Knee Replacement in Pictures

1

Stage One

Surgical Approach & Skin Incision

Anterior view of the knee showing the midline skin incision marked in blue pen over the patella

The skin incision. A straight midline longitudinal incision is marked in blue over the anterior knee, centred over the patella. This single incision gives access to all the structures required for the operation.

Anterior anatomy of the knee showing quadriceps muscle, patellar tendon and the dashed medial parapatellar arthrotomy line

The arthrotomy line. The medial parapatellar arthrotomy — the incision into the joint capsule — runs along the medial border of the quadriceps tendon, patella and patellar tendon (dashed line). This gives access to the joint while preserving the extensor mechanism.

The Medial Parapatellar Approach

Total knee replacement is performed through a straight midline skin incision approximately 15–20 cm in length, centred over the patella. This gives excellent access to the entire knee joint while minimising soft tissue disruption.

Through this skin incision, a medial parapatellar arthrotomy is made — an incision into the joint capsule running along the inner border of the quadriceps tendon, the patella and the patellar tendon. This divides the joint capsule and allows the patella to be reflected laterally, exposing the arthritic femoral condyles, tibial plateau and — importantly — the joint line that must be accurately restored by the reconstruction.

The quadriceps muscle itself is not divided or detached — the approach passes through the tendon medial to the muscle belly, preserving the extensor mechanism that is so important to post-operative function and recovery.

Single straight midline skin incision — no muscle detachment
Medial parapatellar capsulotomy gives full joint access
Patella is subluxed or everted laterally to expose the joint
The approach is closed in layers at the end of the procedure

2

Stage Two

Exposing the Joint

From Skin to Joint — The Surgical Layers

After the skin incision is made, the layers of tissue are divided one by one until the joint is fully exposed. Each illustration here shows a progressively deeper layer, from the subcutaneous fat immediately beneath the skin through to the joint cavity itself.

Once the skin is divided, the subcutaneous fat layer is encountered — a thick pad of adipose tissue that surrounds and cushions the knee. This is carefully retracted to reach the deep fascia. Below the fascia lies the quadriceps tendon and capsule, which are divided along the medial parapatellar line.

When the joint capsule is opened, the arthritic knee is revealed in its entirety. The worn and damaged surfaces of the femoral condyles and tibial plateau are immediately apparent — with loss of articular cartilage, eburnated (polished) bone surfaces, osteophytes around the joint margins, and often a swollen, inflamed synovial lining. This is the diseased anatomy that the operation aims to replace.

Subcutaneous fat layer exposed directly beneath the skin incision
Deep fascia and quadriceps tendon/capsule divided along arthrotomy line
Patella subluxed or everted to expose the full joint surface
Osteophytes around the joint margins removed before bone cutting begins

Intraoperative illustration showing subcutaneous fat exposed between retractors after the skin incision, with the deep fascia visible at the edges

Subcutaneous fat layer. Immediately beneath the skin incision, the yellow subcutaneous fat pad is exposed between retractors. This layer must be divided and retracted to reach the deep fascia and the joint capsule below.

Intraoperative illustration showing the deep quadriceps tendon and joint capsule exposed between retractors after division of the fat layer

The quadriceps tendon & capsule. Below the fat layer, the dense white quadriceps tendon and joint capsule are exposed. The medial parapatellar arthrotomy is made along the medial border of this structure, opening the joint.

$Intraoperative illustration showing the knee joint opened with the patella everted, revealing the arthritic femoral condyles and tibial plateau$

The joint exposed. With the capsule opened and the patella everted, the arthritic knee joint is fully visible. The destroyed cartilage surfaces, eburnated bone and osteophytes characteristic of advanced osteoarthritis are clearly seen.

3

Stage Three

Bone Preparation — Tibial Cuts

Illustration of the surgeon holding the extramedullary tibial alignment rod against the leg, checking alignment from ankle to knee

Extramedullary tibial alignment. The surgeon checks the tibial alignment using an extramedullary rod running from the ankle to the knee. This confirms the correct varus/valgus angle and tibial slope for the proximal tibial cut before the cutting guide is fixed in position.

Illustration showing the tibial slope cutting guide in situ labelled TIB 0 DEG RIGHT, 4mm offset, with the arthritic tibial plateau visible

Tibial slope guide. The tibial cutting block set to 0° slope, right knee, with 4 mm offset. The guide controls the posterior slope of the tibial cut — a critical parameter that influences the kinematics and stability of the completed replacement.

Preparing the Tibia

Bone preparation begins with the tibia. A carefully planned resection of the proximal tibial surface — removing only the minimum amount of bone necessary — creates a flat, well-aligned platform on which the tibial implant will be seated.

The tibial cut is controlled by a cutting guide that is precisely aligned using either an extramedullary alignment system (a rod running from the tibial plateau down to the ankle) or an intramedullary rod passed into the tibial canal. The guide controls three critical parameters: the varus/valgus angle of the cut (which must be perpendicular to the mechanical axis of the tibia), the posterior slope (typically 0–5°, which influences flexion kinematics), and the resection depth.

