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The Reproducibility of Radiographic Measurement of Medial Meniscus Horn Position
The Reproducibility of Radiographic Measurement of Medial Meniscus Horn Position Philippe Wilmes, M.D., Konstantinos Anagnostakos, M.D., Christian Weth, Dieter Kohn, M.D., and Romain Seil, M.D.
Purpose: The objective of this investigation was to evaluate the possibility of locating and reproducing the tibial insertion areas of the anterior and posterior horns of the medial meniscus on preoperative radiographs according to an established method for the lateral meniscus. Methods: In 20 tibia heads, we prepared anterior and posterior horn insertions and marked their circumference with radiopaque steel balls of 1.6 mm in diameter. Standardized anteroposterior and lateral radiographs were made. On these radiographs, different landmarks were defined, their distances measured (tibial width and depth, distance from lateral tibia border to meniscus insertion midpoint, distance from anterior tibia border to meniscus insertion midpoint, distance from anterior and lateral tibia border to medial intercondylar spine), and ratios determined. Results: The anterior horn midpoint is located at 57.3% ⫾ 2.7% of tibial width and 12.0% ⫾ 1.0% of tibial depth, and the posterior horn midpoint is located at 56.5% ⫾ 1.6% of tibial width and 81.6% ⫾ 3.4% of tibial depth. The statistical analysis of these measures showed a precise and constant positioning of the medial meniscus insertions on the tibia plateau. We also found constant topographic relations to the medial intercondylar spine. Conclusions: The midpoints of both insertion areas of the medial meniscus have constant positions at 57.3% and 56.5% of tibial width and at 12.0% and 81.6% of tibial depth for the anterior and posterior horn, respectively. They can precisely and reproducibly be defined on radiographs. Clinical Relevance: We have developed a technique for precise radiographic tibial horn determination, exact placement of the tibial tunnels, and thus reconstruction of meniscus insertion anatomy in medial meniscus transplantation. Key Words: Medial meniscus—Meniscus transplantation—Meniscus insertion anatomy—Bony landmarks
R
ecent publications on midterm and long-term survival of lateral and medial meniscal allografting report results suggesting that the procedure induces a significant reduction of pain and improvement of
From the Klinik für Orthopädie und Orthopädische Chirurgie, Universitätskliniken des Saarlandes (P.W., K.A., C.W., D.K.), Homburg/Saar, Germany, and Department of Orthopaedic and Trauma Surgery, Centre for Sports and Preventive Medicine, Centre Hospitalier de Luxembourg-Clinique d’Eich (R.S.), Luxembourg. The authors report no conflict of interest. Address correspondence and reprints requests to Philippe Wilmes, M.D., Klinik für Orthopädie und Orthopädische Chirurgie, Universitätskliniken des Saarlandes, Kirrberger Strasse Gebäude 37, D-66421 Homburg/Saar, Germany. E-mail: p_wilmes@ yahoo.com © 2008 by the Arthroscopy Association of North America 0749-8063/08/2406-7383$34.00/0 doi:10.1016/j.arthro.2007.12.012
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function in the midterm.1-7 However, the long-term outcomes show failure rates of up to 55% for transplanted menisci.7 In a review of the first free medial meniscal allografts performed in the mid 1980s, the authors describe decreasing knee score values and increasing degenerative articular changes after a follow-up of 20 years.1 The survival analysis of the clinical outcomes of their first 100 viable medial and lateral meniscal allografts led Verdonk et al.2 to conclude that the beneficial effect of meniscus transplantation remained in approximately 70% of the patients at 10 years. Misplacement of the meniscal allografts is one major cause for transplantation failure. It has been suggested that anatomic positioning of meniscus transplants is needed for restoration of normal knee biomechanics and graft survival.8 In an animal study it has been shown that incongruous and non-isometric
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 24, No 6 (June), 2008: pp 660-668
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FIGURE 1. (A) Anterior and (B) posterior views of tibia. Black marks indicate radiopaque steel balls outlining the anterior and posterior horn circumference. (A) The close relation of the tibial insertion of the anterior horn of the medial meniscus (MM, AH) to the anterior cruciate ligament (ACL), the insertion of the anterior horn of the lateral meniscus (LM, AH), and the medial intercondylar spine (MIS) are well represented on the anterior view. (B) The posterior view allows identification of the relation between the posterior horn insertion of the medial meniscus (MM, PH), the insertion of the posterior cruciate ligament (PCL), the bony ridge at the transition from the posterior intercondylar area into the tibia shaft (row of ellipsoids), and the posterior insertion of the lateral meniscus (LM, PH).
placement of a medial meniscal graft will lead to degeneration and failure of the graft.9 Furthermore, a biomechanical investigation on cadaveric knees concluded that medial meniscal transplantation requires anatomic fixation of bone plugs attached to the anterior and posterior horns to restore contact mechanics closest to normal.10 In particular, the posterior horn of the medial meniscus should be placed within a tolerance tighter than 5 mm medial and 5 mm posterior to the anatomic location because nonanatomic placement significantly alters the contact pressure distribution.11 However, there is wide agreement that exact graft placement remains difficult, and therefore restoration of meniscus insertion anatomy is still problematic.12-14 Recently, a study on the reproducibility of radiographic measurement of lateral meniscus horn positioning gave evidence of the constant locations of the tibial insertions of the lateral meniscus and their relation to constant bony landmarks.15 The authors described a method for exact determination of the tibial insertions of the lateral meniscus, allowing the development of a technique for precise reconstruction of the insertion anatomy. The purpose of this study was to determine the exact insertion areas of the anterior and posterior medial meniscus horns on preoperative radiographs and to reproduce these locations according to the established method for the lateral meniscus in relation to meniscus transplantation. Our hypothesis was that these locations would be precise with a low variability and that their determination on the radiographs would be reproducible.
