Not every hip or knee replacement is the same

The first question is how much of the knee is actually worn. A partial knee replacement resurfaces one compartment — the inner side, the outer side, or the groove behind the kneecap (patellofemoral arthroplasty) — and leaves both cruciate ligaments and the healthy cartilage alone. Dr. Morton performs each type, and occasionally a bicompartmental replacement, which resurfaces two worn compartments while the ligaments are kept.

You may be a candidate when standing X-rays show wear confined to one compartment, your ACL is intact, the knee still straightens well, any deformity is mild and correctable, and pain persists despite therapy, medication and injections. A partial is usually the wrong choice when wear involves two or three compartments, when the ACL is torn or missing, when an inflammatory arthritis such as rheumatoid arthritis is present, or when the deformity is severe. Age by itself does not settle it.

The trade-off is real. A partial tends to recover faster and feel more like your own knee, but over a lifetime partial knees need a second operation somewhat more often, usually because arthritis advances in a compartment that was left in place. Converting a partial to a total is generally simpler than redoing a failed total, yet it is still a revision. A total knee treats any pattern of wear in exchange for a bigger operation. The partial vs total comparison sets out both sides.

For decades the traditional total knee was aimed at one straight, neutral target, whatever shape the leg had before arthritis. That method has a long and proven record, but legs are not all built alike, and forcing each knee to the same target can mean releasing ligaments to make it fit. Dr. Morton uses personalized alignment: working on a 3D model, he places the implant to fit the line of your own leg and the natural balance of your ligaments.

Personalized does not mean unlimited. The plan stays inside published “safe zone” limits, because setting an implant far from neutral raises a concern about loosening of the shin-bone component. If your natural alignment falls outside that zone, the plan is restricted toward it rather than abandoned. Early research points to a knee that feels more like your own, with short-term results that match or modestly exceed the traditional method. Long-term durability data are still accumulating, and that uncertainty is discussed before surgery. Personalized alignment is also usually not the framework for a revision knee, where exposure, bone loss and fixation drive the plan.

A robot does not perform your knee replacement. Before surgery Dr. Morton builds a 3D plan for implant size, position and alignment. During the operation the robot follows the position of your bones, measures how the ligaments tighten and loosen through motion, and holds the cutting tools to the plan — positioning a cutting guide on ROSA®, or stopping the saw at the planned boundary on Mako; each cut is checked once it is made. It never cuts by itself, and it decides nothing. More on robotic knee replacement.

The platform depends on your case and on where you have surgery. On O‘ahu it is matched to both, and ROSA® is used at The Queen’s Medical Center; ROSA builds its plan from standard X-rays taken with calibration markers, so it needs no CT scan. On Hawai‘i Island, knees at Hilo Community Surgery Center are planned on Mako from a CT scan, with no IV contrast. Robotic assistance is billed as a standard joint replacement, with no technology fee and no separate patient fee.

What the robot cannot do: decide whether you need surgery, substitute for judgment when the anatomy surprises, or guarantee a result. Old hardware in the bone or unusual anatomy can sometimes alter the plan.

There are two accepted ways to fix an implant to bone. Bone cement secures the components during surgery and has the longest track record of any knee fixation. A cementless knee uses porous titanium components pressed tightly onto the prepared bone; in the weeks after surgery your bone grows into that surface, so the implant is held by your own bone rather than by a layer of cement.

Cementless fixation depends on strong bone, because the initial press-fit must be solid for bone to grow in. Dr. Morton uses it where bone quality allows: he judges your bone on X-ray beforehand and confirms it in the operating room. Soft or osteoporotic bone is usually cemented instead. Because that last check happens during surgery, you consent to both methods, and the knee receives whichever fixation your bone can support.

The honest caution is that modern cementless designs have a shorter registry history than cement, and on rare occasions a component fails to integrate and causes pain that needs revision. With either method, most patients walk the day of surgery.

To reach the joint, the standard knee approach splits the quadriceps tendon above the kneecap. The subvastus approach lifts the inner quadriceps muscle (the vastus medialis) and works beneath it, so the tendon that straightens your knee is never divided. Dr. Morton uses it on nearly every first-time total knee. Published randomized trials report an earlier straight-leg raise and less pain on the first day; after a few months the two approaches perform alike, and implant durability does not differ.

The trade-off is room. The subvastus window is narrower and adds a little operating time, and robotic guidance helps make up for the tighter view. It is not used when that narrower view would put safety or implant position at risk: a very muscular thigh or a very tight knee, marked deformity, heavy scarring from earlier surgery, and most revisions, because those need a wider view. For such knees Dr. Morton chooses the standard approach and explains why before surgery.

Early recovery depends heavily on how the tissue around the joint is treated. Three parts of Dr. Morton’s technique aim to disturb less of it:

• No tourniquet. Many surgeons inflate a pressure cuff around the upper thigh for the length of the operation. Dr. Morton performs every primary knee without a tourniquet, controlling bleeding step by step with regional anesthesia, cautery and tranexamic acid, which spares the quadriceps from prolonged compression. Cemented knees are done this way too.
• A smaller incision. Dr. Morton typically performs a total knee through a 4–6 inch incision. The exact length depends on your anatomy and any earlier scars, and the skin cut matters less than how the deeper tissue is handled.
• Fewer releases. When the plan respects your own ligament balance, less cutting or stretching of ligaments is needed to make the implant fit.

Any smaller exposure means less room to see, which is why the cuts are planned and verified robotically. These steps aim at an easier start; they do not replace physical therapy or decide how long the implant lasts.

Going home the same day is an option, not a requirement. Same-day knee replacement is possible at The Queen’s Medical Center and Adventist Health Castle for qualified patients, and Hilo Community Surgery Center is a same-day setting only, with no overnight stay. You are likely a candidate if your health is stable and any conditions are under good control, someone can be with you through at least the first night, you have worked out how to manage any steps into your home, and you are ready to walk early.

