(Alternate title) Evaluation of Meniscal Extrusion with Posterior Root Disruption and Repair using Ultrasound

Transcription

1 Evaluation of lateral meniscal position with weight bearing: Ultrasonography to measure extrusion with intact, torn and repaired posterior root attachments (Alternate title) Evaluation of Meniscal Extrusion with Posterior Root Disruption and Repair using Ultrasound By Grant Rowland MD, Damon Mar MS, Gary Hinson MD, Terence McIff, PhD, and Joshua Nelson MD, PharmD Investigation performed at The University of Kansas Medical Center, Kansas City, Kansas Background: Meniscal extrusion is associated with increased contact pressure and decreased contact area in the ipsilateral joint space. The altered stress pattern can contribute to the advancement of knee osteoarthritis. The purpose of this study was to measure the relative position of the lateral meniscus within the knee under physiologic loads to determine the integrity of the posterior root. A novel technique was used to measure meniscal position with a portable ultrasound machine under physiologic loads. Our hypotheses were that (1) a significant increase in the amount of lateral meniscal extrusion would be exhibited with 50% and 100% posterior root tears compared to intact menisci, (2) imaging under loaded conditions would yield significantly larger extrusion measurements compared to unloaded state, and (3) meniscal position and extrusion following posterior root repair would correlate with the intact state. Materials & Methods: Ten unmatched, fresh frozen cadaver legs were utilized (mean age, 68.5 years; range, years). A mechanical load frame (MLF) was used to apply a static, physiologic (70 kg) axial load through the knees. A portable, hand held ultrasound was utilized for image capturing of the lateral meniscus in association with (1) an intact posterior root attachment, (2) a 50% cut posterior root, (3) a 100% cut posterior root, and (4) repaired posterior root attachment. Images were obtained on each knee while in an unloaded condition, and again while loaded with 70 kg for each of the above injury levels, and again following repair. Lateral meniscal extrusion was defined as the distance from the outer rim edge of the meniscus to the lateral most edge of the tibial plateau. Results: Significant differences in extrusion were noted between the intact and 50% cut groups (p=0.028), between the intact and 100% cut groups (p<0.001), and between the 50% cut and 100% cut data groups (p=0.016) all in the loaded position. No significant difference was found in extrusion between intact state and repaired posterior root in the axially loaded position (p=0.174). A two factor ANOVA with replication revealed both load (p=0.003) and injury level (p=0.005) to have significant effects on the mean extrusion of the lateral meniscus. Discussion: Using a cadaver model, we demonstrated that sectioning of the lateral meniscus posterior root will produce significantly increased lateral extrusion of the meniscus under weight bearing at physiologic loads. Unlike MRI evaluation, weight bearing ultrasound images produce a functional assessment of meniscus integrity. After trans tibial root repair, lateral meniscus position was shown to be similar to the intact state, under physiologic loading. In addition, this dynamic weight bearing ultrasound technique may be a better functional assessment of meniscus integrity than traditional non weight bearing MRI. Further clinical studies are needed to discern indications and technique to best address this often under appreciated clinical presentation.

