Evaluation of a new injury model to study medial collateral ligament healing: primary repair versus nonoperative treatment

The medial collateral ligament (MCL) of the rabbit left hindlimb was ruptured by a rod placed beneath it, resulting in a "mop-end" tear of the ligament substance with simultaneous injury to the insertion sites. Using this model, we compared primary ligament repair and nonoperative treatment using biomechanical and histologic techniques at time zero, 10 days, and 6 and 12 weeks postoperatively. Biomechanical evaluation included measurement of varus-valgus (V-V) knee rotation, in situ load on the MCL, and tensile testing of the femur-MCL-tibia complex (FMTC). The V-V rotation of all experimental knees decreased over time. At 12 weeks, V-V rotation of experimental knees was still 1.3 times larger than that of controls. Primary repair initially decreased V-V rotation, but at 6 and 12 weeks there was no statistical difference between operated and nonoperated knees. The in situ load on the MCL followed the same trends. There was no significant effect of MCL repair on any of the tensile properties. However, postoperative healing time significantly improved the FMTC structural properties in both experimental groups. Failure modes of the FMTCs and histologic sections of the ligament insertion sites indicated that after injury the ligament insertion to bone recovered more slowly than the ligament substance. Tensile testing of the FMTC showed that even at 12 weeks postoperatively the mechanical properties of the healed ligament material remained significantly different from those of the controls.     

Healing of the medial collateral ligament following a triad injury: a biomechanical and histological study of the knee in rabbits.

The effect of a partial medial meniscectomy and anterior cruciate ligament (ACL) transection on medial collateral ligament (MCL) healing was studied in skeletally mature rabbits. Two groups of animals, group I (isolated MCL rupture) and group II (MCL rupture with ACL transection and partial medial meniscectomy), were examined. At 6 and 12 weeks postoperatively, histological examination of the healing MCL and biomechanical evaluation of the varus-valgus (V-V) knee rotation and tensile properties of the femur-MCL-tibia complex (FMTC) were performed. Group II animals experienced substantial joint degeneration by 6 weeks. Progressive osteophyte formation was observed adjacent to the MCL insertions along with proximal migration of the MCL tibial insertion between 6 and 12 weeks. Histologic examination of the healing MCL substance from both groups showed disorganized collagen, inflammation, and fibroblast proliferation that decreased over time. For group II knees, the V-V knee rotation was found to be significantly elevated (4.7 to 5.2 times the contralateral control), and did not decrease with time. In contrast, the V-V knee rotations of the group I specimens were 1.8 times greater than control immediately following injury, and approached control values by 12 weeks. Tensile testing of the FMTCs revealed that the ultimate load increased with time for both groups, but group I had significantly higher values than group II. The linear stiffness in group I was not different than that group II and did not increase with time. For the mechanical (material) properties of the healed MCL substance, the modulus of the healing tissue for group II was only 40% that of group I. The structural properties of the FMTC and the mechanical properties of the MCL substance from both groups at 6 and 12 weeks were significantly different from the contralateral controls. We further demonstrated that immediately after ACL reconstruction, the V-V rotation of group II knees could be restored to group I levels. Recent clinical studies of MCL healing following isolated complete ligament tears have suggested that nonoperative management without immobilization leads to excellent treatment outcome. However, in more severe injuries involving additional tissues, poor quality of the healed ligament tissue and articular degeneration are observed. Our results demonstrate the deleterious effects of an untreated triad injury on the healing of the MCL substance and its insertions. Examination of the MCL substance suggests that a much larger healing mass is formed following a triad injury, which partially compensates for inferior ligament mechanical properties.(ABSTRACT TRUNCATED AT 400 WORDS)     

The healing medial collateral ligament following a combined anterior cruciate and medial collateral ligament injury--a biomechanical study in a goat model.

