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A 12-year-old boy with a right knee injury

Issue: July 2014

ByScott T. Ferry, MD

ByLaith Al-Shihabi, MD

ByPeter N. Chalmers, MD

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Peter N. Chalmers

 

Laith Al-Shihabi

A 12-year-old boy landed awkwardly while attempting a flip and sustained a forced eccentric knee flexion injury. He had immediate anterior knee pain and an inability to bear weight. He was seen in a local emergency department, where he was placed into a knee immobilizer and told to bear weight as tolerated prior to follow-up with an orthopedic surgeon. He had no past medical or surgical history and took no medications. He had no pain prior to the injury.

The patient was evaluated in our clinic 4 days post injury. On physical examination, he had ecchymosis and swelling at the anterior knee, but had no breaks in his skin. He was unable to actively extend the knee and had significant pain with knee motion. He had a palpable defect inferior to the patella, but had significant guarding that limited delineation of the exact location of the defect. His examination was otherwise within normal limits.

Anteroposterior and lateral views of the right knee upon presentation demonstrated a high-riding patella, a large knee joint effusion and significant prepatellar swelling. Osseous fragments are visible between the inferior pole of the patella and the tibial tubercle (Figure 1).

Figure 1. Anteroposterior (a) and lateral (b) views of the right knee upon presentation demonstrate a large suprapatellar joint effusion and significant prepatellar swelling and prominence as well as osseous fragments in the interval between the inferior pole of the patella and the tibial tubercle. There was also evidence of a high-riding patella.

Images: Ferry ST

What is your diagnosis?

See answer on next page.

Extensor mechanism disruption

The patient was diagnosed with an extensor mechanism disruption with a combined tibial tubercle avulsion fracture and a partial patellar tendon avulsion. The management was open reduction and internal fixation (ORIF) with supplemental suture fixation.

Background and work-up

Rupture of the knee extensor mechanism is an uncommon pediatric injury. The apophyses at which the patella and quadriceps tendons attach to the patella serve as biomechanical weak points, with characteristic fracture patterns occurring as the skeleton matures. In childhood, osteochondral avulsion fractures off of the patella are most common. In adolescent populations during the transitional phase of physeal closure, the proximal tibial physis becomes the weakest point, leading to tibial tubercle avulsion fractures. The proximal tibial physis closes from posterior to anterior and thus the specific fracture pattern depends upon the degree of physeal closure. For avulsions of the patella, while radiographically this avulsion only appears to include a small and narrow osseous segment, intraoperatively the ligament will be avulsed with a wide thick “sleeve” of cartilage and retinaculum, hence the name “sleeve fractures”. Although most frequently the patellar tendon is avulsed from the inferior pole of the patella, avulsion can also occur at the superior pole of the patella. While pediatric extensor mechanism injury usually occurs sporadically due to acute trauma, it can be associated with osteogenesis imperfecta, Osgood-Schlatter’s disease, and patella baja.

History and physical examination are critical for patients with these injuries. History should include a full accounting of the mechanism of injury, which is typically associated with a forceful eccentric quadriceps contraction. A careful examination of the skin should be performed given the subcutaneous nature of the extensor mechanism. In addition, important portions of the physical examination include a thorough neurovascular exam, testing of the patient’s ability to perform a straight-leg-raise, palpation to determine the level of the patella as well as the location of the palpable “gap” within the extensor mechanism, and/or the site of maximal tenderness. A thorough examination of the lower extremity compartments should be performed for tibial tubercle avulsion fractures.

Recommended imaging includes an anteroposterior, lateral, oblique and patellofemoral (i.e., “Sunrise” or Merchant) view of the knee. In subtle injuries, imaging of the contralateral side may be helpful. The borders of the patella and the tibial tubercle should be carefully inspected for cortical irregularities and radio-opacities within the soft tissues signaling a possible sleeve avulsion. In addition, quantification of patellar height with the Insall-Salvati and Blackburn-Peel ratios can be helpful, especially in comparison to the contralateral side. In cases with negative radiographs and a high clinical suspicion, MRI may be helpful. Review of the examination and imaging should include a thorough search for associated periarticular injuries, although pediatric extensor mechanism injuries are usually isolated injuries.

