An Effective Surgical Strategy for Anteromedial Osteoarthritis of the Knee with Simultaneous Popliteal Cysts Drainage

Summary

Popliteal cysts are frequently found during the pre-operative examination of patients with osteoarthritis being prepared for the unicompartmental knee arthroplasty. These symptomatic cysts usually require treatment. To do this, a unicompartmental knee arthroplasty was performed with internal drainage of the popliteal cyst under the same anesthetic.

Abstract

Unicompartmental knee arthroplasty (UKA) is an established treatment option for anteromedial osteoarthritis, and popliteal cysts are a common finding in the knee among patients with chronic osteoarthritis pain. The two are so closely related that popliteal cysts are commonly discovered during the unicompartmental knee arthroplasty preoperative examination. However, only a few reports exist on the management and outcome of popliteal cysts in the patients receiving UKA for knee osteoarthritis (OA) and popliteal cysts. As such, it is crucial to evaluate different treatment strategies and their management of popliteal cysts. In this paper, we evaluate a surgical strategy for patients with knee anteromedial osteoarthritis and symptomatic popliteal cysts. These patients were treated with UKA and internal drainage of the popliteal cyst. The results shown here, spanning 1-year post-operation follow-up, demonstrated that UKA and internal drainage is an effective surgical protocol for treating anteromedial osteoarthritis with symptomatic popliteal cysts.

Introduction

A popliteal cyst is a mass located in the popliteal area, filled with fluid, which is prevalent in locations of intra-articular lesions of the knee¹. Multiple reports suggest a strong correlation between popliteal cysts and knee osteoarthritis (OA)^2,3. As a result, ~20%-42% of patients with knee OA also experience popliteal cysts^{1,3,4,5,6,7,8}. Most of the cysts are rarely symptomatic and do not generally require therapy, while the symptomatic cysts warrant surgical resection⁹.

Unicompartmental knee arthroplasty (UKA) is widely used in the treatment of anteromedial knee OA^10,11. Popliteal cysts are commonly discovered during the UKA preoperative examination. However, only a few reports exist on the management and outcome of popliteal cysts in patients that received UKA for knee OA and popliteal cysts. This article describes a protocol on how to treat popliteal cysts together with UKA.

Protocol

The present study was approved by the ethics committee of Second Hospital of Shanxi Medical University and all the patients provided written informed consent.

1. Inclusion and exclusion criteria for patients

1. Use the following inclusion criteria.
   1. Select patients diagnosed with anteromedial osteoarthritis of the knee where conservative treatment failed. Diagnose anteromedial osteoarthritis of the knee by anteroposterior x-ray, based on a narrowed medial compartment of the knee but a normal lateral compartment.
   2. Verify the presence of an intact anterior cruciate ligament using clinical and intraoperative assessments. Identify the anterior cruciate ligament through preoperative magnetic resonance imaging (MRI) and a negative sign in the anterior drawer test; then, verify its integrity intraoperatively by probing with the hook instrument. An intact anterior cruciate ligament is a prerequisite for the patients undergoing UKA.
   3. Select patients having a <10° flexion contracture. Flexion contracture means that the knee is unable to fully extend to 0°, either actively or passively.
   4. Select patient with a >90° range of motion (ROM) of the knee. It is also a prerequisite for the patients undergoing UKA.
   5. Select patients diagnosed with popliteal cysts after ultrasonography and MRI examinations.
      1. With the ultrasound, identify a popliteal cyst as a well-defined and unilocular collection of anechoic or hypoechoic fluid between the tendons of the medial head of the gastrocnemius and semimembranosus.
      2. With the MRI, identify a popliteal cyst as a delineated mass with low signal intensity on the T1-weighted image, high signal intensity on the proton density-weighted fat saturation image, and a fluid-filled neck of the cyst communicating with the joint on the axial images.
   6. Classify popliteal cysts based on the Rauschning and Lindgren (R-L) knee grade, which is used to evaluate the severity of popliteal cysts¹². Based on the R-L knee grade, classify the cysts as grade 0, grade I, grade II, and grade III. Select pre-operative grade II, and grade III cysts, which are symptomatic, for treatment.
2. Use the following inclusion criteria.
   1. Exclude patients with a history of prior knee joint surgery.
   2. Exclude patients diagnosed as having asymptomatic popliteal cysts.
   3. Exclude patients who dropped out of follow-up or patient with incomplete follow-up data.

2. Surgical techniques

NOTE: The same group of surgeons conducted all the operations included in the study. Moreover, ensure that all the participants underwent the standard Oxford UKA surgical procedure with spinal anesthesia¹⁰. In case of a symptomatic popliteal cyst, Oxford UKA was performed, along with internal drainage of the popliteal cyst before implantation of the Oxford phase III medial unicondylar knee prosthesis. Perform the internal draining of the popliteal cyst as described below.

