DEFORMITIES OF THE KNEE
dr.Mushtaq Talib Hussein
F.I.B.M.S(Ortho.) C.A.B.O(Ortho.)
At growth is completed, the knees are normally in 5–7 degrees of valgus. Any deviation from this
may be regarded as ‘deformity’, there are three common deformities: bow leg (genu varum), knock
knee (genu valgum) and hyperextension (genu recurvatum).
Bow legs and knock knees in children
Bilateral bow leg can be recorded by measuring the distance between the knees with the child
standing and the heels touching; it should be less than 6 cm.
Similarly, knock knee can be estimated by measuring the distance between the medial malleoli
when the knees are touching with the patellae facing forwards; it is usually less than 8 cm.
1- Physiological bow legs and knock knees; bow legs in babies and knock knees in 4-year-olds are
so common that they are considered to be normal stages of development.
2- Compensatory deformities; persistent anteversion of the femoral neck may be associated with
genu valgum.
3- Pathological bow leg and knock knee; unilateral deformity is likely to be pathological. Disorders
which cause distorted epiphyseal and/or physeal growth; these include some of the skeletal
dysplasias ,rickets, injuries of the epiphyseal and physeal growth cartilage and Blount’s disease
(overweight child, walking early, 80% bilateral, more in black race. X-ray shows flattened medial
proximal tibial epiphysis as beak-shaped. Spontaneous resolution is rare, a corrective osteotomy
should be performed).
Treatment in children: usually conservatives by tonics, braces, in the occasional case where, by the
age of 10, the deformity is still marked (i.e. the intercondylar distance is more than 6 cm or the
intermalleolar distance more than 8 cm), operative correction should be advised.
Deformities of the knee in adults
Genu varum and genu valgum:
are common, usually bow legs in men and knock knees in
women. If the deformity is associated with joint instability, this can lead to osteoarthritis of the
medial compartment in varus knees and the lateral compartment in valgus knees.
The causes are:
1- Sequel to childhood deformity.
2- Secondary to arthritis: usually varus in osteoarthritis and valgus in rheumatoid arthritis.
3- Ligament injuries.
4- Malunited fractures,
5- Paget’s disease.
Genu recurvatum (hyperextension
of the knee);
causes:
1- Congenital recurvatum: due to abnormal intra-uterine posture; usually recovers spontaneously.
2- Ligamentous laxity.
3- Chronic synovitis; which lead to overstretching of the ligaments as in rheumatoid arthritis.
4- Rickets.
5- Poliomyelitis and Charcot's disease.
6- Growth plate injuries and malunited fractures.
CHONDROMALACIA PATELLAE
(PATELLOFEMORAL OVERLOAD SYNDROME)
This disorder is a mechanical overload of the patello-femoral joint, commonly has a repetitive load
due to either (1) malcongruence of the patello-femoral surfaces because of some abnormal
shape of the patella or intercondylar groove, (2) malalignment of the lower extremity and/or the
patella, (3) muscular imbalance of the lower extremity and (4) overactivity.
Patello-femoral overload leads to changes in both the articular cartilage and the subchondoral bone;
there may be obvious cartilage softening and fibrillation, with or without subarticular
intraosseous hypertension.
Clinical features
The patient, often a teenage girl or an athletic young adult, complains of pain over the front of the
knee or‘underneath the knee-cap’. Occasionally there is a history of injury or recurrent
displacement. Symptoms are aggravated by activity or climbing stairs, or when standing up after
prolonged sitting. The knee may give way and occasionally swells. It sometimes
‘catches’ but this is not true locking. Often both knees are affected.
On examination; malalignment or tilting of the patellae, quadriceps wasting, fluid in the knee,
tenderness under the edge of the patella and crepitus on moving the knee.
Patello-femoral pain is elicited by pressing the patella against the femur and asking the patient to
contract the quadriceps.
Patellar alignment can be gauged by measuring the quadriceps angle, or Q-angle – the angle formed
by the line of quadriceps pull (a line running from the anterior superior iliac spine to the middle of
the patella) and the line of the patellar ligament. It normally averages 15 degrees and an angle of
more than 20 degrees is regarded as a predisposing factor in the development of anterior knee pain.
