Steve White DM FRCS
Consultant Orthopaedic Surgeon
Robert Jones & Agnes Hunt Orthopaedic & District Hospital NHS Trust
Oswestry
Shropshire SY10 7AG 	 	

INTRODUCTION
Advances in arthroscopy and knee replacement have led to high expectations and unprecedented demand. The knee is the most commonly injured joint and can often be treated conservatively, but many doctors, including consultants, frequently get the diagnosis wrong on first seeing a patient. Accurate identification of patients who need an orthopaedic opinion is needed. The aim of this report is to clarify history-taking and examination of the painful knee and to indicate appropriate management.
THE HISTORY
In acute knee injuries the history is all important. For example 'I felt my knee pop when I landed', is typical of rupture of the anterior cruciate ligament (ACL): examination in such instances is limited due to swelling and guarding. The average delay in diagnosis is over 18 months! In contrast, examination is more revealing in patients with chronic knee problems when the joint is nicely relaxed. Indeed, it is the history which may be misleading. For instance 'my knee gives way, and it locks' more often reflects a patellofemoral disorder than a cruciate or meniscal problem.
The anterior cruciate ligament will tear in many different activities but usually by non-contact twisting mechanisms such as landing awkwardly from a jump, or by a twisting movement with varus or valgus or hyper-extension strain. The lateral or medial meniscus and a collateral ligament may also tear with it. In higher velocity injuries the knee may sublux or even dislocate.
The meniscus is usually torn with a weight-bearing twisting movement which may be a violent event as in a football tackle in a previously normal meniscus of a young patient (< 35 years), or a trivial event as in getting up from crouching in a weakened, degenerate meniscus of an older patient. 
Generalised aching or swelling will suggest a degenerative or arthritic disorder. 
Pain
Ask the patient to show you their knee as they describe the pain. If they point to the tibiofemoral joint margin medially or laterally, the menisci or joint surfaces are implicated. If they put their hand over their knee cap (the 'grab sign') this indicates a patellofemoral disorder.
Swelling
Patients often say their knee swells. This is often an unreliable symptom but if there was an injury it is important to ask whether the swelling appeared within the first 8 hours (haemarthroses are commonly due to ACL rupture) or later which is typical of a torn meniscus.
Locking
Do not bother asking whether the patient's knee 'locks' but ask 'does your knee get stuck in a position so that you cannot straighten it'? With true locking the knee suddenly becomes unable to extend fully. This happens when a torn meniscus is caught in front of the femoral condyle. By wriggling or manipulating the knee the patient may be able to 'unlock it'.
Pseudo-locking is difficulty in bending or straightening the knee from the 90° flexed position due to pain at the front of the knee joint, and this is characteristic of patellofemoral problems. However, occasionally the patient with a posterior horn meniscal tear will describe difficulty straightening the knee when getting up from crouching. This will be distinguished by the site of pain and tenderness at the side of the knee joint, not at the front. If the patient doesn't admit to locking, ask about 'jamming' or 'catching as though something gets caught in the joint' and judge their response.
Giving way
'Does your knee give way?' Reflex relaxation of the quadriceps due to anterior knee pain causes the knee to give way; it is usually partial giving way as opposed to complete giving way which will occur with a patellar dislocation. The main symptom of anterior cruciate ligament deficiency will be giving way but this usually occurs in pivoting situations when the patient turns as in running and changing direction.
Since full examination of the knee is very time consuming and much is irrelevant for an individual patient it is helpful with the history to try and narrow down the problem to one of six likely categories (see Table 1): 
1.	Internal derangement 
2.	Possible torn ligament 
3.	Osteoarthritis 
4.	Anterior knee pain 
5.	Patellar instability 
6.	The rest - the smallest group 
Table 1. The six main categories of knee problems	
1) Internal derangement	Torn meniscus
- bucket handle tear
- Flap tear	Chondral flap
- femoral condyle	Loose body
- chondral loose body
- osteochondral loose body
(eg osteochondritis dissecans)	
2) Possible torn ligament	Anterior cruciate ligament	Medial collateral ligament	Posterior cruciate ligament	Lateral collateral ligament	
3) Arthritis	Varus knee
- medial OA	Valgus knee
- lateral OA	Inflammatory arthropathy
eg rheumatoid arthritis	
4) Anterior knee pain	Anterior knee pain syndrome	Chondromalacia patellae	Lateral compression syndrome	Patellofemoral   osteoarthritis 	
5) Patellar instability	Lateral sub-luxation	Lateral dislocation
- single, recurrent or habitual	
6) The rest	For example, extensor mechanism rupture, cysts, Osgood Schlatter's syndrome, etc	
CLINICAL EXAMINATION
Common to all examinations will be an assessment of alignment, range of flexion, muscle bulk and the presence or absence of an effusion; the rest will be dictated by the category of problem suspected. This can only be done with both lower limbs exposed. 
