The definitive anterior knee pain discussion Part 2: Physical exam and imaging. 0.5 CME credits

So we have taken a look at what anterior knee pain (AKP) is, now let's turn our attention to how to examine for AKP, and what investigations might be helpful... read on!

PHYSICAL EXAMINATION

In 1997, Post outlined four key points in the evaluation and examination of anterior knee pain.

1. Confirm the location of pain.
2. Reproduce the complaint.
3. Evaluate anatomical alignment and flexibility.
4. Locate painful structures.

Developing a routine for examination is one of the keys to making an accurate and expedient diagnosis. 

Comparison of the injured limb with the noninjured limb in unilateral anterior knee pain is a critical reference point. The TOTAPS approach to examination is a key to producing effective routines in examination.
• Talk – already covered in the history, but continue to ask questions and listen to answers.
• Observe – observation commences from the time the patient walks from the waiting room to the office. However a formal appraisal of relaxed stance and walking patterns must be undertaken. Once this has been achieved, the practitioner can search for obvious physical signs of injury, including swelling, redness and spasm.

It is particularly important to remember that anterior knee pain may be referred.

This is especially important in children and adolescents and careful examination of the joints above (i.e. hip) and below (i.e. ankle) are a fundamental principle of all knee examination.

Two important conditions, Perthe’s Disease and Slipped Capital Femoral Epiphysis present as anterior knee pain in adolescents and children. In addition, tight neural structures can contribute to anterior knee pain and careful examination of neural tension with slump testing and straight leg raise testing is critical.

Furthermore, lumbar radiculopathy and peripheral nerve entrapment are possible causes of anterior knee pain in patients or all ages.

Passive range of motion testing – this will include all components of the knee joint and will incorporate gross knee flexion/extension, quadrant patellar range of motion testing, as well as key muscle flexibility testing. It is important to assess patellar mobility for range of motion prior to examination for pain as palpation may cause discomfort and apprehension in the patient and inhibit normal mobility testing.

Comparison of patellar tilt, medial to lateral excursion and superior-inferior glide to the noninjured side is undertaken. Kolowich et al (1990) suggest that medial glide of ¼ or less of the width of the patella indicates tight retinacular structures. Conversely medial glide of ¾ or more of patellar width suggests hypermobility. Comparing superior/inferior glides of the patella gives important clues compared to the noninjured side for those patients who have undergone surgery.

• Touch – palpation of all the structures surrounding the patella is critical. The following should be examined in a step-wise progression;

• Quadriceps tendon
• Central quadriceps tendon insertion
• Vastus lateralis insertion
• Lateral patellar retinaculum
• Patellar tendon, including origin, mid substance and insertion
• Medial retinaculum
• Medial parapatellar plica which is located between the medial border of the patella and the medial femoral epicondyle
• Vastus medialis obliqueus muscle insertion

It is important to match areas of palpated pain to the presenting symptoms. Remember there is a tolerance of discomfort for all these structures and tenderness to palpation does not necessarily equate to an injury. To assess patellar tracking, stabilise the patella centrally and check pain with quadriceps recruitment through a range of 90, 120 and 180 of extension of the knee. Medial or lateral distraction of the patella whilst repeating this test may change pain perception and give an important clue as to the pathomechanics of the condition. 

• Active range of motion testing – this should not only evaluate the active range the injured athlete can achieve through extension and flexion of the knee joint, but every effort should be made to gauge motor control and quadriceps strength. These can be observed with functional testing, for example squats, one legged squat, lunge and step up - step down (Brukner and Khan 1993). The timing of VMO/VL contractions can be estimated, knowing normally they fire simultaneously and act to balance the quadriceps moment acting on the patella (Ramsay 1999). Post (1998) reports the visualisation of early vastus lateralis firing in patients with anterior knee pain.
• Special tests – some of the specific testing for anterior knee pain has already been mentioned including neural tension testing and examination for lumboradiculopathy. Radiographic investigations provide the backbone for other special testing of this condition.

IMAGING ANTERIOR KNEE PAIN

There is no “standard” imaging for anterior knee pain, but its use is primarily to screen for bony, neoplastic, infectious or loose body complications of anterior knee pain. These conditions can usually be excluded with routine knee views i.e. anteroposterior (AP) projection and lateral projection. 

AP projections are taken weight bearing wherever possible and may provide useful early indications of knee joint osteoarthritis. Both AP and lateral views will give good visualisation of bony injury and soft tissue swelling around the knee. 

Imaging of the patellofemoral joint is achieved with the patellar skyline, axial or merchant view. This is commonly used to give some indication of patellofemoral malalignment, however, the axial view is insensitive to this parameter because it cannot be obtained at angles less than 30 where abnormalities are most frequent (Anderson 1998). 

Computed Tomography (CT) is much more sensitive in this regard (Post 1998) and in the case of non-resolving chronic anterior knee pain, axial CT is the imaging of choice.

It should be noted however that radiographic studies beyond plain film imaging are not appropriate until comprehensive nonoperative management has failed.

The skyline view is, however, useful to determine patellofemoral joint space and to exclude rare or unusual conditions of the patella, for example, osteochondritis dissecans. A bipartite patella is a developmental abnormality of the patella where one of more ossification centres of the superolateral corner of the patella remain ununited. Bipartite patella is usually asymptomatic and occurs in a male-female ratio of 9: 1 (Ogden et al 1982). It can occasionally become symptomatic after trauma to the anterior knee. In this instance isotopic bone scanning is useful to confirm bone activity.
Ultrasound and magnetic resonance imaging (MRI) studies are used to investigate for the presence of tendinopathy and bursitis.

Anderson et al (1998) cite the following advantages of US and MRI for bursitis and patellar or quadriceps tendinopathy:
1. They will provide a diagnosis when clinical features are equivocal
2. If there has been a lack of response to the therapy applied, US and MRI will help to make a differential diagnosis
3. US and MRI will assist in defining the type and extend of the tendon change
4. They will provide an accurate pathway for the infiltration of specific bursae with local anaesthetic or corticosteroid.

In our next exciting instalment, we shall take a look at specific conditions causing anterior knee pain!