Physeal-Sparing Medial Patellofemoral Ligament Reconstruction With Patellar Tendon Shortening and Guided Growth

Abstract

Background:

In skeletally immature patients, alternative surgical approaches should be undertaken for the treatment of patellofemoral instability that respect the open physis. Remaining growth can be exploited for correction of genu valgum, a known anatomic risk factor of patellofemoral instability.

Indications:

A skeletally immature 14-year-old boy with bilateral genu valgum and patella alta presented with symptomatic, recurrent left knee patellar instability precluding sports participation and causing dysfunction in his activities of daily living.

Technique Description:

A midline approach to the knee was used. Medial patellofemoral ligament reconstruction (MPFL-R) was completed up until the point of femoral-sided allograft fixation. The socket for femoral-sided graft fixation was reamed with an all-epiphyseal technique. Next, growth modulation with temporary hemiepiphysiodesis of the medial distal femoral physis was undertaken with an 8-plate bilaterally. Patellar tendon shortening was completed. Femoral-sided graft fixation for the MPFL-R was then completed.

Results:

There were no acute complications associated with surgery. Surgical management led to resolution of the patient’s patellar instability. The patient is being followed for timing of hemiepiphysiodesis plate removal.

Discussion/Conclusion:

In skeletally immature patients, a physeal-sparing MPFL-R is a viable treatment option to address recurrent patellar instability. Other anatomic risk factors, such as genu valgum and patella alta, may be concomitantly addressed using techniques that are respective of the open physis.

Patient Consent Disclosure Statement:

The author(s) attests that consent has been obtained from any patient(s) appearing in this publication. If the individual may be identifiable, the author(s) has included a statement of release or other written form of approval from the patient(s) with this submission for publication.

Graphical Abstract

This is a visual representation of the abstract.

Video Transcript

In this video, we will discuss the indications, surgical technique, and outcomes for physeal-sparing medial patellofemoral ligament reconstruction (MPFL-R) in a skeletally immature patient, along with patellar tendon shortening and guided growth.

Here are our disclosures.

The following topics will be covered in this video.

Background and Indications

A skeletally immature 14-year-old boy presented to our clinic with symptomatic left knee pain and recurrent patellar instability, precluding soccer participation and causing dysfunction in his activities of daily living. He had attempted exhaustive physical therapy and bracing measures without relief.

Standing assessment of the lower extremities revealed bilateral genu valgum. Otherwise, the patient had full active left knee range of motion. He had a small effusion of the left knee, as well as tenderness to palpation at the medial patellar facet and patellar apprehension with lateral translation. On the moving apprehension test, the patella could not be passively subluxated with the quadriceps relaxed beyond 60° of flexion, whereas the contralateral knee engaged the trochlea in the same manner at 45° of flexion.

Left knee radiographs were obtained, demonstrating open physes and patella alta, with a Caton-Deschamps index (CDI) of 1.56.

Full-length, standing, lower extremity radiographs were obtained, demonstrating and quantifying the patient’s bilateral valgus alignment.

Magnetic resonance imaging (MRI) demonstrated a torn MPFL, with a small bony avulsion from the medial patella and an osseous contusion pattern of the lateral femoral condyle consistent with lateral patellar instability. The tibial tuberosity-to-trochlear groove (TT-TG) distance was 20 mm and patellar tendon-to-lateral trochlear ridge distance (PT-LTR) was 18 mm. ³