METHODS In this study 20 formaldehyde-fixed human cadaveric knees (10 pairs) with a mean age of 73 years (range, 57 to 91 years) were dissected and all soft tissues removed. Of the knees, 12 showed no macroscopic signs of degenerative articular cartilage changes (according to Jackson et al.16), 7 had grade I changes, and 1 had grade II changes. None of the grade I and II knees showed alterations of the insertion sites. Tibial insertions of the cruciate ligaments were removed and meniscus horns exposed. The medial meniscus horns were sectioned from the tibia, their insertions marked, and their circumferences outlined with radiopaque steel balls of 1.6 mm in diameter (Fig 1). For standardization of the radiographs, the tibial condyles were fixed in a custom-designed L-shaped box allowing fixation of the specimen with the 2 posterior parts of the tibia head applied against the posterior wall of the box (Fig 2). Anteroposterior (AP) and lateral radiographs were obtained for all specimens (Fig 3). A measuring method using different bony landmarks on the proximal tibia as references was developed (Figs 4 and 5). On AP radiographs, 2 parallel lines (A and B) were drawn, tangential to the lateral and medial border of the tibia plateau (Fig 4). A line perpendicular to these ran tangentially to the medial intercondylar spine (C). Different reference points were projected from the tibia plateau and the anterior and posterior horns of the medial meniscus on this
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FIGURE 2.
Custom-made L-shaped box used for standardization of radiographs.
line: the distance from the lateral to the medial border of the tibia plateau (ab), the distance from the lateral border of the tibia plateau to the meniscus midpoint (X), and the distance from the lateral border of the
tibia plateau to the midpoint of the medial intercondylar spine (Y). On lateral radiographs, drawing of reference lines was more difficult because of the different shape of the anterior and posterior borders of
FIGURE 3. Standardized AP and lateral radiographs of tibia heads with prepared (A, B) anterior and (C, D) posterior horn sites; white marks indicate radiopaque steel balls (arrows). (lat, lateral; med, medial; ant, anterior; post, posterior.)
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FIGURE 4. Medial meniscus: schematic (A) AP and (B) lateral representation of anterior horn measures. Black marks indicate anterior horn localization, and x (diamond) indicates the meniscus midpoint. T designates the medial intercondylar spine. On the AP representation, A and B are tangents to the lateral and medial tibia plateau, and C is a tangent to T intersecting A and B on intersection points a and b. X is the distance from the lateral tibia border to the meniscus midpoint, and Y is the distance from the lateral tibia border to T; ab defines the tibial width. On the lateral representation, A is parallel to the posterior cortex of the tibial shaft, tangential to the transition from the posterior intercondylar area into the tibial shaft; B is perpendicular to A, tangential to T, intersecting A in b and C in a; and C is parallel to the anterior border of the tibia plateau. X is the distance from the anterior tibia border to the meniscus midpoint, and Y is the distance from the anterior tibia border to T; ab defines the tibial depth. (lat, lateral; med, medial; ant, anterior; post, posterior.)
the tibia plateau. Therefore the first reference line was drawn parallel to the posterior cortex of the tibial shaft (A) and tangential to the transition from the posterior intercondylar area into the tibial shaft where, on standardized radiographs, a rough bony ridge defines a consistent and reproducible radiographic landmark.17 The second reference line (B) was perpendicular to line A and ran tangentially to the medial intercondylar spine. The third reference line (C) was parallel to the anterior border of the tibia plateau. Its most anterior
reference point was represented by its intersection with the second line (B). Several other reference points were projected from the tibia plateau on this line: the distance from the anterior to the posterior reference point (ab), the distance from the anterior reference point to the meniscus midpoint (X), and the distance from the anterior reference point to the midpoint of the medial intercondylar spine (Y). The same procedures were used for the posterior horn insertion (Fig 5).
FIGURE 5. Medial meniscus: schematic (A) AP and (B) lateral representation of posterior horn measures, in which x= marks the meniscus midpoint and X= is the distance from the anterior tibia border to the meniscus midpoint. The other distances correspond to the descriptions in Fig 4. (lat, lateral; med, medial; ant, anterior; post, posterior.)
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TABLE 1.
Results for Anterior and Posterior Medial Meniscus Horn Insertion and for Medial Intercondylar Spine AP Radiographs
X(X=)/ab (%) (Mean ⫾ SD) AH PH MIS
57.3 ⫾ 2.7 56.5 ⫾ 1.6
Lateral Radiographs
Y/ab (%) (Mean ⫾ SD)
Range (%)
59.2 ⫾ 2.7
52.0-62.2 53.0-59.7 53.9-63.8
X(X=)/ab (%) (Mean ⫾ SD) 12.0 ⫾ 1.0 81.6 ⫾ 3.4
Y/ab (%) (Mean ⫾ SD)
Range (%)
62.8 ⫾ 2.1
7.8-14.1 74.1-91.0 59.7-67.9
Abbreviations: AH, anterior horn; PH, posterior horn; MIS, medial intercondylar spine.
