Patellar taping: is clinical success supported by scientific evidence?

Patellofemoral pain syndrome (PFPS) is a common condition presenting to physiotherapy and sports medicine practices. Despite its prevalence, the aetiology, pathogenesis, and recommended treatment remain unclear. One component of treatment for PFPS that has been subjected to scrutiny is patellar taping. This taping was designed to realign the patella within the femoral trochlea, thus reducing pain from PFPS and improving both quadriceps and patellofemoral joint function. Clinical and research findings confirm that the pain associated with PFPS is significantly reduced with patellar taping. Therefore, research has aimed at determining the mechanisms of this pain relief. The means by which patellar tape can relieve pain may provide insight into the aetiology and risk factors for PFPS, thus allowing more appropriately designed treatment regimes and preventative strategies. There is evidence to suggest that patellar tape improves patella alignment (measured radiographically) and quadriceps function (torque production and extensor moments). Evidence that patellar tape enhances the activation of individual vastii (magnitude or timing) is limited in quality and quantity, which probably reflects the difficulties inherent in measuring this complex question. There is preliminary evidence for improved knee control during gait in association with patellar tape. This paper critically reviews the studies that have examined the effects of patellar taping and makes informed recommendations for further research and clinical practice.     

In vivo and noninvasive six degrees of freedom patellar tracking during voluntary knee movement

OBJECTIVE: The purpose of this study was to investigate in vivo and noninvasively patellar tracking in six degrees of freedom during voluntary knee extension and flexion. DESIGN: Patellar tracking was evaluated in vivo and noninvasively with corroboration using in vivo fluoroscopy and in vitro cadaver measurements. BACKGROUND: Patellofemoral pain is closely related to abnormal patellar tracking and malalignment. However, there is a lack of quantitative and convenient methods to evaluate six degrees of freedom in vivo patellar tracking, partly due to difficulty in evaluating 3-D patellar tracking noninvasively. METHODS: Six degrees of freedom patellar tracking was measured in vivo and noninvasively using a small clamp mounted onto the patella and an optoelectronic motion capture system in 18 knees of 12 healthy subjects during voluntary knee extension and flexion. RESULTS: The patella tracked systematically following a certain pattern during knee extension and flexion. Patellar tracking patterns during knee extension and flexion were not significantly different in the 18 knees tested. When the knee was voluntarily extended from 15 degrees flexion to full extension, the patella was extended 8 degrees, laterally tilted 2 degrees, and shifted 3 mm laterally and 10 mm proximally. The results were consistent with previous in vitro and in vivo studies. CONCLUSION: Six degrees of freedom patellar tracking can be evaluated in vivo and noninvasively within the range of 20 degrees flexion to full knee extension. RELEVANCE: The study provided us quantitative six degrees of freedom information about patellar tracking during knee flexion/extension, which can be used to investigate patellar tracking in vivo and noninvasively in both healthy subjects and patients with patellofemoral disorder and patellar malalignment.     

Usefulness of skyline view in the evaluation of acute patellar dislocation: A case study

Skyline view is routinely used for the evaluation of patellofemoral abnormalities in general practitioner, orthopaedic and rheumatology patients but rarely forms part of the trauma radiographic series. A 16-year-old male was referred for an x-ray of the right knee after patellar dislocation following a football injury. The lateral view showed an osteochondral lesion in the lateral femoral condyle and a skyline was suggested to be performed. Despite the patient could manage only 70° of flexion from full extension, a skyline view was obtained by adapting the standard technique which revealed an avulsion fracture at the medial aspect of the patella. Advanced imaging is used for further evaluation when x-ray findings are equivocal, or as a management or intervention tool(s). But not every patient is referred for advanced imaging unless there is an informed clinical reason. Skyline view should therefore be performed as part of trauma knee radiographic series when it is clinically indicated that patellar dislocation has occurred. When the standard skyline view positioning technique is not possible due to limited flexion, it can still be achieved depending on the degree of flexion at the knee.     

