Treating Patellofemoral Instability with Bony and Soft Tissue Procedures

    A high school athlete presents with left knee patella dislocation, her first dislocation after 8 incidents of subluxation of the patella in a 1-year period.


    Bradford S. Tucker, MD


    Dr. Tucker has disclosed that he is a consultant for Mitek and the owner of Johnson & Johnson stock.


    Multiple factors contribute to the pathology of patellar instability. [1] Stability in the patellofemoral joint depends on bony and soft tissue structures (Table 1) [2]

    Table 1. Bony and Soft Tissues Structures Involved in Stability in the Patellofemoral Joint

    Bony Structures

    Soft Tissue Structures

    Lower limb alignment such as femoral-tibial angle and rotation, quadriceps femoris angle (Q angle) and tibial tuberosity trochlear groove distance (TT-TG distance)

    Static: Medial patellofemoral ligament (MPFL) and lateral retinaculum

    Trochlear shape

    Dynamic: Quadriceps femoris and hip abductors


    During initial knee flexion (<30°), the major restraints to lateral translation and dislocation are soft tissue. Beyond 30°, however, the bony structures are the primary determinants of patellar stability as the patella reduces within the trochlear groove. [3]

    The medial patellofemoral ligament (MPFL) is the primary soft tissue restraint against lateral translation of the patella within the patellofemoral joint. [4,5] During primary dislocation, commonly the result of a rotational injury during early knee flexion or stance, the MPFL may be injured as it undergoes failure from excessive lateral translation of the patella. [4,5]

    MPFL reconstruction in patients with otherwise normal joint morphology and lower limb alignment is an effective surgical procedure with favorable outcomes for patients presenting with recurrent patellar dislocations.[6,7]

    Patellar malalignment is characterized by:

    • Increased tubercle-trochlear groove (TT-TG) distance
    • Increased quadriceps femoris angle (Q angle)
    • Excessive knee valgus
    • Increased femoral anteversion
    • Excessive external tibial torsion
    • Combination of these factors

    Patients who present with patellar malalignment may report patellar instability and experience frequent low-energy patellar dislocations. Surgical stabilization for these patients has traditionally centered around tibial tubercle transfer to correct the underlying biomechanics at the patellofemoral joint. [1] 

    Tibial tubercle transfer is a realignment procedure designed to reduce contact forces across the patellofemoral joint and medialize the extensor mechanism. [8] Specifically, tibial tubercle transfer is used to correct excessive TT-TG distance, thereby increasing the stability of the patellofemoral joint. [9]

    For patients presenting with a ruptured MPFL and patellar malalignment, restoring physiologic load transmission across the patellofemoral joint while optimizing stability is a challenge for the treating sports medicine surgeon. A combined bony and soft tissue procedure such as MPFL reconstruction, lateral retinacular lengthening, and tibial tubercle transfer surgery can be performed to address the soft tissue insufficiency and the underlying skeletal abnormality.

    The following case illustrates a classic presentation of a young female athlete with recurrent patella instability who underwent successful treatment via combined soft tissue and bony reconstruction.

    Case Presentation

    A 15-year-old female high school athlete presents with a left knee patella dislocation. She plays soccer and lacrosse year-round for high school and travel teams.

    The patient says she was running (actually dribbling the soccer ball) during a game and twisted her knee, causing her patella to pop off the side. The patella was reduced on the field by the athletic trainer, who extended her knee with gentle medial correcting force.

    Her first patella instability episode was 1 year prior while running and twisting during gym class; however it didn’t fully dislocate at that time. Since then, she has subluxated her patella 8 times, but this is the first time she fully dislocated.

    After her first subluxation, she began working with the athletic trainer on stretching and strengthening and says that although she has been feeling a little better, her kneecap always feels unstable.

    Physical Exam

    • 5 feet 4 inches, 145 pounds, BMI of 24.9
    • Normal femoral tibial alignment, hip version, and thigh-foot angle
    • Elevated Q angles
    • Full extension and full flexion of both knees
    • Effusion in the left knee
    • Both knees ligamentously stable to varus and valgus stress, anterior and posterior drawer, and anterior and posterior Lachman
    • Extremely loose medial patellofemoral ligament on the left
    • Left patella can be dislocated with the knee bent to 30°; extremely apprehensive and painful


    • X-rays
      • Standing AP, standing PA, lateral, and Merchant views of the left knee (Figure 1) show that the growth plates are fused, with no obvious fractures, lesions, or arthosis.
    • MRI
      • Multiple axial, coronal, and sagittal views show a TT-TG distance of 21 mm (Figure 2), trochlear dysplasia, and lateral patellar subluxation and tilting; the medial patellofemoral ligament is deficient (Figure 3).
      • An impaction fracture is seen on the medial side of the patella, but the cartilage looks fine.
      • A bone bruise on the lateral aspect of the lateral femoral condyle indicates a recent dislocation.

    Figure 1. Merchant X-Ray view shows lateral subluxation and tilting.

    Figure 2. MRI Axial PD FS shows the Increased TT-TG distance of 21.2mm.

    Figure 3. MRI Axial PD FS shows the patella subluxated and tilted laterally with medial patellar facet impaction fracture and deficient MPFL.