Mean values, SDs, and maximum and minimum values were determined for the different parameters. The results were normalized; relative values for the position of the meniscus midpoint and the medial intercondylar spine were obtained for AP radiographs by dividing the measured distances (X, X=, and Y) by ab, and those for lateral radiographs were obtained by dividing the measured distances (X, X=, and Y) by ab. Thus, on the one hand, the absolute position of a meniscus insertion midpoint was located on a specific radiograph; on the other hand, the position of this insertion midpoint relative to the tibia could be determined, allowing positioning on every type of radiograph independent of image magnification. The different combinations of the measures were plotted onto scatter diagrams for regression analysis. To evaluate the constancy of the position of the anterior and posterior horns, specific diagrams representing the lines ab (from AP and lateral radiographs) on the x-axis and X(X=) (from AP and lateral radiographs) on the y-axis were made. Measurements were performed in duplicate by a single observer with a 1-month interval between observations. Regression analysis was performed, and the slope, correlation coefficient (r), and P value were determined. The level of statistical significance was set at P ⱕ .05. Intraobserver error (method error) was determined with the Dahlberg formula18 and a t test for paired samples. The relative values of the meniscus insertion midpoints permitted the determination of percentage references. The reproducibility of the insertion midpoints with these references was verified by the 2 senior authors (D.K., R.S.), both experienced in the field of meniscus replacement. Each determined on 10 radiographs without any marks— chosen from those used for the study of cadaveric specimens, according to the previously described method—insertion midpoints using the mean percentage values. The difference between their results and the original midpoints, deter-
mined by the single observer from the same specimens, was statistically assessed with the Dahlberg formula and a t test for paired samples. RESULTS The mean percentage values for the anterior and posterior horn positions as well as for the position of the medial intercondylar spine showed SDs between 1.0% and 3.4% (Table 1). On AP radiographs, the data revealed a high correlation between the absolute anterior and posterior meniscus positions and the width of the tibia plateau, with a positive regression coefficient and thus a positive slope of the regression line (Fig 6, Table 2). Normalization was performed by dividing the data by the width of the tibia. With this parameter removed as a variable, we found SDs between 1.6% and 2.7% around the percentage width of the tibia, indicating that the meniscus insertion site remains relatively constant with regard to bony landmarks (Table 1). On lateral radiographs, the findings were similar. A high correlation could be found between ab and X(X=), representing the absolute positions of the anterior and posterior horns (Fig 7, Table 2). Normalization resulted in percentage values with SDs between 1.0% and 3.4% around the percentage depth of the tibia (Table 1). Statistical analysis showed a high correlation between the position of the medial intercondylar spine and the width and depth of the tibia plateau (Table 2); SDs between 2.1% and 2.7% around the percentage width and depth of the tibia were obtained (Table 1). Intraobserver error according to the Dahlberg formula was low (Tables 3 and 4). The t tests for paired samples showed correlation coefficients between 0.88 and 0.99 between observations, with P values varying from .20 to .90 (always above the level of statistical significance). Variations between the 2 observers according to the Dahlberg formula were low (Tables 3 and 4). The t
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FIGURE 6. Scatter diagram with linear regression lines for AP radiographs of anterior horn, posterior horn, and medial intercondylar spine, with ab (in millimeters) on x-axis and X, X=, and Y (in millimeters) on y-axis. (X, triangles [corresponding regression line with 1 long dash followed by 1 short dash]; X=, squares [line with long dashes]; Y, circles [line with 1 long dash followed by 2 short dashes].)
tests for paired samples showed correlation coefficients between 0.78 and 0.99 and P values between .68 and .99 (always above the level of statistical significance). DISCUSSION This study must be considered complementary to that of Wilmes et al.15 on the tibial insertions of the TABLE 2. Regression Analysis: Regression Coefficients, Correlation Coefficients, and P Values for Measured Values of Anterior and Posterior Medial Horn Insertion and for Medial Intercondylar Spine
AH AP radiographs Lateral radiographs PH AP radiographs Lateral radiographs MIS AP radiographs Lateral radiographs
Regression Coefficient (Slope)
Correlation Coefficient (r)
P Value
0.50 0.20
0.77 0.71
⬍ .0001 .0004
0.55 0.93
0.94 0.89
⬍ .0001 ⬍ .0001
0.46 0.50
0.80 0.77
⬍ .0001 ⬍ .0001
Abbreviations: AH, anterior horn; PH, posterior horn; MIS, medial intercondylar spine.
lateral meniscus. With the use of identical methodologies, the percentage values resulting from both studies should allow the easy and precise determination of the essential landmarks for the location of the lateral and medial meniscus horn insertions on standard AP and lateral radiographs. As with the lateral meniscus insertions, the prerequisite for these conclusions was the demonstration of low variability of the medial meniscus insertion areas on the tibia plateau. The regression analysis permitted us to state that the positions of the anterior and posterior medial horns vary closely with the surface of the tibia (Tables 1 and 2). The same conclusion could be made for the position of the medial intercondylar spine in relation to the tibia plateau and the meniscus insertions. By normalizing our data, tibial width and depth could be eliminated as variables; the obtained small SDs around the percentage width and depth of the tibia indicate that the meniscus insertion site remains relatively constant with regard to the bony landmarks. Reproducibility of these findings was shown by blinded determination of meniscus insertions by 2 independent examiners and statistical assessment of their results. Consequently, the percentage references calculated from our data for the medial meniscus midpoint insertions will allow us to determine the medial meniscus insertions with a high precision.
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FIGURE 7. Scatter diagram with linear regression lines for lateral radiographs of anterior horn, posterior horn, and medial intercondylar spine, with ab (in millimeters) on x-axis and X, X=, and Y (in millimeters) on y-axis. (X, triangles [corresponding regression line with 1 long dash followed by 1 short dash]; X=, squares [line with long dashes]; Y, circles [line with 1 long dash followed by 2 short dashes].)
Considering the SDs of the mean anterior and posterior horn insertion midpoints of the medial meniscus, we found that these midpoints were almost aligned in the AP direction. This is an important TABLE 3. Intraobserver Error and Reproducibility: Results From Evaluations With Dahlberg Formula Method Error Intraobserver error AH: X/ab AP radiographs Lateral radiographs PH: X/ab AP radiographs Lateral radiographs MIS: Y/ab AP radiographs Lateral radiographs Reproducibility AH: X AP radiographs Lateral radiographs PH: X= AP radiographs Lateral radiographs
0.002% 0.002% 0.002% 0.013% 0.003% 0.004%
0.143 mm 0.064 mm 0.110 mm 0.188 mm
Abbreviations: AH, anterior horn; PH, posterior horn; MIS, medial intercondylar spine.
difference when comparing our results with those obtained in the lateral meniscus study, where on AP radiographs, even with respect to the SDs, the posterior horn insertion midpoint was always located more medially on the tibia plateau than the midpoint of the anterior horn insertion.15 Similar statements can be made for the lateral radiographs; the anterior horn of the medial meniscus was located more anterior than the anterior horn of the lateral meniscus, and the posterior horn of the medial meniscus was more posterior than the posterior horn of the lateral meniscus.15 This is perfectly consistent with our macroscopic observations and the anatomic findings in the literature. Both horns of the lateral meniscus are located very close to the lateral intercondylar spine, almost forming a circle, whereas the horns of the medial meniscus open widely on the tibia plateau, thus forming a Cshaped figure. Thus our data on medial meniscus anatomy are consistent with previously described anatomic and radiologic landmarks as well as their relations on the tibia plateau. Close relations between the posterior medial horn insertion, the tibial insertion of the posterior cruciate ligament, and the medial intercondylar tubercle, as well as the continuity between the anterior medial horn insertion with the anterior intercondylar
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Intraobserver Error and Reproducibility: Results From Evaluations With t Test for Paired Samples AH
Intraobserver error Correlation coefficient P value Reproducibility Correlation coefficient P value
PH
AP Radiographs
Lateral Radiographs
AP Radiographs
Lateral Radiographs
0.99 .36
0.98 .20
0.98 .20
0.88 .90
0.99 .68
0.78 .84
0.99 ⬎ .99
0.97 .68
Abbreviations: AH, anterior horn; PH, posterior horn.