Signs with the patient upright
Observe the exposed limb with the patient standing and walking. Is there varus or valgus malalignment, does the knee fully straighten, is there a limp?
Signs with the patient on the couch
Ask the patient to show exactly where the pain is felt in the knee. They should then lie flat with only one or two pillows under the head so as to completely relax the hamstring muscles.
Skin
Look at the colour of the skin, observe for sinuses or scars.
Wasting 
Wasting of the quadriceps can be seen with the patient's muscles relaxed or felt with the instruction 'push your knees into the couch' to tense the quadriceps.

Figure 1a
Bursitis of the knee may be:
1. Prepatellar bursitis: common, usually red, obscures patella, easily diagnosed, may also be sympathetic mild knee effusion.
2. Superficial infrapatellar bursitis: common, usually red, easily diagnosed.
3. Deep infrapatellar bursitis: less common, not so red, signs less marked. 
Figure 1b.
Effusions of the knee occupy the entire joint, the suprapatellar pouch extends 3 finger breadths above the patella. 
•	patella is easily palpated. 
•	if it appears in less than 8 hours - most likely haemarthrosis (usually ACL   rupture). Aspirate: if contains fat globules (lipohaemarthrosis) suspect osteochondral fracture. 
•	chronic synovial thickening produces boggy consistency and cross          fluctuation may be absent if knee dry. 	
Swelling
The knee may be swollen because of bursitis, a haemarthrosis or an effusion (Figure 1).
A large effusion of the knee will be obvious. There are three tests for an effusion:
1. The bulge test. A subtle sign of a small effusion. The medial compartment is emptied by pressing on that side of the joint; the hand is then lifted away and the lateral side is sharply compressed; a distinct ripple is seen on the flattened medial surface.
2. The patellar tap. The suprapatella pouch is compressed with one hand whilst the other hand pushes the patella sharply backwards; with a positive test the patella can be felt striking the femur and bouncing off again.
3. Cross fluctuance. A large effusion can be defined by cross fluctuance provided the effusion has not become very tense. 
At this stage it is useful to examine the full range of motion. Stand at the foot of the couch and cup the heels in the palms of one's hands. Do the knees have the normal 2½° to 5° of hyperextension? Is there a block to extension? (Bucket handle tear of meniscus, stiffness due to arthritis).
Ask the patient to flex both knees and compare the range of flexion.
The rest of the examination will be dictated by the history as follows (see Table 1).
1) Internal derangement?
Tenderness
To locate a meniscal or chondral flap, sit at the foot of the couch with the patient's knee flexed to 90°, supporting the sides of the knee with both hands. Palpate around the tibio-femoral joint margin feeling for tenderness of the menisci or joint surface. Be especially careful to feel with the index finger around the back of the medial and the lateral tibio-femoral joint for the common tears of the posterior horns of the menisci. The differential diagnosis is damage to the collateral ligaments which may give rise to joint line tenderness but these injured ligaments will also be painful if they are stretched on varus or valgus stress tests.

Figure 2. McMurray test.
Span the knee joint with your hand so that the thumb can feel one side of the tibio-femoral joint line, the palm sits across the patella and the middle finger palpates the other side of the tibio-femoral joint. In this way, as the knee is rotated by the other hand and extended one can distinguish painful clicking which arises from the medial meniscus, the lateral meniscus and the patello-femoral joint.	
McMurray test 
In this test for a torn meniscus the flap tear can be trapped between the articular surfaces and then snapped free with a palpable and/or audible click (Figure 2). The test is repeated, altering the varus or valgus stress on the medial or lateral side respectively, feeling and listening for a click. A chondral flap may mimic a torn meniscus.
2) Possible torn ligament
Medial collateral ligament
The medial collateral ligament is usually stressed with the knee slightly flexed to relax the posterior capsule. A grade 1 injury is pain but no instability (ie, mild tear). Grade 2 is a little valgus laxity compared to the good knee (ie, severe tear) and grade 3 is gross valgus laxity (often associated with an anterior cruciate ligament injury).
Lateral collateral ligament
The lateral collateral ligament is tested by holding the joint in extension with the ankle tucked under one arm and both hands holding the knee and lower femur. The joint is stressed into varus. Any movement in this plane is abnormal. 