Diagnostic value of five clinical tests in patellofemoral pain syndrome

The current study is aimed at examining the validity of five clinical patellofemoral tests used in the diagnosis of patellofemoral pain syndrome (PFPS). Forty-five knee patients were divided into either the PFPS or the non-PFPS group, based on the fulfilment of the diagnostic criteria for PFPS. An investigator, blinded to the group assignment, performed the vastus medialis coordination test, patellar apprehension test, Waldron's test, Clarke's test, and the eccentric step test. The positive likelihood ratio was 2.26 for both the vastus medialis coordination test and the patellar apprehension test. For the eccentric step test, the positive likelihood ratio was 2.34. A positive outcome on either the vastus medialis coordination test, the patellar apprehension test, or the eccentric step test increases the probability of PFPS to a small, but sometimes important, degree. For the remaining tests, the positive likelihood ratios were below the threshold value of 2, indicating that given a positive test result, the probability that the patient has PFPS is altered to a small, and rarely important degree. The negative likelihood ratios for all tests exceeded the threshold value of 0.5, suggestive of clinically irrelevant information. These data question the validity of clinical tests for the diagnosis of PFPS.     

Irreducible lateral patellar dislocation: the importance of impaction fracture recognition

Irreducible lateral patellar dislocation may occur in the older patient with a previous history of patellofemoral arthritis. The only subtle finding on physical examination to suggest this diagnosis will be positioning of the knee in less flexion than a typical lateral patellar dislocation, anterolateral position of the patella and internal rotation of the patella from the coronal plane. That is, the patella is dislocated laterally but the lateral border comes to lie in a position of variable degrees of anterior displacement relative to the medial patellar border. Plain x-rays may reveal the rotation of the patella along the vertical axis and an anterolateral rather than lateral positioning of the patella. Computed tomographic scanning is of benefit if the diagnosis is suspected or if an initial attempt at closed reduction is unsuccessful. Open reduction is recommended, if a single closed reduction attempt is not successful, to prevent any potential worsening of the patellar impaction fracture. A laterally dislocated patella that displays internal rotation about the vertical axis or the "flipped patella" sign is pathognomonic of an irreducible patellar dislocation and suggests patellar impaction on a lateral femoral condylar ridge osteophyte. Open reduction is easily achieved through a vertically oriented quadriceps tenotomy without the need for medial repair.     

AN UPDATE FOR THE CONSERVATIVE MANAGEMENT OF PATELLOFEMORAL PAIN SYNDROME: A SYSTEMATIC REVIEW OF THE LITERATURE FROM 2000 TO 2010

Purpose/Background:

Patellofemoral pain syndrome (PFPS) is one of the most common and clinically challenging knee pathologies. Historically, clinicians have used a myriad of interventions, many of which have benefited some but not all patients. Suboptimal outcomes may reflect the need for an evidence-based approach for the treatment of PFPS. The authors believe that integrating clinical expertise with the most current scientific data will enhance clinical practice. The purpose of this systematic review is to provide an update on the evidence for the conservative treatment of PFPS.

Methods:

The PubMed, CINAHL, and SPORTDiscus databases were searched for studies published between January 1, 2000 and December 31, 2010. Studies used were any that utilized interventions lasting a minimum of 4 weeks for subjects with PFPS. Data were examined for subject sample, intervention duration, intervention type, and pain outcomes.

Results:

General quadriceps strengthening continues to reduce pain in patients with PFPS. Data are inconclusive regarding the use of patellar taping, patellar bracing, knee bracing, and foot orthosis. Although emerging data suggest the importance of hip strengthening exercise, ongoing investigations are needed to better understand its effect on PFPS.

Conclusions:

Current evidence supports the continued use of quadriceps exercise for the conservative management of PFPS. However, inconsistent or limited data regarding the other interventions precluded the authors'' ability to make conclusive recommendations about their use. Future investigations should focus on identifying cohorts of patients with PFPS who may benefit from the other treatment approaches included in this systematic review.     

Patellafraktur nach MPFL-Plastik bei erhöhtem TTTG-Abstand

A 19-year-old patient suffered recurrent patellar dislocations and was treated by medial patellofemoral ligament (MPFL) reconstruction with a gracilis ligament autograft. Normal knee flexion while bowling led to a patella fracture 4 years after surgery. Further diagnostics showed a normal mechanical axis, no torsional deformity, no patellar or trochlear dysplasia and normal patella height. Source of the patellar instability was an increased tibial tuberosity-trochlea groove distance (19 mm). Surgical treatment was carried out with screw fixation of the patella fracture and tibial tuberosity transfer. The source of the patellar instability was not completely analyzed before surgery and ultimately led to a patellar fracture. A complete diagnostics of a patellar dislocation is always necessary before surgery.     

Traumatic patellar tendinopathy

Purpose. In patellar tendinopathy, there is anterior knee pain with tenderness of the attachment of the patellar tendon over the lower pole of the patella. The condition is commonly associated with athletic overuse, but we have encountered it in some patients following direct blunt trauma to the anterior aspect of the knee. We describe the history and management of patients with traumatic patellar tendinopathy.

