Patellar Stabilization Surgery Research Articles

Evaluation of Differences in Patellar Height After Patellar Stabilization Procedures Not Intended to Address Patella Alta: A Multicenter Study.

Recent studies have reported conflicting results as to whether isolated medial patellofemoral ligament reconstruction (MPFLr) leads to decreased patellar height. To investigate if patellar stabilization surgery not intended to address patella alta influences patellar height. Cohort study; Level of evidence, 3. A multicenter retrospective chart review was conducted, and patients who underwent MPFLr, medializing tibial tuberosity osteotomy (TTO), and/or trochleoplasty between 2016 and 2020 were included. The Caton-Deschamps index (CDI) was calculated from radiographs obtained preoperatively, 2 weeks postoperatively, and 3 months postoperatively. The preoperative CDI value was compared with the 2-week postoperative and 3-month postoperative values according to stabilization procedure (isolated MPFLr, isolated TTO, MPFLr + TTO, MPFLr + trochleoplasty, and MPFLr + trochleoplasty + TTO) using the paired t test. Analyses of the 1-bundle versus 2-bundle MPFLr technique and the presence of lateral retinacular release or lateral retinacular lengthening were conducted on the isolated MPFLr and combined MPFLr + TTO cohorts. A total of 356 knees were included. Statistically significant pre- to postoperative decreases in CDI were seen in all stabilization procedures analyzed (P≤ .017 for all). Within the isolated MPFLr cohort, this significant decrease was seen at 2 weeks postoperatively with the 2-bundle technique (ΔCDI = -0.09; P < .001) but not with the 1-bundle technique (ΔCDI = -0.01; P = .621). The different surgical techniques analyzed in the current study affected patellar height, even when a distalizing TTO was not performed. The decrease was dependent on surgical technique, with a 2-bundle MPFLr leading to a statistically significant decrease and a 1-bundle MPFLr effecting no change.

Poster 296: Incidence and Risk Factors for Contralateral Patellofemoral Instability

Objectives: Background: Patellofemoral joint instability is common in young athletes and often requires surgical intervention. Incidence and risk factors for ipsilateral instability recurrence have been more discussed in the literature than contralateral instability events. Purpose: To evaluate the incidence and risk factors for contralateral patellofemoral instability in patients who have undergone patellar stabilization surgery. Methods: This retrospective study included 543 patients who had undergone medial patellofemoral ligament reconstruction and/or Fulkerson osteotomy as surgical management for lateral patellofemoral instability. The medical records of these patients were examined to evaluate the non-surgical knee. Available imaging of each affected knee was examined to evaluate for patella alta, skeletal maturity, trochlear dysplasia, tibial tubercle to trochlear groove (TT-TG) distance, and tibial tubercle to posterior collateral ligament (TT-PCL) distance. Demographic factors such as BMI, age, and sex were also examined. A second arm was done excluding patients with previous history of bilateral instability, assessing risk factors using the same methods. This yielded information about incidence and risk factors of “new onset” contralateral instability post-stabilization surgery. Results: Of the 543 patients examined, 205 (37.8%) had evidence of contralateral instability. Patella alta (OR, 2.4), skeletal immaturity (OR, 2.67), and younger age (p&lt;0.0001) were associated with increased risk of bilateral instability. Sex, BMI, TT-TG distance, and TT-PCL distance, and trochlear dysplasia were not associated with increased risk of bilateral instability. In the second study, 63 out of 401 (15.71%) of patients had evidence of new onset contralateral instability post-surgery. Skeletal immaturity (OR, 3.65) was found to be associated with increased risk of instability. Conclusions: The incidence of bilateral patellofemoral instability was found to be 37.8%. Lower age, skeletal immaturity, and patella alta were found to be associated with increased risk of bilateral instability. Incidence of new-onset contralateral instability was found to be 15.71% and was only associated with skeletal immaturity.

