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Research in Osteochondritis Dissecans of the Knee: 2016 Update
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Jeffrey Nepple, Matthew Milewski, Kevin Shea
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Special Focus Section
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Research in Osteochondritis Dissecans of the Knee: 2016 Update Jeffrey Nepple1
Matthew Milewski2
Kevin Shea3Q2
1 Orthopedic Surgery, Washington University in Saint Louis, Saint
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Louis, MissouriQ3 2 Sports Medicine, Connecticut Children’s Medical Center, Hartford, Connecticut 3 Sports Medicine, Saint Luke’s Boise Medical Center, Boise, Idaho
Q2 Address for correspondence Jeffrey Nepple, Q4 Orthopedic Surgery, Washington University in Saint Louis, 1 Children’s Place, Saint Louis, MO 63130 (e-mail:
[email protected]).
J Knee Surg 2016;00:1–6.
Abstract
Keywords
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► osteochondritis dissecansQ5 ► Research in osteochondritis dissecans of the Knee
Osteochondritis dissecans (OCD) of the knee remains a relatively common and poorly understood pediatric and adolescent knee condition. Both conservative and surgical treatments have major impact on the lives of young active, athletic patients with knee OCD. OCD has been recently redefined as a “focal, idiopathic alteration of subchondral bone with risk for instability and disruption of adjacent articular cartilage that may result in premature osteoarthritis.” The 2011 American Academy of Orthopedic Surgeons Clinical Practice Guidelines found limited evidence for all aspects of the treatment of knee OCD. The multicenter study group Research in Osteochondritis dissecans of the Knee (ROCK) was formed to advance the understanding and treatment of this condition. This article will review our current understanding of the pathophysiology, treatment options, and outcomes of OCD of the knee, with a focus on the past, present, and future research including the work of the ROCK study group.
Osteochondritis dissecans (OCD) of the knee remains a relatively common and poorly understood pediatric and adolescent knee condition. Both conservative and surgical treatment can have major impact on the lives of young active, athletic patients with knee OCD. OCD has been recently redefined as a “focal, idiopathic alteration of subchondral bone with risk for instability and disruption of adjacent articular cartilage that may result in premature osteoarthritis”1. OCD is commonly referred relative to the two components: the parent bone and progeny fragment (lesion that could become unstable or detached). Stability of the progeny fragment remains a key factor in guiding treatment decisions. Since its original description by Konig in 1887, many questions regarding the etiology and optimal treatment of knee OCD remain unanswered. Conservative treatment methods have high rates of healing in skeletally immature patients with stable OCD lesions. Surgical treatment with drilling of stable lesions or fixation of unstable lesions remains the
primary surgical options in skeletally immature patients requiring surgical intervention. In 2011, the American Academy of Orthopedic Surgeons (AAOS) Clinical Practice Guideline on knee OCD emphasized the lack of evidence for guiding the treatment of this condition but did provide the groundwork for appropriate future research questions.2,3 As with many conditions in orthopedics, answering key research questions in a singlecenter research setting will always be difficult. Multicenter prospective research studies will best allow for the ability to perform well-designed, appropriately-powered studies to answer key research questions. The multicenter study group Research in Osteochondritis Dissecans of the Knee (ROCK) has advanced the research in this field through studies over the past 5 years and will continue to do so in the years to come. This article will review our current understanding of the pathophysiology, treatment options, and outcomes of OCD of
received April 11, 2016 accepted June 23, 2016
Copyright © 2016 by Thieme Medical Publishers, Inc., 333 Seventh Avenue, New York, NY 10001, USA. Tel: +1(212) 584-4662.
DOI http://dx.doi.org/ 10.1055/s-0036-1586723. ISSN 1538-8506.
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the knee, with a focus on the past, present, and future research including the work of the ROCK study group.