Method. Between April 2000 and August 2006, we managed eight otherwise healthy well trained athletes who developed signs and symptoms compatible with classical patellar tendinopathy after a direct trauma to the anterior aspect of the patellar tendon during sport activity.

Results. The clinical diagnosis of patellar tendinopathy was confirmed clinically and at imaging by MRI and ultrasound scans. Patients responded to conservative or surgical management, in the same way as patellar tendinopathy secondary to overuse.

Conclusion. A single direct traumatic event can lead to chronic tendon problems. Hence, in addition to overuse injury, patellar tendinopathy can follow a direct trauma and exhibit the same clinical features. Further research is required to better understand the pathophysiology of the clinical condition.     

Determinants of patellar tracking in total knee arthroplasty

BACKGROUND: Optimizing patellar tracking in total knee arthroplasty is a surgical priority. Despite this, a comparison of the effects of different component placements on patellar tracking is not available; the biomechanical impact of the patellar resection angle has not been studied; and the similarity between intraoperative and postoperative effects, fundamental to improving patellar tracking, is unknown. Our objective was to compare the impact of the major controllable femoral, tibial and patellar component positions on patellar kinematics during both passive and loaded flexion. METHODS: We tested eight cadaveric knee specimens in two rigs, simulating intraoperative and weightbearing flexion. Optoelectronic marker arrays were attached to the femur, tibia and patella to record kinematics throughout the range of motion. We modified posterior-stabilized fixed-bearing knee components to allow for five types of variations in component placement in addition to the neutral position: femoral component rotation, tibial component rotation, patellar resection angle, patellar component medialization and additional patellar thickness, for a total of 11 individual variations. FINDINGS: The major determinants of patellar tilt and shift were patellar component medialization, patellar resection angle and femoral component rotation. The relative order of these variables depended on the structure (bone or component), kinematic parameter (tilt or shift) and flexion angle (early or late flexion). Effects of component changes were consistent between the intraoperative and weightbearing rigs. INTERPRETATION: To improve patellar tracking, and thereby the clinical outcome, surgeons should focus on patellar component medialization, patellar resection angle and femoral component rotation. These have been linked with anterior knee pain as well. Neither tibial component rotation nor patellar thickness should be adjusted to improve patellar tracking.     

保留髌骨膝关节置换的症状及影像学评价

背景：膝关节置换中是否置换髌骨是一个持续争论的话题。目的：侧重评价保留髌骨膝关节置换后髌骨的影像学稳定性和症状改善。方法：对39例（48膝）骨关节炎及类风湿性关节炎患者行保留髌骨的全膝关节置换。结果与结论：术中记录髌骨软骨退变分级Ⅲ级和IV级达36膝,占75%,置换后HSS评分及FELLER髌骨评分较置换前明显改善,明显膝前痛病例为5例,占10%,其髌骨病理分级均达到Ⅳ级。保留髌骨膝关节置换前后影像学评价髌股关节的对线差异无显著性意义,下肢力线校正满意。提示对于置换前髌股轨迹不良、术中软骨病理分级较低者应该进行选择性的髌骨置换,恰当选择病例采用保留髌骨的膝关节置换可减少髌股关节并发症,置换前仔细评估,综合考虑多种因素操作可进一步改善髌股轨迹。     

全膝关节置换中是否需要髌骨置换

背景：全膝关节黄换中髌骨冠换与否一直存在争议。目的：对临床全膝关节簧换中是否进行髌骨簧换进行对比观察。方法：随机选取2009年7月至2012年4月在曲城市第一人民医院膝关节骨性关节炎患者56例,兆60膝,按全膝关节置换时是否进行髌骨置换分为髌骨置换组和髌骨未置换组。结果与结论：令膝关节置换3个月后,髌骨置换组忠者在膝关节功能评定量表评分、髌骨评分、活动度和Q角与髌骨未置换组比明显降低（P〈0．05）,而膝前痛评分和膝外翻角与髌骨未置换组患者的差异无显著性意义（P〉0．05）。提示全膝关节置换中合理进行髌骨处理可有效改善髌股关节运动轨迹,明混降低髌骨并发症。对于髌股关节匹配及力线良好的忠者保留髌骨可提高关节的功能恢复,在全膝关节胃换中进行髌骨置换较髌骨不置换总休效果好。     

