Tibiofemoral alignment: contributing factors to noncontact anterior cruciate ligament injury

Abstract

Background: The mechanisms of noncontact anterior cruciate ligament injury remain undefined. The purpose of this study was to identify the tibiofemoral alignment in the lateral compartment of the knee for three variations of a one-limb landing in noncontact sports activities: the safe, provocative, and exaggerated provocative positions. These positions were chosen on the basis of a previous study that measured the average joint angles of the limb at the point of ground contact for athletes who landed without injury (safe) and those who sustained an anterior cruciate ligament injury (provocative). It was hypothesized that, in the provocative positions, altered tibiofemoral alignment predisposes the knee to possible subluxation, potentially leading to an anterior cruciate ligament injury.

Methods: Magnetic resonance images were acquired for a single knee in twenty-five noninjured athletes for the three landing positions. The angle between the posterior tibial slope and the femur along with three distances (from the tibiofemoral point of contact to [1] the femoral sulcus point, [2] the posterior tibial point, and [3] the most anterior point of the circular posterior aspect of the condyle) were measured for each acquisition.

Results: The tibial slope relative to the femur was directed significantly more inferior to superior in the provocative and exaggerated positions than in the safe landing position. Similarly, as the limb transitioned from the safe to the provocative positions, the tibiofemoral joint contact point was significantly closer to the femoral sulcus point and to the most anterior point of the circular posterior portion of the lateral femoral condyle.

Conclusions: As the limb moves toward the provocative landing position, the anatomical alignment based on slope and contact characteristics places the knee at possible risk for noncontact anterior cruciate ligament injury. An enhanced understanding of the mechanism of anterior cruciate ligament injury may lead to improved preventative strategies.

Trial registration: ClinicalTrials.gov NCT00855023.

Figures

Fig. 1

This diagram shows a limb in the anatomically neutral position and in the three study positions: safe, provocative, and exaggerated provocative. Compared with the safe position, the positions of potential injury of the anterior cruciate ligament (provocative and exaggerated provocative) were associated with less plantar flexion of the ankle (A), greater extension of the knee (K), and greater flexion of the hip (H). The dark gray line behind the knee represents the splint used to maintain the proper knee angle. A rigid wedge (triangle below the foot) was used to position the ankle.

Fig. 2

Photograph of a subject in the safe position for a magnetic resonance imaging scan. The subject is standing with partial weight support provided by a small seat, a posterior fiberglass splint to support the knee, and a firm wedge under the foot to maintain ankle position.

Fig. 3-A Fig. 3-B

Figs. 3-A through 3-D Magnetic resonance imaging measurements in the safe (Figs. 3-A and 3-B) and provocative (Figs. 3-C and 3-D) positions. Fem = femoral, and Tib = tibial. Fig. 3-A The control (safe) position. The femoral shaft line was the line that bisected the angle created by two lines (dashed) that defined the anterior (Fa) and posterior (Fp) femoral shaft just proximal to the sulcus groove. The tibial plateau line paralleled the tibial plateau. Fig. 3-B The control (safe) position, shown with use of the same base figure as Figure 3-A, but with different markers. The lateral posterior femoral condyle was visually fit with an ellipse (Post Condyle Ellipse). The line of contact (dashed straight line) was visually defined. Post = posterior. The red dots match those shown in Figure 3-D to demonstrate how the points move between the control and the provocative position.

Fig. 3-A Fig. 3-B

Figs. 3-A through 3-D Magnetic resonance imaging measurements in the safe (Figs. 3-A and 3-B) and provocative (Figs. 3-C and 3-D) positions. Fem = femoral, and Tib = tibial. Fig. 3-A The control (safe) position. The femoral shaft line was the line that bisected the angle created by two lines (dashed) that defined the anterior (Fa) and posterior (Fp) femoral shaft just proximal to the sulcus groove. The tibial plateau line paralleled the tibial plateau. Fig. 3-B The control (safe) position, shown with use of the same base figure as Figure 3-A, but with different markers. The lateral posterior femoral condyle was visually fit with an ellipse (Post Condyle Ellipse). The line of contact (dashed straight line) was visually defined. Post = posterior. The red dots match those shown in Figure 3-D to demonstrate how the points move between the control and the provocative position.

Fig. 3-C Fig. 3-D

Fig. 3-C The provocative position. Fap was defined as the line perpendicular to the femoral shaft line and defined the femoral anterior direction. Fig. 3-D The provocative position, shown with use of the same figure as Figure 3-C, but with different markers. The point of contact (PC) was defined as the midpoint of the line of contact (Fig. 3-B) between the tibia and femur. The femoral sulcus point (FS) was defined as the most indented point on the lateral femoral condyle sulcus of the center of the most convex surface. The most anterior point on the circular portion of the posterior aspect of the condyle (APC) was defined as the point at which the posterior condyle ellipse (Fig. 3-B) and femoral surface lost contact. The posterior tibial point (PT) was defined as the most posterior point on the tibia.

Fig. 3-C Fig. 3-D

Fig. 3-C The provocative position. Fap was defined as the line perpendicular to the femoral shaft line and defined the femoral anterior direction. Fig. 3-D The provocative position, shown with use of the same figure as Figure 3-C, but with different markers. The point of contact (PC) was defined as the midpoint of the line of contact (Fig. 3-B) between the tibia and femur. The femoral sulcus point (FS) was defined as the most indented point on the lateral femoral condyle sulcus of the center of the most convex surface. The most anterior point on the circular portion of the posterior aspect of the condyle (APC) was defined as the point at which the posterior condyle ellipse (Fig. 3-B) and femoral surface lost contact. The posterior tibial point (PT) was defined as the most posterior point on the tibia.

Fig. 4

Measures of tibiofemoral placement (mean and standard deviation). The circle, square, and star represent the safe (S), provocative (P), and exaggerated provocative (E) positions, respectively. A positive value indicates that the point of contact (PC) was anterior to the posterior tibial point, that the femoral sulcus (FS) was anterior to the PC, or that the most anterior point on the circular posterior portion of the condyle (APC) was anterior to the PC. A significant difference between two positions is indicated by a bar. *p

Fig. 5

Pictorial representation of the tibial plateau as the patient is transitioned from the safe to the provocative position and from the provocative to the exaggerated provocative position.