area, were described by Kohn and Moreno.19 The authors described the surface of the anterior horn as flat and fan-shaped, whereas the posterior horn insertion was more often found to be cylindrical. In their macroscopic anatomic study, Johnson et al.20 came to similar conclusions, and in addition to this, they pointed out the fact that the medial meniscus inserts on the downslope of the posterior intercondylar fossa, directly behind the posterior horn insertion of the lateral meniscus. Therefore the posterior horn insertion of the medial meniscus must be considered significantly more complex in 3 dimensions than the relatively planar anterior horn insertion. A thorough description of radiographic meniscus insertion sites and different radiographic landmarks was made by Urban et al.21 They found that the lateral and medial borders of the tibia, the anterior border of the tibia, the ridge at the transition from the posterior intercondylar area to the tibia shaft, and the medial intercondylar spine were well-defined landmarks. Nevertheless, the flaws criticized for their description of the lateral meniscus insertions must be considered for the medial meniscus as well: all data were presented in absolute values, and hence the different parameters in relation to the bony landmarks were not exactly defined, making a precise and reproducible determination of the medial meniscus horn insertion very difficult. The correct anatomic and isometric horn fixation by precise and reproducible intraoperative horn determination and tunnel drilling remains problematic in medial meniscus transplantation. Intraoperative errors in insertion site determination in combination with a complex 3-dimensional meniscus anatomy often leads to tunnel misplacements and, consequently, to nonanatomic graft fixation. Depending on the operative technique used, the knowledge of the radiographic anatomy of the tibial medial meniscus horn insertions provided by this study might enhance the placement of
tibial tunnels as well as verify the AP alignment of the tibial slot in the bony bridge method. In fact, we see several clinical applications of our data. On preoperative radiographs, the percentage values should allow the determination of the meniscus insertion sites and thus give the surgeon a first hint on where to position the drilling guide. Then, during surgery, after standard arthroscopic placement of the guide, a radiologic control would allow correlation between the actual guide position and the predicted position of the meniscal insertion sites and verify the correct location. We think that using this method complementary to the established procedure will result in much more precise drilling of the tibial tunnels and would consequently allow more precise fixation of the graft at its anatomic insertion sites. Furthermore, the ability to precisely determine the lateral and medial meniscus horn insertions on radiographs with the help of easily determinable landmarks could lead to further improvements in computer-assisted techniques in meniscus transplantation. Indeed, our method and data could be useful in the development of a computer program for navigation-assisted placement of the drilling guide. This study has the same limitations as that of Wilmes et al.15 All specimens were of Caucasian origin, with a mean age of 73 years. Even with few degenerative changes of the examined tibia plateaus, there might be bias as a result of age, especially bearing in mind the fact that meniscus transplantation is performed in young patients. Differences in tibial meniscus insertion anatomy in other populations cannot be excluded. Another limitation might be the fact that our radiographic measurements were merely tested on cadaveric specimens, not on films obtained in a clinical setting. For further clinical use, this radiographic method should be adapted to the in vivo conditions encountered during the surgical procedure.
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The midpoints of both insertion areas of the medial meniscus have constant positions at 57.3% and 56.5% of tibial width and at 12.0% and 81.6% of tibial depth for the anterior and posterior horn, respectively. They can be precisely and reproducibly defined on radiographs.
8. 9.
10.
Acknowledgment: The authors thank Dr. T. Georg, former assistant at the Institute for Biometrics, University of Saarland, for his assistance with the statistical assessment of the data.
11.
REFERENCES
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1. von Lewinski G, Milachowski KA, Weismeier K, Kohn D, Wirth CJ. Twenty-year results of combined meniscal allograft transplantation, anterior cruciate ligament reconstruction and advancement of the medial collateral ligament. Knee Surg Sports Traumatol Arthrosc 2007;15:1072-1082. 2. Verdonk PC, Demurie A, Almqvist KF, Veys EM, Verbruggen G, Verdonk R. Transplantation of viable meniscal allograft. Survivorship analysis and clinical outcome of one hundred cases. J Bone Joint Surg Am 2005;87:715-724. 3. Verdonk PC, Verstraete KL, Almqvist KF, et al. Meniscal allograft transplantation: Long-term clinical results with radiological and magnetic resonance imaging correlations. Knee Surg Sports Traumatol Arthrosc 2006;14:694-706. 4. Stone KR, Walgenbach AW, Turek TJ, Freyer A, Hill MD. Meniscus allograft survival in patients with moderate to severe unicompartmental arthritis: A 2- to 7-year follow-up. Arthroscopy 2006;22:469-478. 5. Sekiya JK, West RV, Groff YJ, Irrgang JJ, Fu FH, Harner CD. Clinical outcomes following isolated lateral meniscal allograft transplantation. Arthroscopy 2006;22:771-780. 6. Deie M, Sumen Y, Adachi N, et al. The long-term results of meniscus transplantation for articular cartilage defects in the knee joint. Knee Surg Sports Traumatol Arthrosc 2007; 15:61-66. 7. Hommen JP, Applegate GR, Del Pizzo W. Meniscus allograft
