Surgical Approach to Acute Osteochondral Fracture With Patellar Instability in Skeletally Immature Patients

Abstract

Background:

Patellar instability is a common condition that affects many young, active patients and can lead to long-term disability. This video aims to provide insights in the treatment of acute osteochondral fractures in skeletally immature patients after acute patellar dislocation.

Indications:

Patients who present with acute patellar dislocation and evidence of osteochondral fracture or osteochondral fracture with a loose body are potential candidates for medial patellofemoral ligament reconstruction (MPFLR) with osteochondral fragment fixation.

Technique Description:

In case 1, arthroscopy revealed a medial patellar facet defect. A medial patellar incision was made with dissection down to the vastus medialis oblique fascia and medial retinaculum. Before continuing to capsulotomy, the dissection for the MPFLR is completed by dissecting down to create a plane between layers 2 and 3. Capsulotomy is then performed with retrieval of the loose body, preparation of the patellar defect, and fixation of the osteochondral fragment. The MPFLR is then performed. An allograft is fixed to the patella with 2 pushlock anchors, and to a distally directed femoral tunnel using a 7-mm pitchfork SwiveLock tenodesis anchor, with care to avoid the medial femoral physis. The capsulotomy is then closed underneath the graft, with layer 2 closed above it. In case 2, a large osteochondral fracture of the lateral femoral condyle with loose cartilage flaps was arthroscopically identified. An anterior incision was made and a lateral lengthening was completed to perform a laterally based arthrotomy to expose the defect on the lateral femoral condyle. The defect site was prepared and the loose body was secured and fixated into the donor site lesion using bioabsorbable screws. The MPFLR was completed as in case 1, and the wound was closed in standard fashion.

Results:

Acute patellar dislocation with osteochondral fracture has been shown to lower both subjective and functional patient outcome measures. A recent study suggests that in large osteochondral fractures after patella dislocation, internal fixation improves mid- and long-term outcomes when compared with debridement alone.

Conclusion:

The MPFLR with concurrent osteochondral fracture fixation in patients with open physes is a reliable option for improving patellar stability and protecting articular cartilage from further injury.

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.

Graphical Abstract

This is a visual representation of the abstract.

Video Transcript

In this video, we will demonstrate the surgical approach for acute osteochondral fractures with patellar instability in 2 skeletally immature patients.

The author disclosures are listed here.

For each case, we will review the pertinent history, physical examination, and imaging findings. We will then discuss the preoperative planning pearls and demonstrate 2 surgical approaches as dictated by each patient's pathology.

We will then briefly discuss the postoperative management and rehabilitation protocol as well as postoperative outcomes and complications from the available literature.

In the pediatric population, the rate of osteochondral fractures following acute patellar dislocations ranges from 25% to 75% with the most common sites being the medial patellar facet or lateral femoral condyle.^2,6

The cases we are presenting will focus on the surgical approach to the 2 types of fracture patterns commonly seen in patellar dislocation. A medial facet defect is usually approached through a standard medial incision, while the lateral femoral condyle defect can be approached through a lateral lengthening approach to allow easier access.

The first patient is a 15-year-old male who presented with acute right knee pain after a noncontact sports injury. He reported twisting of the leg on a planted foot and felt a “pop.” He had no history of previous injury to that knee.

On examination of the right knee, there was a large effusion and positive patellar apprehension. He had limited flexion; the knee was otherwise stable. An arthrocentesis performed in the office revealed hemarthrosis.

Plain radiographs were obtained and were suspicious for a loose fragment. He was indicated for an magnetic resonance imaging (MRI), which demonstrated a large effusion, medial patellofemoral ligament (MPFL) tear, lateral patellar translation, and a displaced 3-cm osteochondral fragment with a donor site at the medial patellar facet.

Preoperative planning for patellar instability cases include careful evaluation of cartilage injuries and the presence and characteristics of any loose fragments. Successful management of the osteochondral injuries includes reducing and fixing the fragment if amenable while being prepared to change course if intraoperative findings do not support the fixation due to the fragment quality or size.

The bony anatomy and the lower extremity alignment are also closely scrutinized to determine the need for adjunct procedures. Illustrated here are the tibial tubercle-trochlear groove (TT-TG) distance and Caton-Deschamps index for patellar height. Although, it is also important to note that bony procedures used to address elevated TT-TG or patella alta are generally avoided in skeletally immature patients.

Consideration of the physeal status is critically important given the close proximity of the distal femoral growth plate to the anatomic landmarks for MPFL reconstruction (MPFLR). Biomechanical studies demonstrate that trajectories aimed anteriorly and distally provide safe drill paths in pediatric patients. ⁹

Although numerous graft options are available, allograft reconstruction have demonstrated reliably good outcomes while avoiding the morbidity associated with autograft for MPFLR,^7,8 semitendinosus allografts were utilized for both of the cases presented here.

