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Contact analysis of horizontal cleavage tear treatment.

Abstract

Horizontal cleavage tears (HCT) commonly occur in the posterior horn of the medial meniscus due to aging and degeneration. The purpose of this study was to investigate the surgical treatment of HCTs and their effect on dynamic tibiofemoral contact mechanics. The tibiofemoral contact mechanics of 10 cadaver knees were investigated using a custom dynamic loading apparatus, pressure sensor, and motion sensing camera. Three loading conditions were analyzed: 500 N compressive load, 500 N compressive load with 100 N posterior shear, and 500 N compressive load with 2.5 Nm of internal torque. Real-time peak contact pressures and contact areas were recorded throughout the full range of motion. After testing the intact meniscal state, a horizontal cleavage tear was created and included 50% of the width of the meniscus. The following procedures were performed, and the loading conditions described above were analyzed: HCT superior flap removal (5 specimens), HCT inferior flap removal (remaining 5 specimens), and both flaps removed (all 10 specimens). Statistical analysis was performed using a mixed linear effects model using the R-statistical package. The mixed linear effects statistical model identified statistically significant differences between independent variables, including the procedure performed, meniscal flap removed, meniscal region, loading condition, and knee flexion angle with respect to contact area and peak contact pressure. Peak contact pressure and contact area were not affected by selective flap removal (superior vs. inferior) or removal of both flaps of the HCT. We recommend that in the treatment of horizontal cleavage tears of the posterior horn of the medial meniscus, the outer 50% of the posterior horn of the medial meniscus should be maintained for load transmission.

The medial meniscus of the human knee is important for load distribution to the articular cartilage and surrounding soft tissues. It is estimated that the medial meniscus is involved in distributing 60% of the knee's load. (1,2) Injury to the meniscus disrupts the normal contact mechanics of the knee by altering the distribution of stresses to the underlying articular cartilage. A deficiency in meniscal function can be caused by trauma but also by arthroscopic partial meniscectomy. Meniscectomy decreases the overall contact area and increases peak contact pressures on tibial cartilage. (3-6) Altered contact mechanics in the knee are believed to result in Fairbank changes that characterize degenerative osteoarthritis (OA): sclerosis, joint space narrowing, squaring of the tibial margin, flattening of the femoral condyles, and osteophyte formation. (7,8)

Horizontal cleavage tears (HCT) are degenerative tears often found in the posterior horn of the medial meniscus and are believed to be the result of shear force fatigue in older patients. (9,10) These lesions result in a meniscus separated into a superior and inferior flap. (10,11) HCT have been shown to be associated with an increased risk of OA. (11,12) Arno and coworkers investigated alterations in tibiofemoral contact mechanics due to HCT pathology of the posterior horn of the medial meniscus. (13) In this follow-up study, we aim to investigate the treatment of HCT lesions and their effect on tibiofemoral contact area and peak contact pressures throughout the range of motion. This study utilized the same specimens as Arno and coworkers but evaluates the surgical treatment of HCT lesions as opposed to the HCT pathology that was described. (13) We hypothesize that partial meniscectomy of either the superior or inferior flap of a horizontal cleavage tear will result in increased contact pressures on the uncovered cartilage and on the remaining posterior horn of the meniscus.

Materials and Methods

Ten fresh frozen human cadaveric knee specimens (7 male and 3 female; 3 left and 7 right) with average age of 77 years (range: 55 to 91 years) were obtained. Subcutaneous soft tissues were removed from each cadaveric specimen until the knee capsule was reached; all ligaments and the quadriceps tendon were preserved. Afterward, each specimen underwent MR imaging on a Siemens MAGNETOM Skyra 3 Tesla (3T) MRI machine (Siemens, Malvern, PA) with a 15 channel transmit and receive knee coil, including two sequences:

1. 3D-Proton Density-Non-Fat Suppressed-SPACE (Sampling Perfection with Application optimized Contrasts using different flip angle Evolutions) sequence (flip angle = 120[degrees]; repetition time (TR) = 1,000 msec; echo time (TE) = 46 msec; bandwidth = 460 Hz/pixel; Field of View (FOV) = 160 mm x 160 mm; matrix size = 320 x 300 pixels; voxel size = 0.5 x 0.5 x 0.5 mm (3) ) and

2. 3D-T2* mapping with Gradient Echo (GRE) sequence (TR = 30 msec; TE = 10 echoes (2.01 msec - 25.50 msec); flip angle = 25[degrees];, bandwidth = 450 Hz/pixel; FOV = 220 mm x 84.4 mm; matrix size = 384 x 100; voxel size = 0.6 x 0.6 x 0.6 mm (3)). These sequences were obtained to verify the integrity of the cartilage and ligaments and the meniscus, respectively.