The Past OCD of the knee was first described by Konig in 1887.4 Our understanding of the pathophysiology of knee OCD remains limited more than 100 years later. The initial theory of the role of inflammation as a primary cause of OCD appears to be unsupported by subsequent research. A variety of other etiologies have been proposed over the years including vascular supply, trauma, repetitive injury, malalignment, or genetic causes. A recent study suggested vitamin D deficiency could play a role in the pathophysiology of OCD in some patients.5 Early genetic studies have demonstrated several genetic loci that may play a role in knee OCD.6 Clear underlying factors contributing to knee OCD exist in a subset of patients, including malalignment or genetic syndromes. However, the majority of knee OCD patients are active, young patients without associated medical comorbidities or a history of knee injury. The initial symptoms of individuals presenting with knee OCD is often mild and nonspecific.7 Recent studies have helped to best define the epidemiology of knee OCD and demonstrated an incidence of 9.5 per 100,000 individuals between 6 and 19 years of age.8 Males are 3.8 times more likely than females to be affected. Similarly, the 12- to 19-year age group is 3.3 times more likely to be affected than the 6- to 11-year age group. OCD-like conditions are not unique to humans but also present in many animal species where it is referred to as osteochondrosis. Osteochondrosis is a leading cause of lameness in the equine world. Computed tomography, magnetic resonance imaging (MRI), and histologic evaluations suggest subchondral vascular failure within the epiphysis at a very young age plays a role in the predisposition to osteochondrosis.9,10 Animal models of osteochondrosis will provide implications into our understanding of knee OCD in humans. Further delineation of the similarities and differences in the pathophysiology of human OCD and animal osteochondrosis will be important for better understanding. Radiographs play a key role in the initial diagnosis of knee OCD given the nonspecific clinical findings in early stages of knee OCD (►Fig. 1). Anteroposterior (AP), notch (tunnel), merchant, and lateral knee radiographs are commonly used. The use of the notch radiograph is particularly useful to identify OCDs in the posterior aspect of the condyles that may not be well seen on AP radiographs. Radiographs of the contralateral knee in patients with knee OCD can be useful to identify contralateral OCD lesions given the 29% rate of bilateral involvement.11 Bilateral lower-extremity alignment radiographs can also be useful to assess for underlying malalignment. Skeletal age assessment with left hand radiographs may be useful in surgical treatment planning to accurately assess the amount of growth remaining. Knee OCD most commonly affects the medial femoral condyle (64% of knee OCDs) and is classically located on the lateral aspect of the medial femoral condyle. OCDs of the lateral femoral condyle are also fairly common (32% of knee The Journal of Knee Surgery
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Fig. 1 Variable radiographic appearances of knee osteochondritis. (A) Medial femoral condyle osteochondritis in skeletally immature knee with ossification of progeny fragment, (B) medial femoral condyle osteochondritis in skeletally immature knee without ossification of progeny fragment, (C) medial femoral condyle osteochondritis in skeletally mature knee with ossification of progeny fragment, (D) lateral femoral condyle osteochondritis without ossification of progeny fragment.
OCDs) and are often much larger than OCDs in other locations.8 OCDs also occur in other locations including the patella and the trochlea. As the pathophysiology of OCD progresses, lesions may transition from stable to unstable. Further progression may lead to subsequent breakdown of the articular cartilage, loose body formation, and significant focal bone and cartilage loss. The presence of a knee effusion or significant mechanical symptoms can indicate an unstable OCD. Since radiographs are generally not helpful indicators of lesion stability, MRI plays a significant role in evaluation of OCD. OCD instability is suggested by the presence of hyperintense T2 signal between the parent–progeny interface or the presence of articular cartilage breach.12 The presence of multiple underlying cystlike foci and a single focus greater than 5 mm also may indicate OCD instability.12 Treatment of knee OCD attempts to maximize the healing of parent–progeny bone interface and minimizing damage to
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Fig. 2 Q6 Examples of surgical treatment options in knee Osteochondritis. (A) Transarticular drilling of stable osteochondritis, (B) retroarticular drilling of stable osteochondritis, (C) fixation of unstable osteochondritis with variable pitch compression screw, (D) fresh osteochondral allograft transplantation for an unsalvageable knee osteochondritis.