The ideal treatment of a combined anterior cruciate ligament (ACL) and medial collateral ligament (MCL) injury to the knee is still debated. In particular, the question of whether reconstruction of the ACL can provide the knee with sufficient multidirectional stability to allow for effective MCL healing needs to be better elucidated. Therefore, the first objective of this study was to quantify the changes in the function of goat knees between time-zero and 6 weeks following a combined ACL/MCL injury treated with ACL reconstruction. Using a robotic/universal force-moment sensor testing system, the kinematics of the knee and in situ forces in the ACL/ACL graft as well as in the sham-operated and healing MCL were evaluated in response to (1) a 67 N anterior-posterior (A-P) tibial load and (2) a 5 Nm varus-valgus (V-V) moment. The second objective was to evaluate the structural properties of the healing femur-MCL-tibia complex (FMTC) and the mechanical properties of the healing MCL at 6 weeks under uniaxial tension.In response to the 67 N A-P tibial load, the A-P translations for the experimental knee increased by as much as 4.5 times from time-zero to 6 weeks (p<0.05). Correspondingly, the in situ forces in the ACL graft decreased by as much as 45% (p<0.05). There was no measurable changes of the in situ force in the healing MCL. In response to a 5 Nm V-V moment, V-V rotations were twice as much as controls, but similar for both time periods. From time-zero to 6 weeks, the in situ forces in the ACL graft dropped by over 71% (p<0.05), while the in situ force in the healing MCL was as much as 35+/-19 N.In terms of the structural properties of the healing FMTC, the stiffness and ultimate load values at 6 weeks reached 53% and 29% of sham-operated contralateral controls, respectively (p<0.05). For the mechanical properties of the healing MCL substance, the values for tangent modulus and tensile strength were only 13% and 10% of sham-operated controls, respectively (p<0.05). These results suggest that the ACL graft stabilized the knee initially, but became loose over time. As a result, the healing MCL may have been required to take on excessive loads and was unable to heal sufficiently as compared to an isolated MCL injury.     

The early effects of joint immobilization on medial collateral ligament healing in an ACL-deficient knee: a gross anatomic and biomechanical investigation in the adult rabbit model.

In this study, the short-term effects of immobilization on joint damage and medial collateral ligament (MCL) healing were investigated in unstable, anterior cruciate ligament (ACL)-deficient knees in rabbits. Forty-six 12-month-old female New Zealand white rabbits were separated into three groups. Animals from each group had surgery on their right knees: group I, sham controls (n = 9); group II, complete transection of the ACL and removal of a 4 mm segment (gap injury) of MCL midsubstance with no immobilization of the limb (n = 19); and group III, same injuries to the ACL and MCL (as group II) but with immobilization of the limb (n = 18). No surgical repair of disrupted ligaments was performed. Left knees served as unoperated contralateral controls. All animals were allowed unrestricted cage activity until sacrifice in subgroups at 3, 6, and 14 weeks of healing when biomechanical properties of all MCLs were measured. All knee joints were systematically examined for gross evidence of damage to articular cartilage, menisci, and periarticular soft tissues. To monitor relative in vivo loads on injured limbs during healing, hindlimb weight bearing was assessed at biweekly intervals. Results indicated that animals in both groups II and III bore relatively lower loads (compared to preinjury values) on their injured hindlimbs. Mechanical testing of MCLs showed only minor changes in sham controls, while group II and III healing MCLs demonstrated significantly lower force and stress at MCL complex failure compared to contralateral controls. In specific comparisons of group III to group II animals, we noted that immobilization prevented joint damage over the early intervals studied. In addition, immobilization resulted in MCL laxity similar to contralateral control values but inhibited development of structural strength and stiffness in healing MCLs. These results suggest that in the rabbit, short-term immobilization of an ACL-deficient knee offers some advantages to the joint and to certain low load behaviors of the healing MCL, but it also results in a smaller quantity of scar tissue that is less able to resist higher loads. Longer-term studies involving remobilization are necessary before the effects of brief immobilization on joint damage and MCL healing in this ACL-deficient model can be fully defined.     

