Effectiveness of early quadriceps exercises after anterior cruciate ligament reconstruction

Objective. To systematically review the published information regarding the effectiveness and safety of early postoperative quadriceps muscle exercise training on pain, joint laxity, function and range of motion in postoperative anterior cruciate ligament (ACL) reconstruction adult patients. Data sources. Five databases (CINAHL, PEDro, Pubmed, Science Direct and the Cochrane Library) were searched for studies published from January 1990 to May 2007. Study selection. Publications describing research into the effectiveness of early quadriceps exercises after ACL reconstruction were included. A total of three eligible articles met the inclusion criteria. Data extraction. A review of the three eligible studies was undertaken to describe the key study components. The PEDro Scale was used to determine the methodological quality of the selected trials and the level of evidence of all the eligible studies was categorised according to the evidence hierarchy by Lloyd-Smith.24 Relevant data were extracted by the two reviewer groups to reduce bias. Data synthesis. Due to study heterogeneity a meta-analysis could not be conducted. Effect sizes were calculated provided that sufficient data were provided. Outcome measures included range of motion (ROM), functional performance, pain  and knee laxity. The methodological quality of the studies did not vary considerably across the studies and the average PEDro score was 66%. Marginal significant differences were noted in knee ROM at 1 month postoperatively, pain day 1 postoperatively, knee laxity and subjective evaluation of function at 6 months postoperatively. Conclusion. Early quadriceps exercises can be performed safely in the first 2 postoperative weeks, but clinically significant gains in ROM, function, pain and knee laxity were not evident. Further research should include standardised interventions, measurement time frames and outcome measurement tools to allow for a meta- analysis to be conducted


Introduction
Anterior cruciate ligament (ACL) rupture is one of the most common debilitating knee injuries. 36 This knee injury is commonly sustained by individuals participating in sporting activities that require pivoting, jumping and decelerating actions. 6,36 Immediately after an ACL injury, the athlete experiences significant functional limitations due to significant swelling and pain. 14,37 Athletes are generally eager to return to their usual level of sporting activity and often also experience psychological distress as the recovery process usually lasts for a few months. 18,37 The management of an ACL injury may be conservative or surgical. 16,18 However, surgical reconstruction is currently the most common approach in the management of ACL injuries. 8,22,41 The functional outcome after surgical reconstruction appears to be more favourable compared with that of non-surgical management approaches. 1 However, despite advances in ACL repair after reconstructive surgery to optimise the mechanical stability, functional instability of the knee may still be evident in the post-surgery stage. 2 Physical rehabilitation plays an important role in retraining functional stability of the knee joint after knee surgery. 18 It has also been found that functional rehabilitation was the most important positive prognostic factor for predicting early return to sport. 18 Physiotherapists have the opportunity to select the most appropriate rehabilitation protocol for the specific ACL-injured individual from a range of rehabilitation approaches. Prolific research has been published on rehabilitation protocols after ACL reconstruction. 34 Published research in the 1980s focused on the effectiveness of electrical stimulation of the quadriceps muscle in the acute postoperative stage to decrease the effect of muscle atrophy and weakness. 28 More recently, the focus of published research has been on accelerated versus non-accelerated rehabilitation programmes, as well as open-kinematic chain versus closed-kinematic chain exercises in early rehabilitation after ACL reconstruction. 5,9 Anecdotally, it is proposed that accelerated rehabilitation programmes that allow early range of motion (ROM), immediate weight-bearing and early return to previous functional level should be advocated as best practice. However, these recommendations for best practice are often based on clinical opinion and not on research evidence. 9 Clinical decision-making regarding the most appropriate exercises should be based on research evidence. 9 Appropriate neuromuscular function of the quadriceps muscle group is required during static and dynamic function of the lower limb. 27 Inadequate quadriceps muscle strength may result in functional instability of the knee joint after ACL injury or reconstruction. 21 Quadriceps muscle weakness is a common sequel after ACL surgery. 40 Quadriceps dyskinesia and weakness follow ACL injury due to neural and physiological changes such as the loss of ACL mechanoreceptor feedback, abnormal gamma loop function of the quadriceps femoris muscle, atrophy of muscle fibres and neural activation deficits. 17,30 To prevent weakness of the quadriceps muscle and knee extension lag, physiotherapists commonly prescribe quadriceps exercises after ACL reconstruction as early as possible during the inpatient rehabilitation phase. 34 However, given the high costs of surgery and lengthy rehabilitation, the costeffectiveness of prescribing early quadriceps exercises has been questioned. 34 Furthermore, the safety of early quadriceps muscle strengthening after ACL reconstruction may also be of concern as postoperative anterior-posterior laxity could compromise the integrity of the ACL. 15 Quadriceps muscle contraction produces a rotatory component around the knee joint axis, and also creates a translatory component that causes an anterior shear of the tibia on the femur. 20 The ACL creates an antagonistic pull to resist this anterior shear produced by the quadriceps contraction and by doing so, provides stability to the knee. 20 There is thus strain on the ACL during active quadriceps muscle contraction, mainly in the last 45 degrees of extension, which could compromise the integrity of the graft. 30 The aim of this review was therefore to systematically appraise the effect of early postoperative quadriceps exercise training on pain, joint laxity, ROM and function, compared with a rehabilitation programme not allowing early quadriceps exercises or restricting quadriceps exercise training to only isometric quadriceps contractions in postoperative ACL reconstruction patients aged between 17 and 44 years.

