Patellofemoral Pain in Female Athletes:

IMMEDIATE EFFECTS OF SEMI-CUSTOM INSOLES AND STRUCTURED KNEE SLEEVES ON LOWER EXTREMITY KINETICS AND KINEMATICS IN RECREATIONAL MALE ATHLETES WITH PATELLOFEMORAL PAIN

The aim of this experiment was to provide insight into the immediate influence of both semi-custom insoles and knee sleeves in recreational male runners/athletes suffering from patellofemoral pain and also to explore the association between the extent of patellofemoral pain and psychological wellbeing. Experiment 1 examined 17 male recreational runners with patellofemoral pain, in semi-custom insole and no-insole conditions. Experiment 2 examined 13 male recreational athletes with patellofemoral pain, undertaking run, [Formula: see text] cut and single-leg hop movements in knee sleeve and no-sleeve conditions. In both experiments, motion capture and ground reaction forces were collected, allowing kinetics and three-dimensional kinematics to be calculated alongside patellofemoral joint loading quantified using musculoskeletal modeling. In both experiments, patellofemoral pain symptoms were examined using the KOOS patellofemoral pain subscale and psychological wellbeing using the COOP-WONCA questionnaire. The findings from both experiments showed that pain symptoms significantly predicted psychological wellbeing ([Formula: see text] in experiment 1 and [Formula: see text] in experiment 2). Experiment 1 showed that orthoses significantly reduced tibial internal rotation range of motion (no-[Formula: see text] and [Formula: see text]) whilst also increasing the peak knee adduction moment (no-[Formula: see text][Formula: see text]N[Formula: see text]m/kg and [Formula: see text][Formula: see text]N[Formula: see text]m/kg). The findings from experiment 2 revealed that the knee sleeve reduced the peak patellofemoral force (no-[Formula: see text][Formula: see text]BW and [Formula: see text][Formula: see text]BW) in the run movement and the patellofemoral load rate in the cut movement (no-[Formula: see text][Formula: see text]BW/s and [Formula: see text][Formula: see text]BW/s). Overall, the findings confirm that pain symptoms are predictive of psychological wellbeing in recreational male athletes with patellofemoral pain. Furthermore, the findings suggest that both insoles and knee sleeves may provide immediate biomechanical benefits in recreationally active individuals with patellofemoral pain, although when wearing insoles this may be at the expense of an increased knee adduction moment during running.

The immediate effect of lumbopelvic manipulation on knee pain, knee position sense, and balance in patients with patellofemoral pain: A randomized controlled trial

BACKGROUND

Patellofemoral pain (PFP) is a common musculoskeletal disorder. Quadriceps and core muscle neuromuscular control impairments are frequently associated with PFP. Lumbopelvic manipulation (LPM) has been shown to improve quadriceps and core muscle activation and decrease their inhibition, but changes in balance and knee joint position sense (JPS) after this intervention remain unknown.

OBJECTIVE

To determine whether LPM decreases knee pain and JPS error and increases balance performance in patients with PFP.

DESIGN

Randomized controlled trial.

SETTING

Biomechanics laboratory at a rehabilitation science research center.

METHODS

Forty-four patients with PFP participated in this study that randomly divided into two equal groups. One group received LPM and the other received sham LPM (positioning with no thrust) in a single session. At baseline and immediately after the intervention, the outcomes of pain using a visual analog scale, balance using the modified star excursion balance test (mSEBT), and JPS at 20° and 60° of knee flexion using a Biodex dynamometer.

RESULTS

There was a statistically significant improvement in pain, balance control (anterior direction) and JPS in the LPM group immediately after the intervention. In addition, we observed significant differences between groups in pain, balance control (anterior direction) and JPS at 60° of knee flexion immediately after the intervention.

CONCLUSION

A single session of LPM immediately improved balance control, knee JPS, and pain in patients diagnosed with PFP.

CLINICAL REHABILITATION IMPACT

Findings suggest that LPM may be used as a therapeutic tool for immediate improvement of symptoms of PFP. However, more research is needed to determine long term results.

