A Measurement of Anterior Tibial Displacement in the Closed and Open ~inet ic Chain Walter I. )en kins, MS, PT, A TC ' Stephen W. Munns, MD2 Gopal layaraman, PhD Kenneth I. Wertzberger, MD Kurt Neely, MS, PT5

R ehabilitation following anterior cruciate liga- ment (ACL) injury is quite controversial and has progressed from the

exclusive use of open kinetic chain exercise to an emphasis on closed kinetic chain training. Human stud- ies, both cadaveric (6) and in vivo (2,8), have shown increased anterior tibial translation with open kinetic chain exercise. More limited study of closed kinetic chain exercise (8,15) suggests less anterior tibial displace- ment compared with the open chain.

An open kinetic chain can be defined as movement with the distal segment being free to move, while a closed kinetic chain is defined as the distal segment being fixed to a sur- face (19). Knee rehabilitation is com- monly performed in either of these two forms. Due to its specificity for the quadriceps, ease of equipment use, and the prevalent philosophy that squat.. were "bad for the knees," open kinetic chain knee extension exercises became the traditional form of quadriceps rehabilitation (17). The quadriceps are especially sensi- tive to atrophy following knee injury, often leaving the patient with pro- longed weakness of the knee exten- sion movement. If the clinicians' sole concern following injury was quadri-

Anterior displacement of the tibia during knee extension movement has been identified as a possible factor in anterior cruciate ligament (ACL) reconstruction failure due to the increased stress placed on the graft, leading to a creep response in the healing graft. Nineteen healthy subjects with a unilateral ACL deficiency were evaluated in an open and closed kinetic chain. A KT-1000 was used to measure anterior displacement of the tibia on the femur during isometric open and closed kinetic chain exercise at 30 and 60'. An analysis of variance for repeated measures followed by Newman-Keuls multiple comparison tests were performed to determine the differences between the open and closed kinetic chain for the involved and uninvolved knee. Statistically significant differences were found when comparing the amount of anterior displacement between the open and closed kinetic chain for the involved and uninvolved knee at 30 and 603 Clinicians utilizing isometric exercise in rehabilitation of the anterior-cruciate-deficient and the anterior-cruciate- reconstructed patient should be aware of the increased amount of anterior tibial displacement when comparing open and closed kinetic chain exercise.

Key Words: arthrometer, passive knee motion, therapeutic exercise

' Associate Clinical Professor, Department of Physical Therapy Education, School of Allied Health Sciences, East Carolina University, Greenville, NC 27858. At the time of this study, Mr. lenkins was an assistant profes- sor, Departments of Orthopaedic Surgery and Physical Therapy, Kansas University, Kansas City, KS.

Associate Professor, Department of Surgery, Orthopaedic Section, Sports Medicine Institute, Kansas Univer- sity Medical Center, Kansas City, KS ' Associate Professor, Department of Mechanical Engineering, Michigan Tech University, Houghton, MI

Orthopaedic Surgeon, Orthopaedic Surgery Associates, PA, Lawrence, KS Physical Therapist, VA Medical Center, Kansas City, M O

ceps strengthening, open kinetic chain knee extension exercise is clearly the most specific. However, one must consider the other effects such exercise has on the knee joint. A significant anterior tibial displace- ment and anterior shear force have been reported with open kinetic chain knee extension exercises (6,8,9, 26). This anterior tibial displacement can produce attenuation of the sec- ondary restraints of the ACMeficient

knee and of the ACL graft in the re- constructed knee (1). These anterior tibial displacements with resultant shear forces on the tibiofemoral and patellofemoral joints can also have detrimental effect. on the articular cartilage (4,7).

Closed kinetic chain exercises, particularly the squat, have been used for decades as the foundation for lower extremity strengthening. In the past decade, closed chain exercise

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has become the standard of care for many lower extremity disorders, in- cluding the rehabilitation of the ACLdeficient and the ACLrecon- structed knee (5.20). The primary reason for this change is the percep tion of reduced shear and reduced anterior tibial translation associated with closed chain exercise as well as the "more functional trainingn achieved when the kinetic chain is closed.