Methodology
The specific objectives of the review were to: • describe the type of quadriceps exercises implemented in eligible randomised controlled trials • describe the outcome measures used to assess pain, knee joint laxity, ROM and function after ACL reconstruction • assess the effectiveness and safety of early postoperative quadriceps exercise training on pain, joint laxity, function and ROM when compared with a rehabilitation programme not allowing early quadriceps exercises or restricting quadriceps exercise training to only isometric quadriceps contraction in postoperative ACL reconstruction patients aged between 17 and 44 years.
The following definitions were used in this review: • Early quadriceps exercises: Any active lower limb activity aimed specifically at contraction of the quadriceps to achieve full-range knee extension and performed within the first 2 weeks or in the in-patient phase after ACL reconstructive surgery. 32,34,38 • ACL reconstruction: The surgical repair of the ACL after complete ACL rupture or recurrent ligament injury. 10 All types of grafts including bone-patellar tendon-bone, bone-tendonbone, semitendinosus-hamstring and semitendinosus-gracilis grafts were included in this review. 35 • Knee instability: The lack of physiological anteriorposterior (A-P) and rotational steadiness of the knee joint. 42 Manual clinical tests to evaluate knee instability include the anterior draw, Lachman's and pivot shift tests. 33 The KT-1000 arthrometer is a popular instrument for measuring knee instability. 33 • Function: The ability to safely perform weight-bearing activities including gait, stair climbing and pre-injury function. 21 • Range of motion (ROM): The amount of motion, measured in degrees, available to a joint within the anatomic limits of the joint structure. 20 Active and passive range of flexion and extension of the knee can be assessed objectively with a goniometer.

Search strategy
Prior to commencing this project, the Cochrane Library and PEDro were searched to ascertain if a similar review had not been published within the past 5 years. The search findings indicated that a similar review had not been published.
Search strategies were developed for the following computerised bibliographical databases: CINAHL, PEDro, Pubmed, Science Direct and the Cochrane Library. These databases were available via the University of Stellenbosch Library and the World Wide Web. All databases from January 1990 to May 2007 were searched. Each search strategy was developed according to the functions of each database group as follows: • Group 1: Databases where papers are classified according to their medical subject headings (MeSH) and key terms. These databases allow for terms to be combined (PubMed, CINAHL, The Cochrane Library).
• Group 2: Databases where key terms are used to classify papers. These databases have a limited ability to combine key terms (Science Direct, PEDro).
A detailed search strategy for each of the selected databases was designed. The key search terms were anterior cruciate ligament, ACL, reconstruction, repair, rehabilitation, strengthening, pain, function, exercises. MeSH terms were used in PubMed.
In addition, a secondary search (PEARLing) was conducted by screening the reference lists of all potential full-text articles. To ensure that eligible articles not indexed in the electronic databases were not missed, the authors of the eligible articles were contacted via e-mail.

Eligibility criteria for inclusion
This review included primary research randomised-controlled clinical trials with an acceptable methodological quality appraisal score of at least 4 out of 11 on the PEDro scale. 7 Studies reporting on males and females aged between 17 and 44 years, who underwent unilateral ACL reconstruction of either the right or left knee by the use of any type of graft, were considered eligible for this review. The eligible age was determined by skeletal maturity that is present over the age of 16 years. 36 Articles reporting on patients with common ACL-associated injuries such as medial meniscal injuries were considered eligible since isolated ACL injuries are rare and do not replicate the population of ACL reconstructions generally managed by physiotherapists.
Studies reporting on participants who underwent previous ACL reconstruction on the reconstructed knee, sustained injury to the contralateral knee or presented with any other rheumatological, neurological, cardiovascular or congenital condition that could affect lower-limb function and result in disability, were excluded from this review as they would not reflect the true outcome of this specific intervention. 36 The interventions of the studies also determined eligibility. Studies that included one treatment group who performed early quadriceps exercises within the first 2 weeks postoperatively and a control group who underwent rehabilitation excluding early quadriceps exercise training or only allowing early isometric quadriceps exercise training were considered eligible for this review.
Eligible studies reporting on the following outcome measures were considered for this review: • Active range of flexion and extension of the knee as measured with a goniometer.

