The overall aims of this prospective, randomised, single-blinded controlled trial are to compare functional, radiological and clinical outcomes in Mako robotic-arm assisted cementless Total Knee Arthroplasty (TKA) versus Mako robotic-arm assisted cemented TKA.

Osteoarthritis of the knee accounts approximately for 85% of the disease burden across the globe10. Almost one in six people is affected by knee arthritis and according to the latest National Joint Registry (NJR) report; over the last three years in England and Wales more than 100,000 patients underwent total knee replacement each year.

Registry-based studies have shown good clinical outcomes and survivorship following TKA, however despite these results aseptic loosening and lysis remain the leading indications for revision. Furthermore, there is a higher incidence of patient dissatisfaction compared to total hip arthroplasty, with up to 20% of patients reporting dissatisfaction in an otherwise uncomplicated TKA. There has been an exponential rise in the number of TKAs performed in the UK and around the world, with a sharp increase in the percentage of younger patients undergoing TKA11. Notwithstanding, younger patients have consistently shown poorer outcomes following TKAs and younger age has been recognised as a risk factor of aseptic loosening; thus raising a concern given the demographic trend of younger patients seeking TKA.

The optimal component fixation mode has been contentious, and it is yet to be established whether one is superior to the other. Early reports of cementless TKAs had risen concerns in relation to suboptimal fixation and early failure. However, since then, there has been a dramatic improvement in the design and technique of cementless TKA, reflected on several studies reporting promising and favourable outcomes with cementless fixation; a recent systematic review and meta-analysis has shown a 96% - 100% survival at ten- to 15-years. Proponents of the technique highlight the potential of biologic fixation and better osseointegration, given highly porous surfaces on TKA designs prevent a mismatch in stiffness and approximate the pore size and elasticity of trabecular bone. Moreover, cementless implants do not produce cement debris, averting the risk of cement degradation leading to prosthesis loosening. Commonly, cementless prostheses are more expensive than cemented, however a recent study reported a lower overall cost associated with cementless TKA; showing that the additional cost could be offset when additional variables are taken into account such as operating time, implant, cement and cementing accessories.

The evolution of surgical technology has led to the development of robotic-arm assisted TKA, which uses three dimensional images of each patient's unique anatomy to guide bone resection, implant positioning, and optimise limb alignment. The robotic arm interactive orthopaedic (RIO) system (Mako surgical) uses preoperative computerised tomography scans to build a computer-aided design (CAD) model of the patient's knee joint. The Mako robotic software processes this information to calculate the volume of bone requiring resection and creates a three-dimensional haptic window for the robotic arm to resect. The robotic arm has tactile and audio feedback to resect bone to a high degree of accuracy and preserve as much bone stock as possible. The surgeon can then plan and execute optimal sizing and positioning of the prosthesis to achieve the required bone coverage, minimise bone resection, and obtain the desired limb alignment. The Mako software also creates a patient-specific computer aided design model using the preoperative CT scan, which means that only bone anatomy is segmented. The surgeon is able to compensate for wear when creating the surgical alignment plan and uses intraoperative bone registration to map the patient's anatomy.

There are very few randomised prospective studies exploring clinical and radiological outcomes in cemented versus uncemented TKA. Prospective studies comparing functional outcomes between the treatment groups have been performed but the main limitation of these studies has been the inability to achieve the implant position to a high degree of accuracy. Furthermore, there is a paucity of long-term studies and limited data correlating radiological outcomes to clinical findings.

Since its introduction in 1974, radiostereometric analysis (RSA) has been widely used in the assessment of implant stability and survivorship in joint arthroplasty. The model-based RSA technique involves the insertion of inert tantalum beads into the bone around the prosthesis. These bone markers act as fixed reference points from which the spatial resolution and rotation of the implants are calculated. Early implant migration as assessed by RSA has been shown to accurately reflect the risk of loosening.

The most recent data comes from Hasan et al that conducted a RCT comparing the cementless Tritanium 3D-printed Tritanium TKA with its cemented counterpart using RSA and clinical outcomes. Authors reported a larger migration of the cementless TKA in the first three months, after which stabilisation was noted in in all cases with the exception of one malaligned TKA that was revised early. No intraoperative navigation or robotic systems were used, therefore weakening reproducibility of implant positioning.

While there have been RCTs comparing cemented to cementless TKA, there is no published study comparing these two groups utilising robotic-arm assistance, which is one of the fastest growing procedures in TKA. Cementless TKA is growing exponentially along with robotic TKA and it would be valuable to ascertain whether there is an advantage of cementless vs cemented TKA.

With the altering demographics of TKA, it is projected that by 2030, 55% of the patients pursuing TKA will be younger than 65 years old. There is a need for high quality evidence on the radiological and clinical benefits of cementless TKA compared to cemented TKA. It is possible to improve on previous studies by incorporating RSA, assessing implant migration and calculating the risk of early implant failure. Our study will also be characterised by high validity; recording a more comprehensive range of clinical and functional outcome measures, blinding patients and using long follow-up times. Furthermore, Mako robotic-arm assistance will be used to improve accuracy of bone resection, guide implant positioning, reduce soft tissue injury, and provide intraoperative assessment of limb alignment; therefore, minimising bias related to surgical variability and inconsistent implant positioning. Findings of this study will enable an improved understanding of the radiological, clinical and functional benefits of cementless fixation compared to cemented fixation in TKA. Findings of the trial could also be used to improve outcomes in total knee arthroplasty; better patient functional outcomes and satisfaction; improved cost-effectiveness by reducing operating time and cement cost; improved long-term implant survival; better outcomes for the exponentially growing number of younger patients pursuing TKA.

The overall aims of this prospective, randomised single-blinded controlled trial are to compare functional, radiological and clinical outcomes in Mako robotic-arm assisted cementless TKA (cementless TKA) versus Mako robotic-arm assisted cemented TKA (cemented TKA). Patients undergoing cemented TKA will form the control group and those undergoing cementless TKA will form the investigation group. A superiority trial design will be used to evaluate whether cementless TKA provides superior outcomes compared to cemented TKA. Radiostereometric analysis (RSA) will be used to assess differences in early and late implant migration between cementless TKA and cemented TKA.

The primary objective of this study is to compare Forgotten Joint score (FJS) at one year following surgery.

This study is a prospective, single-centre, randomised, single-blinded, controlled study. Patients undergoing cemented functionally aligned TKA will form the control group and those undergoing the cementless functionally aligned TKA will form the investigation group.

Inclusion Criteria:

1. Patient has symptomatic knee osteoarthritis requiring primary TKA
2. Patient and surgeon are in agreement that TKA is the most appropriate treatment
3. Patient is fit for surgical intervention following review by surgeon and anaesthetist
4. Patient is over 18 years old at time of surgery
5. Gender: male and female
6. Patient must be capable of giving informed consent and agree to comply with the postoperative review program
7. Patient must have sufficient postoperative mobility to attend follow-up clinics and allow for radiographs to be taken

Exclusion Criteria:

1. Patient is not suitable for routine primary TKA e.g. patient has ligament deficiency that requires a constrained prosthesis
2. Patient has bone loss that requires augmentation
3. Patient is not medically fit for surgical intervention
4. Patient requires revision surgery following previously failed correctional osteotomy or ipsilateral TKA
5. Patient has a DEXA scan with T-score < -2.5 at any point
6. Patient is immobile or has another neurological condition affecting musculoskeletal function
7. Patient is less than 18 years at time of surgery
8. Patient is unable or unwilling to sign the informed consent form specific to this study
9. Patient is unable to attend the follow-up programme
10. Previous pathological fracture