Open anterior synovectomy for diffuse pigmented villonodular synovitis of the knee

Pre-operative AP radiograph of the right knee showing joint effusion and some subtle early degenerative changes in the medial tibio-femoral compartment (osteophytosis and subchondral sclerosis) but no bony erosions.

Lateral radiograph of the distal femur and knee showing a solid soft-tissue mass in the suprapatellar pouch and no erosions of the bone preserved patello-femoral articulation.

Pre-operative T2-weighed coronal MRI sequence showing high signal medial and lateral intra-articular soft-tissue masses representing the PVNS. There is no evidence of any erosion into the bone demonstrated by the absence of any signal change in the bone of the distal femur.

Sagittal T2-weighted MRI scan through the centre of the joint showing evidence of a high signal soft-tissue mass extending throughout the suprapatellar pouch with an effusion and extension of the disease to the posterior portion of the joint around the PCL and posterior capsule.

Axial T1-weighted MRI scan showing intra-articular soft tissue tumour consistent with PVNS in the anterior and posterior portions of the joint, almost encircling the distal femur circumferentially.

A thigh high tourniquet is applied with an exclusion U-drape. Initial skin prep is with alcoholic chlorhexidine. This is repeated prior to further draping.

After double chlorhexidine skin preparation, a bowel bag is placed over the foot and Ioban incisional drapes are applied as shown. The setup is the same as for a knee replacement with a lateral support and a bolster under the foot.

Pre-operatively the anatomy has been marked on the skin showing the patella, the patellar tendon, the quadriceps tendon and the joint line between the tibia and the femur. Medial to the patellar tendon is the planned surgical incision to facilitate resection of the tumour via a medial para-patellar approach in an expectation that the patient may require further surgery through this approach for a knee replacement, hence the positioning of the incision.

A medial para-patellar skin incision is made extending from just below the tibiofemoral joint line to proximal to the suprapatellar pouchThe midline skin incision is made identical for a knee replacement . After the dermis, the fat is dissected using diathermy until the joint capsule is reached.

Identify patella and medial border of patella tendonThe (PT) patellar tendon and medial border of the (P) patella has been identified. In this photograph the anatomy has been drawn using a marker pen with a dotted line marking the medial para-patellar capsulotomy: identify the natural edge of the patella tendon medially (illustrated here with the continuous line). This is the landmark when making your medial para-patellar incision between the tibial tuberosity and the quadriceps tendon. The incision curves around the patella medially until you reach the quadriceps tendon where a 1cm cuff of tendon should be left medially as you extend up the quadriceps tendon leaving the majority of the tendon lateral to the incision.

leaving a cuff of soft-tissue on the medial border of the patella for closure.

A medial para-patellar arthrotomy is made, leaving a cuff of soft-tissue on the medial border of the patella for closure.The medial para-patellar arthrotomy is made and the PVNS tumour is seen immediately beneath this layer bulging into the wound.
It has a yellow brown appearance consistent with recurrent bleeding into the tumour causing haemosiderin deposition. This is responsible for the characteristic ‘blooming’ MRI artefact due the paramagnetic effect of the iron in haemosiderin (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3640717/).

Begin synovectomy medially deep to vastus medialisUsing McIndoe’s dissecting scissors, the plane between the synovially based tumour and the deep surface of the joint capsule, vastus medialis and the (quadriceps) tendon of vastus medialis is developed; a tip here is to use your assistant to maintain tension on the soft-tissues being retained to make this easier. The quadriceps muscles of the anterior thigh include vastus medialis, intermedius and lateralis and rectus femoris.

Elevate a medial flap, including the medial joint capsule and the vastus medialis.The medial soft tissues have been elevated as a flap (using soft-tissue holding forceps) and the plane between the tumour and the muscle has been developed up to the capsule and the muscular attachments onto bone, as shown in this photograph. Once the dissection takes you beyond tumour tissue onto the bone and outside of the joint the deepest plane of dissection has been reached.

Tip: Once in the right plane, sometimes blunt dissection using fingers can speed the dissection.
Here the distal portion of vastus medialis is being retracted as a flap to enable dissection of the tumour off the distal femur, almost as deep as the inter-muscular septum. The inter-muscular septum is the thick fascial border of the thigh separating the anterior compartment from the medial adductor compartment.

The dissection now moves to the lateral side again using McIndoe’s dissecting scissors to develop the plane between the tumour and the deep surface of the capsule and quadriceps tendon.
A soft-tissue holding forceps is placed onto the quadriceps tendon to maintain tension. The same plane is identified between the lateral capsule, muscle and tendon round to the lateral inter-muscular septum as it arises from the lateral femur. The lateral inter-muscular septum separates the anterior compartment of the thigh from the posterior hamstring compartment.

Again, once the correct plane has been identified, blunt digital dissection can aid the speed of dissection on the lateral side.

Once the medial and lateral gutters have been cleared of PVNS, the apex of the tumour at the proximal extent of the suprapatellar pouch is identified and released off the periosteum using scissors (or diathermy).
The soft-tissue holding forceps are used to retract the leaves of the quadriceps both medially and laterally to improve exposure as shown.