In order to assess dynamic contact mechanics of the knee, the testing apparatus (Fig. 1) described by Arno and coworkers was implemented. (13,14) This system has three major components: a mechanical apparatus to mount the specimen and apply a full range of motion, an optical motion tracking system (MicronTracker Sx60, ClaroNav Technology Inc., Toronto, Ontario, Canada) to quantify the range of motion, and a thin (0.1 mm) pressure sensor (4,011 N, Tekscan Inc., Boston, MA) to record peak pressures and total contact area. The femur and tibia were fixed to the testing apparatus using cemented intramedullary rods and screws; the tibia was positioned vertically, and the femur was positioned such that the epicondylar axis was horizontal.

Two transverse rods were placed in the femoral frame in-line with the epicondyles. Cables were connected from the rods to the servo motors in order to apply compression, shear, and torque. Normal patellar tracking through the range of motion was accomplished by quadriceps tensioning using Krackow suturing through the quadriceps and attached via cables to the testing apparatus. Elastic bands in combination with cabling from a pneumatic cylinder were used to take each specimen through the full range of motion (-5[degrees]; to 135[degrees];, unless anatomically blocked) dynamically in 15 seconds. The MicronTracker optical motion tracking system using black and white targets on the femoral frame was used to track the specimen through the range of motion.

With the cadaveric specimen mounted in the testing apparatus, an anterior arthrotomy was carefully created under the medial and lateral menisci being sure to avoid disrupting the anterior root attachments and patellar tendon. A thin (0.1 mm) Tekscan pressure sensor was inserted below the menisci and held in place with sutures through the posterior capsule. Prior to insertion, each sensor was equilibrated, calibrated, and conditioned according to the manufacturer's recommendations. The I-Scan software (Tekscan Inc., Boston, MA) was used to record measurements from the pressure sensor throughout the range of motion.

Each medial meniscus intact specimen was taken through its full range of motion starting at full extension and pro gressing to full flexion (135[degrees];) for one cycle. During the range of motion, one of three loading conditions was applied in the following order: 500 N compressive load, 500 N compressive load with 100 N posterior shear (PS), and 500 N compressive load with 100 N of internal torque (IT). The compression-shear and compression-torque ratios used were based on the instrumented knee data from Heinlein and colleagues and D'Lima and associates. (15,16) The force combinations were performed in the same order for each specimen. Using the synchronized motion capture system and pressure sensor, the knee position and corresponding pressure and contact area data were continuously recorded through the range of motion. The intact meniscus (prior to HCT lesion) serves as a reference for the cases of superior, inferior, and both meniscal flap removal that follow.

After testing of the knees with an intact medial meniscus, a horizontal cleavage tear was created arthroscopically with a Beaver [R] Mini-Blade (Beaver-Visitec International Inc., Waltham, MA) in the posterior horn of the medial meniscus by an orthopaedic surgeon as described by Arno and coworkers (13) (Fig. 2A-C). This lesion equally divided the meniscus into superior and inferior flaps, extending 70% of the total length of the posterior horn starting 0.5 cm from the root attachment. The tear included 50% of the width of the posterior horn; the width was determined by MRI for each subject. After creation of the HCT lesion, five specimens underwent removal of the superior flap, and five specimens underwent removal of the inferior flap using standard arthroscopic instrumentation (Fig. 2D). A new pressure sensor was positioned, and the above mentioned testing protocol was repeated. Next, the remaining superior or inferior flap was removed arthroscopically using standard arthroscopic instrumentation (Fig. 2E). Again, a new pressure sensor was positioned and the testing protocol was repeated.

To verify the reproducibility of the sensors, the tests were repeated under the 500 N compression, 500 N compression with 100 N PS, and 500 N compression with 2.5 Nm IT in six intact knees. The average error between the two trials was determined for peak contact pressure and contact area.

