Approach to Chondral Damage in the Patellofemoral Joint

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CHAPTER 17 Approach to Chondral Damage in the Patellofemoral Joint

Chondral defects of the patellofemoral joint are the most common type of articular cartilage defect found in the knee.¹ They also comprise a significant portion of most isolated grade IV articular cartilage defects in the knee joint. These lesions may be found incidentally but also may be a common source of pain and discomfort in the knee.² Trochlear articular cartilage defects can be symptomatic. The approach to this joint can be complex and may require a combination of arthroscopic and open surgical techniques, up to and including arthroplasty, which is beyond the scope of this chapter.³^,⁴ I shall primarily discuss arthroscopic techniques for chondral defects.

ANATOMY AND PATHOANATOMY

The patellofemoral joint of the knee is a complex articulation, with multiple facets on the patella and a complex, saddle-shaped trochlear groove.⁵^–⁷ The articular cartilage on the patella itself is the thickest articular cartilage in the body, measuring up to 7 mm thick on the medial facet. Chondral defects on the patella may be have several causes, including degeneration, direct trauma, malalignment, and patellar instability.⁸^–¹⁰ The mechanics of the patellofemoral joint are complex and are determined by a number of factors, including neuromuscular coordination, geometry of the trochlea, overall alignment of the extensor mechanism, including the quadriceps tendon, trochlear groove, and tibial tubercle, and soft tissue restraints such as the medial patellofemoral ligament.³^,¹¹^–¹³ These restraints help guide patellofemoral motion and often determine whether articular cartilage damage occurs and is symptomatic. For example, excessive patellar malalignment with a laterally tilted and subluxated patella can contribute to excessive articular cartilage wear on the lateral facet of the patella.¹⁴^,¹⁵ Direct trauma to the patella, such as from a dashboard-type injury, in which a flexed knee contacts the dashboard, may result in a central articular cartilage damage to the patella or trochlea.¹⁶^–¹⁹ In addition, many central articular cartilage defects are noted in young athletic individuals. These often have a linear fissure in the center of the trochlea. This reflects the significant forces placed on the patellofemoral joint during activities of daily living and other forms of physical exertion. For example, the joint reaction forces on the patellofemoral joint during stair climbing are up to two to four times body weight, and jumping can create forces up to six to eight times body weight.²⁰^–²⁵ These loads can result in failure of the underlying articular cartilage and subchondral bone.

PATIENT EVALUATION

History and Physical Examination

Patients with symptomatic articular cartilage lesions of the patellofemoral joint generally complain of anterior knee pain, particularly when ascending or descending stairs or after sitting.⁴ Occasionally, patients may complain of crepitus or a symptomatic click as the knee goes into flexion or extension. Elements of the history to obtain from the patient also include known or suspected rheumatologic disease, history of trauma to the knee from a direct blow, history of patellar instability, activity level of the patient, recent changes in activity level, timing of the injury, and whether the pain is acute or chronic. In patients who have already sought previous treatment, it is important to identify the nature of treatment, including physical therapy, bracing, and taping and any previous surgery. Complaints of recurrent or consistent effusions should also be identified. Knee pain diagrams often provide relevant clinical information.²⁶

Physical examination should combine static and dynamic evaluation. The presence or absence of any effusion should be noted and the knee should be carefully palpated and evaluated for ligamentous and patellar instability. At 30 degrees of knee flexion, the patella will typically translate laterally approxi mately 9 mm and have a relatively firm end point because of the check rein of the medial patellofemoral ligament.²⁷ The patella should also translate medially 7 mm and the lateral patellar retinaculum should allow the patella to be tilted to a neutral position, where the anterior surface of the patella is parallel to the ground while the patient is supine. Quadriceps development, particularly that of the vastus medialis obliquus muscle, should be assessed.⁴ Extensor alignment including femoral version, Q angle, and tibial rotation can provide insights into patellar tracking.

A specific evaluation of the articular cartilage of the patellofemoral joint should be performed. The knee should go through an active range of flexion and extension and the presence of any significant crepitus should be assessed. I prefer to perform this examination with the patient lying supine, with the hip flexed to 90 degrees and the knee actively flexed and extended against gravity. In my clinical practice, this has been found to identify and elicit patellofemoral or articular cartilage complaints more precisely than while the patient is sitting. This also allows an assessment of hamstring tightness, which may contribute to patellofemoral symptoms. Another specific test to assess for chondral defects in the patellofemoral joint is the Clark patellar compression test. Two fingers of the examiner are held at the top of the patella to stabilize it in the trochlea with the knee extended, and the patient is asked to activate the quadriceps mechanism. This tightens the quadriceps and forces the patella into the patellofemoral joint; it is positive if pain is elicited. In addition, the medial and lateral facets of the patella can sometimes be directly palpated for tenderness. However, unlike many parts of the femoral tibial articulation, the central trochlea usually cannot be directly assessed by palpation.

The Q angle with the knee extended is of limited benefit. The Q angle with knee flexed to 30 degrees is a more accurate representation of the actual location of the patella and the trochlea groove compared with the location of the tibial tubercle.

Dynamic examination of the knee should be performed as well. Abnormalities of gait should be identified.²⁸ Evaluation of knee stability and identification of pain or crepitus while doing a step-up or step-down maneuver may help elicit specific complaints. A single leg squat test may also elicit pain and will allow evaluation of relative knee valgus or internal rotation, which can increase patellofemoral forces.

Diagnostic Imaging

Radiography

An anteroposterior (AP) radiograph can provide information about the existence of a bipartite patella. The relative location of the patella to the trochlear groove and tibial tubercle can be determined as a secondary bony density on the proximal tibia.

A true lateral view with overlapping femoral condyles, with less than 5% displacement, can provide valuable information regarding the relative patellar height. This can be assessed using various ratios, including the Insall-Salvati index and Blackburne-Peel method (Fig. 17-1)—the articular surface length compared with the distance from its inferior margin to the tibial plateau. This technique has been demonstrated to be the most reliable. A true lateral view can also yield information about the degree of trochlear dysplasia. The trochlear groove can be identified on the lateral x-rays, on which a dense white line of the trochlea should not intersect vvthe bone of the lateral femoral condyle (Fig. 17-2). A sunrise or Merchant view at 45 degrees of flexion can give indicate patellar tracking within the trochlea and the presence of lateral patellar tilt or subluxation. A number of measurements have been described; however, I agree with Merchant that “(f)or most patients, it is quicker and just as good to eyeball the film rather than spend time drawing lines and calculating measurements.”²⁹

FIGURE 17-1 Methods of measuring patellar height. Normal for all ratios 1:1(± 0.2)—Blackburne-Peel (most reliable), A:Y; Caton, A:X; Insall-Salvati, B:Z.

(Adapted from Merchant AC. Patellofemoral imaging. Clin Orthop Relat Res. 2001;(389):15-21.)

FIGURE 17-2 Lateral radiograph demonstrating trochlear dysplasia. The arrow shows the trochlear groove. Note how it starts after the curve of the femoral condyle.

Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) is currently the best modality to image articular cartilage defects.³⁰^,³¹ Appropriate articular cartilage sequences and thin cuts often reveal articular cartilage damage, such as chondromalacia, chondral flaps, or delamination. In addition, it can also identify areas of underlying subchondral bony edema. MRI is also useful to assess abnormalities of soft tissue that may be contributing to underlying chondral damage or patellofemoral pain, such as synovitis, lesions of the medial patellofemoral ligament, tendinopathy, and articular cartilage loose bodies. MRI can also be used to perform measurements of tibial tubercle to trochlear groove distance. This can indicate conditions that could lead to patellar instability and subsequent articular cartilage damage.

TREATMENT

Treatment options for chondral lesions of the patellofemoral joint can be conservative or surgical. Many patients have symptoms of patellofemoral pain. Diagnostic imaging studies other than plain radiography may not be clinically indicated.

Conservative Management

In most cases, initial management should consist of physical therapy for quadriceps strengthening, with or without patellar bracing, relative rest, and appropriate analgesic medications, including acetaminophen or nonsteroidal anti-inflammatory drugs (NSAIDs). Patients with symptomatic patellofemoral pain may have been previously shown to have substantial weakness of quadriceps muscle activity and, specifically, weakness of the vastus medialis obliquus.³²

Arthroscopic Technique

Surgical approaches to symptomatic chondral defects of the patellofemoral joint can vary, ranging from arthroscopic débridement to articular cartilage transplantation techniques and realignment techniques. In this chapter, the focus will be limited to the arthroscopic treatment of these lesions. However, the treating physician should be aware that open surgical techniques may be critically important in the treatment of these disorders, particularly in the case of gross malalignment, to provide increased stability or unload a damaged area of articular cartilage.

Arthroscopic surgical techniques for the patellofemoral joint vary from simple débridement to microfracture procedures and osteochondral autograft transplantation. In addition, in rare cases, arthroscopic lateral release or medial plication can assist in the realignment of soft tissues affecting the patellofemoral joint and patellar tracking. However, isolated lateral release has extremely limited application and may result in medial instability.⁴^,³³

Arthroscopic chondroplasty should consist of débridement of unstable articular cartilage flaps to a stable margin. These flaps can be a source of pain and discomfort. Patients may experience a click at a specific degree of knee flexion or significant crepitus. Such delaminations often occur at the calcified cartilage layer and can easily progress. I recommend the use of mechanical débridement ²^,³⁴ with an arthroscopic shaver to remove these flaps rather than electrocautery or radiofrequency devices, because there is a concern for adjacent articular cartilage damage caused by the heat produced by the electrocautery.³⁵^,³⁶ Technical recommendations for the mechanical débridement of grade II or III chondromalacia include the use of a small-radius (3.5- to 4.5-mm), high-speed, smooth-edged shaver. Arthroscopic portal placement may need to be adjusted distally to allow instruments access to the undersurface of the patella. Typically, in cases in which there is significant grade III or crabmeat-type chondromalacia, the noncutting part of the shaver blade is placed at the base of the articular cartilage surface so that the fronds can be sharply amputated at their base (Fig. 17-3). The irregular strands and rough surface can lead to symptomatic crepitus and recurrent effusions in the joint. If there are full-thickness articular cartilage flaps, it is sometimes easier to amputate them sharply at their base by using an arthroscopic Beaver blade. Occasionally, it is useful to use a curved shaver to access the undersurface of the patella.

FIGURE 17-3 Arthroscopic chondroplasty with shaver blade parallel to surface. Note that noncutting part of blade is at base of the fronds.

A microfracture procedure for chondral defects of the patellofemoral joint is typically less successful than microfracture involving the femoral condyles.³⁷ The lesion is typically prepared by débriding unstable articular cartilage edges until a very sharply defined margin of the defect is created. The calcified cartilage layer in the bed of the defect must be removed. This is sometimes easier to perform by using sharp curettes or an arthroscopic Beaver blade to scrape away the calcified cartilage layer. Multiple perforations are then made in the bone, starting at the periphery and separated by approximately 3 to 4 mm. This can be done with a sharp awl or K wire or drill bit. Particularly on the patella, drilling rather than an awl may be preferred because the underlying subchondral bone is thick, and it can be difficult to stabilize both the patella and awl enough to allow adequate perforation of the underlying bone. If an awl is chosen, a 90-degree angle may be helpful to avoid skiving.³⁸ Drilling can be performed by using accessory nontraditional portals located more posteriorly than the standard medial inferior lateral or proximal superior lateral portals (Fig. 17-4).

FIGURE 17-4 A, B, Posterior portal for perpendicular patellar drilling for the osteochondral allograft procedure.

Osteochondral Autograft Transplantation

Osteochondral autograft transplantation has been demonstrated in some studies to be effective in the patellofemoral joint.⁸^,¹⁰^,³⁹^,⁴⁰ With relatively larger defects. there is difficulty in reproducing the saddle-shaped geometry of the trochlear articulation. In addition, the articular cartilage thickness of the patella is typically not replicated by the use of osteochondral plugs harvested from the femoral condyle. Despite this, the results for osteochondral autograft transplantation for this area are relatively good, and is my preferred technique for significant articular cartilage lesions of the patellofemoral joint, in particular for those involving damage to or cystic changes of the subchondral bone.

With arthroscopically performed osteochondral autograft transplantation, it is critical to have appropriate orientation of grafting and harvesting tools. Ideally, these should be perpendicular to the articular cartilage surface. Therefore, a considerable amount of time is spent in using a spinal needle as a localizer to identify the appropriate trajectory for the orientation of harvesting and grafting equipment. Accessory portals may need to be created to perform this procedure.

Typically, the area of the defect is débrided and the margins of the defect identified. After appropriate identification of the perpendicular orientation to the articular cartilage defect, the sizing tools are placed arthroscopically through the appropriate portal to determine the circumference of the defect (Fig. 17-5A) and the number of appropriate osteochondral autograft transplant plugs that will be needed to fill in the defect. In the case of articular cartilage defects on the patella it may be extremely difficult to use standard arthroscopic portals to achieve a perpendicular location to the patella. The spinal needle can be used to identify the appropriate trajectory and orientation of a portal. I have used a more posterior nonstandard portal.