Knee

Question 1

Knee joint

Answer 1

The knee joint consists of the medial and lateral compartments of the tibiofemoral joint and the patellofemoral joint. Although these “joints” are often considered separately, they all communicate with each other as one synovial “knee” joint.

Question 2

Knee surfaces

Answer 2

The surfaces are covered with hyaline cartilage with the retropatellar surface having the thickest hyaline cartilage in the body (a reflection of the load placed on the patella; especially when descending stairs.

Question 3

The tibiofemoral joint

Answer 3

contains the fibrocartilaginous menisci which ensure congruence between the concave femoral condyles and the flattish tibial plateau.

Question 4

The menisci

Answer 4

important “shock absorbers” and act to distribute load evenly.

Question 5

four main ligaments

Answer 5

ithe anterior cruciate ligament (ACL)

the posterior cruciate ligament (PCL)

the two collateral ligaments – the medial (MCL) and lateral (LCL) collateral ligaments.

Question 6

ACL

Answer 6

principal role of the ACL is to prevent abnormal internal rotation of the tibia (although it is clinically tested by assessing anterior translation of the tibia).

Question 7

PCL

Answer 7

The PCL prevents hyperextension and anterior translation of the femur (although it is tested by assessing posterior translation of the tibia).

Question 8

MCL & LCL

Answer 8

The MCL resists valgus force whilst the LCL resists varus force and abnormal external rotation of the tibia.

Question 9

Knee arthritis causes

Answer 9

Early OA of the knee may be predisposed by previous meniscal tears, ligament injuries (especially ACL deficiency) and malalignment (genu varum > medial OA, genu valgum > lateral OA).

Arthritis may also be due to seropositive and seronegative inflammatory arthritis.

Many cases of OA are “primary” OA with no obvious causative factor.

Primary knee OA may have genetic influences and hobbies (eg football, distance running) or occupation may play a role however this has not been conclusively proven.

Patellofemoral dysfunction and instability predispose to the development of patellofemoral OA.

Question 10

Knee replacement in OA

Answer 10

can be considered in a patient with substantial pain and disability where conservative management is no longer effective.

Knee replacements can resurface all 3 compartments of the knee (total knee replacement, TKR) or be a partial knee replacement (unicompartmental knee replacement, UKR or patellofemoral replacement).

Question 11

Risks of TKR

Answer 11

risks of surgery are similar to hip replacement in terms of infection rates, thrombosis and medical complications.

Whilst there is very little risk of joint dislocation compared with hip replacements, there is a higher chance of unexplained pain after TKR (around 15% have moderate pain compared to 5‐10% of THR).

This may be due to the complexity of and reliance upon the tension of the soft tissues around the knee (whereas the hip is not so reliant on soft tissue tension).

Question 12

Meniscal injuries
& Symptoms

Answer 12

twisting force on a loaded knee (eg turning at football, squatting).

patient localizes pain to the medial (majority) or lateral joint line and an effusion develops by the following day.

complains of pain and usually has mechanical symptoms – either a catching sensation or “locking” where they have difficulty straightening the knee with a 15° or so block to full extension.

Patients knees may feel about to give way if a loose meniscal fragment is caught in the knee when walking.

Question 13

True knee “locking”

Answer 13

mechanical block to full extension and is caused by the significantly torn meniscus flipping over and becoming stuck in the joint line.

clinical sign associated with a meniscal tear.

is possible to have a meniscal tear without “locking” if the torn meniscus isn’t sufficiently unstable to flip and become caught in the joint.

Question 14

“pseudo-locking”

Answer 14

Patients with other knee pathologies, such as arthritis, will describe that their knee can “become stuck” with temporary difficulty in straightening the joint.

occurs after rising from sitting and it will either spontaneously resolve or the patient will describe a ‘trick manoeuvre’ that relieves the issue.

distinguished from “locking” by careful history and examination.

It is not a sign of meniscal injury.

Question 15

Meniscal tears

Answer 15

occur due to a sports related injury.

also that around 25% of acute ACL ruptures also have a meniscal tear.

History findings with a torn meniscus are detailed in the previous section.

Question 16

Meniscal tear symptoms & investigations

Answer 16

Clinical exam may reveal an effusion, joint line tenderness and pain on tibial rotation localizing to the affected compartment (Steinmann’s test).

A locked knee with a displaced bucket handle meniscal tear will have a 15° or so springy block to full extension.

MRI will confirm the clinical suspicion.

Question 17

Meniscal tear patterns

Answer 17

longitudinal tears, radial tears, oblique tears and horizontal tears.

