J. Biomechanics Vol. 25, No. 6, pp. 637643, 1992. Printed in Great Britain

00214290/92 $5.00+.00 Pergamon Press Ltd

TECHNICAL NOTE

IN VI VO TRACKING OF THE HUMAN PATELLA TIMOTHY J. KOH,*~ MARK D. GRABINER,* and ROBERT J. DE SWARTt *Department of Biomedical Engineering and Applied Therapeutics, and :~Department of Orthopaedic Surgery, The Cleveland Clinic Foundation, Cleveland, OH 44196, U.S.A. Abstract--The purpose of this study was to describe the dynamic, in vivo, three-dimensional tracking pattern of the patella for one normal male subject. Intracortical pins were inserted into the patella, tibia, and femur. The subject performed seated and squatting knee flexion/extension, and maximum voluntary quadriceps contractions. In addition, the vastus medialis oblique was subjected to maximal electrical stimulation. Motions of the markers attached to the intracorticai pins were analyzed using an automated video system. Patellar and tibial motions were determined relative to a femoral reference system. While the tibia flexed 50° from full extension (seated condition), the patella flexed 30.3°, tilted laterally 10.3°, and shifted laterally 8.6 ram. In general, these results show qualitative agreement with the data collected from cadaveric specimens [van Kampen and Huiskes, J. orthop. Res. 8, 372-382 (1990)]. The differences present may reflect different passive constraints to patellar motions, and different relative loading of the individual quadriceps components, in our study compared to the cadavetic study. Only small differences were found between patellar motions in the seated and squatting conditions. Differences in patellar displacements produced by (1) maximal electrical stimulation of the vastus medialis oblique, and (2) maximum voluntary quadriceps contraction, at 30° knee flexion and full extension, may reflect the dominant influence of passive constraints, and the vastus lateralis, on normal patellar motions. Further in vivo study of patellar tracking seems warranted to evaluate surgical and conservative interventions for patellofemoral disorders.

INTRODUCTION

METHODS

Patellofemoral disorders, which are among the most common knee disorders, are often assumed to be related to an abnormal tracking of the patella (Fulkerson and Hungerford, 1977). However, little quantitative data on patellofemoral joint kinematics is available in the literature. The majority of the existing data have been collected under static conditions. Veress et al. (1979) and Sikorski et al. (1979) measured static orientations and positions of the patella in vivo at different angles of knee joint flexion using radiological techniques. Reider et al. (1981) and Fujikawa et al. (1983) measured static orientations and positions of the patella in vitro. These studies produced inconsistent results, and did not account for tibial rotation, which has been shown to influence patellar orientations and positions (van Kampen and Huiskes, 1990). Lafortune (1984) presented the only dynamic patellar tracking data found in the literature in his study of in vivo knee joint kinematics during gait. Forces produced by components of the quadriceps fernotis, particularly vastus medialis oblique and vastus lateralis, are thought to influence the tracking of the patella (Lieb and Perry, 1968). Of the aforementioned studies of patellofemoral kinematics, Reider et al. (1981) and van Kampen and Huiskes (1990) produced quadriceps forces in their cadaveric specimens by static weighting of the four components of the muscle. Veress et al. (1979) and Sikorski et al. (1979) had their subjects perform isometric quadriceps contractions. Only Lafortune (1984) studied patellar tracking with dynamic in vivo quadriceps contractions. The purpose of our study was to describe the dynamic, in vivo, three-dimensional tracking pattern of the patella for one normal male subject.

One male subject (age 30 yr, height 1.83 m, weight 794 N), with no history of knee joint disorder, volunteered for partidpation in this study. Informed consent was obtained before the experiment. Using standard surgical procedures, the skin over the right knee joint was shaved and cleaned. Lidocaine (2%) was used to anesthetize the skin, subcutaneous tissue, and periosteum at three locations: (1) the anterolateral aspect of the patella, (2) the medial condyle of the femur, and (3) the tibia slightly superior and medial to the tibial tuberosity. At each location, a small incision was made in the soft tissue, and a threaded intracortical pin (1.6 mm diameter) was inserted into the bone using a surgical drill (no predrilling was required). The subject reported no discomfort during the insertion of the pins. A triad of reflective markers (1.25 cm spheres separated by 7.5 cm) was attached to each of the intracortical pins (Fig. 1), and the stability oftbe triad-pin-bone junctions was verified by manipulation and visual observation. Reflective skin markers (2 cm hemispheres) were placed over the greater trochanter of the femur, and the medial and lateral condyles of the femur (approximately on the line of flexion/extension of the knee joint). Patellofemoral kinematics were analyzed during four experimental conditions: (1)while seated, the subject performed five trials of flexion/extension of the right knee joint at an approximate rate of 30° s- 1. The range of motion was limited approximately to the initial 60° of flexion because the soft tissues impinged on the femoral pin past 60° flexion despite the incision made at the insertion site. (2)With the muscles around the knee joint relaxed, the vastus medialis oblique was subjected to maximal electrical stimulation (that which produced a maximal displacement of the patella). Three trials were performed at each of the following two knee joint angles: full extension (0° flexion) and 30° flexion. The

Received in final form 26 September 1991.

