Patellofemoral Malalignment, Tibial Tubercle Osteotomy, and Trochleoplasty

Introduction

This chapter is meant to offer the practicing orthopedist a practical management approach to dealing with patellofemoral disease. The key to successful treatment relies on an accurate diagnosis of the underlying pathomechanics responsible for the pain.

Chronic patellofemoral pain is a common and problematic management issue. The term “chondromalacia” has often been applied to anterior knee pain. Chondromalacia (soft cartilage), a pathologic term, may not even be present. Pain is a multifactorial perception. It is important to ensure that the pain is local and not referred, that it is not caused by a local soft tissue inflammatory or neurogenic process, and that it arises from the patellofemoral joint. This is usually determined by a careful history and physical examination. The emotional well-being of the patient may modify the subjective response of pain. Even with obvious patellofemoral pathomechanics, if physical therapy has not been performed adequately to address these problems, a repeated course of carefully directed physical therapy is worthwhile.

Many factors have been implicated as a source of abnormal forces across the patellofemoral joint. These include patella alta, trochlea dysplasia, an abnormally increased quadriceps or Q-angle, with secondary soft tissue problems, weakened or hypoplastic vastus medialis oblique (VMO) quadriceps muscle with a contracted lateral retinaculum. These pathomechanics lead to abnormal forces across the patella resulting in secondary degenerative changes or injury to the articular surfaces with cartilage defects of the patellofemoral joint acutely or chronically.

The prevalence of patellofemoral cartilage defects is controversial because it is unknown what percentage of lesions become symptomatic enough to prompt evaluation. Several studies have reported the presence of high-grade focal chondral defects in 11%–20% of knee arthroscopies. Among these defects, 11%–23% were located in the patella and 6%–15% in the trochlea. A group investigating asymptomatic NBA basketball players with knee magnetic resonance imaging (MRI) found articular cartilage lesions in 47%, patellar lesions in 35%, and trochlear lesions in 25% of players; however, only approximately half of these defects were characterized as high-grade lesions. These reports emphasize the importance of a thorough history and physical evaluation of the entire kinetic chain from pelvis to foot, a gait analysis, and assessment of all knee structures (tendons, ligaments, and soft tissues) before attributing a patient’s symptoms solely to the presence of a chondral defect.

History

Patellofemoral articular defects frequently present as anterior knee pain; patients often report their pain to be located retropatellar, peripatellar, occasionally radiating down the shin bone, or in the instance of trochlear defects, the pain at times is located posteriorly in the popliteal area. Secondary pain may be from synovial or capsular irritation from joint distension secondary to an effusion or caused by exposed subchondral bone overload from a chondral defect. Thus, in light of this secondary nature of pain, other factors may also contribute, making it difficult to assign a percentage of pain to the cartilage pathology. Large defects can cause clicking or popping, giving way, and activity-related swelling. Distension of the joint often causes an aching sensation with a loss of motion and function but not necessarily complaints of pain. Standard patellofemoral symptoms are often reported such as increased pain with prolonged flexed knee position and stair climbing as maximal patellofemoral forces are in the flexed knee position when patellar engagement in the trochlea occurs greater than 30 degrees ( Fig. 12.1A,B ). Patients are approximately evenly split in reporting a traumatic versus a more gradual onset of symptoms; sports participation was the most common inciting event associated with the diagnosis of chondral lesions. Patellar dislocation is associated with damage to the articular surface, with chondral defects of the patella seen in up to 95% of patients ( Fig. 12.2A,B ). It is the author’s opinion that patellar dislocations usually occur because of baseline mechanical abnormalities with increased quadriceps angles (Q-angles) and/or dysplasia of the trochlea; despite the history of trauma, it is usually a minor twist during participation in sports. Patients often report extended courses of physical therapy, bracing and taping, or prior knee surgery.

