**3. Revision TKA**

Bone loss in revision TKA could always be considered as a consequence of the previous arthroplasty. In these cases, on preoperative radiographs bone loss is often underestimated relative to the true bone loss found during revision surgery. In a retrospective analysis of 31 patients with symptomatic TKAs who had osteolytic lesions confirmed by computed tomography, plain radiography detected only 17% of the osteolytic lesions (Reish et al, 2004).

The final evaluation of bone loss is made more accurately during surgery, after component removal; so that various classification systems used are mainly based on the size and type of the defect found intraoperatively.

Clatworthy and Gross firstly classified defects as contained central forms, and uncontained peripheral forms (with involvement of the peripheral cortical rim), then further distinguishing between intact metaphyseal bone or not (Clatworthy & Gross, 2003). The most practical system is the Anderson Orthopedic Research Institute (AORI) classification described by Engh, that considers bone loss from the tibia and femur independently (T and F) (Engh & Ammeen, 1999); distinction is then made depending on involvement of 1 condyle/plateau (A) or 2 (B) (Table 2,3).

Management of Bone Loss in Primary and Revision Knee Replacement Surgery 391

Main causes of bone loss during revision arthroplasty are stress shielding, wear debris and

 Stress shielding causes an "osteopenic" type of bone loss behind the prosthetic components, due to pressure shielded by the implant and redistributed to the bone-

 Wear debris of polyethylene, cement and metal particles; in contrast to the less common osteopenic type of bone loss seen in stress shielding, wear causes an "osteolytic" type of bone loss, around apparently stable implants (Van Loon et al, 1999). Osteolysis is defined as the periprosthetic replacement of bone by chronic inflammatory tissue without evidence of loosening. This type of osteolysis is more common in young, male,

Implant aseptic loosening resulting in direct mechanical bone loss at the cement-bone

 Iatrogenic damage resulting directly from implant removal, thus representing an important factor in preserving bone stock during revision TKA. Removal of components with no loosening or with an intercondylar box or stems will create large bone defects. Cement should be removed using small sagittal saw and flexible

The objectives of revision surgery include reestablishment of the anatomic joint line, longterm joint stability, and restoration of bone stock with a fast return to full weight-bearing

So that, implant selection should be based not only on the status of the ligamentous and soft

Various options exist to manage bone defects, available in both primary and revision surgery. Indication to whether option to use, depends on knee-related and patient-related

This option is useful when marginal bony defect exist particularly at the tibial side. Nevertheless smaller tibial tray determines lesser contact surface and greater load

The use of cement seems to be applicable in knee arthroplasty, either alone or in combination with screws, but only in cases of relatively small defects (Figure 3). Some authors (Lotke et al., 1991; Ritter et al., 1993) have observed good medium or long term results, while others (Brooks et al., 1984; Freeman et al., 1982; Insall & Ealsey, 2001) had obtained poor ones. Moreover these studies showed that weak biomechanical characters of

So that we currently suggest cement only for peripheral small defects with defect extension of less than 50% of bone surface and less than 5mm of depth. In larger lesions, alone or in

implant loosening; these factors may be interrelated (Lombardi et al, 2010):

osteotomes, avoiding levering which could cause a fracture.

tissue stabilizing structures, but also on the severity and type of bone loss.

**4.1 Translating the prosthetic component away from the bone defect** 

cement do not improve in resistance of the implant with use of support screws.

combination with support screws, it is not recommended.

cement-implant interface;

interface;

and function.

factors.

Implant septic loosening;

**4. Management of bone defects** 

concentration (Figure 2).

**4.2 Cement filling** 

overweight patients with osteoarthritis;

Table 2. Classification of femoral defect (modified from Engh & Ammeen, 1999). Contained defect is considered as a loss of metaphyseal cancellous bone with a significant loss of surrounding cortical support

Table 3. Classification of tibial defect (modified from Engh & Ammeen, 1999).

Main causes of bone loss during revision arthroplasty are stress shielding, wear debris and implant loosening; these factors may be interrelated (Lombardi et al, 2010):


390 Recent Advances in Arthroplasty

**Femoral defect** F1 F2a F2b F3

Table 2. Classification of femoral defect (modified from Engh & Ammeen, 1999). Contained defect is considered as a loss of metaphyseal cancellous bone with a significant loss of

> **Tibial defect** T1 T2a T2b T3

Damaged bicondylar structural bone (noncontained)

Damaged bilateral metaphyseal bone needing augmentation to maintain joint line (noncontained)

Significant bone loss compromising a major portion of the condyles with ligamentous instability (noncontained)

> Significant bone loss compromising a major portion of the plateau, that may involve detachment of the patellar tendon (noncontained)

Damaged unicondylar structural bone (noncontained)

Damaged unilateral metaphyseal bone needing augmentation to maintain joint line (noncontained)

Table 3. Classification of tibial defect (modified from Engh & Ammeen, 1999).

Small amounts of bone loss not compromising component stability (contained, minor defects)

surrounding cortical support

Small amounts of bone loss not compromising component stability (contained)

 Iatrogenic damage resulting directly from implant removal, thus representing an important factor in preserving bone stock during revision TKA. Removal of components with no loosening or with an intercondylar box or stems will create large bone defects. Cement should be removed using small sagittal saw and flexible osteotomes, avoiding levering which could cause a fracture.

The objectives of revision surgery include reestablishment of the anatomic joint line, longterm joint stability, and restoration of bone stock with a fast return to full weight-bearing and function.

So that, implant selection should be based not only on the status of the ligamentous and soft tissue stabilizing structures, but also on the severity and type of bone loss.
