Use of distal femur replacement implants in advanced bone defects after multiple bone-damaging revision surgery on the knee joint.
Advanced femoral bone defects (AORI IIb and III defects) in revision arthroplasty of the knee joint.
Persistent or current joint infection, general infection, defect and/or nonreconstructable insufficient extensor apparatus.
Standard access including existing skin scars, arthrotomy, removal of cement spacer if necessary and removal of multiple tissue samples; preparation of tibia first to define the joint line, then preparation of the femur. Determining the resection height of the remaining femur corresponding to the preoperative planning. Gradual drilling using flexible medullary drills and then preparation by femoral rasps. Two stem systems are available for coupling to the distal femur (MUTARS). First there is the standard MUTARS stem (available lengths of 90, 120 and 160 mm); if longer shafts are required, so-called revision shaft (RS) stems are necessary (stems available in 150, 200 and 250 mm). In case of extensive femoral defects extension sleeves in different lengths can be used to reconstruct the femur. After preparation the implant position and the joint line height is checked.
Full weight bearing, in case of existing bony defects possibly partial load of a maximum of 10 kg für 6 weeks; regular wound control; limitation of the degree of flexion only with weakened or reconstructed extensor apparatus.
Between February 2015 and August 2018, a total of 34 distal femurs were implanted. In 19 patients, the implantation was performed after septic and aseptic loosening of a knee prosthesis. All patients had an intraoperative AORI III defect of the femur. Of the 19 patients who underwent a distal femur implantation, 7 had to be revised due to a persistent infection; 4 of these 7 patients had to be revised several times and, finally, had a conversion to a knee arthrodesis. One patient had to undergo a revision with a stem change due to a secondary aseptic loosening of the cemented stem. The mean follow-up period was 11.2 months (range 4-29 months). The follow-up included clinical examination, KSS (Knee Society Score) and X‑ray analysis. A significant improvement in range of motion from 65 ± 16° to 83 ± 14° (p < 0.01) was noted. The KSS improved significantly from 69 ± 9 points preoperatively to 115 ± 15 points postoperatively. Four patients complained of persistent symptoms during exercise after 9 months; femoral shaft pain was denied by all patients. After about 11 months, an implant survival rate of 73.7% was observed in the patient collective.