An exploration of the effect of proprioceptive knee bracing on biomechanics during a badminton lunge to the net, and the implications to injury mechanisms

The aim of this study was to determine changes in knee biomechanics during badminton lunges due to fatigue, lunge strategy and knee bracing. Kinetic and kinematic data were collected from 16 experienced right-handed badminton players. Three factor repeated measures ANOVAs (lunge direction—fatigue—brace) were performed with Least Significant Difference pairwise comparisons. In addition, clinical assessments including; Y-balance test, one leg hop distance and ankle dorsiflexion range of motion were performed pre- and postfatigue. The knee showed significantly greater flexion during the forehand lunge compared to backhand. In contrast, the internal rotation velocity and the knee extension moment were greater during backhand. Knee angular velocity in the sagittal plane, peak knee moment and range of moment in the coronal plane and stance time showed significantly lower values postfatigue. In addition, the peak knee adduction moment showed significantly lower values in the braced condition in both the fatigued and nonfatigues states, and no significant differences were seen for peak vertical force, loading rate, approach velocity, or in any of the clinical assessment scores. There appears to be greater risk factors when performing a backhand lunge to the net compared to a forehand lunge, and proprioceptive bracing appears to reduce the loading at the knee.

Comparing goniometric and radiographic measurement of Q angle of the knee

Background

The Q angle is a relevant clinical diagnostic measurement to detect various disorders of the knee. The common method used to measure the Q angle in the routine clinical practice is by radiography. An alternative to radiographic measurement is goniometry, by which exposure to x-rays can be avoided.

Objectives

To compare and correlate the goniometric measurement of Q angle with radiographic measurement of the Q angle in patients with acute knee pain.

Methods

We selected 45 patient participants with a mean age of 32.5 years who satisfied the inclusion criteria for this study. All the patients underwent goniometric measurement of the Q angle followed by x-ray imaging of the entire lower limb. Later the bony prominences were marked on the x-ray image and the Q angle formed was measured using a protractor. The Pearson correlation coefficient between the goniometric and radiographic measurements was determined.

Results

We found a significant relationship between Q angles obtained using a goniometer and x-ray imaging in the supine position (r = 0.91, P = 0.001). The mean difference between the goniometric measurement of Q angle and the radiographic measurement was 0.1°, which is not significant.

Conclusions

Goniometry can be used to measure Q angle as accurately as radiography, and can be used as an inexpensive and radiation free alternative.

Síndrome da dor patelofemoral não altera as características baropodométricas durante a marcha em rampa e escadas

RESUMO Este estudo teve como objetivo avaliar as características baropodométricas durante a fase de apoio da marcha em escadas e rampa de sujeitos com e sem síndrome da dor patelofemoral (SDPF). Participaram 55 indivíduos do gênero feminino, 24 com SDPF (GSDPF) e 31 clinicamente saudáveis (GC), pareados em idade, estatura e massa corporal. Foram avaliadas as variáveis pico de pressão, área de contato e tempo de contato em seis regiões plantares (antepé medial, antepé lateral, médio pé, retropé medial, retropé central e retropé lateral), por meio do sistema Pedar-X, durante a realização de quatro atividades funcionais (subir e descer escadas e rampa). A ordem de realização das avaliações foi randomizada. A intensidade da dor dos sujeitos antes e após as atividades foi avaliada pela Escala Visual Numérica (EVN). Os dados foram analisados por meio da estatística descritiva e inferencial (Testes T-independente, Wilcoxon e ANOVA 2x6), com nível de significância de p≤0,05. Não foram observadas diferenças entre os grupos em relação ao pico de pressão, área de contato e tempo de contato nas seis regiões plantares analisadas durante as quatro atividades funcionais. Houve exacerbação da dor dos sujeitos após a realização das quatro atividades funcionais (p=0,01). Sendo assim, os resultados deste estudo, nas condições experimentais utilizadas, sugerem que não existe um padrão de comportamento em relação às variáveis baropodométricas estudadas que diferencie sujeitos com e sem SDPF durante as atividades de subir e descer escadas e rampa.

Influence of a knee brace intervention on perceived pain and patellofemoral loading in recreational athletes

BACKGROUND

The current investigation aimed to investigate the effects of an intervention using knee bracing on pain symptoms and patellofemoral loading in male and female recreational athletes.

METHODS

Twenty participants (11 males & 9 females) with patellofemoral pain were provided with a knee brace which they wore for a period of 2weeks. Lower extremity kinematics and patellofemoral loading were obtained during three sport specific tasks, jog, cut and single leg hop. In addition their self-reported knee pain scores were examined using the Knee injury and Osteoarthritis Outcome Score. Data were collected before and after wearing the knee brace for 2weeks.