The patient’s presentation was consistent with left knee pain and recurrent patellar instability in the setting of patella alta and bilateral genu valgum, which had failed conservative management. The patient and family elected to undergo left knee MPFL-R with gracilis allograft, patellar tendon shortening, and distal femoral growth modulation with temporary hemiepiphysiodesis for alignment correction. In the skeletally immature population, alternative surgical approaches must be undertaken for the treatment of patellofemoral instability that respect the open physis. In addition to the known morphologic risk factors of increased TT-TG, patellar tilt >20°, CDI >1.3, and trochlear dysplasia, younger age and skeletal immaturity have been demonstrated as risk factors for recurrent patellar instability. Remaining growth can be exploited for correction of genu valgum, a known anatomic risk factor of patellofemoral instability. ⁵ Patient-specific anatomy and associated risk factors were assessed in preoperative planning. Given the measured CDI of 1.56, we had a goal to correct this with patellar tendon imbrication to 1.1, which equated to 14 mm of shortening. The multiplier application was used to calculate estimated age of removal of the plate used for temporary hemiepiphysiodesis by inputting shown data points. ² This is estimated at the distal femoral physis to be about 0.6° to 0.7°/month. We planned to assess the growth modulation effect on serial radiographs.

Technique Description

Requisite materials for the planned procedures are listed here. The surgery was performed on an outpatient basis, using regional anesthesia and tranexamic acid. A thigh tourniquet was used with the patient in a supine position on a radiolucent operating room table.

The order of operations intraoperatively is key. Patellar tendon shortening should be completed before final femoral-sided MPFL graft fixation to ensure appropriate graft tensioning and evaluation of ligament isometry. Additionally, hemiepiphysiodesis plate application should be completed after the establishment of the location for femoral-sided MPFL graft fixation so that these do not overlap or converge.

A midline incision to the knee is utilized, and full-thickness flaps above the paratenon are created, exposing the patella and patellar tendon for later shortening. A counterincision is also made medially to be used for both hemiepiphysiodesis and patellar-sided MPFL graft fixation.

After a standard medial parapatellar arthrotomy is made along the length of the patella, the soft tissue plane between layers 2 and 3 of the medial knee is developed toward the adductor tubercle using a tonsil, and a shuttling suture is passed for later use. Two Mitek GII QUICKANCHOR suture anchors (Depuy Mitek) are then placed into the medial aspect of the patella, centered between the articular cartilage margin and the anterior cortical bone. The anchors are placed in the upper one-third to one-half of the patella, spaced by approximately 1 cm. The intervening bone is then prepared by curetting it to encourage healing of the graft to bone. The graft is then centered on the suture anchors and secured in place. The graft ends are shuttled between layers 2 and 3 to the medial knee using the previously placed shuttling suture. Schottle’s point is then identified with a beath pin on a perfect lateral radiograph. Trajectory is verified on an anteroposterior (AP) view and confirmed to be distal to the physis and to avoid the trochlea and intercondylar notch. The distal femoral physis may appear to overlap Schottle’s point on the lateral view. The AP view will help demonstrate that a trajectory aimed approximately 20° both anterior and distal will remain all-epiphyseal. Placement of a long tonsil clamp with the tip at the desired exit point on the lateral cortex of the knee can give the surgeon a target when advancing the beath pin. Graft isometry is then assessed. After overreaming the beath pin with a 7-mm reamer, a nitinol wire is placed for later fluoroscopic visualization of the tunnel and a passing suture placed. The graft is not passed at this point, and attention is turned to performance of our medial distal femur hemiepiphysiodesis.

We position the 1.6-mm guidewire for the OrthoFix 8-plate (Orthofix Medical) at the medial distal femur physis, aiming to be colinear with the physis and centered on the lateral view. Once this alignment is achieved, the guidewire is advanced 1 cm into the physis by hand. The 16-mm OrthoFix 8-plate is then placed over the guidewire down to bone. This allows for adequate screw spread while avoiding the physis and our socket for femoral-sided fixation of our MPFL graft. The guidewires for the screws are inserted in a divergent manner while aiming anterior to avoid convergence with the socket for femoral-sided MPFL graft fixation, as visualized by the retained beath pin. C-arm fluoroscopy is used to confirm appropriate implant positioning on orthogonal views. The cortex is drilled, and then appropriately sized 4.5-mm cannulated screws are placed over the guidewires for final plate fixation.