The variation in the amounts of shear and compressive force during knee extension exercise in the open and closed kinetic chain appears to be one of the primary differences between these two forms of exercise. When the kinetic chain is closed, there is an increase in compression and a decrease in shear forces, while the opposite can be said of an open kinetic chain. Possible explanations for this include the presence of weight bearing and the hamstring- quadriceps cocontraction that are noted during closed kinetic chain but absent when the kinetic chain is open (15,16). Additionally, the soleus muscle contraction at the ankle to stabilize the tibia has an indirect ef- fect that results in a reduced amount of anterior shear forces at the knee (15).

Despite empirical evidence that the closed kinetic chain is effective in reducing the long-term complications following injury to the ACL, there has been a relative void in the litera- ture to support the efficacy of closed as opposed to open chain exercise in this patient population. In a study of two human subjects utilizing an im- plantable strain gauge on a grade I1 anterior cruciate ligament injury, Henning et a1 (8) described the amount of anterior displacement in a variety of open and closed kinetic chain activities. Cycling and one-leg half squat activities resulted in 7 and 21 %, respectively, as much elonga- tion as an 80-lb Lachman test. Hen- ning et a1 also noted that knee exten- sion exercises, from 22" of flexion to full extension with a 20 Ib-weight,

resulted in a peak elongation ranging from 87 to 121 % of an 80-lb Lach- man test in these two subjects. Quad- riceps contraction with a knee exten- sion movement against a 20-lb weight at 45" of flexion produced 50% as much elongation as the 80-lb Lach- man test according to Henning et al.

The open kinetic chain knee ex- tension exercise was also studied in five cadaver limbs by Grood et a1 (6) using an Instron actuator attached to the patellar tendon with a wire cable through a series of cables. Movement of the actuator was used to force the knee into extension. These authors determined that very large quadri- ceps forces are required to produce movement of the tibia into a fully extended position from 15" of flex- ion. The quadriceps force was found to be significantly less, between 15 and 50" of flexion in an open kinetic chain. When these authors selectively cut the ACL on their specimens, they found that there was an increase in displacement of the tibia anteriorly during a weighted knee extension (31 N) in 30" of knee flexion to the fully extended position when com- pared with the knee with an intact ACL. According to these authors, the alignment of the patellar tendon dur- ing the last 30" of knee extension results in more anterior shear force and less joint compression, which results in an increase in anterior tib- ial displacement.

Nisell et a1 (14) and Jurist and Otis (9) have studied several variables related to the use of isokinetic de- vices in an open kinetic chain. Place- ment of the lever arm distally was found to result in an increase in an- terior tibial shear force in both of these studies. In Nisell et al's study, the maximal anterior tibial displace- ment was observed between 30 and 60" of flexion while Jurist and Otis found very little anterior displace- ment (1.5 mm) between 30 and 90" of flexion. Wilk and Andrews (23) also reported that proximal pad placement and faster velocity training on an open kinetic chain isokinetic

device resulted in a decrease in the amount of anterior tibial displace- ment when compared with distal pad placement and slower velocity train- ing.

The closed kinetic chain form of exercise incorporates the hamstring musculature, particularly if there is the presence of trunk flexion during knee extension activity, as in the squat, while open kinetic chain knee extension results in an isolated quad- riceps contraction unless there is arti- ficial activation of the hamstring mus- cles (15). The effect of the hamstring musculature as a counterforce to the anterior pull of the quadriceps mus- cle has been studied by Renstrom et a1 (18) and Solomonow et a1 (22) in separate studies. Each of these au- thors concluded that the quadriceps muscle was responsible for the ante- rior tibial displacement during open kinetic chain knee extension activity and that the amount of displacement may be decreased when the ham- string musculature was activated.