:~Author to whom correspondence should be addressed.

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Technical Note

stimulation was delivered using an isolated stimulation unit (pulse duration 0.5 ms, frequency 80 Hz, Model $44, Grass Instrument) and bipolar electrodes placed over the belly of the muscle. The stimulation voltage was increased until the motion of the patella ceased. (3) The subject performed three trials of maximum voluntary isometric quadriceps contraction at each of the two knee joint angles (0 and 30° flexion). (4) Starting from the standing position, the subject performed three trials of a squatting exercise during which knee flexion/extension occurred at an approximate rate of 30° s- 1. The anesthesia was active throughout the experiment, and the subject reported discomfort only when the knee joint angle approached 60 ° flexion. After the experiment, the subject reported soreness only at the femoral location (lasting three days), likely due to the impingement of the soft tissues at this site. The three-dimensional motions of the reflective markers were recorded at 60 Hz with four video cameras and analyzed using a Motion Analysis system and custom software. The X-, Y-, and Z-coordinates of the resulting trajectories were smoothed independently using a Butterworth filter with a cutoff frequency of 3 Hz. Cartesian reference systems were defined for the patella, tibia and femur similar to van Kampen and Huiskes (1990). The origin of the patellar reference system was located at the estimated center of the patella (determined from surface measurements), and the origin of the femoral reference system was located at the midpoint between the skin markers on the medial and lateral condyles of the femur. The axes of the three reference systems were defined to be parallel in full active knee extension (the neutral position). The directions of the reference system axes in this neutral position (Fig. 2) were determined from the skin markers placed on the thigh, and were directed medially (X-axis), superiorly along the long axis of the thigh (Y-axis), and anteriorly (Z-axis). The reliability of determining the directions of these axes in the neutral position (including the placement of markers) was within 2 °. Patellar and tibial rotations, and patellar translations were determined relative to the femoral reference system. The reference system for each bone was conceptually imbedded in the appropriate marker triad, and the relative motions of these reference systems were determined from 4 x 4 homo-

Medial/lateral tilt Y

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Fig. 2. Patellar reference system and the associated motions. Flexion/extension, medial/lateral rotation and medial/lateral tilt indicate Cardan rotations about the X-, Z-, and Y-axes, respectively. Medial/lateral shift indicates translation along the X-axis. Terms before the slashes indicate motions with positive values, and those after, motions with negative values.

