Computer-Assisted High Tibial Osteotomy (CAS-HTO)

Computer-assisted high tibial osteotomy (CAS-HTO) encompasses several technologies that improve surgical precision compared to conventional fluoroscopic technique. The fundamental challenge in HTO is achieving the planned mechanical axis correction (typically targeting 62.5% Fujisawa point or 3-6° valgus from neutral mechanical axis), as small errors in correction angle (>3° from plan) significantly affect long-term survival.

Major CAS-HTO modalities: (1) Patient-specific instrumentation (PSI)—based on preoperative CT scan and 3D planning software, custom 3D-printed cutting guides match the tibial anatomy and contain the planned osteotomy plane; the surgeon uses the guide for cut, then the planned wedge size determines correction; high precision but requires preoperative imaging and lead time. (2) Computer navigation—infrared tracking with reference arrays attached to tibia and femur, real-time intraoperative axis calculation, allows dynamic correction adjustment; no preoperative custom guide needed. (3) Robotic-assisted HTO—emerging technology using haptic feedback or autonomous cutting; still in early adoption. (4) Augmented reality systems—still investigational.

Clinical benefits demonstrated in multiple studies: more accurate mechanical axis correction (within ±2° of target in 85-95% of CAS cases vs 60-75% conventional), better correction in multiplanar deformities (combined varus and tibial slope correction), reduced fluoroscopy time (especially with PSI and navigation), better reproducibility for low-volume surgeons, and slightly lower revision rates at 5 years. Limitations: significantly higher cost (PSI $2000-3000 per case, navigation system $200-300K capital), longer initial operative time (steep learning curve, 30-60 minutes longer first 10-20 cases), CT radiation exposure for PSI planning, technical errors if reference arrays move during navigation, and limited evidence for cost-effectiveness vs conventional in straightforward cases. Patient selection: greatest benefit for complex multiplanar deformities, posttraumatic deformity, double-level osteotomy, and surgeon learning curve. PSI is most accessible globally; navigation and robotics remain limited to specialized centers.