**2. Primary TKA**

Bone loss observed during primary arthroplasty of the knee is less frequent than during revision surgery. In primary implants causes of bone defect include:


However final cause is always represented by bone erosion, secondary to varus or valgus deformity of the knee; the consequent overload of medial or lateral compartment bring to collapse of the subchondral bone (Tigani et al., 2004).

Typically, in varus knee bone defect contribute to collapse of the medial tibial plateau, firstly in the posteromedial site. Instead, in valgus knee, bone defect may involve the tibia (with a

Management of Bone Loss in Primary and Revision Knee Replacement Surgery 389

First classification of bone defects thus consists on distinction between central forms (with defect confined within the peripheral bone cortex), and peripheral forms (characterized by involvement of the peripheral cortex). In 1991 Rand proposed a classification that considers the percentage extent of the defect into the tibial plateau or femoral condyle, distinguishing

The most common defect is observed in the presence of a varus knee, with defect located in the posteromedial region of the tibia; the lesion is characterized by the presence of an important sclerosis of the subchondral bone and its depth usually doesn't exceed 8 to 10mm. In such simple cases, resection of the tibial plateau allow to completely remove the defect,

Instead, in deeper and more severe lesions, tibial resection of more than 12 mm, could lead to sacrifice important ligamentous structures and has been observed to considerably alters

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

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

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

I *(a/b)* minimal < 50% < 5 II *(a/b)* > 50 < 70% 5-10 III *(a/b)* > 70% < 90% > 10 IV *(a/b)* > 90% > 10

*involvement (%) Depth(mm)*

*Type Single condylar/hemiplate* 

Table 1. Rand classification of bone loss (modified from Rand JA, 1991).

between four grades of increasing severity of the lesion (Rand, 1991) (Table 1).

*a) Intact peripheral rim b) Deficient peripheral rim* 

**3. Revision TKA** 

without requiring further procedures.

osteolytic lesions (Reish et al, 2004).

the defect found intraoperatively.

condyle/plateau (A) or 2 (B) (Table 2,3).

bone quality, thus requiring other options (Laskin, 1989).

contained central defect) and the external femoral condyle, that is defective in the distal and posterior sites (Insall & Easley, 2001) (Fig. 1).

Fig. 1. Usually varus knee appears with bone defect in posteromedial site of tibial plateau. Instead, in valgus knee bone defect usually involves the central part of lateral tibial hemiplateau and the external femoral condyle.



*a) Intact peripheral rim* 

388 Recent Advances in Arthroplasty

contained central defect) and the external femoral condyle, that is defective in the distal and

Fig. 1. Usually varus knee appears with bone defect in posteromedial site of tibial plateau. Instead, in valgus knee bone defect usually involves the central part of lateral tibial

hemiplateau and the external femoral condyle.

posterior sites (Insall & Easley, 2001) (Fig. 1).

*b) Deficient peripheral rim* 

Table 1. Rand classification of bone loss (modified from Rand JA, 1991).

First classification of bone defects thus consists on distinction between central forms (with defect confined within the peripheral bone cortex), and peripheral forms (characterized by involvement of the peripheral cortex). In 1991 Rand proposed a classification that considers the percentage extent of the defect into the tibial plateau or femoral condyle, distinguishing between four grades of increasing severity of the lesion (Rand, 1991) (Table 1).

The most common defect is observed in the presence of a varus knee, with defect located in the posteromedial region of the tibia; the lesion is characterized by the presence of an important sclerosis of the subchondral bone and its depth usually doesn't exceed 8 to 10mm. In such simple cases, resection of the tibial plateau allow to completely remove the defect, without requiring further procedures.

Instead, in deeper and more severe lesions, tibial resection of more than 12 mm, could lead to sacrifice important ligamentous structures and has been observed to considerably alters bone quality, thus requiring other options (Laskin, 1989).