Treatment
Conservative management: in majority of patients by adjustment of stressful activities and
physiotherapy, directed specifically at strengthening the medial quadriceps.
Operative management: indicated in;
(1) there is a demonstrable abnormality that is correctable by operation.
(2) conservative treatment has been tried for at least 6 months.
(3) the patient is incapacitated.
Operation is intended to improve patellar alignment and patello-femoral congruence and to
reduce patello-femoral pressure. Various measures are employed: lateral release, with or without
bony surgeries, or patellar ligament elevation procedure or patellectomy.
OSTEOCHONDRITIS DISSECANS
In this disorder; a small, well-demarcated, avascular fragment of bone and overlying cartilage
sometimes separates from one of the femoral condyles and appears as a loose body in the joint. The
most likely cause is trauma, either a single impact with the edge of the patella or repeated
microtrauma from contact with an adjacent tibial ridge. The fact that over 80 per cent of lesions
occur on the lateral part of the medial femoral condyle, exactly where the patella makes contact in
full flexion.
At first the overlying cartilage is intact and the fragment is stable; over a period of months the
fragment separates but remains in position; finally the fragment breaks free to become a loose body
in the joint. The small crater is slowly filled with fibrocartilage, leaving a depression on the articular
surface.
Clinical features
The patient, usually a male aged 15–20 years, presents with intermittent ache or swelling. Later,
there are attacks of giving way such that the knee feels unreliable;‘locking’ sometimes occurs.
The quadriceps muscle is wasted and there may be a small effusion. Soon after an attack there are
two signs that are almost diagnostic: (1) tenderness localized to one femoral condyle; and (2)
Wilson’s sign: if the knee is flexed to 90 degrees, rotated medially and then gradually straightened,
pain is felt; repeating the test with the knee rotated laterally is painless.
Plain x-rays may show a line of demarcation around a lesion in situ.
Radionuclide scans show increased activity around the lesion.
MRI may also allow early prediction of whether the lesion will heal or not.
Treatment
In the earliest stage, when the cartilage is intact and the lesion is ‘stable’, no treatment is needed but
activities are curtailed for 6–12 months. Small lesions often heal spontaneously.
If the fragment is ‘unstable’, i.e. surrounded by a clear boundary with radiographic sclerosis of the
underlying bone, or showing MRI features of separation, treatment will depend on the size of the
lesion. A small fragment should be removed by arthroscopy and the base drilled; the bed will
eventually be covered by fibrocartilage, leaving only a small defect. A large fragment (more than 1
cm in diameter) should be fixed in situ with pins or screws.
OSGOOD–SCHLATTER DISEASE
(APOPHYSITIS OF THE TIBIAL TUBERCLE)
In this common disorder of adolescence the tibial tubercle becomes painful and swollen.
A traction injury of the apophysis into which part of the patellar tendon is inserted (the remainder is
inserted on each side of the apophysis and prevents complete separation).
There is no history of injury and sometimes the condition is bilateral. A young adolescent
complains of pain after activity, and of a lump. The lump is tender and its situation over the tibial
tuberosity is diagnostic.
Sometimes active extension of the knee against resistance is painful and x-rays may reveal
fragmentation of the apophysis.
Spontaneous recovery is usual but takes time, and it is wise to restrict activities.
SWELLINGS OF THE KNEE:
Causes of acute swellings of the knee:
1- post-traumatic haemarthrosis.
2- bleeding disorders as hemophilia.
3- acute septic arthritis.
4- traumatic synovitis.
5- aseptic non-traumatic synovitis as gout or pseudogout.
Causes of chronic swellings of the knee:
a) arthritis as in osteoarthritis and rheumatoid arthritis.
b) synovial disorders as synovial chondromatosis and pigmented villonodular synovitis.
Causes of anterior knee swellings:
1" prepatellar bursitis (Housemaid's knee).
2" infrapatellar bursitis (Clergyman's knee).
Causes of posterior knee swellings:
a- semimembranosus bursa.
b- Popliteal cyst (Baker's cyst).
c- Popliteal aneurysm.