Poster 245: Clinical Measurement of the Standard Q-Angle Correlates Poorly with Tibial Tuberosity to Trochlear Groove Distance in Awake Patients and Anesthetized Patients with Patella Alta and Trochlear Dysplasia

Objectives: The quadriceps angle (Q-angle) measures the force vector of pull of the extensor mechanism of the knee. A larger Q-angle is thought to be a predisposing factor for patellar dislocation, but previous literature has reported poor reliability and validity of clinically measured Q-Angle. In response to poor reliability, a new “Standard Q-Angle” (SQA) was developed by Merchant et al. (Merchant 2020) in an attempt to create a standardized and repeatable method of clinically measuring the Q-Angle. The SQA may be a practical, inexpensive, and valuable part of physical examinations to help clinicians decide if concomitant medializing osteotomy is indicated in patellar stabilization procedures. However, SQA has not yet been validated in patients with anatomic risk factors for recurrent patellar instability such as patella alta and trochlear dysplasia. Furthermore, while SQA has previously been demonstrated to have strong interrater reliability, it has never been shown to correlate with standardized measurements for a lateralized tibial tuberosity, such as the Tibial Tuberosity – Trochlear Grove (TT-TG) distance. Therefore, the purpose of our study was to determine the correlation between SQA and TT-TG distance in patients with recurrent patellar instability. We hypothesized that there would be a positive correlation between SQA and TT-TG distance. 1. Merchant AC, Fraiser R, Dragoo J, Fredericson M. A reliable Q angle measurement using a standardized protocol. Knee. 2020;27(3):934-939. Methods: Patients at a single institution treated by a single surgeon with recurrent patellar instability who had previously obtained a dynamic 4D CT scan were included in this study. Patients who had previous patellar stabilization procedures were excluded. The Standard Q-angle was measured as previously described by Merchant et al. (Merchant 2020). The patient was placed in the supine position with the knee extended. A long-arm goniometer was centered over the patella with the distal arm over the tibial tuberosity and the proximal arm extended up to the anterior superior iliac spine (ASIS). The examiner then centered the patella within the trochlear groove and the SQA was measured. A second examiner stood at foot of the patient’s bed to confirm positioning. Measurements were taken in the office, as well as in the operating room after the induction of general anesthesia. All measurements were performed by the senior author (***). Utilizing 4D CT scans, the TT-TG, Caton-Deschamps index (CDI), and lateral trochlear inclination (LTI) were measured as previously described. Patients whose CDIs were between 0.8 and 1.2 were considered to have normal patellar height. Patients whose LTIs were &gt;11° were considered to have normal LTI, which has been shown to have a sensitivity of 93% and a specificity 87% for detecting trochlear dysplasia. Mean and standard deviation values were calculated for patient demographic information, and correlation coefficients were calculated to compare SQA with TT-TG distance in both awake and anesthetized patients. The statistical software Stata was utilized for all analyses (StataCorp. 2021. Stata Statistical Software: Release 17. College Station, TX). Results: Fifty-seven patient knees were included in the study. The mean age was 22 years-old (±6 years). For awake patients, the correlation coefficient (R2) between SQA and TT-TG was -0.006 (Figure 1), and in anesthetized patients R2 = 0.093 (Figure 2). In the “normal patellar height” group, the R2 value was higher in the anesthetized group (R2 = 0.334) than the awake group (R2 = 0.239). In the normal lateral trochlear inclination group, there was also a greater R2 value in the anesthetized group (R2 = 0.403) than the awake group (R2 =0.093). The correlation between SQA and TT-TG was the strongest in anesthetized patients with both a CDI &lt; 1.2 and LTI &gt;11° (R2 = 0.635). Conclusions: There was a strong positive association between SQA and TT-TG in anesthetized patients with normal patellar height and a normal lateral trochlear inclination. However, in awake patients and patients with anatomic risk factors for recurrent patellar instability there was only a weak association between SQA and TT-TG. The SQA may be able to provide useful information, but only in selected cases. Therefore, it remains important to have objective radiographic measurements to characterize the position of the tibial tuberosity when planning patellar stabilization surgery.

The remaining parameters of patellar instability could be affected for osteoarthritic change after medial patellofemoral ligament reconstruction with or without anteromedialization of the tibial tubercle osteotomy for patellar instability: a retrospective cohort study

