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Quadriceps strength and the ACL deficient non-coper

Dissertation
Author: Wendy J. Hurd
Abstract:
Most individuals who sustain anterior cruciate ligament (ACL) injury experience knee instability (non-copers ), and have marked quadriceps muscle weakness. There are some individuals, however, with good dynamic knee stability early after ACL injury (potential copers ) who are able to asymptomatically resume pre-injury activities for a limited period of time. The University of Delaware has developed a screening tool that prospectively classifies patients with different levels of dynamic knee stability early after ACL injury. The first goal of this work was to characterize an entire population of highly active patients with acute, isolated ACL rupture using the results of this screening algorithm. Analysis of 300 consecutive subjects indicated potential copers have greater quadriceps strength on bilateral limb comparison (X=88%) than non-copers (X=84%). Quadriceps weakness in non-copers is clinically significant, as quadriceps strength contributed substantially to their functional performance measured during hop testing. The amount of passive anterior knee laxity present after ACL rupture does not contribute to knee instability after injury. A 10 year review of screening results indicated there are specific patient groups who are more likely to experience knee instability after ACL injury, including female athletes and individuals who sustain injury via non-contact mechanisms. Overall, the average individual who sustains an ACL injury is young and likely to experience knee instability. The second goal of this work was to garner insight to the movement strategies of the non-coper, and determine their responsiveness to physical therapy intervention designed to improve quadriceps strength. Gait analysis of 21 subjects classified as non-copers during the mid-stance (peak knee flexion to peak knee extension) portion of stance we identified a control strategy novel to this phase of the gait cycle that includes a shift in the support moment from the knee to the ankle and variable combinations of muscle adaptations that produce joint stiffness. Preliminary results from a clinical trial indicate a stable knee may be more permissive of quadriceps strengthening, as individuals who participated in neuromuscular training and quadriceps strengthening exercises had greater improvements in strength than those who performed only strengthening exercises. Both improved knee stability and quadriceps strength contributed to the normalization of movement patterns after the clinical intervention. These results indicate there is a complementary relationship between strength and stability after ACL injury.

TABLE OF CONTENTS

LIST OF TABLES ................................................................................................. ix LIST OF FIGURES ................................................................................................ xi ABSTRACT ………………………………………………………………………. xiii

Chapter 1 INTRODUCTION: QUADRICEPS STRENGTH, KNEE INSTABILITY, AND THE ACL DEFICIENT NON-COPER............................................ 1

REFERENCES................................................................................... 15

2 QUADRICEPS STRENGTH, LAXITY, AND FUNCTION AFTER ACUTE ISOLATED ACL RUPTURE: RELATIONSHIP TO DYNAMIC STABILITY……………………………………………………………….. 19

ABSTRACT....................................................................................... 20 INTRODUCTION............................................................................. 21 MATERIALS AND METHODS....................................................... 26 DATA ANALYSIS............................................................................ 30 RESULTS.......................................................................................... 30 DISCUSSION.................................................................................... 37 REFERENCES.................................................................................. 44

3 INFLUENCE OF AGE, GENDER, AND INJURY MECHANISM ON THE DEVELOPMENT OF DYNAMIC KNEE STABILITY AFTER ACUTE ACL RUPTURE………………………………………………………….. 48

ABSTRACT....................................................................................... 49 INTRODUCTION............................................................................. 50 MATERIALS AND METHODS....................................................... 52 DATA ANALYSIS............................................................................ 57 RESULTS.......................................................................................... 57 DISCUSSION.................................................................................... 61 REFERENCES.................................................................................. 66

viii 4 KNEE INSTABILITY AFTER ACUTE ACL RUPTURE AFFECTS MOVEMENT PATTERNS DURING THE MID-STANCE PHASE OF GAIT………………………………………………………………………. 70

ABSTRACT....................................................................................... 71 INTRODUCTION............................................................................. 73 MATERIALS AND METHODS....................................................... 76 DATA ANALYSIS............................................................................ 82 RESULTS.......................................................................................... 82 DISCUSSION.................................................................................... 94 REFERENCES.................................................................................. 100