Markolf et a1 (12) and Shoemaker and Markolf (21) have studied the type of load in cadaver ACMeficient knees. In each of these studies, the authors concluded that the closed kinetic chain had less displacement than did the open kinetic chain. Markolf et a1 found that the closed kinetic chain at the fully extended position, and to a greater extent the 20" of flexion position, resulted in a decrease in the percentage of dis- placement when compared with the open kinetic chain. Shoemaker and Markolf also studied the amount of load in both an open and closed ki- netic chain at the 0 and 20" positions (21). The open kinetic chain move- ment always resulted in an increased amount of anterior tibial displace- ment than did closed kinetic chain movement, regardless of the position or amount of applied force. Closed kinetic chain movement was more effective in limiting anterior displace- ment at low levels of applied force (50 N). When higher levels of a p plied force (200 N) were utilized, the

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FIGURE 1. Standard KT-1000 test.

effect. of joint congruency were over- come and the ligament. became a restraint to anterior tibial displace- ment. Closed kinetic chain loading reduced the anterior tibial displace- ment to a greater extent at the 0" position than at the 20" position.

Yack et al (25) have also studied the amount of displacement and the position in the range of motion where anterior displacement occurs in an open and closed kinetic chain. These authors used the Knee Signa- ture System to observe the anterior displacement of the tibia on the fe- mur with knee extension exercise (open kinetic chain) and the parallel squat (closed kinetic chain) in a sam- ple of unilateral ACLdeficient pa- tient.. Loads used in this study were full body weight for the parallel squat and an amount of weight equivalent to the load used in the squat for the knee extension exercise. A major conclusion of this paper is that the open kinetic chain has significantly more anterior displacement than the closed kinetic chain in a range of motion from 0 to 64" of flexion.

The purpose of this investigation is to delineate the amount of dis- placement that occurs in an open and closed kinetic chain exercise in an ACL-deficient sample comparing the uninvolved limb with the involved limb. The amount of resistance used for both the open and closed kinetic

chain was varied in order to deter- mine if the resistance could be de- fined as a possible variable in relation- ship to the amount of displacement.

MATERIALS AND METHODS

Subjects

Nineteen patient. (14 males and five females; x age = 33.7 t 2.3) with one ACL-deficient knee and one normal knee were selected from our patient records and asked to take part in three test.. Criteria for inclu- sion in this study were a positive physical examination for ACL defi- ciency and a standard KT-1000 test of greater than 3 mm of difference be- tween the involved and uninvolved side with the total drawer measure- ment. All patients were asked and subsequently signed an informed consent form prior to taking part in this study.

Procedures

The standard KT-1000 (MedMet- ric, San Diego, CA), the open kinetic chain KT-1000, and the closed kinetic chain KT-1000 were performed on each subject. All tests were per- formed by the senior author. The standard KT-1000 test was always per- formed first followed by either the open or the closed kinetic chain test.

The open and closed kinetic chain tests were randomly selected to be performed first or second to mitigate problems with subject familiarity.

The standard KT-1000 was per- formed as described by Daniel et a1 (3). with the patient supine on a plinth and the knee fixed at a 25" angle. The amount of tibial rotation was established to be the same bilat- erally by use of a foot plate (Figure 1). Once the joint line had been lo- cated, the KT-1000 ligament arthrom- eter was placed on the limb, with both the proximal and distal lower leg straps tightened equally. A poste- rior force of 67 N (15 Ibs) followed by an anterior force of 133 N (30 Ibs) was imparted on the knee, with recordings taken at each of these po- sitions. Total drawer was determined by adding the posterior value to the anterior value. The testing sequence was performed on both knees for each subject. Each test was per- formed until the numerical values for posterior displacement, anterior dis- placement, and total drawer were the same for three consecutive repeti- tions. Support for the KT-1090 as a research tool ha. been objectively outlined (13,24).

The open kinetic chain test was performed with the patient sitting on a standard knee extension machine (Body Master, Rayne, LA) (Figure 2). The resistance was achieved by way of an ankle cuff attached to a weighted pulley system. For standardization, the ankle cuff was placed and se- cured at 10 inches from the medial joint line. Onequarter body weight was used as a resistance during the knee extension movement. Each s u h ject was weighed and onequarter body weight was calculated. One- quarter body weight was then at- tached to the pulley and the ankle cuff was secured to the lower leg. The KT-1000 ligament arthrometer was then placed on the lower leg with the joint line position arrow on the joint line and the lower leg straps tightened equally proximally and dis- tally. Each subject was then asked to

JOSPT Volume 25 Number 1 January 1997

FIGURE 2. Open kinetic chain KT-1000 test.

isometically contract with a knee ex- tension movement against the pulley system. The knee extension move- ments were performed at 30 and 60" of knee extension on the normal knee first followed by the involved knee. Subject. performed the 30 or 60" position first or second in a ran- dom fashion. Recordings of anterior displacement were taken with the KT-1000 for three consecutive repeti- tions, with the means of these record- ings calculated for each subject at both the 30 and 60" positions.