Numerous studies have demonstrated that the natural history of osteochondral fragments is poor in both short and longer-term follow-ups.^3,5,10 Surgical repair of loose osteochondral fragments is optimal, but must be done acutely to avoid degeneration or swelling of the fragment. ¹²

If repair is not possible due to the size or the quality of the fragment, other resurfacing techniques can be used such as microfracture, osteochondral plugs, or autologous chondrocyte implantation. However, it is important to note that these secondary restoration procedures result in less optimal tissue properties compared to acute osteochondral fixation. ¹¹ The fixation method can be performed using either metal or bioabsorbable screws and pins, with the benefit of bioabsorbable implants being the lack of a second implant removal procedure although both options have comparable clinical outcomes in the literature. ¹⁴

For the surgical approach, the patient is positioned supine on an operating table with the foot of the bed lowered to allow for a standard knee arthroscopy using a lateral post. Bony landmarks are identified, and the skin incision is marked over the medial border of the patella.

Arthroscopy reveals the medial patellar facet defect and significant lateral translation of the patella in the trochlea.

The foot of the bed is then flattened, and the knee is placed in a sliding knee positioner at 45° flexion.

The medial patellar incision is made and the dissection proceeds down to the vastus medialis oblique (VMO) fascia and medial retinaculum.

Instead of performing the capsulotomy at this stage, we proceed with the dissection for the MPFLR first. This becomes more difficult once the capsulotomy is performed.

A new 15 blade is used to incise along the medial border of the patella, leaving a cuff of tissue to allow for later closure. This is carried up through to the VMO, which facilitates identifying the plane between the first 2 layers and the capsular tissue which will be used to pass the MPFL allograft, illustrated here with a Kelly clamp.

After this is achieved, the medial capsulotomy is performed, and the osteochondral fragment is retrieved and assessed, to determine whether it is amenable to fixation, which it was in this case. Evaluation for fixability is dependent on the fragment having adequate bone, reasonable quality of cartilage surface, and enough continuity to complete a successful construct. If the fragment has extensive fragmentation, poor surface quality, or no significant bone, our preferred approach is a staged matrix-induced autologous chondrocyte implantation (MACI) with MPFLR. The fragment can generally be used for the MACI biopsy in this case.

The patellar is then everted to expose the fragment donor site. This is prepared with curettage to clear the hematoma and identify the stable rim. The fragment is then positioned in the native orientation, and K wires are placed for provisional fixation. Four 3.5-mm bioabsorbable screws are then placed to complete the fixation. The knee is then cycled to confirm integrity of the fixation construct.

Attention is then redirected to the MPFLR. The patella is exposed under the medial tissue sleeve, and fluoroscopy is obtained to confirm positioning of 2 pushlock anchors at the 1 and 3 o'clock positions on this right knee. Care is taken to ensure the drill does not penetrate the patellar cartilage. The semitendinosus allograft, which was prepared by an assistant on the back table, is then introduced to the surgical field preloaded on 2 pushlock anchors. These are sequentially placed, with the graft positioned superficially and sutures exiting on the deep side of the eyelet. Tensioning occurs before and during anchor seating.

A free needle is then used to pass the free ends of the sutures from deep to superficial 3 mm from the graft-bone interface and tied over the graft. This creates a larger graft-bone footprint.

The graft is wrapped in a vancomycin-soaked sponge and placed within the incision.

Fluoroscopy is obtained to identify Schottle point on the lateral projection, and an incision is made, with blunt and sharp dissections carried out to the medial distal femur. Once identified, the tunnel is drilled to at least 30 mm with an 8-mm reamer. Studies of pediatric patients have demonstrated that Schottle point is consistently located distal to the medial femoral physis, but only by about 9 mm. As such, the pin trajectory is directed distally to avoid physeal violation.

Here, the surgeon demonstrates the plane created previously between layers 2 and 3 and a Kelly clamp is passed through to retrieve the graft using a free suture passed through the U-limb of the graft. Care is taken to ensure that the synovial layer remains between the graft and the articular surface, thus keeping the graft extra-articular.

The graft is then marked at the entrance of the tunnel, and again 25 mm beyond the insertion point. The 2 limbs are then whipstitched together along this length, and the additional tails of the graft are amputated to avoid bottoming out.