5 THE EFFECTS OF A QUADRICEPS STRENGTHENING PROGRAM WITH PERTUBATION TRAINING VERSUS QUADRICEPS STRENGTHENING ALONE IN NON-COPERS AFTER ACUTE ACL INJURY: A CASE SERIES……………………………………………………………………. 103

ABSTRACT....................................................................................... 104 INTRODUCTION............................................................................. 106 MATERIALS AND METHODS…………………………………... 112 DATA ANALYSIS............................................................................ 125 RESULTS………………………………………………………….. 127 DISCUSSION.................................................................................... 141 REFERENCES.................................................................................. 149

6 SUMMARY.................................................................................................. 154 REFERENCES.................................................................................. 166 7 APPENDIX………………………………………………………………… 168

INFORMED CONSENT FORMS STRENGTH TRAINING PROTOCOL

ix LIST OF TABLES

Table 2.1. Activity Level Classification…………………………………………… 23

Table 2.2. Subject Information (Mean (SD))……………………………………... 32

Table 2.3. Quadriceps Strength, Laxity, Self-Assessment, and Hop Test Results……………………………………………………………………………….. 33

Table 2.4. Knee Laxity Distribution for Groups………………………………… 36

Table 3.1. Activity Level Classification…………………………………………... 54

Table 3.2. Potential Coper/Non-Coper Distribution Based on Gender………… 60

Table 3.3. Potential Coper/Non-Coper Distribution Based on Mechanism of Injury........................................................................................................................... 60

Table 3.4. Potential Coper/Non-Coper Distribution Based on Gender and Mechanism of Injury………………………………………………………………. . 60

Table 4.1 Lower Extremity Kinematic and Kinetic Results. ¹Angles and excursions expressed as degrees; ²Moments normalized to subject mass x height (Nm/kgm); **p < 0.001 …………………………………………………………….. 84

Table 4.2. Lower Extremity Muscle Activity. *Expressed as Average Rectified Value ………………………………………………………………………………… 89

Table 5.1. Screening Results. ………………………………………………….... . 115

Table 5.2. Perturbation Exercise Protocol………………………………………. 124

Table 5.3. Demographics of Non-Responders and Responders. 1In Weeks; 2In Years; 3F=Female, M=Male…………………………………………………………… 126

Table 5.4. Clinic Measures for Non-Responders and Responders Before and After Rehabilitation. 1Injured limb quadriceps force normalized to BMI (N x [kg/m2]-1)………………………………………………………………… 132

Table 5.5. Subject Demographics by Group……………………………………. 133

Table 5.6. Sagittal Plane Knee Kinematics and Kinetics. 1XMS=Excursion Mid- Stance. 2PKE=Peak Knee Extension; 3KFMPKE=Knee Flexion Moment, Peak Knee Extension; *=Greater Knee Extension After Training………………………………………… 136

x Table 5.7.

Magnitude of Muscle Activity (Average Rectified Value). VL=Vastus Lateralis, VM=Vastus Medialis, MH=Medial Hamstring, LH=Lateral Hamstring, MG=Medial Gastrocnemius, LG=Lateral Gastrocnemius, SOL=Soleus………….. 138

Table 5.8.

Muscle Co-contraction. VLLH=Vastus Lateralis-Lateral Hamstring, VLLG=Vastus Lateralis-Lateral Gastrocnemius……………………………………. 140

xi LIST OF FIGURES

Figure 2.1. Quadriceps Strength Comparison In Non-Copers And Potential Copers………………………………………………………………………………. 34

Figure 3.1. Percentage Of Males And Females Who Completed The Screening Examination.……………………………………………………………………….. 58

Figure 3.2. Percentage Of Contact And Non-Contact Injuries Sustained By Individuals Who Completed The ACL Screening Examination.……………………………………………………………………….. 58

Figure 3.3. Percentage Of Total Patient Population Who Completed The ACL Screening Examination Based On Age. …………………………………………. 58

