title: Iatrogenic medial patellar instability following lateral retinacular release of the knee joint.
abstract: OBJECTIVE
  Iatrogenic medial patellar instability (IMPI) is a disabling but easily missed condition that is most often seen as a late complication of lateral retinacular release (LRR) procedures. The purposes of this study were (1) to summarize the available diagnostic methods and (2) to explore the contributing factors of IMPI following LRR procedures.
  
  
  METHODS
  The MEDLINE, PubMed, EMBASE and Cochrane Library databases were searched for studies including diagnosed IMPI cases following LRR procedures. All patients were first divided into IMPI group and non-IMPI group based on the diagnostic methods of IMPI collected from studies. Univariate analysis was performed by comparing the two groups with regard to individual patient data (age at initial LRR, gender) and surgical details (type, releasing scope, combined surgeries and indication) of LRR procedures. Multivariate logistic regression was carried out to identify independent contributing factors for IMPI and to calculate odds ratios (ORs).
  
  
  RESULTS
  Eight studies with 274 patients (300 knees) were finally included. Of those, 161 patients (171 knees, 57.0 %) had IMPI and 113 patients (129 knees, 43.0 %) had no IMPI. Univariate analysis revealed a statistically significant difference between both groups for releasing scope (P 1 < 0.001) and indication of LRR procedures (P 2 < 0.001), with releasing lateral retinaculum (LR) + vastus lateralis (VL) tendon and absence of tight LR during the initial LRR procedures being more common in patients with IMPI. The independent contributing factors for IMPI identified in the multivariate logistic regression analysis were releasing LR + VL (OR1 = 16.49) and absence of tight LR (OR2 = 14.37).
  
  
  CONCLUSIONS
  The IMPI was more common in patient with an over-released LRR and patient who was absent of tight LR during the initial LRR procedures. Aggressive surgical corrections and inappropriate indications of initial LRR were two contributing factors for the late complications of IMPI. This study suggests that the IMPI may occur as a major complication of LRR, especially when the VL tendon is extensively released or when there is no confirmative clinical evidence of a tight LR preoperatively.
  
  
  METHODS
  IV.
authors.affiliation: Sports Medicine Service, Beijing Jishuitan Hospital, No. 31, Xin Jie Kou East Street, Xi Cheng District, Beijing, 100035, China.
authors.forename: Guan-Yang
authors.initials: GY
authors.lastname: Song
authors.affiliation: Sports Medicine Service, Beijing Jishuitan Hospital, No. 31, Xin Jie Kou East Street, Xi Cheng District, Beijing, 100035, China.
authors.forename: Lei
authors.initials: L
authors.lastname: Hong
authors.affiliation: Sports Medicine Service, Beijing Jishuitan Hospital, No. 31, Xin Jie Kou East Street, Xi Cheng District, Beijing, 100035, China.
authors.forename: Hui
authors.initials: H
authors.lastname: Zhang
authors.affiliation: Sports Medicine Service, Beijing Jishuitan Hospital, No. 31, Xin Jie Kou East Street, Xi Cheng District, Beijing, 100035, China.
authors.forename: Jin
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Sports Medicine Service, Beijing Jishuitan Hospital, No. 31, Xin Jie Kou East Street, Xi Cheng District, Beijing, 100035, China.
authors.forename: Yue
authors.initials: Y
authors.lastname: Li
authors.affiliation: Sports Medicine Service, Beijing Jishuitan Hospital, No. 31, Xin Jie Kou East Street, Xi Cheng District, Beijing, 100035, China. fenghua20080617@126.com.
authors.forename: Hua
authors.initials: H
authors.lastname: Feng
mesh_terms: D006801:Humans; D007593:Joint Instability / Q000175:diagnosis / Q000209:etiology*; D007719:Knee Joint / Q000601:surgery*; D011183:Postoperative Complications / Q000175:diagnosis / Q000209:etiology*; D012307:Risk Factors; D058971:Tenotomy / Q000009:adverse effects*
keywords: Contributing factor; Diagnostic method; Iatrogenic medial patellar instability; Lateral retinacular release