    • Acute lateral patella dislocation of the left knee with history of chronic instability
    • Deficient MPFL
    • Patellofemoral malalignment and trochlear dysplasia, with an increased TT-TG distance of 21 mm
    • Medial patellar facet impaction fracture


    The patient underwent diagnostic arthroscopy, open tibial tubercle anteriomedialization, MPFL reconstruction with autologous hamstring, and lateral retinacular Z-lengthening. Following are the steps in this combined technique:

    • Place the patient supine on a radiolucent table for fluoroscopy.
    • Perform diagnostic arthroscopy to evaluate patellofemoral tracking (Figure 4) and the articular cartilage (Figure 5) for possible chondroplasty or secondary cartilage restoration procedure.
    • Make a midline incision and full-thickness skin flaps to expose 6 cm distal to the tibial tubercle, medial epicondyle, and lateral retinaculum.
    • Make a tibial tubercle osteotomy 6 cm long, anterior on the medial side and posterior on the lateral side, with an osteotome. Anteriomedialize 1 cm and fix with small fragment compression screws.
    • Harvest the semitendinosus, cut down to 210 mm, and place a running locking whip stitch in each end with #2 permanent suture.
    • Expose the medial aspect of the patella though small medial arthrotomy. Drill 2 small tunnels in the patella parallel to each other, from medial to lateral, 15 mm apart and 15 mm deep in the superior aspect of the patella. Fix each end of the hamstring tendon in the tunnel with tenodesis screw.
    • Make a small opening in the fascia over the medial epicondyle and create a soft tissue tunnel between this incision and the medial parapatella arthrotomy. The tunnel should be between the capsule and the native MPFL.
    • Pass the looped end of the hamstring graft though the soft tissue tunnel and fix it at the isometric point on the medial epicondyle though the bone tunnel and interference screw. Fix the graft at 30° of knee flexion and make sure it either stays the same length or loosens with knee flexion to avoid over-constraining the patellafemoral joint.
    • Close the arthrotomy and fascia over the medial epicondyle with #1 Vicryl.
    • Z-lengthen the lateral retinaculum by cutting through layers 1 and 2 just adjacent to the lateral aspect of the patella, skive between layer 2 and 3 for at least 1cm, and then cut through layer 3 (capsule). Sew the 2 cut ends together with #1 Vicryl.
    • Check the tracking and balance of the patellofemoral joint through the full range of motion visually and with the arthroscope (Figure 6).
    • Close the subcutaneous tissue with 2-0 Vicryl and the skin with staples.

    Figure 4. Arthroscopic view of patella laterally subluxated and tilted out of the trochlea.

    Figure 5. Arthroscopic view of patella manually dislocated laterally and showing patella chondral partial thickness damage.

    Figure 6. Arthroscopic view of patellofemoral joint at end of surgery to show the patella tracking perfectly in the trochlea.

    Postoperative Course

    • Non-weight-bearing for 6 weeks until the osteotomy heals, and then to progression to full weight-bearing
    • Knee brace for 3 to 4 weeks until return of quadriceps control
    • Immediate progression to full range of motion
    • Immediate quadriceps sets and straight leg raises, then progressive resistance exercises as osteotomy heals
    • Return to sports around 6 months, when FROM, full quadriceps strength, no swelling, no instability, and osteotomy fully radiographically healed (Figure 7)

    Figure 7. AP and Lateral X-Rays at 6months post op showing good position and healing of the osteotomy and good positioning of the hardware and tunnels.

    Final Follow-up

    At 1 year postop, the patient has FROM, with normal strength, no recurrence of dislocation, and no feelings of instability. She is back playing varsity soccer and lacrosse for her high school and travel teams.

    She also says she is very happy she had the surgery and her knee has never felt more stable. In fact, it feels more stable than her uninjured knee.


    The MPFL is the primary soft tissue restraint to lateral translation of the patella. [4,5]  During primary dislocation, the MPFL is damaged and studies have shown that the ligament heals poorly with a non-operative approach. [4,5] Reconstruction of the MPFL is an effective surgical technique that is designed to stabilize the patella, restore proper kinematics, and reconstitute load transmissions throughout the patellofemoral joint.

    In addition to the soft tissue insufficiencies, patellofemoral malalignment has also been identified as a risk factor for patellar dislocation [9] in patients with patellar instability and patellar malalignment, a tibial tubercle transfer is frequently performed (when patients have excessive TT-TG distance) to reduce contact forces across the patellofemoral joint, as well as to medialize the extensor mechanism. [8]

    A case series investigating outcomes of combined Fulkerson osteotomy and a lateral release procedure in 34 athletes (41 procedures) with patellofemoral instability from 1999-2004 represents the largest case series of realignment osteotomies to date in athletes. The average reported Lysholm score of these patients was 91.8 at an average of 46 months postop. [10]

    MPFL reconstruction combined with tibial tubercle transfer has a high rate of success for patients presenting with patellar instability due to combined MPFL rupture and patellar malalignment. [11] The risk of recurrence with this technique is low (5.0%), and the risk of complications with the combined surgeries is equivalent to that of patients who undergo isolated MPFL reconstruction or tibial tubercle transfer surgeries. [11]

    Therefore, for patients presenting with a ruptured MPFL and malalignment with an increased TT-TG distance, combined MPFL reconstruction and tibial tubercle transfer is a safe technique that provides patients with improved patellofemoral stability and a decompressed patellofemoral joint.

    The recurrence rate is very favorable considering that patients who undergo combined surgery are deemed to be at the highest risk for recurrent subluxation due to skeletal malalignment and attenuation of the MPFL.

    Author Information

    Bradford S. Tucker, MD, is an Assistant Professor at Jefferson Medical College, Philadelphia, Pennsylvania. He specializes in sports medicine at The Rothman Institute.

    Sports Medicine Section Editor, Rothman Institute Grand Rounds

    Fotios P. Tjoumakaris, MD


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