Figure 4.1. Sagittal Plane Knee Kinematics. Injured (solid line) and uninjured limb (dashed line) sagittal plane knee motion during stance. Peak knee flexion (*) and peak knee extension (**) angles on the injured limb were significantly reduced compared to the uninjured limb………………………………………………………………….. 85

Figure 4.2. Co-contraction Indexes During Mid-Stance. VLLH and VMMH indexes are significantly greater on the injured limb compared to the uninjured limb.…….. 86

Figure 4.3. Sagittal Plane Knee Moments. Injured (solid line) and uninjured limb (dashed line) sagittal plane knee moments during stance. Peak knee flexion (*) and peak knee extension (**) moments on the injured limb were significantly lower compared to the uninjured limb…………………………………………………………………… 87

Figure 4.4. Percent Support Moment Contribution For The Hip, Knee, And Ankle During Mid-Stance. The ankle contribution to the total support moment is significantly greater on the injured limb compared to the uninjured limb (*)…………………… 88

Figure 4.5. Co-contraction Indexes During Weight Acceptance. VLLH and VMMH indexes are significantly greater on the injured limb compared to the uninjured limb………………………………………………………………………………… 91

Figure 4.6. Percent Support Moment Contribution For The Hip, Knee, And Ankle During Weight Acceptance. The hip contribution to the total support moment is significantly greater on the injured limb compared to the uninjured limb (*) while the knee contribution is significantly lower (**)………………………………………. 93 Figure 5.1. Perturbation Training Tasks: (A) Rollerboard, (B) Rockerboard, and (C) Rollerboard and Block. ……………………………………………………. 110

Figure 5.2 (A-C). Individual Subject Results For The Perturbation Group. (A) Normalized quadriceps force (N x [kg/m2]-1), (B) global rating, and (C) Knee Outcome

xii Survey-Activities of Daily Living Scale (KOS-ADLS). Values are changes in test results (Post-Pre). Solid bars represent Non-Responders, striped bars represent Responders………………………………………………………………………..... 128

Figure 5.3 (A-C) . Individual Subject Results For The Exercise Group. (A) Normalized quadriceps force (N x [kg/m2]-1), (B) global rating, and (C) Knee Outcome Survey-Activities of Daily Living Scale (KOS-ADLS). Values are changes in test results (Post-Pre). Solid bars represent Non-Responders, striped bars represent Responders…………………………………………………………………………. 129

Figure 5.4. Quadriceps Force (Normalized to BMI (N x [kg/m 2 ] -1 )) Before And After Rehabilitation For Both Groups…………………………………………… 130

xiii

ABSTRACT

Most individuals who sustain anterior cruciate ligament (ACL) injury experience knee instability (non-copers), and have marked quadriceps muscle weakness. There are some individuals, however, with good dynamic knee stability early after ACL injury (potential copers) who are able to asymptomatically resume pre-injury activities for a limited period of time. The University of Delaware has developed a screening tool that prospectively classifies patients with different levels of dynamic knee stability early after ACL injury. The first goal of this work was to characterize an entire population of highly active patients with acute, isolated ACL rupture using the results of this screening algorithm. Analysis of 300 consecutive subjects indicated potential copers have greater quadriceps strength on bilateral limb comparison (X=88%) than non-copers (X=84%). Quadriceps weakness in non-copers is clinically significant, as quadriceps strength contributed substantially to their functional performance measured during hop testing. The amount of passive anterior knee laxity present after ACL rupture does not contribute to knee instability after injury. A 10 year review of screening results indicated there are specific patient groups who are more likely to experience knee instability after ACL injury, including female athletes and individuals who sustain injury via non-contact mechanisms. Overall, the average individual who sustains an ACL injury is young and likely to experience knee instability.

xiv The second goal of this work was to garner insight to the movement strategies of the non-coper, and determine their responsiveness to physical therapy intervention designed to improve quadriceps strength. Gait analysis of 21 subjects classified as non-copers during the mid-stance (peak knee flexion to peak knee extension) portion of stance we identified a control strategy novel to this phase of the gait cycle that includes a shift in the support moment from the knee to the ankle and variable combinations of muscle adaptations that produce joint stiffness. Preliminary results from a clinical trial indicate a stable knee may be more permissive of quadriceps strengthening, as individuals who participated in neuromuscular training and quadriceps strengthening exercises had greater improvements in strength than those who performed only strengthening exercises. Both improved knee stability and quadriceps strength contributed to the normalization of movement patterns after the clinical intervention. These results indicate there is a complementary relationship between strength and stability after ACL injury.