Physical Examination

Gait abnormalities, such as intoeing or hip abductor weakness, and an increase in femoral anteversion and valgus malalignment of the lower extremity are frequently seen in this patient population, especially adolescents. Adaptations in gait are also seen such as hip and knee external rotation and contractures of the hip abductors and iliotibial band. Traditionally, the Q-angle ( Fig. 12.3 ) has been used in the evaluation of patellofemoral symptoms. Many different methods of measuring this angle have been reported and the high interobserver variability makes its usefulness questionable. As described, the Q-angle should be evaluated in both full extension and approximately 30 degrees of flexion, because in some cases a laterally subluxated patella in full extension can falsely decrease the Q-angle (the patella should be repositioned in the central sulcus before measuring the Q-angle). My preference is to examine and measure the Q angle is full extension with the patella manually reduced in the trochlea with medially directed force on the patella (I call it the Thumb Reduction Test). Ask the patient to contract the quadriceps and you can see and feel the patella sublux laterally. Q-angles in asymptomatic patients are 14 degrees in males and 17 degrees in females. Quadriceps wasting, especially of the vastus medialis, is common in long-standing patellofemoral symptoms. Recently, more emphasis has been placed on core muscle weakness, especially of the hip abductors, hip extensors, and pelvic stabilizers. Weakness in this group can be demonstrated by asking the patient to single-leg stand on the affected limb, resulting in a pelvic drop on the contralateral side. In addition to poor pelvic support, dynamic internal rotation of the femur and dynamic valgus positioning of the limb can be observed. Activity-related swelling and, in particular, a joint effusion indicate more advanced disease. Palpation of the medial and lateral retinaculum can elicit pain; the lateral structures are often contracted (tested by attempting to reverse patellar tilt) and the medial soft tissues can be attenuated (such as chronic patholaxity of the medial patellofemoral ligament [MPFL]). Patellar mobility, tilt, and subluxation should be assessed and quantified medially and laterally. Normally the patella should be able to “glide” 30% of its width medially and laterally without the patient experiencing apprehension of a subluxation or dislocation. Catching with mobilization of the patella against the trochlea is suggestive of larger defects. Knee range of motion is usually preserved but may be inhibited by pain or large effusions in acute cases. The J-sign (the patient slowly extends the knee from full flexion, the patella subluxes laterally once it leaves the constraints of the trochlear groove near full extension) may occur in normal patients but is exaggerated in patients with patellar maltracking and often implies incompetence of the medial restraining structures, including the MPFL.

Physical Therapy

The goal of physical therapy is to restore soft-tissue balance in the patellofemoral joint, including muscular and capsuloligamentous balance often remote from the joint. Rehabilitative exercises should include a stretching regimen to restore flexibility of the quadriceps, hamstrings, and iliotibial band, as well as patellar mobilizations as needed to optimize capsular structure balance (e.g., reverse tilt) of the quadriceps and patellar tendon. After flexibility has been restored, a strengthening program should be instituted, emphasizing the core proximal musculature, including the hip abductors and external rotators, because most patients have previously received too much emphasis on isolated quadriceps strengthening. When quadriceps strengthening is emphasized it should be performed with closed-chain activities such as elliptical trainer, leg presses, and squats with the knee less than 30 degrees of flexion from full extension to prevent maximal patellofemoral contact forces. Open-chain resisted quadriceps extensions should be avoided so that patellofemoral pain or cartilage damage are not aggravated. Short-arc open-chain quadriceps extensions are performed when the patella is not engaged in the trochlea in the first zero to 20 degrees of flexion of the knee. Gait training should focus on avoidance of an intoeing gait, which results in functional femoral anteversion. Throughout rehabilitation, it is important to protect the patellofemoral articulation by using isometric and short-arc closed-chain concentric and eccentric muscle strengthening, which is individually designed to avoid specific arcs of pain or loading of cartilage defects. A trial of patellar McConnell taping or patellar bracing to centralize a maltracking patella is worthwhile, especially when symptoms are limited to certain activities, such as athletic endeavors. The patient should understand the comprehensive McConnell approach, which uses taping to allow pain-free rehabilitation, i.e., the taping is not an end in itself. Patients should understand that they have mechanical reasons for their imbalance and resultant pain in their extensor mechanism. Therefore it is important that they maintain their stretching and strengthening regimen to stay within their envelope of function, their own personal equilibrium. If they are able to experience benefit with physical therapy but have recurrent relapses of discomfort, they should rest, elevate, and ice the extremity along with taking nonsteroidal anti inflammatory medications until they are able to resume their quadriceps rehabilitation regimen. Only when they fail therapy should they then seek definitive surgical intervention for resolution of symptoms and restoration of function.

