Patellofemoral Realignment for Arthritis

Frank V. Thomas MD

John P. Fulkerson MD

History of the Technique

Patellar arthritis is all too common in the general population. However, rarely does a primary degenerative process affect only the patella. The chondral abnormalities are usually seen in the face of instability or are secondary to a blunt trauma to the front of the knee causing a breakdown of the cartilage. Instability may be posttraumatic or is seen in a number of anatomic or biologic predispositions. A recent case series review by Nomura and Inoue¹ documented cartilage damage in 67 of 70 patients surgically treated for recurrent patellar instability. Because of the strong association, instability will get considerable mention throughout this chapter. In addition, many of the procedures that have been designed to treat one entity have been found to be effective in the treatment of the other.

Understanding patellofemoral anatomy and kinematics is essential to discerning the physical findings, and when warranted, selecting the correct surgical procedure. There is a complex relationship between the bone and soft tissue structures about the extensor mechanism, but only the osseous morphology and soft tissue stabilizers will be reviewed as they are the areas that can be surgically addressed. This will help in understanding the rationale for surgical decision making.

The facets of the patella consist of the lateral, medial, and odd; while there are only two facets of the trochlea—the medial and lateral. On the axial view of the patellofemoral articulation, the wider lateral aspect of the joint can be appreciated. This is where a majority of the pathology is found. There are two retinacula; a medial one and a thicker lateral one. Their major attachment sites are on the femur, but more distally, they become confluent with the capsule and its meniscal attachments. The medial patellofemoral ligament is part of the medial retinaculum and acts as a vital stabilizer against lateral patellar subluxation. The two retinacula not only function to tether the patella from contralateral displacement, but also act to buttress the patella on their respective sides as indicated by the observation that the lateral retinaculum actually helps to prevent lateral translation.²

Goodfellow et al.³ made great contributions to our understanding of the patellofemoral articulation pattern. In full extension the patella articulates with the supratrochlear fat pad. At 10 degrees, the trochlea is first contacted. The lateral facet aligns at 20 degrees, but the central ridge does not articulate until 35 degrees of flexion is reached. These first 20 degrees are when the patella is most at risk for lateral subluxation.⁴ From an axial standpoint, the initial contact area on the patella is distal. The patellar articulation is through the central third at 45 degrees and ends up proximally at 90 degrees. Up to this point, the contact area involves the central ridge in addition to the medial and lateral facets of the patella, but only at a flexion arc of 135 degrees does the odd facet become involved. This approximate sequence was arthroscopically supported by Sojbjerg et al.⁵

Pathogenesis of Patellar Instability

The focus of this chapter is the treatment of patellar arthritis. As mentioned, this more often than not is seen in patients with instability or malalignment. Patellar instability can present in several ways. For some, it is a traumatic event that can initiate the condition of recurrent instability. The management of acute dislocations is beyond the scope of this chapter, but it should be noted that as many as one half of these patients will have continued instability or chronic pain.⁶ Generalized laxity may be the underlying cause of the instability.⁷^,⁸ It is frequently uncovered in patients whose trauma is apparently trivial in nature, and the individuals will often present with bilateral complaints. A genetic predisposition for this has been suggested.⁹ Fulkerson¹⁰ originally described a pattern of nerve
injury in the peri-patellar retinaculum of some patients with anterior knee pain. Later, Sanchis-Alfonso¹¹ has done considerable work to identify and quantify the neural innervation of the lateral retinaculum, which may account for much of the pain seen in association with patellar instability.

Patellar tilt is a type of malalignment that can usually be detected on physical examination. It is revealed by a relatively tight lateral retinaculum. A computed tomography (CT) study by Dejour et al.¹² demonstrated tilt in 83% of patients with patellar instability.

There is a frequent association between patella alta and patellar instability. This was found to be present in more than a third of patients with anterior knee pain according to a radiographic review by Davies et al.¹³ and was seen in more than half of the patients evaluated by Greenen et al.¹⁴ Trochlear dysplasia, as indicated by a high sulcus angle and a shallow trochlea, was found to be present in a majority of patients in both series. One study suggested that the dysplastic joint may be characterized by a small medial patellar facet and was frequently noted in their series of patients with instability.¹⁵ Dysplasia may have even more of a profound effect on patellar stability than patella alta. We feel that the surgical procedures designed to address these problems (i.e., trochleoplasty, patellar tendon shortening, or tubercle distalization) are not reproducible and carry significant risk of complication.

Ficat¹⁶ first described excessive lateral pressure syndrome (ELPS) in 1978. Insufficient medial or excessively tight lateral restraints leading to lateral instability allow for an increased load to the lateral aspect of the patellofemoral joint throughout the arc of flexion. The result of this process is severe degenerative changes in this region.

