SPECIAL FOCUS: Patellofemoral Problems
Guest Editor: Ronald P. Grelsamer, MD

Patellofemoral Semantics
The Tower of Babel

INTRODUCTION
Our knowledge of the patellofemoral joint lags behind that of other parts of the knee. There are a number of reasons for this:

  • the mechanics of the patellofemoral joint are even more complex than those of other knee structures,
  • until recently, there has been less clinical interest in the patella than in other knee structures such as the meniscus and the anterior cruciate ligament,
  • there are many causes of "patellar pain,"
  • there is disagreement with regard to the correlation between symptoms. physical findings, and radiographic findings. and
  • there is also disagreement with respect as to what constitutes 'normal ."

This relative lack of knowledge is reflected in more variable surgical results compared with the results of other types of knee surgery.

For the field to advance. communication must exist between interested parties. Therefore, progress in the area of the patellofemoral joint will remain limited as long as health-care professionals continue to use terms on which there is little agreement. The same word has different mean ings to different people. and conversely, a concept is given different names in different communities. To make things worse, terms are not defined even in scientific publications.

This leads to confusion and misunderstanding. The confusion cuts across all fields pertaining to the patella: the physical examination, the description of patients' symptoms, diagnostic imaging, and surgical eponyms. The Roux pro-

cedure, for example, means one thing in parts of Europe and another in the United States. Such disagreement seriously limits our ability to communicate-a problem not encountered to this degree in most other area of orthopedic surgery.

As if the orthopedic nomenclature issue were not complicated enough, common words written and pronounced the same way can mean different things in different languages, and this can lead to serious errors of translation. For example, the French word "resume" cannot be translated to "resume" but to "summarize"; "invalidant" means "crippling," not invalidate; and "reparations" means "repair," not reparation (Reparation is what the lawyerseeks when the repair is unsuccessful.)

The issue of nomenclature was highlighted at the first meetings of the PatelloFemoral Study Group in Orlando, Florida, and in Benodet, France. Twenty orthopedists from five countries gave their definition of subluxation.

One of the most commonly used terms; this essentially led to 20 different definitions.

In this review, we would like to take a step toward providing some uniformity of language by highlighting certain terms subject to misinterpretation. Because of the composition of the initial study group, this will be done in English and French, but clearly, this can and needs to be done across the board for all languages. Surely, each reader will think of other such terms, and we welcome all suggestions.

PROPOSED DEFINITIONS OF TERMS
Luxation/Dislocation
This concerns the position of the patella relative to the trochlea. It can reflect:

  • A clinical conditiozl. The patella completely leaves the trochlea and remains in that position. This is a sudden and painful event due to direct trauma or due to a contraction of the quadriceps with the leg inopportunely poSitioned. The condition can be further subdivided into reCurrent (happens repeatedly although not necessarily predictably nor with any specific frequency), habitual (occurs with each flexion), and permanent (the patella is always completely outside the trochlea). The etiology of these various subtypes varies significantly, and this can have considerable treatment implications.
  • A sign on the phvsical examination. As the knee extends from a flexed position, the patella can be pushed laterally to the point where it leaves the trochlea. The patient who knows all too well what is about to happen resists the examiner as the patella starts its exit (known as Fairbank's sign in the United States and Smillie's sign in France).
  • A radiographic sign. The patella is noted to have no contact with the trochlea. There is complete "incongruence."

French and German investigators use the term "luxation" while their English and American counterparts use the term "dislocation." Interestingly, luxation was the English language term used in the mid-20th century. Admittedly, the prefix "dis" does not add much, and the term luxation leads naturally into "subluxation." However, because the term luxation is unfamiliar and confusing to English-language orthopedists, it should be abandoned.

Subluxation
Adding the prefix "sub" to the word luxation implies a minor, lesser form of the full-fledged condition. This is something most people would agree to-even when it comes to the patella. There is disagreement as to whether the term subluxation should be reserved for a clinical symptom, a clinical diagnosis, a finding on the physical examination, or a finding on diagnostic imaging.

  • A clinical symptom. The patient notes giving way that can be attributed to the displacement of the patella. The patient may note that the patella does not smoothly return to its normal position and may describe "slipping." They may also tell of "catching." This is a subjective symptom since the physical examination (with the patient awake or under anesthesia) does not reveal any mechanical block.
  • A finding on the physical examination. The patella occasionally can be seen to slip out of the normal path in a lateral direction when the knee is extended. This is referred to as the "J" sign. In other patients, there is a positive Fairbanks' (or Smillie's) sign (see above) similar to what is seen in patients with a dislocation even though there is only a partial loss of articular contact.
  • A finding on diagnostic imaging, ie, a lateral or medial displacement as seen on an axial view (plain film, computed tomography, or magnetic resonance imaging).