FINDINGS

Significant reductions were found in the run and cut movements for peak patellofemoral force/pressure and in all movements for the peak knee abduction moment when wearing the brace. Significant improvements were also shown for Knee injury and Osteoarthritis Outcome Score subscale symptoms (pre: male=70.27, female=73.22 & post: male=85.64, female=82.44), pain (pre: male=72.36, female=78.89 & post: male=85.73, female=84.20), sport (pre: male=60.18, female=59.33 & post: male=80.91, female=79.11), function and daily living (pre: male=82.18, female=86.00 & post: male=88.91, female=90.00) and quality of life (pre: male=51.27, female=54.89 & post: male=69.36, female=66.89).

INTERPRETATION

Male and female recreational athletes who suffer from patellofemoral pain can be advised to utilise knee bracing as a conservative method to reduce pain symptoms.

Sex differences in knee loading in recreational runners

Patellofemoral pain is the most common chronic pathology in recreational runners. Female runners are at greater risk of developing patellofemoral pain, although the exact mechanism behind this is not fully understood. This study aimed to determine whether female recreational runners exhibit distinct knee loading compared to males. Fifteen males and 15 females recreational runners underwent 3D running analysis at 4.0 ms(-1)±5%. Sagittal/coronal joint moments, patellofemoral contact forces (PTF) and pressures (PCP) were compared between sexes. The results show that females exhibited significantly greater knee extension (p<0.008, pη(2)=0.27: males=3.04; females=3.47 N m kg(-1)) and abduction (p<0.008, pη(2)=0.28: males=0.54; females=0.82 N m kg(-1)) moments as well as PTF (p<0.008, pη(2)=0.29: males=3.25; females=3.84 B.W.) and PCP (p<0.008, pη(2)=0.26: males=7.96; females=9.27 MPa) compared to males. Given the proposed relationship between knee joint loading and patellofemoral pathology, the current investigation provides insight into the incidence of patellofemoral pain in females.

High-intensity stepwise conditioning programme for improved exercise responses and agility performance of a badminton player with knee pain

OBJECTIVE

To examine the effect of a high-intensity stepwise conditioning programme combined with multiple recovery measures on physical fitness, agility, and knee pain symptoms of an injured player.

DESIGN

A single case study.

SETTING

University-based conditioning training laboratory.

PARTICIPANTS

One 26-year-old male world-class badminton player (height, 190.0 cm; weight, 79.3 kg; left dominant hand; playing experience, 16 years; former world champion) with patellar tendinosis and calcification of his left knee.

HIGH-CONDITIONING STEPWISE CONDITIONING PROGRAMME

The player received seven conditioning sessions over three weeks. During the programme, there was a gradual increase in training duration and load across sessions while cold therapy, manual stretches and massage were administered after each session to minimise inflammation.

MAIN OUTCOME MEASURES

The training outcome was evaluated with three different testing methods: standard step test, badminton-specific agility test, and tension-pain rating.

RESULTS

The conditioning programme reduced knee pain symptoms and improved actual performance and cardiopulmonary fitness during the agility task. The player was able to return to sport and compete within a month.

CONCLUSIONS

A high-intensity stepwise conditioning programme improved the physical fitness while sufficient recovery measures minimised any possible undesirable effects and promoted faster return to elite level competition.

Avaliação isocinética, dor e funcionalidade de sujeitos com síndrome da dor patelofemoral