Large longitudinal tears may result in a “bucket handle tear” where a large meniscal fragment is able to flip out of its normal position and displace anteriorly or into the intercondylar notch where the knee locks and is unable to fully extend due to mechanical obstruction from the trapped meniscal fragment.

Question 18

Degenerate Meniscal tear

Answer 18

Degenerate meniscal tears can occur as the meniscus weakens with age.

The meniscus can tear spontaneously or with a seemingly innocuous injury.

Degenerate tears tend to have complex patterns with horizontal, longitudinal and radial components.

first stage in many cases of knee osteoarthritis.

tears should be distinguished from acute tears by history and examination (degenerate tears will be Steinmann’s negative

Question 19

Meniscal tear repair

Answer 19

More than 90% of meniscal tears are not suitable for repair.

do not usually heal, the pain and inflammation may settle with time, particularly with degenerate meniscal tears.

knee can also “smooth off” its own meniscus given time.

Steroid injection in degenerate tears may help symptoms in the early period.

In acute tears, if the pain or mechanical symptoms do not settle within around 3 months then arthroscopic partial menisectomy can be performed with around 70‐80% improvement in symptoms.

Knees with degenerate changes on xray (loss of joint space, sclerosis, osteophytes) or MRI (hyaline cartilage loss, bone marrow oedema) are unlikely to benefit from arthroscopic menisectomy as removal of meniscal tissue may increase the stress on already worn / damaged surfaces.

Question 20

ACL rupture

Answer 20

usually occur with a higher rotational force, turning the upper body laterally on a planted foot (leading to internal rotation force on the tibia), often at football, rugby, skiing or another high impact sport.

Question 21

ACL rupture symptoms

Answer 21

A “pop” is usually felt or heard and the patient usually develops a haemarthrosis (an effusion due to bleeding in the joint, in this case from the vascular supply within the ACL) within an hour of the injury and deep pain in the knee.

Chronically, the patient may then complain of rotatory instability with their knee giving way when turning on a planted foot (due to excessive internal rotation of the tibia).

Question 22

ACL rupture investigation & symptoms

Answer 22

Clinical examination with reveal knee swelling (haemarthrosis or effusion) with excessive anterior translation of the tibia on the anterior drawer test and Lachman test.

(Rotatory subluxation may also be demonstrated by the pivot shift test however this needs a relaxed patient and can cause pain and therefore should probably only be performed by a specialist.)

Question 23

ACL rupture primary repair

Answer 23

Primary repair of
the torn ACL is not effective and overall around 40% of patients with ACL rupture end up having a
reconstruction.

Professional sportsmen or women who need to get back to their profession as quick as possible usually proceed straight to ACL reconstruction and those whose knees give way on sedentary activity or those who have a strong desire to get back to high impact sport but cannot do so despite physiotherapy are good candidates for ACL reconstruction.

Question 24

ACL rupture reconstruction

Answer 24

involves tendon graft (usually patellar tendon or semitendinosis & gracilis autograft) being passed through tibial and femoral tunnels at the usual location of the ACL in the knee and secured to the bone.

Intensive rehabilitation is required and it may take up to a year to get back to high impact sports.

Question 25

PCL rupture

Answer 25

in isolation is not common. A direct blow to the anterior tibia with the knee flexed (eg motorcycle crash) or hyperextension may rupture the PCL whilst hyperextension. PCL reconstruction is usually performed for reconstruction of the multiple ligament injured knee. With isolated PCL rupture only those with severe laxity and recurrent instability with frequent hyperextension or feeling unstable descending stairs (with anterior subluxation of the femur) are considered for surgical reconstruction (usually with cadaveric achilles tendon allograft).

Question 26

MCL rupture

Answer 26

Valgus stress injuries (eg rugby tackle from the side) will usually tear the medial collateral ligament (MCL) fairly forgiving knee ligament with healing expected in the majority of partial and complete tears and little or no instability. Patients may have laxity and pain on stress with tenderness over the origin or insertion of the MCL. Acute tears are usually treated in a hinged knee brace. Chronic MCL instability can be treated with MCL tightening (advancement) or reconstruction with tendon graft

Question 27

LCL rupture/ injury

Answer 27

A varus stress injury may rupture the lateral collateral ligament (LCL) with or without damage to the PCL. Treatment of LCL ruptures is usually surgical with early repair or late reconstruction with tendon graft. Patients usually have marked instability on rotational movement (excessive external rotation of the tibia and varus).

