Joint Line Obliquity Classification for Knee Arthroplasty Planning

Total knee arthroplasty (TKA) surgery varies in required alignment adjustments across different patient anatomies. Mako Surgical introduces a method that determines each patient’s unique joint line obliquity (JLO) and hip-knee-ankle (HKA) angles, compares these values to predetermined targets, and adjusts surgical technique accordingly. This personalized approach improves implant positioning and knee function outcomes by accounting for individual anatomical variation.

The Problem

Traditional knee replacement surgery relies on standard mechanical alignment principles that may not account for individual patient anatomy. Patient-specific characteristics like natural joint line slope, femoral and tibial morphology, and soft tissue properties significantly influence optimal implant positioning and alignment. Applying generic alignment protocols to patients with unique anatomical patterns often results in suboptimal outcomes, including persistent pain, instability, or accelerated implant wear.

Determining optimal alignment intra-operatively remains challenging. Surgeons must assess complex three-dimensional anatomy while making time-sensitive cutting and positioning decisions. Current alignment techniques often do not fully account for individual anatomical differences, leading to disparities between surgical outcomes and patient expectations. The growing adoption of kinematic alignment approaches in TKA highlights the clinical need for more precise methods that restore patient-specific anatomy rather than applying one-size-fits-all mechanical principles. Surgeons lack systematic tools for quantifying and comparing patient anatomy to predetermined optimal states.

What This Invention Does

Mako Surgical’s method begins by determining a patient’s joint line obliquity (the slope of the knee joint line relative to mechanical axes) and calculating the hip-knee-ankle angle (alignment through the major lower limb joints). These measurements establish the patient’s baseline anatomical state. The method then compares these values to predetermined target angles that represent optimal alignment for that patient’s anatomy type. If measurements fall within acceptable ranges, standard surgical protocols proceed. If measurements diverge significantly from targets, the surgical technique adjusts through modified cutting angles, implant positioning, or pre-resection considerations.

The system integrates patient-specific assessment into the surgical workflow, enabling real-time decisions about bone resections and implant placement. Surgeons can evaluate whether the patient’s natural knee kinematics should be preserved if they align with predetermined targets, or whether modifications are necessary. This personalized approach replaces generic protocols with anatomy-specific optimization, improving the match between implant position and patient anatomy.

Key Features

• Joint Line Obliquity Determination. The method precisely measures the slope of the patient’s knee joint line in multiple positions, capturing the natural obliquity of the joint that will influence optimal implant alignment.
• Hip-Knee-Ankle Angle Assessment. The system evaluates limb alignment through the entire lower extremity chain, understanding how hip and ankle alignment influence knee requirements.
• Predetermined Target Comparison. Patient measurements are compared against established optimal values for that anatomical type, with predetermined thresholds defining acceptable ranges.
• Extension and Flexion Evaluation. Joint line obliquity is measured in both knee extension and flexion positions, capturing dynamic alignment characteristics that influence long-term function.
• Adaptive Surgical Planning. Based on comparison results, surgeons receive guidance on whether to preserve native kinematics or implement modified surgical techniques, guiding real-time decision-making.
• Patient-Specific Classification System. The method uses a classification framework based on individual anatomical characteristics, moving beyond generic protocols toward personalized surgical planning.

Who Is Behind It?

Mako Surgical Corp., based in the United States, develops robotic surgical systems and planning software for orthopedic procedures. The invention credits four inventors: Azhar Ali, Robert Marchand, Yogesh Mittal, and Paul Jacob, representing the company’s surgical technology and planning algorithm expertise. The application prioritizes US Patent Application 63/688,944, filed 30 August 2024. Spruson & Ferguson provides patent representation, supporting comprehensive intellectual property protection.

Why It Matters

This personalized approach to knee arthroplasty planning addresses a critical gap in current surgical practice. Patient satisfaction with knee replacement correlates strongly with achieving alignment that matches individual anatomy rather than enforcing generic mechanical axes. The method enables surgeons to quantify and compare patient anatomy systematically, improving surgical decision-making. Integration with robotic surgical platforms amplifies the benefit, allowing precise implementation of anatomy-specific surgical plans. As kinematic alignment approaches gain acceptance in TKA, systematic methods for identifying and implementing patient-specific modifications become increasingly valuable. This technology supports improved outcomes, higher patient satisfaction, and potentially extended implant longevity through better anatomical alignment.

Related Concepts

The debate between mechanical and kinematic alignment in total knee arthroplasty centres on whether to restore a patient’s pre-arthritic anatomy or impose a standardised neutral limb axis. Kinematic alignment proponents argue that restoring individual anatomy more faithfully reproduces natural joint mechanics and improves functional outcomes, particularly for patients whose anatomy deviates significantly from population averages.

Robotic-assisted surgery platforms enable sub-millimetre accuracy in bone resection and implant placement, making patient-specific surgical plans practically achievable. When combined with anatomical classification frameworks like joint line obliquity measurement, robotic systems can execute personalised plans that manual technique cannot reliably replicate.

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AU 2025220731 was published in the Australian Official Journal of Patents on 19 March 2026 and is open for public inspection. Patent applications represent inventions that are sought to be protected and do not necessarily reflect commercially available products.