A Case of ACL Graft Failure with Segmental Meniscal Deficiency

    A 35-year old female patient with a history of two failed anterior cruciate ligament (ACL) reconstructions presents with persistent right knee instability and pain. Imaging shows a vertical femoral tunnel, significant widening of the tibial tunnel, torn ACL graft, and posterior medial meniscus deficiency without chondral damage. Nonoperative management is no longer an option. Would she benefit from a Collagen Meniscus Implant and revision ACL reconstruction?


    Ashley J. Bassett, MD; Donald W. Mazur, MD


    The meniscus, a crescent-shaped wedge of fibrocartilage composed of mainly type I collagen, plays a crucial role in knee function and long-term joint health. The functions of the medial and lateral menisci are to: [1]

    • Distribute axial load by increasing the contact area between the concave distal femoral condyle and relatively flat tibial plateau
    • Increase knee stability
    • Absorb shock
    • Provide lubrication and nutrition to the knee joint

    The peripheral one third of the meniscus is well vascularized by geniculate branches, while the inner two thirds receive nourishment from synovial fluid. This has important implications for healing of meniscal tears.

    When non-operative treatment of a meniscus tear fails, surgical options include partial meniscectomy and meniscal repair. Repair is typically limited to acute peripheral, vertical, and longitudinal tears, which have a high probability of healing. Consequently, the vast majority of meniscal surgeries are partial meniscectomies, with approximately 700,000 cases performed annually in the US. [2]

    Although partial meniscectomy is often successful at alleviating symptoms of an irreparable meniscus tear, loss of meniscus integrity has been shown to alter the biomechanics of the knee joint and predispose the patient to accelerated joint degeneration. [3] In vitro studies using human cadaveric models have demonstrated that removal of meniscus tissue results in decreased tibiofemoral contact area and increased articular cartilage contact pressures that are directly related to the volume of meniscus resection. [4,5] The elevated tibiofemoral contact pressure can lead to degenerative changes of the articular cartilage, with radiographic joint space narrowing found in up to 60% of patients after partial meniscectomy. [6]

    To minimize the risk of early joint degeneration, meniscal restoration has been proposed when preservation of adequate native meniscus tissue is not possible. Options for restoring a deficient meniscus include:

    • Meniscal allograft transplantation
    • Meniscus replacement with a variety of synthetic materials: [7]
      • Type I collagen implant
      • Hydrogel-based biomaterial
      • Polyurethane implant
      • Stem cell-seeded scaffold

    Meniscal allograft transplantation (MAT) is the most widely studied and has demonstrated excellent patient satisfaction, functional improvement and tibiofemoral pain relief in 66% to 97% of patients. [8-11] However, meniscus transplantation has several disadvantages for the treatment of meniscal deficiency:

    • MAT is a complete meniscus substitution and is therefore not the ideal procedure for a partial meniscus defect.
    • The surgical technique is complex and requires anatomic reapproximation of the native meniscal horn insertion, as well as inside-out meniscus repair for stability, which has associated neurovascular risks.
    • The number of grafts available is limited.
    • Allograft is associated with concerns about risk of infectious disease transmission and immunologic reaction.

    In light of these concerns, alternative options for meniscal replacement with use of synthetic scaffolds have been developed.

    The Collagen Meniscus Implant (CMI, Stryker; Runnemede, New Jersey) is a bioresorbable scaffold made from type I collagen fibers purified from bovine Achilles tendon. It was the first biologic scaffold proposed for the surgical treatment of partial meniscal deficiencies and supports the formation of meniscus-like tissue by means of cellular ingrowth and production of extracellular matrix.

    • Indications for CMI use include a partial meniscal defect comprising less than 90% of the total meniscus volume, with a preserved meniscal rim and intact anterior and posterior meniscal horns.
    • Contraindications include concomitant full-thickness chondral lesion(s) in the same compartment and untreated ligament insufficiency or limb malalignment.

    Compared with the MAT surgical technique, the CMI surgical technique is less complex and more suitable for partial meniscal defects, and it avoids issues of implant sizing, immunologic reaction, and disease transmission.

    In this article, we present a case of a symptomatic medial meniscus deficiency in a patient with a failed anterior cruciate ligament (ACL) reconstruction surgically treated with CMI implantation and concomitant ACL reconstruction.

    Case Presentation

    A 35-year-old female patient presents with right knee pain and instability. She has a significant past surgical history involving that knee:

    • In 2002, she sustained an ACL tear and underwent right knee ACL reconstruction with a soft tissue allograft and partial medial meniscectomy.
    • In 2004, she underwent right knee ACL revision reconstruction with a soft tissue allograft and partial medial meniscectomy to treat an ACL graft re-tear.

    Both prior ACL surgeries were performed at another medical facility.

    Over the past 5 years, she has noted increased right knee pain, intermittent swelling, and more-frequent episodes of instability. The pain is predominantly along the medial aspect of the knee. She reports an intermittent catching sensation and buckling of the knee.

    The patient says she has been unable to participate in recreational sports as desired and now feels her knee pain and instability are impacting her activities of daily life. Her symptoms have persisted despite use of oral anti-inflammatory medications, brace immobilization, and a course of formal physical therapy.

    Physical Exam

    • Height: 5 feet, 3 inches; weight: 135 pounds; BMI: 23.91 kg/m2
    • Normal gait and limb alignment
    • Well-healed surgical incisions from previous ACL reconstructions
    • No erythema or warmth
    • Trace knee effusion
    • Medial joint line tenderness
    • Knee range of motion 0 to 132
    • McMurray’s test positive
    • Lachman test with 8 mm translation and no endpoint
    • Pivot shift test positive
    • Anterior drawer test with 8 mm translation compared with contralateral knee
    • Posterior drawer test stable
    • Stable to varus and valgus stress at 0 and 30 of knee flexion
    • Dial test symmetric bilaterally with firm endpoint
    • No calf tenderness
    • Full strength and intact sensation distally
    • Palpable dorsalis pedis and posterior tibial pulses, with a warm foot

    Imaging: Radiographs

    • Anteroposterior and lateral radiographs of the right knee show prior ACL reconstruction, with a vertical femoral tunnel and anteriorly located cortical button fixation device (Figure 1).
    • The tibia is translated anteriorly relative to the femur and the old tibial tunnel demonstrates significant widening.
    • Medial and lateral tibiofemoral joint space is preserved.

    Figure 1. AP and lateral radiographs of the right knee showing the prior ACL reconstruction.

    Imaging: MRI

    • Magnetic resonance images of the right knee showing prior ACL reconstruction, with tibial tunnel widening of 15 mm on the coronal image and 20 mm on the sagittal image (Figure 2).
    • There is deficiency of the medial meniscus with intact anterior and posterior roots and peripheral rim.
    • The medial femoral condyle and medial tibial plateau cartilage are preserved.
    • There is a horizontal tear of the lateral meniscus.

    Figure 2. Magnetic resonance images of the right knee showing the prior ACL reconstruction.


    • Right knee symptomatic ACL graft failure and medial meniscal defect involving the posterior horn and body


    We had a long discussion with the patient regarding her diagnosis, treatment thus far, and next best steps in management. Conservative treatment options were discussed, including:

    • Pain control with oral anti-inflammatory medications
    • Formal physical therapy
    • Bracing
    • Intraarticular corticosteroid injections

    The patient explained that she had exhausted all non-operative treatment and was interested in proceeding with surgical treatment. Surgical intervention was reviewed and included:

    • Right knee examination under anesthesia
    • Diagnostic arthroscopy
    • Partial medial meniscectomy versus medial CMI implantation
    • Removal of hardware
    • ACL revision reconstruction versus bone grafting of the ACL tunnels followed by second-stage ACL revision reconstruction

    We discussed the nature of the surgery and the associated risks, as well as the postoperative recovery and rehabilitation protocol. The patient communicated her understanding of the risks and the decision was made to proceed with surgical intervention.


    • The patient was placed in the supine position with appropriate padding of all bony prominences. A non-sterile thigh tourniquet was applied. General anesthesia was induced.
    • Examination under anesthesia was performed and the following were noted:
      • Full passive knee range of motion
      • Lachman test with 8 mm translation and no endpoint
      • Anterior drawer test with 8 mm translation
      • Pivot shift test positive
      • Knee stable to varus and valgus stress at 0 and 30 of knee flexion
      • Posterior drawer test stable.
      • Dial test stable and symmetric

      Diagnostic arthroscopy was performed using standard anterior inferolateral and inferomedial portals and the following were noted:

      • 2-cm deficiency of the medial meniscus involving the posterior horn and body; rim intact
      • Intact anterior and posterior roots
      • Stable grade I change to the medial femoral condyle articular cartilage
      • Normal medial tibial plateau cartilage (Figure 3)
      • Vertically oriented ACL graft with partial tearing and increased laxity; positive anterior drawer test under arthroscopic vision
      • Intact posterior collateral ligament (PCL)
      • Small tear of the lateral meniscus posterior horn involving 20% of the meniscus volume; debrided to a stable rim
      • Normal lateral femoral condyle and tibial plateau cartilage
      • Normal patellofemoral articular cartilage
      • Endobutton device visualized just proximal to the trochlear cartilage; cleared from soft tissue and removed (Figure 4)

    Figure 3. Arthroscopic image of the right knee showing the deficient medial meniscus.

    Figure 4. Arthroscopic image of the right knee showing removal of the intraarticular Endobutton with a grasper.

    • The ACL graft was debrided using an arthroscopic motorized shaver.
    • The prior ACL tunnels were identified, cleared of soft tissue, and bone grafted.
      • An incision was made through the old tibial tunnel scar and the tibial tunnel was sequentially reamed using 8-mm, 9-mm, and 10-mm reamers.
      • The arthroscope was placed up the tibial tunnel and all remaining soft tissue from the failed graft was removed with a curette.
      • A 10-mm tunnel dilator was placed and there was considerable tunnel widening. Given the size of the defect, the decision was made to bone graft the tunnels and perform a 2-stage ACL revision reconstruction.
      • The femoral tunnel was identified and sequentially reamed using 8-mm, 9-mm and 10-mm reamers to remove all soft tissue.
      • Two 12-mm allograft bone plugs (OsteoSponge SC, Bacterin International Inc.; Belgrade, Montana) were placed into the femoral tunnel to fill the defect (Figure 5).
      • On the tibial side, a single 12-mm allograft bone plug was placed at the joint line (Figure 6). The remainder of the defect was filled in a retrograde fashion using cancellous bone chips and then lightly tamped.

    Figure 5. Arthroscopic image of the right knee showing bone graft placed in the femoral tunnel.

    Figure 6. Arthroscopic image of the right knee showing bone graft placed in the tibial tunnel.

    • Attention was then turned back to the medial meniscal defect and CMI implantation was performed.
      • The meniscal defect area was prepared with an arthroscopic motorized shaver and a rasp (Figure 7).
      • The defect was measured to 2.4 cm. The CMI implant was marked and cut to the appropriate size (Figure 8).
      • The CMI implant was introduced into the joint and secured posteriorly with 1 Fast-Fix all-inside meniscus repair device (Fast-Fix, Smith and Nephew Inc.; Andover, Massachusetts).
      • The central and anterior portions of the implant were secured with inside-out sutures using zone-specific cannulae (Linvatec Corp.; Largo, Florida).
      • A posterior-medial incision was made and blunt dissection down to the capsule was performed, taking care to protect the saphenous nerve.
      • The inside-out sutures were passed, retrieved, and secured to the capsule.
      • The CMI implant was stable to probing and knee range of motion (Figure 9).

    Figure 7. Arthroscopic image of the right knee showing the prepared meniscus.

    Figure 8. Image showing the CMI implant cut to the appropriate size and marked.

    Figure 9. Arthroscopic image of the right knee showing the CMI implanted.

    • The knee was copiously irrigated and then all surgical incisions were closed.
    • The patient was placed into a hinged-knee brace locked in full extension and instructed to remain touch-down weight bearing (less than 25% body weight).

    Five months later, the patient returned to the operating room for the second stage of the ACL revision reconstruction.

    • Diagnostic arthroscopy revealed that the medial CMI implant was healed and well-incorporated, with a smooth transition between implant and native meniscus (Figure 10). It had the appearance of a normal meniscus and was stable with probing.
    • Revision ACL reconstruction was performed in a standard fashion, first with tibial tunnel drilling followed by transtibial femoral tunnel drilling, passage of the soft tissue allograft, femoral suspensory fixation (ToggleLoc, Zimmer Biomet; Warsaw, Indiana) and tibial screw and sheath fixation (Figure 11).
    • Postoperative anteroposterior radiograph of the right knee shows the revision ACL reconstruction with improved orientation of the femoral tunnel and cortical button fixation laterally. The medial and lateral tibiofemoral joint spaces are maintained (Figure 12).

    Figure 10. Arthroscopic image of the right knee showing the healed CMI implant.

    Figure 11. Arthroscopic image of the right knee showing revision ACL reconstruction with soft tissue allograft.

    Figure 12. Anteroposterior radiograph of the right knee showing revision ACL reconstruction.

    Postoperative Protocol

    The postoperative rehabilitation protocol is structured to encourage maximum tissue growth following CMI implantation.


    • A hinged knee brace is applied and locked in extension immediately postoperatively. The patient wears the brace for 6 weeks, locked in extension while ambulating.
    • The brace is unlocked to allow passive range of motion exercises: 0 to 60 for the first 4 weeks and 0 to 90 for weeks 4 to 6.
    • At 6 weeks postoperatively, full active and passive range of motion is permitted. The patient may gradually discontinue the brace.


    • Non-weight-bearing is prescribed for the first 2 weeks postoperatively.
    • Partial weight-bearing (less than 50% body weight) is permitted in weeks 3 and 4.
    • Partial weight-bearing gradually progresses through weeks 5 and 6 to 50% to 90% body weight with crutches.
    • At week 6, full weight-bearing is permitted as the patient weans off crutches.


    • Isometric quadriceps and hamstring exercises begin immediately postoperatively.
    • Elastic resistance and isotonic strengthening exercises start at week 4.
    • The patient may begin cycling at week 6.
    • Resistance strengthening is permitted at week 8.
    • Return to full physical activity is generally achieved around 6 months postoperatively.
    • High-impact sports are not allowed before 9 months after surgery.

    Surgical Pearls

    • When preparing the meniscus rim, debride all damaged tissue to reach healthy meniscus tissue in the red-white or red-red zones. CMI implantation in the white-white zone will not have sufficient vascularity to promote new tissue formation.
    • The meniscus rim can be perforated with a microfracture awl or 18-gauge spinal needle extending into the vascular zone to help generate a bleeding bed for the CMI implant.
    • Once the CMI implant is inserted into the joint, the blunt obturator for the arthroscope can be used to gently stabilize the CMI implant for fixation. Use of a blunt object is less traumatic to the fragile CMI tissue than use of a suture or probe.
    • Use horizontal mattress sutures to secure the CMI to the anterior and posterior horns of the native meniscus and vertical mattress sutures to secure the CMI to the meniscus rim and capsule. A combination of all-inside and inside-out suture devices can be used. The distance between each suture should be approximately 5 mm.
    • Take care to avoid over-tightening the sutures and cutting through the implant. The blunt obturator can be used to stabilize the CMI implant as slack is removed from the all-inside meniscus repair device to avoid tearing the suture out of the fragile CMI tissue. Placing an arthroscopic probe between the suture and the implant also allows the surgeon to approximate without damaging the implant. Approximate, don’t strangulate.
    • Arthroscopically visualize the CMI implant as the inside-out sutures are sequentially tied to avoid excessive tightening.


    The meniscus plays a vital role in knee joint load transmission and articular cartilage health. Meniscal deficiency has been shown to biomechanically decrease the tibiofemoral contact area and increase the articular cartilage contact pressures, ultimately leading to the development of osteoarthritis.

    To avoid early degenerative joint disease of the knee in young active patients, meniscal replacement strategies have been proposed using meniscus allografts and a variety of synthetic scaffolds.

    The CMI is a flexible, C-shaped disc composed of purified and crosslinked type I collagen. It is designed to serve as a template for ingrowth of new meniscal tissue. Clinical studies of CMI have shown significant improvements in knee function, activity level, pain, and reoperation rates at short- and mid-term follow-up. [12-17]

    A long-term prospective study by Zaffagnini et al [18] found that medial CMI significantly improved clinical outcomes compared with partial medial meniscectomy and that these improvements were maintained at 10-year follow-up. Radiographic evaluation demonstrated less medial joint space narrowing in the CMI group compared to the partial meniscectomy.

    Monllau and colleagues [19] also reported minimal to no radiographic progression of joint space narrowing following CMI at final 10-year follow up, supporting the chondroprotective effect of the implant.

    CMI may also be combined with other intraarticular procedures, including ligament reconstruction. Bulgheroni et al [20] found that patients undergoing ACL reconstruction with concomitant medial CMI had significantly lower levels of knee pain and less knee laxity than patients who underwent ACL reconstruction with partial medial meniscectomy.

    There is a growing body of evidence to support use of CMI to restore meniscal integrity and minimize development of articular cartilage degeneration.

    Author Information

    Ashley J. Bassett, MD, is a sports medicine fellow at The Rothman Orthopaedic Institute, Philadelphia, Pennsylvania. Donald W. Mazur, MD, is a board-certified orthopaedic surgeon specializing in sports medicine at The Rothman Orthopaedic Institute, Philadelphia, Pennsylvania.

    Sports Medicine Editor, Rothman Institute Grand Rounds

    Sommer Hammoud, MD


    The authors have no disclosures relevant to this article.


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