After completion of testing, the cadaveric knee was stripped of all pericapsular soft tissues. Using a probe, the inner boundary of the medial meniscus on the sensor was mapped in the I-Scan software. Based on this map of the unloaded meniscus, four regions were defined on the pressure maps from testing: 1. Anterior region--anterior meniscal horn contained, 2. Central region--central meniscal body contained, 3. Posterior region--posterior meniscal horn contained, and 4. Uncovered cartilage--where no meniscus was contained (Fig. 3). For the three loading conditions, the peak contact pressure and total contact area were recorded in each region of the medial compartments at -5[degrees]; and then in 15[degrees]; increments from full extension to 135[degrees]; of flexion.

In order to evaluate differences of independent variables (predictors) in repeated measurements on contact area and peak contact pressure, a linear mixed-effect model was used. The statistical model was designed to evaluate contact area and peak contact pressure as a function of these independent variables within specimens. A random statement with study knees (subjects) as the random effect was included to account for the correlation within knees (subjects) because of the repeated nature of the data. Statistical analysis was conducted using the R-statistical package (www.r-project.org) using the linear and nonlinear mixed effects models (nlme) package to generate the mixed model. Statistical significance of p < 0.05 was considered to be relevant.

Results

The pre-testing MRI using the 3D-Proton Density-Non-Fat Suppressed-SPACE sequence demonstrated that all specimens contained fully intact ligamentous structures. The T2* mapping with Gradient Echo (GRE) sequence which was confirmed at the time of arthroscopy demonstrated fibrillation in three menisci, and mild intra-substance degeneration was present in the remaining seven menisci. The region of greatest meniscal degeneration was the posterior horn.

The pressure sensor reliability study indicated that the average discrepancy between trials was 18.43 [+ or -] 15.47 KPa for peak contact pressure and 0.02 [+ or -] 0.02 cm (2) for contact area. Tables 1 and 2 provide peak contact pressure and contact area averaged for all knees and angles for each loading condition, respectively. Figure 4 demonstrates one example of the pressure map of the medial portion of the tibial plateau with the pre-defined meniscal regions.

The mixed linear effects statistical model identified statistically significant differences between independent variables, including the procedure performed, portion of meniscus removed, meniscal region, loading condition, and angle with respect to contact area (Table 3) and peak contact pressure (Table 4). With regard to the performed procedure, there was a difference in contact area but not peak pressure between the intact state, HCT flap removed state, and both HCT flaps removed (all p < 0.001). With respect to the portion of the meniscus that was removed, there was no significant difference between the superior and inferior flap being removed with regard to contact area and peak contact pressure. There was, however, a difference between removal of the inferior flap and the intact state, removal of the superior flap and the intact state, and removal of both flaps and the intact state with regard to contact area but not peak contact pressure (all p < 0.001).

With regard to the meniscal region, there was statistically significant differences between each of the regions and the anterior horn of the meniscus both with regard to contact area and peak contact pressure (all p < 0.001). With regard to loading condition, there was no significant difference between compression and compression with IT; however, there was significant difference between compression versus compression with PS and compression with PS versus compression with IT with regard to contact area (p < 0.001, p < 0.006) and peak contact pressure (p < 0.015, p < 0.019). With regard to angle of the arc of motion, there was statistically significant differences identified in both contact area and peak contact pressure throughout the arc of motion and also between multiple positions with respect to full extension.

Discussion

The arthroscopic treatment of horizontal cleavage tears is common as these degenerative tears comprise at least 50% of all meniscal tears and are correlated with chondral defects and other traumatic tears. (11,12,17) The postoperative contact mechanics of the treatment of HCT has not been previously reported to our knowledge. Herein, we suggest that treatment of HCTs alter the contact area and peak contact pressure of the medial meniscus, but treatment with selective flap removal is not statistically different from removal of both HCT flaps when 50% of the width of the posterior horn of the medial meniscus is involved.

With regard to contact area, our data shows a trend toward decreasing contact area in the posterior horn with progressive removal of the HCT lesion in all three loading conditions and procedures; this change was expected and correlated with arthroscopic removal of the meniscal flap during the procedure and resulted in statistically significant differences in nearly all conditions that were tested. On closer examination of the mean contact area values shown in Table 1, it should be noted that the anterior horn, central body, and uncovered cartilage regions show relatively stable contact areas especially when considering the associated standard deviations. The statistical comparison between contact area between the superior and inferior HCT flap removal demonstrated no significant difference between the procedures. Given the inner 50% of the meniscus was involved in our HCT lesion, our results suggest that the outer (peripheral) 50% of the meniscus carries the bulk of the load with regard to contact area throughout the dynamic range of motion and the tested loading conditions.