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transplantation: Ten-year results of cryopreserved allografts. Arthroscopy 2007;23:388-393. Chen MI, Branch TP, Hutton WC. Is it important to secure the horns during lateral meniscal transplantation? A cadaveric study. Arthroscopy 1996;12:174-181. Lazovic D, Wirth CJ, Sieg A, Gosse F, Maschek HG. Effect of surgical technique on meniscus transplants. A histological, animal experiment study. Unfallchirurg 1997;100:541-546 (in German). Alhalki MM, Howell SM, Hull ML. How three methods for fixing a medial meniscal autograft affect tibial contact mechanics. Am J Sports Med 1999;27:320-328. Sekaran SV, Hull ML, Howell SM. Nonanatomic location of the posterior horn of a medial meniscal autograft implanted in a cadaveric knee adversely affects the pressure distribution on the tibial plateau. Am J Sports Med 2002;30:74-82. Rodeo SA. Meniscal allografts—Where do we stand? Am J Sports Med 2001;29:246-261. Klimkiewicz JJ, Shaffer B. Meniscal surgery 2002 update: Indications and techniques for resection, repair, regeneration and replacement. Arthroscopy 2002;18:14-25 (suppl 2). Kelly BT, Brophy RH, Rodeo SA. Meniscal allograft transplantation: Surgical technique. Tech Knee Surg 2004;3:8-18. Wilmes P, Pape D, Kohn D, Seil R. The reproducibility of radiographic measurement of lateral meniscus horn position. Arthroscopy 2007;23:1079-1086. Jackson DW, McDevitt CA, Simon TM, Arnozcky SP, Atwell EA, Silvino NJ. Meniscal transplantation using fresh and cryopreserved allografts. An experimental study in goats. Am J Sports Med 1992;20:644-656. Racanelli JA, Drez D Jr. Posterior cruciate ligament tibial attachment anatomy and radiographic landmarks for tibial tunnel placement in PCL reconstruction. Arthroscopy 1994;10: 546-549. Dahlberg G. Statistical methods for medical and biological students. New York: Wiley Interscience, 1940. Kohn D, Moreno B. Meniscus insertion anatomy as a basis for meniscus replacement: A morphological cadaveric study. Arthroscopy 1995;11:96-103. Johnson DL, Swenson TM, Livesay GA, Aizawa H, Fu FH, Harner CD. Insertion-site anatomy of the human menisci: Gross, arthroscopic, and topographical anatomy as a basis for meniscal transplantation. Arthroscopy 1995;11:386-394. Urban WP Jr, Nyland J, Caborn DN, Johnson DL. The radiographic position of medial and lateral meniscal horns as a basis for meniscal reconstruction. Arthroscopy 1999;15:147-154.
Purpose: The objective of this investigation was to evaluate the possibility of locating and reproducing the tibial insertion areas of the anterior and posterior horns of the medial meniscus on preoperative radiographs according to an established method for the lateral meniscus. Methods: In 20 tibia heads, we prepared anterior and posterior horn insertions and marked their circumference with radiopaque steel balls of 1.6 mm in diameter. Standardized anteroposterior and lateral radiographs were made. On these radiographs, different landmarks were defined, their distances measured (tibial width and depth, distance from lateral tibia border to meniscus insertion midpoint, distance from anterior tibia border to meniscus insertion midpoint, distance from anterior and lateral tibia border to medial intercondylar spine), and ratios determined. Results: The anterior horn midpoint is located at 57.3% ⫾ 2.7% of tibial width and 12.0% ⫾ 1.0% of tibial depth, and the posterior horn midpoint is located at 56.5% ⫾ 1.6% of tibial width and 81.6% ⫾ 3.4% of tibial depth. The statistical analysis of these measures showed a precise and constant positioning of the medial meniscus insertions on the tibia plateau. We also found constant topographic relations to the medial intercondylar spine. Conclusions: The midpoints of both insertion areas of the medial meniscus have constant positions at 57.3% and 56.5% of tibial width and at 12.0% and 81.6% of tibial depth for the anterior and posterior horn, respectively. They can precisely and reproducibly be defined on radiographs. Clinical Relevance: We have developed a technique for precise radiographic tibial horn determination, exact placement of the tibial tunnels, and thus reconstruction of meniscus insertion anatomy in medial meniscus transplantation. Key Words: Medial meniscus—Meniscus transplantation—Meniscus insertion anatomy—Bony landmarks
R
ecent publications on midterm and long-term survival of lateral and medial meniscal allografting report results suggesting that the procedure induces a significant reduction of pain and improvement of
From the Klinik für Orthopädie und Orthopädische Chirurgie, Universitätskliniken des Saarlandes (P.W., K.A., C.W., D.K.), Homburg/Saar, Germany, and Department of Orthopaedic and Trauma Surgery, Centre for Sports and Preventive Medicine, Centre Hospitalier de Luxembourg-Clinique d’Eich (R.S.), Luxembourg. The authors report no conflict of interest. Address correspondence and reprints requests to Philippe Wilmes, M.D., Klinik für Orthopädie und Orthopädische Chirurgie, Universitätskliniken des Saarlandes, Kirrberger Strasse Gebäude 37, D-66421 Homburg/Saar, Germany. E-mail: p_wilmes@ yahoo.com © 2008 by the Arthroscopy Association of North America 0749-8063/08/2406-7383$34.00/0 doi:10.1016/j.arthro.2007.12.012
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function in the midterm.1-7 However, the long-term outcomes show failure rates of up to 55% for transplanted menisci.7 In a review of the first free medial meniscal allografts performed in the mid 1980s, the authors describe decreasing knee score values and increasing degenerative articular changes after a follow-up of 20 years.1 The survival analysis of the clinical outcomes of their first 100 viable medial and lateral meniscal allografts led Verdonk et al.2 to conclude that the beneficial effect of meniscus transplantation remained in approximately 70% of the patients at 10 years. Misplacement of the meniscal allografts is one major cause for transplantation failure. It has been suggested that anatomic positioning of meniscus transplants is needed for restoration of normal knee biomechanics and graft survival.8 In an animal study it has been shown that incongruous and non-isometric
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 24, No 6 (June), 2008: pp 660-668
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FIGURE 1. (A) Anterior and (B) posterior views of tibia. Black marks indicate radiopaque steel balls outlining the anterior and posterior horn circumference. (A) The close relation of the tibial insertion of the anterior horn of the medial meniscus (MM, AH) to the anterior cruciate ligament (ACL), the insertion of the anterior horn of the lateral meniscus (LM, AH), and the medial intercondylar spine (MIS) are well represented on the anterior view. (B) The posterior view allows identification of the relation between the posterior horn insertion of the medial meniscus (MM, PH), the insertion of the posterior cruciate ligament (PCL), the bony ridge at the transition from the posterior intercondylar area into the tibia shaft (row of ellipsoids), and the posterior insertion of the lateral meniscus (LM, PH).