Imaging Studies

Useful tests to assist in determining the diagnosis include standard radiographs to include standing AP, 45-degree PA (Rosenberg views), lateral and skyline (Merchant views), and standard 54” axial alignment x-ray examinations. X-ray images are useful with any patellofemoral joint to determine joint space narrowing or osteoarthritis on a standard Merchant view. Merchant view is taken at 45 degrees of flexion during which the patella is normally well engaged in the trochlea distally. It is not an effective view for assessing maltracking. When maltracking occurs, it is usually in the first 0–30 degrees of flexion from extension. The dislocated or subluxed patella in full extension travels medially as it travels distally capturing the trochlea as it reduces. This is the clinical finding of a J-sign. Dejour et al. have shown the advantages of a true lateral radiograph in assessing trochlear dysplasia and patellar tilt not appreciated on the Merchant view.

Assessment of articular cartilage injury is receiving more attention with high-resolution 3.0 Tesla MRI magnets and thin 1-mm slice acquisitions orthogonal to the axis of the joint surface, improved upon with cortical enhancement magnets. Although intravenous gadolinium as an indirect arthrogram with MRI scan was popular in early 2006, reports of complications related to injury to the kidneys have discontinued its use in our practice. The high-resolution MRI images that are presently available rarely require an arthrogram to enhance the effect of the imaging. If so, direct injection of gadolinium is necessary prior to the MRI scan. Although the gold standard for assessing articular injury remains arthroscopy, sensitivity and specificity > 90% can be obtained with high-resolution MRI scan using even a standard 1.5 Tesla magnet with appropriate orthogonal gantry tilting to surfaces of the trochlea and appropriate sequences. This is our preferred method of assessing articular cartilage injury to localize the site and size of articular injury in the patellofemoral articulation.

To assess patella subluxation accurately, spiral computed tomography (CT) of the patellofemoral joint is performed with the leg in full extension, once with the quadriceps relaxed and again with the muscle maximally contracted ( Fig. 12.4 ). It is especially helpful in determining dysplasia of the bony patellofemoral joint ( Figs. 12.5 and 12.6 ). Computed tomography also allows a more precise evaluation of patellar and trochlear anatomy than the Merchant view ( Fig. 12.7 ). Accurate documentation of subluxation can be determined with a CT scan when clinical findings are difficult, especially in obese patients.

The addition of intra-articular contrast gadolinium helps to reveal any articular cartilage defects on the patella or the trochlea or both and the exact location and size. I have found that my preferred test for patellofemoral maltracking, location of the articular cartilage defect, and assessment of dysplasia of the trochlea, is a CT arthrogram performed with the quadriceps first relaxed and then contracted in the fully extended position of the knee ( Fig. 12.8 ).

Furthermore, superposition of two CT images, one through the patellofemoral articulation, the other through the tibial tubercle, allows calculation of the tibial tubercle to trochlear groove (TT-TG) distance: the center of the trochlear groove and the center of the tibial tubercle are marked, and the medial-to-lateral distance between the two is measured ( Fig. 12.9 ). A TT-TG distance of >15 mm is considered normal; values >20 mm are abnormal and these cases should be considered for a tibial tubercle osteotomy. It is also possible to use MRI images obtained during routine knee evaluation to measure the TT-TG distance (Schoettle et al. demonstrated the equivalency of CT and MRI TT-TG measurements) and the Caton-Deschamps measurement of patellar height (alta, infera, normal), thus providing additional information without added cost.

Despite the enthusiasm over the use of the TT-TG distance, I am reluctant to use solely that measured reference to determine patellar maltracking. In a small person’s knee, 15 mm is a large distance and would often result in severe subluxation of the patella in comparison with a very large person. I am more inclined to use clinical examination and CT arthrogram with the knee in the extended position both relaxed and contracted to determine patellar subluxation rather than the use of the TT-TG distance.

When the pain pattern is suggestive of arising from the patellofemoral articulation, a bone scan may be useful in difficult cases of evaluation when other studies are negative to determine increased activity in that part of the joint, but is rarely necessary.