2 Background The lateral meniscus has well documented anatomic features that provide stability within the knee and protection of the articular cartilage. The structural makeup of the meniscus enables the adaptation of the incongruent knee joint; which is essential to meniscal function. The anterior and posterior root attachments create a firm anchor to the subchondral bone through the insertional fibers or meniscal root. [1] Furthermore, the lateral meniscus is loosely attached to the surrounding capsule and popliteus tendon. Load transmission is considered an integral function of the meniscus, in addition to lubrication, proprioception and joint stabilization. The position and shape of the meniscus provide structural support between the incongruent semicircular femoral side and the rather flat tibial side of the knee joint. [2] In full extension the lateral meniscal body absorbs nearly 70% of the weight-bearing load, which reduces stress on the articular cartilage and subchondral bone. [2] The menisci will experience tensile, compressive, and shear stresses while transmitting forces during the gait cycle. Due to the microstructure and orientation of the collagen fibers, the compressive loads are distributed in a circumferential manner, also known as hoop stresses. [1] Disruptions of meniscal fibers, including radial tears and root tears, have been shown to cause dysfunction of the meniscus as a load-bearing structure. [3] As Ode et al [4] demonstrated, radial tears of the lateral meniscus produce increased pressure forces and decreased contact area between the femoral and tibial articulations. In addition to structural integrity, the location of the menisci between the femoral and tibial articulations is essential for functional load-sharing and stability. Significant meniscal extrusion also increases contact forces through the knee. These additional stresses and associated decreased contact surface area can contribute to the advancement of knee osteoarthritis. [5] To our knowledge, there have been no published studies detailing the extrusion of lateral menisci in the setting of posterior root tears. The purpose of our study was to accurately detail the position of the lateral meniscus in cadaver knees under physiologic loads to determine the integrity of the posterior root. A novel ultrasound technique was utilized for measuring meniscal position following serial sectioning of the posterior root and following meniscal root repair. We hypothesized that: (1) a significant increase in the amount of lateral meniscal extrusion would be exhibited with 50% and 100% posterior root tears compared to intact menisci, (2) imaging under loaded conditions would yield significantly larger extrusion measurements compared to unloaded state, and (3) meniscal position and extrusion following posterior root repair would correlate with the intact state. Materials and Methods Approval for use of cadaver specimens was granted by our institutional research review board. A pilot trial was performed on an initial three cadaveric knees (not included in the reported data set of ten specimen) in order to obtain data for sample size

3 determination and procedural standardization. An a priori power analysis was performed with the alpha-error set to 0.05 and the power level at We determined that a sample size of 5 specimens would be required to achieve significance in our extrusion measurements. Utilizing the a priori power analysis and available specimens at our institution, ten fresh-frozen cadaveric lower extremities were obtained from male and female donors (mean age, 68.5 years; range, years) (Table 1). Specimen Preparation All specimens were initially inspected, radiographically evaluated, and arthroscopically evaluated to ensure there was no evidence of previous knee surgery, significant medial or lateral meniscal tears, gross osseous abnormalities, or deficient ligamentous structures. The specimens were then prepared by transecting the femur approximately centimeters (cm) above the joint line and transecting the tibia approximately cm below the joint line. The fibula was transected approximately 4 cm proximal to the tibial cut. Care was taken to preserve the collateral and cruciate ligaments and the popliteus muscle in order to maintain native anatomic stability of the knee. Approximately 5cm of the transected proximal femur and distal tibia were then skeletonized. Finally, the proximal femur and distal tibia of each cadaver knee were fixated in Bondo cement; creating a square potting fixture for the specimen. Our study utilized a custom-built mechanical load frame (MLF) to apply static, axial loads through the cadaver knees (Figure 1). Testing A Sonosite MicroMaxx (***Company info here) Ultrasound machine and 13-6MHz HFL38E transducer with a scanning depth of 6cm was utilized for image capturing. Prepared and potted knees were initially placed into the MLF and ultrasound images were obtained of the lateral meniscus in the unloaded position and loaded position with 70 kg. All menisci were visualized by placing the transducer longitudinally at the joint line slightly anterior to the lateral collateral ligament. These steps were then repeated after arthroscopically sectioning the posterior root of the lateral menisci approximately 50% and then 100% using straight and angled biters. Meniscal sectioning was estimated at 50% under direct visualization of the posterior root with the arthroscope. Ultrasound images were uploaded to a Dicom image viewing system for extrusion measurements. We defined extrusion as the distance measured from the lateral-most edge of the tibial plateau at the level of the joint to a line drawn from the lateral-most edge of the meniscus approximately parallel to the joint (Figure 2). After all data was collected from specimens with 100% posterior root tears, attention was turned to meniscal repair. Using a standard ACL-drill guide, a 2.7mm anteromedial bone tunnel was created that exited near the anatomical footprint of the posterior root attachment. A Smith&Nephew (Company info here) straight Suture Shuttle was used to pass a number 2 Ethibond suture through the posterior horn meniscal tissue. This step was repeated to create a mattress suture within the posterior meniscus. A 14mm fixation button (Smith&Nephew) was then snugly tied directly to the anteromedial tibia to secure posterior root repair. Lastly, ultrasound imaging was then

