Gait mechanics after ACL reconstruction: implications for the early onset of knee osteoarthritis

Transcription

1 Gait mehanis after ACL reonstrution: impliations for the early onset of knee osteoarthritis R J Butler, 1 K I Minik, 1 R Ferber, 2 F Underwood 1 1 Department of Physial Therapy, University of Evansville, Evansville, Indiana, USA; 2 Faulties of Kinesiology and Nursing, University of Calgary, Calgary, Alberta, Canada Correspondene to: Dr R J Butler, Department of Physial Therapy, 1800 Linoln Avenue, Evansville, Indiana 47722, USA; rb83@evansville. edu Aepted 11 November 2008 Published Online First 26 November 2008 ABSTRACT Bakground: Individuals who sustain a rupture of the anterior ruiate ligament (ACL) are at an inreased risk for developing early-onset knee osteoarthritis (OA). The mehanism behind the early onset of the disease is still unknown. Knee OA progression has been previously examined by alulating the internal knee-abdution moment during gait. However, knee-joint moments have not been examined in individuals after ACL reonstrution as a potential mehanism for disease progression in early knee OA. Objetive: To determine if individuals who have undergone ACL reonstrution exhibit altered gait mehanis that may be assoiated with knee OA progression. Methods: In total, 17 people who had previously undergone ACL reonstrution were enrolled in the study. A mathed ontrol group was reruited for omparison. All partiipants underwent gait analysis at an intentional walking speed to examine variables previously assoiated with knee OA progression, primarily the internal peak knee-abdution moment, during gait. One way ANOVAs were performed to examine differenes in gait mehanis between the two groups. All joint moments were alulated as internal moments. Results: The peak knee-abdution moment was inreased by 21% in the ACL ompared with the ontrol group (p = 0.04). No other differenes were seen in frontal plane knee or hip mehanis. Conlusion: It seems that individuals who have undergone ACL reonstrution exhibit an inreased peak kneeabdution moment that may establish a potential mehanism of the earlier onset of knee OA in this population. The Healthy People 2010 Initiative, introdued by the US government, enourages exerise to maintain healthy lifestyles. 1 However, one hurdle to this initiative is the greater risk for injuries that are sustained during exerise ativities, whih an lead to long-term pain and disability. 2 One of the most traumati musuloskeletal injuries that an individual an inur during exerise is a tear of the anterior ruiate knee ligament (ACL) in the knee, whih is assoiated with long-term joint degeneration in addition to the initial trauma. 3 4 It is reported that 1 in 3500 individuals (estimated total of ) in the general population sustain an ACL rupture eah year. 5 To redue the risk of this injury, a large number of researh studies are urrently being onduted to identify ways to redue the rate of ACL injuries and to improve rehabilitation after the injury However, no urrent researh has foused on the long-term effets of the injury, suh as premature degenerative joint disease. It has been reported that approximately 45% of individuals who sustain an ACL rupture experiene premature knee osteoarthritis (OA) within 10 years of the injury. 20 Thus, it seems that although ontinued researh on treatment of the initial injury is important, there is also a need for a greater understanding for the mehanism of the early onset and progression of knee OA in people who have undergone ACL reonstrution. Knee OA is typially onsidered a disease of wear and tear, whih is seen most frequently in people aged.65 years, and is diagnosed using radiography and MRI. 21 However, urrent researh suggests that an inreased number of individuals will exhibit premature knee OA in their 30s and 40s as a result of a knee-joint injury It has been estimated that an ACL rupture ages the knee by 30 years. 3 Epidemiologial studies have reported that individuals who suffer a knee injury are at a.5-fold greater risk of developing knee OA. 23 This risk is muh greater than the relative risk of 1.7 for inreasing body weight, whih has been previously strongly orrelated with the development of knee OA. 23 Thus, it is important to examine the mehanism behind the early onset of knee OA in individuals who have sustained an ACL injury. Previous researhers have suessfully assoiated variables measured during gait analysis with knee OA progression, and individuals with knee OA have been reported to have altered gait mehanis ompared with an asymptomati population These mehanis are thought to be related to dynami frontal plane knee malalignment, whih an ause inreased displaement between the resultant ground reation fore and the knee joint entre, ausing greater frontal plane moments about the knee joint. The inreased frontal plane moment at the knee has been suggested to promote degradation of the medial tibiofemoral ompartment of the knee, and has been seen to be a signifiant preditor of knee OA disease progression It has also been reported that for every 1% inrease in the internal abdution moment, the risk of knee OA progression inreases 6.46 times, as measured by Kellgren Lawrene grade and jointspae narrowing. Although hanges in gait mehanis in individuals with diagnosed medial knee OA have established a potential mehanism of disease progression, no researh has examined hanges in the frontal-plane moments in individual who have undergone ACL reonstrution. Individuals who have sustained ACL reonstrution are at inreased risk for sustaining early onset knee OA; however, the mehanism behind the early development of knee OA has not been established. The use of gait analysis has been 366 Br J Sports Med 2009;43: doi: /bjsm