placement of a medial meniscal graft will lead to degeneration and failure of the graft.9 Furthermore, a biomechanical investigation on cadaveric knees concluded that medial meniscal transplantation requires anatomic fixation of bone plugs attached to the anterior and posterior horns to restore contact mechanics closest to normal.10 In particular, the posterior horn of the medial meniscus should be placed within a tolerance tighter than 5 mm medial and 5 mm posterior to the anatomic location because nonanatomic placement significantly alters the contact pressure distribution.11 However, there is wide agreement that exact graft placement remains difficult, and therefore restoration of meniscus insertion anatomy is still problematic.12-14 Recently, a study on the reproducibility of radiographic measurement of lateral meniscus horn positioning gave evidence of the constant locations of the tibial insertions of the lateral meniscus and their relation to constant bony landmarks.15 The authors described a method for exact determination of the tibial insertions of the lateral meniscus, allowing the development of a technique for precise reconstruction of the insertion anatomy. The purpose of this study was to determine the exact insertion areas of the anterior and posterior medial meniscus horns on preoperative radiographs and to reproduce these locations according to the established method for the lateral meniscus in relation to meniscus transplantation. Our hypothesis was that these locations would be precise with a low variability and that their determination on the radiographs would be reproducible.
METHODS In this study 20 formaldehyde-fixed human cadaveric knees (10 pairs) with a mean age of 73 years (range, 57 to 91 years) were dissected and all soft tissues removed. Of the knees, 12 showed no macroscopic signs of degenerative articular cartilage changes (according to Jackson et al.16), 7 had grade I changes, and 1 had grade II changes. None of the grade I and II knees showed alterations of the insertion sites. Tibial insertions of the cruciate ligaments were removed and meniscus horns exposed. The medial meniscus horns were sectioned from the tibia, their insertions marked, and their circumferences outlined with radiopaque steel balls of 1.6 mm in diameter (Fig 1). For standardization of the radiographs, the tibial condyles were fixed in a custom-designed L-shaped box allowing fixation of the specimen with the 2 posterior parts of the tibia head applied against the posterior wall of the box (Fig 2). Anteroposterior (AP) and lateral radiographs were obtained for all specimens (Fig 3). A measuring method using different bony landmarks on the proximal tibia as references was developed (Figs 4 and 5). On AP radiographs, 2 parallel lines (A and B) were drawn, tangential to the lateral and medial border of the tibia plateau (Fig 4). A line perpendicular to these ran tangentially to the medial intercondylar spine (C). Different reference points were projected from the tibia plateau and the anterior and posterior horns of the medial meniscus on this
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FIGURE 2.
Custom-made L-shaped box used for standardization of radiographs.
line: the distance from the lateral to the medial border of the tibia plateau (ab), the distance from the lateral border of the tibia plateau to the meniscus midpoint (X), and the distance from the lateral border of the
tibia plateau to the midpoint of the medial intercondylar spine (Y). On lateral radiographs, drawing of reference lines was more difficult because of the different shape of the anterior and posterior borders of
FIGURE 3. Standardized AP and lateral radiographs of tibia heads with prepared (A, B) anterior and (C, D) posterior horn sites; white marks indicate radiopaque steel balls (arrows). (lat, lateral; med, medial; ant, anterior; post, posterior.)
MEDIAL MENISCUS HORN POSITION MEASUREMENT
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FIGURE 4. Medial meniscus: schematic (A) AP and (B) lateral representation of anterior horn measures. Black marks indicate anterior horn localization, and x (diamond) indicates the meniscus midpoint. T designates the medial intercondylar spine. On the AP representation, A and B are tangents to the lateral and medial tibia plateau, and C is a tangent to T intersecting A and B on intersection points a and b. X is the distance from the lateral tibia border to the meniscus midpoint, and Y is the distance from the lateral tibia border to T; ab defines the tibial width. On the lateral representation, A is parallel to the posterior cortex of the tibial shaft, tangential to the transition from the posterior intercondylar area into the tibial shaft; B is perpendicular to A, tangential to T, intersecting A in b and C in a; and C is parallel to the anterior border of the tibia plateau. X is the distance from the anterior tibia border to the meniscus midpoint, and Y is the distance from the anterior tibia border to T; ab defines the tibial depth. (lat, lateral; med, medial; ant, anterior; post, posterior.)
the tibia plateau. Therefore the first reference line was drawn parallel to the posterior cortex of the tibial shaft (A) and tangential to the transition from the posterior intercondylar area into the tibial shaft where, on standardized radiographs, a rough bony ridge defines a consistent and reproducible radiographic landmark.17 The second reference line (B) was perpendicular to line A and ran tangentially to the medial intercondylar spine. The third reference line (C) was parallel to the anterior border of the tibia plateau. Its most anterior
reference point was represented by its intersection with the second line (B). Several other reference points were projected from the tibia plateau on this line: the distance from the anterior to the posterior reference point (ab), the distance from the anterior reference point to the meniscus midpoint (X), and the distance from the anterior reference point to the midpoint of the medial intercondylar spine (Y). The same procedures were used for the posterior horn insertion (Fig 5).
FIGURE 5. Medial meniscus: schematic (A) AP and (B) lateral representation of posterior horn measures, in which x= marks the meniscus midpoint and X= is the distance from the anterior tibia border to the meniscus midpoint. The other distances correspond to the descriptions in Fig 4. (lat, lateral; med, medial; ant, anterior; post, posterior.)
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TABLE 1.
Results for Anterior and Posterior Medial Meniscus Horn Insertion and for Medial Intercondylar Spine AP Radiographs
X(X=)/ab (%) (Mean ⫾ SD) AH PH MIS
57.3 ⫾ 2.7 56.5 ⫾ 1.6
Lateral Radiographs
Y/ab (%) (Mean ⫾ SD)
Range (%)
59.2 ⫾ 2.7
52.0-62.2 53.0-59.7 53.9-63.8
X(X=)/ab (%) (Mean ⫾ SD) 12.0 ⫾ 1.0 81.6 ⫾ 3.4
Y/ab (%) (Mean ⫾ SD)
Range (%)
62.8 ⫾ 2.1
7.8-14.1 74.1-91.0 59.7-67.9
Abbreviations: AH, anterior horn; PH, posterior horn; MIS, medial intercondylar spine.
