Acute traumatic patellar dislocations are the most common cause of an acute hemarthrosis of the knee, with a reported incidence of approximately 77 per 100,000.1 Complications are not uncommon and may include acute complications, such as osteochondral fractures (OCFs), and chronic sequelae, such as recurrent instability and early joint degermation.1
OCFs are injuries of the cartilage and underlying subchondral bone and are common in the pediatric and adolescent population. They are often secondary to low-energy trauma or sports injury.2 OCFs are most commonly seen after an acute patellar dislocation, resulting in an OCF at the medial patellar facet and/or lateral femoral condyle.3–5 The mechanism of dislocation can either be a direct force to the patella, resulting in a traumatic dislocation, or more frequently, an indirect force when the tibia is externally rotated and the knee is in a semiflexed position.4,6 The incidence of OCF has been reported to be between 39% and 71% in the setting of an acute patellar dislocation.7,8 Younger population is more susceptible to these injuries because of a combination of ligamentous laxity (more risk of shearing with a twisting mechanism) and an abrupt change in mechanical properties at the interface between articular cartilage and subchondral bone.6 These injuries can easily be missed and can lead to premature degenerative joint disease if not treated promptly.2,9
OCF can present as acute or chronic injuries. Sparse literature exists to define these terms accurately. An acute injury is most commonly defined as less than 2weeks.3,10 This is important because chronic OCF can undergo chondral degeneration, causing necrosis of the fragment. For the purpose of this article, acute injuries are defined as an injury less than 2 weeks and a chronic injury as an injury older than 2 weeks.
Chondral-only injuries are defined as a fragment without the presence of bone. However, studies have described many of these fragments containing minimal bone (<5 mm) attached on the undersurface.6,11 Although these injuries were believed to have poor healing potential because of the avascular nature of chondral tissue, Fabricant et al6 demonstrated favorable outcomes (56% restoration of cartilage contour and full return to sports) when chondral-only injuries in patients <18 years were fixed acutely.
In this article, we review the recent literature on the evaluation and diagnosis of a suspected OCF after patellar dislocation, how to minimize the risk of missing these injuries, and explore the available management options allowing clinicians to render the best possible clinical outcomes.
History and Examination
Establishing a thorough history is critical in determining the timing of injury. This can be challenging in very young patients (<10 years) because of their inability to properly describe the injury.12 Most of the patients will present with a painful and swollen knee after patellar trauma, which is most commonly secondary to a patellar subluxation or dislocation event.12 A hemarthrosis has been reported to be in 31% of patients with a patellar dislocation.13 Wessel et al reported that in patients presenting with a hemarthrosis, 5.7% were associated with a patellar fracture and 17.9% were associated with a patellar dislocation.
Orthogonal views of the knee should be taken, including anteroposterior, lateral, and merchant patellar views. Typical features of the OCF fragment in the knee include a thin wafer of subchondral bone and an irregular bony contour or bony fragmentation.14 However, the radiographic findings may be subtle, especially if the bone fragment is small, which can lead to a missed lesion in up to a third of cases.9,14 In these cases, an OCF may be recognized arthroscopically (Figure 1).8
Radiographs are not only useful to establish the fracture fragment but help determine the level of skeletal maturity. This is important because younger patients with an open physis have a better prognosis.2 When attempting fixation in skeletally immature patients, surgeons must be careful that the implant placed does not damage or cross the distal femoral physis. Lateral trochlea OCF fixation is at higher risk because of the proximity of the physis to the cortex. In addition, a tibial tubercle osteotomy (TTO) is not an option until the patient has reached skeletal maturity. When patients have open physes, other soft-tissue distal realignment procedures that do not threaten the physis, such as the Roux-Goldthwait procedure, should be used.
Magnetic resonance imaging (MRI) is superior to other imaging modalities in the evaluation of osteochondral fragments. It is recommended to establish the size, location, and quality of the lesion and assessing the quality of the physis when planning surgical procedures.15 MRI has an 86% sensitivity and 97% specificity in identifying hyaline cartilage lesions in the knee.2 Fat-suppressed three-dimensional spoiled gradient echo sequences have shown to be the most sensitive compared with standard sequences.16 Fracture lines are best shown on the T1-weighted images as a linear hypointensity, commonly seen at the inferior aspect of the patellar facet and lateral margin of the lateral femoral condyle.17 The donor location is defined by a fluid-filling void, best seen as a hyperintense signal on the T2-weighted image.17 These sequences help detect lesions with greater ease, picking up approximately 44% of OCF that were originally missed on plain radiographs (Figures 1 and 2)16.
Although MRI has several advantages, it has been shown to overestimate the size of OCFs because of the bone marrow edema.18 CT is useful in further defining the origin and bony extent of the OCF, rendering surgical fixation easier to plan.
Diagnostic arthroscopy is the benchmark method for confirming an OCF. This is usually done concomitantly with definitive surgical treatment to confirm the diagnosis and to assess the quality of the OCF and fracture surface (Figure 2). During an arthroscopic evaluation, surgeons should ensure thorough visualization of the lateral gutter to look for the fragment, without compromising their standard diagnostic approach.