2 established as a suessful tool to assess the progression of knee OA in individuals with a diagnosis of the disease, and may be a tool to examine the mehanism of earl-onset knee OA after an ACL rupture. Therefore, the aim of this study was to examine the internal knee moments and knee joint angles in individuals who have undergone ACL reonstrution ompared with a group of mathed ontrols with no history of knee injury. In addition, beause movements at the knee may be affeted by movement further up the kinemati hain at the hip, we wanted to examine if the frontal plane abdution moment and addution angle at the hip were altered in individuals who have sustained ACL reonstrution, in order to examine more proximal auses for the early onset of knee OA. We hypothesized that the individuals who have undergone ACL reonstrution would have an inreased peak knee and hip frontal plane moments ompared with the ontrol group. METHODS The study was given ethis approval by the institutional review board. Before entering the study, all subjets read and signed an approved informed onsent doument. An a priori power analysis based upon data using similar methods in individuals with knee OA and a meaningful hange of 10% revealed that 15 subjets were neessary to examine differenes in the peak knee-abdution moment. 34 In order to fulfil this riterion, 17 subjets (13 women, 4 men) with a previous ACL reonstrution were reruited for the study (ACL). To be inluded in the ACL group, it was neessary for all potential subjets to have returned to their previous ativity level and to have no urrent musuloskeletal or neurologial onditions that limited their ativities of daily living. All of the subjets had undergone a surgial repair at least 1 year before entering the study. For omparison, a ontrol group of individuals who had never sustained a knee injury were reruited, and mathed for gender, age (+/2 2 years), ativity level (Tegner sale) and body mass index (BMI) (+/22.5 kg/m 2 ), All individuals in the ontrol group also had no urrent musuloskeletal or neurologial onditions that limited their ativities of daily living. Upon ompleting the informed onsent, eah subjet was sheduled for gait analysis. Analysis of eah individual s gait was olleted unilaterally using a previously published and established marker set (fig 1). 35 For the ACL group, the gait data were olleted on the injured limb, while gait data on the ontrol group was olleted on their dominant leg (defined as the leg they would use to kik a ball the farthest). Clusters of four retrorefletive markers on thermoplasti shells were attahed to the thigh and shank of the involved leg. Pelvi markers were plaed on the anterior superior ilia spine, ilia rest and L5-S1 junture. Traking markers for the rear foot were plaed in the midline of the heel ounter of the shoe and just lateral to the midline of the heel ounter. To define and establish segmental oordinate systems and inertial parameters, anatomial markers were plaed bilaterally on the greater trohanter, and on the medial and lateral epiondyles of the knee, medial and lateral malleoli, first metatarsal head, fifth metatarsal head, and the distal end of the foot. The anatomial markers were removed after a standing alibration trial to allow for a more normal gait pattern that would not be inhibited by the anatomial markers plaed on the medial aspet of the leg. All subjets walked in a standardized laboratory shoe that was a neutral running shoe (New Balane 1022, Boston, MA, USA). Segmental position data, as defined by the retrorefletive markers, were reorded as the subjet walked at an individualized intentional walking speed (defined as the speed that they would use when getting mail from their mailbox ) along a walkway where the subjet s speed was monitored by traking the average veloity of the L5 S1 marker. The subjet s intentional walking speed was maintained within +/2 5% to be onsidered as an aeptable trial. An eight-amera motion analysis system (VIontrol, Oxford, UK) was used to reord the kinemati data at 60 Hz. A fore platform (Berte Corporation, Columbus, Ohio, USA), plaed in the entre of the walkway and flush with the floor, was used to ollet ground reation fore data at 1080 Hz as subjets traversed the walkway. All gait analysis data were analysed from heel strike until toe lift