Extensile Anterior and Posterior Knee Exposure for Complete Synovectomy of Diffuse Tenosynovial Giant Cell Tumor (Pigmented Villonodular Synovitis)
Authors: Lingamfelter Max , Novaczyk Zachary B. , Cheng Edward Y. 
Published: May 2022

Background:
Diffuse tenosynovial giant cell tumor (TGCT), also known as pigmented villonodular synovitis, is a benign, neoplastic disease of the synovium that can lead to joint destruction, osteoarthritis, and long-term morbidity
1,2
. Often, there is extra-articular involvement in the intercondylar notch and posterior soft tissues. A complete anterior and posterior synovectomy of the knee is indicated for treating diffuse TGCT when the anterior and posterior compartments of the knee joint are involved. Additionally, either an anterior or posterior synovectomy may be performed when the TGCT is limited to 1 compartment of the knee. Although an anterior synovectomy is relatively straightforward technically, a posterior synovectomy is challenging because of the presence of the neurovascular and muscular structures, which limit access, and because of the infrequency of the procedure.

Description:
The surgical technique for open anterior and posterior knee synovectomy is performed under 1 anesthetic via separate exposures with the patient initially supine and then prone. In cases of focal TGCT, in which both the anterior and posterior compartments are involved, either an anterior or posterior approach can be utilized in isolation to target the affected compartment. The anterior approach is performed via anteromedial parapatellar arthrotomy, with care to preserve the meniscal attachments and ligaments. Once the suprapatellar pouch is visualized, all tissue deep to the quadriceps muscle and tendon, extending around to the femoral periosteum, is excised en bloc. Attention is then turned to the undersurface of the patella, fat pad, distal aspect of the femur, and proximal aspect of the tibia. The tumor may be embedded within the fat pad and must be removed. Any tumor remnants within the medial or lateral gutter or beneath the menisci are excised with use of a standard or pituitary rongeur or curets. The quadriceps tendon, subcutaneous tissue, and skin are closed over a deep drain, and the patient is turned prone and re-prepared for the posterior approach. The posterior synovectomy utilizes an S-shaped incision either superolateral to inferomedial or superomedial to inferolateral, depending on the location of the TGCT. The popliteal artery and vein and the tibial and common peroneal nerves are identified, mobilized, and protected during retraction. This step requires ligating the geniculate and other small branches of the popliteal artery and vein. To expose the posterior femoral condyle, the medial and/or lateral heads of the gastrocnemius must be tagged and released by dividing the myotendinous origin from the posterior aspect of the femur at the proximal extent of the condyle.

Alternatives:
Although surgical resection is the primary treatment for TGCT, nonsurgical alternatives include radiation therapy (either external beam or radiosynoviorthesis) and the use of pharmacologic agents. Radiation therapy is associated with complications such as irreversible skin changes, arthrofibrosis, arthritis, osteonecrosis, and radiation-induced sarcoma
1,2
. Systemic agents such as tyrosine kinase inhibitors (e.g., nilotinib and imatinib) or agents targeting the CSF-1 (colony-stimulating factor-1) pathway (e.g., pexidartinib and emactuzumab) are active against TGCT. The agents are typically employed in recurrent, advanced, and unresectable situations in which surgical morbidity would outweigh the therapeutic benefit
2
. Aside from open synovectomy, arthroscopic synovectomy—usually anterior—has been utilized by some centers.

Rationale:
To our knowledge, there is no Level-I study indicating the superiority of 1 surgical technique over the other treatments for diffuse TGCT. Anterior arthroscopic synovectomy, in isolation, for diffuse TGCT has demonstrated recurrence rates as high as 92% to 94%
1
. Recent studies comparing anterior and posterior open and arthroscopic synovectomy have demonstrated mixed results, are limited by being retrospective, and are subject to selection bias because of the open synovectomy being selected for more extensive disease
2,3
. The mixed results may a result of variation in both tumor size and location about the knee joint
2
. The benefit of an open anterior and posterior synovectomy is that it can provide optimal exposure for large and extra-articular tumor masses that would not be accessible using an arthroscopic approach and allows for complete, gross total excision without morsellization of the tumor. The surgeon must be familiar and facile with vascular dissection techniques, even if the soft tissues surrounding the vascular structures are preserved as much as possible, in an effort to minimize postoperative edema
4
.

Expected Outcomes:
Open anterior and posterior synovectomy provides improved exposure for large and extra-articular tumor masses and has a 5-year recurrence-free survival of 29% to 33%
5–7
. Pain associated with diffuse TGCT has been demonstrated to improve in 59% of cases, with swelling reported to improve by 72% in patients following surgical intervention
7
. No significant difference has been reported when comparing open versus arthroscopic synovectomy in terms of arthritic progression, with 8% of patients progressing to a total knee arthroplasty at a mean follow-up of 40 months3.

Important Tips:

Careful preoperative planning is crucial: note all locations of posteriorly located tumor on magnetic resonance imaging and in relation to anatomic landmarks and neurovascular structures in order to guide dissection.It can be advantageous to have multiple blunt retractor options available when dissecting in tight spaces.Be prepared for vessel ligation with free ties, vessel clips, and additional clamps.The technical ability to dissect and mobilize the popliteal vessels is essential, but this step can be tedious.At the time of incision, preserve the integrity of the popliteal fascia to facilitate a good closure later, as this step avoids the herniation of tissues in the popliteal fossa. Because this fascial tissue is fragile, the use of a monofilament rather than braided suture in addition to the placement of far-near-near-far-type figure-of-8 sutures minimizes the risk of tearing the fascia during reapproximation.To ease retraction of the soft tissues, slightly flex the knee to relax the hamstring and other muscles and neurovascular structures. This will also reduce the risk of a postoperative nerve palsy.Although separate instruments for the anterior and posterior portions of the procedure are not necessary, separate drapes, gown, and gloves and other preoperative preparation should be readied in advance for the second portion of the procedure in order to save operative time.

Acronyms & Abbreviations:

PVNS = pigmented villonodular synovitisROM = range of motionMRI = magnetic resonance imagingGastroc = gastrocnemiusPDS = polydioxanone sutureCAM = controlled ankle motionASA = acetylsalicylic acid (aspirin)