Conclusion. For now, we have agreed to restrict the term subluxation to objective abnormal mediolateral displacement of the patella. This would be abnormal displacement noted on imaging or instrumented testing. Although tilting of the patella could be considered a form of rotational subluxation, the term "tilting" is wellaccepted and should be kept. The patella is considered laterally tilted when the lateral side is down (posterior).

However, it is not so simple.

  • If an element of mediolateral translation is normal. what point does that translation become a subluxation'? This pertains particularly to imaging reports.
  • The patient may have patellar subluxation that is not detected on routine plain films or even routine computerized imaging. This is because we only image the knee at certain degrees of flexion, and the patient is usually supine and nonweightbearing. For subluxation to be evident, the patient sometimes has to be able to contract the quadriceps, and sometimes the foot needs to be held in external rotation. Even then, some forms of subluxation may not be detected.
  • Since the articular cartilage of the patella does not follow the subchondral bone, imaging modalities that do not visualize articular cartilage can over- or underestimate subluxation.

Not all patients who exhibit subluxation actually suffer from this condition. Those who suffer usually do so in only one knee. Does this mean that the patient's subluxation is not the factor that causes symptoms, or is the subluxation simply the predisposing factor, the keg waiting for a spark? If one uses the most liberal definition of "subluxation," then this is indeed a common condition- a condition with a very variable clinical expression.

Conversely, some patients have pain attributable to the patella although there is no (currently detectable) subluxation. Does this point out the irrelevance of subluxation or does this reflect our limited ability to detect all forms of subluxation?

Anterior Knee Pain
Like "chondromalacia," this term is vague. It does not differentiate between pain from malalignment and pain from arthritis, neuromas, tendinitis, loose bodies, and the like. It is best reserved to describe the patient who has yet to be evaluated.

Patellofemoral Pain Syndrome
This term is used by some practitioners who find no identifiable cause of anterior knee pain. As such, it is related to the terms 'anterior knee pain" and "chondromalacia" (see below). Since all pain must have a specific cause, use of the term "patellofemoral pain syndrome" signifies that the practitioner has not been able to determine this cause.

Chondromalacia Patellae
This is a classic example of a term meaning different things to, different people. It literally means "cartilage softening." Used in this sense. it continues to be appropriate. However, because it has other possible meanings, it is best to qualify the term with another term such as "literally" or in the "literal sense." For example, "It appears that the patient has pain secondary to chondromalacia in the literal sense, ie, abnormal softening of the patellar articular cartilage."

To a number of orthopedists and other health-care professionals, the term chondromalacia has come to reflect the vague notion of "pain pertaining to the patella for any number of reasons." In the United States, there is even a specific code for this diagnosis (717.7). Use of the term in this manner is currently frowned on because it encompasses too many separate conditions. For example, a patient may have pain due to severe tilt and lateral displacement of the patella and be told that she has chondromalacia. She then sustains blunt trauma to the knee. She sees a second orthopedist who performs an arthroscopy and notes a cartilage lesion. She is now told that she has developed chondromalacia. But, as far as she is concerned, didn't she already have chondromalacia?

Conclusion. Chondromalacia should not be used to describe a clinical condition. Moreover, it should not be used to describe a cartilage lesion unless one is truly describing abnormally soft cartilage. Even then, the term should be clarified since the reader may have a different understanding of the term.

Description of Cartilage Lesions
If chondromalacia is too confusing to describe a cartilage lesion, what other term should we use? Chondritis? This implies an inflammatory process. Chondrosis? This sounds like an erosion down to bone. Chondropathy? Sounds like a metabolic process.
Conclusion. "Cartilage lesion" remains the best term.

Staging of Cartilage Lesions
Most people refer to grade I, II, III, or IV, but many classifications use these four grades and they do not necessarily refer to the same condition. Grade IV usually implies bare bone in all classifications. The other grades may be based on depth. width, color, and/or texture. A distinction is not always made between degenerative and traumatic lesions.
Conclusion. The practitioner had best clearly describe a lesion rather than simply assign it a grade.

