Knee
Ligament
injuries of the knee
The four major ligaments of the knee (anterior and posterior cruciate,
medial and lateral collateral) maintain its stability and guide its motion. The
anterior cruciate ligament (ACL) provides the major restraint to anterior
translation of the tibia on the femur, and the posterior cruciate ligament (PCL)
to posterior translation. The medial collateral ligament (MCL) resists valgus
deformation but the lateral collateral ligament (LCL) is the weakest of the four
and does little to prevent varus deformity, the majority of restraint coming
from the dynamic input of the iliotibial band. All four ligaments work in close
harmony and injury to one affects the function of the others. The following
combination of injuries is roughly in their frequency of occurrence:
• MCL;
• ACL;
• ACL and MCL;
• PCL;
• PCL and posterolateral structures;
• ACL, MCL, PCL (knee dislocation, rare).
MCL
injury
These occur after a valgus injury, commonly during snow skiing. There is
pain and tenderness localised to the site of injury, usually the midsubstance or
proximal insertion and valgus instability may be elicited. Grade I injuries may
be treated symptomatically; grade Il—Ill should be braced with knee motion
restricted from 10degree to 90degree for 3—4 weeks. Athletes should be warned of ‘tweaking’ pains that
persist for up to a year following MCL injury.
ACL
and ACL-MCL injury
The history of a noncontact injury when the athlete was running and
tried to change direction, felt the knee ‘jump’, heard a pop and developed
immediate swelling is almost diagnostic of ACL injury. If the knee took 2—3
weeks to settle down and the athlete is left with a feeling of, or experiences,
instability then any lingering doubts over the diagnosis can be dispelled.
Clinical confirmation comes from increased anterior tibial translation with the
knee held in 300 of flexion (positive Lachmann test) and abnormal anterior
subluxation of the lateral tibial plateau (positive Pivot shift test). The main
indication for surgery is the recurrent episodes of instability that patients
experience when changing direction or landing from a jump.
ACL
rupture is commonly associated with injury to other structures in the knee.
Meniscal tears are present 80 per cent of the time and unstable meniscal tears
should be repaired at the time of ACL reconstruction. ‘Bone bruises’ visible
on MRI scans represent subchondral oedema and are evidence of impact damage
sustained at the time of injury.
All
patients with ACL injury should undergo an intensive rehabilitation programme,
with special emphasis on hamstring
Surgery
should be delayed until the swelling and range of motion have improved in order
to avoid a painful stiff knee postoperatively (arthrofibrosis). Combination ACL—MCL
injuries should be braced for 3—6 weeks to allow the MCL to heal and then have
the ACL reconstructed.
Techniques
of ACL reconstruction
The child’s ACL usually avulses with a fragment of bone from the
tibia. It is relatively simple to fix this fragment back into the tibia either
with a bone screw or with sutures passed through to the front of the tibia. The
adult ACL tears midsubstance or at the femoral insertion but rarely heals.
Extra-articular
reconstructions
These prevent the abnormal anterior subluxation of the lateral tibial
plateau by re-routing the iliotibial band around the LCL. Whilst they abolish
the pivot shift phenomenon they do not restore normal knee kinematics and the
majority of surgeons no longer uses them routinely.
lntra-articular
reconstruction
Suturing the ends of the ACL back together is only possible in the acute
injury, but the long-term stability of the knee is poor and the technique has
largely been abandoned. The ACL is therefore replaced with a graft placed
through bone tunnels which enter the joint at the sites of attachment. Graft
positioning is critical to the success of ACL reconstruction, and ideally the
graft should not lengthen or shorten by more than 2 mm when the knee is
put through its full range of motion, i.e. it is isometric. Prosthetic
grafts are very attractive because of the lack of donor morbidity and their high
initial strength. However, the early optimism with their use has been dampened
as problems have developed due to particulate debris when the grafts fail. They
are usually only used if a viable alternative is not available.
Allografts
have no donor morbidity but all methods of sterilisation (to prevent disease
transmission) significantly reduce the biomechanical properties and delay the
revascularisation of the graft.
Autografts are the most widely employed at present, the two most common ones being the middle third of the patellar tendon with patellar and tibial bone blocks at either end, and the quadrupled semitendinosus and gracilis tendon graft. These may be secured with interference screws within the bone tunnels or via sutures to screws/posts on the external cortex (Fig. 29.7). The surgery may be performed open or with the arthroscope, drilling the tunnels from within the joint. The modern trend for accelerated rehabilitation permits early weight-bearing without braces, and athletes can return to contact sport 6 months after reconstructions
PCL
injury
Commonly sustained during road traffic accidents from a direct blow to
the front of the tibia, PCL injuries are much less common than ACL injuries
(occurring in a ratio of about 1:10). Examine the patient with both knees flexed
to 900 and you will see the tibia sagging back on the side of PCL injury. The
knee of patients who have a femoral shaft fracture should always be examined to
exclude injury to the PCL.
Isolated
PCL injuries probably do very well if rehabilitated and, as the surgery to
reconstruct them is not as well developed as ACL surgery, nonoperative treatment
is recommended.
PCL
and posterolateral structures