1

Chapter 1 INTRODUCTION: QUADRICEPS STRENGTH, KNEE INSTABILITY, AND THE ACL DEFICIENT NON-COPER

2 The anterior cruciate ligament (ACL) is one of the primary ligamentous stabilizers of the tibio-femoral joint. Coursing from the posterior-lateral aspect of the femur to the anterior-medial tibia, the ACL contributes to knee stability by serving as a primary restraint to anterior tibial translation and a secondary restraint to transverse and frontal plane knee motions (Inoue, McGurk-Burleson et al. 1987; Markolf, Gorek et al. 1990). Injury to the ACL is common among individuals who participate in high demand sporting activities. Knee instability, meniscus and articular cartilage destruction, and a decline in function are often associated with the ACL deficient knee (Noyes, Mooar et al. 1983). Surgical stabilization is rarely perfect and does not unconditionally restore knee joint stability, however, or prevent joint degeneration (Logan, Williams et al. 2004; Lohmander, Ostenberg et al. 2004). Consequently, management of the highly active patient with ACL injury is a clinical challenge. The ACL is a commonly injured knee ligament (Corry and Webb 2000; Majewski, Susanne et al. 2006), with an estimated 100,000-200,000 individuals sustaining an ACL injury annually in the United States (National Hospital Discharge Survey 1996). Approximately 70% of all ACL injuries occur via non-contact mechanisms (McNair, Marshall et al. 1990; Boden, Dean et al. 2000). The most common athletic maneuvers resulting in ACL injury include planting and cutting, straight knee landings from a jump, and rapid, 1-step stops (McNair, Marshall et al. 1990). Injury to the ACL can occur during these athletic maneuvers as a consequence of the collective positioning of the hip, knee and ankle. Lower extremity positioning at the time of injury which may result in increased ACL strain often includes relatively low hip and knee flexion angles accompanied by high femoral internal rotation, adduction, and knee valgus

3 angles, and external rotation of the foot relative to the knee (Boden et al., 2000; McNair et al., 1990; Noyes et al., 1983; Feagin and Lambert, 1985; Dufek and Bates, 1991). The most common deleterious consequence of ACL injury is knee instability, which can present as occult giving way of the knee (subluxation of the femur relative to the tibia in a weight bearing position) or as a perception that the knee is unstable. Instability may be noted during activities of daily living but more often occurs with strenuous activities. Consequently, individuals with the intention of returning to high demand sporting- activities are presumed to be at greater risk for knee instability secondary to repeated performance of provocative movements. Functional outcome is variable after ACL injury. The majority of individuals cannot return to high level athletic activities after ACL injury because of continued episodes of knee giving way (non-copers) (Daniel, Stone et al. 1994; Eastlack, Axe et al. 1999). Patients with ACL deficiency who are able to asymptomatically resume all pre- injury activities for one year, including sports, have been termed copers (Daniel, Stone et al. 1994; Eastlack, Axe et al. 1999). Copers are rare, comprising an estimated 15% of the total population of individuals with ACL injury (Eastlack, Axe et al. 1999). Copers compensate for the loss of ligamentous knee stability through enhanced dynamic stability, which we have operationally defined as the ability to control excessive joint movement via muscle activation while still allowing normal motion. Despite evidence of a differential recovery after ACL injury, most orthopaedic surgeons in the United States advocate early ACL reconstruction for young, active individuals (Marx, Jones et al. 2003). The bias towards surgical management of the patient with ACL deficiency has been influenced by surgical techniques that predictably restore knee stability and function

4 (Kapoor, Clement et al. 2004), as well as poor outcomes associated with non-operative management of the highly active individual after ACL rupture (Andersson 1993; Engstrom, Gornitzka et al. 1993; Shelton, Barrett et al. 1997).