The closed kinetic chain test was performed on a standard supine leg press machine (Body Master, Rayne, LA) with the feet placed in equal amounts of rotation bilaterally (Fig- ure 3). After the patient was posi- tioned on the leg press, the KT-1000 ligament arthrometer was then placed on the lower leg with the joint line arrow positioned along the me- dial joint line and the proximal and distal straps tightened equally. Sub- jects were then asked to perform an isometric leg press first on the nor- mal knee, then followed by the in- volved knee, with the 30 or 60" posi- tions performed first or second in a random fashion against a 1,780 (400

Ibs) force. Recordings of anterior displacement were taken with the KT-1000 for three consecutive repeti- tions, with the means of these record- ings calculated for each subject at both the 30 and 60" positions.

Data Analysis

A fixed effects model intraclass correlation coefficient was calculated across the three trials at each mode and position to determine reliability of the measurements. Data were ana- lyzed with a 2 X 2 X 3 analysis of variance with repeated measures on all variables. Variables analyzed were mode (open vs. closed), knee (in- volved vs. uninvolved), and trials (first, second, and third). Each posi- tion (30 and 60") was analyzed sepa- rately. Student-Newman Keuls multi- ple post hoc comparison tests were also performed to determine the dif- ference between the open and closed kinetic chain and the differences be- tween the involved and uninvolved knee. The level of significance was established at p < .05.

RESULTS

The fixed effects model intraclass correlation in the open kinetic chain

was .96 for both the 30 and 60" posi- tions, while the coefficients for the closed kinetic chain were .76 for 30" and .74 for the 60" position. Landis et a1 have described that .99-.81 was considered almost perfect, while .80- .61 is considered to be substantial according to their criteria (1 1).

The results of the analysis of vari- ance (ANOVA) showed that there were significant differences between the modes and between the involved and uninvolved knee, and there was significant mode by knee interaction at 30" (Table 1). There was not a significant difference between the repetitions nor were any interactions involving repetitions significant. The means for the 30" position for both the open and closed kinetic chain are shown in Table 2.

At the 60" position, the ANOVA showed significant difference be- tween modes, but the difference be- tween the involved and uninvolved knee was not significant (Table 3). The mode by knee interaction was not significant. There was no signifi- cant difference between the repeti- tions nor were any interactions in- volving repetitions significant. The means for the 60" position for both the open and closed chain are shown in Table 4.

FIGURE 3. Closed kinetic chain KT- 1000 test.

Volume 25 Number 1 January 1997 JOSPT

.- . - .-. .. . . . . , . . - . . . . . . . R E S E A R C H S T U D Y . - .-,-..-.- .. - ..-,...- * . - -. - . . ..--- -.-.. -----..-.

Source of Variation Sum of f Tail Sauares df ~auare Probabilitv

Mean error

Mode error

Knee error

Mode x Knee interaction error

Repetitions error

Mode X Repetitions error

Knee X Repetitions error

Mode X Knee X Repetitions error

TABLE I . ANOVA with repeated measures (2 X 2 X 3) at 30'.

Involved Uninvolved Repetitions

i SD X SD

Open* 1 8.26 3.56 3.61 1.93 2 8.03 2.91 3.32 1.74 3 8.00 2.80 3.34 1.92

8.10* 3.42* Closedt 1 2.82 2.1 7 1.53 1.81

2 2.87 1.97 1.55 1.57 3 2.71 2.10 1.55 1.64

2.80* 1.54+

* Diiterence in involved and uninvolved ior open cham: 4.68 mm. t Difference in involved and uninvolved for closed chain: 1.26 mm. * Grand mean.

