SELECTED KNEE JOINT FORCES DURING LANDING ACTIVITIES

S. Zhang (1), B. Bates (2), J. Dufek (2)
(1) Exercise Science, University of Tennessee, Knoxville, TN 37996
(2) Biomechanics Laboratory, University of Oregon, Eugene, OR 97403

Presented at the 20th Annual Meeting of the American Society of Biomechanics
Atlanta, Georgia. October 17-19, 1996

INTRODUCTION

The study was conducted to investigate the mechanical loadings on selected knee joint structures during a landing activity and comparisons with other activities were attempted.

REVIEW AND THEORY

Overuse injuries to the lower extremity are of major concern to both participants and researchers. Of all injuries to the lower extremity, the knee is the most frequently injured site among runners, volleyball players and other athletes. Landing is a phase in many activities during which the human body experiences tremendous impacts and loadings. The knee joint, in particular, endures the highest loadings among the lower extremity joints during landing (Zhang, 1996). Among the knee joint structures, the patellar tendon and patellofemoral joint are often the sites of long-term problems. The forces experienced by the structures during walking and running have been documented (Nisell, 1985; Scott et al., 1990) but little information is available for landing activities. Therefore, the purpose of the study was to investigate the patellar tendon, quadriceps tendon and patellofemoral compressive forces during a landing activity, using a modified Nisell's model (1985) with the addition of the gastrocnemius as an antagonist muscle.

PROCEDURES

Nine healthy males, semi-skilled in jump/landing activities, volunteered to participate as subjects (18 - 35 yrs). Subjects were asked to perform 5 step-off landings in each test condition. Nine experimental conditions included the combinations of 3 landing heights: 0.32 m, 0.62 m and 1.03 m, and 3 landing techniques: soft (SFL), normal (NML) and stiff (STL) with maximum knee flexion being monitored by an electrogoniometer to assure proper performance of each landing technique. Two high speed video cameras (200 Hz, Motion Analysis) were used to obtain right sagittal kinematic data. One camera focused on the total body while the other camera focused only on the lower extremity during the activity. The lower extremity view was later mapped onto the view for the total body movement in order to obtain better lower extremity marker accuracy. Two force platforms (1000 Hz, AMTI) were used to obtain ground reaction force data from both limbs and the data from the right side were used for further calculations. Inverse dynamic approach was adopted to compute the joint kinetics while a modified Nisell's model was used to calculate selected knee joint forces. The gastrocnemius moment arm about the knee joint center was estimated using the method provided by Grieve et al. (1978) and Bobbert et al (1986). The patellar tendon moment arm as well as three force vector angles were estimated using the data provided by Nisell. The original data were first fitted with a fourth order polynomial with respect to knee joint angle, and the values of the moment arm and the angles were then calculated based upon actual knee joint angles for each subject. All data were normalized to 100 percent for the landing phase and the kinetic data were normalized to body mass.

RESULTS

A typical mean patellar tendon curve (Figure 1) demonstrated a first maximum (FPA1) and a second maximum (FPA2) while the quadriceps tendon and patellofemoral compressive forces exhibited similar features, which occurred approximately at the time of toe- contact and heel-contact (first and second vertical lines in Figure 1). The mean group data were collapsed across heights and techniques for FPA1, FPA2, first (FCA1) and second (FCA2) maximum patellar compressive forces, and first (FQA1) and second (FQA2) maximum quadriceps tendon forces (Table 1). Two-way group ANOVAs (Height Technique) demonstrated overall significant effects of the maximum forces for all test conditions (p < 0.0001). Significant increases (p < 0.05) for the first and second maximum forces were observed across the three landing heights while the increases across landing stiffness were comparatively smaller in magnitude with some decreased values for STL for some variables (FCA1, FCA2 and FQA2).

TABLE 1. Group Means of Maximum Knee Joint Forces Collapsed by Height and Technique

DISCUSSION

The knee joint force values were extremely high compared with those observed in other more moderate activities. In level walking, Nisell reported 1400 N for maximum patellar tendon force, 900 N for maximum patellofemoral compressive force, and 1500 N for maximum quadriceps tendon force. The data from the present study showed an average of 3420 N for FPA2, 4682 N for FCA2, and 4839 N for FQA2 for SFL from 0.32 m. In running, Scott et al. (1990) found maximum patellar tendon forces of 2767 N during support. Compared with the above average patellar tendon force, the FPA2 is 1.2 times greater. For STL at 1.03 m, the average FPA2 was 6433 N or 2.3 times greater than those found during running. These results indicate a greater demand overall on the knee joint during landings.

Zenicke et al. (1977) reported the only case of acute patellar tendon rupture of a weight lifter during an actual competition in which a biomechanical analysis was done. The patellar tendon tension at the time of rupture was estimated at 14,500 N (17.5 body weight-BW). The tendon was ruptured at the time when the knee joint angle was in 89.2ø of flexion. The average first maximum patellar tendon force (FPA1) observed in this study was 11,473 N (15.7 BW) for STL at 1.03 m. The average knee joint angle at the time when the FPA1 occurred was 39.7ø. Even though the average FPA1 was close to the values observed for the tendon rupture, the knee joint was on average in a relatively more extended position and the patellar tendon was not in as stretched a state. The highest individual FPA1 value was 181.72 N/kg for S9 in one of the STL trials from 1.03 m, representing a normalized value of 18.5 BW. This extreme value was observed earlier in the landing phase with an extended knee position. The mechanical response of a tendon increases with the increased strain rate (loading rate), and a tendon generally requires greater force to rupture in the earlier stretch state. Therefore, the first patellar impact force is less likely to cause acute injuries to the patellar tendon.

REFERENCES

Bobbert, M. F. et al. J. Biomech., 19, 887- 898, 1986.

Grieve, D. W. et al. Biomechanics VI-A. (pp 405-412), University Park Press, 1978.

Nisell, R. Acta Orth. Scand., suppl. 2-42, 1985.

Scott, S. H., et al. Med Sci Sports Exerc, 22, 357-369, 1989.

Zenicke, R. F. et al. J. Bone Joint Surg., 59-A, 179-183, 1977.

Zhang, S. Dissertation, 1996.