Muscle weakness secondary to a pathologic abnormality may also contribute to symptoms in some patients with an unstable patella.¹⁷ This certainly requires further investigation, but probably is one of the inciting factors to a lesser extent.

Indications and Contraindications

History

Taking a careful history is crucial to identifying the problem. Patellofemoral abnormalities can give patients a sense of overall knee instability identical to that seen in anterior cruciate ligament (ACL) deficiency. Without a high index of suspicion, it is possible to overlook the patella as a source of instability and focus on evaluating the ligamentous components of the knee. The same pivoting activities can injure either structure. However, most patients with an actual dislocation will provide an accurate history even when spontaneous reduction occurs.

Sometimes pain is the only presenting complaint. Patients who do not have a history of trauma are occasionally unaware that it is their patella causing their sensation of instability. It is important to ascertain whether the knee is clicking, popping, swelling, or “giving way” without ignoring the patellofemoral joint as a source of these symptoms. At the same time, a snapping chondral lesion may be mistaken for patella subluxation. Identifying exacerbating and alleviating factors will aid in understanding how the problem affects the individual on a daily basis.

Sudden episodes of knee buckling without any forewarning are more indicative of medial than lateral instability. This is critical to note: medial patella subluxation is a complication of previous surgery and may actually be misconstrued as persistent lateral instability.

Physical Examination

Observation should be the initial part of the physical examination. It gives an accurate idea of the severity of the abnormality. Along with monitoring gait, the examiner should also pay attention to the patient’s ability to rise from a chair. A meticulous integumentary examination is vital, particularly looking for evidence of reflex sympathetic dystrophy or subcutaneous neuromas in patients with prior surgeries. Many patients with patellofemoral abnormalities have had previous operations. The size, number, appearance, and location of the incisions should be noted. Close observation may yield muscle atrophy. A large percentage of patients with weakness can be successfully cared for with nonoperative means that include physical therapy, reassurance, and bracing.

A quick examination of the hips will sometimes indicate a degenerative process, which may be the true cause of the knee pain. The internal and external range of motion of each hip and any inequality should be noted. This information, in addition to the lower limb alignment both on standing and during gait observation, can help to identify underlying anatomic abnormalities. Either rotational or angular deformities may account for patellar malalignment and instability. Have the patient stand and perform a single-leg knee bend to discern if there is weakness of hip external rotators, which should be addressed during physical therapy.

Asking the patients to simply squat into a catcher’s position is helpful in evaluating the overall function of the knee. This is an easy and sensitive test that can quickly determine the condition of the patellofemoral joint. An inability to do this, however, can be caused by a variety conditions such as meniscal, articular cartilage, or cruciate pathology. The presence or absence of a “J sign” can also be determined during this maneuver.

Strength evaluation should be part of any lower extremity exam. In addition to the quadriceps muscles, the hip rotators should be looked at since weakness with external rotation can predispose the patella to lateral tracking.

During palpation of the patellofemoral joint, the examiner should try to identify the area of tenderness and at what degree of motion pain is elicited. Crepitus should be looked for. Ascertaining the degree or degrees of flexion where the crepitus is found will give an idea of the location of the
chondral lesions. The soft tissues should not be forgotten since retinacular tenderness may indicate this structure as the primary cause of the knee pain. Patellar tilt may be appreciated by a tight lateral retinaculum. At the same time, insufficient medial restraints may be detected in severe lateral instability. Palpation will define this in a thin individual.

Evaluating patellar tracking is the most difficult part of the exam. First, note whether the patella is starting medially or laterally and then displacing to articulate with the sulcus in flexion or whether the perceived displacement with flexion is actually subluxation out of the sulcus. With the exception of severe instability, every patella will find the groove at some point in flexion. Active extension is also important to observe. The subluxation of the patella may better manifest itself as the knee nears full extension. However, this may be difficult for some very symptomatic patients to achieve.

It is always important to check apprehension in full extension, but, similar to a shoulder evaluation, it should be left for last as it may make the remainder of the examination difficult. Overall ligamentous stability should be determined with particular attention paid to the posterior cruciate ligament (PCL). Chronic PCL laxity frequently presents as anterior knee pain.

Be cognizant of generalized ligamentous laxity as a cause of patellar instability. It is a good idea to quickly evaluate every patient for this condition, which ultimately makes treatment of patellar instability more difficult. Knee, elbow, and metacarpophalangeal hyperextension as well as the ability to touch the forearm with an abducted thumb are quick and easy to perform. Most patients are aware of whether or not they have excessive laxity.

