Abstract
Distal femoral replacement (DFR) is a common limb-salvage option for bone tumors. Postoperative outcomes partly depend on the integrity of the extensor mechanism, yet patellar height and joint line position have not been well studied in oncologic reconstructions.
We retrospectively reviewed 86 patients who underwent modular DFR with rotating-hinge prostheses (1992 to 2024). Demographics, surgical parameters, and functional outcomes were collected, including knee flexion, extensor lag, and Musculoskeletal Tumor Society (MSTS) scores. Postoperative patellar height was assessed with the Insall-Salvati ratio (ISR) and Blackburne-Peel index (BPI). Joint line position was measured relative to the fibular head. Statistical analyses included linear, multivariable, and segmented regression.
The mean ISR was 0.99 ± 0.22, BPI 0.78 ± 0.20, and joint line height was 17.7 ± 6.1 mm. Patellar height was classified as baja (14.0%), pseudobaja (18.6%), normal (59.3%), and alta (8.1%). Higher ISR correlated with greater knee flexion up to 120° (P < 0.001), after which the effect plateaued. BPI was associated with increased knee flexion (P < 0.001) and MSTS score (P = 0.005). A higher number of prior surgeries predicted lower BPI (P = 0.009). Patients who had patella baja demonstrated significantly reduced flexion, higher extensor lag, and inferior MSTS scores compared with other groups (P < 0.05). Joint line position itself was not associated with differences in functional outcomes, although longer resection length and prior radiotherapy were linked to joint line elevation.
Increased patellar height was associated with superior functional outcomes following DFR, while patella baja and pseudobaja were linked to poorer knee motion arc and functional scores. Multiple prior surgeries were associated with decreased patellar height. Careful restoration of the joint line to its proper position, along with prevention of patella baja, may improve outcomes in patients undergoing distal femoral replacement.