Narrative Review — Knee Pain in the Pediatric Athlete

Purpose of reviewThis review article seeks to highlight common youth athlete knee conditions due to overuse or trauma and elucidate differences from the adult populations.Recent findingsOveruse conditions presented include apophysitis, osteochondritis dissecans plica syndrome, and discoid meniscus. Traumatic conditions presented include patellar instability, patellar sleeve fracture, and patellofemoral osteochondral fractures.SummaryKnee injuries affect a significant proportion of youth athletes. These injuries place athletes at higher risk of chronic pain and potentially osteoarthritis. We have reviewed common overuse and traumatic knee injuries and differentiating factors between the adult population to improve and expedite the diagnosis, treatment, and prognosis for youth athletes with knee injuries.     

Effects of patellar taping on knee joint proprioception in patients with patellofemoral pain syndrome

The aim of this study was to assess the effect of patellar taping of the proprioceptive status of patients with patellofemoral pain syndrome (PFPS). A total of 32 subjects (18 males, 14 females of age 31.9 +/- 11.2, body mass index 25.8 +/- 5.3) with PFPS were tested for Joint Position Sense (JPS) using a Biodex dynamometer. Outcomes of interest were the absolute error (AE), the variable error (VE) and the relative error (RE) of the JPS values for both active (AAR) and passive (PAR) angle reproduction at an angular velocity of 2 degrees /s with a start angle at 90 degrees and target angles of 60 degrees and 20 degrees . Taping was applied in random order across the patella of each subject with each of the subjects acting as their own internal control. Results indicated initially that application of patellar tape did not enhance and in some cases worsened the JPS of the subjects (P > 0.05). However, when the subjects' proprioceptive status was graded according to their closeness to the target angles into 'good' (5 degrees , N = 10) and 'poor' ( > 5 degrees , N = 22) taping enhanced nearly all values of those with 'poor' proprioception, with AE at 20 degrees to statistical significance (P = 0.021). In conclusion, this study has shown that patellar taping did not improve the AAR and PAR JPS tests of a whole sample of 32 PFPS patients. It also has shown that a subgroup of PFPS patients with poor proprioception may exist and be helped by patellar taping.     

Sinding-Larsen-Johansson syndrome: A case report

The Sinding-Larsen-Johansson syndrome has a pathogenesis similar to that of the Osgood-Schlatter disorder and is the result of excessive force exerted by the patellar tendon on the lower pole of the patella. Clinically it is characterized by pain, which increases when the patellar is loaded during flexion, subpatellar swelling and functional limitation. The authors present a case of a 13-year-old boy who was a competitive youth team football player. He presented with anterior, spontaneous knee pain and swelling at the inferior pole of the patella. Ultrasonography (US) confirmed clinical diagnosis showing lesions typical of the Sinding-Larsen-Johansson syndrome. The patient was told to refrain from sports activity; after five months recovery was complete and US follow-up revealed no anomaly. The authors consider the case worthy of reporting because it is paradigmatic and to emphasize the role of US in the evaluation of the Sinding-Larsen-Johansson syndrome.     

根据患者类型选择不同类型人工膝关节假体植入后临床应用效果的回顾性分析

背景:人工全膝关节置换术被认为是治疗终末期或严重的膝关节炎的最有效、最成功的手术之一。如何降低假体返修率、提高膝关节置换术后的疗效是亟待解决的主要问题。目的:回顾性分析不同类型人工膝关节假体的临床应用及其疗效。设计:以膝关节置换术后患者为观察对象,手术前后对照观察,以对比不同类型人工膝关节假体置换术后效果。单位:解放军总医院骨科。对象:选择解放军总医院2002-01/2005-01收治的398例患者(523个置换膝关节),其中单膝关节置换术276例,276膝,双膝同时置换122例,244膝。诊断分别为骨性关节炎、类风湿关节炎、强直性脊柱炎、色素绒毛结节性滑膜炎。方法:根据患者病情适当选择不同类型人工膝关节假体进行全膝关节置换术。假体的类型包括:①按置换范围,分单髁、全髁型;在全髁置换分为后交叉韧带保留型和后交叉韧带替代型假体。②按限制程度又分限制性、非限制性和半限制性。③按是否模拟半月板功能,又分为胫骨平台垫可旋转滑动型和固定型。半年后对以上患者进行随访,膝关节评分采用美国特种外科医院膝关节评分系统(HSS评分,满分为100分,85分以上为优;70～84分为良;60～69分为尚可;60分以下为差),髌骨评分采用Feller等评分标准(满分30分,得分越高越好),随访时调查膝前区疼痛轻重、膝关节活动范围及稳定程度比较,拍摄膝关节正、侧及髌骨30°,90°轴位X射线片。主要观察指标:患者手术前后HSS评分、髌骨评分、膝前痛评分、髌骨功能评分、膝关节最大屈曲度、股胫角。结果:完成随访372例(490膝),随访率93.4%。①疗效:手术优良率89%。患者术后在疼痛、功能方面都有明显改善,尤其在缓解疼痛及膝关节活动范围方面效果显著。②患者术后随访的HSS评分、髌骨评分、膝前痛评分、髌骨功能评分、最大屈膝度均较术前增加(P<0.01)。③不同类型人工膝关节假体置换术后的HSS评分、髌骨评分、膝前痛评分、髌骨功能评分、最大屈膝度、股胫角比较差异无显著意义(P>0.05)。结论:依据各种人工膝关节假体的适应证、禁忌证及预期可达到的功能与使用寿命,根据不同的病情,慎重选择适当的假体,均可达到良好的疗效。     