BackgroundIn literature, studies evaluating the factors associated the postoperative progression of patellofemoral (PF) osteoarthritis (OA) following patellar stabilization surgery are limited. This study aimed to compare the clinical outcomes after medial patellofemoral ligament reconstruction (MPFLR) as an isolated procedure (iMPFLR) and in combination with anteromedialization (AMZ) of the tibial tubercle osteotomy (TTO) and investigate the factors related to the postoperative progression of PFOA after patellar stabilization surgery.MethodsBetween 2009 and 2020, 30 knees of 23 consecutive patients underwent MPFLR with or without AMZ, using an autologous semitendinosus tendon graft; they were followed up for more than 2 years in the retrospective nature of the study. iMPFLR was performed in cases of recurrent patellar dislocation with normal tibial tubercle-trochlear groove (TT-TG) distance and no PFOA, and MPFLR+AMZ was performed for cases of excessive TT-TG distance, preoperative PFOA of recurrent patellar dislocation, or habitual patellar dislocation. Clinical findings and radiographs of the PF joint were evaluated pre- and postoperatively with PF alignment parameters and PFOA and were compared between surgical procedures. Factors for the postoperative progression of PFOA were compared between the OA progression and non-progression groups.ResultsPostoperative clinical score, radiographic parameters except for sulcus angle, TT-TG distance, and progression of PFOA were not significantly different between the iMPFLR and MPFLR+AMZ groups. Postoperative lateral patellar displacement (p = 0.001) and congruence angle (p = 0.017) were significantly different between the OA progression and non-progression groups.ConclusionSimilar to MPFLR for recurrent cases, MPFLR with AMZ can improve the clinical and radiographic outcomes in severe cases. The remaining parameters of patellar instability could be affected in the postoperative progression of PFOA after MPFL reconstruction with or without AMZ of TTO for patellar instability.

Poster 234: Radiographic Predictors of Failure of Patellar Instability Surgery in Adolescents

Objectives:Adolescents often benefit from surgical management of recurrent patellofemoral instability (PFI). However, the debate continues as to which preoperative radiographic factors can be used to predict the risk of failure of patellar stabilization surgery. The purpose of this study was to determine the rate of failure, defined as recurrence of instability, in a large cohort of adolescent athletes undergoing primary surgery for PFI, and to identify preoperative radiographic risk factors for recurrence.Methods:We retrospectively reviewed patients aged 19 years and younger who underwent primary surgery for PFI at our institution between 2008 and 2017. Patients underwent surgical procedures including medial retinacular plication (MRP), medial patellofemoral ligament reconstruction (MPFLR), tibial tubercle osteotomy (TTO), or a combination thereof. Preoperative magnetic resonance imaging (MRI) studies were reviewed and radiographic parameters were recorded. We excluded patients with incomplete imaging data, BMI >30kg/m2, those that underwent surgery for fixation of a chondral fracture >1cm, and patients with a diagnosis of syndromic disorder. Demographic and radiographic variables were compared between patients who experienced recurrence of instability and those that did not. Logistic regression was utilized to determine if any imaging characteristics were associated with recurrent instability while controlling for age and sex.Results:Three-hundred three patients, average age 15.1 years, underwent primary surgical stabilization for PFI with median follow up time of 3.0 years. At final follow-up, 25% of patients (76/303) experienced recurrent instability with 41 patients (14%) requiring additional surgery because of this instability. Patients who had recurrent instability were younger (14.3vs15.4 years; p<0.001) and were more likely to have undergone MRP surgery alone (66% vs 35%; p<0.001) (Table 1). They were also more likely to have an open physeal status (62% vs 49%; p<0.001), a larger sulcus angle (163.9 vs 159.2; p<0.001), a larger patellar tilt angle (26.3 vs 23.6; p=0.04), and larger Caton-Deschamps ratio (1.3 vs 1.2; p=0.03) (Table 2). Each additional degree of sulcus angle increased the odds of recurrent instability by 5% (OR=1.05; p=0.002). Notably, each additional year of age at the time of surgery, decreased the odds of failure by 23% (OR=0.77; p<0.001).Conclusions:In conclusion, 25% of adolescents experienced recurrent instability after primary patellar stabilization surgery. These patients who failed initial surgical treatment were younger and had more MRP procedures. Radiographically, they had more open physes, flatter trochleae, more patellar tilt, and larger patellar height. This information can be used to guide treatment decisions and inform the risk of failure of surgical stabilization procedures in adolescents with PFI.Table 1.Patient Demographics by Presence or Absence of Recurrent Instabillity (N=303).Table 2.Imaging Measurements by Presence or Absence of Recurrent Instability (N=303).

Is Caton–Deschamps Index Reliable and Reproducible in Preoperative Assessment of Patellar Height for Patellar Instability Surgery?

