Knee Immobilization on Meniscal Healing After Suture

CLINICAL ORTHOPAEDICS AND RELATED RESEARCH Number 395, pp. 227–233 © 2002 Lippincott Williams & Wilkins, Inc. Knee Immobilization on Meniscal Healing After Suture An Experimental Study in Sheep Iñigo Guisasola, MD, PhD*; Javier Vaquero, MD, PhD*; and Francisco Forriol, MD, PhD** Immobilization and nonweightbearing may influence the healing of sutured meniscal lesions in the avascular zone. In 12 sheep, 3 to 4 months of age, a 0.5-cm longitudinal lesion was made in the middle segment and posterior portion of the medial meniscus of the left knee in the avascular zone. The lesion was sutured immediately. The knees of six sheep were immobilized with a monolateral external fixator, which crossed the knee, and the knees in the other six sheep were not immobilized. The animals were sacrificed 6 weeks after the operation. Specimens from the anterior meniscus were used for histologic and vascular studies, and the posterior meniscus was used for mechanical testing. Repair was observed in two of 12 sheep in the form of fibrous tissue. Fibrochondrocytes and synovial cells were involved. Meniscal fibrochondrocytes from the nearest meniscal tissue, synovial cells from the femoral and tibial meniscal surfaces, and fibroblastic cells migrating through the suture channel provide cell access to the meniscus lesion. Sutured menisci, immobilized or not, support less than 50% of a normal load and are mechanically weak. In clinical practice, peripheral tears of the meniscus must be repaired, although the clinical success of meniscal healing away from the periphery has not been proven. Immobilization and nonweightbearing may influence healing of meniscal lesions in the avascular zone,11,34 but there is no agreement regarding postoperative care and rehabilitation when a meniscal suture has been used. Valen and Molster31 applied a cast for 6 weeks and did not allow weightbearing. Lerat et al20 allowed early mobilization of the knee and full weightbearing. Rubman et al28 protected the surgically treated knee against weightbearing, allowing and promoting early mobilization of the knee. Dowdy et al11 reported collagen formation in the sutured meniscus after 4 weeks immobilization. Inferior results were seen at 10 weeks. After 8 weeks immobilization, the decrease in collagen content was not regained. The meniscus is a fibrocartilaginous tissue composed of fibrochondrocytes and collagen fibers which are orientated in different ways.6,9,22 Collagen fiber has a circumferential orientation with fibers running parallel to the external peripheral border, forming bundles From the *Orthopaedic Surgery Department, Gregorio Marañon Hospital, Madrid, Spain; and the **Orthopaedic Research Laboratory, School of Medicine, University of Navarra, Pamplona, Spain. Reprint requests to Francisco Forriol, MD, PhD, Department of Orthopaedic Surgery, CUN, 31008, Pamplona, Spain. Received: July 19, 2000. Revised: January 16, 2001; February 28, 2001; May 30, 2001. Accepted: June 6, 2001. 227 228 Clinical Orthopaedics and Related Research Guisasola et al approximately 50 to 150
m in diameter and continuing with tibial insertions in the anterior and posterior horns.6,22 Moreover, radial fibers act as tensors, preventing rupture of the meniscus when it is loaded in the axial axis,6 which explains the anisotropic and unhomogeneous behavior under strain.13 The current authors attempted to determine whether it is possible to heal a meniscal lesion in the avascular area and what role immobilization of the knee plays. MATERIALS AND METHODS The authors used 12 Merino sheep that were 3.5 months of age and weighed 30 to 35 kg. Surgery was done on left knees only. After internal arthrotomy, a complete 0.5-cm longitudinal lesion was made in the anterior and posterior parts of the medial meniscus of the left knee, always in the avascular zone. The lesion was sutured immediately with absorbable material (Dexon® 3⁄0, Braun, St Louis, MO). The knees in six sheep were immobilized (Group A) with a monolateral external fixator (MonotubeTriax®, Stryker Trauma, Geneva, Switzerland) which crossed the knee (two Apex® pins in the femur and two in the tibia, Stryker Trauma). The knees in the other six sheep were not immobilized (Group B). The animals were killed 6 weeks after the operation under general anesthesia with sodium pentobarbital and intravenous administration of potassium chloride. Specimens from the middle segment of the medial meniscus were used for histologic and vascular studies, and the posterior portion of the medial meniscus was used for mechanical tests. Specimens were embedded in paraffin and 4-