Mean values, SDs, and maximum and minimum values were determined for the different parameters. The results were normalized; relative values for the position of the meniscus midpoint and the medial intercondylar spine were obtained for AP radiographs by dividing the measured distances (X, X=, and Y) by ab, and those for lateral radiographs were obtained by dividing the measured distances (X, X=, and Y) by ab. Thus, on the one hand, the absolute position of a meniscus insertion midpoint was located on a specific radiograph; on the other hand, the position of this insertion midpoint relative to the tibia could be determined, allowing positioning on every type of radiograph independent of image magnification. The different combinations of the measures were plotted onto scatter diagrams for regression analysis. To evaluate the constancy of the position of the anterior and posterior horns, specific diagrams representing the lines ab (from AP and lateral radiographs) on the x-axis and X(X=) (from AP and lateral radiographs) on the y-axis were made. Measurements were performed in duplicate by a single observer with a 1-month interval between observations. Regression analysis was performed, and the slope, correlation coefficient (r), and P value were determined. The level of statistical significance was set at P ⱕ .05. Intraobserver error (method error) was determined with the Dahlberg formula18 and a t test for paired samples. The relative values of the meniscus insertion midpoints permitted the determination of percentage references. The reproducibility of the insertion midpoints with these references was verified by the 2 senior authors (D.K., R.S.), both experienced in the field of meniscus replacement. Each determined on 10 radiographs without any marks— chosen from those used for the study of cadaveric specimens, according to the previously described method—insertion midpoints using the mean percentage values. The difference between their results and the original midpoints, deter-
mined by the single observer from the same specimens, was statistically assessed with the Dahlberg formula and a t test for paired samples. RESULTS The mean percentage values for the anterior and posterior horn positions as well as for the position of the medial intercondylar spine showed SDs between 1.0% and 3.4% (Table 1). On AP radiographs, the data revealed a high correlation between the absolute anterior and posterior meniscus positions and the width of the tibia plateau, with a positive regression coefficient and thus a positive slope of the regression line (Fig 6, Table 2). Normalization was performed by dividing the data by the width of the tibia. With this parameter removed as a variable, we found SDs between 1.6% and 2.7% around the percentage width of the tibia, indicating that the meniscus insertion site remains relatively constant with regard to bony landmarks (Table 1). On lateral radiographs, the findings were similar. A high correlation could be found between ab and X(X=), representing the absolute positions of the anterior and posterior horns (Fig 7, Table 2). Normalization resulted in percentage values with SDs between 1.0% and 3.4% around the percentage depth of the tibia (Table 1). Statistical analysis showed a high correlation between the position of the medial intercondylar spine and the width and depth of the tibia plateau (Table 2); SDs between 2.1% and 2.7% around the percentage width and depth of the tibia were obtained (Table 1). Intraobserver error according to the Dahlberg formula was low (Tables 3 and 4). The t tests for paired samples showed correlation coefficients between 0.88 and 0.99 between observations, with P values varying from .20 to .90 (always above the level of statistical significance). Variations between the 2 observers according to the Dahlberg formula were low (Tables 3 and 4). The t
MEDIAL MENISCUS HORN POSITION MEASUREMENT
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FIGURE 6. Scatter diagram with linear regression lines for AP radiographs of anterior horn, posterior horn, and medial intercondylar spine, with ab (in millimeters) on x-axis and X, X=, and Y (in millimeters) on y-axis. (X, triangles [corresponding regression line with 1 long dash followed by 1 short dash]; X=, squares [line with long dashes]; Y, circles [line with 1 long dash followed by 2 short dashes].)
tests for paired samples showed correlation coefficients between 0.78 and 0.99 and P values between .68 and .99 (always above the level of statistical significance). DISCUSSION This study must be considered complementary to that of Wilmes et al.15 on the tibial insertions of the TABLE 2. Regression Analysis: Regression Coefficients, Correlation Coefficients, and P Values for Measured Values of Anterior and Posterior Medial Horn Insertion and for Medial Intercondylar Spine
AH AP radiographs Lateral radiographs PH AP radiographs Lateral radiographs MIS AP radiographs Lateral radiographs
Regression Coefficient (Slope)
Correlation Coefficient (r)
P Value
0.50 0.20
0.77 0.71
⬍ .0001 .0004
0.55 0.93
0.94 0.89
⬍ .0001 ⬍ .0001
0.46 0.50
0.80 0.77
⬍ .0001 ⬍ .0001
Abbreviations: AH, anterior horn; PH, posterior horn; MIS, medial intercondylar spine.
lateral meniscus. With the use of identical methodologies, the percentage values resulting from both studies should allow the easy and precise determination of the essential landmarks for the location of the lateral and medial meniscus horn insertions on standard AP and lateral radiographs. As with the lateral meniscus insertions, the prerequisite for these conclusions was the demonstration of low variability of the medial meniscus insertion areas on the tibia plateau. The regression analysis permitted us to state that the positions of the anterior and posterior medial horns vary closely with the surface of the tibia (Tables 1 and 2). The same conclusion could be made for the position of the medial intercondylar spine in relation to the tibia plateau and the meniscus insertions. By normalizing our data, tibial width and depth could be eliminated as variables; the obtained small SDs around the percentage width and depth of the tibia indicate that the meniscus insertion site remains relatively constant with regard to the bony landmarks. Reproducibility of these findings was shown by blinded determination of meniscus insertions by 2 independent examiners and statistical assessment of their results. Consequently, the percentage references calculated from our data for the medial meniscus midpoint insertions will allow us to determine the medial meniscus insertions with a high precision.
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FIGURE 7. Scatter diagram with linear regression lines for lateral radiographs of anterior horn, posterior horn, and medial intercondylar spine, with ab (in millimeters) on x-axis and X, X=, and Y (in millimeters) on y-axis. (X, triangles [corresponding regression line with 1 long dash followed by 1 short dash]; X=, squares [line with long dashes]; Y, circles [line with 1 long dash followed by 2 short dashes].)