geneous transformations. No rigid-body constraints were used. Rotations were defined as Cardan rotations with an X Y Z order of rotation. Patellar Cardan rotations (Fig. 2) were termed, in order (positive/negative), flexion/extension, medial/lateral rotation, and medial/lateral tilt. Tibial Cardan rotations were likewise termed flexion/extension, varus/valgus, and internal/external rotation. Patellar translation along the femoral X-axis was termed medial/lateral shift. Translations along the femoral Y- and Z-axes were also measured, but are not discussed for the sake of brevity. The sensitivity of medial/lateral shift measurements to variations of 5 mm in the relative positions of the origins of the patella and femur was determined. Such a variation produced a maximum variation in the maximum shift of the patella (from experimental data) of 1 mm. A separate study was conducted to determine the error in calculating the linear and angular positions of the reflective markers and marker triads. Data collection and analysis procedures were similar to those described above. To determine the error in linear positions, markers were placed at known locations in the laboratory reference frame. The deviation of the calculated positions (from the video data) from the known positions was less than 1 mm. To determine the error in angular positions, a marker triad was placed in a testing rig which allowed known rotations about three mutually perpendicular axes. The deviation of the calculated positions from the known positions was less than 1°. RESULTS AND DISCUSSION Figure 3 shows the plots of the mean values of patellar Cardan rotations, patellar translation, and tibial Cardan rotations as a function of knee flexion angle (averaged over trials) for seated knee flexion/extension. Only knee flexion data are shown in these plots; knee extension produced similar curves (with opposite trends). Internal/external rotation of the tibia was quite small, showing little of the so-called 'screw home' mechanism (unlocking or internal rotation in Fig. 3) during the initial part of knee flexion (Hallen and Lindahl, 1966). This suggests that the screw home mechanism is not obligatory for this subject and, thus, supports the conclusions of Blankevoort et al. (1988). van Kampen and Huiskes (1990) showed that internal/external tibial rotation of up to 25 ° strongly influenced patellar tracking. However, it is not likely that the small amount of rotation seen in the present study was an important determinant of patellar motions. The patella flexed with knee flexion, but patellar flexion lagged behind knee flexion. The patella also tilted laterally (rotated such that the front of the patella faced laterally) with knee flexion, and showed very little medialflateral rotation (rotation about an axis perpendicular to the patellar plane). Finally, the patella shifted laterally with knee flexion. Standard deviations over trials were generally less than 1° (range 0.2-1.2 °) for all patellar Cardan rotations and approximately 1 mm (range 0.7-1.4 mm) for medial/lateral shift. These standard deviations did not appear to be related to the knee flexion angle. van Kampen and Huiskes (1990) reported that, in four cadaveric specimens, the patella showed flexion, very little medial/lateral rotation and lateral shift within the range of knee flexion used in our study. Their data were inconsistent with respect to tilt-- two specimens showed medial tilt, and two showed lateral tilt. In general, the results of our study agree qualitatively with those of van Kampen and Huiskcs. This suggests that van Kampen and Huiskes were mostly successful in simulating normal in vivo patellar tracking in their cadaveric specimens. However, the results of our study show a greater flexion lag, and greater lateral tilt and shift than those of van Kampen and Huiskes. These differences may reflect intersubject differences in passive constraints to patellar motion (e.g. bony and ligamentous). In addition, the

Fig. 1. Intracortical pins inserted into the patella, femur and tibia of the right knee joint, and the associated marker triads.

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Fig. 3. Average patellar and tibial motions for seated knee flexion (n = 5 trials). Terms before the slashes indicate motions with positive values, and those after, motions with negative values.

difference in lateral tilt and shift may be due, in part, to different relative loading of individual quadriceps components between studies--a large vastus lateralis force (relative to vastus medialis oblique force) may tend to tilt and shift the patella laterally. Finally, the differences in flexion and tilt may reflect a difference in the order of Cardan rotations used in the two studies (although not stated explicitly, van Kampen and Huiskes appeared to use an X Y Z order of rotation as compared to the X Z Y order used in our study). However, Blankevoort et al. (1988) have shown that, if the final two Cardan rotations (rotation and tilt in this study) have small magnitudes (as in this study), the order of these rotations has little effect on the magnitude of each Cardan rotation. Lafortun¢ (1984), in his study of in viva patellar tracking during gait, also found a predictable 'lag' in patellar flexion

with respect to knee flexion. However, patellar tilt, rotation, and shift showed more complicated relationships with knee flexion, likely involving tibial rotation and dynamic quadriceps contraction. It is, thus, difficult to compare the results of our study with those of Lafortune. Figure 4 shows the plots of the mean values of patellar Cardan rotations, patellar translation, and tibial Cardan rotations as a function of knee flexion angle (averaged over trials) for squatting flexion/extension. The tibia externally rotated a small amount (again contradicting the notion of an obligatory screw home mechanism), and showed a relatively large varus rotation (compared to the seated condition) as the knee flexed. Despite the difference in tibial rotations between the seated and squatting conditions, and the assumed greater quadriceps activation in the squatting condition, the patellar rotations and translation were quite similar. The small

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differences present occurred predominantly during the initial degrees of knee flexion, when passive constraints to patellar motion (e.g. the intercondylar groove of the femur) are minimal. Displacements of the patella during maximal electrical stimulation of the vastus medialis oblique and maximum voluntary isometric quadriceps contraction are presented in Table 1. Stimulation of the vastus medialis oblique produced smaller patellar displacements at 30° knee flexion than at 0° flexion. Isometric contraction of the quadriceps, initiated from rest, also produced smaller patellar displacements at30 ° knee flexion than at 0 ° flexion. These results suggest that quadriceps contraction has less influence on patellar tracking at 30° knee flexion than at 0 ° flexion, likely reflecting the increased stability of the patella as it moves into the inter-

condylar groove with increased knee flexion. At 0 ° knee flexion, stimulation of the vastus medialis oblique produced medial rotation, tilt and shift, while isometric quadriceps contraction produced lateral rotation, tilt and shift. These results suggest that knee extensors that pull the patella laterally (primarily the vastus lateralis) act to counter the medial rotation/tilt/shift produced by the vastus medialis oblique. In fact, the former muscles appear to dominate the motion of the patella, producing lateral rotation/tilt/shift. As the data were collected from only one subject, the findings of this study should be considered with caution. However, in vivo research such as ours must be performed to verify the data collected from cadaverie specimens. In addition, only in vivo experiments can be used to investigate the influence of in vivo muscle force, and of muscle-training

