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.
Investigation performed at the NorthShore University Health System, Evanston, Illinois
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