m sections were obtained and stained with hematoxylin and eosin, Masson trichrome, and safranin O. The Spalteholz technique24 was done after intraarterial injection of Berlin blue into the femoral artery before sacrifice. The posterior parts of eight medial menisci that were operated on were separated (four from sheep in Group A and four from sheep in Group B) for the mechanical testing. They were stored fresh for 2 to 3 hours (0–4 C), and tested the same day as the sacrifice. The mechanical tests also were done on seven posterior parts of the medial meniscus with no lesion obtained from the right legs of the animals at sacrifice. This enabled the authors to determine the standard mechanical behavior of healthy meniscal tissue when subjected to indentation. Mechanical testing was done using the indentation technique, by doing a test in the center of each lesion with a 1-mm stainless steel cylindrical gauge using universal test machine (Instron, 4.400, High Wycombe, UK) with a 500 N cell load. Testing was done at 4 mm per minute speed and a maximum penetration of 3 mm. The meniscus was located over a metallic device designed for the study. This device has a ramp where the meniscus is located. The authors used plaster of Paris to fix each specimen to the device, which prevented movement of the specimen. A test was done in the center of each meniscal lesion. The data that were obtained were used to draw a graph (N/mm), which showed a relationship between tissue resistance and gauge displacement, the maximum load under compression of meniscus tissue, and the slope of the curve in the linear zone. The load under compression shows the resistance of the tissue to compression and the slope of the curve indicates tissue elasticity. A descriptive and comparative statistical analysis was done between groups (control, immobilized, and not immobilized), comparing maximum load value and slope of the curve. Analysis of variance (ANOVA) and Mann-Whitney U tests were used. All of the comparisons showed differences. The level of significance was established as p  0.05. RESULTS Studying coronal sections of meniscus, the authors observed that all the animals in Group A (knees that were not immobilized) had an empty space between both lesion lips. In Group B (knees that were immobilized), two animals had an active healing response. Chondrocytes in all the specimens were observed but this was not an effective response because active cells were not found in the lesions’ borders (Fig 1). Cells seemed to have come from the synovium of the superior and inferior meniscal surfaces (Fig 2). The characteristics of the repair tissue that bridges lesion lips in animals are fibroblastlike cells (uninuclear or polynuclear) that fill the space. They form connective tissue without Fig 1. Groups of chondrocytelike cells in the lesion border are shown (Stain, Masson trichrome; magnification, 200). A B Fig 2A–B. The response of the avascular meniscus zone to the suture is shown. (A) Cells and tissue penetration from the femoral surface of the meniscus are shown (Stain, Masson trichrome; magnification, 200). (B) The healing response in the avascular meniscus zone is shown (Stain, hematoxylin and eosin; magnification, 100). 230 Guisasola et al any orientation of the fibers. Safranin O did not stain the repair region, so there seemed to be no chondral participation in the repair. The coronal section of the menisci was aligned with the suture in some cases with a proliferative cellular response with uninuclear and polynuclear cells in the suture channel. There was no progression of vascular ingrowth in the lesion in any case. However, an angiogenic response existed with increased vascularization in the peripheral region of the studied menisci. The meniscal lesion in the avascular zone remained avascular 6 weeks after suture, regardless whether the knee was immobilized and spared weightbearing. There Clinical Orthopaedics and Related Research was a vascular response in the red zone of the meniscus and progression of vascularized synovium from tibial and femoral meniscal surfaces (Fig 3). Values of maximum load under compression and slope of the curve in the linear zone were inferior to the controls in all cases. The mean value of maximum load in the control group was 202 N (standard deviation, 16.42 N) and the slope of the curve in the linear zone in controls was 0.7265 N/mm (standard deviation, 0.0371 N/mm). The maximum load in the healing zone of studied menisci never reached 50% of the control value (Fig 4). Slope values also were inferior to controls. A B Fig 3A–B. (A) The meniscus vascularization after the meniscal suture is shown at 6 magnification and (B) at 10 magnification (Spalteholz technique). Number 393 December, 2001 Knee Immobilization and Meniscal Healing A 231 B Fig 4A–B. (A) The maximum compression loads in the three groups, free weightbearing, immobilized, and control, are shown. (B) The curve slopes in the three groups, free weightbearing, immobilized, and control are shown. Table 1 shows the values of the parameters studied. DISCUSSION Only 10% to 30% of the meniscal periphery is vascularized.2,3,7,8 Vessels come from branches of the genicular arteries forming a vascular plexus in the outer rim of the meniscus. It seems reasonable that a suture could be the best treatment for lesions in the outer 1⁄3 of the meniscus, TABLE 1. Mechanical Results of the Different Groups Group Number Control 1 Control 2 Control 3 Control 4 Control 5 Control 6 Control 7 Immobilized-40 Immobilized-158 Immobilized-45 Immobilized-47 Free weightbearing-42 Free weightbearing-43 Free weightbearing-48 Free weightbearing-49 Maximum Load (N) Slope (N/mm) 239 140 220 140 210 281 190 70 56 66 28 102 84 12 46 0.75 0.72 0.55 0.78 0.73 0.87 0.67 0.42 0.21 0.16 0.09 0.42 0.38 0.14 0.23 because DeHaven et al9,10 reported good results