Recurrent Patellar Instability
Anterior knee pain due to recurrent patellar instability is one of the most common entities seen in a sports medicine practice. In the 17 year old population, the incidence of patellar instability is 29 cases per 100,000 (1). These injuries will typically occur when the leg internally rotates with a fixed foot with simultaneous quadriceps contraction (7). The challenge in treating patellar instability is that the rate of subsequent patellar dislocation increases after the first episode (1). These dislocations can also cause patellofemoral cartilage damage, osteochondral fracture, pain, and development of patellofemoral arthritis (3).
A) Physical therapy for 6 weeks
B) Referral to Orthopedic Surgery
C) MRI with contrast to evaluate the osteochondral defect
D) RICE for 4 weeks and then closed chain exercises
Patella stability relies on the patella, femoral trochlea, medial-patella femoral ligament, quadricep muscle, and limb alignment (1). Radiographic imaging with both lateral and Merchant views help assess for patella instability (1). A Merchant view allows for assessment of patella tilt and trochlear dysplasia (1). It is also important to assess the Q angle, which is the angle between the lines of action of the patella and the quad tendon (1). An increased Q angle causes a lateral directed vector on the patella and can lead to patella instability (8). Another marker of MPFL alteration is the tibial tubercle lateralization (TT-TG) with an abnormal TT-TG being reported as >25 mm. The TT-TG distance suggests lateralization of the tibia tubercle compared to the trochlear groove (4).
When assessing a patient for patella instability, the trochlear groove needs to be assessed. The patella makes maximal osseous contact with the femur when the knee is in full extension and the patella and quadricep tendon provide maximal constraint in knee flexion (1). As a result, the point of maximal knee instability is when the knee is in full extension (1). Having a flat or decreased depth to the trochlear groove is a risk factor for patellar instability (4). Evidence suggests that, in patients with open physes and trochlear dysplasia, there is a 69% patella dislocation recurrence rate (3).
Figure 1 – Trochlear Dysplasia (4)
Patella alta is a risk factor for patella dislocation because there is less osseous stability in these patients (1). A higher patella requires higher degrees of knee flexion for the patella to slide into the trochlear groove (4). The most popular measurement techniques are the Insall-Salvati, Grelsamer-Meadows, Caton-Deschamps, and Blackburne-Peel indexes (4). A lateral radiograph can also suggest patella alta if a supra-trochlear spur is present (1). A supratrochlear spur (Figure 2) can also cause the patella to be kicked laterally increasing the risk of patella dislocation (8).
Figure 2 – Supra-trochlear spur (1)
It is also important to assess the surrounding soft tissues including the IT band, IT patellar band, and medial patellofemoral ligament (1). A tight iliotibial band causes the patella to track laterally (1). The medial patellofemoral ligament is a continuation of the deep retinacular fibers of the vastus medialis obliquus (5). Tears along the medial patellofemoral ligament can occur at any location along the ligament (2). Studies show that the MPFL is injured in over 90% of patella instability episodes (4). Tears at the femoral attachment have higher rates of future instability (2). Physicians can evaluate for MPFL damage with lateralization of the patella and a lack of a firm end point (5). Other physical exam tests to consider are tenderness at the medial femoral epicondyle at the MPLF attachment site and tenderness over the medial patella facet (7).
An MRI is ordered to evaluate for osteochondral fracture, osteochondral lesion, and for evaluate of the MPFL ligament (3).
Non-operative treatment is typically used for first time dislocators. Short term goals in a first time dislocator include controlling the knee effusion, activating the vastus medialis and gluteal activity, and improving knee range of motion (1). Patients can typically be placed in a brace in full extension or partial flexion (5). Those patients treated just with a patella support brace have a 3x risk of redislocation (5).
The evidence for conservative options is based on a metaanalysis that looked at four studies comparing conservative measures to surgical treatment for patellar dislocations (2). They found no significant difference in pain and instability episodes between the groups (2). However, surgery is preferred if there is a chondral or osteochondral fracture (2). Physicians should also evaluate for significant trochlear dysplasia, young age, and patella alta as potential indications for surgery following the first dislocation (2). It is also important to evaluate the pattern of tearing of the MPFL when making surgical decisions. If the ligament has a single discrete tear or multiple sites of tearing, surgery should be considered (2).
Physical therapy exercises should be closed-chain quadriceps and gluteal strengthening (5). Gluteal strengthening is indicated because weak gluteal musculature can lead to increased internal rotation of the femur, which may facilitate patella instability (1). Vastus medialis strengthening will help bring the patella into the trochlear groove (5). An imbalance between the strength of the vastus medialis and vastus lateralis is a risk factor for instability (1). Taping the patella can also help activate the vastus medialis (1). A lateral patella stabilization brace will help encourage the patient’s sense of patella stability (7).
Surgical repair is also undertaken in cases of recurrent patella instability. These surgeries include lateral release of the patella, medial patellafemoral ligament reconstruction, trochleoplasty, and tibial tubercle transfer (1).
Although debatable, consensus typically calls for conservative measures for first time patella dislocators. However, it is important for providers to evaluate first time dislocators with an MRI to rule out osteochondral injury and for the pattern of MPFL tearing. If patients have recurrent patella instability, there are multiple surgical techniques for dealing with these patients. However, no consensus has been made as to the preferred surgery or technique. All in all, patella instability is a multifactorial problem that is frequently seen in sports medicine clinics. It requires a team of providers, therapists, and trainers to properly treat these patients.
Read More: https://wikism.org/Patellar_Instability
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