TABLE 2. Means for anterior displacement at 304

Source of Variation Sum of i Tail Squares df %"are Probability

Mean error 3584.28 1 3584.28 187.00 0.00 345.01 18 19.17

Mode error 733.69 1 733.69 59.51 0.00 221.94 18 12.33

Knee error 501.07 1 501.07 37.01 0.00 243.72 18 13.54

Mode X Knee interaction error 166.77 1 166.77 16.52 0.08 181.68 18 10.09

Repetitions error 0.94 2 0.47 0.84 0.44 20.15 36 0.56

Mode X Repetitions error 0.94 2 0.47 0.50 0.62 34.81 36 0.97

Knee X Repetitions error 0.1 1 2 0.53 0.09 0.91 20.73 36 0.58

Mode X Knee X Repetitions error 0.47 2 0.23 0.03 0.97 29.12 36 0.81

TABLE 3. ANOVA with repeated measures (2 X 2 X 3l at 60'.

Each knee (involved and unin- volved) was then considered sepa- rately when comparing the mode in the Newrnan-Keuls multiple compari- son tests due to the significant find- ings in the ANOVA for the mode vs. the knee interaction at 30". For the Newman-Keuls, the repetitions were combined and compared as means because there was no significant dif- ference among the three repetitions and there were no significant interac- tion involving repetitions.

The Newman-Keuls test at 30" showed a significant difference be- tween the open and closed kinetic chain modes for both the involved and uninvolved knees (Figure 4). At the 60" position, there was also a sig- nificant difference between the open and closed kinetic chain for both the involved and uninvolved knees (Fig- ure 5). An additional finding of inter- est was that when the involved and the uninvolved knees were compared, there were significant differences ex- cept for the closed positions at 60" (Figures 6 and 7). During the Newman-Keuls post hoc testing, the degrees of freedom were 18, with the critical values being 2.97 for .05 and 4.07 for .O1 (10).

DISCUSSION

The purpose of this paper was to evaluate the anterior displacement of the tibia relative to the femur during knee extension activities in the closed and open chain in an ACMeficient sample. This was performed to gain a better understanding of the rehabili- tation in an ACMeficient knee as well as the postoperative ACLrecon- structed patient. Although rehabilita- tion following ACL injury and ACL reconstruction is better understood at this time, there remains an incom- plete knowledge of the many parame- ters involved in a therapeutic exercise program. While it is generally under- stood that an open kinetic chain ex- ercise program results in an increased amount of anterior displacement compared with a closed kinetic chain,

JOSPT Volume 25 Number 1 January 1997

.. - -r-- -iTin;ol~- .." Repetitions

$ SD x SD ~ -

Open* 1 2.1 3 3.29 0.78 1.84 2 2.1 3 3.16 1 .OO 1.69 3 2.23 3.07 1.02 1.72

2.1 7* 0.94* Closedt 1 -0.16 2.1 1 -0.1 3 2.28

2 -0.1 3 2.25 -0.21 2.05 3 -0.1 5 2.24 -0.29 2.26

-0.15* -0.21*

Diiirrrnc-p in in\,olwd ,~nd u n r n d , r d tor opcn ch'lin: 1 .?.I nm. t Diiierence in involved and uninvolved ior closed chain: - .06 mm. * Grand mean.

TABLE 4. Means for anterior displacement at 604

the precise degree to which this oc- curs is still subject to discussion. The exact range of motion at which dis- placement occurs, the amount of dis- placement in the open and closed chain, and how the amount of load affects the amount of displacement is poorly understood in the human s u b ject.

Currently, rehabilitation follow- ing ACL reconstruction utilizes a pre- dominance of closed kinetic chain exercise, including the leg press, squats, or a stationary bicycle, partic- ularly during the early phases of re- habilitation when the fixation and graft strength is at its weakest (5,20). It is not recommended that full range of motion open kinetic chain exercises be performed on the recon- structed patient until the later stages of rehabilitation. The patient who has an ACMeficient knee is gener- ally asked to refrain from full range of motion open kinetic chain knee extension activities in order to pre- serve the secondary restraints in the capsular ligament5 of the knee and

FIGURE 4. Neuman-Keuls multiple comparison test. Open vs. closed chain at 30". level of significance: * p < .05; **p < .01.

prevent an increase in laxity leading to further pathology. At the knee, the meniscus and articular cartilage pa- thology have been commonly linked to the anterior-cruciate-deficient knee (4,7).