4 captured of the repaired lateral meniscus and extrusion measurements were repeated as described above. Results A summary of mean meniscal extrusion across serial sectioning of the posterior root is provided in Table 2. The average lateral meniscal extrusion measured 1.51mm, 1.65mm, 1.88mm, and 1.30mm for the intact, 50% cut, 100% cut, and repaired posterior root attachment, respectively, in the non-axially loaded (unloaded) position. Extrusion measurements in the 70-kg loaded position averaged 1.60mm, 1.92mm, 2.48mm, and 1.86mm for the intact, 50% cut, 100% cut, and repaired posterior root attachments. Significant differences in extrusion were noted between the intact and 50% cut groups (p=0.028), between the intact and 100% cut groups (p<0.001), and between the 50% cut and 100% cut data groups (p=0.016) all in the loaded position. No significant difference was found in extrusion between the intact state and repaired posterior root (p=0.174) in the axially loaded position. Data were then analyzed using a two-factor ANOVA with replication to detect significance in the amount of extrusion between loading groups (unloaded versus loaded) and meniscal root states (intact, 50% cut, and 100% cut). ANOVA revealed both load (p=0.026) and injury level (p=0.001) to have significant effects on the mean extrusion of the lateral meniscus. Discussion The purpose of this study was to measure the relative position of the lateral meniscus within the knee under physiologic loads and as a function of the status of the posterior root. Our hypotheses were that (1) a significant increase in the amount of lateral meniscal extrusion would be exhibited with 50% and 100% posterior root tears compared to the intact meniscus, (2) imaging under loaded conditions would yield significantly larger extrusion measurements compared to unloaded state, and (3) meniscal position and extrusion following posterior root repair would correlate with the intact state. Using an in vitro cadaver model, we demonstrated that both axial-loading of the knee and sectioning of the lateral meniscus posterior root will produce significantly increased lateral extrusion of the meniscus. Previous studies have established that lateral meniscal extrusion, in addition to meniscal injury, is associated with progression of osteoarthritis. [5] Ko et al [6] reported that knees with radiographic evidence of osteoarthritic changes have significantly more medial meniscus extrusion with weight bearing as compared to age-matched controls. They did not report a single subject in whom radiographic evidence of osteoarthritis was present in the absence of meniscal extrusion. [6] Being able to identify knees in which pathologic meniscal extrusion was present prior to advanced articular cartilage degeneration could become essential in the orthopedic surgeon s treatment plan. Although there are no strict criteria that define how much extrusion is too much, one can conclude that greater amounts of extrusion interfere with efficient load-transmission and produce greater contact forces across the knee.

