Clinical Anatomy 6:129-134 (1993)

Clinical Anatomy 6:129-134 (1993)

ORIGINAL COMMUNICATIONS

Insertion Orientation of Terminal Vastus Lateralis Obliquus and Vastus Medialis Obliquus Muscle Fibers in Human Knees

WILLIAM F. BENNETT, NEVILLE DOHERTY, MICHAEL J. HALLISEY, AND JOHN P. FULKERSON

University of Connecticut School of Medicine, Department of Orthopaedic Surgery, Farnrington

The quadriceps mechanism consists of the patellar ligament distally and the quadriceps tendon proximally. The quadriceps tendon is the confluence of the tendinous portions of the vastus medialis, vastus lateralis, vastus intermedius, and rectus femoris. Lieb and Perry (J. Bone Joint Surg. SOA:1535-1547, 1968) have described the vastus medialis obliquus (VMO and Hallisey et al. (J. Bone Joint Surg. 69A:545-549, 1987) have described the vastus lateralis obliquus (VLO). These muscles are the terminal medial and lateral insertions of the vastus medialis and vastus lateralis. This study delineates and quantifies anatomic sex differences for the medial and lateral angular terminal insertions of the vastus lateralis obliquus and vastus medialis obliquus in relationship to the longitudinal axis of the patella in 40 embalmed cadaver knees. A mathematical model is developed and discussed using least steps regression equations y = Ax + B, where y = the VLO insertion angle, x = the VMO insertion angle, A = the coefficients, and B = the y intercept. These equations are different in males and females, with males having more horizontally oriented VLO fibers than females. The vastus lateralis obliquus (VLO insertion angle can be predicted based upon measurement of the vastus medialis obliquus insertion angle and sex: Log VLO = 1.36 + .00531 VMO - 0.000166 (S x VMO), where S = 1 for females and S = 0 for males. In embalmed cadaver knees, the angular terminal insertion of the vastus lateralis obliquus related to the longitudinal axis of the patella is more horizontally oriented in males than in females. The angular terminal insertion of the vastus medialis obliquus of males and females does not increase equally with increases in the angular terminal insertion of the vastus lateralis obliquus. ® 1993 Wiley-Liss, Inc.

Key words: quadriceps, patella, vastus medialie, vastus Iateralie

INTRODUCTION

Patellar support is influenced by multiple variables including bony anatomy, muscles, retinaculum, and ligaments. The geometry of the femur, femoral trochlear depth, and femoral trochlear angle and the geometry of the patella and the medial and lateral facets create the articulation. Schutzer et al. (1986) showed that the depth and angle of the trochlea contribute to patellar support during patellar tracking. The amount of patellar lateral facet convexity and medial facet concavity contribute to its articular support. In addition, the relative geometric configuration of the femur and tibia contribute to the Q-angle. The Q-angle is an angle

between a line from the anterosuperior iliac spine through the midpoint of the patella and a line from the midpoint of the patella to the tibial tubercle. Hungerford and Barry (1979) have stated that the Q-angle results in a net lateralizing effect on the patella. With increasing valgus of the femur and tibia and increasing femoral anteversion, the Q-angle increases. ~

The quadriceps mechanisms consists of the patellar ligament distally and the patellar tendon proximally.

Received for publication June 30, 1992; revised August 19, 1992.

Address reprint requests to Dr. William F. Bennett, The liniversiry of Texas Medical School, Division of Orthopaedic Surgery, 6431 Fannin, Suite 6.154, Houston, TX 77030.

130Bennett et al.

The patellar tendon is the confluence of the tendinous portions of the vastus medialis, vastus lateralis, vastus intermedius, and rectus femoris (Fig. 3A). The terminal insertions of the vastus medialis and vastus lateralis may provide horizontal stability to the patella. The terminal insertion of the vastus lateralis at the lateral border of the patella was reported by Hallisey et al. (1987) to be a separate muscle belly from the vastus lateralis proper, termed the vastus lateralis obliquus (VLO). The terminal insertion of the vastus medialis at the patellar junction has been termed the vastus medialis obliquus (VMO) by Lieb and Perry (1968).

The medial and lateral retinaculum, the iliotibial band, and the epicondylopatellar and patellotibial ligaments contribute to static support. Hallisey et al. (1987) found that the iliotibial band does receive a few fibers of vastus lateralis obliquus insertion.