There are instances in which delayed surgery is advantageous to the patient. For example, a senior in high school competing for a collegiate athletic scholarship who sustains an ACL injury during pre-season or the beginning of the competitive season. Practice patterns in countries other than the United States are often quite different (Mirza, Mai et al. 2000; Kapoor, Clement et al. 2004). In some countries patients are counseled to undergo surgery only if non-operative care has failed. For patients who are advised to have ACL reconstruction, resources may be limited and the patient can be placed on a lengthy waiting list before surgery can be performed. In these instances patients are counseled to refrain from participation in sporting activities. The ability to accurately identify patients with the potential to develop dynamic knee stability would help clinicians appropriately counsel their patients with acute ACL rupture. A classification algorithm is necessary to prospectively identify individuals with good potential to cope non-operatively with ACL deficiency (potential copers). Eastlack (Eastlack, Axe et al. 1999) studied homogenous groups of highly active (level I or II) subjects with isolated ACL injury who had been retrospectively identified as either copers or were symptomatically ACL deficient (non-copers). In this study, non-copers and copers were distinguished by quadriceps strength, global rating, Knee Outcome Survey-Sports, and cross-over hop scores. Knee laxity, age, time from injury, and activity levels were similar for both groups. Based on these results, Eastlack (Eastlack,

5 Axe et al. 1999) suggested a group of clinical tests would be necessary to prospectively discriminate patient functional abilities. The University of Delaware has developed a prospective treatment algorithm to classify the level of dynamic knee stability soon after ACL injury among patients who are highly active. Building on Eastlack’s work (Eastlack, Axe et al. 1999), Fitzgerald (Fitzgerald, Axe et al. 2000) validated a screening examination that consisted of clinical measures (episodes of giving way, hop testing, and self-report of function questionnaires). From a series of 93 consecutive patients with acute, isolated rupture, thirty-nine subjects (42%) met the criteria for classification as appropriate rehabilitation candidates (potential copers). Of the twenty-eight individuals who elected to pursue non- operative management, 79% were successful (i.e., they did not experience giving way of the knee) in returning to pre-injury activity levels for a short period of time (Fitzgerald, Axe et al. 2000). These results indicate the decision making scheme is an effective mechanism for identifying highly active patients with different levels of dynamic knee stability early after ACL injury. Successful identification of non-operative candidates based on functional abilities rather than the magnitude of anterior tibial translation emphasizes the distinction between laxity and instability. Joint laxity is a clinical measure of available joint motion; joint instability is a symptom reflecting the inability to control the available motion whether it is congenital or acquired. In the studies by Eastlack (Eastlack, Axe et al. 1999) and Fitzgerald (Fitzgerald, Axe et al. 2000), the magnitude of anterior knee laxity was not different between groups despite their distinct functional abilities. Other investigators have also reported no relationship between passive anterior knee laxity and function after

6 ACL injury. These studies have been limited, however, by use of submaximal force during knee arthrometer testing (Lephart, Perrin et al. 1992), and small sample sizes (Snyder-Mackler, Fitzgerald et al. 1997). The relationship between laxity and function has not previously been validated with a large, homogenous population of patients with ACL deficiency. There is a differential recovery of quadriceps muscle strength among patients with varying levels of dynamic knee stability. Eastlack (Eastlack, Axe et al. 1999) reported only non-copers demonstrated large quadriceps strength deficits. Wojtys (Wojtys and Huston 1994) reported similar findings: patients who were categorized as the “best” ACL deficient group had no significant difference in quadriceps strength compared to a control group. Conversely, the ACL deficient patients who were in the “worst” group had appreciable quadriceps strength deficits. The prevalence and magnitude of quadriceps strength deficits among patients with poor dynamic knee stability prompted Rudolph (Rudolph, Eastlack et al. 1998; Rudolph, Axe et al. 2001) to call quadriceps weakness the hallmark of the non-coper patient. The influence of quadriceps strength on function early after ACL injury has not been established. Over the past 10 years, we have used the University of Delaware algorithm to prospectively classify all highly active individuals with acute, isolated ACL injury from the practice of a single orthopaedic surgeon (MJA). Patients were determined to have either good (potential copers) or poor (non-copers) dynamic knee stability based on screening results. In Chapter 2 we used results from this screening examination to evaluate the relationship between quadriceps strength, knee laxity, and function to identify the primary determinants of knee stability after ACL rupture:

7

Hypothesis 1.1. Quadriceps muscle strength will be higher in potential copers than non- copers. Hypothesis 1.2. There will be no difference in anterior knee laxity between non-copers and potential copers. Hypothesis 1.3. Function measured during unilateral hop tests and self-assessment questionnaires will be strongly influenced by quadriceps strength among non-copers, but not potential copers. Hypothesis 1.4. Function measured during unilateral hop tests and self-assessment questionnaires will not be influenced by anterior knee laxity in either non-copers or potential copers.

Neuromuscular system responses after ACL injury dictate in large part which patients are able to maintain dynamic knee stability in the absence of ligamentous support. The neuromuscular system can also be a factor contributing to ACL injuries. In a non-contact ACL injury scenario dynamic contribution to joint stability is reduced secondary to delayed muscle contractions and deviant muscle recruitment order (e.g., quadriceps before hamstrings, an ACL agonist) (Williams, Chmielewski et al. 2001). This increases the demand on the static joint stabilizers and places the ACL at high risk for injury during provocative activities such as jumping, cutting, and pivoting. Neuromuscular deficits have been identified both in female athletes and in the general population with increasing age. In comparison to male athletes, females sustain non-contact ACL injuries at a much higher rate during sports such as soccer, volleyball,

8 and basketball (Cox and Lenz 1984; DeHaven and Lintner 1986; Lindenfeld, Schmitt et al. 1994; Arendt and Dick 1995; Griffin, Agel et al. 2000; McClay Davis and Ireland 2001). Environmental, hormonal, anatomical, and biomechanical factors have been proposed as reasons why there is such a discrepancy in injury rates between genders. Neuromuscular factors such as timing of muscle contractions and strength imbalances have been the focus of the female ACL injury epidemic as these are factors modifiable through training intervention. Age related changes in neuromuscular performance have also been documented. Decreases in joint position sense (Skinner, Barrack et al. 1984; Kaplan, Nixon et al. 1985; Madhavan and Shields 2005), slower muscle response time (Mackey and Robinovitch 2006), and slower time to peak torque (Mackey and Robinovitch 2006) have been reported in older versus young populations. Most studies evaluating the influence of age on neuromuscular performance include age groups not associated with ACL injuries. Regression in neuromuscular performance would occur across a continuum and not at a specific age. Therefore, the risk for non-contact ACL injuries may increase with age. In Chapter 3, we used the 10 year results from our classification algorithm to determine if populations at risk for ACL injury secondary to neuromuscular deficits are more likely to experience knee instability after injury:

Hypothesis 2.1. Significantly more females will be classified as non-copers than potential copers. The distribution of non-copers and potential copers will not be significantly different among males.

9 Hypothesis 2.2. Significantly more individuals sustaining a non-contact ACL injury will be classified as non-copers than potential copers. The distribution of non-copers and potential copers will not be significantly different among individuals sustaining contact ACL injuries. Hypothesis 2.3. There will be significantly more non-copers than potential copers across age groups with more individuals classified as non-copers with increasing age, and more individuals categorized as older adults would be classified as non-copers than potential copers.