With regard to peak pressure, there was no significant difference in peak pressures between the removal of the superior and inferior HCT flap. There was also no significant difference between removal of a single flap and both flaps with regard to peak contact pressures. This further supports our assertion that the outer 50% of the meniscus carries the bulk of the load throughout the dynamic range of motion and the tested loading conditions.

Arno and colleagues is the only published study that the investigators are aware of that has investigated contact mechanics of HCT of the posterior horn of the medial meniscus. (13) This study demonstrated small increases in peak contact pressure and decreases in contact area in this pathology. They suggest that these subtle alterations in joint mechanics may be a factor in cartilage degeneration and progression of osteoarthritis changes over many years.

Kim and colleagues performed a clinical outcome study on patients who underwent partial meniscectomy, horizontal cleavage tear flap removal, or subtotal meniscectomy for HCT. (18) This study investigated 312 patients with clinical function scores with a follow-up of 5 years; they also evaluated radiographs of these patients. They demonstrated that horizontal cleavage lesion flap removal resulted in the least amount of joint space narrowing in comparison to the other procedures. Furthermore, they demonstrated no statistically significant differences in functional outcome scores between partial meniscectomy and HCT flap removal but inferior scores for subtotal meniscectomy.

Our study has demonstrated statistically significant differences in peak contact pressure and contact area with regard to loading condition, contact region, and performed procedure. Our results suggest that the outer 50% of the posterior horn of the medial meniscus supports the majority of the load as inferior HCT, superior HCT, and both HCT flap removal did not result in statistically significant differences in contact area and peak contact pressure. This study did not investigate the effect of flap removal on joint stability; however, others have found that resection of greater than 46% of the posterior horn of the medial meniscus results in increased joint laxity. (14)

Changes in contact area and contact pressure after partial meniscectomy affect joint function but may take many years to develop measureable osteoarthritic changes. Kim and colleagues has described that functionally no differences may be seen in the first 5 years. (18) This study finds no difference in removal of the inner 50% of the inferior flap, superior flap, or both HCT flaps with regard to contact area and peak contact pressure. This study did not evaluate the outer 50% of the posterior horn of the medial meniscus, which is a limitation. Other limitations of this study are inherent to the use cadaveric tissues and small sample size.

Conclusion

Horizontal cleavage tears (HCT) are degenerative tears often found in the posterior horn of the medial meniscus and have been shown to be associated with an increased risk of OA. We have demonstrated that statistically significant changes to peak contact pressure and contact area are associated with treatment of HCT lesions in comparison to the intact meniscus. In this study, peak contact pressure and contact area were not statistically different between selective flap removal (superior vs. inferior) and removal of both flaps. When making intraoperative decisions, at least the outer 50% of the posterior horn of the medial meniscus should be maintained for load transmission. This raises important clinical questions about the role of horizontal cleavage meniscal repair versus subtotal meniscectomy.

Acknowledgments

We thank Daniel Hennessy, Daniel F. Martinez, and Michael Lowry for their contributions to the design and construction of the testing apparatus.

Disclosure Statement

None of the authors have a financial or proprietary interest in the subject matter or materials discussed, including, but not limited to, employment, consultancies, stock ownership, honoraria, and paid expert testimony.

References

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(7.) Roos H, Lauren M, Adalberth T, et al. Knee osteoarthritis after meniscectomy: prevalence of radiographic changes after twenty-one years, compared with matched controls. Arthritis Rheum. 1998 Aug;41(4):687-93.

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(10.) Peters TJ, Smillie IS. Studies on the chemical composition of the menisci of the knee joint with special reference to the horizontal cleavage lesion. Clin Orthop Relat Res. 1972 Jul-Aug;86:245-52.

(11.) Christoforakis J, Pradhan R, Sanchez-Ballester J, et al. Is there an association between articular cartilage changes and degenerative meniscus tears? Arthroscopy. 2005 Nov;21(11):1366-9.

(12.) Noble J, Turner PG. The function, pathology, and surgery of the meniscus. Clin Orthop Relat Res. 1986 Sep;(210):62-8.

(13.) Arno S, Bell CP, Uquillas C, et al. Tibiofemoral contact mechanics following a horizontal cleavage lesion in the posterior horn of the medial meniscus. J Orthop Res. 2015 Apr;33(4):584-90.

