Sagittal plane translation during level walking in poor-functioning and well-functioning patients with anterior cruciate ligament deficiency

Sagittal plane translation during level walking in poor-functioning and well-functioning patients with anterior cruciate ligament deficiency

Joanna Kvist

Some patients with ACL deficiency can function well and participate in high-level sports, whereas others have functional limitations even during activities of daily living. Considerable effort has been spent toward elucidating the mechanisms adopted by the well-functioning patients. Alteration in gait pattern has been demonstrated in ACL-deficient patients. (1,8,14) However, a subgroup of the patients who functioned well showed no alternation in gait pattern compared to uninjured subjects. (13,14) There are contradictory results concerning differences in proprioceptive ability between well-functioning and poor-functioning patients. (5,11)

The primary function of the ACL is to prevent anterior translation of the tibia. After an ACL injury, anterior tibial translation increases. However, the amount of joint laxity is not correlated to function, (9,15) and joint laxity has no clear correlation to translation during activity. (9) Some patients with ACL deficiency do not use the whole available static laxity space during activity, (8,19) and the question that arises is if well-functioning patients use different amounts of translation during activity compared to patients with poor function. The aim of this study was to describe differences in anterior tibial translation during walking in a group of patients who functioned well after an ACL injury and a group of patients who did not. Based on previous preliminary results, (6) the hypothesis was that patients who function well after an ACL injury can stabilize the knee joint during gait by an anterior positioning of the tibia.

MATERIALS AND METHODS

Twenty patients with a complete unilateral non-operated ACL injury verified by arthroscopy participated in this study. The patients were placed in 1 of 2 groups according to their knee function as determined by the Lysholm knee score. The Lysholm score is a discrete rating score in which the patient can achieve a maximum score of 100. Scoring less than 84 points indicates problems from the knee joint during daily life. (16) In this study, 11 patients scored 84 or more and were placed in the well-functioning group. Nine patients reported knee problems during daily life (scored less than 84 in the Lysholm knee score) and were placed in the poor-functioning group. Patient demographics are presented in Table 1. There were no differences between the groups regarding sex, age, injured leg, concomitant injuries, time from injury, or activity level before or after the injury as determined by the Tegner score. (16) The well-functioning group scored higher compared to the poor-functioning group in the Knee Injury and Osteoarthritis Outcome Score (12) (Table 2). The study was approved by the local ethics committee, and informed consent was obtained from all subjects.

A computerized arthrometer linkage (CA-4000, OSI Inc, Hayward, Calif) was used to measure the flexion angle and sagittal tibial position (Figure 1). The system is composed of 3 parts–the femoral and tibial frames and a rotation module. Three potentiometers in the rotation module measure the relative rotations between the femur and tibia. A fourth potentiometer for sagittal motion was mounted in the tibial frame to register the difference in position between a spring-loaded patellar pad and the fixation point on the tibial tuberosity during knee motion. The potentiometer registering knee extension and flexion was aligned with an approximate knee flexion axis in the center of the lateral femur epicondyle, and the alignment was checked repeatedly during the examination. The system was zeroed at the beginning of the test with the subject lying on the examination table and the knee relaxed in full extension. To identify the reference position at each flexion angle for the calculation of translation during activity, a passive knee extension was done with the subject sitting on an examination table in a start position of 70[degrees] of hip flexion and 90[degrees] of knee flexion. When the subject relaxed, the examiner first flexed the knee to more than 100[degrees] and then extended it into hyperextension.

[FIGURE 1 OMITTED]

Data were sampled from the 4 potentiometers by a computer at a rate of 2000 Hz. Sagittal plane translation (millimeters) and the knee flexion angle (degrees) were analyzed. The reproducibility (6,8) and validity (20) of the measurement system have been tested in our laboratory and shown to be satisfactory.

Static knee translation was assessed by an instrumented Lachman test using the CA-4000 arthrometer: The subjects were seated on a special seat with the upper and lower leg fixed so that knee flexion was approximately 20[degrees]. The total translation at 90 N is reported.

Dynamic translation was assessed with the subjects walking barefoot along a 3.5-m walkway. The instruction was to walk as normally as possible, at a free speed. Several practice trials were allowed to ensure foot contact with a force plate. After practice, subjects walked 3 times, and data were collected in the second stride. Stance phase was identified from the force plate, and sagittal plane motions (flexion and translation) were analyzed.

Data Analysis

Tibial position is given in relation to the patella (femur) with the relative position at passive extension as the neutral reference. A position anterior to the neutral reference is referred to as positive and posterior as negative. Tibial translation is calculated by subtracting the tibia position values during the passive knee extension from the position values during walking. Calculation in the described manner eliminates the change in position resulting from rollback of the femur. The concurrent validity of the calculation method and the repeatability of the passive extension test have been described before. (6,8)

Statistics

Mean values and [+ or -]1 SD are given in the text and tables. Student t test for independent variables was used to compare translation and flexion angle between the groups. With [alpha] = .05 and [beta] = .80, the design of this study allowed for detection of a translation difference of 0.5 mm.

