Patellofemoralinstability is a broad term that includes general symptomatic instability,patellar dislocation, and patellar subluxation.
1,2 Patellofemoral instability is acomplex, disabling musculoskeletal condition.1,2 The estimated incidence ofpatellofemoral dislocation or subluxation has been recorded 43 per 100,000people.2,3 Patellofemoral dislocation orsubluxation is more prevalent in women than men with the highest incidenceoccurring in women from age 10 to 17.2,4,5 The etiology of patellofemoralinstability is multifactorial.
1 The causes can be divided intobiomechanical impairments and soft tissue faults.1 The biomechanical impairments includerotational defects such as femoral anteversion and external tibial torsion.1,3 Supplementary biomechanicalabnormalities include several at the knee: genu valgum, genu recurvatum,trochlear groove deformities, patella alta, and lateral insertion of thepatellar tendon.1,3,5 A biomechanical component distal tothe patella that is a factor in patellar dislocation or subluxation isexcessive foot pronation.1 Soft tissue defects occur in themuscles and ligaments surrounding the patella.
Hypotrophy of the vastusmedialis oblique (VMO) with hypertrophy of the vastus lateralis causes a muscleimbalance leading to the patella to be pulled laterally.1,3,5 In addition to the VMO, the adductormuscle group acts as a medial force. The patella loses a medial stabilizer whenthe adductors are weak.3 On the lateral side, the iliotibialband (IT band) is a thick fibrous band arising from the tendons of the tensorfasciae latae (TFL) and the gluteus maximus traveling along the lateral aspectof the thigh and inserts on the lateral epicondyle of the femur.(need to site some anatomy book) When the IT band is tight, it causesthe patella to track laterally, predisposing the patella to dislocate.3 All of these factors are potentialstress imbalances placed on the patella, increasing the risk of subluxation ordislocation.
1,3,5The trochlear groove provides a bonycontribution to patellar stability.3 The lateral trochlea is elevatedcompared to the medial aspect to counterattack the lateral forces on thepatella. Lateral forces that pull on the patella are the tight IT band andhypertrophied vastus lateralis. The patella remains stable in the trochlea from20 to 60 degrees of knee flexion. From 0 to 20 degrees of kneeflexion, the patella relies on soft tissue to prevent lateral subluxation ordislocation.
The medial patellofemoral ligament (MPFL) is the mainligament responsible for preventing lateral subluxation or dislocation duringthis range. The MPFL provides 60% of the restraint to the lateral forcespulling on the patella.3 Rupture of the MPFL can lead tolateral patellar subluxation or dislocation.1,3 Stability of the patella relies onstatic and dynamic stabilizers, osseous structure, and limb alignment.
1,3,5 After anacute patellar dislocation or subluxation, the recurrence of experiencinganother instability episode ranges from 15-44%.5 From a primary patellar dislocation,55% of patients do not return to sports.5 After a second patellar dislocation,the chance of a third dislocation increases to 50%.2,4,5 Patients become symptomatic withwalking on uneven terrain, descending stairs, running, and changing direction.2 Patients with patellofemoralinstability become symptomatic with fast, multidirectional movements.2 Patellofemoral instability results indecreased activity, pain, long-term risk of osteoarthritis (OA), and decreasedquality of life (QoL).6 Thereare several treatment options for patellofemoral instability. Conservativetreatment consists of physical therapy with an emphasis on VMO, gluteusmaximus, gluteus medius, and gluteus minimus strengthening.
5 Patellar taping or bracing may bedone for added stability.5 If one of the etiologies of thedislocation is osseous abnormality or a rupture of the MPFL, surgical treatmentis recommended.5 Physical therapy is indicated afterthe surgical intervention to reduce edema, increase range of motion (ROM), and increasestrength in the musculature surrounding the patella.3 Whether a surgical or conservative approachis selected, the goal is to regain function. Within treatment, measuring the progressof patients is critical.6–8 The use of standardized outcomemeasures provides a baseline of the patient and quantifies the change in functionof the patient throughout physical therapy.
8 Outcome measures is defined as a toolthat measures change over a period of time.8 Outcome measures are important forunderstanding the effectiveness of interventions.6,8 Understanding the resultsof the treatment for specific diseases or disorders will provide guidance forfuture treatment options.6–8 Outcome measures can be completed bythe patient or completed by the clinician.6 Outcome measures can obtain objectiveor subjective information. Patient-reportedoutcome measures (PROM) allow the clinicians to understand the perspectives ofthe patients in regard to their health, quality of life, and functionalcapacity.
6 PROMs provide additional informationwhich allows the clinician to understand the patient’s perspective in how thedisorder, disease, or injury is impacting their life.7 Also, PROMs give the patients a voiceon how they believe the treatment is working.7 Outcome measurement tools aredesigned for a specific patient population.8 The reliability and validity of thetools are diminished when used outside of the patient population.8 Patient-Reported OutcomeMeasuresIn the literature, the Kujala AnteriorKnee Pain Scale (AKPS) and the Lysholm Knee Scoring Scale are the most commonlyused in patients with patellofemoral instability.9 These tools were not specificallydesigned for patients with patellofemoral instability.6,9 The AKPS was developed in 1993.6 The AKPS is a patient-reportedquestionnaire designed for patients with patellofemoral pain.
The constructs ofthe questionnaire are subjective symptoms and functional limitations. Thequestionnaire examines difficulties with weight bearing, presence of a limp,daily pain, pain with prolonged sitting in knee flexion, edema, weakness ofquadriceps, and decrease in flexion ROM of the knee. Limitations in walking,climbing stairs, running, jumping, and squatting are examined. One questionexamines perceived patellar instability.