33
• Pain experienced as measured with the Visual Analogue Scale or other published validated pain scales. 4 • Knee stability as measured with the KT-1000 arthrometer or other validated knee-instability scales. 33 • Lower-limb function as determined by functional tests including the single and triple hop tests, timed hop tests, vertical jump tests, stairs hopple test, figure eight running and other relevant functional tests. 33 The two reviewer groups screened all hits and selected relevant titles independently. Differences between pairs were discussed until consensus was reached and the fifth author was consulted to resolve any disagreements.

Assessment of methodological quality
In order to determine the internal validity of the eligible trials, the PEDro Scale was used (Table I). The PEDro scale is commonly used in research to critically evaluate randomised controlled trials. 25

Evidence hierarchy
The level of evidence of all the studies included in this review was evaluated using the evidence hierarchy by Lloyd-Smith. 24 • 1a: Meta analysis of randomised controlled trials • 1b: One individual randomised controlled study • 2a: One well-designed, non-randomised controlled study • 2b: Well-designed quasi-experimental study • 3: Non-experimental descriptive studies -comparative/case studies • 4: Respectable opinion.
Study designs fulfilling the '1b' criteria were considered eligible for inclusion.

Data extraction
The four reviewers were divided into two reviewer groups to extract the data. This was done independently by each of the two reviewer groups. The fifth author was consulted to resolve any discrepancies between the two reviewer groups. The following information was extracted: publication date, authors, journal, study design, setting, PEDro score, aim, description of participants, type of grafts, author's conclusion, clinical relevance, number of participants, description of interventions and outcome measures used.

Data synthesis
The three eligible studies presented heterogeneity with respect to the exercise interventions performed, the outcome measurement tools used and the time frames of measurement. Therefore it was not possible to perform a meta-analysis.
The effect size was calculated with the available data where significant differences between groups were reported by the authors. The effect size represents the clinical magnitude of difference between groups. 29 A greater observed effect represents a larger significant difference. 29 One of the eligible studies, Shaw et al. reported sufficient data (mean and SD) to calculate the effect size. 34

Search results
The results of the search strategy are presented in a flow chart ( Fig. 1). Three articles were considered eligible -from Australia, Sweden and Germany.

Evidence hierarchy
The three selected studies were RCTs, representing level '1b' evidence according to the grading system of Lloyd-Smith. 24

Methodological quality appraisal
There was 100% agreement between the two reviewer groups regarding the methodological score. The average methodological quality score was 66% (Table I).    34 Isberg et al. 15 Friemert et al. 11 Sample

Description of study samples
Information regarding participants in each study according to the sample size, age, surgical procedure and inclusion and exclusion criteria was tabulated (Table II). Sample sizes differed across the three studies and the means sample size was 61. The mean age of the samples in the three studies was comparable and none of the studies included participants older than 41 years of age. According to the inclusion and exclusion criteria, all three studies excluded contralateral knee injuries or multiple ligament injuries of the reconstructed knee. A history of previous knee injury or surgery of the reconstructed knee was excluded for Shaw et al. and Isberg et al.

Description of exercise interventions
The exercise programmes performed by the intervention and control group for each of the three studies are described in Table  III. The intervention groups of all three studies performed early quadriceps exercises within the first 2 postoperative weeks. The control groups did not perform early quadriceps exercises except for Friemert et al., where only early isometric strengthening exercises were allowed in the first postoperative week.

Description of the outcome measures
The outcomes measures and measurement time frames utilised are summarised in Table IV. Range of motion was the only outcome measure utilised in three studies.

Effectiveness of early quadriceps exercises
The effectiveness of early quadriceps exercise training is presented according to each outcome measure.