An in vivo determination of patellofemoral contact positions

OBJECTIVE: To determine patellofemoral contact patterns in two-dimensions for normal and implanted patients. DESIGN: An in vivo, weightbearing fluoroscopy analysis of 14 subjects with normal knees, 12 with anterior cruciate ligament deficient knees, 14 with a posterior cruciate retaining implant, and 25 with a posterior cruciate substituting implant. BACKGROUND: Most previous experimental studies involving the knee joint have been either in vitro or under nonweightbearing conditions. METHODS: Subjects were studied under fluoroscopic surveillance performing deep knee bends to maximum flexion. Video images were analyzed on a computer with a two-dimensional technique of digitizing discrete points on the patella, femur, and tibia. RESULTS: The contact position, measured from the patella mass center, was inferior on the patella at extension and moved superior during flexion. Average contact positions of the implanted knee groups were more superior than the normal knee group throughout the flexion cycle. Analysis of patellar tilt angle demonstrated a flexed posture of the patella relative to the tibia. Increase in patellar tilt angle with increasing femorotibial flexion was substantially greater in implanted knees versus normal knees. Separation of the patella from the femur in full extension was absent in normal knees, but present in 86% and 44% of posterior cruciate retaining and posterior cruciate substituting total knee arthroplasties, respectively. CONCLUSIONS: The patellofemoral kinematics of the total knee arthroplasties analyzed in the study was statistically different than the normal and anterior cruciate ligament-deficient knees. The kinematic variations observed between normal and implanted knees may be related to disturbed femorotibial kinematics previously observed to occur following total knee arthroplasty. RELEVANCE: Patellofemoral complications, including polyethylene wear, are a major concern in total knee arthroplasty. Since the causes of polyethylene wear are multi-factorial, abnormal patellofemoral kinematics may play a role in patellar failure.     

Quadriceps tendinopathy — a forgotten pathology for physiotherapists? A systematic review of the current evidence-base

Abstract

Background: The evidence-base surrounding the pathophysiology and management of specific tendinopathies has evolved over the past 20 years. Recent research examining lower limb tendinopathies has focussed primarily on Achilles and patellar tendon injuries. However, on further examination of the different types of patella/knee tendinopathies, confusion has arisen surrounding the diagnosis and management of patellar compared to quadriceps tendinopathy.

Objectives: The purpose of this paper was to critically examine the evidence-base surrounding the diagnosis and management of quadriceps tendinopathy.

Methods: A systematic literature search of published and unpublished literature databases was conducted to identify literature pertaining to quadriceps tendinopathy. Data from each paper were extracted to examine four key areas related to quadriceps tendinopathy: nomenclature, prevalence, assessment, and management.

Results: Twelve studies satisfied the eligibility criteria and were included in the review. On analysis, little literature has been published solely informing clinicians on the pathology, diagnosis, or management of quadriceps tendinopathy. The terms patellar tendinopathy and jumper’s knee have been incorrectly used interchangeably with quadriceps tendinopathy. Activities such as repetitive squatting and prolonged knee flexion have been associated with the development of this tendinopathy. Sports such as football and volleyball have been cited as causative factors. Quadriceps tendinopathy’s principal diagnostic feature is pain on palpation of the quadriceps/patella interface, and resisted knee extension with the knee hyperflexed. There are no clear recommendations on how to specifically treat quadriceps tendinopathy.