Considering the SDs of the mean anterior and posterior horn insertion midpoints of the medial meniscus, we found that these midpoints were almost aligned in the AP direction. This is an important TABLE 3. Intraobserver Error and Reproducibility: Results From Evaluations With Dahlberg Formula Method Error Intraobserver error AH: X/ab AP radiographs Lateral radiographs PH: X/ab AP radiographs Lateral radiographs MIS: Y/ab AP radiographs Lateral radiographs Reproducibility AH: X AP radiographs Lateral radiographs PH: X= AP radiographs Lateral radiographs
0.002% 0.002% 0.002% 0.013% 0.003% 0.004%
0.143 mm 0.064 mm 0.110 mm 0.188 mm
Abbreviations: AH, anterior horn; PH, posterior horn; MIS, medial intercondylar spine.
difference when comparing our results with those obtained in the lateral meniscus study, where on AP radiographs, even with respect to the SDs, the posterior horn insertion midpoint was always located more medially on the tibia plateau than the midpoint of the anterior horn insertion.15 Similar statements can be made for the lateral radiographs; the anterior horn of the medial meniscus was located more anterior than the anterior horn of the lateral meniscus, and the posterior horn of the medial meniscus was more posterior than the posterior horn of the lateral meniscus.15 This is perfectly consistent with our macroscopic observations and the anatomic findings in the literature. Both horns of the lateral meniscus are located very close to the lateral intercondylar spine, almost forming a circle, whereas the horns of the medial meniscus open widely on the tibia plateau, thus forming a Cshaped figure. Thus our data on medial meniscus anatomy are consistent with previously described anatomic and radiologic landmarks as well as their relations on the tibia plateau. Close relations between the posterior medial horn insertion, the tibial insertion of the posterior cruciate ligament, and the medial intercondylar tubercle, as well as the continuity between the anterior medial horn insertion with the anterior intercondylar
MEDIAL MENISCUS HORN POSITION MEASUREMENT TABLE 4.
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Intraobserver Error and Reproducibility: Results From Evaluations With t Test for Paired Samples AH
Intraobserver error Correlation coefficient P value Reproducibility Correlation coefficient P value
PH
AP Radiographs
Lateral Radiographs
AP Radiographs
Lateral Radiographs
0.99 .36
0.98 .20
0.98 .20
0.88 .90
0.99 .68
0.78 .84
0.99 ⬎ .99
0.97 .68
Abbreviations: AH, anterior horn; PH, posterior horn.
area, were described by Kohn and Moreno.19 The authors described the surface of the anterior horn as flat and fan-shaped, whereas the posterior horn insertion was more often found to be cylindrical. In their macroscopic anatomic study, Johnson et al.20 came to similar conclusions, and in addition to this, they pointed out the fact that the medial meniscus inserts on the downslope of the posterior intercondylar fossa, directly behind the posterior horn insertion of the lateral meniscus. Therefore the posterior horn insertion of the medial meniscus must be considered significantly more complex in 3 dimensions than the relatively planar anterior horn insertion. A thorough description of radiographic meniscus insertion sites and different radiographic landmarks was made by Urban et al.21 They found that the lateral and medial borders of the tibia, the anterior border of the tibia, the ridge at the transition from the posterior intercondylar area to the tibia shaft, and the medial intercondylar spine were well-defined landmarks. Nevertheless, the flaws criticized for their description of the lateral meniscus insertions must be considered for the medial meniscus as well: all data were presented in absolute values, and hence the different parameters in relation to the bony landmarks were not exactly defined, making a precise and reproducible determination of the medial meniscus horn insertion very difficult. The correct anatomic and isometric horn fixation by precise and reproducible intraoperative horn determination and tunnel drilling remains problematic in medial meniscus transplantation. Intraoperative errors in insertion site determination in combination with a complex 3-dimensional meniscus anatomy often leads to tunnel misplacements and, consequently, to nonanatomic graft fixation. Depending on the operative technique used, the knowledge of the radiographic anatomy of the tibial medial meniscus horn insertions provided by this study might enhance the placement of
tibial tunnels as well as verify the AP alignment of the tibial slot in the bony bridge method. In fact, we see several clinical applications of our data. On preoperative radiographs, the percentage values should allow the determination of the meniscus insertion sites and thus give the surgeon a first hint on where to position the drilling guide. Then, during surgery, after standard arthroscopic placement of the guide, a radiologic control would allow correlation between the actual guide position and the predicted position of the meniscal insertion sites and verify the correct location. We think that using this method complementary to the established procedure will result in much more precise drilling of the tibial tunnels and would consequently allow more precise fixation of the graft at its anatomic insertion sites. Furthermore, the ability to precisely determine the lateral and medial meniscus horn insertions on radiographs with the help of easily determinable landmarks could lead to further improvements in computer-assisted techniques in meniscus transplantation. Indeed, our method and data could be useful in the development of a computer program for navigation-assisted placement of the drilling guide. This study has the same limitations as that of Wilmes et al.15 All specimens were of Caucasian origin, with a mean age of 73 years. Even with few degenerative changes of the examined tibia plateaus, there might be bias as a result of age, especially bearing in mind the fact that meniscus transplantation is performed in young patients. Differences in tibial meniscus insertion anatomy in other populations cannot be excluded. Another limitation might be the fact that our radiographic measurements were merely tested on cadaveric specimens, not on films obtained in a clinical setting. For further clinical use, this radiographic method should be adapted to the in vivo conditions encountered during the surgical procedure.
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P. WILMES ET AL. CONCLUSIONS
The midpoints of both insertion areas of the medial meniscus have constant positions at 57.3% and 56.5% of tibial width and at 12.0% and 81.6% of tibial depth for the anterior and posterior horn, respectively. They can be precisely and reproducibly defined on radiographs.
8. 9.
10.
Acknowledgment: The authors thank Dr. T. Georg, former assistant at the Institute for Biometrics, University of Saarland, for his assistance with the statistical assessment of the data.
11.
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