Indications for the use of metaphyseal fixation in revision total knee replacement

In total knee arthroplasty (TKA) revision surgery, surgeons are often faced with periprosthetic bone loss. Bone loss may even be the ultimate reason for the revision, eg, in patients with aseptic loosening. Additionally, removing a prosthetic component may create further defects. The quantity and quality of bone ultimately drives the decision which type of anchorage to choose for the revision prosthesis. Part 1 of the newsletter will explain the different types of bone defects and the treatment modalities available to address them, with a special focus on metaphyseal anchorage.

Bone defect classification

Bone defects are an important challenge faced by surgeons when revising a TKA, because they make it difficult to securely anchor an implant. The level of difficulty depends on the severity and location of the defect. Various techniques have been devised to overcome the problem. A wide range of classifications have been developed to classify bone defects based on size, severity, and location of the defects. Some of them may be used for preoperative planning and to guide treatment.

Glen Purnomo, Orthopaedic and Traumatology Specialist at St. Vincentius a Paulo Catholic Hospital, Surabaya, Indonesia, points out: “There is no perfect classification system that would allow to accurately evaluate bone loss for preoperative planning, provide guidelines for management, have proven intra- and interobserver reliability, and predict outcome. Take the Anderson Orthopaedic Research Institute (AORI) classification, which is currently the most widely used: it does not unequivocally prescribe the method to measure defect sizes, so the evaluation remains somewhat subjective. It also misses to include the patella in the evaluation. While some other classifications clearly define the size of the defect, in practice, the radioopaqueness of the implants pose great difficulties to determine the true size of the defect.” 

Table 1 provides an overview about the most important classification systems with regard to the type of assessment, ie, preoperative or intraoperative, the features taken into account, ie, dimensions, morphology, and implant stability, as well as the possibility to act as guide for treatment [1].

The different classification systems all use similar assessment criteria. For instance, the minimal type in the Rand classification, the small type in the Slooff and Malefijt classification, the type 1 defect in the AORI classification, the uncontained minor type in the Massachusetts General Hospital classification, the type 1 in the Clatworthey and Gross classification, the cystic type in the Huff and Sculco classification, and the cavitary type in the Bargar and Gross classification—all describe a defect that is small and contained, not requiring complex reconstruction. The massive type in the Rand classification, the discontinuity type in the Bargar and Gross classification, the type 3 defect in the AORI classification, the peripheral type in the Dorr classification, the segmental type in the Huff and Sculco classification, the ice-cream type in the Insall classification—all describe severe defects that reach into the condyles and may even affect the integrity of collateral ligaments [2].