Healing ligament mechanical properties are improved by repair with interpositional allografts but not by concomitant treatment with hyaluronic acid

Healing ligaments have inferior mechanical properties compared to normal ligaments during early healing intervals. The purpose of this study was to investigate if in vivo ligament repair with an interpositional allograft and treatment with hyaluronic acid (HA) would improve the mechanical properties of a medial collateral ligament (MCL) healing from a gap injury. Twenty rabbits were assigned equally to either a donor or recipient group. A gap injury of the MCL was created in both hindlimbs of 10 recipient animals. The right hindlimb was treated with allograft plus HA while the left hindlimb was treated with allograft only. Low‐load and high‐load mechanical properties, including laxity, relaxation and failure, and histology were evaluated after 6 weeks of healing. Mechanical results were compared to previously published normal MCL and MCL gap scar data. MCL allografts had greater initial force during cyclic relaxation testing and maximum force during failure testing than MCL scars, but were weaker than normal MCLs. Failure stress was the only parameter to demonstrate a statistically significant effect of treatment with HA on the allografts. However, the failure stress of the HA‐treated MCL allografts was not different than MCL scars and was less than normal MCLs. In conclusion, interpositional allografts could enhance some mechanical properties of ligament healing but HA, in the way we applied it, did not produce an obvious improvement. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27:400–407, 2009     

A quantitative analysis of matrix alignment in ligament scars: a comparison of movement versus immobilization in an immature rabbit model

This investigation quantified the alignment of fibrillar matrix in normal rabbit medial collateral ligaments (MCLs) and in healing MCLs from animals treated with or without knee immobilization. Twenty-four immature female rabbits were given complete midsubstance injuries to their right MCLs. Fifteen of them had that knee pin immobilized in flexion, while the remaining nine were allowed unrestricted cage activity. Animals were sacrificed in groups of three at intervals of 3, 6, or 14 weeks after injury, and both healing MCLs and unoperated contralateral controls were fixed in situ for subsequent removal, freeze-fracture, and preparation for scanning electron microscopy (SEM). A random sampling of SEM photographs followed by automated, statistically validated image processing was used to quantify alignment of matrix in all samples. Results showed that nonimmobilized MCL scars in this model do remodel over 14 weeks of healing, returning to normal alignment values in that time. Surprisingly, MCL scars in immobilized knees were even better, with mean matrix alignments falling statistically within normal MCL limits at all healing intervals studied. If not due to an unknown sampling or fixation artifact, these results suggest that gross knee flexion and extension is not a prerequisite for scar matrix alignment in this immature model of ligament healing.     

The effects of initial end contact on medial collateral ligament healing: a morphological and biomechanical study in a rabbit model

In this investigation, the effect of initial end contact on medial collateral ligament (MCL) healing was studied in the rabbit model. Sixty-eight 1-year-old New Zealand white rabbits were separated into two groups. In one group, a 4 mm saggital Z-plasty was performed in the right MCL midsubstance (contact group), and in the other group, an analogous 4 mm midsubstance segment was removed (gap group). Left knees were unoperated to serve as internal contralateral MCL controls. Animals had unrestricted cage activity until sacrifice in groups of eight at 3, 6, 14, and 40 weeks postoperatively. Early results demonstrated that contact and gap injuries healed with what appeared to be scar tissue both morphologically and biomechanically. In both groups, laxities recovered to their contralateral values within 6 weeks and biomechanical viscoelastic behaviors recovered to 68-92% of contralaterals by 14-40 weeks. Despite these similarities, contacts showed morphological and biomechanical evidence of improved healing over gaps. Contact scars remodeled more quickly, recovered laxity more quickly, and were generally closer to contralaterals than gaps in terms of their structural strength, stiffness, and material behaviors, after 40 weeks of healing. With the exception of appearances and failure stress, all measured properties of contact healing MCLs were statistically indistinguishable from contralateral MCLs at 40 weeks of healing. These advantages of contact healing in this model support speculations that there are differences in the early rate and possibly in the later quality of ligament healing when cut rabbit MCL ends are in proximity. Longer-term studies to define end points and mechanisms of healing are required.     