Range of motion
Shaw et al. measured three ranges over the 6-month follow-up period, namely: active knee flexion, active knee extension and passive knee extension relative to neutral, but the measurement tool was not mentioned. 34 They used mean differences and 95% confidence intervals to determine significant differences between the intervention and control groups. 34 Significant between-group differences (Table V) in active knee flexion and extension 1 month postoperatively were reported. However, it is notable that the lower 95% confidence intervals for both active knee flexion and extension are only marginally significant as they are close to zero. The effect size for knee flexion was 0.44 (medium effect) and 0.48 (medium effect) for extension 1 month postoperatively.
The effect size for active knee flexion in the study by   (Table VI). 34 Measurements are given as a percent-  34 Isberg et al. objectively evaluated function pre-operatively, at 6 months postoperatively and at 2 years follow-up by means of the single-leg-hop test. 15 No significant differences between the groups were found. The third study by Friemert et al. did not report on function objectively. 11 Function was subjectively evaluated using outcome measurement scales in two of the studies. 15,34 The Lysholm score, Tegner score and International Knee Documentation Committee (IKDC) evaluation system were used by Isberg et al. 15 These measurements were taken preoperatively and at 2- year follow-up. Negligible differences were found between the groups at 2 years.
Shaw et al. used the Cincinnati Knee Rating System (CKRS) for subjective assessment of function. 34 The CKRS is a unique rating system that consists of several subdivisions that provide questionnaires for symptoms, function and occupation. 33 The  measures were taken at 1, 3 and 6 months postoperatively. At 6 months postoperatively, statistically significant differences between the groups were demonstrated for the subdivision 'Problems with Sport'. The intervention group had a higher (more favourable) score than the control group for the 'Problems with Sport' category (Table  VII). However, the 95 % CI spans 0 and the effect size we calculated were 0.33, indicating that the effect of the early quadriceps exercises was small.

Pain assessment
According to Shaw et al. there was no statistically significant difference between the groups for pain perception at any follow-up intervals ( Table  VIII). 34 However, in the quadriceps exercise group, significantly greater pain with exercise performance was measured on the first postoperative day.
Findings of the studies conducted by Friemert et al. did not demonstrate significant differences in preoperative pain measurements on the operative day and on the second and seventh day postoperatively (Fig. 2). 11 Isberg et al. did not report on pain as an outcome measure. 15 Shaw et al. further evaluated pain by means of die CKRS evaluation system. 34 Six months postoperatively the intervention group reported significantly higher (more favourable) results for pain calculated under the CKRS subdivision 'Symptoms' (Table IX).
However, the lower confidence interval is marginally significant (0.2). The effect size calculated as 0.62, indicating that the early quadriceps exercises had a moderate on pain perception.

Knee laxity
Shaw et al. measured A-P laxity by means of the KT-1000 using a 15-pound, 20pound and maximal manual test force. 34 Measurements, presented in Table X, were taken 3 and 6 months postoperatively. A-P side-to-side differences of greater than 3 mm or greater than 5 mm were used as cut-off points during testing as these were seen as indications of abnormal laxity.    lax knees and compared this with the number of subjects measured. 34 The total number of subjects presenting with lax knees were calculated with the available data. The control group demonstrated a significantly greater number of subjects with laxity at each test force 6 months postoperatively. No significant differences were noted 3 months postoperatively.
Isberg et al. used the KT-1000 and radiostereometric analysis (RSA) to evaluate AP laxity preoperatively, 6 months postoperatively and at 2-year follow-up. 15 No significance between group differences was found at any point of measurement. However, there was a statistically significant reduction in A-P laxity within each group from the pre-operative period until the 2-year follow-up (Table XI).