1. Sedate the patient with spinal anesthesia as per the standard operating procedure. Ensure complete loss of sensation below the patient's waist to confirm proper anesthetization.
2. Use an oscillating saw blade to excise the plateau. Lever the plateau up with a broad osteotome and remove it. Identify a wide space between the tibia and the femur following which the internal exit of the cyst can be visualized (Figure 1).
3. Open the internal exit of the cyst to 5-8 mm with a knife. This will help in widening and clearing the communication between the joint and the cyst and restore the bidirectional fluid flow.
4. Squeeze the popliteal cyst by hand outside the skin until all the viscous cyst fluid flows into the joint cavity through the exit of the cyst. Draw out the remaining cyst fluid by applying 30 kPa of negative pressure.
5. Mill the femoral condyle using the number of spigots required by the ligament balancing technique and a spherical cutter. Cement the prosthesis sequentially from the tibial side to the femoral side when the trial implantation test is satisfactory. Complete the reconstruction by snapping the chosen bearing into place and the procedure is ended.

3. Postoperative rehabilitation

1. Ask the patients to perform straight-leg raises and isometric exercises on the first day after surgery. To improve the knee function, ask the patients to perform full weight-bearing exercises, including standing and walking slowly with the assistance of a walker, 2 days after operation.
2. For postoperative analgesia, ensure that all the patients receive postoperative administration of 40 mg of parecoxib intravenously every 8 h. To prevent blood clots, give patients anticoagulant therapy with a 10 mg dose of rivaroxaban daily at day 1 to 2 weeks post operation.

4. Efficacy evaluation

1. Obtain a visual analog scale (VAS) score for all the patients¹³. Use the VAS score to indicate the degree of pain by asking the patient to make a mark on the horizontal line according to their feeling: 2-4 points represent mild pain, 5-7 points represent moderate pain, and 8-9 points represent severe pain.
2. Obtain a hospital for special surgery (HSS) score for all the patients¹⁴. The HSS score mainly includes six aspects of pain, function, joint mobility, muscle strength, knee flexion deformity, and knee stability. Classify the score as follows: >85 as excellent, 70-84 as good, 60-69 as fair, and <59 as poor.
3. Obtain a Western Ontario and McMaster Universities Arthritis Index (WOMAC) score for all the patients¹⁵. The WOMAC score assesses the knee through three domains: pain, stiffness, and joint function. Scores range from 0 to 96 for the total WOMAC, where 0 represents the best health status and 96 the worst possible status. The higher the score, the poorer the function.
4. Assign a Rauschning and Lindgren (R-L) knee grade¹² to evaluate the severity of the popliteal cysts. Based on the R-L knee grade, classify the cysts as grade 0, grade I, grade II, and grade III as described below.
   1. Grade a cyst as 0 for no swelling or pain, no limitation of range of motion, no instability or weakness, and no limitation in work or sports participation.
   2. Grade a cyst as I for slight swelling and discomfort after strenuous exercise, some giving-way or weakness, muscular atrophy of <1 cm, negligible limitation of range of motion (<10°), no hard labor, and no strenuous sports such as athletics or a ball game.
   3. Grade a cyst as II for moderate swelling, pain following moderate exertion, slight or moderate instability, locking, and muscular atrophy of 1-2 cm, limitation of range of motion between 10° and 20°, no physical work, limited participation in sports.
   4. Grade a cyst as III for considerable and tense swelling, severe pain interfering with activities of daily living, pain at rest, disabling instability, contractures, and muscular atrophy of >2 cm, limitation of range of motion >20°, stopped working due to knee derangement, no participation in sports.

Results

Clinical evaluation
Each patient was followed up for at least 1 year after the operation. At 1 year postoperatively, the postoperative VAS score significantly decreased from 7.0 ± 0.9 to 0.6 ± 0.7 (P < 0.05); the HSS score improved from 48.3 ± 8.5 preoperatively to 87.8 ± 4.6 (P < 0.05); and the WOMAC score decreased from 56.0 ± 9.6 preoperatively to 11.6 ± 5.0 (P < 0.05). The symptoms of popliteal cysts were instantly relieved for all the eight patients af...

Discussion

A popliteal cyst, otherwise known as a Baker's cyst, is the knee joint disorder that is prevalent among the middle-aged and older population^16,17. The incidence of popliteal cysts, in combination with symptomatic knee joint disease, is between 9.2% to 38%, depending on the location and the analysis^18,19,20. Approximately 20%-42% of the patients with knee OA also have...

Materials

Name	Company	Catalog Number	Comments
Excel	Microsoft		digital table software
Magnetic resonance inspection (MRI)	General Electric Company		Imaging examination of popliteal cyst before and after surgery.
Oxford® Partial Knee surgery system	ZIMMER BIOMET	NONE	For the catalog numbers refer to Oxford Partial Knee Microplasty Instrumentation (femoral component, tibial component, meniscus bearing)
ultrasound	General Electric Company		we used ultrasound to observe changes in the postoperative cysts