Technical Note

643

Table 1. Displacements of the patella during maximal electrical stimulation of the vastus medialis oblique and maximal voluntary isometric contraction of the quadriceps Knee joint flexion (°)

Flexion/extension (°)

Medial/lateral rotation (°)

Medial/lateral tilt (°)

Medial/lateral shift (mm)

Electrical stimulation 0 - 1.08 (0.67) 30 0.26 (0.41)

1.99 (0.50) 0.32 (0.60)

2.16 (0.38) 0.43 (0.78)

1.4 (0.5) 0.3 (1.0)

Isometric contraction 0 -4.52 (0.37) 30 - 1.20 (0.60)

- 1.61 (0.81) 0.07 (0.98)

-'0.62 (0.52) 0.99 (0.37)

-4.5 (2.2) - 1.5 (3.0)

Note. Values are means over three trials (and the associated S.D.s). Positive values indicate flexion, medial rotation, tilt, and shift; negative values indicate extension, lateral rotation, tilt, and shift.

exercises, on patellar tracking. Lateral retinacular release and tibial tubercle elevation (surgical interventions for patellofemoral disorders) have had varying degrees of effectiveness in producing the desired changes in patellofemoral kinematics and pressures in cadaveric specimens (cf. van Kampen, 1987). Lateral release, in conjunction with quadriceps rehabilitation exercises, appeared to produce the desired kinematic changes and produce good clinical outcomes for patients diagnosed with 'maltracking' patellae (Dzioba, 1990). As only in vivo studies are likely to be useful in evaluating clinical interventions which include rehabilitation exercises, further in vivo study seems warranted to reveal the mechanisms underlying the success (or failure) of these interventions. Acknowledgements--The authors acknowledge John Brems,

M.D., for performing the surgical procedures, and Greg Delozier for his work on the biomechanics programming language (GX) used to analyze the kinematic data. REFERENCES

Blankevoort, L., Huiskes, R. and Lange, A. de (1988) The envelope of passive knee joint motion. J. Biomechanics 21, 705-720. Dzioba, R. B. (1990) Diagnostic arthroscopy and longitudinal open lateral release. Am. J. Sports Med. 18, 343-348. Fujikawa, K., Seedhom, B. B. and Wright, V. (1983) Bio-

mechanics of the patellofemoral joint. Part I. Eng Med. 12, 3-11. Fulkerson, J. P. and Hungerford, D. S. (1977) Disorders of the Patellofemoral Joint (2nd edn). Williams and Wilkins, Baltimore. Hallen, L. G. and Lindahl, O. (1966) The 'screw-home' movements in the knee joint. Acta orthop, scand. 37, 96-106. Kampen, A. van (1987) The three-dimensional tracking pattern of the patella. Doctoral dissertation, University of Nijmegen, The Netherlands. Kampen, A. van and Huiskes, R. (1990) The three-dimensional tracking pattern of the human patella. J. orthop. Res. 8, 372-382. Lafortune, M. A. (1984) The use of intra-cortical pins to measure the motion of the knee joint during walking. Unpublished doctoral dissertation, Pennsylvania State University. Lieb, F. J. and Perry, J. (1968) Quadriceps function. An anatomical and mechanical study using amputated limbs. J. Bone Jt Sur9. 50A, 1535-1548. Reider, B., Marshall, J. L. and Ring, B. (1981) Patellar tracking. Clin. Orthop. Rel. Res. 157, 143-148. Sikorski, J. M., Peters, J. and Watt, I. (1979) The importance of femoral rotation in chondromalacia patellae as shown by serial radiography. J. Bone Jt Surg. 61B, 435-442. Veress, S. A., Lippert, F. G., Hou, M. C. Y. and Takamoto, T. (1979) Patellar tracking patterns measurement by analytical X-ray photogrammetry. J. Biomechanies 12, 639-650.

In vivo tracking of the human patella.

The purpose of this study was to describe the dynamic, in vivo, three-dimensional tracking pattern of the patella for one normal male subject. Intraco...
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