Blauth and Tillman (1983), Lieb and Perry (1968), and Reynolds et al. (1983) have studied the terminal fiber insertions of the vastus lateralis and vastus medialis anatomically, biomechanically, and electromyographically. Limited work has studied the vastus lateralis obliquus and vastus medialis obliquus. To date, no research has shown gender differences between the interrelationship of the vastus medialis obliquus and vastus lateralis obliquus insertional orientation at the patellar junction, nor has any research shown gender differences between the vastus medialis obliquus insertional orientation at the patellar junction. Also, no research has delineated and quantified the relationship between the angular terminal insertions of the vastus lateralis obliquus (VLO) and the vastus medialis obliquus (V>\10) in relation to the longitudinal axis of the patella.

Hallisey et al. (1987) previously demonstrated that the VLO in males is more horizontally oriented to the patella. The major points of this study ~are to determine if this is true for the vastus medialis obliquus and to develop a mathematical model to illustrate the relationship of the vastus lateralis obliquus to the vastus medialis obliquus in males and females.

This study quantifies the horizontal orientation of the angular terminal insertions of the vastus lateralis obliquus and vastus medialis obliquus and delineates sex differences. To quantify these differences, a uniplanar mathematical model is developed.

MATERIALS AND METHODS Subjects

Forty human cadavers (23 males and 17 females) with no disruption of the muscular anatomy at the knee or hip were used for the analysis of medial and lateral

patellar support. All knees were from fixed specimens of eadavera (Yale University and the University of Connecticut Anatomy Laboratories). Limbs were left intact. The age of the knees studied varied between 52-96 in males and 56-92 in females.

Each cadaver was placed supine with the patella upward. The skin and subcutaneous fat were removed at the knee and the anterior-superior iliac spine. The dissection was carefully performed in a manner to allow complete visualization of the fiber alignment of the vastus medialis obliquus and the vastus lateralis obliquus at the patellar junction. The longitudinal axis of' the patella was drawn with a straight edge and scalpel.

The longitudinal axis is one axis of the Q-angle. A straight edge was placed along this axis. With the knee in full extension, the angles of insertion of the V%10 and VLO terminal fiber orientation to the longitudinal axis of the patella were measured in uniplanar fashion. One arm of a goniometer was placed along each muscle belly's respective fasicular insertion at the patellar junction, delineated anatomically by the perimvsiurn. The second arm of the goniometer was placed along the longitudinal axis of the patella resulting in a measurement oriented obliquely between frontal and syittal planes. The longitudinal axis was equal to zc:ro degrees. Variation in the obliquity of the plane measured did not affect angular measurements.

Olerud and Berg (1984) found that the Q-angle changes with version of the hip and with tibial torsion. Therefore, to standardize the measurements of ~,)angle, the lower extremity and corresponding joints were fixed at 0° of knee flexion, extension, rotation, and 0 degrees of ankle plantar/dorsiflexion and no supination or pronation. The in vitro and in vivo Q-angle may be different.

Measurements

1)' Q-angle: The patellar ligament deviates laterally from the longitudinal axis of the patella and forms the Q-angle (see Fig. 3A). 2) VLO-Vastus Lateralis Obliquus: The angle the distal fibers of the Vastus Lateralis Obliquus makes with the patellar longitudinal axis is termed the VLO (Fig. 1).

3)VMO-Vastus Medialis Obliquus: The angle the distal fibers of the Vastus Medialis makes with the longitudinal axis of the patella is termed the

VMO represented by the angle "c" in Figure ?. 4)VN1P, Vastus Xlcdialis Proximal: The angle the proximal fibers of the Vastus \iedialis makes with the patellar longitudinal axis is termed the VL'IP represented by the angle "f" in Figure 2. This measurement is found in Figure Z but is not used in the equation. In addition, insertion areas along

Insertion Orientation of Terminal Vastus131

Fig. 1.Lateral view of male cadaver knee illustrating Vastus Lateralis Obliquus Insertion Angle: (a) vastus lateralis, (b) vastus lateralis obliquus, (c) patella, (d) patellar ligament, (e) quadriceps tendon, (f) iliotibial tract reflected, (g) fatty, fascial division, (h) fat pad, VLO-vastus lateralis obliquus insertion angle, L-LEN, insertion length of VLO along lateral border of vastus lateralis and patella. P-LEN, patellar length.

the medial and lateral borders of the patella were represented by length measurements. L"I'EN equals length of insertion of the Vastus Lateralis Obliquus along the Vastus Lateralis tendon and patella. MLEN equals length of insertion of the Vastus Medialis Obliquus along the medial border of the patella. PLEN equals longest proximal-distal patellar length. Note that the terms VMO and VLO, from this point on, refer to the VMO angle and VLO angle with respect to the longitudinal axis of the patella.