Non-copers have distinct movement patterns. Alterations in lower extremity motion and muscle activity are a result of non-copers’ inability to dynamically stabilize the knee. Rudolph and colleagues systematically investigated the movement patterns of highly active ACL-deficient non-copers identified with the University of Delaware screening algorithm during walking, jogging, hopping, and stepping tasks (Rudolph, Eastlack et al. 1998; Rudolph, Axe et al. 2000; Rudolph, Axe et al. 2001; Rudolph and Snyder-Mackler 2004). Rudolph reported non-copers implemented a joint stiffening strategy that consisted of lower sagittal plane knee excursion and angles, and higher levels of muscle co-contraction on their injured limb compared to uninjured subjects. This stabilization strategy is not only unsuccessful at maintaining knee stability, but may also lead to excessive joint contact forces that have the potential to damage articular surfaces. Other alterations in non-coper movement patterns include a lower knee flexion moment and a shift in the total support moment away from the knee to the hip on the ACL deficient limb. These findings were consistent across activities, prompting the

10 hypothesis non-copers use a single movement strategy regardless of the demands of the task. Previous investigations of individuals with ACL deficiency have focused on movement patterns during the weight acceptance phase of gait (heel strike to peak knee flexion). The muscle activity and knee motions during weight acceptance create an unstable weight bearing posture (Perry 1992). Thus, evaluation of movement patterns during weight acceptance has provided tremendous insight to the neuromuscular strategies of the ACL deficient knee. Comparatively, few investigations have evaluated movement patterns of the ACL deficient knee during mid-stance. The period of stance occurring from peak knee flexion to peak knee extension, mid-stance is the first half of single limb support. Limb stability is therefore a major objective during this phase of gait. Because there are unique biomechanical demands placed on the lower extremity during mid-stance compared to weight acceptance, evaluating movement patterns during this phase of gait may provide further insight to the neuromuscular strategies of patients with knee instability after ACL rupture. The study in Chapter 4 evaluated 21 patients identified as non-copers with the objective of characterizing movement patterns during the mid-stance phase of gait. We hypothesized unique gait asymmetries would be present during mid-stance that reflected the different demands on and actions of the knee during this portion of the gait cycle.

Hypothesis 3.1. Movement patterns of the injured limb will include a significantly lower sagittal plane knee excursions and peak knee extension angles, and higher muscle co- contraction compared to the uninjured limb.

11 Hypothesis 3.2. Sagittal plane knee moments will be significantly lower, with lower knee and higher ankle contributions to the total support moment on the injured limb compared to the uninjured limb. Hypothesis 3.3. Significant differences in muscle activity will include higher soleus and hamstring, and lower quadriceps muscle activity on the injured limb compared to the uninjured limb.

Quadriceps muscle weakness among non-copers is persistent despite physical therapy intervention early after ACL injury (Zatterstrom, Friden et al. 1998; Keays, Bullock-Saxton et al. 2000; Williams, Buchanan et al. 2005). There is a positive relationship between quadriceps strength and function (Wilk, Romaniello et al. 1994; Wojtys and Huston 1994; Eastlack, Axe et al. 1999; Keays, Bullock-Saxton et al. 2003) that suggests rehabilitation that improves knee extensor strength may result in better outcomes for the non-coper with ACL deficiency. Physical therapy interventions that effectively improve quadriceps strength in the non-coper have not been reported. Diminished sensory feedback after ACL injury may contribute to quadriceps weakness (Konishi, Fukubayashi et al. 2002), prompting the question of whether quadriceps strengthening is even possible in the ACL deficient knee. Alternatively, it may be possible exercise interventions in the acute stages of ACL injury simply are not aggressive (e.g., progressive overload exercises that include open kinetic chain movements and eccentric training) enough in their attempt to restore quadriceps strength.

12 Traditional strengthening exercises may need to be complemented by neuromuscular exercises that promote knee stability. Non-copers have deviant tibia positions (Chmielewski, Hurd et al. 2005; Chmielewski, Ramsey et al. 2005) and motions (Barrance, Williams et al. 2006) after ACL rupture that can deform the joint capsule and trigger mechanoreceptors in and around the knee joint, leading to diminished quadriceps activity. More normal tibia-femoral kinematics through improved knee stability would therefore would facilitate normal sensory feedback and be permissive of quadriceps strengthening, while an unstable knee joint would not. Perturbation training is one type of neuromuscular exercise that has been shown to be effective in improving dynamic knee stability in potential copers with ACL deficiency (Fitzgerald, Axe et al. 2000). No reports, however, have described the effects of perturbation training on non-copers. Improving quadriceps strength may normalize non-coper movement patterns. Snyder-Mackler (Snyder-Mackler, Ladin et al. 1991) attributed the quasi-static knee position non-copers assume during the stance phase of gait to quadriceps weakness. If improving quadriceps strength, however, is predicated on normalization of sensory feedback via enhanced joint stability, changes in muscle activity during gait other than the quadriceps may occur after an exercise intervention. Further elucidation of the relationship between knee joint stability, quadriceps strength, and movement patterns for non-copers has not been possible secondary to the inability to identify a cohort of non- copers with normal quadriceps strength.

