Chapter 24
Anterior Knee Pain

with Jenny McConnell and Jill Cook

Anterior knee pain is possibly the most common presenting symptom in clinical sports medicine practice. Two common causes of anterior knee pain in sportspeople are the patellofemoral syndrome and patellar tendinopathy. Patellar tendinopathy was formerly known as patellar tendinitis but this misnomer is progressively falling out of favor (see page XX in chapter 2) [1]. Fat pad impingement is an underdiagnosed cause of anterior knee pain that may mimic features of both patellofemoral syndrome and patellar tendinopathy. Anterior knee anatomy is depicted in Figure 24.1 

In this chapter, we first outline a practical approach to assessing the patient with anterior knee pain, particularly with a view to distinguishing the conditions, and we then detail their management. The chapter concludes with an outline of other causes of anterior knee pain.

24.1 Anterior aspect of the knee
(a) Surface anatomy 

Clinical approach 

Distinguishing between patellofemoral syndrome and patellar tendinopathy as a cause of anterior knee pain can be difficult as their clinical features can be similar. Furthermore, the two conditions may both be present. Both conditions may appear simultaneously as a result of the same biomechanical abnormality or because of overuse, or one may occur first and predispose to the other (see below). The causes of anterior knee pain are listed in Table 24.1.

(b) Anatomy (ADAPTED FROM THE CIBA COLLECTION OF MEDICAL ILLUSTRATIONS REPRODUCED BY COURTESY OF CIBA-GEIGY LIMITED, BASEL, SWITZERLAND. ALL RIGHTS RESERVED)

Table 24.1 Causes of anterior knee pain

History 

There are a number of important factors to elicit in the history of an athlete with general presentation of 'anterior knee pain'. These include the specific location of the pain, the nature of aggravating activities, the history of the onset of the pain, and any associated clicking, giving way or swelling.

Although it is difficult for the patient with anterior knee pain to be very specific in pinpointing the pain, the area of pain often gives an important clue as to which structure is causing pain. For example, medial patellar pain suggests the patellofemoral joint is a likely culprit, predominantly lateral patellofemoral pain indicates excessive lateral pressure syndrome or iliotibial friction syndrome (chapter 25), and inferior patellar pain indicates patellar tendon or infrapatellar fat pad involvement.

The type of activity producing pain also aids diagnosis. Consider two contrasting scenarios that both cause tenderness at the identical infrapatellar site. In one case, precipitating activities involve repetitive eccentric loading of the patellar tendon, such as basketball, volleyball, high, long or triple jumps. This suggest the diagnosis of patellar tendinopathy. On the other hand, if a swimmer presented reporting pain following tumble turning or vigorous kicking in the pool, where there had been no eccentric load on the tendon, but a forceful extension of the knee, the practitioner should suspect an irritated fat pad. The mechanism of injury and the aggravating features are critical to accurate diagnosis.

The onset of typical patellofemoral pain is often insidious, but it may present after an acute traumatic episode (e.g. falling on the knee). The patient presents with a diffuse ache, which may be exacerbated by either prolonged sitting ('movie-goer's knee') or activity. Pain during running that gradually worsens is more likely to be of patellofemoral origin, whereas pain that occurs at the start of activity, settles after warm-up and returns after activity or the next morning is more likely to be tendinopathy. Pain with prolonged sitting is characteristic of the patellofemoral syndrome. Table 24.2 is an aid to clinical differentiation of the patellofemoral syndrome, patellar tendinopathy, and fat pad irritation. As these conditions can coexist, accurate diagnosis can be a challenge.

A history of recurrent clicking may suggest patellofemoral syndrome. A feeling of instability or a feeling that the patella moves laterally at certain times suggests recurrent patellar subluxation. An imminent feeling of giving way may be associated with patellar subluxation, patellofemoral syndrome or meniscal pathology, although actual giving way is usually associated with ACL instability (Chapter 23).