Este estudo visou determinar a influência da Síndrome da Dor Patelofemoral (SDPF) sobre o pico de torque e trabalho da musculatura flexora e extensora do joelho, além de avaliar a dor e funcionalidade de sujeitos com a disfunção. Participaram 52 sujeitos do gênero feminino, 23 com SDPF e 29 clinicamente saudáveis similares em idade, estatura e massa corporal. A avaliação isocinética foi realizada no modo concêntrico para os flexores e extensores do joelho nas velocidades de 60 e 180°/s. Também foi aplicada a Escala Visual Numérica antes e após cada velocidade do teste isocinético e o questionário de Kujala. Os dados foram analisados pela estatística descritiva e inferencial (testes U de Mann-Whitney, Wilcoxon e t independente) com nível de significância de α=0,05. O Grupo com Síndrome da Dor Patelofemoral (GSDPF) apresentou menor pontuação (p=0,01) no questionário de Kujala (75,7±12,3 pontos) em relação ao Grupo Controle (GC) (100±0,0 pontos), além de menor pico de torque, tanto em 60 como 180°/s, dos flexores (0,82±0,24 Nm/kg; 0,51±0,22 Nm/kg) e extensores (1,85±0,48 Nm/kg; 1,13±0,44 Nm/kg) do joelho, bem como menor trabalho total dos extensores do joelho a 180°/s (6,46±2,54 J/kg) e 60°/s (9,42±3,27 J/kg). Além disso, foi observado aumento da dor do GSDPF após a avaliação isocinética a 180°/s (0,9 cm) e 60°/s (2,3 cm). Os resultados evidenciaram que sujeitos com SDPF possuem menor capacidade funcional e menor pico de torque e trabalho dos flexores e extensores do joelho, sugerindo que o fortalecimento desta musculatura deve ser considerado na reabilitação destes sujeitos.

Greater Q angle may not be a risk factor of patellofemoral pain syndrome

BACKGROUND

A greater Q-angle has been suggested as a risk factor for Patellofemoral Pain Syndrome. Greater frontal plane knee moment and impulse have been found to play a functional role in the onset of Patellofemoral Pain Syndrome in a running population. Therefore, the purpose of this investigation was to determine the relationship between Q-angle and the magnitude of knee abduction moment and impulse during running.

METHODS

Q-angle was statically measured, using a goniometer from three markers on the anterior superior iliac spine, the midpoint of the patella and the tibial tuberosity. Thirty-one recreational runners (21 males and 10 females) performed 8-10 trials running at 4m/s (SD 0.2) on a 30m-runway. Absolute and normalized knee moment and impulse were calculated and correlated with Q-angle.

FINDINGS

Negative correlations between Q-angle and the magnitude of peak knee abduction moment (R²=0.2444, R=-0.4944, P=0.005) and impulse (R²=0.2563, R=-0.5063, P=0.004) were found. Additionally, negative correlations between Q-angle and the magnitude of weight normalized knee abduction moment (R²=0.1842, R=-0.4292, P=0.016) and impulse (R²=0.2304, R=-0.4801, P=0.006) were found.

INTERPRETATION

The findings indicate that greater Q-angle, which is actually associated with decreased frontal plane knee abduction moment and impulse during running, may not be a risk factor of Patellofemoral Pain Syndrome.

The effects of exercise for the prevention of overuse anterior knee pain: a randomized controlled trial

BACKGROUND

Anterior knee pain (AKP) is the most common activity-related injury of the knee. The authors investigated the effect of an exercise intervention on the incidence of AKP in UK army recruits undergoing a 14-week physically arduous training program.

HYPOTHESIS

Modifying military training to include targeted preventative exercises may reduce the incidence of AKP in a young recruit population.

STUDY DESIGN

Randomized controlled trial; Level of evidence, 1.

METHODS

A single-blind cluster randomized controlled trial was performed in 39 male and 11 female training groups (median age: 19.7 years; interquartile range, 17-25) undergoing phase 1 of army recruit training. Each group was randomly assigned to either an intervention (n = 759) or control (n = 743) protocol. The intervention consisted of 4 strengthening and 4 stretching exercises completed during supervised physical training lessons (7 per week). The control group followed the existing training syllabus warm-up exercises. The primary outcome was a diagnosis of AKP during the 14-week training program.

RESULTS

Forty-six participants (3.1%; 95% confidence interval [CI], 2.3-4.1) were diagnosed with AKP. There were 36 (4.8%; 95%CI, 3.5-6.7) new cases of AKP in the control group and 10 (1.3%; 0.7-2.4) in the intervention group. There was a 75% reduction in AKP risk in the intervention group (unadjusted hazard ratio = 0.25; 95% CI, 0.13-0.52; P < .001). Three participants (0.4%) from the intervention group were discharged from the military for medical reasons compared to 25 (3.4%) in the control group.

CONCLUSION

A simple set of lower limb stretching and strengthening exercises resulted in a substantial and safe reduction in the incidence of AKP in a young military population undertaking a physical conditioning program. Such exercises could also be beneficial for preventing this common injury among nonmilitary participants in recreational physical activity.