The results of our study show that the open kinetic chain causes significantly more anterior tibial dis- placement than does the closed ki- netic chain in both the 30 and 60" positions. The open kinetic chain knee extension test at both the 30 and 60" positions had more anterior displacement than did either of the closed kinetic chain test positions. Likewise, it is important to note that the 30" position had more displace- ment than did the 60" position in both the open and closed kinetic chain. Therefore, if a clinician was designing a conservative therapeutic exercise program for the ACMefi- cient or ACLreconstructed patient, the 30" position in the open chain must be avoided if anterior displace- ment of the tibia on the femur a p pears to be a concern. The closed kinetic chain 60" position having the least amount of anterior displace- ment appears to be the most favor- able therapeutic exercise mode and position for the clinician who wishes to decrease anterior tibial displace- ment during rehabilitation.

The amount of resistance used in the open and closed kinetic chain testing was different for several rea- sons. Previous studies have investi-

gated the differences between open and closed kinetic chain exercise in the ACMeficient knee and subjects with normal ligamentous structures at the knee. In these previous works, it has been established that open ki- netic chain exercise results in a greater amount of displacement than does closed kinetic chain if the weight is constant or relatively similar (12.20,25). Since open kinetic chain exercise resulted in greater amounts of displacement than did closed ki- netic chain exercise, given a similar weight, this study chose to manipu- late the resistance to determine if a large difference in the amount of resistance (onequarter body weight vs. 1,780 N) was, in fact, a critical factor when comparing the two forms of exercise. At least one author be- lieves that in the closed kinetic chain mode of exercise, the greater amounts of resistance result in greater amounts of anterior tibial displacement (21). Shoemaker and Markolf determined that, in a closed kinetic chain, if the resistance was increased, the amount of anterior displacement also increased. Our study utilizes a high load of 1,780 N in a closed chain with a small amount of displacement noted when compared with the open kinetic chain. With Shoemaker and Markolf s result5 in mind, the results of our study are even more impor- tan t.

A second reason why there was a difference in the amount of resis- tance is that, in a clinical setting, it is not at all uncommon for a patient to be able to use a greater amount of weight in a closed kinetic chain than in an open kinetic chain. An open kinetic chain form of exercise is able to isolate the quadriceps mechanism when working against a resistance; however, in part due to the recruit- ment of the hamstrings when per- forming a closed kinetic chain exer- cise, the body appears to have the ability to lift greater amount5 of weight during this type of exercise. Therefore, an attempt was made in

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Involved unvolved K m

FIGURE 5. Newman-Keuls multiple comparison test. Open vs. closed chain at 609 Level of significance: p < .05; **p < .01.

this paper to investigate if, in fact, the amount of resistance was a factor in the amount of displacement o b served during these types of exercise.

The amount of anterior displace- ment in the ACMeficient and the ACLreconstructed patient is believed to be a concern due to the problem of graft and/or capsular ligament creep that may occur if therapeutic exercise modes and positions result- ing in this phenomenon are pro- longed or repeated. The amount of anterior tibial displacement that is pathological has been defined by Daniel et al when comparing the ACLintact knee to the ACMeficient knee in a group of unilaterally ACL deficient patients (3). Daniel et al found that there was a minimum of 3 mm and a mean of 8.4 mm of differ- ence between the involved and unin- volved knees. It is important to recog- nize that the 3 mm of anterior tibial displacement utilized in this study is expressed as the difference between the involved and uninvolved knee. Therefore, it follows that when assess- ing a patient with an ACMeficient knee or postoperatively following an ACL reconstruction, the 3 mm of increased anterior tibial displacement is an assessment in relationship to the uninvolved knee. The amount of anterior tibial displacement that is disruptive to the healing process in the ACLreconstructed patient is un- known; however, it is generally rec- ommended that patients avoid activi- ties that result in anterior displace- ment, particularly early in the reha- bilitation process.

