Angular limit for coronal joint deformity correction using intramedullary guidance in total knee arthroplasty. A...

Area of Science:

• Orthopedic surgery
• Biomechanical analysis
• Arthroplasty research

Background:

• Post-operative lower limb mechanical axis misalignment after total knee arthroplasty (TKA) is linked to clinical failure.
• Intramedullary (IM) guidance for TKA alignment may not guarantee a horizontal joint line despite a neutral global mechanical axis.
• Separate analysis of femoral and tibial axes is crucial for accurate TKA alignment evaluation.

Purpose of the Study:

• To define pre-operative mechanical tibial and/or femoral angle thresholds for optimal post-operative alignment correction in TKA using IM guides.
• To investigate the relationship between pre-operative tibial and femoral angles and post-operative TKA alignment.
• To identify potential limitations of IM guidance in correcting complex tibial deformities.

Main Methods:

• A single-center prospective pilot study included 50 patients undergoing TKA for osteoarthritis.
• Femoral and tibial cuts were performed using IM guides.
• Standing anteroposterior long-leg radiographs were used to measure femorotibial angle (FTA), mechanical femoral angle (MFA), and mechanical tibial angle (MTA) pre- and post-operatively.

Main Results:

• The pre-operative mechanical tibial angle (MTA) was the only parameter showing a threshold effect.
• An pre-operative MTA exceeding 94° was associated with potentially suboptimal post-operative alignment correction.
• No specific threshold was identified for the mechanical femoral angle (MFA) or femorotibial angle (FTA).

Conclusions:

• Bony correction achieved with IM guides in TKA is primarily dependent on the initial tibial deformity.
• IM guides may result in sub-optimal corrections when the pre-operative MTA indicates a varus exceeding 94°.
• Alternative surgical strategies should be explored for TKA cases with significant pre-operative tibial varus.