Question 28

Knee dislocations

Answer 28

Complete knee dislocations result in rupture of all four of the knee ligaments and have a high incidence of neurovascular injury. They should be reduced as an emergency and may require external fixation for temporary stabilization. Intimal tears can occur which later thrombose and therefore regular checks on the circulation of the foot are mandatory. Any concern with the distal circulation mandates a vascular surgery assessment and vascular stenting or by‐pass may be required. Reperfusion may result in compartment syndrome especially after prolonged ischaemia and fasciotomies may be necessary. Patients usually require multiple ligament reconstruction.

Question 29

Extensor mechanism ruptures

Answer 29

the tibial tuberosity, the patellar tendon, the patellar, the quadriceps tendon and the quadriceps muscles. The patellar tendon or quadriceps tendon can rupture with rapid contractile force which can occur after lifting a heavy weight, after a fall or spontaneously in a severely degenerate tendon. Patellar tendon ruptures tend to occur in a younger age group (<40) with quadriceps tendon rupture in older patients (over 40).

Question 30

Extensors mechanism ruptures Risk factors

Answer 30

history of tendonitis, chronic steroid use or abuse (body builders), diabetes, rheumatoid arthritis and chronic renal failure. Quinolone antibiotics (eg ciprofloxacin) can cause tendonitis and can risk tendon ruptures. Steroid injections for tendonitis of the extensor mechanism of the knee should be avoided due to high risk of tendon rupture.

Question 31

Extensors mechanism ruptures Investigations

Answer 31

assessment of any acute knee injury should include the Straight Leg Raise Test (SLR) to determine if the extensor mechanism is intact. Any doubt requires specialist assessment and investigation. Patients will also usually have an obvious palpable gap in the extensor mechanism and Xrays may reveal a high (PT rupture) or low lying (quads rupture) patella. Partial tears can also occur which may have some extensor mechanism function but reduced power. In obese patients the gap may not be obvious and ultrasound may determine the extent of the injury.

Question 32

Extensors mechanism ruptures Treatment

Answer 32

treatment of complete and substantial partial tears is surgical with tendon to tendon repair or reattachment of the tendon to the patella.

Question 33

Patellofemoral dysfunction

Answer 33

describes disorders of the patellofemoral articulation resulting in anterior knee pain. It encompasses and in many cases is synonymous with various diagnoses including chondromalacia patellae (softening of the hyaline cartilage), adolescent anterior knee pain and lateral patellar compression syndrome. The pull of the quadriceps muscle tends to pull the patella in a slight lateral direction. In some people, excessive lateral force produces anterior knee pain and the lateral facet of the patella is compressed against the lateral wall of the distal femoral trochlea

Question 34

Patellofemoral dysfunction risk factors

Answer 34

Patellofemoral dysfunction is commoner in females (due to wider hips resulting in a more lateral pull of the quadriceps, particularly during adolescence (due to a greater degree of ligamentous laxity). Other pre‐ disposing factors include joint hypermobility, genu valgum and femoral neck anteversion.

Question 35

Patellofemoral dysfunction symptoms

Answer 35

Patients tend to complain of anterior knee pain, worse going downhill, a griniding or clicking sensation at the front of the knee and stiffness after prolonged sitting causing “pseudolocking” where the knee acutely stiffens in a flexed position (in contrast to true locking from a bucket handle meniscal tear).

Question 36

Patellofemoral dysfunction treatment

Answer 36

The vast majority (at least 90%) of sufferers improve with physiotherapy aimed at rebalancing the quadriceps muscles (specifically strengthening vastus medialis obliquus, VMO). Taping may alleviate symptoms Surgery is a last resort with about a 70% success rate and may involve either releasing a tight lateral retinaculum or if there is a relatively lateralized tibial tubercle, a tibial tubercle transfer to aid patellar tracking.

Question 37

Patellar dislocation

Answer 37

can occur with a direct blow or sudden twist of the knee. The patella virtually always dislocates laterally and may spontaneously reduce wen the knee is straightened or rarely may require to be manually manipulated back into position.

Question 38

Patellar dislocation Risk factors

Answer 38

Predisposing factors include ligamentous laxity, female gender, shallow trochlear groove, genu valgum, femoral neck anteversion and a high riding patella (patella alta). The risk of recurrent instability decreases with age and physiotherapy to strengthen the quadriceps may help. The risk of recurrent dislocation after first time dislocation is around 10%.

Question 39

Patellar dislocation investigation

Answer 39

the medial patellofemoral ligament tears and osteochondral fracture - small opacification on Xray. A lipo‐haemarthrosis occurs with characteristic Xray appearance.

Question 40

Patellar dislocation treatment

Answer 40

If recurrent dislocation is frequent, tibial tubercle transfer or medial patellofemoral ligament (MPFL) reconstruction with tendon autograft may help.