When faced with this injury, the surgeon's options are dictated by the size, location, and the quality of the OCF.2
Some authors have demonstrated nonsurgical reasonable results if the size of the fragment is <15 mm and on non–weight-bearing surfaces, such as the patella.5,19 In the study by Seeley et al, 20 patients (41.6%) were treated nonsurgically, with 85% of them sustaining a lesion on the patella. Higher International Knee Documentation Committee (IKDC) scores were noted in this group compared with patients with OCF located on the femur (91.12 versus 72.31). A theoretical lower risk is that these non–weight-bearing lesions progress to cause degenerative changes in the joint.20 A more recent study demonstrated failure of conservative management if the OCF was larger than 20 mm or located on the inferomedial facet of the patella involving the central ridge, eventually requiring fragment excision. Both studies reported no significance in redislocation rates.21
The key feature of the rehabilitation program is to prevent additional episodes of patellar dislocation.2,5 Patients will typically wear a patellar-stabilizing brace for 3 months and return to sport when normal motion and strength have returned to participate in sport without symptoms.19 Palmu quoted that approximately 30% of children younger than 16 years returned to a high level of activity without a recurrent patellar dislocation and approximately 50% returned to sport.19 These patients also took part in a dedicated rehabilitation program for the first 6 months after their injury.19
Historically, loose fragments were removed because of the lack of tools and techniques for fixation.2,22 These patients demonstrated poor long-term results (radiographic healing 29% and high rate of degeneration 79%), leading to the development of a fibrocartilaginous clot at the fracture bed defect.22 Small lesions (<15 mm) or lesions of non–weight-bearing areas can be excised if they cause pain or mechanical symptoms, such as locking and catching, and have demonstrated favorable outcomes.2,5 If the fragment is loose, it is advisable to remove it, but there are no studies comparing acute versus chronic fragment excision.
Sometimes, fragment excision is the only salvage option if the OCF is not diagnosed acutely. Fragment swelling occurs, and although this can be trimmed to size, it renders it not suitable for fixation because of necrosis of the osteochondral junction, impairing healing capabilities.3 If a lesion has to be excised, modern techniques now involve using cartilage restoration procedures, such as autologous chondrocyte implantation (ACI), to replace lost cartilage and help mitigate later complications.
Microfracture is a suitable treatment option if the fragment cannot be repaired and exhibits better short-term outcomes in patients with OCF compared with patients with osteochondritis dissecans.2,23 Although it is a straightforward, minimally invasive, and cost-effective treatment method, the results seem to deteriorate over time, especially in patients older than 40 years, with lower IKDC scores and poorer healing cartilage on MRI after the procedure.24 Patients younger than 40 years with lesions less than 2 cm had a better return to contact sports and more minutes played on the sports field.24 However, the overall outcomes deem this modality not suitable as a stand-alone first-line treatment.
Multiple techniques of suture repair of the OCF fragment have recently been described.10,25,26 One technique involves drilling Kirschner wires through the fragment and patella. Absorbable suture is then passed through the holes and tied on the nonarticular surface of the patella.25 Successful results were reported in a small cohort of patients over a 2-year follow-up using an absorbable suture material to repair the fragment.25 A second technique involves using appropriately spread knotless suture anchors placed laterally off the articular surface, compressing the fragment with a crossing V-shaped suture. This technique compresses the OCF adequately, without violating the articular cartilage of the fragment. Second-look arthroscopy at 10 weeks demonstrated complete healing of the OCF.10 This technique has also been successful when done arthroscopically for a thinly delaminated chondral defect.26 All three studies report the technique to be simple, reproducible, and provide solid stability.10,25,26 Future studies are needed to quantify outcomes and complications of these new techniques (Figure 1).
Large OCFs (>15 mm) are best treated with surgical fixation.2,27 This can be done arthroscopically or through an open arthrotomy based on the location of the OCF. Loose fragments that should be repaired acutely are possible for the reasons mentioned above.3,28 Before fixation, preparation of the fracture donor site should be done, including debriding fibrous tissue between the fragment and the bone surface and curetting down to the base to encourage subchondral bleeding.23
Metallic Headed Screws
Fixation using metallic screws for osteochondral lesions was first described in 1957 by Smillie who reported good success in the form of symptom resolution and successful radiographic union, with excellent compressions of the OCD lesion.2,23 It has also been shown to provide rotational stability to the lesion.29 Some prominent heads have caused damage to the opposing articular cartilage, and therefore, these screws require removal with a second surgery.23,30 This gives the surgeon an opportunity to confirm healing and stability of the OCF.17,23 In addition, headed screws have shown to break, loosen, and cause skin erosions.30 In cases of a thin or absent subchondral bone, flathead screws can be placed and removed in a timely manner to avoid chondral injury (Figures 2 and 3).