Some conditions, such as unstable heart disease or severe sleep apnea, can make a night of observation the safer choice, and patients who may need overnight monitoring are scheduled at a hospital from the outset. The decision rests on health and home situation rather than age, and Dr. Morton makes it with the anesthesia team before surgery. You leave once you are walking safely, eating and drinking, and comfortable on oral pain medicine, not after a set number of hours, and at Queen’s or Castle an overnight stay remains available if you need it. See same-day knee replacement and the outpatient program.

Dr. Morton’s standard hip approach is the direct anterior approach. He works through a natural interval at the front of the hip, moving muscles aside rather than cutting them or lifting them off bone, and opens only the joint capsule. Most patients have no formal hip precautions afterward. Because you lie on your back, X-rays during the operation can confirm cup angle and leg length before closing.

A small skin nerve runs near the incision, and temporary numbness on the outer thigh is the most common nuisance; it usually fades and does not weaken the leg. The approach is technically demanding, so it belongs with a surgeon who does it routinely. A well-performed posterior hip is still a good operation, and implants last about as long whichever route is used; the gap between approaches shows mostly in the first weeks.

Another approach may be safer if you have had hip surgery before, have metal hardware still in the bone, have a significantly deformed hip, carry a large overhanging skin fold, or have a condition that slows wound healing. When that applies, Dr. Morton tells you. Revision hips may be approached through the earlier scar.

A bikini incision changes only the skin cut. Instead of running down the front of the thigh, it follows the groin crease along the skin’s natural tension lines, where a swimsuit waistband sits. The deep anterior surgery, the implants, the robotic checks and the recovery stay the same.

It is offered when your anatomy allows, not promised. Good fits include a first-time anterior hip, a wish for a scar hidden under swimwear, an active or ocean-going lifestyle, and a history of prominent or widened scars. A standard anterior incision may be wiser if a large abdominal skin fold overhangs the crease, if a condition slows your wound healing, or if earlier incisions or your anatomy call for more room.

Two trade-offs are specific to this incision: the crease stays warmer and moister than the thigh while it heals, and the oblique cut is somewhat harder to lengthen. If more room is needed during surgery, Dr. Morton lengthens the cut into a standard anterior incision instead of accepting a compromised implant position.

Dr. Morton uses robotic guidance on essentially every hip. Before surgery he plans cup size and angle, stem size, leg length and offset on a 3D model. Spine X-rays taken standing and sitting reveal how your pelvis rocks between those positions, which can move the ideal cup angle away from a textbook target. On Hawai‘i Island, hips at Hilo Community Surgery Center are planned on Mako from a CT scan of the pelvis and hip, and small temporary pins hold the tracking arrays during the operation; on O‘ahu the platform depends on your case and hospital. Read more on robotic hip replacement and the Mako platform.

During surgery the system checks cup position against the plan — on Mako, the arm holds reaming and cup placement inside it — and reports leg length and offset as he works. The robot never holds a scalpel or makes a decision, the femoral stem is still sized by hand, and the plan changes if your anatomy calls for it. Hardware left from earlier surgery, a badly deformed joint or major bone loss can alter the plan or the platform. As with knees, robotic assistance carries no technology fee.

Most of Dr. Morton’s hips use a titanium cup, a highly cross-linked polyethylene liner and, usually, a ceramic head, with cementless fixation when bone quality allows. That combination wears slowly, runs quietly and avoids metal-on-metal concerns. It is a starting point, not a rule, and the hip bearings guide explains the alternatives:

• Ceramic-on-ceramic wears least on paper, but it carries a small risk of squeaking, a rare risk of ceramic fracture, and less tolerance for imperfect position.
• Larger heads resist dislocation but leave thinner plastic inside the same cup, so head size is matched to your anatomy.
• A dual-mobility bearing, which adds a second moving surface, is reserved for hips at higher risk of dislocation rather than used routinely.
• For a documented nickel sensitivity, ceramic or oxidized zirconium heads with titanium parts are options; see metal allergy and joint replacement.

You have a real say in the choice. What drives it is your age, bone, anatomy, activity and the robotic plan — never a preference for a particular brand.

Patients notice leg length quickly. Offset — how far the thigh bone sits from the pelvis — matters too: too much can put extra pressure on the hip and cause pain, and too little can leave the hip unstable. Both are planned before surgery and checked during it, with X-rays taken while you lie on your back and, with robotic guidance, measured on screen against the plan.

Even so, equal leg length cannot be guaranteed by any surgeon or any robot. Length is weighed together with stability, offset and soft-tissue tension, and a stable, well-balanced hip is the priority. In the early weeks the operated leg often feels longer because the pelvis and muscles are still adjusting after years of arthritis, and that feeling frequently settles. A shoe lift should wait for a proper measurement rather than the first few days. A difference that persists is evaluated with an exam and imaging to tell a true difference from an apparent one. More in leg length after hip replacement.

Many hip patients go home on the day of surgery, helped by the muscle-sparing approach and opioid-sparing pain control; others stay one night. The checklist is the one used for knees: stable health with conditions under good control, a companion at home for the first night or longer, a way to handle any steps or stairs, and readiness to walk early. Unstable heart disease, severe sleep apnea or other conditions that may need a night of monitoring point toward a planned stay at The Queen’s Medical Center or Adventist Health Castle.

Hawai‘i Island patients who qualify can have a same-day Mako hip at Hilo Community Surgery Center. Because that center is same-day only, someone needs to drive you home and stay with you through the first days. Age alone does not decide candidacy, and neither does the clock: you go home after the milestones are met. Details are on the outpatient joint replacement page.