Eccentric hip muscle function in females with and without patellofemoral pain syndrome

CONTEXT

Patellofemoral pain syndrome (PFPS) is a common knee condition in athletes. Recently, researchers have indicated that factors proximal to the knee, including hip muscle weakness and motor control impairment, contribute to the development of PFPS. However, no investigators have evaluated eccentric hip muscle function in people with PFPS.

OBJECTIVE

To compare the eccentric hip muscle function between females with PFPS and a female control group.

DESIGN

Cross-sectional study.

SETTING

Musculoskeletal laboratory.

PATIENTS OR OTHER PARTICIPANTS

two groups of females were studied: a group with PFPS (n = 10) and a group with no history of lower extremity injury or surgery (n = 10).

INTERVENTION(S)

Eccentric torque of the hip musculature was evaluated on an isokinetic dynamometer.

MAIN OUTCOME MEASURE(S)

Eccentric hip abduction, adduction, and external and internal rotation peak torque were measured and expressed as a percentage of body mass (Nm/kg x 100). We also evaluated eccentric hip adduction to abduction and internal to external rotation torque ratios. The peak torque value of 5 maximal eccentric contractions was used for calculation. Two-tailed, independent-samples t tests were used to compare torque results between groups.

RESULTS

Participants with PFPS exhibited much lower eccentric hip abduction (t(18) = -2.917, P = .008) and adduction (t(18) = -2.764, P = .009) peak torque values than did their healthy counterparts. No differences in eccentric hip external (t(18) = 0.45, P = .96) or internal (t(18) = -0.742, P = .47) rotation peak torque values were detected between the groups. The eccentric hip adduction to abduction torque ratio was much higher in the PFPS group than in the control group (t(18) = 2.113, P = .04), but we found no difference in the eccentric hip internal to external rotation torque ratios between the 2 groups (t(18) = -0.932, P = .36).

CONCLUSIONS

Participants with PFPS demonstrated lower eccentric hip abduction and adduction peak torque and higher eccentric adduction to abduction torque ratios when compared with control participants. Thus, clinicians should consider eccentric hip abduction strengthening exercises when developing rehabilitation programs for females with PFPS.

Atividade eletromiográfica do vasto medial oblíquo em portadoras da síndrome da dor patelofemoral

A síndrome da dor patelofemoral (SDPF) é uma das afecções que mais acometem a articulação do joelho. Embora sua etiologia não seja completamente conhecida, uma disfunção do músculo vasto medial oblíquo (VMO) tem sido apontada como possível fator desencadeante. Este estudo visou avaliar, por meio de eletromiografia, se algum exercício, dentre dez exercícios resistidos usuais, produz ativação seletiva do VMO, com vistas a sua utilização clínica. Vinte voluntárias do sexo feminino, sendo dez com SDPF (24,7±4,35 anos) e dez saudáveis, controle (22,5±1,58 anos), foram submetidas à avaliação eletromiográfica dos músculos VMO, vasto lateral longo e vasto lateral oblíquo (VLO) durante a realização de 10 exercícios, incluindo cadeia cinética aberta e fechada, em diferentes angulações do joelho e posições do quadril. Os resultados mostram que nenhum dos exercícios se revelou seletivo para o VMO, tendo alguns mostrado ativação seletiva do VLO. No grupo com SDPF observou-se menor atividade eletromiográfica de todos os vastos em oito dos dez exercícios propostos, quando comparado ao controle; observou-se ainda, no grupo SDPF, menor relação VMO/VLO (0,63) do que no grupo controle (0,82, p<0,05). Embora, dentre os propostos, nenhum exercício tenha se mostrado eficaz para promover a ativação seletiva do VMO, os exercícios de agachamento unipodal com rotação medial e lateral da tíbia mostraram-se mais indicados para sujeitos com SDPF.

A controlled trial of weight-bearing versus non-weight-bearing exercises for patellofemoral pain

STUDY DESIGN

Randomized controlled trial, pretest-posttest design.

OBJECTIVES

To compare the efficacy of non-weight-bearing single-joint quadriceps exercise (SJNWBE) versus weight-bearing multiple-joint quadriceps exercise (MJWBE) for individuals with patellofemoral pain syndrome (PFPS).

BACKGROUND

PFPS is a common ailment of the knee. Both weight-bearing and non-weight-bearing exercises are considered appropriate for strengthening the quadriceps, a key element in the treatment of this condition.

