Patients outcome after distal femur- and proximal tibia replacement

AIMS AND OBJECTIVES: Mega-knee-arthroplasty are rare and indications are heterogeneous after fracture, tumour and infection. The outcome after distal femur- and/or proximal tibia replacement are unclear. We therefore wanted to analyse the postoperative outcome in case of primary and revision surgery. We hypothesize that I) Implantation of distal femur- and/or proximal tibia replacement are associated with reduced range of motion and function compared to the contralateral side and II) implantation in case of primary surgery is associated with better outcome than in case of revision surgery. MATERIALS AND METHODS: We retrospectively analysed all patients in our trauma department between 1998 and 2017 who underwent a MUTARS distal femur replacement or proximal tibia replacement (Implantcast GmbH, Buxtehude, Germany). We collected general patients’ data, rang of motion, determined the Toronto extremity selvage score (TESS), musculoskeletal tumour society score (MSTS), knee society score (KSS) and Western Ontario MacMaster questionnaire (WOMAC) Score. Knee extension and flexion force was measured. RESULTS: We included 59 patients with a mean age of 65+/-20 years. Out of these we had 19 (32%) male and 40 (68%) female patients. Mean follow up (f/up) was 36+/-57 month (range: 1-218). Indication for R-TKA was periprosthetic fractures (n=14), tumour (n=16), infection (n=10), traumatic fracture (n=14), aseptic loosening (n=3) and pathologic fracture (n=2). Indication for primary implantation was given in 33 (56%) patients and for implantation in case of revision surgery in 26 (44%) patients. Mean TESS was 66+/-33, mean MSTS was 14+/-7, mean KSS was 49+/-30, mean WOMAC was 36+/-26. Mean flexion on the operated side was 83°+/-24° compared to the healthy side (115°+/-20°) (p<0.001). Mean extension force on the operated side at 60° was 20+/-12 (Nm) compared to 77+/-58 (Nm) on the not operated side (p=0.31). Mean flexion force on the operated side at 60° was 32+/-26 (Nm) compared to 53+/-42 (Nm) on the not operated side (p=0.43). In case of revision surgery significant worse function scores in the TESS and KSS could be overserved (both p<0.05). CONCLUSION: Implantation of a distal femur- and/or proximal tibia replacement are associated with loss of flexion, a trend to reduced extension and flexion power compared to the contralateral side. In case of primary surgery better functional results in terms of function Scores can be expected than in case of revision surgery.