Treatment options

Patients with nondisplaced tibial tubercle and patellar sleeve fractures can be treated nonoperatively with a cylindrical cast for 6 weeks. However, any degree of displacement (2 mm to 3 mm) is considered an indication for ORIF. Tibial tubercle fractures are usually reduced via an anterior midline approach and fixated with one or two partially threaded cancellous lag screws from anterior to posterior placed parallel and distal to the physis. In select cases, a closed reduction and percutaneous fixation technique may also be appropriate. Historically, high rates of union and high rates of full return to preinjury activities have been described. A variety of other fixation methods have been used on the patellar side, some of which have also been employed on the tibial side, including tension band fixation, suture fixation with or without use of an anchor, lag screw fixation, use of a basket plate and bypass fixation from the tendon into the patella or tibia. In cases with articular involvement, arthroscopic visualization may also be helpful. One rarely reported variant the surgeon must be prepared for is simultaneous fracture of the tibial tubercle and avulsion of the patellar tendon from the fracture fragment, which may require “bypass” fixation methodology.

While complications are infrequent, they can be potentially devastating and can include compartment syndrome, partial or total physeal arrest, refracture, arthrofibrosis, and scarring of the patellar tendon leading to patella baja and a potential for accelerated patellofemoral degeneration. Minor complications are frequent, such as hardware prominence and, in cases that involve the tibial tubercle, prominence of the tubercle that may interfere with weight bearing through the tubercle, as occurs during kneeling.

Management of our patient

Figure 2. A clinical photograph taken intraoperatively
demonstrates an intact interface between the central
patellar tendon and the inferior pole of the patella.
However, the inferior aspect of the patellar tendon
has been avulsed from the tibial tubercle. There are
also several osseous and cartilaginous fragments
avulsed from the far medial and far lateral aspects
of the inferior patella.

In the present case, based upon the preoperative radiographs, the patient was diagnosed with a patellar sleeve fracture from the inferior pole of the patella. After a full discussion of the risks and benefits, the family choose to pursue ORIF of the fracture. The risks discussed with the patient and family included physeal arrest, angular deformity, limb length discrepancy, compartment syndrome, infection and the need for reoperation. The patient was positioned supine on a radiolucent table with a bump under the hip on the operative side to internally rotate the leg. After induction of general anesthesia, exsanguination of the leg and inflation of a thigh tourniquet, an anterior midline incision was made over the center of the patellar tendon. After dissection through the subcutaneous tissues, creation of full-thickness supraretinacular flaps and evacuation of hematoma, the patient was found to have disruption of the retinaculum medially and laterally at the level of the inferior pole of the patella. At the origin of the patellar tendon, there were nonarticular avulsion fractures on both the far medial and far lateral aspect with a strip of patellar tendon still attached distally to the tubercle. These fragments represented the osseous fragments seen on the radiographs. The central 75% of the patellar tendon was intact proximally with a complete small osteochondral avulsion fracture from the tibia tubercle distally (Figure 2).

Because only a small osseous fragment was available for repair, a hybrid screw and suture construct was used. Running, locking #2 reinforced sutures were placed in the medial and lateral aspects of the patellar tendon exiting distally. Two transverse drill holes were then made in the anterior tibial cortex 3 cm distal to the tubercle with a 2-mm drill. The largest osteochondral fragment on the distal patellar tendon was then anatomically reduced to the tubercle and fixated with a cannulated, partially threaded 4-mm cancellous screw with a washer. The previously placed sutures were then brought through the distal drill holes using a suture passing device and then were tied over a bone bridge with the repair physiologically tensioned. The small medial and lateral strips of the patellar tendon were repaired to the periosteum at the inferior patella with sutures. The proximal retinacular ruptures were repaired with absorbable sutures. The skin was closed and a long-leg cast was placed and bi-valved.

Figure 3. Anteroposterior (a) and lateral (b) views of the right knee at final follow-up demonstrate excellent restoration of patellar height and anatomic patellar tendon length. The fracture appears to have healed and remodeled, and the hardware appears in excellent position. The drill hole for the supplemental suture fixation of the repair can also be seen.

Postoperatively, the patient did well. He was initially instructed to be non-weight bearing and was immobilized in a long-leg cast in extension for 6 weeks. He was then transitioned to weight bearing as tolerated in a hinged knee brace, and physical therapy was started to assist in recovery of motion. The patient subsequently rapidly regained his range of motion and strength.

Radiographically, the patient progressed to union at 7 weeks postoperatively (Figure 3). By 5 months postoperatively, the patient had no extensor lag, 130° of flexion and was released to full activity. At final follow-up 8 months postoperatively, the patient had a normal examination without radiographic evidence of physeal arrest or angular deformity.