(14.) Arno S, Hadley S, Campbell KA, et al. The effect of arthroscopic partial medial meniscectomy on tibiofemoral stability. Am J Sports Med. 2013 Jan;41(1):73-9.

(15.) Heinlein B, Kutzner I, Graichen F, et al. ESB Clinical Biomechanics Award 2008: Complete data of total knee replacement loading for level walking and stair climbing measured in vivo with a follow-up of 6-10 months. Clin Biomech (Bristol, Avon). 2009 May;24(4):315-26.

(16.) D'Lima DD, Patil S, Steklov N, et al. In vivo knee moments and shear after total knee arthroplasty. J Biomech. 2007;40 Suppl 1:S11-7.

(17.) Noble J, Hamblen DL. The pathology of the degenerate meniscus lesion. J Bone Joint Surg Br. 1975 May;57(2):180-6.

(18.) Kim SJ, Lee SK, Kim SH, et al. Does decreased meniscal thickness affect surgical outcomes after medial meniscectomy? Am J Sports Med. 2015 Apr;43(4):937-44.

Caption: Figure 1 Dynamic knee contact mechanics testing rig with knee in full extension (left) and 135[degrees] of flexion (right).

Caption: Figure 2 Arthroscopic images of the posterior horn of the medial meniscus demonstrating A, an intact meniscus, B, a pediatric Beaver [R] blade creating a HCT, C, an HCT, D, the superior flap of the HCT removed, and E, both flaps of the HCT lesion removed. To view this figure in color, see www.hjdbulletin.org.

Caption: Figure 3 The Tekscan sensor was divided into four regions based on the unloaded position of the meniscus on the tibial plateau measured directly after dissection of each specimen: anterior, central, and posterior meniscus portions, and uncovered cartilage on the tibial plateau. To view this figure in color, see www.hjdbulletin.org.

Caption: Figure 4 Tekscan peak contact pressure maps following application of 500 N compression from one knee at full extension (top row), 60[degrees] flexion (middle row), and 120[degrees] flexion (bottom row) for the cases of the intact (left column), HCT flap removed (middle column), and both HCT flaps removed (right column) cases of the posterior horn of the medial meniscus. To view this figure in color, see www.hjdbulletin.org.

Carlos A. Uquillas, M.D., Sally Arno, Ph.D., Austin J. Ramme, M.D., Ph.D., Cheongeun Oh, Ph.D., Peter S. Walker, Ph.D., and Robert J. Meislin, M.D.

Carlos A. Uquillas, M.D., Sally Arno, Ph.D., Austin J. Ramme, M.D., Ph.D., Peter S. Walker, Ph.D., and Robert J. Meislin, M.D., Department of Orthopaedic Surgery, New York University Hospital for Joint Diseases, New York, New York. Cheongeun Oh, Ph.D., Department of Environmental Medicine, NYU School of Medicine, New York, New York

Correspondence: Robert J. Meislin, M.D., Department of Orthopaedic Surgery, NYU Langone CMC, 333 East 38th Street, 4th Floor, New York, New York 10016; robert.meislin@nyumc.org.
Table 1 Overall Mean (Standard Deviation) of the Contact Area for Each
Loading Condition, Meniscus State, and Meniscal Region Across the Arc
of Motion

Region               Loading Condition  MCA Intact Knee   MCA Superior
                                             (cm(2))      HCT Flap
                                                          Removed
                                                          (cm(2))

Anterior Horn        Comp               0.64 (0.59)       0.72 (0.52)
Central Body         Comp               0.93 (0.26)       0.87 (0.31)
Posterior Horn       Comp               1.17 (0.67)       1.65 (0.60)
Uncovered Cartilage  Comp               1.17 (0.68)       1.01 (0.72)
Anterior Horn        Comp + PS          0.72 (0.58)       0.72 (0.53)
Central Body         Comp + PS          0.92 (0.29)       0.86 (0.31)
Posterior Horn       Comp + PS          1.59 (0.65)       1.62 (0.55)
Uncovered Cartilage  Comp + PS          0.98 (0.65)       0.87 (0.71)
Anterior Horn        Comp + IT          0.82 (0.71)       0.86 (0.61)
Central Body         Comp + IT          0.92 (0.31)       0.92 (0.30)
Posterior Horn       Comp + IT          1.57 (0.68)       1.63 (0.55)
Uncovered Cartilage  Comp + IT          1.10 (0.63)       1.02 (0.66)

