What Mako actually is — and what it is not

Mako is the same operation done differently — not a separate procedure in its own right. Whether a patient is having a total knee replacement (TKR) or a unicompartmental (partial) knee replacement (UKR), Mako SmartRobotics is the platform the surgeon uses to carry out that procedure with greater planning precision. The implants placed are standard Stryker knee components; what changes is the method of preparation and positioning.

Developed by MAKO Surgical Corp., which was acquired by Stryker in December 2013, the system has three working elements: a pre-operative CT scan, a patient-specific 3D virtual model of the knee built from that scan, and a robotic arm that the surgeon guides throughout the operation. The CT-derived model allows implant size, fit, and alignment to be planned before the patient enters theatre — a step that conventional surgery, relying on 2D X-rays and manual cutting jigs, does not include.

The robotic arm does not operate independently. The surgeon remains in direct control at every point; the arm's role is to enforce the pre-agreed plan via AccuStop™ haptic technology, which physically resists movement outside the planned resection boundary. 'Robotic' here means constrained precision, not autonomy — a distinction that matters when patients are weighing up whether to accept the approach.

Planning and theatre workflow: CT-guided vs conventional jigs

In a conventional knee replacement, pre-operative planning relies on standing 2D X-rays from which the surgeon estimates alignment and selects implant sizes. The resection plan is not finalised until the patient is on the operating table. In theatre, the surgeon aligns manual cutting jigs to bony landmarks — the femoral shaft, the tibial plateau, and the mechanical axis — adjusting them by eye and by feel before each bone cut is made. The plan, in other words, takes shape intraoperatively, guided by surgical experience and real-time assessment.

The Mako workflow shifts a significant portion of that planning upstream. Before the patient arrives in theatre, a pre-operative CT scan is used to construct a patient-specific 3D virtual model of the knee. The surgeon uses this model to map resection boundaries, select implant size and positioning, and simulate alignment — decisions that in conventional surgery are made on the day. Patients undergoing Mako-assisted surgery therefore attend an additional pre-operative appointment for the scan before their admission.

In theatre, the virtual plan is loaded into the system, and the surgeon can reassess soft tissue tension and make real-time adjustments before committing to any bone cut. When cutting begins, AccuStop™ haptic technology enforces the planned boundaries physically: the robotic arm resists movement outside the pre-defined resection zone. Conventional cutting jigs offer no equivalent enforcement — they guide position, but cannot prevent a deviation if one occurs during the surgeon's hand movement.

Alignment accuracy: what the AccuStop system delivers

AccuStop™ works as a physical constraint, not a software alert. As the surgeon guides the robotic arm through a bone cut, the system generates haptic resistance — a mechanical push-back felt directly in the handle — the moment the arm approaches the boundary of the planned resection zone. The arm cannot cross that boundary; bone or soft tissue outside the pre-agreed margins cannot be removed, regardless of hand movement. This physical enforcement is what structurally separates Mako from conventional technique, where cutting jigs guide position but impose no equivalent barrier.

A 2024 prospective real-world study of 155 patients quantifies what that constraint delivers in practice. The hip–knee–ankle (HKA) axis — the principal alignment parameter in TKR — was restored to within 0.76 ± 1.9° of the intraoperative plan. Femoral coronal accuracy reached 0.08 ± 1.36°, sub-millimetre in clinical terms. Across the cohort, 98.1% of patients achieved ≤ 2 mm difference in extension–flexion gap symmetry — the measurement that governs how the joint loads through its arc of movement. Importantly, accuracy did not decline as more cases were performed, suggesting the system's precision holds in routine use rather than only in high-volume specialist hands.

For context, older studies of conventional manual TKA typically report alignment outliers greater than 3° from the neutral mechanical axis in roughly 20–30% of cases — though those series involve different patient populations and surgical contexts, making the comparison approximate rather than head-to-head.

Mako for TKR vs Mako for UKR: the same tool, different goals

The same robotic platform serves two procedures with meaningfully different goals.

Mako and total knee replacement

Total knee replacement resurfaces all three knee compartments — medial, lateral, and patellofemoral — using metal and polyethylene implants, removing the cruciate ligaments in the process. Around 80–90% of TKRs remain functional at 20 years. In this setting, Mako's principal contribution is alignment: the pre-operative plan and AccuStop enforcement reduce bone-cut variability across all three surfaces, which matters because small deviations in any one cut compound across the joint.

