The goal of this study is to assess the efficacy and safety of a navigation system providing personalized soft tissue balance data in medially-stabilized total knee arthroplasty (TKA).

This is a prospective, multicentre, single-arm, open, confirmatory clinical investigation to assess the efficacy and safety of a navigation system providing personalized soft tissue balance data in medially-stabilized total knee arthroplasty (TKA).

Participants will be informed about the study, both orally and in writing, during a preoperative visit. The investigator will answer any questions that may arise and will collect the informed consent. During the study, enrolled participants will be able to withdraw at any time and for any reason.

The study is conducted according to the following schedule:

• V1 : Inclusion during a preoperative visit
• V2: Surgery
• V3: Follow-up visit at 2 month post-surgery
• V4: Follow-up visit at 6 months post-surgery
• V5: Follow-up visit at 12 months post-surgery

The following data will be collected:

• Oxford Knee Score (OKS), Knee Society Score (KSS), Forgotten Joint Score (FJS) and patient satisfaction at 6 months and 12 months of follow-up;
• Radiological analysis at 2 and 12 months of follow-up;
• Surgical time (min);
• Necessity of soft tissue release to obtain ligament or patellar balance;
• Time to discharge (days);
• Device deficiencies and peri- and postoperative adverse events.

A web-based data collection tool will be used as Electronic Data Capture (EDC). All the information required by the protocol will be collected in electronic case report forms (eCRF).

The statistical analysis will be performed according to a pre-established statistical analysis plan. Missing values will not be replaced by estimated values but will be considered as missing in the statistical analysis.

Inclusion Criteria:

1. Males and females aged over 18 years at time of surgery.
2. Patients who are scheduled to receive Medacta GMK® Sphere system for primary TKA (class III, CE-marked).
3. Patients with functional contralateral knee (i.e. without the need to use walking aids).
4. Patients willing and able to provide written informed consent for participation.
5. Patients willing to comply with the pre and post-operative evaluation schedule.

Exclusion Criteria:

1. Patients with one or more medical conditions identified as a contraindication defined by the labelling on any Medacta implants used in this study:

   • Patients presenting with progressive local or systemic infection
   • Muscular loss, neuromuscular disease or vascular deficiency of the affected limb, making the operation unjustifiable.
   • Severe instability secondary to advanced destruction of condralar structures or loss of integrity of the medial or lateral ligament

2. Patients whose prospects for a recovery to independent mobility would be compromised by known coexistent, medical problems.

3. Patients affected by concomitant spine, hip, ankle or contralateral knee pathologies that can affect walking capacity.

4. Patients unable to understand and take action.

5. Patients with known allergy to the materials used.

6. Patients in which Medacta GMK® Sphere system is used in emergency interventions.

From signature of the informed consent up to 12 months postoperatively.

All Serious adverse events are reported. Adverse events with at least "Unknown/Possible" relation with the procedure and/or the device are reported if rate exceeds 2.5%