Knee Flashcards
Knee joint
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.
Knee surfaces
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.
The tibiofemoral joint
contains the fibrocartilaginous menisci which ensure congruence between the concave femoral condyles and the flattish tibial plateau.
The menisci
important “shock absorbers” and act to distribute load evenly.
four main ligaments
ithe anterior cruciate ligament (ACL)
the posterior cruciate ligament (PCL)
the two collateral ligaments – the medial (MCL) and lateral (LCL) collateral ligaments.
ACL
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).
PCL
The PCL prevents hyperextension and anterior translation of the femur (although it is tested by assessing posterior translation of the tibia).
MCL & LCL
The MCL resists valgus force whilst the LCL resists varus force and abnormal external rotation of the tibia.
Knee arthritis causes
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.
Knee replacement in OA
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).
Risks of TKR
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).
Meniscal injuries
& Symptoms
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.
True knee “locking”
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.
“pseudo-locking”
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.
Meniscal tears
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.
Meniscal tear symptoms & investigations
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.
Meniscal tear patterns
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.
Degenerate Meniscal tear
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
Meniscal tear repair
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.
ACL rupture
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.
ACL rupture symptoms
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).
ACL rupture investigation & symptoms
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.)
ACL rupture primary repair
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.
ACL rupture reconstruction
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.
PCL rupture
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).
MCL rupture
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
LCL rupture/ injury
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).
Knee dislocations
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.
Extensor mechanism ruptures
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).
Extensors mechanism ruptures Risk factors
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.
Extensors mechanism ruptures Investigations
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.
Extensors mechanism ruptures Treatment
treatment of complete and substantial partial tears is surgical with tendon to tendon repair or reattachment of the tendon to the patella.
Patellofemoral dysfunction
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
Patellofemoral dysfunction risk factors
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.
Patellofemoral dysfunction symptoms
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).
Patellofemoral dysfunction treatment
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.
Patellar dislocation
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.
Patellar dislocation Risk factors
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%.
Patellar dislocation investigation
the medial patellofemoral ligament tears and osteochondral fracture - small opacification on Xray.
A lipo‐haemarthrosis occurs with characteristic Xray appearance.
Patellar dislocation treatment
If recurrent dislocation is frequent, tibial tubercle transfer or medial patellofemoral ligament (MPFL) reconstruction with tendon autograft may help.