METHODS AND MEASURES

Forty-five male subjects with PFPS between 18 and 35 years of age were randomized into 1 of 3 groups. Group 1 (SJNWBE) performed knee extension exercises, group 2 (MJWBE) performed seated leg press exercises, and group 3 (control group) received no treatment. Subjective symptoms, knee extensor muscle strength, and functional performance were evaluated at the time of the initial examination and at the end of the 6-week treatment period.

RESULTS

Individuals in both exercise groups demonstrated a statistically significant decrease in pain and an increase in muscle strength and functional performance, as compared to the control group (P<.05). All measures showed no significant differences in outcome between the 2 exercise groups (P>.05).

CONCLUSION

This study demonstrates that both weight-bearing and non-weight-bearing quadriceps exercises can significantly improve subjective and clinical outcomes in patients with PFPS.

Functional and EMG responses to a physical therapy treatment in patellofemoral syndrome patients

There are several pathologies related to the patellofemoral joint, in which the patellofemoral syndrome is one of the most common and challenging to treat. The patellofemoral syndrome results from a malalignment of the knee extensor mechanism. The purpose of our study was to describe and compare EMG responses of the vastus medialis and vastus lateralis muscles while walking up and down stairs and other clinical and functional responses in PFS subjects before and after a physical therapy intervention. Eleven subjects were studied and divided in two groups: six subjects with clinically diagnosed patellofemoral syndrome and five healthy control subjects. Subjects were evaluated by a functional and biomechanical evaluation protocol: postural evaluation, pain and knee function evaluation, and electromyographic activity of vastus medialis and lateralis muscles while walking up and down a staircase. Results showed higher efficiency of the vastus medialis muscle in carrying out eccentric exercises and increased muscle activity in both the vastus medialis and vastus lateralis muscles while climbing stairs after physical therapy treatment. We were able to identify an improvement in postural alignment of lower limb muscles and knee functionality among patellofemoral syndrome group subjects after treatment.

Efeitos na medida do ângulo Q com a contração isométrica voluntária máxima do músculo quadricipital

A proposta deste estudo foi verificar a diferença entre o ângulo quadricipital em indivíduos sintomáticos e assintomáticos, em duas diferentes situações de exame, com o quadríceps relaxado e em contração isométrica voluntária máxima (CIVM) através da mensuração radiográfica para contribuir na avaliação e tratamento de pacientes com disfunção femoropatelar (DFP). Foram avaliadas 20 mulheres (40 joelhos), com idade média de 21 anos, através de método radiológico padronizado. Os indivíduos foram posicionados em decúbito dorsal com um estabilizador podálico em "U", com os membros inferiores relaxados, com a utilização de película de chumbo sobre a tuberosidade anterior da tíbia. Para a análise estatística foram utilizadas as médias dos grupos assintomático e sintomático, em estado de relaxamento e em CIVM, e o teste t de Student, com nível de significância de p < 0,05. Os valores médios do ângulo Q para os assintomáticos foram de 17,15° em relaxamento e de 14,5° em CIVM, enquanto os sintomáticos apresentaram 21,45° e 15,8°, respectivamente. Nos resultados para a análise da igualdade entre os grupos sintomáticos e assintomáticos no estado de relaxamento obteve-se p = 0,004, e para o estado de contração isométrica voluntária máxima, p = 0,29. Considerando os dados obtidos no presente estudo, pode-se verificar que em estado de relaxamento há diferença entre o valor do ângulo Q entre indivíduos sintomáticos e assintomáticos, sendo este maior nos portadores da DFP, enquanto que em estado de contração isométrica máxima do músculo quadricipital não houve diferença estatística, ocorrendo redução do ângulo em ambos os grupos.

The three in one procedure: How I do it

Recurrent patella dislocation is common, and selection of an appropriate stabilisation procedure is important for a successful outcome. We describe a combined proximal and distal realignment procedure to adjust soft tissue tension around the patella. This procedure, the 'Three in One' involves a combination of a lateral release, vastus medialis obliquus muscle advancement, and transfer of the medial third of the patellar tendon to the medial collateral ligament. This is a safe, reliable procedure for patients with recurrent dislocation of the patella resulting from an imbalance of soft tissue tension around the patella, but with a normally sited patella and normal trochlea.