Metallic Headless Screws
Headless screws have shown to provide excellent compression across the fragment in the subchondral bed and demonstrate secure fixation.2,31 Headless compression screws work best with larger bone fragments.23 The screw is designed, so the proximal end can be countersunk beneath the articular surface, avoiding opposing articular cartilage damage.32 Many authors have reported union rates between 88% and 100%, including that of detached flaps.32–35 Excellent IKDC and improved Lysholm scores (preoperative 79, SD 9.9, range 50 to 86 versus postoperative 97, SD 9.4, range 64 to 100) were seen in up to 86.7% of patients.32,33 Implant removal is not necessary in these cases because the screw is countersunk beneath the bone. It is imperative that surgeons follow patients to confirm that the lesion has fully healed. Complications with headless screws theoretically are still reported with this method, including loosening and erosion of the opposing cartilage.30
Fixation of OCFs with bioabsorbable implants has increased in popularity in recent years. The two most common types of bioabsorbable materials used for implants are self-reinforced poly-L-lactide or polyglycolide acid. The self-reinforced poly-L-lactide has shown to have the best mechanical strength in vitro and in vivo, compared with other bioabsorbable implants but does not exhibit the same compression as metallic, headless compression screws.29
Multiple authors have reported excellent outcomes and healing using either bioabsorbable pins or biocompression screws.2,23,27,29,36,37 The advantage of these implants is the decreased need for a subsequent surgery for screw removal and minimal interference with MRI postoperatively.32 Bioabsorbable screws seem to exhibit better compression compared with pins but are larger implants and better suited for large fragments27 (Figure 1).
Large OCFs (>4 cm) have been demonstrated to have excellent outcomes with 100% intact articular cartilage on MRI at 5 to 11 years, when fixed with bioabsorbable polyglycolic rods.27 Smaller OCF and OCD lesions (2 × 2 cm) have shown to have excellent postoperative Lysholm and IKDC scores, with a 0% failure rate over a mean follow-up of 47 months. The application of bioabsorbable pins is straightforward while providing compression across the fracture site and early mobilization.38
These implants are not without complications. Because they cannot exhibit the same compression as metallic screws, over time they can become loose and cause an osteolytic type reaction, leading to reactive synovitis.29,39 This is more common with the polyglycolide acid implants, occurring in less than 10% of patients. The implants can also back out and be resorbed, damaging the opposing articular cartilage, requiring an 18% revision surgery rate to remove them.39 Cysts and loose bodies can form from the uneven resorption of part or all the screw.40,41
If the fragment cannot be salvaged, other options can be used in addition to fragment excision.2 ACI is a two-stage procedure whereby chondrocytes are harvested from a fresh margin of the knee and cultured in vitro and then implanted into the articular defect.42 Randomized controlled trials have shown that the functional outcome was significantly better in patients who underwent ACI compared with mosaicplasty (P = 0.02).42 The complications are rare, but when they occur (graft failure, delamination, and tissue hypertrophy), repeat surgical intervention might be required.24
Osteochondral autograft and allograft transplantation have both shown to be successful in managing OCFs, with an average return to sport at 9 to 12 months with complete graft incorporation by 2 years.2 However, the best results of these techniques are seen in the adult populations.6
Preventing Recurrent Patellar Dislocation
Performing a medial patellofemoral ligament reconstruction (MPFLR) concomitantly with an OCF has become a new trend over the past decade.43 The focus is to prevent recurrent patellar instability and additional articular damage. Pedowitz et al43 demonstrated a 61% recurrent instability rate if the MPFL was not repaired or reconstructed with a loose OCF. They demonstrated, along with other centers, excellent clinical outcomes (zero recurrent patellar dislocations at a 2.8-year follow-up), when a concomitant MPFLR was done along with OCF fixation. Schlichte et al44 reported a 22% incidence of pediatric MPFL, OCF procedures needing a second surgery. Some of these patients (8%) underwent additional patellar-stabilizing techniques, such as a TTO.44 These studies show that if the surgeon fails to address patellar instability or malalignment, after any cartilage repair technique, the outcomes are likely to be suboptimal and affect the overall OCF repair. This may also involve the surgeon addressing a primary cause of patellar instability, such as trochlea dysplasia, increased tibial tubercle to trochlear groove distance, or patellar dysplasia. It is, therefore, the senior author's preference to perform a patellar stabilization or alignment procedure (MPFLR, TTO, trochleoplasty, or Roux-Goldthwait) in the presence of a patellar dislocation with cartilage injury or OCF.
Patellar dislocation is the most common mechanism of injury precipitating OCFs, which are challenging injuries to diagnose and treat because of their prevalence in younger patients. These fractures can be missed on plain radiographs, and therefore, any adolescent patient presenting with a patellar dislocation should be investigated further with an MRI because there should be a high index of suspicion. Younger patients with an open physis have a better prognosis. The goals of management are to prevent recurrent patellar dislocation and restore integrity of the cartilage as best as possible to minimize the risk of these injuries to cause future degenerative changes. Many surgical options are available to manage these injuries, with no universally accepted single technique on which is superior. Patients with OCFs > 10 to 15 mm across a weight-bearing surface have a better prognosis if the fragment is repaired with metallic screws, suture material, or bioabsorbable pins. Evidence supports fixation of the fragment to be done in the acute setting to allow the best functional outcome.
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