Femoral Component TKA: Extramedullary vs Conventional Intramedullary Guide

Total Knee Arthroplasty (TKA) is a widely performed surgical procedure aimed at relieving pain and restoring function in patients with advanced knee arthritis. The success of TKA is contingent upon precise implant positioning, particularly in relation to the femoral component. The femoral component's alignment significantly influences postoperative knee biomechanics, patient satisfaction, and long-term implant survival.

Conventional methods for femoral component positioning involve the use of intramedullary (IM) guides, which are inserted into the femoral canal to align the cutting block for bone preparation. While IM guides offer precise alignment, they can also lead to complications such as intraoperative fractures, fat embolism, activation of coagulation and excessive blood loss.

To address these limitations, extramedullary (EM) guides have emerged as an alternative option. EM guides are placed on the external surface of the femur without entering the medullary canal and avoiding complications that may occur reaming the canal.

In the recent past years, kinematic alignment (KA) has become widespread in use as a new technique for TKR that considers the patient's individual alignment and biomechanics. By restoring the pre-arthritic kinematic axes of the femur and tibia, KA aims to mimic the natural knee joint's function and movement.

In this study a specific EM guide - Anterior Cortex Stylus - is used to address the alignment of the femoral component in the context of a KA approach. The guide uses the anterior cortex of the distal femur as reference for cutting block positioning. The study aims to evaluate the performance of this EM guide in comparison to a traditional IM guide (used in previous group of patients).

This is an open, multi-centre, retro-prospective, observational, controlled study.

The primary aim is to evaluate whether the Anterior Cortex Stylus (in a retro-prospective collected series) is not inferior to the traditional intramedullary guide (previous group of patients) in term of positioning of the femoral component in TKA.

A total of 75 patients will be included in the extramedullary group (to be compared with a corresponding previous group of 75 patients treated with intramedullary guide). Both groups will be treated with a total knee arthroplasty using GMK Sphere (CE marked, class III) and a kinematic alignment approach.

Inclusion criteria

• Male or female ≥ 18 years old
• Indication to primary TKA, for any diagnosis operated with EM or IM guides
• Signature of the informed consent (only for prospective cohort)
• Been operated upon between January 2021 and September 2025 (only for retrospective cohort)

Exclusion criteria

• Revision surgery of knee arthroplasty
• Patients with malignant diseases (at the time of surgery)
• Patients with proven or suspect infections (at the time of surgery)
• Pregnancy end/or lactating (auto declaration)
• Patient with known allergy to the specific metallic components of the prosthesis (at the time of surgery)