The study in chapter 5 is a case series including 20 non-copers. We compared the effects of quadriceps strengthening exercises to quadriceps strengthening exercises

13 performed in conjunction with perturbation training. We further evaluated the effect of improved quadriceps strength on self-rated knee function and movement patterns. Our goal was to identify an effective rehabilitation program for improving quadriceps strength, and provide insight to the relationship between quadriceps strength and knee stability in the ACL deficient non-coper.

Hypothesis 4.1. The combination of perturbation and strengthening exercises will be more effective in improving quadriceps strength than performing strengthening exercises alone. Hypothesis 4.2. After rehabilitation, individuals with meaningful improvements in quadriceps strength will demonstrate improvements in self-reported knee function while those with no change in quadriceps strength will have no change in knee function. Hypothesis 4.3. Individuals who participated in perturbation and strengthening exercises, and those who performed strengthening exercises and had improved quadriceps strength after rehabilitation, will demonstrate normalization of movement patterns during the mid-stance phase of gait including greater peak knee extension angles, sagittal plane knee excursion, and knee moments; muscle activity changes that include higher soleus and lower hamstring muscle activity, and lower muscle co-contraction.

SUMMARY Collectively, this work will contribute to the body of work that characterizes those with and without knee stability early after ACL injury, and provide insight to the movement strategies and the effect of rehabilitation on the ACL deficient non-coper. The

Full document contains 193 pages
Abstract: Most individuals who sustain anterior cruciate ligament (ACL) injury experience knee instability (non-copers ), and have marked quadriceps muscle weakness. There are some individuals, however, with good dynamic knee stability early after ACL injury (potential copers ) who are able to asymptomatically resume pre-injury activities for a limited period of time. The University of Delaware has developed a screening tool that prospectively classifies patients with different levels of dynamic knee stability early after ACL injury. The first goal of this work was to characterize an entire population of highly active patients with acute, isolated ACL rupture using the results of this screening algorithm. Analysis of 300 consecutive subjects indicated potential copers have greater quadriceps strength on bilateral limb comparison (X=88%) than non-copers (X=84%). Quadriceps weakness in non-copers is clinically significant, as quadriceps strength contributed substantially to their functional performance measured during hop testing. The amount of passive anterior knee laxity present after ACL rupture does not contribute to knee instability after injury. A 10 year review of screening results indicated there are specific patient groups who are more likely to experience knee instability after ACL injury, including female athletes and individuals who sustain injury via non-contact mechanisms. Overall, the average individual who sustains an ACL injury is young and likely to experience knee instability. The second goal of this work was to garner insight to the movement strategies of the non-coper, and determine their responsiveness to physical therapy intervention designed to improve quadriceps strength. Gait analysis of 21 subjects classified as non-copers during the mid-stance (peak knee flexion to peak knee extension) portion of stance we identified a control strategy novel to this phase of the gait cycle that includes a shift in the support moment from the knee to the ankle and variable combinations of muscle adaptations that produce joint stiffness. Preliminary results from a clinical trial indicate a stable knee may be more permissive of quadriceps strengthening, as individuals who participated in neuromuscular training and quadriceps strengthening exercises had greater improvements in strength than those who performed only strengthening exercises. Both improved knee stability and quadriceps strength contributed to the normalization of movement patterns after the clinical intervention. These results indicate there is a complementary relationship between strength and stability after ACL injury.