Arthroscopy: The Journal of Arthroscopic & Related Surgery
Level V EvidenceIatrogenic Medial Patellar Instability: An Avoidable Injury
Section snippets
IMPI—A Rare Condition
Of the 168 cases of medial patellar instability reported in the literature, 153 (91%) occurred in patients who had undergone a previous lateral retinacular release (LRR), either isolated or associated with realignment surgery.13 Of the remaining 15 non-iatrogenic cases (9%), 8 were the result of trauma and 7 occurred spontaneously.13 Because there is little written about IMPI, we sought to learn the extent of this injury. When IMPI is encountered, its disability is so severe and the treatment
Diagnosing IMPI
IMPI patients usually present with incapacitating, chronic, and disabling AKP along with serious psychological problems.13 Most of our patients had undergone an “extensive” isolated LRR according to the index operative reports.13 Typically, the patient felt a new pain and new instability after that index surgery that were distinct from, and much worse than, those before surgery. In general, IMPI occurs in the first 30° of knee flexion. IMPI is often overlooked as a cause of symptoms because
Preventing IMPI
It is clear that extensive release, or over-release, of the LR is a major cause of IMPI.13, 18, 19 This can be a result of excessive severance of the LR with transection of the vastus lateralis tendon (Fig 5) or can result from releasing an LR that was already lax, showing poor patient selection. An isolated LRR should never be performed in the face of trochlear dysplasia, patella alta, or hyperelasticity. If the LR is not tight, the surgeon should not release it. The goal of a proper LRR is to
Conclusions
IMPI is an objective condition with its own characteristics that causes incapacitating AKP. It can be readily suspected in a patient who has undergone previous patellar realignment surgery that has made the pain worse. The diagnosis can be established by physical examination and simple therapeutic tests and confirmed by imaging techniques. This iatrogenic condition should no longer exist and could almost be eliminated by avoiding over-release of the LR, only releasing a tight LR, and focusing
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The authors report that they have no conflicts of interest in the authorship and publication of this article.