Postoperative Alignment in Hinge Total Knee Arthroplasty - "Are Hinge Knees too Valgus?"

Background: Hinged knee prostheses are a potentially beneficial treatment approach in complex primary and revision total knee arthroplasty (TKA). Previous reports have demonstrated good long-term outcomes and survivorship with appropriate indications. However, adequate restoration of joint line and limb alignment remain challenging, with the implant design playing a significant role. Optimal limb alignment is generally within 0° to 3° of the mechanical axis. However, little data exists on limb alignment results following hinged knee procedures. The aim of this study was to evaluate the limb alignment of patients following hinged TKA. Methods: A retrospective review was performed of 117 operations in 114 patients who received a TKA with hinged prosthesis at one academic institution between 2008 and 2021. Ten were excluded due to inadequate follow-up or imaging, leaving 107 procedures in 104 patients for analysis. Demographics, indications, and postoperative weight-bearing radiographs were analyzed. Alignment measurements included the mechanical axis (hip-knee-ankle angle) and anatomic tibiofemoral axis. Results: Mean patient age was 67.6 years (range: 36-90), 59% were female. Mean BMI was 35.2 kg/ m2. Mean mechanical alignment was 0.53° ± 3.33 valgus (range 12.55° valgus to 8.42° varus) and 6.18° ± 2.82 valgus (range 16.3° valgus to 1.62° varus) for anatomic. Nineteen patients (18%) had a postoperative mechanical alignment >3 degrees valgus, and 9 patients (8%) were greater than 3 degrees varus. Conclusion: The incidence of valgus malalignment is greater than varus following TKA with a hinged prosthesis. Future studies should focus on the impact of alignment on patient reported outcomes.