The patellar height measurement is fundamental for surgical planning in patellar instability. The Caton–Deschamps index (CDI) is a widely employed method, but a gold standard is still lacking. The aim of this study was to evaluate the reliability and reproducibility of the CDI in a patellar height assessment and to hypothesize its employment in the preoperative planning of patellar stabilization surgery. A total of 29 cases of recurrent patellar instability undergoing surgical treatment were analyzed. The preoperative and postoperative CDI were measured by six different raters (three seniors and three juniors). The interclass correlation coefficient (ICC) of the six raters was calculated to evaluate the interobserver agreement. The seniors’ and juniors’ measurements were compared to assess the CDI reproducibility. The Fleiss kappa was calculated among the six raters to estimate the agreement in favor of an anterior tibial apophysis (ATA) transposition surgery. This study shows excellent absolute agreement in terms of the ICC for the raters’ average and for single raters as units, both preoperatively (p &lt; 0.001) and postoperatively (p &lt; 0.001). The agreement of the surgical choice between the six observers corresponds to “substantial agreement”. This study demonstrates that the CDI is reliable and reproducible, and it could represent a valuable tool in the clinical assessment, treatment choice and pre-surgical planning of patellar instability surgery.

Outcomes of Patellar Stabilization Utilizing a Combined Arthroscopic and Open Technique: A Retrospective Review With 5-Year Follow-up

Background:Few studies have reported the long-term outcomes of patellar stabilization surgery in an active duty military cohort.Purpose:To evaluate the long-term results of a combined open and arthroscopic patellar stabilization technique for the treatment of recurrent lateral patellar instability in members of a military population.Study Design:Case series; Level of evidence, 4.Methods:We performed a retrospective review of a consecutive series of 63 patients who underwent operative management for patellar instability at a tertiary military medical center between 2003 and 2017. All cases were performed by a single sports medicine fellowship–trained orthopaedic surgeon. Patients with recurrent lateral patellar instability whose nonoperative management failed were included. All patients underwent arthroscopic imbrication of the medial patellar retinaculum, an open lateral retinacular release, and an Elmslie-Trillat tibial tubercle osteotomy. Outcome measures at final follow-up included recurrent instability, need for surgical revision, subjective assessments, and military-specific metrics. We also analyzed anatomic risk factors for failure: patella alta, coronal plane alignment, trochlear dysplasia, and tibial tubercle–trochlear groove distance.Results:A total of 51 patients were included (34 men, 17 women; mean ± SD age at surgery, 27.2 ± 5.8 years; mean follow-up, 5.3 years). The mean postoperative SANE score (Single Assessment Numeric Evaluation) was 75.0 ± 17.7, and the mean visual analog scale pain score was 2.5 ± 2.1. Four patients (7.8%) reported redislocation events, and 4 underwent revision surgery. Twenty-five patients (49.0%) reported a decrease in activity level as compared with preinjury, while 10 (19.6%) cited restrictions in activities of daily living. Of the 21 patients remaining on active duty, 6 (28.6%) required an activity-limiting medical profile. Of the 48 active duty patients, 12 (25.0%) underwent evaluation by a medical board for separation from the military. Differences in the Caton-Deschamps Index and tibial tubercle–trochlear groove distance between surgical success and failure were not statistically significant.Conclusion:Surgical management of patellar instability utilizing a multifaceted technique resulted in low recurrence rates and may be independent of predisposing anatomic risk factors for instability. At 5-year follow-up, most patients retained their active duty status, although nearly half experienced a decrease in activity level.

Articular Cartilage Damage Worsens from First-time to Recurrent Patellar Dislocation—A Longitudinal Magnetic Resonance Imaging Study

PurposeTo compare the frequency and severity of articular cartilage injury on longitudinal magnetic resonance imaging (MRI) in patients after their initial dislocation and subsequent recurrent dislocations for those undergoing patellar stabilization surgery.MethodsBetween January 2012 and December 2017, patients undergoing patellar stabilization surgery were retrospectively reviewed. Only patients with an MRI after both the initial dislocation and subsequent dislocation events were included. The MRI scans were blindly examined to assess the Outerbridge classification grade of articular cartilage injury following each dislocation. Comparison was performed of each MRI for grade of articular cartilage damage and location.ResultsThirty-five patients undergoing patellar stabilization surgery with recurrent instability were eligible. The incidence of articular cartilage injury following initial dislocation was 45.7%. Following a second dislocation, the incidence of articular cartilage injury increased to 62.9%, a statistically significant increase of 17.2% (P = .031). Furthermore, of the 16 patients with articular cartilage injury following their initial dislocation, 56.2% of patients (9) had an increase in grade of articular cartilage injury following the second dislocation, whereas 43.8% (7) of patients had no progression in their articular cartilage injury. Six (17.1%) patients had no articular cartilage injury following their initial dislocation but did have articular cartilage injury following their second dislocation.ConclusionsArticular cartilage injury following patellar dislocation is common, and delayed surgical treatment may lead to an increase in articular cartilage damage. The incidence of articular cartilage injury following recurrent patellar dislocation was high (62.9%), and the majority of patients experienced an increase in their articular cartilage injury grade between their initial and recurrent dislocation on MRI evaluation.Level of EvidenceLevel IV, retrospective case series.