Once the apex of the tumour has been released off the femur and periosteum, the tumour can start to be elevated off the bone.
Dissection is made using diathermy and gentle traction to release the tumour off the femur from a proximal to distal direction. There are no vital structures at risk during this step.

Elevate the tumour off the distal femurThe tumour has been lifted almost completely off the periosteum of the distal femur revealing the (ME) medial epicondyle.

The same process of elevation and dissection away from the femur is repeated on the lateral side. The tumour is now able to fall out of the wound.

Dissection now turns to the peri-patellar region; care is taken to ensure that macroscopically all the tumour is excised from around the (P) patella, the (QT) quadriceps tendon and (PT) patella tendon.The patella cartilage is useful to identify the depth of dissection when performing any synovectomy for tumour or infection. Although I would initially try to release the tumour off the patella with scissor dissection rather than diathermy to avoid thermal necrosis to the articular cartilage, the tissues tend to be tightly adherent here and often I have to resort to using diathermy with care.

The tumour has been dissected off the (P) patella and the deep surface of the (PT) patellar tendon and now remains attached to the femur around the joint surface of the femoral condyles and onto the tibia.

Dissect tumour off the trochleaLooking from the medial side, the tumour is released off the femur immediately proximal to the trochlear groove articular surface of the distal femur using diathermy. Once again maintaining gentle traction aids identification of the correct plane to dissect and care is taken with the diathermy not to damage the articular surface.

The cartilage surface of the femoral condyles and (T) trochlear groove emerge once the tumour has been dissected around the superior trochlea, further revealing the (ME) medial epicondyle. The tumour has not caused any obvious juxta-articular erosions or damage to the articular surface in this particular case despite being fairly extensive.

The tumour is released around the medial femoral condyle, again taking care not to damage the cartilage surface of the distal femur and preserving the MCL origin.One tip at this stage is to use quite firm retraction on the tumour to peel the synovially based tumour off the medial side of the femur. Identifying the correct layer is key to avoiding damage to the stabilising MCL origin which lies 2.5cm posterior to the articular surface of the medial femoral condyle and is identified by palpating for the prominence of the medial epicondyle. Anatomically, because the synovium is the superficial layer and the medial collateral ligament origin is deep to the synovium, the tension pulls the tumour in a layer off the femur without damaging the MCL.
The MCL has a single femoral origin but two divisions: the distal tibial insertion lies at the pes anserinus approximately 6cm distal to the joint line. The proximal tibial insertion blends with the semimembranosus insertion approximately 2cm from the tibial joint line.

Dissection now on the lateral side moves around to the popliteal hiatus, care is taken not to damage the popliteus and LCL tendons which are at risk on the lateral side of dissection. The femoral insertion of the popliteus tendon lies 18mm anterior and inferior to the lateral collateral ligament origin identified by the prominence on the lateral epicondyle. Another origin is from fibula and from the posterior horn of the lateral meniscus in some people (https://www.ncbi.nlm.nih.gov/pubmed/2732260). The femoral and fibular origins of popliteus form the arms of the oblique Y shaped arcuate ligament.
Again, firm tension on the tumour pulls the synovial based PVNS off the sub-synovial tendon origins without damaging them.

Dissect tumour from the cruciate ligaments in the femoral notchHaving released the medial and lateral sides from around the femur, the tumour is dissected carefully from the femoral notch taking care not to damage the anterior cruciate (ACL) or posterior cruciate ligaments (PCL). The tumour can infiltrate into the ligaments and erode into their origins on the posteromedial lateral condyle. Using McIndoe’s scissors and diathermy the ligaments are cleared of tumour down to their insertions onto the tibial spine.
There are two functional bundles of the ACL, an anteromedial bundle (AMB) and posterolateral bundle (PLB), named for the relationship of their insertion on the tibial plateau. Both bundles also attach to the posteromedial aspect of the lateral femoral condyle. Cadaveric studies have demonstrated that in extension the PLB is taut and experiences the greatest force, whereas the AMB is taut in flexion with the highest transmission of forces at 60 degrees of flexion.

Having cleared the femoral notch and released the last remaining tumour off the synovial insertions onto the menisci, the tumour can be removed en-bloc from the patient’s knee joint.

The tumour has been resected on block and is shown on the back table prior to submission for historical analysis.

Photograph of the knee post-resection of the tumour: any final macroscopic signs of disease are now removed with surgical instruments prior to washing and closure.

Photograph from the lateral side showing the disease had been removed from the lateral gutter revealing the (LE) lateral epicondyle and from the deep surface of the (QT) quadriceps tendon inserting onto the (P) patella.

Closure of the jointAfter thorough lavage and haemostasis, the joint is closed over a drain using interrupted 2.0 vicryl sutures to approximate and then a looped PDS monofilament suture for a watertight closure.

The superficial layers are closed with interrupted 1.0 vicryl and then a continuous 2.0 vicryl to the dermis before clips are applied to the skin.

Aquacel dressings are applied plus dressings for the drain which is exiting on the lateral side (not shown). Wool and crepe bandages and a splint are applied in extension for the first 36 hours for pain relief and wound healing.