We have documented in this pa- per that the open kinetic chain form of exercise does result in more ante- rior displacement than does the closed kinetic chain. Differences of 4.68 mm for open kinetic chain test- ing and 1.26 mm for closed kinetic chain testing at 30" were noted. At the 60" position, the differences are 1.23 mm for the open kinetic chain and -.06 mm (posterior movement) for the closed kinetic chain. When one considers that the 3 mm figure that Daniel et a1 has proposed as the difference between the ACLintact and ACMeficient knee, it is clear that the 30" open kinetic chain posi- tion is one that may need to be avoided in the patient with a healing ACL graft. Open kinetic chain exer- cise at 60" and closed kinetic chain exercise at 30" have very similar val- ues and may also need to be consid- ered as positions that cause anterior displacement, leading to possible creep of the healing ACL graft. The 60" position in a closed kinetic chain is one that appears to prevent ante- rior tibial displacement.

This study is restricted to open and closed kinetic chain activities performed in a very standardized form with a specific amount of resis- tance at designated points in the range of motion and measured in the sagittal plane. Motion in the frontal and transverse planes was not studied here and has not been studied in v i v o by other authors. Considerable varia- tion in exercise technique is possible, which may produce variations in any or all planes of motion. Further in- vestigation is necessary to delineate

FIGURE 6. Newman-Keuls multiple comparison test. lnvolved vs. uninvolved at 30". Level of significance: * p < .05; **p < .01.

Mode

FIGURE 7. Newman-Keuls multiple comparison test. lnvolved vs. uninvolved at 609 Level of significance: p < .05; '* NS = Not significant.

ideal techniques and to determine if such closed chain exercises are a p propriate in the early postoperative period. Clinical parameters of postop erative timing, range of motion, and resistance need this future investiga- tion in order to determine the most appropriate guidelines for the ACL reconstructed patient.

This study is also restricted to several isometric testing positions in an open and closed kinetic chain rather than an isotonic or isokinetic movement. Isometric testing is not generally associated with rotary joint movement (rolling) ; however, it is impossible to totally restrict joint mo- tion with this form of testing. There- fore, the joint motion that does take place during muscle activation iso- metrically may be in the form of a glide between the two joint surfaces. Both isotonic and isokinetic move- ments are performed with either a fixed speed (isokinetics) or a variable speed (isotonics). Isokinetic and iso- tonic movements do not restrict joint movement and can result in both rotary and gliding movements at the joints where muscles are activated. Other studies have investigated the amount of anterior displacement with isotonic and isokinetic activity throughout a range of motion with similar results to the present work (8,23,25). While it may be stated that isometric activity is not as functional as isotonic activity, it is commonly performed in the immediate postop erative period with the ACLrecon- structed patient (5,19).

Despite the current enthusiasm for "accelerated rehabilitationn fol-

JOSPT Volume 25 Number 1 January 1997 55

lowing anterior cruciate reconstruc- tion, many questions remain unan- swered. How much tension should be placed on the graft initially? How secure should the fixation be? When can the graft tolerate physiological stress? How quickly and how much can this stress be progressed? This paper has not attempted to answer these questions; however, if we as a profession are to continue to pro- gress, there must be a better under- standing and documentation of these parameters in order to continue our advancement.

CONCLUSIONS

Our study demonstrates that, un- der our testing conditions, open ki- netic chain knee extension exercise in the 30 and 60" positions of knee flexion result.. in more anterior tibia1 displacement than does closed ki- netic chain knee extension exercises performed in the same range of mo- tion. This occurred despite manipu- lating the amount of resistance to keep the open kinetic chain form of exercise at a lower level of resistance than the closed kinetic chain. The 30" position was found to have an increase in anterior displacement compared with the 60" position in both the open and closed kinetic chain. JOSPT

ACKNOWLEDGMENTS

The authors would like to thank Ruth Hassenein, PhD, and Janice Loudon, PhD, ATC, for their statisti- cal support with this research.

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Volume 25 Number 1 January 1997 JOSF'T