Fig. 2.Medial view of male cadaver knee illustrating Vastus Medialis Insertion Angle: (a) patella, (b) proximal fibers vastus medialis, (c) distal fibers vastus medialis, (d) medial epicondyle, (e) VMO insertion angle, (f) VMP insertion angle of the vastus medialis proximal, (g) line dividing proximal and distal vastus medialis; M-LEN, insertion length of vastus medialis obliquus along medial border of patella.

Model. A regression equation is specified v --Ax + B, where y equals the dependent v°nriablc, z equals the independent variables, B cduals the intercept, and A equals the coefficients. The dependent variable is the VLO. The independent variables are hypothesized to be related to the \'1.0 and are \ -\11), VMO, Q-angle, LTEN, LPAT, LLI:N, -\II_1,:N, PLEN, and Sex.

Statistics. Each independent variable was analyzed using descriptive statistic techniques. Correlation data were derived for analysis of length measurements. The independent variables were entered into the model using least steps regression. Since sex is a nominal statistic, an interactive variable was included to develop the regression equation.

RESULTS

The results of descriptive statistic tcchniqucs are found in Table 1. Preliminary analysis dcmonstrjtcd no correlations between length measurements and the VLO insertion angle. This variable did not enter our model. The VMP variable did not enter our model. The final form of the model including the interactive variable is: Ln VLO = A + B1 (VN10) + B2 (S x VMO), where A equals the "y" intercept, B 1 and B? are the parameters to be estimated, V':\IO equals Vastus Medialis Obliquus insertion angle, VLO equals Vastus Lateralis Obliquus insertion angle, (S x WIO) equals Interactive variable, and S equals 1 if female, 0 if male.

Ln VLO was the logarithm of the VLO angle and was performed in order to normalize the resicluals. Statistically, this step was included to allow the data points to be interpreted more linearly. This allov s for a more accurate derivation of the coefficients.

The equation developed contained \A10 and an interactive term (S x V'J10) as the indepcndcnt variables; S equals 0 for males and S eduals 1 for fcmales. The interactive variable is used in regression to Illustrate how a numerical value is affected by a nominal characteristic, in this case, sex. "hhe equation wus ,t:rtistically significant (P < .O1) with the \'.\1() representing 43% "r2" of the variation in \'I,O.

Equation 1, Table 2, allows one to quantify sex differences in the terminal insertions of the VNIO and VLO by using an interactive variable. .

Equation 1, Table 3, shows the relationship between the VMO and VLO; for each one degree of \A1() insertion angle there is an associated 0.53 degree and 0.37 degree increase in the \17 LO insertion angle, respectively, for males and females. Both effects and the sex differences are statistically significant (P < O1).

Regardless of sex, the VLO was found to be inversely related to the Q-angle for all knces; however,

132Bennett et al.

TABLE I. Descriptive statistics: medial-lateral quadriceps support

Sample
.Male knee, age:
Q-an / N
range 52-96, mean =
23 / Sum
70
262.00 / Mean
11.39 / S. D.
4.53 / Min
4.00 / N1 a s
20.00
VLO / 23 / 1,033.00 / 44.91 / 9.17 / 30.00 / 73.00
VN1 D / 23 / 1,200.00 / 52.17 / 8.42 / 38.00 / 74.00
VMP / 23 / 834.00 / 36.26 / 6.47 / 25.00 / 48.00
Viti1A / 23 / 1,007.00 / 43.78 / 6.70 / 32.00 / 56.00
Lten / 23 / 66.30 / 2.88 / 1.02 / .00 / 5.00
L pat / 23 / 13.50 / .59 / .82 / 00 / =.5u
Ltot / 23 / 79.80 / 3.47 / 1.25 / 1.50 / ;.OU
.\11en / 23 / 73.40 / 3.20 / .97 / 2.00 / 5.U0
Plen / 23 / 132.80 / 5.77 / .53 / 5.00 / 6.tS0
Female knee, age: / range 56-92, mean = 72
Q-an / 17 209.00 / 12.29 / 4.95 / 5.00 / 24.00
VLO / 17 / 609.00 / 35.82 / 4.75 / 21.00 / 42.00
VMD / 17 / 845.00 / 49.71 / 6.69 / 36.00 / 62.00
VMP / 17 / 563.00 / 33.12 / 5.79 / 22.00 / 45.00
VMA / 17 / 694.00 / 40.82 / 5.04 / 29.00 / 49.00
Lten / 17 / 45.00 / 2.68 / 1.67 / .00 / 4.50
Lpat / 17 / 10.40 / .61 / .77 / .00 / 1.70
Ltot / 17 / 55.90 / 3.29 / 1.30 / 1.50 / 6.20
1-11en / 17 / 50.50 / 2.97 / .84 / 2.00 / s.00
Plen / 17 / 86.20 / 5.07 / .62 / 4.00 / b.Uu

this relationship failed to achieve statistical significantTABLE 3. Percent increase in VLO for one degree change

