Orthopedics

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Radiologic Case Study 

Your Diagnosis?

Laura W. Bancroft, MD; Jeffrey J. Peterson, MD; Kurt E. Blasser, MD

Abstract

A 61-year-old man presented with a painful right knee. The patient reported instability and restricted motion, which had become progressively worse and painful. AP and lateral radiographs (Figure) of the knee are shown.

Figure: AP (A) and lateral (B) radiographs of the right knee.

For answer click here.

This case illustrates tibial polyethylene liner dissociation and instability after placement of a rotating platform total knee arthroplasty (TKA). Although dissociation of the patellar polyethylene component from its metal backing is a recognized complication with TKA, tibial polyethylene liner dissociation is less commonly reported in the literature.1-5

Radiography is the first (and most often the only) imaging modality used for identification of arthroplasty complications related to the polyethylene components. In this case, the frontal radiograph demonstrates a cemented, unstabilized version of a rotating platform (DePuy Orthopaedics Inc, Warsaw, Indiana). There is mild lateral subluxation of the cemented tibial component and mild genu varum (Figure 1A).

Figure 1: Failed total knee arthroplasty with dislocated rotating platform polyethylene component. AP radiograph demonstrates mild lateral subluxation of the tibial metallic component and mild genu varum. The polyethylene insert (arrows) is narrower than expected and asymmetrically located within the central joint space (A). Lateral radiograph shows marked posterior subluxation of the cemented tibial component and 907 rotation of the polyethylene liner relative to the tibial and femoral components. The posterior aspect of the femoral component rests within the concave polyethylene contour (B).

Upon closer inspection, the hypodense polyethylene liner is narrower than expected and located asymmetrically within the central joint space. The lateral radiograph (Figure 1B) is more impressive, with marked posterior subluxation of the tibial component and spacer.

Ninety degrees of rotation of the polyethylene liner relative to the tibial and femoral components can be appreciated, with contrast provided between the liner and the adjacent joint fluid and soft tissues. Note the posterior subluxation of the tibial component is due to the posterior aspect of the femoral component resting within the concave polyethylene contour. In addition to rotational dissociation of the polyethylene component, as in this case, anterior dislocation of the tibial insert inferior to the patella has also been reported.1

The patient, a 61-year-old man, had a clinical presentation of polyethylene liner dissociation that is typical for others presented in the literature.1,2 He reported pain and a sensation of instability and restricted motion, which had become progressively worse and painful. Clinical examination revealed a stiff-legged gait, mild varus malalignment of the right leg, and sensation of posterior subluxation during gait and arising from a seated position. Patients may also present with knee swelling or gait difficulty.2 Symptoms related to arthroplasty failure may be insidious in onset or acute after a traumatic event, such as a fall.2

The treatment in this particular patient included revision of both the femoral component and tibial insert. At surgery, the polyethylene component was found to be malrotated 90° relative to the femur and the tibial base plate, and subsequently removed. The patient’s flexion and extension gaps were assessed, with the extension gap substantially smaller than the flexion gap even without posterior cruciate ligament removal. The femoral component was then exchanged to a posterior cruciate sacrificing prosthesis with augments, and a posterior stabilized rotating platform polyethylene component was placed. Postoperative imaging demonstrated satisfactory alignment of the revision prosthesis (Figure 2).

Figure 2: Revision total knee arthroplasty. AP (A) and lateral (B) radiographs demonstrate satisfactory positioning of a posterior cruciate sacrificing femoral component and posterior stabilized rotating platform polyethylene component.

Advances in arthroplasty component design have made tibial polyethylene liner dissociation an uncommon occurrence. Polyethylene dissociation is not isolated to any…

The Case:

A 61-year-old man presented with a painful right knee. The patient reported instability and restricted motion, which had become progressively worse and painful. AP and lateral radiographs (Figure) of the knee are shown.

Figure A: Radiograph of the right knee Figure B: Radiograph of the right knee

Figure: AP (A) and lateral (B) radiographs of the right knee.

Your Diagnosis?

For answer click here.















Diagnosis:

Failed Total Knee Arthroplasty With Dislocated Rotating Platform Polyethylene Component

This case illustrates tibial polyethylene liner dissociation and instability after placement of a rotating platform total knee arthroplasty (TKA). Although dissociation of the patellar polyethylene component from its metal backing is a recognized complication with TKA, tibial polyethylene liner dissociation is less commonly reported in the literature.1-5

Radiographs

Radiography is the first (and most often the only) imaging modality used for identification of arthroplasty complications related to the polyethylene components. In this case, the frontal radiograph demonstrates a cemented, unstabilized version of a rotating platform (DePuy Orthopaedics Inc, Warsaw, Indiana). There is mild lateral subluxation of the cemented tibial component and mild genu varum (Figure 1A).

