Aaron J. Krych
by Mario Hevesi, MD; Aaron J. Krych, MD; and Jack Farr, MD
Patellar dislocation represents 2% to 3% of orthopedic knee presentations and an even larger portion of cases for those treating predominantly non-arthroplasty patients. Historically, first-time dislocators were treated with conservative management, as multiple studies demonstrated that acute operative management of dislocation did not improve short-term or midterm patient-reported outcomes in the absence of displaced osteochondral fragments.8, 9 However, recurrence rates for patients treated conservatively are substantial and are reported in 30% to 50% of patients.
Early and targeted intervention following first-time dislocation remains a clinically relevant topic of discussion, especially given that repeat instability has been shown to result in cumulative and substantial osteochondral damage. Perhaps the largest limitation to early management has been the difficulty in predicting which patients will experience recurrent dislocation. In higher-risk patients, early management may be warranted to prevent further instability-related trauma vs. lower-risk patients who can be conservatively followed given that a low rate of recurrence favors observation. Think of this shift in thinking to risk stratification similar to what has evolved for “first-time” ACL tears and is currently considered for first-time shoulder dislocation.
The limitations in accurately predicting recurrent instability include the multivariable nature of risk factors, as well as the relatively long natural history during which recurrent instability occurs, often spanning 3 to 5 years. Recently, the recurrent instability of the patella score (RIP) was published in Arthroscopy, providing recurrence prognostication based on an average of 10-plus years of follow-up on the basis of age, skeletal immaturity, trochlear dysplasia and tibial tubercle to trochlear grove over patellar length (TT-TG/PL) ratio.5 While various prognostication aids have been previously published, the RIP score represents the first available method with statistically significant discriminatory and prognostic value based on long-term follow-up appropriate for the natural history of patellar instability. However, it is noteworthy that while the score provides long-term prognostication of recurrence risk, it does not dictate or recommend management strategy.
A key concept in patellar dislocation is that each patient will have a unique pattern of injury and risk factors and that these will inform patient-specific treatment. For patients with osteochondral fractures, we recommend early open reduction and internal fixation or debridement of osteochondral fragments, as technically allowable, and consideration of medial patellofemoral ligament (MPFL) reconstruction or focused repair in those with an isolated MPFL injury site for patients at high risk of recurrence (ie, RIP 4 to 5). In patients with high-energy injuries, we recommend initial conservative observation for patients with RIP scores 0 to 1, consideration of MPFL repair/reconstruction in patients with moderate recurrence likelihood (RIP 2 to 3) and MPFL reconstruction in patients with high recurrence likelihood, understanding that repair should only be attempted in the setting of a discrete, identifiable tear and that reconstruction should be undertaken once the knee has clinically calmed down, much like the case of the timing for ACL reconstruction.
Patients with low-energy mechanisms comprise a clinically challenging subset of individuals given that they often have concurrent pathology that predisposes to both the index and recurrent dislocation and may not be captured with general clinical aids, such as the RIP score. That is, the RIP score serves to inform the patient, patients and surgeon of the patient’s risk for future patellar instability — not how to surgically manage a specific patient.
For patients with low predicted recurrence rates, we recommend consideration of conservative management while evaluating for underlying patholaxity, femoral anteversion and valgus alignment as otherwise they should be at low risk for patellar dislocation. For those with moderate predicted recurrence, we recommend discussion of MPFL/MQTFL repair/reconstruction and addressing the pros and cons of each approach. Finally, in those with high recurrence likelihood, we recommend combined MPFL and MQTFL reconstruction with consideration of tibial tubercle osteotomy for those with static subluxation or high TT-TG/TT-PCL distances and potential trochleoplasty for those with Dejour D dysplasia.
When evaluating a stepwise algorithm for managing first-time patellar dislocators, it remains critical to treat each patient on a unique, patient-specific basis and to concurrently assess for underlying and potentially less obvious risk factors for recurrent dislocation (think excessive knee valgus, excessive femoral anteversion, etc.). With the emergence of clinical aids such as the RIP score, we have found improvement in the informed consent process with patients/parents during counseling and surgical decision-making, especially as the score is now available for in-clinic access and visualization through MDCalc.com and the MDCalc app. By better involving patients in the multifaceted discussions that follow index instability, we believe we have strengthened decision-making and partnerships with this active, complex and rewarding population.
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Mario Hevesi, MD, and Aaron J. Krych, MD, are from the Mayo Clinic, Rochester, Minnestoa. Jack Farr, MD, is from OrthoIndy in Indianapolis.
1. Christensen TC, et al. Am J Sports Med. 2017;doi:10.1177/0363546517704178.
2. Dragoo JL, et al. Orthop J Sports Med. 2017;doi:10.1177/2325967116689465.
3. Fithian DC, et al. Am J Sports Med. 2004;32:1114-1121.
4. Hawkins RJ, et al. Am J Sports Med. 1986;14:117-120.
5. Hevesi M, et al. Arthroscopy. 2019;doi:10.1016/j.arthro.2018.09.
6. Lording T, et al. Chondral Injury in Patellofemoral Instability. Cartilage. 2014;5:136-144.
8. Nikku R, et al. Acta Orthop. 2005;76:699-704.
9. Palmu S, et al. J Bone Joint Surg Am. 2008;90:463-470.
10. Sanders TL, et al. Knee Surg Sports Traumatol Arthrosc. 2018;doi:10.1007/s00167-017-4505-y
Disclosures: Farr reports he is vice president of the Patellofemoral Foundation. Hevesi and Krych report no relevant financial disclosures.