AI in Joint Replacement: Imageless, Pinless Surgery

Artificial intelligence (AI) in joint replacement is the latest stage in a sequence of surgical guidance tools: patient-specific cutting guides, then computer navigation, then robotics, and now AI working with the robot. Dr. Ishwar Bohra describes AI-guided surgery as imageless and pinless: it maps the joint's alignment, rotation and gap balance in real time, without a pre-operative CT or MRI scan and without pins placed outside the joint.

Dr. Ishwar Bohra, Senior Director - Joint Replacement Programme, BLK-Max Super Speciality Hospital, New Delhi, India, named robotics, computer navigation and AI as the main advances in joint replacement when he conducted a Jivo Masterclass for international doctors in May 2024. He added a fourth advance that needs no machine at all: the surgical approach, the route by which the surgeon reaches the joint. This article covers both, together with his move away from pre-operative templating, high-flexion hip replacement, his choice of anaesthesia, and the move of open shoulder operations to the arthroscope. When a joint needs replacing in the first place is covered in the complete guide to when joint replacement is needed.

From cutting guides to AI: four generations of surgical guidance

Dr. Bohra traced the history in four steps:

1. Patient-specific instrumentation (PSI). Cutting blocks made to fit an individual patient's bone were very common in practice, but they had a limitation: they only guided the bone cuts.
2. Computer navigation. Tracking systems gave the surgeon measurements of the limb during surgery, rather than a fixed guide made in advance.
3. Robotics. The robot added mechanical precision to the bone preparation.
4. AI with the robot. The current stage combines the robot with artificial intelligence that reads the joint in three dimensions.

The same progression has reached sports surgery. Dr. Bohra noted that robotic or navigated techniques are now used in arthroscopic anterior cruciate ligament (ACL) reconstruction as well as in joint replacement.

How AI in joint replacement works

AI in joint replacement gives the surgeon real-time information about the patient's joint during surgery. Dr. Bohra calls it a game changer and expects its importance to grow. The real-time information covers three areas that determine how a replaced knee feels and how long it lasts:

• Alignment: the axis of the limb through the new joint. A well-aligned implant loads evenly.
• Rotation: how the components are turned relative to each other and to the limb, which affects how the kneecap tracks and how the knee bends.
• Gap balancing: making the space between the bone ends equal and stable with the knee straight and bent, so that the ligaments are neither too tight nor too slack. Balancing these gaps is one of the central tasks of a knee replacement.

The AI system provides a three-dimensional picture of the joint's alignment using a virtual camera and a very small laptop, and the whole operation can be carried out with that set-up.

AI versus robotic joint replacement: no scan, no extra pins

Dr. Bohra considers AI-guided surgery better than the robot in two respects. First, it needs no pre-operative CT scan or MRI of the joint, so the patient avoids an extra investigation before surgery. Second, it needs no extra-articular pin placement, meaning no tracking pins driven into the bone outside the joint. He describes it as a pinless, imageless modern technique.

For patients, both points matter. A scan is one more cost and one more appointment before surgery, and every additional pin site is a small additional wound. For a detailed comparison of robotic and conventional knee surgery from another surgeon's practice, see Dr. Rakesh Mahajan's guide to robotic knee replacement.

Does pre-operative templating still matter?

Templating is the practice of planning implant sizes before surgery by overlaying outlines of the components on the patient's X-ray. Dr. Bohra regards it as an old practice. It began as physical templating, moved to digital templating, and software still exists that gives an accurate size for the acetabular cup and femoral stem in the hip, or the femoral component in the knee.

He no longer templates. Having moved to more advanced techniques, he relies on intraoperative, robot-assisted guidance, which gives a more accurate size and dimension of the implant than a plan drawn on a film before the operation. The measurement is taken on the patient's own bone, at the moment it matters.

Direct anterior approach hip replacement

The direct anterior approach (DAA) reaches the hip from the front without cutting muscle, and it is the second line of advance Dr. Bohra described alongside the technology. Most surgeons enter the hip from behind. Dr. Bohra explained the anatomy simply: the bony prominence felt at the side of the hip is the greater trochanter, and in the posterior approach the surgeon enters the joint behind it. The posterior and direct lateral approaches involve a good deal of muscle cutting to open a path into the hip joint.

In the DAA, the surgeon reaches the hip through a natural interval between muscles rather than through them. Dr. Bohra listed what that achieves:

• No major muscle is cut.
• The main nerves are spared, although the lateral femoral cutaneous nerve, which supplies skin on the outer thigh, is at risk of numbness, usually temporary.
• Blood loss is very low.
• The technique is minimally invasive surgery (MIS), and the incision is small.
• The patient can go home after one day, and some patients can be treated as day cases.

For patients travelling for surgery, a one-day stay changes the logistics of the whole trip. Indicative costs are on Jivo Healthcare's pages for unilateral total hip replacement and bilateral total hip replacement.

High-flexion hip replacement and the return to kneeling

Implants have changed as well as approaches. Dr. Bohra now performs hip replacement designed for high flexion, the deep bending of the hip needed to kneel and squat. Three months after surgery, many of his patients are back to praying in the kneeling position, and squatting. Combined with implants that, for most patients, last 25 years or more, this is why he describes the prognosis after hip and knee replacement as very good.

Which anaesthesia is used for joint replacement?

Dr. Bohra uses general anaesthesia together with a regional nerve block, his answer when asked about his preferred mode of anaesthesia. A regional block numbs the limb's nerves and carries pain relief into the first hours after surgery.

Recurrent shoulder dislocation surgery: arthroscopic stabilisation

Recurrent shoulder dislocation, the main problem of the younger shoulder, is treated in Dr. Bohra's practice mainly through the arthroscope, part of the same shift towards less invasive surgery seen in the hip and knee. Dr. Bohra set out the options in the session.

Arthroscopic or open surgery?

There are two kinds of operation for recurrent shoulder dislocation: arthroscopic (keyhole) and open. For most patients, Dr. Bohra described arthroscopic Bankart repair with remplissage as the gold standard:

• Bankart repair reattaches the torn labrum and capsule to the front of the glenoid, the socket of the shoulder.
• Remplissage (French for "filling") fills the dent in the back of the humeral head, known as a Hill-Sachs lesion, by fixing the infraspinatus tendon and capsule into it, so that the dent can no longer catch on the rim of the socket.

Remplissage is generally added when there is a significant Hill-Sachs lesion; when the humeral head is intact, arthroscopic Bankart repair alone is the standard operation.

The exception, in Dr. Bohra's practice, is the patient who has dislocated a very large number of times. For a shoulder that has dislocated more than 10 times, open surgery is probably better.

When bone has been lost

Frequent dislocators often develop bone defects, and these can occur on either side of the joint: the socket (glenoid) or the head (humerus). If the defect is only on the socket side, the glenoid can be rebuilt with bony augmentation. When a defect exceeds 30%, as a large Hill-Sachs lesion on the humeral side can, Dr. Bohra said a bone graft is sometimes needed; otherwise, filling the defect with soft tissue (remplissage) is usually enough.

The Latarjet operation, now done through the arthroscope

The Latarjet operation, which transfers a block of bone with its attached tendon to the front of the socket, has traditionally been an open procedure. Dr. Bohra's team now performs it arthroscopically. It takes a little more time and is technically difficult, but because it is done entirely through the arthroscope, without an open incision, recovery is faster. Any other pathology found at the same time, such as a rotator cuff or biceps problem, is addressed in the same operation.

A fuller account of shoulder instability surgery, including when surgeons choose Bankart repair or Latarjet, is in Dr. Vipin Maheshwari's article on rotator cuff repair and shoulder instability.

What the technology does not replace

Every one of these advances refines the operation; none of them changes who should have it. The indication still comes from the X-ray and the patient's history, and the outcome still depends on how well the patient is prepared, how clean the theatre is, and how carefully infection and nutrition are managed. Those foundations are covered in the article on preparing for joint replacement. The doctors' questions from the session, including on AI and templating, are on the Live Discussion page.