Severe Knee Deformity: Correction, Robotics and Recovery

Severe knee deformity, whether knock knees, bow legs, a windswept pattern or a knee that will not straighten, can be corrected with a knee replacement that brings the hip, knee and ankle back into one straight line. Dr. Subhash Jangid, currently Principal Director & Unit Head Orthopaedics, Fortis Memorial Research Institute, Gurgaon, India, uses CT-based robotic planning to correct these deformities precisely, often in both knees in one operation.

Patients with severe and bilateral deformities come to Dr. Jangid frequently, from within India and from abroad, including from Africa. This article describes the deformity patterns he treats, how the robot plans and executes the correction, and how quickly his patients recover. Indications, age and contraindications are covered in the age limit for joint replacement and who qualifies, and the wider landscape of implants and rehabilitation in recent advances in joint replacement. His background is on the Dr. Subhash Jangid doctor page.

Types of severe knee deformity: varus, valgus, windswept and flexion

Arthritis rarely wears a knee evenly. As one side of the joint collapses, the leg angles, and over years the angle can become severe enough that walking itself fails. Dr. Jangid described four patterns.

Varus deformity (bow legs)

The knee bows outwards, and the inner side of the joint carries most of the load and wears first. In severe cases the patient can barely walk.

Valgus deformity (knock knees)

The knees angle inwards towards each other. Dr. Jangid noted that knock knees are the pattern he sees most often in patients from Africa. In severe valgus deformity the patient cannot put proper weight on the leg, and walking becomes very difficult. When the joint is badly damaged on both sides, no medication will straighten it: the leg has to be corrected surgically.

Windswept deformity

One knee is bowed and the other is knocked, so both legs lean in the same direction, as if blown by the wind. Dr. Jangid sees these complex patients frequently, from India and abroad. They need both knees corrected in one operation, because if only one knee is straightened the patient still cannot walk straight.

Flexion deformity

The knee is fixed in a bent position: even lying flat, the patient cannot straighten the leg. These are challenging cases for a second reason. Over time the muscles that straighten the knee become weak, and once they have weakened, walking straight does not return immediately after surgery. These patients need longer rehabilitation before they walk without difficulty.

Bilateral knee deformity: why correct both knees in one operation

In a windswept deformity, correcting only one knee leaves the patient unable to walk straight, because one straight leg and one deformed leg do not make a functional pair. Dr. Jangid's practice is to correct both knees in one sitting where the deformity requires it. Indicative prices are on the bilateral total knee replacement cost page.

How severe knee deformity correction is planned with a robot

Dr. Jangid uses a CT-based robotic-arm system. He frames its role through two rules. First, a robot must not injure a human being: neither the patient nor the surgeon. Second, it must obey the surgeon. It is not autonomous, and he regards that as essential, because an autonomous robot could cause harm. Within those rules, the robot extends what the surgeon can achieve.

Step 1: A CT scan builds a three-dimensional model

Dr. Jangid describes a CT scan as the most accurate way to capture the three-dimensional shape of the bones around a joint. The scan is loaded into the robot's software, which builds a 3D model of the patient's knee, and the implant can then be sized and positioned for that individual anatomy before surgery begins.

Step 2: Mapping the real knee to the model

In theatre, the surgeon registers the patient's actual bone against the CT model. Dr. Jangid's team maps 40 points on the femur and 40 points on the tibia. The system calculates the error between the model and the real bone, and the error must be less than 0.5 mm, a margin the eye can barely see. If the error exceeds 0.5 mm, the system will not proceed.

Step 3: Virtual planning of the correction

With the model registered, the surgeon plans the operation on screen. In one patient Dr. Jangid showed, the knee had a 13-degree varus deformity and a 6-degree flexion deformity, and the plan brought both to zero. The software shows how much the joint opens on each side, the flexion and extension the patient will achieve, and the slope of the tibial cut. Every element is planned in three dimensions, across the X, Y and Z axes, so the implant fits that particular knee as closely as possible.

Step 4: Haptic cutting within a fixed boundary

During the bone cuts, the robotic arm guides the saw precisely. Trackers tell the system how the robot is oriented in space, and the screen shows exactly how much bone is being cut. The defining safety feature is haptic control: the software defines a boundary, and the blade physically cannot travel beyond it. It does not touch the surrounding soft tissue. As the surgeon moves to each new position, the system shows the next planned cut.

Step 5: Balancing and checking the result

At the end of the operation, the knee is checked through its full range. In the cases Dr. Jangid presented, the knee was balanced, reached full extension and full bending, and the implant sat on the bone matching the patient's native anatomy.

Robotic partial knee replacement

The same planning applies to partial knee replacement. In one example, a knee with a 10.5-degree varus deformity was corrected to 2 degrees of varus. Only the inner half of the joint was replaced, and the outer half remained native. The challenge in a partial knee is to balance the new half against the natural half, and Dr. Jangid regards the robot as very accurate at this.

What precise alignment achieves

Dr. Jangid summarised the clinical case for robotics in one chain of effects. Precise component positioning straightens even badly deformed knees, bringing the hip, knee and ankle into one line. That alignment leads to a quicker recovery and less pain during the recovery period, and is expected, though not yet proven by long-term data, to extend implant life.

Recovery after severe knee deformity correction

In the cases Dr. Jangid presented, patients were walking without any support on the second day after surgery, because, he said, the knee feels so natural. The milestones in the cases he presented:

Rehabilitation is largely unrestricted: patients can do whatever they wish except running and jumping. Pain is controlled with a low-dose opioid skin patch or nasal spray and paracetamol, which spares the stomach and kidneys, as described in recent advances in joint replacement.

Case results

Dr. Jangid presented a series of patients that illustrate the range of what can now be corrected.

A very tall patient with an old ligament injury

A very tall basketball player had undergone an anterior cruciate ligament (ACL) reconstruction years earlier. Despite the reconstruction, the knee had worn out: the bone was eroded and the joint was subluxing. Very tall patients need larger implants, which must be planned and prepared in advance. Robotic planning delivered the exact implant size and a fit that matched the native bone. He left India within 10 days, able to walk unaided, with only the dressing removal left to do at home.

Bilateral knock knees

A woman from the United States with knock knees on both sides was walking normally four days after surgery and had fully recovered, with straight legs, within three weeks.

Four joints in two operations

A woman from West Africa arrived in a wheelchair with all four major weight-bearing joints badly damaged: both hips and both knees. Dr. Jangid replaced both hips in a single sitting, after which she began to walk. Three weeks later he replaced both knees. She left 10 days after the knee operations, had recovered within about a month, and years later still sends him videos of herself walking and doing whatever she wants.

Complex knees after old thigh-bone fractures

A woman who had fractured both thigh bones six or seven years earlier had not walked since and arrived in a wheelchair. Because her bones were weak, Dr. Jangid used complex knee implants with extra stems on both sides. He left the old fracture implants in place, removing only a few screws. Around four weeks after surgery she had started walking.

When to refer a patient with knee deformity

Dr. Jangid's message on deformity is simple: all of these knees can be treated with very good results, but the earlier the patient is referred, the better the outcome. Long-standing flexion deformity, for example, weakens the muscles that straighten the knee and lengthens rehabilitation. The questions doctors raised on the call are answered in the Live Discussion for this masterclass, and related masterclasses sit under the orthopaedics specialty. For a comparison with conventional technique, see Dr. Rakesh Mahajan on robotic vs conventional knee replacement.