the patients on follow-up arthroscopy in one study30. A balance must be maintained between resecting a free edge that will cause a mechanical irritation and preserving tissue that will preserve the knee. A recent study exploring nonoperative treatment of HCTs suggested that there was no significant difference between meniscectomy and nonoperative treatment after 2 years in terms of knee pain, function, and patient satisfaction31. Herrlin et al. reported 5-year follow-up of the nonoperative treatment of degenerative meniscal tears, finding that patients who underwent nonoperative treatment had similar results to those of patients who underwent partial meniscectomy5. Thus, minimal debridement and the reconsideration of partial meniscectomies are warranted, especially in the younger population that may be at risk for arthritis in the future.
We recognize that ours was a biomechanical study performed using cadaveric specimens and thus, our findings may not be completely applicable to in vivo conditions. The tear was created in a simple horizontal fashion and did not involve any complex degenerative component sometimes present in HCTs. Considering that this study focused on the contact pressure of the tibiofemoral joint and not various tears themselves, the tear created was a proper representation of both trauma-induced and degenerative horizontal tears. The meniscal repair was performed as an open inside-out repair with the knee completely exposed, which allowed perfect repair with visualization of reduction, which is different from that experienced in vivo. The inferior leaf meniscectomy was also performed in an open manner instead of arthroscopically; however, we simulated arthroscopic surgery utilizing an arthroscopic biter for the procedure. Dissection of the soft tissues from the knee may have eliminated some inherent stability, thus affecting the contact pressure that may be present with intact soft-tissue structures. The testing jig also had a limited direction of load, limiting the natural translation and rotation inherent in a normal knee. The loads chosen and conditions were similar to those previously described3,4,18; however, these may not reflect the conditions present in vivo. Testing was performed in a static position without dynamic movement, which may have affected the way the meniscus was loaded. Our study only shows the immediate effect of a tear or partial meniscectomy and does not simulate the results after healing of the repair or meniscectomy in the knee. Tekscan sensors are known to be sensitive to temperature changes, and efforts were made to keep the testing environment uniform during testing. The performance of the Tekscan sensors decreased during testing, so they were calibrated between every 2 consecutive experimental conditions to minimize pressure-measurement errors.
In conclusion, nonoperative treatment of an HCT may be a preferred first step, but if further treatment is necessary, repair or minimal resection of meniscal tissue of an HCT may be preferred to a complete leaf resection to avoid excessive tibiofemoral contact pressure.
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