Region               MCA Inferior HCT   MCA Both HCT
                     Flap Removed       Flaps Removed
                     (cm(2))            (cm(2))

Anterior Horn        0.64 (0.60)        0.63 (0.57)
Central Body         0.93 (0.36)        0.92 (0.30)
Posterior Horn       1.17 (0.71)        1.36 (0.68)
Uncovered Cartilage  1.17 (0.67)        1.01 (0.67)
Anterior Horn        0.57 (0.55)        0.60 (0.53)
Central Body         0.84 (0.33)        0.86 (0.31)
Posterior Horn       1.30 (0.78)        1.33 (0.70)
Uncovered Cartilage  0.99 (0.68)        0.85 (0.62)
Anterior Horn        0.64 (0.59)        0.66 (0.62)
Central Body         0.86 (0.35)        0.89 (0.37)
Posterior Horn       1.31 (0.79)        1.33 (0.65)
Uncovered Cartilage  1.09 (0.57)        0.89 (0.57)

MCA = mean contact area, Comp = 500 N compression, Comp + PS = 500 N
compression and 100 N posterior shear, Comp + IT = 500 N compression
and 2.5 Nm internal torque.

Table 2 Overall Mean (Standard Deviation) of the Peak Contact Pressure
for each Loading Condition, Meniscus State, and Meniscal Region Across
the Arc of Motion

Region               Loading    MPCP Intact Knee   MPCP Superior HCT
                     Condition  (KPa)              Flap Removed (KPa)

Anterior Horn        Comp         317.36 (422.50)    401.13 (513.31)
Central Body         Comp         734.32 (500.66)    838.94 (539.51)
Posterior Horn       Comp       1,042.28 (809.09)  1,069.67 (642.62)
Uncovered Cartilage  Comp       1,192.38 (891.95)  1,000.48 (810.85)
Anterior Horn        Comp + PS    281.06 (351.04)    346.36 (420.38)
Central Body         Comp + PS    639.65 (528.96)    715.96 (581.21)
Posterior Horn       Comp + PS  1,262.94 (964.85)  1,221.35 (594.79)
Uncovered Cartilage  Comp + PS  1,032.29 (723.10)    921.39 (818.87)
Anterior Horn        Comp + IT    423.95 (526.83)    542.27 (622.75)
Central Body         Comp + IT    614.81 (608.31)    678.29 (558.62)
Posterior Horn       Comp + IT  1,030.29 (717.53)  1,217.56 (693.12)
Uncovered Cartilage  Comp + IT  1,260.20 (899.23)  1,203.17 (778.79)

Region               MPCP Inferior HCT    MPCP Both HCT
                     Flap Removed (KPa)   Flaps Removed (KPa)

Anterior Horn          245.09 (362.29)      279.41 (382.12)
Central Body         1,169.42 (1,522.94)    923.44 (851.07)
Posterior Horn       1,056.64 (1,205.37)  1,148.16 (1,143.22)
Uncovered Cartilage  1,658.48 (1,488.35)  1,198.62 (963.87)
Anterior Horn          202.64 (251.69)      252.29 (354.42)
Central Body           781.46 (801.31)      788.89 (770.48)
Posterior Horn       1,289.60 (1,230.24)  1,253.28 (1,213.17)
Uncovered Cartilage  1,026.25 (821.72)    1,148.26 (1,240.37)
Anterior Horn          251.95 (314.12)      370.73 (491.60)
Central Body           704.74 (953.04)      932.57 (1,165.67)
Posterior Horn       1,116.53 (1,036.92)  1,310.29 (971.14)
Uncovered Cartilage  1,416.99 (1,358.39)  1,087.76 (839.05)

MPCP = mean peak contact pressure, Comp = 500 N compression, Comp + PS
= 500 N compression and 100 N posterior shear, Comp + IT = 500 N
compression and 2.5 Nm internal torque.

