This talk will be on the critical clinical assessment of the patellar femoral patient. These are my disclosures. Patellar dislocation can be traumatic or atraumatic in nature. Patellar stability is maintained by the ligamentous restraints, dynamic muscular forces, and bony anatomy of the knee. Disruption or abnormalities of any combination of these three components can lead to patellar instability. The risk factors for patellar instability include trochlear dysplasia, patella alta, rotational and angular bony malalignment, and ligamentous laxity. It's also important to remember during the assessment that dislocation and subluxation, which refers to the transient movement of the patella leading to a feeling of instability or pain, should be differentiated from the term maltracking, which refers to the abnormal lateral tracking of the patella throughout range of motion. And this is in contrast to laxity, which simply refers to abnormal translation. The goals during the clinical examination of a patellar femoral patient are to first confirm and quantify patellar stability and mobility, and secondly, to identify the contributing factors. A comprehensive assessment should also always include the assessment of ambulation or gait, presence of effusion or bruising, range of motion, and a thorough ligamentous examination. Assessment of alignment can be performed for the patient standing. This is an example of the miserable malalignment. You can see that the patient's feet are pointing forward, but her patella are almost facing each other. This is a combination of femoral anaversion, sometimes genuvalgum, and external tibial torsion. Pes planus can play a role in this as well. To quantify this, we use the Q angle, which is the angle formed between a line from the patella to the anterior superior iliac spine, with that from the patella to the tibial tubercle. Normal values are 14 and 17 in males and females, respectively, with abnormal values being greater than 20. There is some inner observer variability with this, but a high Q angle has been noted in over half of patients with recurrent instability. The assessment of strength and muscle function is important as well. VMO atrophy can be observed, and this is important because it can increase the lateral pull of the quadriceps mechanism on the patella, if present. Having the patient perform a single leg stance and squat or straight leg raise in comparison to the contralateral side can assess for any deficits in muscle strength or engagement. The assessment for generalized laxity is important as well. The Baton score is a measure of generalized laxity using the patient's ability to passively abduct the thumb to the forearm, passively hyperextend the little finger to 90 degrees, elbow extension greater than 10 degrees, and knee hyperextension greater than 10 degrees. And lastly, trunk flexion, where the patient is standing with the knees straight and bends over and is able to put their palms directly onto the floor. This is out of a score of nine, so the first four are bilateral, so one for each side. And a score of five or greater, or six in children, can indicate generalized laxity. When it comes to patellar-specific tests, the glide test is a way to quantify patellar translation. In this test, the patella is moved laterally and medially and quantified in terms of patellar quadrants, as can be seen in this figure. Normal values are typically two quadrants of medial and lateral mobility, but it is important to compare this to the contralateral side if the other side is not symptomatic. The apprehension test is performed with the knee at 20 to 30 degrees of knee flexion, and a lateralizing force is placed on the patella. If the patient feels that the kneecap is about to dislocate, then this is considered to be a positive test. This can be performed in the medial direction as well. Medial patellar instability is very uncommon. However, it can be present if the patient has had a prior lateral release. I just mention this because it's important not to miss, as the treatments for lateral patellar dislocation and medial dislocation are very different. Imaging won't always show these, and so this is primarily a clinical diagnosis, which appears with increased medial translation of the patella, as well as medial apprehension. Lateral retinacular tightness can be assessed using the patellar tilt test, in which the lateral border of the patella is elevated. It should get to about horizontal, but I think it's more important to look for symmetry with the other side. Additionally, limited medial translation can also be an indication of lateral retinacular tightness. Assessment of pain with patellar loading can be performed either with the patient in a supine position and loading the patella while they actively contract their quadriceps, or with the patient in a sitting position, actively extending the knee while the patella is loaded. Pain with this maneuver is considered indicative of patellofemoral pain. This can occur with or without instability, but it's still important to note during the exam. The J sign is performed with the patient sitting with their knees at 90 degrees, and then actively extending while we observe the motion of the patella, and quantify the amount of lateral translation. Historically there was subjective grading of 1 plus 2 plus 3 plus. More recently it's been shown that greater than three quadrants of lateral translation and extension is actually indicative of patellar instability with a sensitivity of 93%. On x-rays, for AP x-rays, these should be performed to weight bearing to assess for alignment and any degenerative changes. The lateral x-ray can be very helpful during the assessment of these patients to look at patellar height, as well as to assess for trochlear dysplasia on this view. The Caton-Duchant Index is one of the most commonly utilized measurements of patellar height. There are multiple measurements that can be used, but this is one that is not dependent on the position of the tuberosity, so pre- and post-operative measurements can be performed if a patient is undergoing tuberosity osteotomy. This is the ratio between the length of the patellar articular surface with that of the distance from the distal articular inferior pole to the anterior tibial plateau, with values of 1.2 or greater being indicative of patella alta. Axial imaging on radiographs are important as well. The Merchant or Laurent views are preferred over the Sunrise views. The Merchant and Laurent views are performed at 30 and 20 degrees of flexion, respectively, while the Sunrise views are performed at about 45 degrees. As we know, trochlear dysplasia is present in the proximal part of the trochlea, so the Sunrise views may not capture the dysplastic portion. These views will allow for evaluation of the patellofemoral joint in terms of the assessment of trochlear dysplasia, also any lateralization or tilt of the patella, and it also allows us to see any sort of avulsion fractures or the NPFL along the medial border of the patella, which can actually be seen in this x-ray. CT scans are performed for the assessment of patellar position to perform morphologic measurements, especially the TTTG distance. This is a measurement from the deepest portion of the trochlear groove to the tibial tuberosity, and this is thought to denote the pull of the extensor mechanism lateral to the trochlear groove. The original description was performed on CT in full extension with measurements greater than 20 mm, considered to be abnormal. It is important to note here that MRI has been shown to underestimate TTTG by 3.8 mm. TTTG distance can also change with knee flexion angle and decrease by 1 mm for every four degree increase in knee flexion, so it is important to look at the sagittal view as well. This can also be influenced by patient size. On MRI, typical findings after patellar dislocation show a relocation event with a chondral fracture on the lateral formal condyle and medial patella, as well as the presence of an NPFL injury. Obtaining an MRI can help to identify osteochondral injury or presence of loose body, both of which can be indications for early intervention. It's also useful in performing carvilaginous measurements for risk assessment, such as sulcus angle and lateral trochlear index to assess trochlear morphology, and also patellar trochlear index as a measurement of patellar height. Lastly, CT, 4D CT imaging is available at some institutions and is becoming increasingly available. This is where the patient actively extends and flexes their knee during CT imaging, and patellar motion can be quantified during this. This has been shown to be helpful in quantifying maltracking as clinical assessment with J-sign is still somewhat limited. Other imaging that can be added as needed include long leg standing views to assess for coronal alignment, as well as further imaging to assess for hip anversion when needed. In summary, patellar formal disorders are multifactorial in nature, and the physical examination is critical in both detecting and confirming instability and quantifying patellar mobility, as well as to identify the contributing factors. Imaging parameters can identify and quantify the presence of risk factors to help individualized treatment to address the identified deficiencies. Thank you.

patellar instability

clinical assessment

trochlear dysplasia

gait analysis

imaging techniques