Chronic Extensor Mechanism Disruption Following Revision TKA

    A 65-year old female presents with a severe extensor lag following 3 revision knee surgeries. She has also failed a direct repair of her patellar tendon and has undergone an irrigation and debridement for suspected periprosthetic joint infection. What is the best option to manage this patient?


    Anthony J. Boniello, MD; P. Maxwell Courtney, MD; and Scott M. Sporer, MD


    The authors have no disclosures relevant to this article.


    Extensor mechanism disruption is a rare but catastrophic complication following total knee arthroplasty (TKA), with an incidence ranging from 1% to 12% in the literature. [1]

    Although some older and lower-demand patients may be treated non-operatively with a brace, almost all patients require surgical treatment to maintain active extension of their knees. Unfortunately, results have been historically poor. Although direct repair of extensor mechanism injuries has been described, complication rates approach 50% in some series. [2-5]

    Extensor mechanism allograft reconstruction has been studied, but results have been mixed.  Some studies demonstrate high patient satisfaction, [6] while others report failure rates of up to 40%. [7-9] In addition, surgeons have concerns about infection and development of an extensor lag with the use of allograft. The use of synthetic mesh has also been described for treating extensor mechanism injuries, with comparable intermediate-term results. [10]

    These injuries, therefore, continue to pose a management dilemma for the patient and the orthopaedic surgeon. In this article, we present a case of a patient with an extensor lag following multiple revision knee surgeries and a failed attempt at a patellar tendon repair.

    Case Presentation

    A 65-year old female patient presented to clinic with left knee pain and instability that had worsened over the past year. She was unable to navigate stairs, her knee constantly buckled while ambulating, and she now needed a walker at all times. Her history was significant for hypertension and controlled type 2 diabetes mellitus.

    She underwent a primary left TKA in 2004, 2 revisions for presumed aseptic loosening, and finally a patellar tendon repair with revision of her tibial component to a fully cemented stem in 2014. Two months, later she also underwent an irrigation and debridement with a polyethylene liner exchange and was treated with antibiotics for 6 weeks.

    Physical Exam

    • Height: 5 feet, 6 inches; weight: 260 pounds; BMI: 42 kg/m2
    • Well-healed anterior midline incision
    • 40° extensor lag with flexion to 95°
    • No appreciable effusion
    • Significant anteroposterior laxity in flexion
    • Palpable pedal pulses

    Laboratory Tests

    • Erythrocyte sedimentation rate: 18 mm/hour
    • C-reactive protein: 1.2 mg/L
    • Knee aspiration: 1100 white blood cells, with 48% neutrophils
    • Cultures: No growth at 3 days


    Figure 1. Radiographs from 2012 following the patient’s second revision surgery.

    Figure 2. Radiographs done on presentation to our clinic demonstrating patella alta, suture anchors from prior patellar tendon repair, a fully cemented tibial steam, and elevation of the joint line.


    • Chronic extensor mechanism disruption with flexion instability following revision TKA


    Several considerations are relevant in the management of this patient:

    • Should we use an extensor mechanism allograft or a synthetic mesh for reconstruction of her patellar tendon?
    • The tibial component is well-fixed; can we revise the femur only by lowering the joint line, upsizing the femoral component, and achieving more stability in flexion?
    • If we decide to revise the tibial component, what is the best method for removing the fully cemented stem?
    • What level of constraint would be needed following extensor mechanism allograft? Will she need a hinge to protect the reconstruction?
    • Because the patient already has a history of periprosthetic joint infection, should we even offer her sugery, given the high risk of recurrent infection?  

    After carefully discussing the risks and benefits of surgical treatment with this patient, including her elevated risk for infection, we decided to proceed with a revision arthroplasty and extensor mechanism allograft reconstruction.


    • We removed the femoral component with minimal bone loss, removed the cement, and attempted to trial a larger-size femur after distalizing the joint line with augments. The tibial polyethylene liner was already at the largest size for the implant we were using.
    • Because the patient was still grossly loose in flexion, the decision was made to revise the tibia as well.
    • To remove the well-fixed, fully cemented stem, we extended our trough with a micro-sagittal saw for the allograft bone block distally, which acted functionally as a tibial tubercle osteotomy (Figure 3).
    • Through the long trough, we were able to use a burr around the stem to facilitate cement removal. The tibia was then removed.
    • A correctly sized, ipsilateral, fresh-frozen proximal tibial allograft with attached extensor mechanism was prepared on the back table. Care was taken to appropriately measure and match the length of the tubercle trough.
    • We used metaphyseal cones for additional fixation on both the femur and the tibia.
    • The tibia had severe bone loss from prior revisions. Only a 10-mm block augment is available for the hinged prosthesis we were using, so we added a cemented 10-mm augment from the older revision system and used a metal cutting burr to correctly shape the augment.
    • We decided to use a hinged prosthesis for 2 reasons: to correct flexion-extension mismatch and to prevent anterior translation of the tibia to protect the allograft reconstruction.
    • We placed 16-gauge wires before the tibial component was cemented (Figure 3) so that the wires could be tightened around the stem.
    • After reaming the canals to determine the appropriate stem size and trialing the knee to determine stability, the components were cemented into place.
    • The allograft was placed in the trough and secured using the 16-gauge wires with 3.5-mm screws (Figure 4). The graft was then tightened in full extension and oversewn the quadriceps tendon. The patella was not resurfaced.
    • Postoperative images are shown in Figure 5.
    • The patient was immobilized in full extension for 6 weeks.

    Figure 3.  A long tibial trough was created with a micro-sagittal saw to facilitate tibial component removal and to place the bone block from the allograft.

    Figure 4.  Intraoperative photo shows the allograft secured into place with a combination of 16-gauge wires and 3.5-mm screws.

    Figure 5.  Postoperative radiographs following revision to a hinged prosthesis and extensor mechanism allograft reconstruction.

    Postoperative Follow-up

    At 6 months after surery, the patient is doing well with only a residual 5° extensor lag.  She ambulates with the use of a cane, but is pain-free, pleased with her stability, and has flexion to 95°.

    Surgical Pearls

    • The authors prefer to use synthetic mesh to augment acute extensor mechanism injuries and an extensor mechanism allograft for chronic injuries.
    • Consider the use of a tibial tubercle osteotomy to help with exposure and facilitate cement removal when explanting a well-fixed long cemented stem.
    • Place the 16-gauge wires posterior to the stem to allow for tightening over the prosthesis instead of over weakened metaphyseal bone. This will help prevent proximal migration of the allograft bone block.
    • If revising the knee at the time of allograft reconstruction, a hinged prosthesis should be used to prevent anterior tibial translation and protect the repair.

    Author Information

    Anthony J. Boniello, MD, is an orthopaedic resident in the Department of Orthopaedic Surgery at Drexel University, Philadelphia, Pennsylvania. P. Maxwell Courtney, MD, is an Assistant Professor of Orthopaedic Surgery at Thomas Jefferson University Hospital and attending surgeon at The Rothman Institute, Philadelphia, Pennsylvania. Scott M. Sporer, MD, is an Associate Professor of Orthopaedic Surgery at Rush University Medical Center and attending surgeon at Midwest Orthopaedics at Rush, Chicago, Illinois.

    Adult Reconstruction Section Editor, Rothman Institute Grand Rounds

    P. Maxwell Courtney, MD


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