RESULTS

During gait, the well-functioning group had 24% greater anterior translation in the injured leg compared to the noninjured leg. In contrast, the poor-functioning group had 16% less anterior translation in the injured leg. The difference in translation between the groups was statistically significant (P = .0003). During the stance phase, the tibia was anteriorly positioned in all legs (Figure 2). The maximum anterior translation during walking occurred between 10[degrees] and 15[degrees] of knee flexion. There were no differences in tibial translation in the injured leg at the Lachman test between the well-functioning and poor-functioning groups (Table 3). There were no differences in tibial translation during the Lachman test (P = .924) or gait (P = .077) in the noninjured leg between the well-functioning and poor-functioning groups.

[FIGURE 2 OMITTED]

There were no differences between the groups regarding knee flexion angle at initial contact, peak knee flexion during loading response, peak knee extension during stance, and maximum knee flexion at toe off (Figure 3).

[FIGURE 3 OMITTED]

DISCUSSION

The results of this study show that during walking, well-functioning patients have a greater anterior translation in the injured leg than in the noninjured leg. In contrast, patients with poor knee function have smaller anterior translation in the injured leg than in the noninjured leg. That difference was about 2 mm, which is half of the total translation during gait. Both groups had similar amounts of translation during the Lachman test, indicating that the possible joint play area was similar between the groups. This confirms previous studies that have shown similar amounts of joint play in well-functioning and poor-functioning patients. (13,14) The results on tibial translation during walking may be counterintuitive. However, our previous results (6) point in the same direction. With very small external forces, the tibia can move freely and in a random way in the knee joint play area. With application of external forces, the tibia reaches the borders of the joint play area, where the ligaments guide and restrain tibial motion. The restraint from the ligaments increases when the tibia is pressed with greater force on to the borders. When the tibia is moving freely in the joint play area, small changes in external forces result in large positional changes of the tibia until it reaches the borders. This free motion results in a feeling of knee instability. When the tibia is near the border, the external force should cause only small movements due to ligament restraint. Consequently, during the stance phase, when weightbearing results in anterior translation of the tibia, (2,8,9,18) the knee joint feels stable when the tibia is positioned near the anterior border of the joint play.

The greater anterior translation in the well-functioning group indicates that these patients position their tibiae near the anterior border of their joint play during walking. This position is associated with greater functional stability, although it is not the normal position in the knee joint. Large changes in external forces or weight acceptance at knee flexion more than 20[degrees] may result in a sudden posterior translation of the tibia, usually noted as a giving way or pivot shift. (4) This may injure the menisci or cartilage. On the other hand, poor-functioning patients position their tibiae in an unstable position, somewhere in the middle of the joint play area. They feel their knees to be unstable. Although walking is seldom associated with functional instability, we do not know if the same tibial positioning is valid during more strenuous activities, for example, pivoting or jumping situations in which giving way most often occurs.

We do not know if the anterior positioning of the tibia is the cause of the good results for well-functioning patients. Perhaps another factor or factors, not yet known, may be primarily responsible for determining whether an individual will be well functioning or poor functioning. The adaptation may occur in the poor-functioning patients who may compensate for this other factor by pulling the tibia posteriorly, away from the subluxated position. The well-functioning patients do not have a need to adopt this compensatory mechanism and thus allow their tibiae to subluxate anteriorly during gait. Thus, the anterior position reflects the fact that the well-functioning knees are more functionally stable but is not necessarily the cause of that stability.

The noninjured legs in the poor-functioning group of this study bad larger anterior tibial translation during gait than what would be expected for noninjured knees. (7) This may be due to an adaptation of the noninjured knee toward the injured contralateral knee, a phenomenon that has previously been reported. (1,8) This adaptation mechanism in the noninjured knee seems to differ between well-functioning and poor-functioning patients. Another explanation would be that large anterior translation pre-injury predisposes patients to poor postinjury function.

We did not find any difference in knee flexion angles during the stance phase. Reduced knee flexion at stance phase has been demonstrated after ACL injury (1,13,14) In addition, Rudolph et al demonstrated reduced knee flexion (13,14) and a higher degree of coactivation of quadriceps, hamstrings, and gastrocnemius (13) in a poor-functioning group of ACL-deficient patients. The authors interpreted these results as a strategy to stiffen the knee, which may be deleterious and increase the risk for future joint degeneration. Because it appears from the results of our study that an anterior position of the tibia is associated with improved function, a synergistic activation of quadriceps and gastrocnemius should further improve stability. A coactivation of the antagonistic hamstring muscles should decrease the mechanical efficiency, (3) and at large flexion angles (>20[degrees] of flexion), the tibia may be pulled posteriorly causing instability. (10)

In this study, patients were defined as well functioning if they had a Lysholm score of 84 or more, which means that they had no problems from their knees during activities of daily living. Other definitions for grouping the patients have previously been used, (5,11,13,14) especially with patient activity level as a factor. (5,13,14) In the present study, the patient activity level was similar between the groups, with large variation within the groups. For many patients, the activity level is not only adjusted due to knee function but also due to other factors such as a recommendation to avoid contact sports, fear of reinjury, or other social reasons such as pregnancy or having left college. The hypothesis for the present study was based on our previous preliminary results of 12 patients with ACL deficiency. (8) In an attempt to compare these results to other data, we used the method by Jensen ct al, (5) who combined the Lysholm score and Tegner activity score to categorize the groups. Only 7 of the patients in the present study fulfilled these criteria, and of these, only 1 was well functioning. If the results from the present study were combined with the 12 patients from our previous study, (8) there would be 4 patients in the well-functioning group and 8 in the poor-functioning group. The results in this case are similar to the present study.

