Complex and Revision Joint Replacement: Implants and Robots

Complex and revision joint replacement is surgery for joints a standard implant cannot manage: very high body weight, weak or missing bone, fractures around old implants, infected joints and limbs rebuilt after tumour surgery. A revision replaces an earlier implant. Dr. Ramkinkar Jha uses stemmed, constrained and modular implants, bone grafting and megaprostheses in these cases, and sees navigation and robotics earning their place mainly in difficult and redo knees.

A primary knee replacement in a fit patient with a straight leg and good bone is one end of the spectrum. Dr. Jha's practice spans the whole range, and his view of technology is shaped by it: the tools that matter least in a simple case can matter most in a difficult one. This article covers what implants are made of, how they are put in, and how the operation changes as cases become complex. Who qualifies for replacement, and what follows it, is set out in the complete guide to hip and knee replacement surgery; diagnosis and the treatments that come first are covered in osteoarthritis diagnosis and treatment.

What joint replacement implants are made of

Most joint replacement implants are made from cobalt-chromium alloy, with titanium and oxidised zirconium as alternatives.

The alloys

Most implants in use today are made from cobalt-chromium alloy, typically cobalt-chromium-molybdenum, the most widely available option. Dr. Jha regards titanium as the superior material. A third option is oxidised zirconium, a black-coloured implant surface.

Metal allergy and the "gold knee"

Some patients are allergic to cobalt, chromium or related metals. The history usually reveals it: when a patient reports allergy to many things, the history is explored for reactions to artificial jewellery or rings containing these metals, and patients who react to them are presumed to be sensitive to the implant metals. For these patients, Dr. Jha uses what is commonly called a "gold knee". The gold colour comes from a ceramic surface coating, typically titanium nitride or titanium niobium nitride, which separates the patient's tissues from the underlying alloy; the implant is not made of gold.

Allergy, he stresses, is very rare. It is the explanation for a painful replacement only after infection, loosening and malpositioning have been excluded.

Hip replacement bearings and fixation

In the hip, the implant and the bearing surface are distinct. The bearing is where movement actually happens, and it can be made from metal, ceramic or plastic (highly cross-linked polyethylene) in several combinations:

• metal on metal;
• ceramic on ceramic;
• ceramic on highly cross-linked polyethylene;
• ceramic on metal.

The hip can be replaced as a hemiarthroplasty or a total hip replacement, and the components can be fixed in four ways: cemented, uncemented, hybrid (a cemented femoral stem with an uncemented socket) or reverse hybrid (an uncemented stem with a cemented socket).

Robotic vs conventional knee replacement

Robotic and computer-navigated knee replacement place the implant more accurately than conventional surgery, but, as Dr. Jha reads the evidence, long-term outcomes and implant survival are almost the same. Using the knee as his example, Dr. Jha compares three ways of performing the same operation.

Conventional surgery is the time-tested approach. The surgeon uses mechanical jigs and reads the mechanical axis of the leg from anatomical landmarks, by eye and by training, then makes the bone cuts and seats the implant. In the example he showed, it corrected a gross deformity and produced a straight knee.

Computer navigation adds measurement. Sensors are fixed to the bone together with a jig, and the computer calculates exactly how much bone to cut and at what angle. Several generations of the technology are in use.

Robotic surgery adds execution. A robotic arm helps the surgeon make the cuts accurately.

What the evidence shows

Dr. Jha summarises the literature this way. Across range of motion, functional scores and implant performance, conventional and technology-assisted surgery both perform very well. The newer technologies win on one measure only: the accuracy of implant position as seen on X-ray. Short- and mid-term results may differ, but long-term outcomes and implant survival are almost the same. The long-term superiority of robotics over conventional surgery has not been proven.

His conclusion is commercial as well as clinical. Robotic surgery is heavily advertised, but adding cost does not add proportionate value in a routine case. Where navigation and robotics earn their place is in very difficult knees and redo surgery.

Complex knee replacement: when a standard implant is not enough

Bilateral knee replacement in one sitting

When both knees are affected, both can be replaced in a single sitting (bilateral total knee replacement). Dr. Jha also performs bilateral replacement in high-risk patients. The justification is functional: once the patient is mobile, their wider medical condition tends to improve as well. He illustrates the point with a high-risk patient who now tracks her daily walking on a phone app, something that would not have been possible without the operation.

High body weight and weak bone: stemmed implants

In patients with a body mass index above 35 to 40, or with weak bone, a standard implant is under excessive stress. Dr. Jha augments the implant with intramedullary rods (stems) that run into the shaft of the bone and share the load, reducing stress on the joint. These are what he classes as complex total knee replacements.