Mako and unicompartmental knee replacement

Unicompartmental (partial) knee replacement addresses only the damaged compartment — most often the medial — leaving the remaining cartilage, bone, and cruciate ligaments intact. Patients typically experience faster recovery and describe a more natural-feeling knee than after TKR, though the revision rate is higher: approximately one in ten patients requires further surgery within ten years. That figure reflects the narrower candidacy criteria rather than a flaw in the procedure itself — UKR is appropriate when disease is genuinely confined to one compartment and the ligaments are preserved.

Mako's precision is arguably more consequential in UKR than in TKR. With less bone being resected, millimetre-level inaccuracies carry proportionally greater kinematic consequences. The haptic boundary confines the resection to exactly what was planned, and the system additionally allows the surgeon to perform dynamic intraoperative soft tissue tensioning — assessing and adjusting ligament balance against the 3D plan in real time. Conventional UKR technique offers no equivalent capability.

Mako does not alter the clinical criteria that determine whether a patient is a candidate for TKR or UKR. Compartment involvement, ligament integrity, and the degree of deformity remain the deciding factors; the robotic platform changes how the chosen procedure is executed, not which procedure is chosen.

What the clinical evidence shows — and where gaps remain

Perhaps the most direct comparison in the literature involves a same-patient bilateral study (n=55) in which each participant underwent staged TKA on both knees — one side conventional, the other robotic. Despite comparable Oxford Knee Scores across both sides, a statistically significant proportion of patients rated their robotic knee as less painful and more natural-feeling (p<0.01), and achieved faster independent walking after the robotic procedure. The Forgotten Joint Score — a validated PROM that measures how often a patient's knee intrudes on daily awareness — was significantly higher on the robotic side (73 vs 70.3, p<0.01). The margin is modest, but the study design eliminates many of the confounders that burden between-patient comparisons.

The broader functional picture comes from a 2025 systematic review in Bone & Joint Open covering 22 studies and 3,738 TKAs. Pooled PROMs favoured Mako RTKA over manual TKA at medium-term follow-up (3–12 months) and at longer follow-up (>12 months). The Forgotten Joint Score difference at medium term reached a mean of 5.50 (95% CI 2.19–8.81) — statistically significant, though clinically modest in absolute terms. No meaningful PROM difference appeared in the first three months after surgery, suggesting the functional advantage accumulates over time rather than manifesting immediately.

The Cleveland Clinic's propensity-matched cohort of 340 patients sharpens the trade-off picture: Mako outperformed manual technique on hospital length of stay and rates of direct home discharge; manual surgery was faster and produced better early knee flexion; complication rates were equivalent between the two approaches. On current evidence, neither technique dominates across all measures.

The honest ceiling on this data is that most studies are observational, rated predominantly at evidence level IIa. The 2025 systematic review explicitly calls for randomised controlled trials assessing clinical and cost-effectiveness outcomes — questions the existing evidence cannot yet settle. The British Orthopaedic Association recognises a trend towards improved outcomes with Mako in the UK evidence base, while stopping short of a definitive endorsement, which fairly reflects where the field currently stands.

Practical considerations: cost, access, and who may benefit

Three practical factors deserve honest attention before choosing Mako-assisted surgery.

First, the pathway is longer. Mako requires a pre-operative CT scan that conventional surgery does not — adding a scheduling step, a low radiation dose, and associated cost before the patient reaches theatre. Second, operative time is currently longer with Mako than with manual technique: the Cleveland Clinic's propensity-matched cohort of 340 patients confirmed this finding, and it is relevant for anyone with meaningful anaesthetic risk factors. Third, the higher theatre costs of robotic surgery are real; patients should ask their provider whether the Mako premium is reflected in their quote.

The case for accepting those trade-offs is strongest where alignment precision is especially consequential — for instance, in patients with complex bony anatomy, those who have had a previous osteotomy around the knee, or those at the borderline of UKR candidacy where soft tissue balancing carries greater than average kinematic risk. For straightforward primary knee replacement in experienced hands, conventional TKR and UKR carry decades of outcome data and remain clinically valid. The evidence does not support recommending Mako for every patient.

The right question to bring to any surgical assessment is not "which technique?" but rather "does my anatomy and my overall health profile make the precision gains worth the additional steps?" — a determination that requires individual imaging, clinical examination, and a frank conversation with the operating surgeon.