Getting the tibial cut right is one of the most important steps in the entire procedure. An incorrectly oriented tibial resection will compromise the alignment of the entire reconstruction and cannot easily be corrected once made. Mr. Lodge uses meticulous alignment checks before the saw is applied.

Tibial cut made perpendicular to the mechanical tibial axis in the coronal plane
Posterior slope set to 0–5° depending on implant system and patient anatomy
Minimum bone resection to preserve bone stock for any future revision
Cut depth confirmed by reference to the less-worn tibial plateau surface

Why the tibial cut matters: The tibial component must be perpendicular to the mechanical axis of the leg — not the anatomical axis. Even a small error in tibial alignment concentrates load asymmetrically across the bearing surface, accelerating wear and risking early failure. Meticulous alignment at this stage is foundational to a durable outcome.

4

Stage Four

Femoral Bone Preparation & Cutting Guides

Preparing the Femur

With the tibia prepared, attention turns to the distal femur. The femoral bone cuts are more complex than the tibial cut — the femoral component must be sized, positioned and rotationally aligned correctly to restore the natural shape of the femoral condyles and to balance the flexion and extension gaps.

An intramedullary rod is passed into the femoral canal to establish the correct valgus angle for the distal femoral cut (typically 5–7°), which is necessary to restore the mechanical axis of the leg. The femoral sizing guide is then applied to determine the antero-posterior dimension of the femoral component — choosing the correct implant size to avoid overhang or notching of the anterior femoral cortex.

A four-in-one femoral cutting block is then applied, guided by the sizing and rotation measurements. This precision instrument makes five cuts in a single fixation — the distal, anterior, posterior, anterior chamfer and posterior chamfer cuts — that together define the shape of the prepared femur to match the inner surface of the femoral implant.

Intramedullary rod establishes the correct valgus angle for the distal femoral cut
Femoral component sized to avoid anterior notching or posterior overhang
Rotational alignment set to balance the flexion gap and optimise patellar tracking
Four-in-one cutting block makes all five femoral cuts in a single step

$Intraoperative illustration showing the knee joint with the patella subluxed and the arthritic distal femur and tibial plateau fully exposed between retractors with a reamer visible$

Intramedullary referencing. The joint is held open with retractors as the intramedullary alignment system is introduced into the femoral canal. The arthritic distal femur and tibial plateau are visible — the surfaces that will be resected and replaced.

Illustration showing the tibial cutting guide fixed to the proximal tibia with alignment pins, ready for the saw cut

Tibial cutting guide in position. The extramedullary tibial cutting guide is fixed to the proximal tibia with pins. The guide precisely controls the level, slope and alignment of the tibial resection — the flat cut across the top of the tibia that creates the surface on which the tibial tray will sit.

Illustration of the Attune femoral sizing guide seated on the distal femur, with the intramedullary rod and sizing marks visible

Femoral sizing guide. The femoral sizing and positioning guide (Attune system) is seated on the prepared distal femur with the intramedullary rod establishing the valgus angle. This determines the antero-posterior size of the femoral component and sets the rotational alignment before the cutting block is applied.

Detailed labelled illustration of the femoral four-in-one cutting block showing sulcus window, anterior and posterior referencing pin holes, posterior saw capture and narrow size reference cutout

The four-in-one femoral cutting block. A detailed view of the femoral cutting block with all key features labelled — sulcus window for placement reference, anterior down and posterior up referencing pin holes, modular posterior saw capture for gap balancing, and the narrow size reference cutout. All five femoral cuts are made through this single instrument.

5

Stage Five

Trial Components & Gap Balancing

Illustration of the trial femoral component (5R) and tibial tray (Sz5, FB, 6mm) assembled and reduced, viewed from the front of the knee

Trial reduction. Trial components in place — size 5R femoral component and size 5 tibial tray with a 6 mm fixed-bearing polyethylene trial insert. The knee has been reduced to assess stability, range of movement, patellar tracking and gap balance before definitive fixation.

Two-part illustration showing the patellar saw clamp on the left and the normal knee anatomy on the right

Patellar assessment. During trial reduction the patellar tracking is carefully assessed — the patella must glide smoothly and centrally in the trochlear groove of the femoral component throughout the arc of flexion. Where indicated, the patella is resurfaced using a patellar saw guide (left) to create a flat bony surface for the patellar button component.

Trialling the Reconstruction

Before the definitive implants are cemented or press-fitted into position, metal trial components are assembled and the knee is reduced. This "trial reduction" is one of the most important steps in the operation — it allows the surgeon to assess the reconstruction in full before making any irreversible decisions.

During the trial, gap balancing is assessed — confirming that the space between the femoral and tibial components is equal in both extension (the knee straight) and flexion (the knee at 90°), and that the tension in the medial and lateral ligaments is symmetric through the full arc of movement. An unbalanced knee will feel either loose or tight, will not move smoothly, and will experience uneven wear on the bearing surface.