Bone loss and constrained implants

Where bone is lost on both sides of the joint, augmentation is needed in both the femur and the tibia, and the implant chosen is a constrained type. A constrained knee carries more of the joint's stability within the implant itself, compensating for what the damaged bone and ligaments can no longer provide.

Dr. Jha also recommends a constrained implant for post-traumatic stiffness. A knee whose movement has been limited by an old injury can be replaced to restore motion, but the implant moves from a simple to a complex or constrained design.

Periprosthetic fractures: fractures around a replacement

A periprosthetic fracture is a break in the bone around an implant. It can occur around a knee replacement just as it can in any other bone. Some can be fixed; others are better managed by replacing the joint again with a more complex implant. At the most demanding end are cases where the fracture was fixed earlier and the joint could no longer be saved. Replacement with a complex implant in that setting is among the most demanding knee operations Dr. Jha performs.

Complex and revision hip replacement

The hip offers a wider range of reconstruction options than the knee: modular revision stems, impaction bone grafting and navigation.

• Modular revision stems. Where the upper femur is fractured, modular stems allow the surgeon to fix the fracture and replace the hip in one reconstruction.
• Impaction bone grafting. Where bone has been lost, the defect is first packed with impacted bone graft, and the new total hip replacement is implanted on that rebuilt foundation.
• Navigation. In complex hips, navigation is used to achieve very accurate component placement on both anteroposterior and lateral views.

Megaprostheses after bone tumour surgery

The largest reconstructions follow tumour resection. When a bone tumour, such as a chondrosarcoma of the upper femur, is removed together with a large segment of bone and its surrounding soft tissue, the limb is left highly unstable. A megaprosthesis, a specialised replacement that substitutes for the resected bone as well as the joint, restores it. Dr. Jha uses these implants around both the hip and the knee and calls them the highest form of joint replacement.

Shoulder and elbow replacement

Shoulder replacement

For a fracture dislocation of the shoulder, replacement is often the answer. The options are a hemiarthroplasty or a total shoulder replacement. If the rotator cuff is diseased, a reverse total shoulder replacement is used instead, because its design allows the arm to function without a working cuff.

Elbow replacement

Indications for elbow replacement are very selective: severe arthritis, typically in rheumatoid disease, or a fracture dislocation that cannot be salvaged by fixation. In those cases Dr. Jha recommends total elbow replacement. Survival is not as long as for the knee or hip, but over 10 to 15 years it gives the patient a pain-free period.

Hip replacement for athletes: resurfacing and bearing choice

For an athlete whose sport cannot change, Dr. Jha favours hip resurfacing with a metal-on-metal bearing. Athletes are a difficult group because their demands exceed those of the normal population: jumping and contact sports load an artificial joint far more heavily. Every replacement wears, and the general instruction to patients is not to run or jump, because more activity means more wear and more revision surgery.

For an athlete who needs a hip replacement, Dr. Jha's first step is to ask whether the activity level can change. If it cannot, and continued sport is essential, implant choice becomes the lever. His preferred option is hip resurfacing, in which the femoral head is capped rather than removed, with a metal-on-metal bearing. Resurfacing is now used selectively worldwide, because metal-on-metal bearings release metal ions that can damage surrounding tissue, and it is generally reserved for carefully chosen patients, typically younger men with good bone quality. Ceramic bearings, in his view, are not a good choice for athletes because of a higher risk of breakage.

Infected joint replacement: when the implant stays and when it goes

Dr. Jha's protocol for an infected joint replacement depends on how long the infection has been present: acute infection is treated with aggressive surgical debridement (cleaning out infected tissue) with the implant retained, and infection present for more than a month usually calls for two-stage revision. His answers to audience questions on infection, implants and athletes are in the live discussion from his masterclass.

Acute infection: aggressive debridement

In an acute infection, in his view, antibiotics alone will not suffice. His instruction is to go into the joint without hesitation and clean it, with repeated debridement until the joint is clean from the inside. In the knee, the polyethylene component can be exchanged at the same time. A drain is left for three to five days and antibiotics are given, but as an adjuvant, not as the primary treatment.

Long-standing infection: two-stage revision

If the infection has been present for more than a month, the usual answer is a staged revision:

1. Stage one. The implant is removed and an antibiotic spacer is placed in the joint.
2. Interval. For six weeks the patient is monitored with infection markers (ESR, CRP and full blood count) until they return to normal limits, and the skin is allowed to heal.
3. Stage two. A revision total joint replacement is performed.

The principle is simple to state and demanding to execute: early infection calls for aggressive surgical clean-up with the implant retained, and established infection calls for staged revision. Related articles from other surgeons are collected on the orthopaedics specialty page.