A history of previous knee injury or surgery may be significant especially if associated with an effusion. As a result of the effusion, there is reflex inhibition of the vastus medialis obliquus muscle. This may predispose to the development of patellofemoral pain, as the medial quadriceps may be inhibited before the lateral, which has the potential to set up an imbalance of the soft tissue forces and cause lateral tracking of the patella.

Previous treatment and the patient's response to that treatment should be noted. If treatment was unsuccessful, it is essential to determine whether the failure was due to incorrect diagnosis, inappropriate treatment or poor patient compliance.

Knee swelling is rare in anterior knee pain and as a general rule, it suggests intra-articular pathology. A small effusion, however, may be present with patellofemoral syndrome.

Table 24.2 Comparison of the clinical features of 3 common causes of anterior knee pain. Note that these conditions may coexist.

Examination

During clinical assessment, it is critical to reproduce the patient's anterior knee pain. This is usually done with either a double or single leg squat (Fig. 22.2e). This is important both for diagnostic purposes and to provide a baseline in order to determine the effectiveness of treatment. The clinician should palpate the anterior knee carefully to determine the site of maximal tenderness. Biomechanical examination is important in determining any predisposing factors.

1. Observation
(a) standing (Fig. 24.2a)
(b) walking
(c) supine (Fig. 24.2b)

2. Active movements
(a) knee flexion
(b) knee extension
(c) isometric quadriceps contraction
(Fig. 24.2c)

3. Passive movements
(a) knee flexion/extension
(b) patellofemoral joint
(i) superior
(ii) inferior
(iii) medial glide (Fig. 24.2d)
(iv) lateral glide
(c) muscle stretches
(i) quadriceps
(ii) hamstring
(iii) iliotibial band
(iv) calf

4. Functional tests
(a) squats (Fig. 24.2e)
(b) step-up/step-down
(c) jump

5. Palpation
(a) patella (Fig. 24.2f)
(b) medial/lateral retinaculum
(c) inferior pole of patella
(d) patellar tendon
(e) infrapatellar fat pad
(f) tibial tubercle

6. Special tests
a) examination of knee joint (Chapter23)
(b) examination of hip joint (Chapter 20)
(c) biomechanical examination (Chapter 5)
(d) examination of lumbar spine (Chapter 18)
(e) neural tension tests (prone knee bend, slump test)

Investigations 

Indications for X-ray of the knee in the patient with anterior knee pain include suspected patellar stress fracture, clinical suspicion of bipartite patella or Sinding-Larsen--Johansson syndrome. Skyline views may be used to detect osteochondral damage after suspected patellar dislocation.

As early mild osteoarthritis can sometimes present with insidious onset of knee pain, X-rays are indicated in at-risk athletes, such as older athletes, athletes with past meniscal surgery and those with cruciate insufficiency.Ultrasound or MR imaging both display the patellar tendon well. The presence of hypoechogenicity (US) or high signal abnormality (MR) increases the likelihood that patellar tendinopathy is the diagnosis. However, asymptomatic athletes may have patellar tendons that reveal regions of 'abnormal' imaging.

24. 2 Examination of the patient with anterior knee pain 

(a) Observation -- standing. Observe the patient from the front looking at lower limb alignment including femoral torsion, patellar alignment or any signs of muscle wasting.	(b) Observation -- supine. Observe for lower limb alignment, effusion, position of the patella and any evidence of patellar tilt or rotation.	(c) Active movement -- isometric quadriceps contraction. Performed in extension to assess active patellar movement pattern.
(d) Passive movement -- patellar glide. The patella is passively moved medically (shown), laterally, superiorly and inferiorly and the range and quality of movement is noted. Movement should be compared with the other side.	(e) Functional tests. If the patient's pain has not already been reproduced, functional tests such as squat (as illustrated), lunge, hop, step-up, step-down, or eccentric drop squat should be performed. The practitioner should assess pelvic control while the patient performs a single leg squat and note excessive lateral or anterior tilt.	(f) Palpation -- the patella and the medial and lateral facets are palpated for tenderness. Also palpate the inferior pole of the patella, the patellar tendon attachment and the infrapatellar fat pad.