Patients with isolated medial compartment arthritis of the knee are commonly treated with unicompartmental knee arthroplasty (UKA). In contrast with total knee arthroplasty (TKA), UKA shows a higher revision rate, which might be due to implant malpositioning and postoperative malalignment of the lower limb and incorrect soft tissue balancing. Nowadays, robotic-assisted UKA is used which improves accurate positioning, optimizes soft-tissue balancing and optimizes radiographic alignment of the implant. The potential benefit could be that this better alignment and positioning results in improved functional outcome and long-term survivorship. As there is a lack in long-term results, more research is needed to the long-term results of robotic-assisted UKA. As long-term results are related to early migration of the implant, investigating the early migration will have additional value to predict the long-term results of robotic-assisted UKA. In this study, we will investigate the early migration of a unicompartmental knee implant (Restoris MultiCompartmental Knee Implant System (Restoris MCK)) used in robotic-assisted UKA using model-based roentgen stereogrammetric analysis (mRSA) and we will relate the migration of this implant to the long-term results of the implant.

The primary objective is to assess the fixation and migration patterns of the Restoris MutliCompartmental Knee Implant System (Stryker) in vivo, using mRSA, over 5 years. Secondary objectives are to analyse survival, clinical scores and radiographic aspects of the Restoris MultiCompartmental Knee Implant System (Stryker) and to relate these to the migration patterns over 5 years.

A prospective cohort study with 5 years follow-up, in which 33 patients will be enrolled. Patients 18 years or older who require a unicompartmental knee prosthesis as a result of moderately disabling joint disease of the knee will be included. During surgery tantalum markers will be placed to be able to perform mRSA. Patients will be evaluated preoperatively, at 6 weeks, 6 months, 1 year, 2 years and 5 years.

The main study parameters are the migration of the Restoris MCK of both the tibial and femoral component presented in x-, y- and z-direction. Secondary study parameters are the alignment, survival of the Restoris MCK, clinical scores and radiographic aspects (both x-ray and CT scan).

Inclusion Criteria:

• Indication for medial unicompartmental knee replacement as described in the manufacturer's guideline, namely as a result of moderately disabling joint disease of the knee resulting from:

  • Painful osteo- or post-traumatic arthritis
  • As an alternative to tibial osteotomy

• Age > 18 years

• Patient qualified for UKP based on physical exam and medical history

• Patient is able to speak and write Dutch

• Patient is willing to participate

• Patient is able and willing to provide written informed consent

Exclusion Criteria:

• Contraindication as described by the manufacturer:

  • Inflammatory arthritis or tricompartmental disease
  • Greater than 10 degrees of hyperextension
  • Greater than 10 degrees of varus or valgus deformity
  • Presence of infection (including history of infection), acute or chronic, local or systematic
  • Either mental or neuromuscular disorders that do not allow control of the knee joint
  • Insufficient bone stock to allow appropriate insertion and fixation of the prosthesis
  • Insufficient soft tissue integrity to provide adequate stability
  • Insufficient articulation of the hip joint

• Metal in the operative or non-operative leg which lead to the creation of accuracy-reducing artefacts in the CT scan

• Insufficient bone quality to provide adequate stability

• Loss of ligament structures to prevent creation of an ideal intra-operative plan

• Patients has a known or suspected sensitivity or allergy to one or more of the implant materials

• Revision UKP surgery of the same compartment

The population will consist of all patients who present at the Reinier Haga Orthopedisch Centrum, require unicompartmental knee prosthesis (UKP) and satisfy the inclusion and exclusion criteria as stated below.