Effects of ligament repair on laxity and creep behavior of an early healing ligament scar

Background Previous clinical studies have reported that conservatively managed medial collateral ligament (MCL) injuries remained unstable 9 years post injury with subjective complaints of muscle weakness, reinjuries, and post-traumatic osteoarthritis. Animal studies have also reported that healing MCLs were weaker and more lax than controls. Therefore, our purpose was to study the early effects of ligament repair on scar laxity, creep, and creep recovery in a rabbit model of bilateral medial collateral ligament (MCL) injury. Methods Each rabbit had one MCL cut in midsubstance which was not repaired, while the other MCL had a sagittal Z-plasty repair. Six weeks after surgery, isolated bone–MCL–bone complexes were biomechanically tested for MCL laxity, cyclic creep, creep recovery, and then loaded to ultimate failure. Results Nonrepaired scars were significantly more lax than both repaired Z-plasty scars and normal controls. In contrast, there was no significant difference in MCL laxity between repaired scars and normal controls. There were no significant differences between nonrepaired or repaired scars for either cyclic creep and creep recovery. Both crept significantly more and recovered significantly less than normal controls after the same load history. There were no significant differences in the failure load, stiffness, and tensile strength between gap scars and Z-plasty scars. All healing ligaments had significantly lower failure load, stiffness, and tensile strength than normal controls. Conclusions The present study demonstrates that ligament repair is effective in decreasing short-term laxity of ligament scars. These 6-week scars would be prone to abnormal creep if loaded excessively.     

Vascular physiology and long-term healing of partial ligament tears.

Functional outcomes of anterior cruciate ligament (ACL) injury are generally poorer than those of medial collateral ligament (MCL) tears. Following ligament damage, all phases of ligament healing require an adequate blood supply. We hypothesized that the differences in healing properties of the ACL and MCL would reflect their vascular responses to joint injury. This paper examines the long-term changes in blood flow and vascular volume of rabbit knee ligaments after direct injury, and under conditions of chronic joint instability induced by section of the posterior cruciate ligament (PCL). Standardized injuries were surgically induced in adult rabbit knee ligaments: partial MCL transection, partial ACL transection, or complete PCL transection (joint instability). Sixteen weeks later the blood flow and vascular volume of the ACL and MCL were measured and compared to control and sham-operated animals. Direct ligament injury induced significant increases in standardized blood flow and vascular volume of both ACL and MCL after 16 weeks; however, the vascular volume of the ACL was not higher than the control levels in the MCL. We conclude that direct injury to both the anterior cruciate and MCLs induces long-term physiological responses. Joint laxity is a common sequel to PCL injury. Chronic joint laxity failed to induce adaptive vascular responses in the ACL, while the MCL shows significant amplification of blood supply. Although both MCL and ACL showed increased weight after PCL transection, the lack of a long-term vascular response in the ACL may be a major factor in its the diminished healing potential.     

Exogenous transforming growth factor beta 1 alone does not improve early healing of medial collateral ligament in rabbits.

OBJECTIVE: To determine whether transforming growth factor beta 1 (TGF-beta1) improves early ligament healing. DESIGN: Experimental, controlled study of medial collateral ligaments (MCLs) in rabbits' knees. SETTING: Research laboratory. SUBJECTS: Sixteen skeletally mature, New Zealand White female rabbits. INTERVENTIONS: Ten rabbits had a standardized gap injury made in the MCL of both knees. Three weeks later, a second operation was performed to inject 7 microg of TGF-beta1 in a carrier solution into the right knee MCL, while the left knee MCL was injected with carrier alone. The rabbits were killed 3 weeks after the injection of TGF-beta1 (6 weeks after the original injury). Six of the rabbits (12 knees) had no operation on the MCL and served as external normal controls. OUTCOME MEASURES: Biomechanical measures of the femur-MCL-tibia complex. Histologic evaluation of MCL cell and matrix organization. Transmission electron microscopy measures of MCL fibril diameters. RESULTS: There were no statistically significant differences in the biomechanical measures, fibril diameter distributions and histologic evaluation of the injured MCLs treated with TGF-beta1 or carrier alone. Both groups of injured MCLs were significantly different from normal MCLs. CONCLUSIONS: The results indicate that the dosage and route of delivery of TGF-beta1 did not lead to overt improvement in the healing of the injured MCL. Whether different doses or delivery methods, alone or in combination with TGF-beta1, or other growth factors would lead to improvement remains to be determined.     

Strength of medial structures of the knee joint are decreased by isolated injury to the medial collateral ligament and subsequent joint immobilization.

Past studies of the healing of the medial collateral ligament (MCL) in animal models have been conducted over a variety of healing intervals, some as early as 1 week. One concern with testing at early healing intervals is the difficulty in identifying and isolating the tissues that carry load. The purpose of this study was to determine if isolation of the MCL and healing time are critical factors in the assessment of structural strength in this model. Furthermore, the effect of immobilization on these critical factors was investigated. Our approach was to calculate the load-sharing ratio between the MCL and the MCL plus capsule. A 4 mm gap was created in the midsubstance of both hindlimb MCLs of 52 female New Zealand White rabbits (n=104). Of these, 29 rabbits had their right hindlimb pin immobilized (immobilized group), leaving the left hindlimb non-immobilized. Testing was performed at 3 (n=12), 6 (n=22), and 14 (n=24) weeks. The remaining 23 rabbits, which had both limbs non-immobilized (non-immobilized group), were tested at 3 (n=10), 6 (n=12), 14 (n=12), and 40 (n=12) weeks. For both groups, half of the specimens at each healing interval were used to test the MCL alone and half to test the MCL plus capsule, except for 3 week immobilized joints where only the MCL plus capsule was tested. Additionally, MCL (n=12), MCL plus capsule (n=6), and capsule alone (n=5) were tested from normal animals. The load-sharing ratio at MCL failure for the normal joint was 89%, suggesting an MCL-dominated response. For the non-immobilized group, the load-sharing ratio was 24% at 3 weeks of healing, suggesting a capsule-dominated response. At and after 6 weeks of healing, an MCL-dominated response was observed, with the ratio being 68% or greater. Thus, at less than 6 weeks of healing, the structural strength capabilities of the joint may be better represented by the medial structures rather than the isolated MCL. Immobilization delayed the transition from a capsule-dominated response to an MCL-dominated response in this model.     

The use of porcine small intestinal submucosa to enhance the healing of the medial collateral ligament--a functional tissue engineering study in rabbits.

INTRODUCTION: Small intestinal submucosa (SIS) from porcine has been successfully used as a collagen scaffold for the repair of various tissues, including those of the human vascular, urogenital, and musculoskeletal systems. The objective of this study was to evaluate whether SIS can be used to enhance the healing process of a medial collateral ligament (MCL) with a gap injury in a rabbit model. METHODS: A 6 mm wide gap was surgically created in the right MCL of 20 skeletally mature, female New Zealand White rabbits. In 10 rabbits, a strip of SIS was sutured onto the two ends of the MCL, while for the other 10 animals their injured MCL remained untreated and served as a non-treated group. The left MCL of all animals was exposed and undermined serving as the sham-operated side. At 12 weeks post-healing, eight hind limbs from each group were used for mechanical testing. The cross-sectional areas (CSA) of the MCLs were measured. The femur-MCL-tibia complex (FMTC) was tensile tested to failure. The load-elongation curves representing the structural properties of the FMTC and the stress-strain curves representing the mechanical properties of the healing MCL were obtained. The remaining two animals from each group were prepared for histological evaluation. RESULTS: The CSA between the SIS-treated and non-treated groups were not significantly different (p>0.05). Both treatment groups appeared to increase by nearly 40% compared to the sham-operated side, although statistical significance was not found for the non-treated group (p>0.05). The stiffness of the FMTC from the SIS-treated group was 56% higher than the non-treated group (45.7+/-13.3 N/mm vs. 29.2+/-9.2 N/mm, respectively, p<0.05) and the ultimate load also nearly doubled (117.434.5 N vs. 66.4+/-31.4 N, respectively, p<0.05). These values were lower compared to the sham-operated side (89.7+/-15.3 N/mm and 332.0+/-50.8 N, respectively). The tangent modulus of the healing MCL (279.7+/-132.1 MPa vs. 149.0+/-76.5 MPa, respectively) and stress at failure (15.7+/-4.1 MPa vs. 10.2+/-3.9 MPa, respectively) both increased by more than 50% with SIS treatment (p<0.05). Yet, each remained lower compared to the sham-operated side (936.3+/-283.6 MPa and 75.6+/-14.2 MPa, respectively). Blinded histological comparisons between the SIS-treated MCL and the non-treated control demonstrated qualitatively that the SIS treated group had increased cellularity, greater collagen density, and improved collagen fiber alignment. CONCLUSION: Healing of a gap MCL injury was significantly enhanced with SIS. The improved mechanical properties and histological appearance of the MCL suggest that SIS treatment improves the quality of tissue and renders the possibility for future studies investigating functional tissue engineering of healing ligaments.     

Medial collateral ligament autografts have increased creep response for at least two years and early immobilization makes this worse.

Recent evidence has shown that 10-40% of knee joints reconstructed with soft-tissue autografts have a recurrence of abnormal joint laxity over time. One possible explanation is the "stretching out" (or unrecovered creep) of the graft tissue. To test in vitro creep and creep recovery of fresh anatomic ligament autografts in an extra-articular environment, 16 rabbits underwent an orthotopic medial collateral ligament (MCL) autograft procedure to one hindlimb. Three subgroups of animals had either unrestricted cage activity for 1 year (n = 5) or 2 years (n = 5) or pin-immobilization for the first 6 weeks followed by cage activity for the remainder of 1 year (n = 6). Following laxity measurements, to test their creep response, isolated MCL grafts were cyclically and then statically creep tested in vitro at 4.1 MPa, allowed to recover at zero load for 20 min, and finally elongated to failure. Due to differences in cross-sectional area between the grafts and normal MCLs, two normal control groups were tested: stress-matched tested at 4.1 MPa (16.2 N; n = 7) and force-matched tested at 29.1 N (7.1 MPa; n = 6). Ligament grafts had normal laxity but significantly increased creep and decreased creep recovery compared to normal MCLs after I and 2 years of healing (p < 0.0004). Graft failure stress was also significantly less than normal (p < 0.0001). Immobilized grafts had significantly greater creep compared to non-immobilized grafts at 1 year of healing (p < 0.05). These results support previous observations concerning material inferiority of fresh anatomic rabbit MCL autografts, but add the concept that such grafts also have increased potential to creep with either slower or incomplete recovery when subjected to low stresses in vitro. Joint and ligament laxities in situ were normal in this model, however, suggesting either that in vivo MCL graft stresses are lower than those used here in vitro or that these tissues have other mechanisms by which they can recover their functional length in vivo.     

Medial collateral ligament healing in macrophage metalloelastase (MMP-12)-deficient mice.

Medial collateral ligament (MCL) injuries heal by a wound repair scar response controlled by a complex cellular and cytokine environment. Many enzymes participate in wound repair, particularly the matrix metalloproteinases. We hypothesize macrophage metalloelastase (MME/MMP-12) deficiency results in impaired healing of MCL injury. One hundred fifty MME-deficient and 150 WT (MME+/+) mice underwent knee MCL transection with the opposite knee as a sham operated control. Mice were sacrificed at 3, 7, 28, 42, and 56 days. At each of the five time points, 15 mice were utilized for biological and 15 were utilized for biomechanical testing. Outcome measures were the presence of macrophages to represent the inflammatory phase of wound healing, collagen synthesis to assay for matrix repair, and biomechanical testing for repair strength. Immunohistochemistry demonstrated significantly fewer macrophages in cut MCLs from MME-deficient mice versus wild-type (WT) mice at 3, 7, 28, and 42 days (all p相似文献   

Case Study: Rehabilitation of a Surgically Repaired Medial Collateral Knee Ligament Using a Limited Motion Cast and lsokinetic Exercise*

Recent studies indicate that early mobilization of surgically repaired collateral ligaments leads to a more rapid gain in tensile strength compared to immobilized ligaments. Other advantages of early mobilization include prevention of muscle atrophy, joint stiffness, and articular cartilage fibrillation. Because of these observations, a professional Australian Rules footballer with a complete rupture of the right medial collateral ligament of his knee joint, was commenced, after surgical repair, on an early controlled mobilization program using a limited motion cast (LMC) and isokinetic exercise. Rehabilitation was commenced after 2 weeks of immobilization in a LMC, and progressed through four stages, all coupled with isokinetic exercise. Weeks 2-6, exercise in LMC through 20-60 degrees ; weeks 7-8, exercise out of LMC through 15- 1 OOO; weeks 8-9, exercise through a full range of movement, 0-130'; weeks 10- 12, exercise through a full range plus inner range 0-30' repetitions. The footballer returned to full competition approximately 12 weeks postsurgery with no medial collateral laxity and almost normal Cybex IP parameters. J Orthop Sports Phys Ther 1986;7(4):154-158.     

Injury location affects ligament healing: A morphologic and mechanical study of the healing rabbit medial collateral ligament

Based on the heterogeneity of the rabbit medial collateral ligament (MCL) along its length, we tested the hypothesis that injury location would affect its healing response. The right MCL of 80 skeletally mature New Zealand white rabbits was sectioned adjacent to bone at the femoral end (40 rabbits) or the tibial end (40 rabbits) and reapposed with sutures. Animals were killed after 3, 6, 14, or 40 weeks of healing to examine wounds histologically (2 rabbits per healing interval) and mechanically (8 rabbits per healing interval). Results of the mechanical tests were compared to midsubstance MCL repairs (24 rabbits) and to uninjured normal MCLs (20 rabbits). The morphology of the near-insertion repairs was characterized by abnormal callus-like formation and patchy bone resorption, particularly at the tibial insertion. Mechanically, insertional injuries remodeled towards normal MCL low-load, viscoelastic and failure properties more slowly than midsubstance injuries at the early healing intervals. After 40 weeks of healing, few injury-specific differences persisted. All injured ligaments had ultimate strengths 15-35 percent short of normal at 40 weeks and the femo-rally-injured ligaments were weaker than normal at this time. These results suggest that rabbit MCLs, injured near either end, heal more slowly that those injured in their midsubstance and develop abnormal insertion morphology.     

Healing and repair of ligament injuries in the knee

Although methods of treating ligamentous injuries have continually improved, many questions remain about enhancing the rate, quality, and completeness of ligament healing. It is known that the ability of a torn ligament to heal depends on a variety of factors, including anatomic location, presence of associated injuries, and selected treatment modality. A grade III injury of the medial collateral ligament (MCL) of the knee usually heals spontaneously. Surgical repair followed by immobilization of an isolated MCL tear does not enhance the healing process. In contrast, tears of the anterior cruciate ligament (ACL) and the posterior cruciate ligament often require surgical reconstruction. The MCL component of a combined ACL-MCL injury has a worse prognosis than an isolated MCL injury. The results of animal studies suggest that nonoperative treatment of an MCL injury is effective if combined with operative reconstruction of the ACL. Experimentation using animal models has helped to define the effects of ligament location, associated injuries, intrinsic factors, surgical repair, reconstruction, and exercise on ligament healing. New techniques utilizing growth factors and cell and gene therapies may offer the potential to enhance the rate and quality of healing of ligaments of the knee, as well as other ligaments in the body.     

Treating Combined Anterior Cruciate Ligament and Medial Collateral Ligament Injuries Operatively in the Acute Setting Is Potentially Advantageous

Combined injury of the anterior cruciate ligament (ACL) and medial collateral ligament (MCL) remains among the most common knee injury patterns in orthopaedics. Optimal treatment of grade III MCL injuries is still debated, especially when combined with ACL injury. Most patients with these severe injuries are treated conservatively for at least 6 weeks to allow for MCL healing, followed by delayed ACL reconstruction. Although acute treatment of the MCL was common in the 1970s, postoperative stiffness was frequently reported. Moreover, studies of such treatment failed to show clinical benefits of surgical over conservative treatment, and the MCL exhibited intrinsic healing capacity, leading to the consensus that all MCL injuries are treated conservatively. The current delayed treatment algorithm for ACL-MCL injuries has several disadvantages. First, MCL healing may be incomplete, resulting in residual valgus laxity that places the ACL graft at greater risk of failure. Second, delayed treatment lengthens the overall rehabilitation period, thereby prolonging the presence of atrophy and delaying return to preinjury activity levels. Third, the initial healing period leaves the knee unstable for longer and risks further intra-articular damage. Acute simultaneous surgical treatment of both ligaments has the potential to avoid these shortcomings. This article will review the evolution of treatment of ACL-MCL injuries and explain how it shifted toward the current treatment algorithm. We will (1) discuss why the consensus shifted, (2) discuss the shortcomings of the current treatment plan, (3) discuss the potential advantages of acute simultaneous treatment, and (4) present an overview of the available literature.     

The non operative treatment of isolated complete tears of the medial collateral ligament of the knee. A prospective study

In a prospective randomized study, 20 patients with isolated grade-III injuries to the medial collateral ligament (MCL) of the knee were treated by two different conservative methods: immediate mobilization (group A) or plaster immobilization (group B). All patients were examined while under anesthesia. Valgus-stress radiographs were performed to document a 2+ opening (6-10 mm) on the medial side. Associated damage to other structures (cruciate ligaments, menisci, cartilage) was ruled out arthroscopically. Average follow-up was 1.5 years. All patients rated good or excellent, although a minimal laxity of 3 mm on valgus-stress radiographs was present in 60% of the cases. No significant differences between the two treatment modalities were identified, except that group-A patients returned to work sooner. These results confirm that isolated grade-III MCL tears can be treated successfully by immediate mobilization.     

Healing ligaments have decreased cyclic modulus compared to normal ligaments and immobilization further compromises healing ligament response to cyclic loading.

Ligaments help maintain joint stability by resisting excessive strain during the repetitive loading experienced during daily activity. Healing ligaments may be less able to fulfill this role, straining more under equivalent loading than normal ligaments. We examined the cyclic stress-strain response of normal and healing ligaments to repetitive low loads (<10% of the normal ligament failure strength). Rabbit medial collateral ligaments (MCLs) were surgically gapped in either a unilateral (right MCL; n=23) or bilateral (right and left MCLs; n=17) fashion with immobilization of the right hindlimb in the bilateral group. These MCL scars were allowed to heal for 3, 6, and 14 weeks and were cyclic creep tested at 2.2, 4.1, and 7.1 MPa, respectively. Creep test stresses were a constant 30% of the failure strength of non-immobilized scars at the different healing intervals. Normal MCLs were creep tested at 4.1 and 7.1 MPa (n=13). The cyclic modulus of the non-immobilized scars was less than that of normal ligaments. The percent increase in modulus during cycling was greater for scars than for normal ligaments, likely related to increased viscous dissipation or material inferiorities in scars. Furthermore, immobilization significantly decreased the ability of scars to resist strain, with a majority of immobilized scars failing during repetitive loading. Such failures were preceded by a reduction in cyclic modulus indicating damage to the healing ligaments that was predictive of eventual total failure. The implications of this study are that joints with healing ligaments may have increased strain in joint structures while they are under stress, potentially leading to joint instability. Although immobilization could be used temporarily to maintain joint stability, remobilization would likely lead to total failure of the healing ligament.