6 The scoring is hierarchical with a Likertscale ranging from ‘unable – no difficulty’ and ‘severe pain – no pain.’ The totalscore is out of 100.6,9 A lower score represents a higherdegree of disability. The AKPS is free and requires no training. The AKPS is easyto understand and requires a short amount of time to complete.
6,9 The Lysholm Knee Scoring Scale wasoriginally developed in 1982 for patients with knee ligamentous injuries.9,10 In 1985, a revised version of theLysholm was published.10 The Lysholm is an eight-question multiplechoice assessment that is filled out by the patient.9 The questionnaire examines degree oflimp, assistive devices, “locking” sensation, “giving away” sensation, intensityof pain and swelling, and ability to climb stairs and squat.9,10 Each answer has an assigned amount ofpoints and are added to the total score. The highest score is 100.
A higherscore indicates a higher degree of disability. The Lysholm is free and does notrequire training. The Lysholm is easy to understand and easy to score.9,10 Both the Lysholm and the AKPS arereliable and valid measurement tools.9 However, the tools were not designedfor patients with patellofemoral instability.6,9,10In recent years, two PROMs have beendeveloped for patients with patellofemoral instability.2,6,11,12 The Norwich Patellar InstabilityScore (NPI) was developed in March 2013 for patients with patellar instability.6 The NPI was developed by 90 patientsthat were referred after experiencing patellar instability following adislocation.
2 The participants were instructed torate their perceived level of instability during 19 activities. The activitiesconsisted of activities of daily living and sport activities. The 90 patientsassisted in weighting the activities. If patients frequently experiencedsymptoms during an activity, then the task was weighted lower with less points.If fewer patients experienced instability during the task, then the task wasweighted higher with more points. The aim was to rank activities according totheir severity. The questionnaire uses a Likert scale with 250 as the highestpossible points.
The questionnaire is examining which functional activitiesprovoke patellar instability.2 Although it is patient specific, theactivities are more advanced and therefore could not apply to all patients withpatellofemoral instability. 2,6The Banff Patellar InstabilityInstrument (BPII) was published in July 2013.
6,11 The BPII is also disease-specific forpatellar instability. There are 32 questions split into five sections: socialand emotional, lifestyle, sport and recreational, work concerns, and symptoms. TheBPII uses a holistic approach. The questionnaire examines the effects of thepatient’s patellar instability on their QoL.
For each item, a 100 mm visualanalogue scale is provided. For each question, the patient marks an “x” on theline. All the scores are added and converted to a score out of 100. A lowerscore indicates greater disability.
This instrument is free of charge andrequires no training.6,11Clinimetric Properties Withguidance from the COSMIN checklist, the clinimetric properties explored in thispaper are validity, reliability, responsiveness, and feasibility.6 Validity is defined as the instrumentsability to accurately measure what it is intended to.13 The definition of reliability is theability of the instrument to be consistent.
The instrument should produceconsistent results for the same patient on different occasions if they exhibitno change. Responsiveness is the sensitivity of the measurement to detectchange over a period of time.13 Feasibility includes the cost,training required, length of time to administer, and the health literacy levelof the instrument. 1,2,6,12Description of the patient A 19-year-old patient presented tooutpatient physical therapy following right knee MPFL reconstruction andanteromedialization of tibial tubercle (AMZ) in May 2017. The patient has apast medical history (PMH) of a chromosomal 2 abnormality, asthma,ventriculoperitoneal shunt, and left patellar instability. The patient wears apatellar stabilization brace on the left lower extremity (L LE). The patientpresented with patellar instability on the right side with multipledislocations, leading to the MPFL reconstruction and AMZ. Patient ambulatedwith crutches for 12 weeks after surgery with a knee immobilizer that wasremoved at 16 weeks.
Thepatient is not in any pain, rating his pain 0 out of 10 on the virtual analoguescale (VAS). The patient demonstrates full ROM in the right knee. The patient’smanual muscle test (MMT) of bilateral lower extremity (B LE) muscles was 4/5. Thepatient demonstrates slight weakness in right quadriceps with a grade of 3+/5.The patient is unable to perform a single straight leg raise into flexion.Interventions such as neuromuscular electrical stimulation (NMES) combined withclosed kinetic chain, open kinetic chain, and isometric exercises have failedto strengthen the patient’s right quadriceps.
Thepatient has several functional limitations. In gait, the patient lacks bilateralknee extension and bilateral decreased step length. The patient is unable toperform an eccentric contraction of the right quadriceps. The patient cannotdescend stairs in a reciprocal pattern, he must always lead with his R leg. Thepatient is unable to complete high-level activities such as running or plyometrics.The patient is motivated to get back to running and jumping. The patient isalso motivated to get back to his job at a daycare and as a high school footballcoach.
Clinical question The patient is progressing accordingto protocol. It is not unusual for patients to demonstrate quadriceps weaknessand to not be able to perform a single straight leg raise into flexionfollowing AMZ and MPFL reconstruction.3 The patient is still limited infunctional activities like descending stairs, running, and jumping. Once thepatient is able to perform these activities, the therapist should understandhow the patient perceives his symptoms of instability are impacting hisfunction. We decided an importantquestion for our patient is which patient reported questionnaire is the mostaccurate and reflective of change in function in adults with patellarinstability? For the purpose of the paper, we adapted the definition ofpatellar instability to patients who have a medical diagnosis by magneticresonance imaging (MRI) or clinical examination of patellar dislocation,subluxation, or general patellar laxity within the past two years.
Thisquestion focuses on determining the most effective PROM for patients withpatellar instability who are experiencing functional limitations due tosymptoms of instability.