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Complications after MPFL reconstruction

163

these patients still had an average Kujala score

of 92.7 (72-100) indicating that this score is not

sensitive to a minor extensor lag. Smith

et al.

[26] did a comprehensive literature research on

the clinical and radiological results of MPFL

reconstructions. They could only find eight

papers, involving 186 MPFL reconstructions,

which met the criteria of their scoring system.

In only two of these eight papers did the authors

report on the post operative range of motion

and in both there were loss of flexion compared

to the non operated leg. None reported on loss

of active knee extension or extensor lag. Only

one paper, in this review, reported on quadriceps

atrophy with an incidence of 60% not

withstanding a mean Kujala score of 88.6 [7].

Loss of motion after an MPFL reconstruction is

directly related to the tension in the

reconstructed ligament. If it is too tight in

extension (femoral insertion too distal) there

will be an extensor lag although passive full

extension will not be affected. If it is too tight

in flexion (femoral insertion too proximal)

there will be loss of flexion both passive and

active; in this situation the patella might still be

unstable in extension.

Both the gracilis and semitendinosis tendons,

generally used, for reconstructing the MPFL is

stronger and stiffer than the original MPFL

[20]. The strength is a positive factor consi­

dering the underlying predisposing factors

leading to the first dislocation. The stiffness on

the other hand can theoretically lead to overload

in the P-F joint especially in cases where the

reconstructed MPFL is not in the optimal

position.

In our technique of MPFL reconstruction we

try to recreate the normal non isometry of the

ligament so called “favourable anisometry”

[29].

This creates a ligament that is tight in extension

and lax in flexion. There is however the danger

that the ligament can be too tight in extension

resulting in an extensor lag. Post operative

quadriceps inhibition is very common and

should be distinguished from a permanent

extensor lag as a result of an over tight MPFL

reconstruction. At 3 months post operative

follow-up there was on average a 4° (5°-15°)

extensor lag, probably as a result of quads

inhibition, in 45% of our patients. This extensor

lag was however temporary and over the long

term only 4 out of the more than 200 cases had

permanent loss of active full extension which

was caused by an over tight reconstruction in

extension [27].

Elias [8] has shown experimentally that a too

proximal placed femoral position for the MPLF

graft will lead to increased patello femoral load

with potential overload of the articular surface

in the P-F joint. Loss of both active and passive

flexion will also be associated with this. In

techniques where the aim is to have an isometric

reconstructed MPFL, the danger of a having a

ligament that is too tight in flexion is increased.

Femoral insertions near or at the adductor

tubercle, although advocated by some authors,

should be avoided as this will lead to

reconstruction that is too tight in flexion and

too loose in extension [25, 27, 23].

In prevention of motion loss complications

special attention should be given to the

technique of determining the tension in the

reconstructed ligament. Beck showed [2] that

overtensioning can be avoided by applying low

loads to medial patellofemoral ligament recons­

tructions, which reestablished normal transla­

tion and patellofemoral contact pressures. The

aim of the MPFL reconstruction should be to

restore the tension in the MPFL to the same

tension that it had before being torn with a graft

that is stronger than the original ligament. If the

patella of the opposite knee is stable the amount

of transverse patella movement in the

reconstructed patella should be similar to that

of the uninjured knee. This can be achieved

intra operatively by draping both knees and

comparing the amount of transverse movement.

Fithian [13] advises adjusting the graft tension

in such a way that a 5 lb displacing force result

in 7-9mm of lateral displacement of the patella

We recommend that the isometry of the

ligament should be tested till the “favourable

anisometric point” is found by, using a guide

pin in the proposed femoral implantation site.

The “favourable anisometric point” would be a

point where the reconstructed ligament will be