The extensor mechanism of the knee consists of the quadriceps muscle and tendon, the patella, the patellar tendon, and the tibial tubercle. Disruption of any of these can lead to an extensor mechanism rupture and render an otherwise perfectly good total knee replacement (TKR) useless. Quadriceps tears associated with TKR are difficult to treat and associated with a poorer prognosis than in the native knee. Transosseous sutures tied over the distal pole of the patella are recommended. Patella fractures may heal in continuity or may involve a disruption of the extensor mechanism. The blood supply may have been compromised during TKR, so healing may be delayed. The patella component may be loose and need to be removed or revised.
Patellar tendon ruptures are the most common and serious form of extensor mechanism rupture. Prevention is more effective than treatment. Careful exposure during revision surgery includes anticipating the need for a quadriceps snip, pinning the tubercle to avoid avulsion, and preserving the fat pad during primary surgery. Treatment of patellar tendon ruptures is challenging. Primary repair may succeed in early intervention, but in established rupture, allograft reconstruction is often necessary. Achilles tendon allograft is preferred. The calcaneus fragment is embedded into the proximal tibia as a new tubercle, and the tendon is sutured into the remaining extensor mechanism. The repair is then protected using a cable loop from the superior pole of the patella to a drill hole in the upper tibia.
The extensor mechanism of the knee consists of the quadriceps muscle and tendon, the patella, the patellar tendon, and the tibial tubercle. Disruption of any of these can lead to an extensor mechanism rupture and render an otherwise perfectly good total knee replacement (TKR) useless.1,2
Quadriceps Tendon Rupture
Degenerative tears are relatively common, and repair is associated with a good prognosis. However, when associated with a TKR, there may have been too deep a patellar cut or damaging exposure, and the prognosis is not as good. Repair to the superior pole may be tenuous and should be reinforced with transosseous sutures tied over the distal pole.
Too deep a patellar cut may lead to patellar fracture, as may a patellar component with a large central peg. The blood supply of the patella may be compromised by a combination of a medial parapatellar arthrotomy, removal of the fat pad, and possibly also a lateral release with injury to the superior lateral geniculate vessels. As in any fracture, poor vascular supply interferes with healing. The patellar component may be loose and need to be removed or revised.3
Small avulsion fractures may be asymptomatic, or, if necessary, small fragments may be resected. Displaced fractures resulting in extensor mechanism rupture require internal fixation with or without patellar component revision. Cannulated screws supplemented by cerclage wire provide good results.
Tibial Tubercle Fracture
Tibial tubercle fracture is an uncommon cause of extensor mechanism rupture. Treatment depends on the degree of displacement and associated lack of full extension. Screws or wires are most commonly used.
Patellar Tendon Rupture
Patellar tendon ruptures are unfortunately common and difficult to treat. The blood supply of the tendon may have been compromised during TKR, especially if the fat pad was removed. Exposure may have been difficult, and partial or complete avulsion from the tibial tubercle may have occurred, especially during revisions. In most revisions, it is advisable to pin the patellar tendon early to avoid accidental avulsion.
Primary patellar tendon ruptures may be treated with simple suture repair, but these may fail. Long-established ruptures require allograft reconstruction.4-6 In either case, protection of the repair using cables from the superior margin of the patella through a drill hole in the proximal tibia should be considered. In this technique, one cable is passed through the tendonbone junction at the upper margin of the tibia, a second is passed through a tibial drill-hole, and medial and lateral tightening continues until the allograft is relieved of stress as the knee is bent. The allograft of choice is an Achilles tendon, with the calcaneus fragment recessed into a prepared bed as a new tibial tubercle. The Achilles tendon acts as a new patellar tendon and is sutured to the extensor mechanism with a progressively advancing nonabsorbable suture.
Prevention of patellar tendon ruptures is important. Anticipate the need for a quadriceps snip during revision surgery. Pin the tubercle early and remove the tibial insert early to release soft tissue tension. Translate rather than evert the patella. Do not remove the fat pad unnecessarily. Recognize the increased risk to the patellar tendon in revisions, patients with prior tibial osteotomy, and increased flexor tone such as stroke or Parkinsons disease, and use cables and prolonged bracing to protect a repair.
- Dennis DA. Extensor mechanism problems in total knee arthroplasty. Instr Course Lect. 1997; (46):171-180.
- Hungerford DS. Management of extensor mechanism complications in total knee arthroplasty. Orthopedics. 1994; 17(9):843-844.
- Bourne RB. Fractures of the patella after total knee replacement. Orthop Clin North Am. 1999; 30(2):287-291.
- Leopold SS, Greidanus N, Paprosky WG, Berger RA, Rosenberg AG. High rate of failure of allograft reconstruction of the extensor mechanism after total knee arthroplasty. J Bone Joint Surg Am. 1999; 81(11):1574-1579.
- Nazarian DG, Booth RE Jr. Extensor mechanism allografts in total knee arthroplasty. Clin Orthop Relat Res. 1999; (367):123-129.
- Emerson RH Jr, Head WC, Malinin TI. Reconstruction of patellar tendon rupture after total knee arthroplasty with an extensor mechanism allograft. Clin Orthop Relat Res. 1990; (260):154-161.
Dr Brooks is from the Cleveland Clinic, Cleveland, Ohio.
Dr Brooks is a paid consultant for Stryker and Smith & Nephew.
Presented at Current Concepts in Joint Replacement 2008 Winter Meeting; December 10-13, 2008; Orlando, Florida.
Correspondence should be addressed to: Peter Brooks, MD, FRCS(C), Cleveland Clinic, 9500 Euclid Ave A41, Cleveland, OH 44195.