of the gait yle. This period was normalized to 100% of stane. Joint kinematis and kinetis were alulated after the gait analysis using Visual 3D software (C-Motion, Bethesda, Maryland, USA). Marker trajetories were low-pass filtered at 6 Hz using a seond-order reursive Butterworth filter. The fore-platform data were filtered using a low-pass reursive 50 Hz Butterworth filter. All kineti data were normalized to body mass. Joint- moment data were alulated as internal joint moments and were normalized to body mass and height. The alulation of internal joint moments has a different interpretation to that of external joint moments that are ommonly Figure 1 Marker set used for gait analysis. Table 1 Desriptive statistis for the group who had undergone ACL reonstrution and the ontrol group Variable ACL Control Age, years 23.6 (5.8) 23.4 (5.7) Body mass index, kg/m (3.2) 23.3 (2.4) Tegner ativity level 7.7 (1.5) 7.7 (1.6) Intentional gait veloity, m/s 1.44 (0.11) 1.45 (0.12) Time sine surgery, years 5.3 (4.4) NA ACL, anterior ruiate ligament; NA, not appliable. *Signifiant differenes between ACL and ontrol group (p,0.05). Data are mean (SD). Br J Sports Med 2009;43: doi: /bjsm

3 Table 2 Desriptive statistis for the variables of interest during the gait analysis between the group who had undergone ACL reonstrution and the ontrol group. Variable ACL Control Knee Peak abdution moment, Nm/kg.m* (0.08) (0.09) Peak addution, degrees 1.9 (2.9) 0.9 (2.9) Addution exursion, degrees 4.2 (1.7) 4.9 (2.9) Hip Peak abdution moment, Nm/kg.m (0.17) (0.09) Peak addution, degrees 8.8 (2.5) 9.2 (2.9) Addution exursion, degrees 9.6 (3.4) 9.3 (2.6) ACL, anterior ruiate ligament. *Signifiant differenes between ACL and ontrol group (p,0.05). Data are mean (SD). Figure 2 Ensemble average traes of the internal knee-abdution moment during stane for the individuals who had sustained an ACL rupture (mean, ACL) and the mathed ontrol group (mean+/2standard error, ontrol). reported in the knee OA literature, but fundamentally are equal and have the opposite sign. The variables of interest for the study foused on frontalplane motion and moments at the knee and hip along with the vertial ground-reation fores. Peak addution and addution exursion (peak position minus initial position) were examined at the knee and hip. The peak abdution moments at the knee and hip were assessed during the first half of stane. Statistial analyses were performed using a one-way ANOVA (ACL vs ontrol) for all of the variables of interest. SPSS V.14 (SPSS In., Chiago, Illinois, USA) was used for all statistial analysis and a signifiant differene was identified as p,0.05. RESULTS No signifiant differenes existed between the groups for age, ativity level, body mass index or intentional gait veloity (table 1). Individuals in the ACL group exhibited a 21% larger peak knee-abdution moment than the ontrol group, whih was signifiantly different (fig 2). No signifiant differenes were seen for the peak frontal plane moments at the hip (table 2). Additionally, no signifiant differenes were seen for the peak addution or addution exursion at the knee or hip (table 2). thus it is possible that this inreased moment is a potential mehanism ausing the early onset of knee OA after ACL rupture There is relatively little researh involving the potential mehanisms behind the early onset of knee OA and therefore, omparison of our data with previous data is diffiult. Compared with a group of individuals with diagnosed medial knee OA, the peak knee-abdution moment values for the ACL group in our study are similar (20.36 Nm/kg.m to Nm/kg.m). 36 The dereased values seen in our samples are potentially due to the inreased ativity level and lower BMI of our study group, but are within 1SD of previously published results using a similar marker set. In general, the values for the peak knee-abdution moment seem to be similar to previously published data using the same marker set and protool. 36 The results of this study suggest that it may be benefiial to address the potential for early knee-joint degeneration after ACL reonstrution during the rehabilitation proess with the patient. Current researh on reduing the effets of ACL injuries is primarily foused on sreening protools to redue the inidene of injury along with establishing effiaious treatment protools to get patients to return to their pre-injury ativity level. In light of the findings of this study, it seems that interventions that an redue the peak knee-abdution moment DISCUSSION The aim of this study was to examine the internal joint moments and joint angles at the knee and hip during walking in individuals who have undergone ACL reonstrution ompared with a group of ontrols with no history of knee injury. Every year there are an estimated ACL ruptures in the USA. Of this group, it is expeted that will develop knee OA within 10 years based on previous researh estimates. 3 However, little is known about the mehanism behind the early development of knee OA in this group. Based on the findings of this study, it an be suggested that one potential mehanism behind the early development of knee OA in this group is that individuals who have sustained ACL reonstrution exhibit an inreased peak knee-abdution moment ompared with a ontrol group mathed for a gender, age, ativity level and body mass index. The peak knee-abdution moment has previously been orrelated with knee OA progression, and Figure 3 Peak knee-abdution moment values for all subjets in the ACL group (grey bars represent individuals.1 SEM below mean value for ontrols, white bars represent individuals within 1 SEM of mean value for ontrols and the hathed bars represent individuals.1 above mean value for ontrols). 368 Br J Sports Med 2009;43: doi: /bjsm

