Disruption of the extensor mechanism is an uncommon but catastrophic
complication of total knee arthroplasty. We evaluated two techniques of
reconstructing a disrupted extensor mechanism with the use of an extensor
mechanism allograft in revision total knee arthroplasty.
Twenty consecutive reconstructions with the use of an extensor mechanism
allograft consisting of the tibial tubercle, patellar tendon, patella, and
quadriceps tendon were performed. The first seven reconstructions (Group I)
were done with the allograft minimally tensioned. The thirteen subsequent
procedures (Group II) were performed with the allograft tightly tensioned in
full extension. All surviving allografts were evaluated clinically and
radiographically after a minimum duration of follow-up of twenty-four
All of the reconstructions in Group I were clinical failures, with an
average postoperative extensor lag of 59° (range, 40° to 80°) and
an average postoperative Hospital for Special Surgery knee score of 52 points.
All thirteen reconstructions in Group II were clinical successes, with an
average postoperative extensor lag of 4.3° (range, 0° to 15°) (p
< 0.0001) and an average Hospital for Special Surgery score of 88 points.
Postoperative flexion did not differ significantly between Group I (average,
108°) and Group II (average, 104°) (p = 0.549).
The results of reconstruction with an extensor mechanism allograft after
total knee arthroplasty depend on the initial tensioning of the allograft.
Loosely tensioned allografts result in a persistent extension lag and clinical
failure. Allografts that are tightly tensioned in full extension can restore
active knee extension and result in clinical success. On the basis of the
number of knees that we studied, there was no significant loss of flexion. Use
of an extensor mechanism graft for the treatment of a failure of the extensor
mechanism will be successful only if the graft is initially tensioned tightly
in full extension.