Discussion
This paper reports on the effectiveness of early quadriceps exercise after ACL reconstruction and illustrates the sparse literature available to determine the effect of this common physiotherapeutic intervention in this patient intervention. Physiotherapists commonly prescribe static isometric quadriceps exercises early postoperatively, with the aim of restoring neuromuscular function of this muscle as soon as possible. 34 However, the findings of this paper demonstrate that this usual practice procedure may not apply to all patients and requires reconsideration.
The three eligible papers had common methodological limitations. All three studies have not met the blinding of subjects and therapists criterion. Blinding of therapists and patients in exercise intervention studies is impossible in the majority of trials as the therapists and patients can often differentiate between intervention and placebo exercises for a specific patient population. 12 Therefore, although there was heterogeneity with respect to sample size, exercise interventions, outcome measurement and data analysis, the methodological quality of the studies is comparable. The methodological quality of the studies was deemed acceptable, evidenced by the critical appraisal findings and therefore the internal validity is considered to be sound. However, since all the trials were conducted at one conveniently selected clinic, the external validity of the studies may be limited. Furthermore, only one of the studies indicated that a sample size calculation was conducted. 11 The range of the sample sizes was 22 -103 participants among the three studies and, according to Shaw et al., were relatively small when compared with the number of ACL reconstructions performed internationally. 34 A larger sample size is likely to be a more accurate representation of a population and will thus produce more recognisable betweengroup statistically significant differences. 29 Therefore the power of the remaining two studies has not been indicated, highlighting the limitations with respect to external validity of the findings.
The age of participants ranged from 17 to 41 years in the three selected studies. Adolescents and young adults who are physically active in sports are usually at an increased risk of an ACL injury. 24 Therefore the age group of subjects represents the high-risk group for ACL injuries. 6,24,36 The descriptions of the samples, however, lack specific information about the level and type of sporting activity, which may reflect different levels of motivation to engage in exercise therapy and return to sporting activity. A few months' absence from competition and sport may result in detrimental socio-economic consequences for professional athletes, 31 who are usually more motivated to commence their rehabilitation process at an earlier stage compared with recreational athletes or sedentary individuals. It may therefore be important to assess the outcome of this early exercise intervention within patient populations with a specific level of sporting activity as the psychological benefits of early rehabilitation may be advantageous in competitive athletes.
The outcomes measurement tools used in the selected studies were valid and reliable. 13 15 However, differences in outcome measurement time frames and interpretation did not allow for a meta-analysis of the outcome data. Shaw et al. recommended that key outcome measures should be used at specific time frames postoperatively, in order to optimise the sensitivity of these measuring tools and thus enhance its validity and reliability. 33 Future research in this field should attempt to identify the most appropriate outcome measurement type and measurement time frames after ACL reconstruction.
Appropriate descriptions of the exercise intervention regimens were presented in the selected studies. This is a positive aspect of the reviewed papers, as a clear description of interventions is often lacking in physiotherapeutic trials. Poor descriptions of the interventions make it difficult or impossible to apply effective interventions based on robust research evidence. The exercise interventions applied in the papers were mostly representative of usual clinical practice. 32 The findings of this review are therefore relevant to clinicians who prescribe similar exercise regimens as they provide insight into the effect on patient outcomes.   Appropriate function of the quadriceps muscle group is important daily and sporting activities. 27 These review findings indicate that no significant difference in functional performance was noted between the intervention and control group 6 months and 24 months postoperatively. Objective functional performance was not assessed before 6 months due to precautionary limitations related to the surgery. There was no difference between groups with respect to most of the subjective functional scale findings. However, a significant difference for the 'problems with sport category' was reported by Shaw et al., but the effect size indicated that the clinical effect was small. 34 The finding indicated that the intervention group experienced significantly more pain when exercising, and this may contribute further to inhibit quadriceps muscle contraction. 3,34 The improvement in muscle function when performing early quadriceps exercises may thus be relatively small and it appears that functional use of the quadriceps muscle performed when the patient's pain experience is tolerable may be appropriate to produce appropriate strength required for function. A clinical recommendation may thus be that pain may need consideration when prescribing these exercises.
Shaw et al. reported that the subjects in the intervention group had marginally better improvement in active knee flexion and extension ROM, but this was limited to 1 month postoperatively. 34 However, the effect size indicated a medium clinical effect of range of motion at 1 month. According to Milne et al. a minimum of at least 90˚ of flexion is required to safely descend stairs and 105˚ to rise from a toilet seat. 26 However, since both groups achieved these functional range requirements, the clinical effect of the range of motion findings by Shaw et al. is questionable. 34 There is concern that early quadriceps exercises may result in increased anterior-posterior knee laxity, resulting in damage to the graft. 15 Shaw et al. concluded that the prevalence of knee instability 6 months postoperatively was reduced by performing early quadriceps exercises. 34 However, Isberg et al. reported no significant difference between groups 6 months postoperatively. 15 Shaw et al. incorporated a larger sample size and may be representative of the ACL injury population. 29,34 A more notable finding was that A-P laxity was not different between the intervention and control groups in the long term. 34 This may indicate that early quadriceps exercises can be considered safe in this population as they did not compromise stability.

Limitations
In this review, only studies reported in the English language were considered eligible due to time and resource constraints.
In the case of uncertainty regarding information presented in the studies, authors were contacted via e-mail. However, if they did not reply, contact was not made telephonically due to resource constraints. Heterogeneity of the data of eligible studies did not allow for a meta-analysis to be conducted.

Conclusion
Early quadriceps exercises do not compromise the integrity of the graft, as they do not increase ligament laxity. However, it appears that the gains when performing early quadriceps exercises or restricting quadriceps exercise training to only isometric quadriceps exercises with respect to range of motion and function are small or insignificant. Further research is required and should include standardised interventions, measurement time frames

Introduction
Anterior knee pain is a common condition that affects a wide age range of patients. 5 The condition is often self-limiting, but can take up to 2 years to resolve. 16 It frequently interferes with exer-

origiNAl rESEArCh ArTiClE
A conservative programme for treatment of anterior knee pain in adolescents