How coronal alignment affects distal femoral anatomy: an MRI-based comparison of varus and valgus knees.

PURPOSE: In contemporary total knee arthroplasty (TKA), most often, the goal is to align the femoral component to the epicondylar axis (EA). The posterior condylar axis (PCA) is easier to define than the EA, and thus the relationship of PCA to the EA is then used instead to align the femoral component to the EA. However, the relationship of PCA to EA is not constant and has been reported to differ between varus and valgus knees and with increasing deformity. The aim of this large MRI-based study was to evaluate the relationship between PCA and EA with varying coronal deformity especially with increasing valgus deformity. METHODS: EA, PCA, AP (Whiteside's line) and the mechanical axis were obtained from 474 magnetic resonance imaging (MRI) scans used to create patient-specific instrumentation (PSI) for the Biomet Signature (Warsaw, NJ) system. RESULTS: The relationship of EA relative to the PCA showed considerable heterogeneity in both varus and valgus groups. In the valgus group, there was statistically greater external rotation (P < 0.05) of the EA from the PCA with a mean of 2.52° (range - 1.9° to 6°) compared to the varus group with a mean of 2.03° (range - 3.9° to 6.9°). This relationship did not significantly change with increasing severity of coronal malalignment. Externally rotating the femoral cutting guide by 3° from the PCA, 11% (42 of 382) of varus knees would lie outside of ± 3° from EA. In valgus knees, externally rotating the femoral cutting block by 3° or 5° from the PCA, 6.5% (6 of 92) and 33.7% (31 of 92) of knees, respectively, would lie outside of ± 3° from EA. CONCLUSION: The relationship of PCA to EA is heterogeneous and is not altered significantly with increasing valgus coronal deformity. External rotation beyond 3° from PCA in valgus knees may lead to significant femoral component malrotation in a large proportion cases.

Mid-term outcome of total hip replacement using the posterior approach for displaced femoral neck fractures.

Treatment of displaced femoral neck fractures with total hip replacement (THR) in appropriately selected patients has become more widely accepted. The use of the posterior approach for THR remains controversial due to concerns regarding dislocation, the cause of which is multi-factorial. This study is a single surgeon series of 45 consecutive active, healthy patients (mean age 78 years) with displaced femoral neck fractures treated with THR through a posterior approach. Large diameter heads (32mm in 47%, ≥36mm in 48% of patients) and an anatomic posterior soft tissue repair were utilised to minimize the risk of dislocation. Outcomes were reported at a mean of 2 and 6 years. The mortality rate was 13% at 2 years and 40% at 6 years. All revision surgery (4.4%) was performed for dislocations which occurred in 6.7% of patients. Good VAS pain, OHS and SF-12 scores were reported both at 2 and 6 years. Patient satisfaction with the results of surgery was high.