Figure 1A: Failed total knee arthroplasty with dislocated rotating platform polyethylene component Figure 1B: Failed total knee arthroplasty with dislocated rotating platform polyethylene component

Figure 1: Failed total knee arthroplasty with dislocated rotating platform polyethylene component. AP radiograph demonstrates mild lateral subluxation of the tibial metallic component and mild genu varum. The polyethylene insert (arrows) is narrower than expected and asymmetrically located within the central joint space (A). Lateral radiograph shows marked posterior subluxation of the cemented tibial component and 907 rotation of the polyethylene liner relative to the tibial and femoral components. The posterior aspect of the femoral component rests within the concave polyethylene contour (B).

Upon closer inspection, the hypodense polyethylene liner is narrower than expected and located asymmetrically within the central joint space. The lateral radiograph (Figure 1B) is more impressive, with marked posterior subluxation of the tibial component and spacer.

Ninety degrees of rotation of the polyethylene liner relative to the tibial and femoral components can be appreciated, with contrast provided between the liner and the adjacent joint fluid and soft tissues. Note the posterior subluxation of the tibial component is due to the posterior aspect of the femoral component resting within the concave polyethylene contour. In addition to rotational dissociation of the polyethylene component, as in this case, anterior dislocation of the tibial insert inferior to the patella has also been reported.1

Clinical Examination

The patient, a 61-year-old man, had a clinical presentation of polyethylene liner dissociation that is typical for others presented in the literature.1,2 He reported pain and a sensation of instability and restricted motion, which had become progressively worse and painful. Clinical examination revealed a stiff-legged gait, mild varus malalignment of the right leg, and sensation of posterior subluxation during gait and arising from a seated position. Patients may also present with knee swelling or gait difficulty.2 Symptoms related to arthroplasty failure may be insidious in onset or acute after a traumatic event, such as a fall.2

Treatment

The treatment in this particular patient included revision of both the femoral component and tibial insert. At surgery, the polyethylene component was found to be malrotated 90° relative to the femur and the tibial base plate, and subsequently removed. The patient’s flexion and extension gaps were assessed, with the extension gap substantially smaller than the flexion gap even without posterior cruciate ligament removal. The femoral component was then exchanged to a posterior cruciate sacrificing prosthesis with augments, and a posterior stabilized rotating platform polyethylene component was placed. Postoperative imaging demonstrated satisfactory alignment of the revision prosthesis (Figure 2).

Figure 2A: Revision total knee arthroplasty Figure 2B: Revision total knee arthroplasty

Figure 2: Revision total knee arthroplasty. AP (A) and lateral (B) radiographs demonstrate satisfactory positioning of a posterior cruciate sacrificing femoral component and posterior stabilized rotating platform polyethylene component.

Conclusion

Advances in arthroplasty component design have made tibial polyethylene liner dissociation an uncommon occurrence. Polyethylene dissociation is not isolated to any particular manufacturer of arthroplasty components. Despite engineering of monobloc designs such as Anatomic Graduated Component (AGC) TKAs, dissociation of the polyethylene from the baseplate has been reported.5 Radiography remains the primary means to image such complications.

Since the majority of tibial polyethylene inserts do not have radiopaque markers within them, polyethylene dissociation may be overlooked at an early stage. Careful radiographic assessment must be made of the polyethylene components, in addition to the bone-cement and cement-prosthetic interfaces and metallic constructs.

References

  1. Hedlundh U, Andersson M, Enskog L, Gedin P. Traumatic late dissociation of the polyethylene articulating surface in a total knee arthroplasty—a case report. Acta Orthop Scand. 2000; 71(5):532-533.
  2. Davis PF, Bocell JR Jr, Tullos HS. Dissociation of the tibial component in total knee replacements. Clin Orthop Relat Res. 1999; (272):199-204.
  3. Ries MD. Dissociation of an ultra-high molecular weight polyethylene insert from the tibial baseplate after total knee arthroplasty. A case report. J Bone Joint Surg Am. 2004; 86 (7):1522-1524.
  4. Lonner JH, Siliski JM, Scott RD. Prodromes of failure in total knee arthroplasty. J Arthroplasty. 1999; 14(4):488-492.
  5. Poulter RJ, Ashworth MJ. A case of dissociation of polyethylene from its metal baseplate in a “one piece” compression-moulded AGC tibial component. Knee. 2005; 12(3):243-244.

Authors

Dr Bancroft is from the University of Central Florida, Orlando, and Florida Hospital, Orlando, and Drs Peterson and Blasser are from the Department of Radiology, Mayo Clinic College of Medicine, Jacksonville, Florida.

Dr Bancroft is a speaker for the International Institute for Continuing Medical Education and receives royalties from Lippincott Williams & Wilkins. Drs Peterson and Blasser have no relevant financial relationships to disclose.

Correspondence should be addressed to: Laura W. Bancroft, MD, Florida Hospital, 601 E Rollins, Orlando, FL 32803.

DOI: 10.3928/01477447-20090728-47

10.3928/01477447-20090728-47

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