The cruciate ligaments 
The tibial sag test for posterior cruciate ligament injury is shown in Figure 3. First ask the patient to flex both knees to 90° and observe the profile of the tibial tuberosities with respect to the patella above and the front of the shin below. If the posterior cruciate ligament is ruptured then you will observe posterior sagging of the tibia.

Figure 3. Tibial sag test. If the knee feels lax always examine both joints at 90° of flexion. The upper tibia sags posteriorly after the PCL ligament has been damaged.	
Anterior and posterior draw tests. Now, gently sit on the foot to anchor it and using both hands the upper tibia is grasped firmly and rocked backwards and forwards. Excessive posterior glide signifies posterior cruciate laxity. Again, compare both knees.

Figure 4. Lachman test.Compare anterior movement of the tibia relative to the femur for both knees. Increased laxity on this test is nearly always due to ACL rupture and best measured at 20°-30° of flexion whereas the PCL is best examined at 90° of knee flexion.	
Lachman test for ACL rupture (Figure 4) 
With the knee at 20° of flexion, grasp the thigh just above the knee in one hand and the tibia just below the knee in the other, gently rock the knee to and fro (in the sagittal plane) to encourage the muscles to relax and then pull the tibia firmly forward with one hand relative to the femur which is stabilised by the other hand. If there is excessive anterior displacement compared to the uninjured side (positive Lachman test), then the ACL is stretched or ruptured. Not only does one feel more movement but the end point feels soft when the anterior cruciate ligament is completely ruptured. A well defined end point is felt in the intact knee or when the ligament is only partially ruptured or reattached to the PCL. Again, compare both knees. 
3) Arthritis 
Most cases of osteoarthritis are associated with varus deformity of the knee. Early in the disease there is a block to full extension and some restriction of flexion. The quadriceps muscles waste, the knee usually has a small effusion and palpation of the joint margins reveals tenderness and/or osteophytes. The diagnosis is confirmed by x-rays with the instruction 'weight bearing antero-posterior view and lateral x-ray of knees'. In the early disease form, anteromedial osteoarthritis, there is a correctable varus deformity, intact cruciate ligaments and a good lateral compartment. For these patients unicompartment knee replacements may offer a more conservative approach than total joint replacement. 
Less commonly, valgus deformity of the knee will be seen in association with lateral compartment osteoarthritis. Such deformity is more common in inflammatory arthritides such as rheumatoid disease. Look for signs in the hands. Osteophytes of the distal interphalangeal joints (Heberden's nodes) occur with osteoarthritis, and deformity of the metacarpophalangeal joints and proximal interphalangeal joints suggests rheumatoid arthritis.
4) Anterior knee pain
Anterior knee pain is rather analogous to low back pain:
a. It is very common.
b. It rarely requires surgery.
c. The symptoms are often out of proportion to the demonstrable pathology and may mimic other knee disorders.
Anterior knee pain syndrome
During the teenage years, pain is common at the front of one or both knees, particularly after sport. Symptoms are made worse by squatting, jumping, descending stairs, sitting with the knees flexed, and relieved by straightening the legs, resting the feet on a sofa or foot stool. Pain is felt at the front of the knee joints and not at the medial or lateral tibio-femoral margins. Examination will be normal apart from pain on compression of the patello-femoral joint. There may be tenderness behind the margins of the patella.
Seven out of eight patients gain resolution by 21 years of age - no operation can beat this prognosis. Therefore, conservative treatment is probably indicated; an arthroscopy is seldom required. Reduction of precipitating sporting pursuits for a school term usually helps and reassurance and patience is required.
Chondromalacia patellae
Seldom is any physical abnormality found in knees with anterior knee pain syndrome at arthroscopy but, over the age of 21, patients with a similar pattern of symptoms may have visible signs of chondromalacia, ie, softening or fibrillation of the cartilage on the under surface of the patella. Again conservative treatment is called for. A physiotherapist interested in knees will help but a response to treatment will usually take 6 months.
There is a variant called lateral compression syndrome. Throughout the range of 0° to 40° of flexion, observe and palpate the tracking of the patella relative to the trochlea. A band may be felt tightly pulling the patella over laterally and tilting the patella. Such cases will show patellar tilt on MRI or CT arthrography. If no response is made to physiotherapy after 6 months then surgical lateral release may be considered: an abnormal fibrous band can be divided by arthroscopic or open techniques.
The relationship between chondromalacia patellae and patello-femoral osteoarthritis is controversial: some argue it is only a matter of time before the former evolves into the latter. 
5) Patellar instability
Usually there is a clear history of a dislocating episode and often there is x-ray evidence. In lesser cases carry out the patella apprehension test. Start with knee extended, gently pushing the patella laterally. The knee is then slowly flexed thus reproducing the mechanics of patella dislocation. Even slight flexion may induce anxiety and resistance to further flexion.