5 Arthroscopic posterior root repairs on our cadaver knees produced extrusion amounts that were not significantly different from the native, intact attachments. Relatively few other studies have reported the biomechanical effects of lateral meniscus posterior root repair; however, principles can be inferred from medial meniscal root data. Medial meniscal posterior root tears have a significant impact on femorotibial contact mechanics almost identical to complete medial meniscectomy. [3] This disruption in meniscal function was a direct result of meniscal extrusion from the knee. Allaire et al [3] also demonstrated the restoration of effective load-transmission following medial meniscal posterior root repair when compared to intact root attachments. In our study, the measured lateral meniscal extrusion in the unloaded and axially loaded positions following successful root repair closely mimicked that of the intact state. This represents an important finding with regards to restoration of lateral meniscal function and contact mechanics through prevention of extrusion. In addition, our study demonstrates the ability to analyze the lateral meniscal position in an axially loaded knee using a hand-held ultrasound machine. Portable ultrasonography can be a reproducible and purposeful tool for dynamic meniscal examination in the office setting. In contrast to a static examination, such as MRI, ultrasound devices can detail information of meniscal position with weight-bearing or flexion, as well as comparative data to the patient s contralateral knee. Several previous studies have outlined the value of modern ultrasonography in the assessment of meniscal tears [7, 8], citing a relatively high negative predictive value of 87%-98.4% and specificity of 69.2%-95.6%. In these studies, advanced sonography machines were utilized, thus enabling radiologists to identify specific hypoechogenic lesions that corresponded to meniscus tears. In our study, a portable, hand-held ultrasonography machine was used to exclusively identify amounts of meniscal extrusion, as all of the meniscal injuries were to the posterior root attachments. This study is not without limitations. Although the protocol placed emphasis on maintaining normal knee kinematics and structural stability, the in vivo meniscal characteristics cannot be entirely equivalent to our fresh-frozen cadaver models. Also, our average specimen age was 68.5 years. Presence of osteoarthritis with associated baseline meniscal extrusion was more prevalent in our older aged specimens. Thirdly, baseline meniscal characteristics and positions can have deviations within a population. Our cadaver specimen data only included one matched pair of knees, as seen in Table 2. Interestingly, the extrusion measurements were remarkably similar across all data points for these specimens. This finding further supports the benefit of immediate, comparative information using an in-office ultrasound machine. Future prospective, randomized clinical studies are needed to fully assess the value of ultrasound examinations of the menisci as a screening tool for meniscal injury and extrusion. In conclusion, increased meniscal extrusion is a pathologic process that can be measured with portable ultrasound devices. Significant extrusion is associated with axial loads in the setting of disrupted meniscal function, such as posterior root tears. This diagnosis should be considered a critical risk factor for accelerated progression of osteoarthritis. Surgical intervention to stabilize the meniscus within the incongruent femorotibial articulations can help to restore meniscal function and position more closely with the native state. In addition, the dynamic ultrasound evaluation can assist in

6 diagnosis of pathologic meniscal extrusion without a discrete tear. Further clinical studies are needed to discern indications and technique to best address this often underappreciated clinical presentation. Bibliography 1. Bruce D. Beynnon, R.J.J., Lauren Brown, Knee, in DeLee and Drez's Orthopaedic Sports Medicine. 2010, Saunders, An Imprint of Elsevier. p Walker, P.S. and M.J. Erkman, The role of the menisci in force transmission across the knee. Clin Orthop Relat Res, 1975(109): p Allaire, R., et al., Biomechanical consequences of a tear of the posterior root of the medial meniscus. Similar to total meniscectomy. J Bone Joint Surg Am, (9): p Gabriella E. Ode, G.S.V.T., Samuel A. McArthur, Justin Dishkin-Paset, Sue E. Leurgans, Elizabeth F. Shewman, Vincent M. Wang, and Brian J. Cole, Effects of Serial Sectioning and Repair of Radial Tears in the Lateral Meniscus. The American Jounal of Sports Medicine, (8): p Berthiaume, M.J., et al., Meniscal tear and extrusion are strongly associated with progression of symptomatic knee osteoarthritis as assessed by quantitative magnetic resonance imaging. Ann Rheum Dis, (4): p Ko, C.-H., K.-K. Chan, and H.-L. Peng, Sonographic Imaging of Meniscal Subluxation in Patients with Radiographic Knee Osteoarthritis. Journal of the Formosan Medical Association, (9): p Pawel Wareluk, K.T.S., Value of Modern Sonography in the Assessment of Meniscal Lesions. European Journal of Radiology, : p Roberto Azzoni, P.C., Is There a Role for Sonography in the Diagnosis of Tears of the Knee Menisci? Journal of Clinical Ultrasound, (8): p. 5. Table 1 Gender Age Laterality Pilot Specimens 1 Unkown Unknown R 2 M 64 R 3 F 87 L Trial Specimens 1 M 90 R 2 M 90 L 3 F 79 L 4 F 35 L 5 F 94 L 6 F 57 R 7 F 88 L 8 F 62 R 9 F 66 L 10 M 24 L

7 Figure 1 Figure 2

8 Figure 3 Table 2 Intactt Measurement (mm) 50% Cut Measurement (mm) 100% Cut Measurement (mm) Repaired Measurement Specimen Side Angle (deg) Supine Unloaded Loaded Supine Unloaded Loaded Supine Unloaded Loaded Supine Unloaded L L R L L L L L R L L Average: Std. Dev.: