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    MPFL Reconstruction in a Young Athlete

    A 14-year-old female patient presents with left knee pain and swelling after sustaining a non-contact injury to her knee while playing soccer. MRI shows an injury to the medial patellofemoral ligament with patellar subluxation, which is treated conservatively. She returns 11 months later with a recurrent injury. What is the best option to manage this patient?

    Authors

    Neel A. Gupta, MD; Nimit Patel, MD; and Shyam Brahmabhatt, MD

    Disclosures

    The authors have no disclosures relevant to this article.

    Introduction

    Recurrent patellar instability continues to be a challenging problem for orthopaedic surgeons, with incidence increasing each year. [1] The rate of patellar dislocation is highest in the 10- to 17-year-old age group, with reported rates of 29% to 43%. In addition, females have a 33% increased prevalence of acute patellar dislocation compared with males. [2-4]

    Disruption of the medial patellofemoral ligament (MPFL) is thought to be the essential lesion resulting in recurrent patellar dislocation. [2,5-8] According to several anatomic and biomechanical studies, the MPFL is the most important restraint to lateral patellar displacement from 0° to 30° of knee flexion. The MPFL is compromised in the vast majority of acute dislocations, and its capacity to heal is limited.

    There is some debate regarding the management of a first-time patellar dislocation. [9-12] In a randomized controlled trial, Palmu et al [9] and Hennrikus and Pylawka [10] reported no significant difference in long-term subjective or functional results between operative and non-operative treatment of first-time traumatic patellar dislocations. As a result, non-operative treatment continues to be the standard of care for first-time traumatic patellar dislocation, except in cases involving osteochondral fractures, vastus medialis avulsions, large osteochondral fragments, or concomitant intra-articular abnormalities such as meniscal tears. [11,12]

    Conservative treatment is generally successful, with the reported rate of redislocation after simple patellar dislocation from 15% to 44%. [2,13-15]. Most surgeons currently recommend MPFL reconstruction when there is recurrent instability with more than 2 documented dislocations or when conservative treatment has failed. [9-12,16-18]

    MPFL reconstruction involves an autograft or allograft that is fixed into tunnels in the patella and medial femoral condyle, and under appropriate tension, act as a restraint to recurrent lateral instability. The majority of complications are related to tunnel malposition and subsequent overtensioning or undertensioning.

    Concomitant soft tissue or osseous procedures may be indicated to restore native biomechanics and stability of the patellofemoral joint. Preoperative MRI and CT are required for assessment of chondral lesions, as well as tibial tubercle-trochlear grove (TT-TG) distance. A TT-TG of more than 20 mm is a relative contraindication for isolated MPFL reconstruction and should be treated with a tibial tubercle osteotomy, with or without MPFL reconstruction [1]. Various surgical techniques for MPFL reconstruction have been described in the literature, and current evidence does not favor one technique over the other.

    In this article, we present a single case of recurrent patellar instability with a large loose body requiring surgical treatment.

    Case Presentation

    A 14-year-old female patient presented with left knee pain and swelling after sustaining a non-contact injury while playing soccer 2 days prior. She was initially seen in the emergency department, at which time radiographs were done (Figure 1) and she was placed in a knee immobilizer. She denied any previous injuries to the left knee. An MRI of the left knee is shown in Figure 2.

    Figure 1. Radiographs from the patient’s initial emergency department visit show a large effusion, no fractures, and closed growth plates in the left knee.

    Figure 2. MRI of the left knee demonstrates an MPFL injury with lateral patellar subluxation, as well as a contusion of the lateral femoral condyle and medial aspect of the patella. A large joint effusion is also noted.

    The patient sustained a first-time patella dislocation without concomitant intra-articular loose body, meniscal tear, or osteochondral defect. The pathology of the injury and treatment options were discussed at length with the patient and family. Given that this was a first patellar dislocation, conservative management was recommended, including a patellar J brace and physical therapy.

    Eleven months later, the patient presented after sustaining another left patellar dislocation while playing soccer. MRI was consistent with an injury to the MPFL, a full-thickness articular cartilage injury to the patella, and an associated loose body (Figures 3-4). CT scan showed a TT-TG distance of 14 mm.

    Figure 3. Repeat MRI of the left knee demonstrates an MPFL tear and a chondral defect along the medial patella facet.

    Figure 4. CT of the left knee demonstrates a tibial tubercle-trochlear groove (TT-TG) distance of 14 mm, as well as an avulsion fracture of the medial facet of the patella with an intra-articular loose body (13 x 12 mm) in the suprapatellar pouch.

    Physical Exam

    • Height: 5 feet, 5 inches; weight: 150 pounds; BMI: 24.96 kg/m2
    • Large left knee effusion
    • No warmth or erythema
    • Knee range of motion: 0° to 90° flexion; additional flexion limited due to pain
    • Tenderness to palpation over the medial femoral condyle and lateral joint line
    • Positive apprehension sign
    • Stable to varus/valgus stress
    • Negative anterior drawer and Lachman tests
    • Palpable pedal pulses

    Diagnosis

    • MPFL tear with lateral patellar subluxation, full-thickness chondral defect involving the medial facet of the patella, intra-articular loose body

    Treatment

    The natural course of recurrent patellar instability and available treatment options were discussed at length with the patient, including continued conservative treatment versus surgical options. After a discussion of the risks and benefits of surgical treatment, it was decided that we would proceed with a diagnostic left knee arthroscopy, removal of loose body, open MPFL reconstruction with allograft, and implantation of a particulated juvenile hyaline cartilage graft (DeNovo; Zimmer Biomet, Warsaw, Indiana) in the chondral defect. The postoperative recovery and rehabilitation protocol were also discussed with the patient at this time.

    Procedure

    • An examination under anesthesia was performed, noting patellar laxity (Figure 5).
    • Prior to the open procedure, a diagnostic arthroscopy was performed, revealing grade 4 chondromalacia along the medial aspect of the patella, as well as a loose body in the suprapatellar pouch. The loose body was removed, evaluated, and found to have minimal bone (Figure 6), which meant it was not amenable to internal fixation.

    Figure 5. Exam under anesthesia showing patellar laxity.

    Figure 6. Arthroscopic images showing chondral defect on patella and loose body removal.

    • A small incision was made along the superomedial aspect of the patella. The incision was slightly larger than standard to allow for adequate exposure of her patellar defect (Figure 7).

    Figure 7. Skin incisions.

    • The medial retinaculum was identified and subperiosteally dissected off the medial aspect of the patella. An interval between the vastus medialis and capsule was utilized to pass the graft outside the capsule. An arthroscope was introduced into the joint and a hemostat was passed through to ensure that this was the appropriate layer (Figure 8). An arthrotomy was performed to allow for direct visualization of the chondral defect.

    Figure 8. A hemostat was used to tunnel the graft. The arthroscopic image shows an extrasynovial fascial plane between the vastus medialis and the joint capsule.

    • The damaged cartilage was removed with a combination of curettes and rongeurs until a stable rim was present (Figure 9). The defect was then sized and shaped to allow for implantation of an exact matched, particulated juvenile hyaline cartilage graft (DeNovo) into the chondral defect. The graft was secured with fibrin glue (Figure 10). Five minutes of dry time was allowed, and the knee was cycled to ensure that the implanted graft was stable.

    Figure 9. The chondral defect (left) and preparation of the chondral defect (right).

    Figure 10. The particulated juvenile hyaline cartilage graft is placed (left) and secured with fibrin glue (right).

    • Fluoroscopy was utilized to identify the fixation site on the patella (at the junction between the proximal one third and distal two-thirds of the patella) on anteroposterior view.
    • A 2.4-mm guide pin was inserted parallel to the joint line and in the central portion of the patella. A 4.5-mm cannulated reamer was utilized to create a 25-mm unicortical patellar socket (Figure 11). A Frazier suction tip was used to “sound” the tunnel, confirming that the tunnel was in cancellous bone and did not violate either cortex.

    Figure 11. Fluoroscopic image shows the guide pin for the patellar tunnel.

    • Only 1 tunnel was used for the patella. The use of 2 tunnels has been associated with a higher chance of patellar fracture, and both techniques have similar recurrence rates. [19,20]
    • A semitendinosus tendon allograft was whip-stitched with #2 Fiberwire (Arthrex, Naples, Florida) and subsequently fixed into the patellar socket using an 4.75 mm SwiveLock anchor (Arthrex, Naples, Florida) (Figure 12).

    Figure 12. Allograft preparation (left) and fixation on the patella.

    • Fluoroscopy was utilized to identify the anatomic fixation site on the medial femoral condyle. A small incision was made, and soft tissue dissection was carried down to bone with care to protect the saphenous neurovascular bundle.
    • Schottle’s point was identified and a Beathe pin was drilled laterally, anteriorly, and proximally to avoid the notch (Figure 13). Schottle’s point was determined on the lateral view by a line extending from the posterior cortex and another perpendicular line just proximal to the posterior most aspect of the Blumensaat’s line. Schottle’s point is 1 mm anterosuperior to the intersection of these 2 lines. [21]

    Figure 13. The Beathe pin at Schottle’s point (left) and the fluoroscopic setup.

    • The Beathe pin aperture and trajectory were confirmed on fluoroscopy and a cannulated 6-mm femoral tunnel was then drilled to the opposite cortex, but not through, to allow for adequate tensioning of the graft.
    • The free end of the semitendinosus was whip-stitched with #1 Vicryl (Ethicon, Bridgewater, New Jersey) and passed through the previously developed plane. The graft was trimmed to pass through a 6-mm tunnel at approximately 100 mm of total length. The eyelet in the Beathe pin was used to pass the #1 Vicryl through the tunnel to allow for adequate tensioning.
    • The knee was placed in 30 of flexion and all slack was removed from the graft to allow for appropriate tension. The lateral aspect of the patella was lined up with the lateral femoral condyle and the knee was cycled to prevent overtensioning. The graft was fixed on the femoral side using an 6 mm x 23 mm PEEK interference screw (Arthrex, Naples, Florida) (Figure 14).

    Figure 14. Femoral fixation of the allograft with PEEK interference screw.

    • Fixation of the graft on the patella was fortified using #2 Fiberwire running from the anchor through the graft into the medial retinaculum (Figure 15). The wound was then copiously irrigated and closed.

    Figure 15. Closure of the medial retinaculum.

    • The patient was allowed to bear weight as tolerated in a hinged knee brace, which was worn for 6 weeks postoperatively.

    Postoperative Follow-up

    Continuous passive motion was used for the first 2 weeks and physical therapy was initiated thereafter to focus on regaining range of motion and strength. At 6 weeks after surgery, the patient was transitioned into a patellar J brace to be worn for an additional 6 weeks. Physical therapy was continued with sport-specific rehabilitation until return to sport at 4 to 6 months after surgery.

    Surgical Pearls

    • In this case, a slightly larger patellar incision was utilized to allow for an arthrotomy to be performed.
    • A 100-mm-long, semitendinosus allograft provides adequate length for fixation on the patellar and femoral sides.
    • Finding Schottle’s point using a perfect lateral radiograph is essential for recreating the anatomic femoral insertion site of the MPFL.
    • Nitinol wire is introduced in the femoral tunnel before the graft is docked into the socket to allow for appropriate placement of the femoral interference screw.
    • To prevent overtensioning of the graft, the lateral aspect of the patella is brought in line with the lateral femoral condyle with the knee in 20 to 30 degrees of flexion. The knee is then ranged to assess patellar tracking prior to femoral fixation

    Discussion

    Patellar instability continues to be a challenging issue for patients and orthopaedic surgeons alike. There is no consensus on surgical technique or optimal duration of conservative management following an initial patellar dislocation. Furthermore, there is variability in the threshold to treat concomitant soft tissue and osseous injuries. Recurrent instability can be treated with reconstruction to prevent further articular damage. The ultimate goals of surgery are to restore biomechanical stability to the patellofemoral joint and to allow the patient to return to sport and activities of daily living without limitations.

    In this case, we implanted a particulated juvenile hyaline cartilage graft (DeNovo) to address the concomitant peripheral chondral defect on the patella. Osteochondral defects of the patella are a common result of patellar dislocation and may cause significant symptoms that are not addressed with an MPFL reconstruction alone. The juvenile hyaline cartilage graft is intended for repair of articular cartilage defects in a single-stage procedure that precludes the need for a periosteal flap. In a recent MRI study, 82% of knees showed good to excellent fill in patella defects at the 6-month follow-up visit. [22] Further, multiple studies have shown comparable clinical outcomes with the use of microfracture, autologous chondrocyte implantation, and juvenile hyaline cartilage graft when treating patella defects. [23,24]

    In general, surgical reconstruction of the MPFL provides favorable results in terms of functional outcomes and patient satisfaction. Anatomic placement of tunnels leads to better results and prevents overtensioning of the patellofemoral joint. To this end, the technique described here allows for reproducibility of tunnel placement and graft tensioning with consistent clinical outcomes.

    Author Information 

    Neel A. Gupta, MD, is a resident in the Department of Orthopaedic Surgery at Drexel University, Philadelphia, Pennsylvania. Nimit Patel, MD, is an orthopaedic sports medicine fellow at The Rothman Institute, Philadelphia, Pennsylvania. Shyam Brahmabhatt, MD, is an attending surgeon at The Rothman Institute, Philadelphia, Pennsylvania.

    Disclosures

    The authors have no disclosures relevant to this article.

    Sports Medicine Editor, Rothman Institute Grand Rounds

    Sommer Hammoud, MD

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