Table 3 Mixed Linear Model on Contact Area Demonstrating Independent
Variables, Comparisons, and the Corresponding Statistical Coefficient
and P-value

Independent        Comparison                   Coefficient    P-value
Variable                                          (SD)


Procedure          HCT Flap Removed vs.          -0.07 (0.02)  < 0.001
                   Intact
                   Both HCT Flaps Removed        -0.14 (0.02)  < 0.001
                   vs. Intact
                   HCT Flap Removed vs. Both      0.07 (0.02)  < 0.001
                   HCT Flaps Removed

Removed Meniscus   Both Flaps vs. Intact         -0.14 (0.02)  < 0.001
                   Inferior Flap vs. Intact      -0.07 (0.02)    0.007
                   Superior Flap vs. Intact      -0.06 (0.02)    0.005
                   Superior Flap vs. Inferior     0.08 (0.16)    0.593
                   Flap

Region             Central Body vs. Anterior      0.24 (0.02)  < 0.001
                   Horn
                   Posterior Horn vs. Anterior    0.76 (0.02)  < 0.001
                   Horn
                   Uncovered Cartilage vs.        0.31 (0.02)  < 0.001
                   Anterior Horn

Loading Condition  Comp + IT vs. Comp            -0.01 (0.02)    0.518
                   Comp + PS vs. Comp            -0.06 (0.02)    0.001
                   Comp + PS vs. Comp + IT       -0.05 (0.02)    0.006

Angle              All Measured Angles           -0.04 (0.003  < 0.0001
                   -5[degrees] vs. 0[degrees]     0.04 (0.04)    0.234
                   15[degrees] vs. 0[degrees]    -0.11 (0.03)    0.001
                   30[degrees] vs. 0[degrees]    -0.19 (0.03)  < 0.001
                   45[degrees] vs. 0[degrees]    -0.22 (0.03)  < 0.001
                   60[degrees] vs. 0[degrees]    -0.24 (0.03)  < 0.001
                   75[degrees] vs. 0[degrees]    -0.26 (0.03)  < 0.001
                   90[degrees] vs. 0[degrees]    -0.28 (0.03)  < 0.001
                  105[degrees] vs. 0[degrees]    -0.31 (0.03)  < 0.001
                  120[degrees] vs. 0[degrees]    -0.35 (0.03)  < 0.001
                  135[degrees] vs. 0[degrees]    -0.38 (0.03)  < 0.001

Table 4 Mixed Linear Model on Peak Contact Pressure Demonstrating
Independent Variables, Comparisons, and the Corresponding Statistical
Coefficient and P-value

Independe   Comparison                    Coefficient        P-value
Variable                                     (SD)


Procedure   HCT Flap Removed vs.           25.66 (26.13)        0.326
            Intact
            Both HCT Flaps Removed         43.46 (26.10)        0.096
            vs. Intact
            HCT Flap Removed vs.           17.93 (27.30)        0.512
            Both HCT Flaps Removed

Removed     Both Flaps vs. Intact          43.42 (26.13)        0.097
Meniscus    Inferior Flap vs. Intact       18.71 (35.80)        0.602
            Superior Flap vs. Intact       31.47 (33.20)        0.344
            Superior Flap vs. Inferior    -44.05 (134.3)        0.743
            Flap

Region      Central Body vs. Anterior      471.98 (28.20)     < 0.001
            Horn
            Posterior Horn vs. Anterior    844.46 (27.40)     < 0.001
            Horn
            Uncovered Cartilage vs.        839.99 (27.40)     < 0.001
            Anterior Horn

Loading     Comp + IT vs. Comp              -3.08 (26.16)       0.906
Condition   Comp + PS vs. Comp             -63.18 (26.1)        0.015
            Comp + PS vs. Comp + IT        -59.61 (25.4)        0.019

Angle       All Measured Angles             10.20 (3.70)      < 0.0001
            -5[degrees] vs. 0[degrees]      63.80 (54.30)       0.240
            15[degrees] vs. 0[degrees]      33.49 (48.10)       0.486
            30[degrees] vs. 0[degrees]      27.30 (48.10)       0.570
            45[degrees] vs. 0[degrees]      50.07 (48.10)       0.298
            60[degrees] vs. 0[degrees]      98.60 (48.10)       0.040
            75[degrees] vs. 0[degrees]     134.50 (48.10)       0.005
            90[degrees] vs. 0[degrees]     159.80 (48.10)     < 0.001
           105[degrees] vs. 0[degrees]     128.40 (48.10)       0.008
           120[degrees] vs. 0[degrees]      88.30 (48.60)       0.070
           135[degrees] vs. 0[degrees]      22.74 (57.10)       0.691
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Author:Uquillas, Carlos A.; Arno, Sally; Ramme, Austin J.; Oh, Cheongeun; Walker, Peter S.; Meislin, Robert
Publication:Bulletin of the NYU Hospital for Joint Diseases
Geographic Code:1USA
Date:Jul 1, 2017
Words:5215
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