In recurrent dislocation of patella there may be: 
1.	Generalised ligamentous laxity. 
2.	Anatomical abnormality of the patella (small, high patella) or an abnormal lateral femoral condyle (shallow trochlea). 
3.	Valgus deformity of the knee. 
6) The rest
There are of course dozens of less common disorders of which a few examples should be mentioned:
Osteochondritis dissecans
A small osteocartilaginous fragment sometimes separates from the medial femoral condyle and appears as a loose body in the joint. It presents with aching or swelling or giving way and/or locking. Usually x-rays show the defect and/or the fragment. In teenagers referral is required. 
Osgood-Schlatter's disease
An apophysitis chronic traction strain of the insertion of the patellar tendon into the tibial tuberosity produces a painful lump at the tibial tuberosity which usually responds to rest. If an x-ray shows an independent ossicle behind the main body of the tendon then surgical removal may be helpful after skeletal maturation.
Meniscal cysts
A small lump may appear at the side of the knee joint, usually laterally. It is nearly always associated with a torn meniscus. The meniscus can be inspected arthroscopically and the cyst dealt with at the same time.
Baker's cyst
A fluctuant swelling in the back of the knee must be distinguished from a popliteal aneurysm which pulsates. Occasionally synovial herniation leaks into the calf causing sudden pain and swelling suggestive of a deep vein thrombosis. Reassurance is the mainstay of treatment for it is benign, often resolves spontaneously and is rarely seriously symptomatic. Removal is seldom indicated because a scar at the back of the knee is itself liable to be sore; recurrence is common and there are risks involved in operating around the nerves and blood vessels at the back of the knee!
Prepatellar bursitis, infrapatellar bursitis (Figure 1)
These should be distinguished from knee effusions.
Pes anserinus bursitis
This inflammation occurs just below the antero-medial joint line.
Extensor mechanism rupture
Beware of the patient who cannot extend the knee due to an extensor lag. There may be little history of trauma but degeneration of the quadriceps tendon or the patellar tendon can lead to gradual ripping of the extensor mechanism and it usually presents late because it is missed. It requires urgent surgical reconstruction to avoid permanent giving way of the knee joint. The inability to extend the knee and a palpable gap compared to the other knee provide the diagnosis.
MANAGEMENT
Patients often present with relatively mild non-specific problems of the knee joint. Usually, in trauma, the pain is at the front; the patellofemoral joint is affected. In such cases conservative treatment is first indicated. Consider: 
1.	Rest 
2.	Non-steroidal anti-inflammatory medication 
3.	Physiotherapy 
4.	Walking aids where appropriate 
If after a period of time, say 6 weeks, significant symptoms persist, or the condition is obviously more serious from the start, then an orthopaedic opinion may be warranted. Orthopaedic operations are of three main types: 
1.	Arthroscopy 
2.	Arthroscopy assisted 
3.	Open surgery 
Is it worth sending the patient for surgery? I think one can have varying orders of confidence with which one can recommend surgery (Table 2).
With the first order operations a high degree of confidence of cure can be expected (greater than 90% success rate). The second order of operations depend not only on a high degree of specialist surgical skill but also on careful patient selection. Increased emphasis is now being placed upon supervision and training of surgeons by the Royal College of Surgeons, particularly with arthroscopy courses. Anterior cruciate ligament reconstruction can have at least an 80% success rate using autogenous tissue but prosthetic ligaments usually result in failure within 5 years and are now rarely performed. Third order operations are still more controversial with very few surgeons claiming good results at the present time. Diagnostic arthroscopies are rarely required nowadays as clinical examination with or without MRI will usually enable a decision to be made about surgery.
Table 2. Types of knee surgery	
1st order operations
Arthroscopic partial meniscectomy or repair
Arthroscopic removal of loose bodies
Total knee replacement	
2nd order operations
Anterior cruciate ligament reconstruction
Unicompartmental knee replacement
Arthroscopic debridement for early osteoarthritis
High tibial osteotomy
Lateral release for patellofemoral disorders	
3rd order operations
PCL reconstruction
Patellofemoral joint resurfacing
Chondral resurfacing
Prosthetic ligament reconstruction	
CONCLUSION
Technical advances in investigations and surgery are of little value without good clinical skills. It is hoped that this report will encourage clinical examination to be carried out with greater confidence.
© Arthritis Research Campaign 1997	6340-PP10 	
This publication has been made possible because of voluntary donations given to the Arthritis Research Campaign.