Next we proceed with our patellar tendon imbrication. The infrapatellar fat pad is released posteriorly along the entirety of the tendon so that it is not incarcerated at a later time by suture. After the paratenon is incised at its midline and paratenon flaps raised, we mark our preoperatively planned 14 mm of shortening in the central portion of the tendon. Another dotted line is then drawn 7 mm proximal to that. At the marked line inferiorly, the anterior 50% of the distal patellar tendon is divided sharply with partial thickness, and the flap is raised at a partial depth proximally for 14 mm. A new line is then drawn 7 mm proximally to the inferior extent of the raised flap on the remaining, thin tendon. Four No. 1 Vicryl sutures are then passed in a horizontal mattress fashion from the most proximal line to the line created underneath our raised flap, with care taken not to incarcerate the fat pad. Next, two No. 2 Orthocord sutures are passed from proximal to the thickness change distally (at our initially outlined 14-mm lines) in a locking fashion. After the knee is brought into 40° of flexion, the pairs of sutures are tensioned and tied, thereby folding the pleat and shortening the tendon. An additional 0-Vicryl suture is used in an interrupted, figure-of-8 fashion to secure and reinforce the distal flap. The knee is brought into 60° of flexion without creep in the patellar tendon imbrication.

The MPFL-R is then completed with femoral-sided graft fixation. The graft ends are pulled into the blind-ended femoral socket. Femoral-sided graft fixation is performed by placing an interference screw over the nitinol wire with approximately ∼0.5 pounds (2 N) of force being held through the graft with the knee at approximately 40° of flexion, while the patella is ensured to be centered within the trochlea. The medial arthrotomy is closed with No. 1 Vicryl, being careful to not incarcerate the MPFL graft in the capsular repair. Skin and subcutaneous tissue are then closed in a layered fashion.

Postoperatively, the patient was restricted to 50% weightbearing on the operative extremity for 6 weeks. A hinged knee brace was used to restrict motion to 0° to 30° for the first 2 weeks, 0° to 60° for weeks 2 to 4, and 0° to 90° for weeks 4 to 6, after which point, range of motion was unrestricted. Patients are counseled on avoiding high-level activity for 6 to 12 months postoperatively.

Discussion

The complexity of the surgery leads to possible intraoperative and postoperative complications, which are listed here. The effect of growth modulation through the physis should be monitored on serial radiographic evaluation.

There is a relative scarcity of reports of clinical outcomes in the literature with this technique. Patellar tendon shortening with a similar technique has been reported by Patel et al. ⁴ In their study, the authors reported their 2-year outcomes on 27 patients (32 knees). The authors found that on average, this technique provided a correction of patellar tendon length from 6.2 cm preoperatively to 5.1 cm at 3 weeks postoperatively, which was maintained at 5.2 cm at 2 years postoperatively. ⁴ In this series, 2 instances of failure of imbrication with loss of correction occurred after trauma. ⁴ Two additional patients underwent revision MPFL-R and concomitant trochleoplasty for recurrent patellar instability. ⁴

Tomasevich et al. ⁶ reported on the use of temporary medial distal femoral hemiepiphysiodesis with and without MPFL repair for recurrent patellar instability in a population of 31 skeletally immature patients (47 knees) with a mean age of 12.0 years. Average time to hardware removal was 1.2 years after surgery, with 81% of patients achieving an appropriate amount of correction. ⁶ Seventeen knees (36%) underwent subsequent surgery for recurrent patellar instability. ⁶

Recently, Bachman et al. ¹ presented multicenter data looking at 31 patients (37 knees) at an average age of 12.4 years who underwent implant-mediated guided growth with or without MPFL-R. The mean angular correction obtained was from 12.4° of knee valgus to 5.1° over 12.1 months. ¹ The authors reported 10 (27%) complications involving 7 knees and 4 patients. ¹ Five knees (13.5%) experienced recurrent patellar instability, requiring revision surgery. ¹

In summary, physeal-sparing MPFL-R and concomitant patellar tendon shortening and growth modulation appears to be a viable treatment option for skeletally immature patients with recurrent patellar instability associated with patella alta and genu valgum. This remains a challenging problem to treat, and further study is needed to better understand outcomes of this procedure for this indication.

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