The results from this study indicate that patients who function well after an ACL injury position their tibiae anteriorly during gait. This position may encourage functional stability. This is of clinical importance in the effort to understand the stabilization mechanisms after an ACL injury. Further research is needed to identify other factors of importance for a good function after ACL injury.

ACKNOWLEDGMENT

The author especially thanks Professor Per Aspenberg and Professor Jan Gillquist for valuable advice on the manuscript and PhD student Bjorn Skoglund for linguistic advice. This study was supported by grants from the Swedish Center for Research in sports (108/02), the county council of Ostergotland (2002/25), and the faculty of Health Sciences Linkoping University.

TABLE 1

Individual Characteristics(a)

Age Tegner Score

Injured Concomitant Months Before Injury/ Lysholm

Sex Leg Injury to Test At Test Score

Well-functioning

group

M 36 R LM (b) 32 7/5 100

F 27 L 27 4/4 100

M 37 L CL (grade 1) 32 10/9 95

F 17 R 22 4/4 95

M 25 R LM 17 8/8 94

M 31 L MM (b) 46 9/4 94

F 37 L 38 4/4 91

M 27 R 36 8/8 85

F 30 R MM, CL 25 5/5 85

(grade 2)

F 24 L LM (b); MCL 33 5/4 85

(grade 2);

CL (grade 1)

M 32 R CL (grade 2) 15 9/7 84

Poor-functioning

group

M 36 L 29 7/7 80

M 36 L 30 9/4 79

M 21 L LM (b); MCL 25 3/4 75

(grade 2)

M 33 L MCL (grade 2) 36 4/4 73

F 19 L LM 35 6/6 63

F 37 R 42 3/3 61

M 34 R MM (b); 30 9/5 55

LM (b)

M 37 R MM 27 7/4 55

F 19 R MM (c); CL 32 9/4 42

(grade 2)

(a) M, male; F, female; R, right; L, left; LM, lateral meniscus;

CL, cartilaginous lesion (grade of lesion on femur or tibia (17));

MM, medial meniscus; MCL, medial collateral ligament.

(b) Partial meniscectomy.

(c)Total meniscectomy.

TABLE 2

Lysholm Score and Knee Injury and Osteoarthritis Outcome Score (KOOS)

in the Well-Functioning and Poor-Functioning Groups (a)

Well Functioning Poor P Value

Functioning

Lysholm 92 (84-100) 65 (42-80)

KOOS

Pain 93 [+ or -] 8 (88-98) 74 [+ or -] 19 (59-88)

Symptoms 89 [+ or -] 9 (83-95) 73 [+ or -] 21 (57-89)

Function in 98 [+ or -] 3 (96-99) 87 [+ or -] 14 (76-98)

activities

of daily living

Function in sport 83 [+ or -] 15 (73-92) 61 [+ or -] 26 (41-81)

and recreation

Knee-related 70 [+ or -] 19 (57-83) 50 [+ or -] 18 (36-64)

quality of life

Well Functioning

Lysholm .000

KOOS

Pain .005

Symptoms .028

Function in .024

activities

of daily living

Function in sport .032

and recreation

Knee-related .026

quality of life

(a) The Lysholm scores represent medians (range), and the KOOS scores

represent means [+ or -] SD (95% confidence interval).

TABLE 3

Maximal Translation (mm) in Lachman Test and Gait in the

Well-Functioning and Poor-Functioning Groups (mean [+ or -] SD)

Well Functioning

Difference

Between

Noninjured

Noninjured Injured and Injured

Lachman 4.9 [+ or -] 1.1 6.7 [+ or -] 1.8 1.8 [+ or -] 1.7

Gait 4.2 [+ or -] 1.1 5.5 [+ or -] 2.7 1.3 [+ or -] 1.2

Poor Functioning

Difference

Between

Noninjured

Noninjured Injured and Injured

Lachman 4.8 [+ or -] 1.6 6.1 [+ or -] 2.2 1.2 [+ or -] 2.3

Gait 6.1 [+ or -] 1.8 5.1 [+ or -] 2.1 -1.0 [+ or -] 1.0 (a)

(a) Significantly different from the well-functioning group.

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Joanna Kvist, * RPT, PhD

From the Institution of Health and Society, Physical Therapy and the Institution of Neuroscience and Locomotion, Linkoping, Sweden

* Address correspondence to Joanna Kvist, PhD, Institution of Health and Society, Physical Therapy, 581 83 Linkoping, Sweden (e-mail: joanna. kvist@ihs.liu.se).

Neither the author nor her related institution has received financial benefit from research in this study.

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