Radiographic Evaluation

Standard x-rays should consist of weight bearing PA and lateral radiographs of the knee as well as a 45-degree axial view. The lateral should not be overlooked as a source of information regarding the patella and its articulation. Patellar height can be determined by looking at several relationships. As a quick matter of reference, an extension of Blumensaat’s¹⁸ line should be at or just below the distal pole of the patella with the knee flexed 30 degrees. However, after using it in a handful of cases, it will become easily understood how inconsistent this reference is. The Insall/Salvati¹⁹ index can be measured by dividing the patellar tendon length by the height of the patella. A measurement >1.2 is abnormal. Because this measurement does not take into account the morphology of the distal femur and the tibial tubercle shape and height can be variable, we prefer the Bernageau²⁰ index. It is a relationship between the distal patellar articular edge and the proximal central trochlea. However, a lateral x-ray in full extension is required for this, which is not a routine part of most knee series. The Blackburne and Peel²¹ method of measuring patellar height is probably the most reproducible. It references the tibial plateau height and the articular portion of the patella, which are more readily identifiable radiographic landmarks. An index >1.06 is considered abnormal. Another advantage is that the degree of flexion can be anywhere from 0 degrees to 60 degrees to obtain this value.

The lateral view can also provide information about the congruence of the joint. With a true lateral x-ray, as indicated by posterior femoral condyle overlap, the medial patellar edge can be viewed in relationship to the median ridge and lateral edge. One study demonstrated a high specificity and sensitivity for determining subluxation and tilt when radiographs were obtained in both flexion and extension.²² Trochlear depth can also be accurately determined if you have a true lateral.²³

The axial view may be obtained at 30 degrees or 45 degrees. Both knees should be included on the same cassette. This should be performed in all patients with patella-related complaints. In the case of an acute dislocation, osteochondral fragments may be seen in the gutters, which may warrant early surgical intervention. The presence and location of any joint space narrowing should be noted. Trochlear and patellar morphology may be evaluated as well as tilt and subluxation, which are quantified by measuring patellar congruence as described by Merchant et al.²⁴ and the sulcus angle. The sulcus angle should be 130 degrees to 137 degrees.²⁵ A sulcus angle greater than 150 degrees is a sign of trochlear dysplasia and has been reported to be present in conjunction with most other radiographic abnormalities.¹³ A congruence angle greater than 16 degrees is felt to be indicative of malalignment. All of these findings will have a definite impact on any planned surgical intervention. One report supported these radiographic indices but was unable to reproduce them when isolated chondromalacia was encountered in the absence of instability.²⁶

Our use of CT scan has decreased over the past decade. Nonetheless, if physical exam and radiographs provide inconclusive results, a CT scan can help to define the anatomy of the patellofemoral joint and may also be useful in documenting rotational abnormalities of the lower extremity.²⁷^,²⁸ Midtransverse patellar axial images at 15, 30, and 45 degrees will demonstrate the articular contact pattern of the patella with regard to its angle of engagement and progression during flexion.²⁹ CT is also excellent for determination of the relationship between the tibial tubercle (TT) and trochlea groove (TG) on the TT–TG relationship.

Patients often present with a magnetic resonance imaging (MRI) report in hand if they have been referred for the evaluation of patellofemoral instability. These are useful in evaluating the condition of the medial patellofemoral ligament (MPFL) or determining the location of a MPFL injury in the case of an acute dislocation.³⁰ The only time we routinely order an MRI in patients with isolated patellofemoral pathology is if we want to evaluate the chondral surfaces or if primary MPFL injury is suspected.

Nonoperative Treatment of Patellofemoral Arthritis

Cowan et al.³¹^,³² have done considerable electromyographic work to support the use of physical therapy as a first line of treatment in patellar instability. Rehabilitation should start at the hip. The focus should not only be on vastus medialis obliquus (VMO) strengthening, but also hip external rotator strengthening. The hip musculature acts as a vital core stabilizer that plays a crucial role in the kinetic chain. Hanten and Schulthies³³ have suggested that strengthening the hip adductors will even assist in selective VMO strengthening. A study of 45 high school skiers found that 73% reported complaints of anterior knee pain that decreased to 35% a year later following a formal physical therapy program.³⁴

There is a growing understanding of the pathologic significance of proprioceptive loss following injury. The patellar taping technique described by McConnell³⁵ may assist in regaining this. As with any other joint, working to correct proprioception should be part of the rehabilitative process.

If instability is present, a trial of bracing should be employed in conjunction with other nonoperative modalities. Some literature does exist to support its use.³⁶^,³⁷ We initiate the use of orthotics early in the treatment course, usually at the first visit. Our preferred brace is the Tru-Pull brace (DonJoy, Vista, Calif.), which has several appealing characteristics. The circumferential neoprene sleeve has a soft rubber lining from top to bottom that provides excellent maintenance of the brace’s position. Patellar control is accomplished by an adjustable C-shaped, sturdy foam pad that comes in two widths to apply focused pressure to the unstable side of the patella. Once the brace is applied, the tension on the parapatellar pad is adjusted using two hook and loop fasteners.