Patellar tracking is also carefully observed — the patella should glide centrally in the trochlear groove of the femoral component without tilting or subluxing throughout the arc of flexion and extension. Poor patellar tracking produces anterior knee pain and may necessitate modification of component position or rotation.

Trial femoral and tibial components assembled with a trial polyethylene insert
Flexion and extension gaps assessed for equality and symmetry
Patellar tracking observed — central and smooth tracking is essential
Any adjustments to component position or size made at this stage
Patellar resurfacing performed where indicated before final implantation

6

Stage Six

Definitive Implant Insertion

Cementing the Final Components

Once the trial reconstruction has been confirmed to be well-balanced, correctly sized and stable, the definitive implants are prepared for insertion. In Mr. Lodge's standard practice, the components are fixed using acrylic bone cement — the most extensively evidenced fixation method in knee replacement, with decades of outcome data confirming excellent longevity.

The bone surfaces are thoroughly washed with pulsed lavage to remove bone debris and fat, optimising cement penetration. Bone cement is mixed and applied to the prepared bone surfaces before the components are impacted into position. The cement is pressurised into the trabecular bone, filling the spaces and creating a strong mechanical interlock. Excess cement is carefully removed from around the component margins and from within the joint before it sets.

The tibial baseplate is seated first, followed by the femoral component, and finally the polyethylene insert is locked into the tibial tray. The knee is held in extension while the cement cures — typically three to four minutes — before range of movement is tested and the final stability of the reconstruction is confirmed.

Bone surfaces washed with pulsed lavage before cementing
Cement pressurised into tibial and femoral bone surfaces for optimal penetration
Excess cement removed meticulously from the joint margins
Tibial tray seated first, then femoral component, then polyethylene insert locked in
Knee held in extension while cement cures

$Illustration of the tibial baseplate with keel being lowered onto the prepared tibial plateau cut surface$

Tibial baseplate insertion. The tibial tray with its central keel is lowered onto the prepared tibial plateau. The keel anchors the component in the tibial bone; the flat tray provides the platform on which the polyethylene bearing will sit. Cement is applied to the undersurface before the component is impacted into final position.

Illustration of the femoral component being impacted onto the prepared distal femur with a cement mantle visible between component and bone

Femoral component insertion. The definitive femoral component is impacted onto the prepared distal femur. The component fits precisely over the five cut surfaces made by the four-in-one cutting block. A cement mantle between component and bone provides immediate strong fixation while distributing load evenly across the resected surface.

7

Stage Seven

The Completed Reconstruction

Lateral view illustration of the completed total knee replacement showing femoral component, polyethylene bearing and tibial tray in final position

The completed total knee replacement. A lateral view of the reconstructed knee with the definitive components in place — the curved cobalt-chrome femoral component articulating on the polyethylene bearing, supported by the tibial tray. The natural bony contours of the femur, tibia and fibula are visible alongside the implanted components.

Labelled illustration of a partial (unicompartmental) knee implant in situ, with femur, patella and tibia labelled

Partial (unicompartmental) knee replacement. In carefully selected patients where arthritis is confined to a single compartment, a partial knee replacement — replacing only the medial or lateral compartment — may be considered. This preserves the unaffected compartment and all ligaments, resulting in a potentially more natural-feeling knee with a faster recovery.

Wound Closure & Recovery

With all components seated and the reconstruction confirmed to be stable, well-aligned and correctly balanced, the wound is closed in layers. The joint capsule and medial parapatellar arthrotomy are repaired with strong absorbable sutures — restoring the extensor mechanism and the soft tissue envelope around the new joint. Subcutaneous tissue and skin are then closed in layers using absorbable buried sutures with wound glue over the wound to achieve a watertight closure. Very rarely, allergic reactions can occur to the glue — this typically presents as a rash. Whilst it is important to get this reviewed, it is typically very easily and quickly managed with a low-dose topical steroid cream. Please make your surgeon aware if you have had reactions to topical skin glues with previous surgeries, or equally to nail glues used for cosmetic nail extensions.

Local infiltration analgesia is injected into and around the wound at the end of the procedure, providing targeted pain relief into the early post-operative period. A compressive dressing is applied.

Most patients are standing and beginning to mobilise with a physiotherapist within hours of returning from theatre. The commitment put into physiotherapy in the first six weeks — and particularly the effort to achieve good knee flexion early — has a direct and lasting influence on the final functional outcome.

Medial parapatellar arthrotomy repaired with strong absorbable sutures
Local infiltration analgesia injected at wound closure for post-operative pain control
Compressive dressing applied; patient mobilised within hours of surgery
Physiotherapy begins on the day of or morning after surgery
Full recovery typically takes 6–12 months; committed rehabilitation is essential

For more on what to expect after surgery — including the recovery timeline, physiotherapy, VTE prevention, flying advice and dental guidance — see the Your Operation page.