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the overlying articular cartilage to prevent premature osteoarthritis in this young population. Conservative, or nonsurgical, treatment has high rates of success in skeletally immature patients with stable OCD lesions. Conservative treatment generally includes activity modification with temporary cessation of sports, as well as protected weight-bearing on crutches, immobilization with cast/brace, or unloader bracing. The relative success of different conservative treatment regimens is not well established. Wall et al13 identified key patients affecting the likelihood of healing with conservative treatment in a retrospective study. Patient age, lesion size (normalized to knee size), and the presence of mechanical symptoms significantly affected the likelihood of healing. This study includes a nomogram that can be used to predict healing rates in an individual patient. Complete radiographic healing often takes 6 to 12 months, with clinical success and return to activities generally occurring earlier. Surgical treatment of knee OCD is generally recommended for any unstable OCDs or in stable OCDs failing to improve with 3 months of conservative treatment in skeletally immature patients (►Fig. 3). Stable OCDs are generally treated with drilling to stimulate healing of the parent–progeny interface.
Drilling can be performed transarticular (retrograde, traversing the articular cartilage, and directed toward the subchondral progeny bone and then parent bone) or retroarticular (antegrade, traversing the subchondral parent bone initially, and directed toward the progeny bone). Transarticular drilling allows for direct localization and is technically less challenging, but traverses the articular cartilage. Retroarticular drilling avoids penetration of the articular cartilage with K-wires but relies upon localization on fluoroscopy. Drilling errors in which the subchondral bone region is missed are possible using this technique. Intercondylar notch drilling has also been described as an isolated technique or in combination with other techniques and it also has the advantage of not violating articular cartilage. Unstable OCDs are generally treated with some form of fixation including, most commonly, variable pitch metal or bioabsorbable screws or bioabsorbable nails. Debridement of the parent–progeny interface and autogenous local bone grafting may also be incorporated in some lesions. Many surgeons routinely remove metal screws between 3 and 6 months postoperatively in healed lesions. Bioabsorbable implants do not require removal, but in some cases absorption may cause synovitis or partial implant The Journal of Knee Surgery
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Fig. 3 Research in Osteochondritis Dissecans of the Knee arthroscopic osteochondritis classification.
resorption and associated cystic bone lesions, creating loose bodies in some cases. Biologic fixation of unstable OCDs with small osteochondral autograft plugs has also been reported. OCD lesions failing fixation or presenting with advanced articular cartilage damage of the progeny fragment precluding salvage are treated with a variety of salvage techniques. Significant subchondral bone loss is generally present that makes techniques such as microfracture less ideal. Small lesions may be treated with autograft osteochondral transfer (OATS). One study directly comparing microfracture and OATS found improved outcomes in patients treated with OATS. Larger unsalvageable OCD lesions are most commonly treated with fresh osteochondral allograft transplant.14 The 5-year survivorship of osteochondral allografts in this setting has been reported to be 91%.15,16 Autologous chondrocyte implantation (ACI) has also been utilized in the knee OCDs. In the setting of subchondral bone loss, ACI often requires bone graft with a sandwich technique. The role of other recently developed cartilage restoration techniques in knee OCD remains poorly defined. The Journal of Knee Surgery
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The Present: Research in Osteochondritis Dissecans of the Knee Study Group The ROCK study group was founded in 2010 to improve the outcomes of patients with knee OCD through multicenter research. Early efforts of the ROCK group have focused on development and validation of classification systems for knee OCD, as well as identification and reliability testing of imaging features of OCD. Plain radiographs remain a key tool in the diagnosis and continued healing evaluation of OCD lesions. The ROCK study group has investigated key radiographic factors for OCD evaluation and healing, as well as the interobserver reliability of these findings. The ROCK group17 reported at least moderate interobserver reliability of characterization of location, physeal maturity, OCD contour, presence of bone in the progeny fragment, fragmentation, displacement, boundary, and central radiodensity on plain radiographs (►Fig. 1). Radiodensity of the lesion rim and surrounding epiphyseal
2016 ROCK Update bone were found to have fair to poor interobserver reliability. Future studies will further determine the role of these reliable radiographic features in the treatment and outcome of knee OCD. A follow-up radiographic study by the ROCK group then investigated the interobserver reliability of evidence of healing when comparing two or sets of radiographs. Substantial to excellent interobserver reliability was demonstrated for the assessment of overall healing, as well as specific parameters including OCD boundary, sclerosis, size, shape, and ossification using a continuous slider scale. The ROCK arthroscopic classification system was developed in attempts to improve the recognition of variable patterns of OCD disease present at arthroscopy that may ultimately influence outcomes. The classification system was developed based on detailed review and discussion of arthroscopic case examples. The ROCK OCD classification includes 3 immobile and 3 mobile OCD types. Immobile OCDs include (1) cue ball, (2) shadow, and (3) wrinkle in the rug. Mobile OCDs include (1) locked door, (2) trapped door, and (3) crater (►Fig. 3). The reliability of this novel classification was then established in this initial study demonstrating excellent intraobserver and interobserver relability.18 The variability of treatment patterns among ROCK members was demonstrated in a survey-based study. Significant variability in specific treatment decisions (type of drilling, type of fixation) between surgeons for given lesions in the ROCK arthroscopic OCD classification exist, while general principles of treatment (drilling, fixation) are generally well agreed upon. This variability underscores the importance of prospective studies to identify optimal treatment strategies in a given patient.