A 7-mm forked tip SwiveLock tenodesis anchor is then used to reduce the graft into the tunnel with the knee positioned in 45° of flexion to avoid overtensioning the graft. The graft is dunked in this case due to the distal trajectory of the femoral tunnel, which eliminates the ability to complete a pull through of the graft without consequentially violating the femoral physis. At this point, the patellar is reassessed ensuring that it has 1 to 2 quadrants of lateral translation.

The synovial layer is then closed under the MPFL graft with #1 vicryl sutures in an interrupted pattern. The VMO and retinacular incision is closed over the graft with #1 vicryl, and the soft tissue and skin is closed in the standard fashion.

Our second case will describe an alternative approach that can be used when the fracture fragment is from the lateral femoral condyle.

Our second patient is a 13-year-old male who presented with left knee pain after a football injury. He reports the knee buckled and he felt a “pop.” He had no history of previous injury to that knee.

On examination of the left knee, there was a large effusion, positive patellar apprehension, and increased lateral translation. The range of motion was 10° to 95°, and the knee was otherwise stable.

Plain radiographs were obtained and demonstrated a defect on the lateral femoral condyle. He was indicated for an MRI, which demonstrated a large effusion, MPFL tear, and a 2.4 × 1.5 cm osteochondral defect on the lateral femoral condyle with a single fragment in the suprapatellar pouch.

Arthroscopy reveals the large lateral femoral condyle defect and significant lateral translation of the patella in the trochlea.

The patient is positioned in the same manner as the previous case. However, contrary to that case, the lateral femoral condyle can be approached through a smaller midline incision and lateral lengthening approach. This avoids a larger midline incision and keeps the medial synovial layer intact during the MPFLR.

By making sufficient soft tissue flaps, both sides of the knee are readily accessible through this utilitarian approach.

The lateral lengthening is done first, and then the arthrotomy is completed through the deep retinacular layer that was just exposed.

A lateral lengthening is then performed by incising the lateral retinaculum longitudinally just off the lateral border of the patella. The deepest fibers of the retinaculum are left intact with the joint capsule. A flap is then raised laterally in this plane. The deep retinaculum and joint capsule are then incised laterally along the length of the previous retinacular incision.

Once complete, the lateral femoral condyle is then exposed and the patella is retracted medially. The fragment is retrieved and inspected and determined to be amenable to fixation with 4 biocomposite screws. The donor site is prepared with curettage and microfracture.

The fragment is then reduced with K-wire fixation. The K wires are overdrilled and reamed, and the biocomposite screws are placed. Fibrin glue is also placed around the periphery of the fragment to supplement the fixation construct. The lateral lengthening is then closed by approximating the deep layer to the superficial layer, thus increasing the length of the lateral retinaculum. It is important to close the lateral lengthening prior to tensioning the MPFLR to avoid overtensioning the MPFL graft. The MPFLR can then be performed without the need for a medially based arthrotomy, thereby leaving the synovial layer intact and ensuring the graft is placed extra-articular.

Once the MPFLR is complete, tension of the graft is evaluated by palpation, and the knee is cycled, to confirm full range of motion.

Our postoperative rehabilitation protocol is outlined here and describes our preferred timeline for patients undergoing this procedure.

Prior studies have reported excellent clinical outcomes when examining patients that undergo concomitant MPFLR and osteochondral fracture fixation. ¹³ In a study that examined patients who underwent fixation versus debridement alone, there were significantly less re-interventions needed for fixation. In pediatric patients, rates of secondary surgeries have been reported up to 22%.^4,15

One of the more significant complications after MPFLR is redislocation, and a recent systematic review has noted that about 2% of patients sustain a recurrent dislocation, with a larger number experiencing possible subluxation events.^1,13,15

Finally, some of the major complications include patellar fracture, failure of the graft or fixation construct, clinical instability, and loss of knee flexion.^15,17 The use of bioabsorbable screws also carries the risk of screw back out, which can compromise opposing articular cartilage and may require subsequent surgery to remove them. ¹⁶ We have summarized some of the major pitfalls throughout the video, including fragment fixation using a minimum of 3 screws to ensure adequate reduction and control of rotational stability, plane development for graft passage, and the femoral tunnel trajectory in pediatric patients.

This is an important consideration in skeletally immature patients as physeal violation can lead to premature closure of the growth plate leading to limb deformity and subsequent surgical intervention. ¹⁸ Numerous techniques are described in the literature for patellar stabilization in skeletally immature patients, many of which are nonanatomic, but if careful consideration is given to the physis, it is possible to safely reconstruct the MPFL anatomically without physeal injury. Further, concomitant MPFLR alongside fixation is recommended in order to avoid recurrent patellar dislocation and any additional insults to the articular cartilage.

Our references can be found here. Thank you for listening.