in the early years of open meniscal sutures. Doubts arise in the case of lesions in the central zones, and there is no consensus in the literature as to how these should be treated. There is obvious disagreement between clinical and experimental studies. Many clinical reports1,10,12,16,20,23,27,29,31 present good results after a meniscal suture, and in some cases, these are backed up by a longterm arthroscopy control. However, analysis of meniscal repair and anterior cruciate ligament reconstruction should be done at the same time because the intraarticular conditions are different. Experimental studies show a different perspective on inner meniscal lesions15,19,26 suggesting the inability of this part of the meniscus to heal. Ghadially et al14 did a bucket handle lesion in the avascular zone of different animals (rabbits, dogs, pigs, and sheep). They reported no histologic healing in any of the species in the following 6 months. The lesion remained in menisci that were sutured and in menisci that were not sutured. Arnoczky et al4 established a control group and produced a cylindrical lesion in the avascular zone of the meniscus in dogs. Two weeks later, a fine proliferation of fibrous tissue appeared with polygonal cells and amorphous matrix partially filling the defect; it re- 232 Clinical Orthopaedics and Related Research Guisasola et al mained unchanged for the next 6 months. The presence on fibroblasts and cellular matrix apposition suggested that meniscal cells contributed directly to healing. Weber et al33 confirmed that fusiform meniscal cells respond to chemotactic and mitogenic factors. Fibroblasts are target cells for these stimuli, and fibroblasts might originate from meniscal cells. They also showed the capacity of fibrochondrocytes to migrate from the cartilaginous matrix into a fibrin clot. Synovial cells play an important role in graft healing because they may differentiate with a great capacity, producing pluripotential cells.5,18,25,32 In histologic studies of healthy meniscus, the synovial membrane does not take part in vascularization of meniscal surfaces, limiting its action to the synovial fringe. The synovium invagination from femoral and tibial surfaces takes part in the healing response, and cells are abundant, fibroblastlike, and fusiform, with a big nucleus and poor extracellular tissue. In the current study, the fibrous healing process started in two lesions. There was an initial healing response in two of six lesions, both in knees that had been immobilized with an external fixator. Fibroblastlike cells migrate through the suture channel. When a healing response initiates in the avascular meniscal zone, it is a fibroblastic response with a double origin, intrinsic, from meniscal fibrochondrocytes, and extrinsic, from cell invagination of femoral and tibial surfaces synovium and fibroblastic cells that accede from the suture channel. Formed collagen fibers are scarce and lack particular direction. Repair is by fibrous tissue. Meniscal fibrochondrocytes and synovial cells are involved. Cell access to the lesion is through meniscal fibrochondrocytes from the nearest meniscal tissue, synovial cells from femoral and tibial meniscal surfaces, and fibroblastic cells through the suture channel. The indentation test has been used to examine the mechanical properties of biologic tissues and is a valuable and efficient tool.17,21,30 It has some drawbacks, such as measuring tissue resistance under compression in a limited area, but it is an easily reproducible and homogeneous method. The mechanical model of Roeddecker et al26 produces a new longitudinal lesion with a scalpel from the posterior horn to the studied lesion, creating two meniscal flaps where traction is applied. A new lesion modifies meniscal mechanics. Roeddecker et al26 studied the stiffness of a healing meniscal lesion in the posterior horn of rabbits with the tear load propagation test and the healing tissue resistance at 6 weeks was 19% in a meniscus that was not treated, 26% in the meniscus that was sutured, and 42.5% with the fibrin glue. Tissue resistance was the same at 12 weeks. Meniscal sutured lesions in the vascular zone are mechanically weak in the first 6 weeks. Immobilization and nonweightbearing do not improve the outcome. Healthy menisci have a completely different mechanical behavior. Sutured menisci in the avascular zone support less than 50% of a normal load. The load versus displacement curve slope also is 50% inferior in sutured menisci. Healthy menisci present a maximum load mean value of 202 N and a slope of 0.7265 N/mm. The best of repaired menisci have a maximum load mean value of 102 N and a slope of 0.4244 N/mm. Knees that were not immobilized support load better than knees that were immobilized. The knees from Group A supported an average of 78 N and the knees in Group B supported 38 N. Elasticity, measured as the curve slope, is higher in knees that were not immobilized than in knees that were immobilized (0.3612 N/mm versus 0.1542 N/mm). References 1. Albrecht-Olsen P, Bak K: Arthroscopic repair of the bucket-handle meniscus: 10 failures in 27 stable knees followed for 3 years. Acta Orthop Scand 64:446–448, 1993. 2. 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