Overall, the nonoperative treatment of patellar arthritis is more likely to be successful in the absence of anatomic abnormalities.³⁸

Surgical Technique

Arthroscopic Evaluation and Chondroplasty

The physical examination will accurately classify the instability pattern in most cases, but the location and extent of degenerative changes is quite difficult to predict, even with diagnostic studies.³⁹ Since this information greatly influences the treatment and prognosis,⁴⁰ we have a systematic method by which we arthroscopically evaluate the patellofemoral joint prior to performing any realignment procedure.

An exam under anesthesia should be obtained, but mainly adds information in patients who are apprehensive. Passive patella tracking can be determined without the interference of patients’ quadriceps activity.

With the patient in the supine position, we apply a tourniquet, but rarely need to inflate it. A circumferential leg holding clamp hinders a suprapatellar approach arthroscopically and is not used if an open procedure or an isolated lateral release is being considered as it can make extreme flexion difficult and interferes with patella tracking. A post for valgus stressing is preferable and figure-four positioning is used for any needed varus moment. In general, varus and valgus stressing as well as rotation should be avoided while observing tracking as these maneuvers can affect the patellofemoral congruity.

The concept of the arthroscopic exam is simple; view the tracking from as many portals as possible and do it several times with the knee both infused and drained of irrigation fluid. An outflow cannula is not used because it is felt to be unnecessary with our equipment, and it may affect the patellofemoral tracking by either tethering the soft tissues or applying direct compression to the patella during flexion. We start with a lateral parapatellar portal. At 60 mm Hg pressure, the distention will cause the patella to make initial contact with the trochlea later in the flexion arc, usually not until 30 degrees to 40 degrees of knee flexion. We strive to observe flexion and extension through both the medial and lateral portals with the knee in neutral rotation while the joint is distended and then again without fluid distention. Observing tracking through a superior accessory portal, either medially or laterally, may be helpful when the findings of the tracking through the standard portals are inconclusive. Viewing through multiple portals will also help to define the size and location of cartilage defects. On occasion some infrapatellar fat pad resection will be necessary to completely visualize the articulation.

To treat chondral damage on the patella we use a shaver to debride loose fragments and may perform a microfracture technique if there is exposed bone. The same philosophy is employed on the trochlear side. Two reports have indicated that the success of articular debridement is greater in cases of posttraumatic chondral lesions,⁴¹^,⁴² but we do not limit the use of chondroplasty to these instances.

Experience with osteochondral resurfacing on the patella and trochea has been favorable in selected cases. Often in combination with anteromedial tibial tubercle transfer, articular resurfacing is important in patellofemoral joint preservation surgery.

Lateral Release

Lateral retinacular release is the most commonly performed and written about method of altering patellar tracking. It can also be harmful. The use of an isolated lateral release, either arthroscopic or open, should be limited to cases of mild instability caused by rotational patella malalignment (tilt). The beneficial effects have been supported by several reports.⁴³^,⁴⁴^,⁴⁵ Patellar tilt is a sign of mild patellar instability and is commonly found in patients who present with anterior knee pain. As mentioned, physical examination is usually accurate and radiographic examination is ultimately diagnostic. On exam, tilt is characterized by a tight lateral retinaculum that prevents anterior displacement of the
lateral facet with the knee in full extension. Furthermore, the lateral retinaculum has been postulated to be a primary source of pain as evidenced by the presence of small nerve injuries and secondary neural growth factors in this region.¹⁰ This may account for some of the improvement following lateral release, which has been documented in a series published by Krompinger and Fulkerson.⁴⁶

The procedure, nonetheless, is overused, resulting in significant morbidity in some situations. Primary medial instability is an absolute contraindication to lateral release. Be aware that trochlear dysplasia may predispose to medial instability postoperatively. A lateral release should also be used judiciously in cases where medial patellofemoral arthrosis predominates as this side of the joint will experience an increase in loading forces following the procedure. Lastly, the results are less predictable when a lateral release has been performed in patients with patella subluxation or, on the other extreme, when there is no evidence of malalignment at all.⁴⁷^,⁴⁸

Technique

In most instances, a circumferential leg holder is not used to allow for ease of knee flexion. A tourniquet is applied but rarely inflated as we prefer to address bleeding immediately and as completely as possible. After a complete arthroscopic evaluation of tilt (Fig. 54-1), tracking, and any areas of chondromalacia, a moment should be taken to define the anatomy of the lateral retinaculum. Debridement of synovial tissue or an enlarged fat pad is sometimes necessary to visualize the distal extent of the retinaculum, which is usually at the level of the lateral parapatellar portal. The vastus lateralis should also be identified to determine the proximal end of the release and should not be violated. Transillumination and palpation will ensure that the quadriceps tendon is avoided centrally.

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