Prosthesis Selection in Hip Revision Surgery: Femoral Prosthesis (Part I)

• Paprosky Type IV Defects

Paprosky Type IV defects are the most complex, involving extensive bone loss in both the proximal femur and the femoral shaft, with no isthmus to provide support. Generally, cementless prostheses are unsuitable for these defects (Figure 1). Occasionally, a tapered biological stem can achieve stability by utilizing the remaining bone in the metaphyseal-diaphyseal junction. Achieving three-point fixation is the best outcome in this situation while expecting stability through osseointegration is nearly impossible. Sporer and Paprosky only recommend using this tapered stem in Type IV defect cases for patients over 65.

*Figure 1: Paprosky Type IV defect, with extensive bone loss in the metaphyseal and femoral shaft, providing no support*

Other reconstruction methods include impaction grafting and APC, similar to Type IIIB defects. If the proximal femur is intact or there is a presence of new bone endosteum, impaction grafting can be attempted. If not, APC or a megaprosthesis (proximal replacement with a distally cemented prosthesis) should be considered.

The advantage of using APC for revision is that it can restore the proximal femoral bone stock in younger patients. However, APC demands higher surgical skills compared to proximal femoral replacement (PFP), and finding a suitable allograft segment matching the patient’s femur can be challenging. Additionally, APC carries a risk of virus transmission (1:500,000). While dead bone can also become an infection site, no evidence indicates a higher bacterial infection risk for APC compared to PFP.

Megaprostheses should be reserved for older patients with lower functional demands and considered a salvage procedure (Figure 2 A-B). These prostheses are easier to implant than APC, reducing surgical time, which is crucial for elderly patients or those with other comorbidities. Although the abductor muscles are attached to the prosthesis, tendon integration on the metal surface is difficult, possibly leading to limping and hip instability. Malkani et al. reported a postoperative pain incidence of 27%, with a 12-year survival rate of 64%. About 48% of patients experienced limping or inability to walk, and 22% experienced dislocation. Constrained liners can be used to prevent dislocation. Postoperative Harris scores improved by over 30 points. Haentjens et al. reported pain relief in all 16 patients after PFP revision, but issues such as intraoperative fractures, dislocations, deep infections, and poor postoperative function remained.

*Figure 2 A-B: Megaprosthesis can be used as a salvage procedure for Type IV bone defects, suitable for elderly, low-demand cases. Constrained liners can be used to enhance stability.*

• Cement-in-Cement Technique

In some cases, direct cemented prosthesis fixation is the most prudent option. For elderly patients who cannot tolerate prolonged surgery and those with aseptic loosening of a primary cemented stem, this method can be considered. Removing all bone cement (PMMA) is challenging, often resulting in fractures or perforations. Extended Trochanteric Osteotomy (ETO) may even be necessary to remove all cement. If the cement mantle remains intact, a polished tapered stem without a collar can be directly implanted (Figure 3 A-B). Before implantation, the original cement mantle should be roughened to increase the contact area between the new and old cement. This method allows for easy adjustment of the stem's orientation, offset, and limb length. Many studies have reported low early and mid-term failure rates with this technique.

*Figure 3 A-B: For elderly or generally unfit patients, consider cementing a polished stem into the existing cement mantle.*