Conclusion: Quadriceps tendinopathy is less commn than patellar tendinopathy. Possibly as a result of this, little is known about how to assess and manage this particular knee tendinopathy. Further research is required to determine the optimal management strategy for patients diagnosed with quadriceps tendinopathy, acknowledging the biomechanical and anatomical difference of the quadriceps compared to the patellar tendon.     

Infrared thermographic imaging in the detection of sympathetic dysfunction in patients with patellofemoral pain syndrome.

OBJECTIVE: This study investigates the clinical utility of infrared thermography in the detection of sympathetic dysautonomia in patients with patellofemoral pain syndrome. The patients exhibited anterior knee pain, radiographic evidence of patella alta and the clinical signs and symptoms of patellofemoral pain syndrome. DESIGN: A case control study was carried out with two groups of patients: patients with anterior knee pain, and patients with no knee pain as a control SETTING: Private practice. PATIENTS: Group 1 consisted of 30 patients with patellofemoral pain syndrome. Group 2 consisted of 40 control patients with no history or presence of knee pain. Control patients were consecutively selected, and the knee pain patients were consecutively selected from a population-based sample. OUTCOME MEASURE: Infrared thermography scans were obtained on the knee pain patients and control patients to determine the sensitivity and specificity of infrared thermography for detecting patellofemoral pain syndrome. RESULTS: Twenty-nine of the 30 knee pain patients in group 1 had patellar thermal asymmetry from right to left sides (sensitivity 97%). Thirty-six of the 40 control patients exhibited thermal symmetry from right to left sides (specificity 90%). The incidence of patellar thermal asymmetry was found to be statistically significant when tested by chi 2 analysis (p less than .001). CONCLUSION: Infrared thermography appears to be a useful, noninvasive diagnostic test in the diagnosis and management of patellofemoral pain syndrome. The high incidence of patellar thermal asymmetry and dysautonomia at the patella in patients with patellofemoral pain syndrome implicates somatosympathetic mediation in this disorder. This may be helpful in understanding the evolution of patellofemoral disorders.     

MR imaging of patellar dislocation and relocation

Patellar dislocation and relocation (PDR) typically occurs suddenly after trauma or torsional stress on the extensor mechanism. Clinical evaluation after patellar dislocation/relocation usually reveals a swollen knee that is difficult to examine. Radiographs may show hemathroses and a minority of patients will have a chip fracture of the patella. Magnetic resonance (MR) imaging features seen with PDR include disruption or sprain of the medial retinaculum, lateral patellar tilt or subluxation, lateral femoral condylar and medical patellar osseous contusions, osteochondral injury, damage to Hoffa's fat pad, and joint effusion. Up to one third of patients will also show concomitant injury to the major ligaments of the knee or menisci. Without repair of the primary injury, redislocation occurs in greater than one half of patients. Consequently, surgical correction is often advocated. This article reviews the factors predisposing to PDR, the activities associated with PDR, the clinical, radiographic, and MR imaging features of PDR, and (briefly) therapy for this injury.     

Vastus medialis obliquus and vastus lateralis activity in open and closed kinetic chain exercises in patients with patellofemoral pain syndrome: an electromyographic study

OBJECTIVES: To evaluate the electromyographic activities of vastus medialis obliquus (VMO) and vastus lateralis (VL) muscles in open and closed kinetic chain exercises in subjects with patellofemoral pain syndrome (PFPS). DESIGN: Case-controlled study. SETTING: Rehabilitation science center in a tertiary medical center. PARTICIPANTS: Ten patients with bilateral knee pain diagnosed with PFPS and 10 healthy volunteers. INTERVENTIONS: Subjects performed open kinetic chain exercise on an isokinetic dynamometer and closed kinetic chain exercise by squat-to-stand and stand-to-squat tasks. Surface electromyography was done for the VMO and VL muscles. MAIN OUTCOME MEASURES: VMO/VL ratios were calculated after normalization of muscle activities. RESULTS: The VMO/VL ratios of PFPS subjects were significantly lower than were those of unimpaired subjects during knee isokinetic closed kinetic chain exercises (p = .047). However, there was no statistical difference in VMO/VL ratio between subjects with and without PFPS during closed kinetic chain exercises (p = .623). Maximum VMO/VL ratio was obtained at 60 degrees knee flexion in closed kinetic chain exercise. CONCLUSION: In closed kinetic chain exercises, more selective VMO activation can be obtained at 60 degrees knee flexion. Maximal VMO/VL ratio was observed at this knee flexion angle, and muscle contraction intensity was also greatest.