4 may need to be implemented into a patient s plan of are after ACL rupture to redue the risk for the early onset of knee OA. Conservative treatments (eg, wedged foot orthoses and knee braing) that address malalignment for people with diagnosed knee OA have been shown to redue symptoms assoiated with knee OA along with reduing the peak knee-abdution moment Although there are few long-term data using these interventions, it seems that hese interventions may offer an effetive onservative treatment option to slow the progression of knee OA. Conservative interventions that alter mehanial alignment have previously been reported to be most effetive in the early stages of joint degeneration. Thus individuals who do not exhibit radiographi joint degeneration and are asymptomati but are at risk for disease progression due to additional risk fators (ie knee injury) may benefit most from suh interventions. 38 Although these onservative interventions that alter mehanial alignment may serve as potential treatment options for individuals who have sustained an ACL rupture, long-term studies examining effetiveness along with issues involving ompliane and omfort are required to examine the overall effiay of suh an intervention. Additionally, onservative mehanial interventions are designed to redue loading to the ompartment that is affeted by joint degeneration.. In the knee, joint degeneration is more prevalent in the medial ompartment, however individuals still develop knee OA in the lateral ompartment. Individuals who present with lateral knee OA tend to exhibit signifiantly redued internal peak knee-abdution moments at the knee ompared with healthy ontrols. 39 Based on this information, it ould be suggested that two of the subjets in our ACL group may be at a greater risk for progressing to knee OA in the lateral ompartment (fig 3). Therefore, it may be that an initial gait analysis after ACL surgery may be sensitive enough to detet the ompartment of the tibiofemoral joint that is at greater risk for the development of knee OA. This information would be benefiial in guiding the design of any onservative mehanial interventions. Information of this sort is ruial in that if the inorret side is unloaded then the intervention may atually inrease the degenerative disease proess and aelerate the early onset of knee OA. More researh regarding the relationship between gait mehanis and tibiofemoral ompartment knee OA development would be benefiial to assist health are What is already known on this topi Individuals who have undergone ACL reonstrution are at risk for the early onset of knee OA. The inidene of a knee injury plaes an individual at a higher risk for knee OA than an inreased BMI. No studies have examined the potential mehanism of early onset knee OA after ACL reonstrution. What this study adds Individuals who have undergone ACL reonstrution exhibit inreased frontal plane knee moments; suggesting a potential mehanism for the early progression of knee OA. Future researh should fous on reduing the frontal plane knee moment in individuals after ACL reonstrution to redue the inidene of early-onset knee OA. professionals in the presription of onservative mehanial interventions to redue an individual s risk for the early onset of knee OA after ACL reonstrution. In onlusion, individuals who have sustained ACL reonstrution exhibit an inreased peak knee-abdution moment whih suggests a greater risk for knee OA development and may provide a mehanism behind the early onset of knee OA seen in this population. In light of this finding, the long term maintenane of joint integrity may want to be onsidered in the plan of are after the surgial intervention in addition to the desire to return to their previous ativity level for individuals with an ACL rupture. Long term researh studies examining the effiay of onservative treatment options aimed at slowing down knee OA progression should be examined in individuals after an ACL rupture to determine if they are effetive in reduing the inidene of early knee OA onset. Aknowledgements: We thank the Institute for Global Enterprise in Indiana for their finanial support of this work. We also thank New Balane for donating the shoes used in this study. Competing interests: None. Patient onsent: Obtained. 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