Incongruence
This can loosely be defined as "a lack of fit," but the patella does not have a perfect fit to begin with. In fact, when viewed in the saoittal plane, it is extremely incongruent. In the axial plane, it is already much more congruent, although in the unloaded situation. there is still a gap centrally between the articular cartilage of the patella and that of the trochlea. To make things more complicated, the articular cartilage of the patella does not follow the contour of the underlying bone. For example, the apex of the articular cartilage can be medial or lateral to the apex of the subchondral bone. Therefore, what appears to be bony incongruence on plain radiograph or computed tomography may not in fact be cartilaginous incongruence at all (the same applies to congruence).

As with all the terms described so far. one must be quite specific in the use of the term incongruence.

Maltracking
Maltracking is a dynamic condition, and it would appear to be best suited to a finding on the physical examination. However, since there can be radiological evidence of maltracking, it is not uncommon to see the term used in radiological reports.

The difficulty comes in determining what constitutes maltracking and what simply constitutes a normal variant. This depends on how we define normal. As stated in a prior presentation, we can use "normal" in the statistical sense, in which case something is abnormal if it is beyond two standard deviations. "Normal" can be used to mean "common." Finally, "normal" can be used in the medical sense, ie, not causing pain, death, or disability. Heatt disease and cancer could be considered normal in the "common" sense but they are certainly not normal in the medical sense.

Differing opinions with regard to what is and what is not normal may come in part from different interpretations of the word "normal."

Instability
Like beauty, everyone has an intuitive feel for what it is but has a hard time defining it. Giving way a result of the slipping out of the trochlea is considered a form of patellofemoral instability while buckling secondary to quadriceps atrophy is not. The main controversy centers around whether a patient needs to be symptomatic to exhibit instability.
Conclusion. A patient need not be symptomatic to have patellar instability. If a patient is symptomatic, it should be so stated, ie, "25 patients with functional (symptomatic) instability were followed an average of ..."

Excessive Lateral Pressure Syndrome/Lateral Patellar Compression Syndrome
Introduced by Ficat and Hungerford. the excessive lateral pressure syndrome is a direct translation of the original French term "syndrome d'hyperpression externe." Because it makes no reference to the patella. it has been suggested that the term lateral patellar compression syndrome be used instead. Either way, the term refers to a situation in which the lateral retinaculum is abnormally tight and the patella is tilted laterally (lateral side down and medial side up) whereby imposing abnormally high stresses on the lateral aspect of the patella. The tilt is a clinical finding that, under certain circumstances. can be confirmed radiographically Bony changes can occur about the subchondral bone on the lateral side of the patella, and these can be noted on plain radiograph as well as on computed tomography and magnetic resonance imaging. Lesions on the lateral aspect of the patellar articular cartilage noted at the time of an arthroscopy are also consistent with this diagnosis but are not pathognomonic. One can have lateral patellar compression syndrome without a cartilage lesion. and one can have a cartilage lesion laterally without lateral patellar compression syndrome.

Patellar Glide
This term is commonly used by physical therapists, and it refers to the mediolateral excursion of the patella. Radiologists and orthopedists usually refer instead to displacement or translation.

Posterior Displacement
When viewed in the sagittal plane, the inferior (distal) portion of the patella can be displaced posteriorly. This also could be called "flexion" of the patella. Since the term "posterior displacement" does not in itself make it clear that it is just the distal portion of the patella that is posterior, "flexion" is the better term.

The Roux Procedure
More than 100 years ago, C. Roux described a medial transposition of the patellar tendon. To many Europeans, the "Roux procedure" clearly means just that. To Americans, the name Roux is intimately associated with that of Goldthwait-as in the Roux-Goldthwait procedure. This is a very different operation (the lateral half of the patellar tendon is passed under the remaining portion of the tendon).

CONCLUSION
Traditions are hard to overturn. and it is not realistic to expect health professionals to rapidly change their terminology. Therefore, at the very least, there should be a concerted effort to clearly spell out the meaning of the terms listed above, all eponyms, and any other term that could possibly be misinterpreted.

BIBLIOGRAPHY
Aichroth PM, Cannon WD Jr., Patel DV. Knee Surgery Current Practive. New York, NY: Raven Press; 1992

Dupont JY. Subluxation rotulienne: oú en sommes nous en 1995? Acta Orthop Belgica. 1995:61:155-168.

Fulkerson JP Disorders of the Patellofemoral Joint. 3rd ed. Baltimore, Md. Williams and Wilkins. 1996

Grelsamer RP. The asymptomatic woman's knee - counterpoint. Biomechanics. July-August 1995:33.

Merchant AC. Clinical classification of patellofemoral disorders. Sports Medicine and Arthroscopy Review: 1994;2:211-219.
©1998-2005 International Patellofemoral Study Group