The Future: OCD Research The AAOS Clinical Practice Guidelines (CPG) for the diagnosis and treatment of OCD was released in 2011 (Chambers). CPG are designed to “help improve diagnosis and treatment based on the current best evidence,” as well as showing “where good evidence exists, where evidence is lacking, and which topics further research must target to improve the treatment.” The CPG on knee OCD highlights the lack of evidence in the treatment of OCD. Sixteen studies were of adequate evidence to be included in the review and yielded no strong recommendations among the 16 areas, with most being inconclusive. Two weak recommendations included: (1) “For patients with knee symptoms, radiographs of the joint may be obtained to identify the lesion” and (2) “For patients with radiographically apparent lesions, MRI may be used to further characterize the OCD lesion or other knee pathology.” The CPG highlighted several priorities for future research studies in knee OCD including reliability studies, validation of classification systems, and prospective cohort and randomized studies of nonsurgical and surgical treatment options. The CPG also encouraged multicenter studies to improve patient recruitment of a relatively rare disease as well as to maximize external validity.
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MRI remains an important tool in the evaluation and characterization of knee OCDs. MRI reviews variable patterns of bony and cartilaginous pathology not well appreciated on plain radiographs. MRI allows for detailed characterization of the overlying articular cartilage including integrity, contour, and characterization of unossified epiphyseal cartilage. It also allows for detailed characterization of the parent–progeny interface including the presence of hyperintense signal. MRI also characterizes the degree of mineralization and fragmentation of the progeny fragment and the presence of cystic change in the parent bone. Ongoing work of the ROCK study group includes development of a detailed and validated MRI classification system. Future studies will then identify MRI features, which play an important role in treatment decisions and outcomes. Optimal treatment strategies for knee OCD remain to be defined. An ongoing multicenter randomized trial of transarticular versus retroarticular drilling of stable OCDs in skeletally immature patients is ongoing. This study will determine if treatment outcomes for these two techniques appear to be equivalent or if one treatment results in improved patient outcomes. This study will provide level 1 evidence to help guide treatment decisions in these patients. A multicenter prospective cohort of conservative and surgical treatment of knee OCD is recently underway. The ROCK group has recently expanded to include 20 centers in the prospective cohort, which will allow more rapid accumulation of patient cohorts. Utilizing the established infrastructure for radiographic and arthroscopic classification of disease, this prospective cohort will help to identify optimal treatment strategies for patients with knee OCD. The prospective cohort was based upon a series of research questions that were outlined prior to entry of any patients in the study. These studies will increase the level of evidence in OCD outcomes research, and hopefully improve the treatment outcomes of patients with knee OCD in the future.
Conclusion Knee OCD remains one of the most poorly understood conditions in pediatric sports medicine. Decisions regarding conservative and surgical treatment decisions remain poorly supported by the available literature. The ROCK study group has made significant advancements in the area of knee OCD and has ongoing prospective research studies to improve the available evidence for optimal treatment of knee OCD. For further information on the ROCK group, its centers and research efforts, please visit the website: www.kneeocd.org.
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