(P = 0.16).in VMO'

DISCUSSION

The patellofemoral joint is a complex structure consisting of bony articulations, retinacular/ligamentous restraints, and muscular insertions. All contribute to patellar tracking within the trochlea of the femur. Aberrancy in any of the above may lead to patellar malalignment and/or patellofemoral pain with a possible sequelae of articular cartilage degeneration. Patellofemoral pain and/or subluxation seems to occur clinically more often in females. Much speculation has been proposed for this observation. Females typically have a wider pelvis than males which increases the "Q-angle." This in turn results in a greater lateralizing effect on the patella during knee flexion. The medial and lateral border of the patella receive insertions of the vastus medialis obliquus and vastus lateralis obliquus, respectively (Fig. 3A). When these muscles contract, they will create a force along the lines of its fasicular insertion. The

TABLE 2. Estimated regression equation

EQ. 1LnVLO = 1.360 + 00.531VM0 - .00160(S x Vh10) (18.034)* (3.676)* (3.621)*

F = 11.6198* r2 = .434

S equals 1 if female, 0 if male; "t" statistics are in parentheses. 0 (P .O1).

Male Female I' Ratiu EQ. 1 0.531 0.371 Ul 1.43 'Measured VMO, one degree from regression eyuations.

insertion orientation of these muscle fibers will affect the medial and lateral vectors of pull on the patella. This study has directed its attention to this anatomic area. By analyzing the insertional orientation of the vastus medialis obliquus and vastus lateralis obliquus at the patellar junction, hopefully, a better understandin; of how these two muscles affect patellar tracking might be obtained. In addition, this study determined that there was a gender dimorphism amongst the insertional orientations of the vastus lateralis obliquus and vastus medialis obliquus which might add insight into the clinically observed higher incidence of patellofemoral pain and/or subluxation in females.

The above comments are made in reference to the fasicular alignment of each muscle. tio conclusion can be made regarding the actual medial and lateral forces affecting the patella. Based on Hill's (1970) mathematical relationship between force and velocity and subsequent studies on muscle architecture by V'ickiewicz et al. (1983) and Wickiewicz et al. (1984), torque, force, and velocity parameters can be deter-

Insertion Orientation of Terminal Vaams133

mined. Bodine et al. (1982), Sacks and Roy (1982), and Spector et al. (1980) found that architectural parameters explain variation and force better than biochemical properties. Cross sectional areas of muscle which are directly proportional to force have not been addressed in this study.

Correlations between the insertional orientation of the vastus medialis obliquus and vastus lateralis obliquus as well as measurements of insertional length were not known prior to this study. In this setting, one is obliged to analyze data for correlational importance with a statistical methodology known as least steps regression. If any correlations are thus found then the validity of these findings are real. This was performed in this study to determine if there were gender differences in the insertional orientation of the vastus lateralis obliquus and vastus medialis obliquus. Gender differences were found.

Previously, Hallisey et al. (1987) noted that the angular terminal insertion of the vastus lateralis obliquus with respect to the longitudinal axis of the patella was more horizontally oriented in males. We did not measure the angular terminal insertion of the vastus medialis obliquus in our previous study and felt it was necessary to do so.

This study has quantified and delineated sex differences for the terminal fiber insertion of the vastus medialis obliquus and the vastus lateralis obliquus. The horizontal orientation of the vastus lateralis

obliquus is greater in males than females. There is no linear increase in the horizontal orientation of the vastus medialis obliquus insertion angle between males and females. See schematic (Fig. 3B,(:).

If muscular imbalance is believed to be a reason for a clinically observed higher frequency of patellofemoral pain and/or subluxation in females and this population of knees represents a sample of the population, one would expect that female knees would have a more horizontally oriented vastus lateralis obliquus insertion angle. Our study shows the opposite. This su(;gests that there are a number of other variables which intluence patellar tracking.

Forty-five percent of the variation in the vastus lateralis obliquus is explained by the vastus medialis obliquus insertion angle and the interactive variable (S x VMO). The remaining variation may be explained by the multitude of other variables aftcctinb patellar tracking including femoral trochlear depth, femoral troehlear angle, the convexity and concj\,It\, of the lateral and medial patellar facets, the rerinacular constraints, and the "net" effect of the Q-angle axis. The Q-angle was inversely related to the vastus lateralis obliquus but did not achieve statistical significance. In addition, the in vivo Q-angle may be different than the in vitro Q-angle.

Patellar malalignment may be related to muscular imbalance. However, the clinician should remember that muscular support of the patella is only one ofman\,