Strong Agreement Between Magnetic Resonance Imaging and Radiographs for Caton–Deschamps Index in Patients With Patellofemoral Instability

PurposeTo compare the measurements of the Caton–Deschamps index on preoperative magnetic resonance imaging and radiographs of patients undergoing operative management of patellar instability.MethodsPatients who underwent primary medial patellofemoral ligament reconstruction and/or tibial tubercle osteotomy between January 2015 and November 2019 were assessed. Caton–Deschamps indices were measured by 3 independent reviewers on both radiographs and magnetic resonance imaging. Intra- and interclass correlation coefficients and a Bland–Altman analysis were calculated to assess inter-rater reliability and measurement agreement between radiographic and magnetic resonance imaging.ResultsSeventy-two patients (73 knees) were identified. The average Caton–Deschamps index was 1.23 ± 0.18 on radiograph and 1.26 ± 0.18 on magnetic resonance imaging. Strong inter-rater reliability was observed between reviewers for both radiographic and magnetic resonance imaging Caton–Deschamps indices (intraclass correlation coefficients 0.700 and 0.715, respectively). Pooled observer measurements revealed a moderate agreement between radiographic and magnetic resonance imaging for patella to tibia distance, weak agreement for patellar articular cartilage distance, and strong agreement for the Caton–Deschamps index (intraclass correlation coefficients 0.687, 0.485, and 0.749, respectively). Bland–Altman analysis demonstrated a mean difference in Caton–Deschamps index of –0.03 ± 0.15 (95% limits of agreement: –0.29 to 0.23) between radiographic and magnetic resonance imaging, meaning that Caton–Deschamps indices were on average 0.03 lower on radiographic than on magnetic resonance imaging.ConclusionsThe Caton–Deschamps index has strong agreement between radiographic and magnetic resonance imaging in patients undergoing patellar stabilization surgery. Either modality can be reliably used to preoperatively assess patellar height.Level of EvidenceLevel IV, diagnostic case series.

Arthroscopic Patellofemoral Measurements Can Reliably Assess Patellar Instability

To arthroscopically describe patellar position based on lateralization, tilt, and engagement, and compare measurements in normal, medial patellofemoral complex-(MPFC) deficient, and MPFC-reconstructed knees. In 10 cadaveric knees, arthroscopic patellar position was assessed by performing digital measurements on arthroscopic images obtained through a standard anterolateral portal. Lateralization was measured as millimeters overhang of the patella past the lateral edge of the lateral femoral condyle, viewing from the lateral gutter. Patellar tilt was calculated as the difference in medial and lateral distances from the patella to the trochlea, viewing from the sunrise view. Patellotrochlear distance was measured as the anteroposterior distance between the central trochlear groove and patella on the sunrise view. Measurements were obtained at 10° intervals of knee flexion from 0° to 90°, in intact knees (group 1), after arthroscopically transecting the MPFC fibers (group 2), and after MPFC reconstruction (group 3). Optimal cutoff values were identified to distinguish between intact versus MPFC-deficient states. When compared to group 1, group 2 demonstrated increased patellar lateralization by 22.5% at 0°-40° knee flexion (P= .006), which corrected to baseline in group 3 (P= .006). Patellar tilt measurements demonstrated no differences between groups. Patellotrochlear distance increased by 21.0% after MPFC transection (P= .031) at 0°-40° knee flexion, with correction to baseline after MPFC reconstruction (P= .031). More than 7 mm of lateral overhang at 20°-30° flexion and >6 mm of patellotrochlear distance at 10°-20° flexion were found to indicate MPFC deficiency. Utilizing standardized arthroscopic views, we identified significant increases in patellar lateralization and patellotrochlear distance in early knee flexion angles after MPFC transection, and these changes normalized after MPFC reconstruction. Arthroscopic assessments of patellar position may be useful in evaluating patellofemoral stability during patellar stabilization surgery.

MPFL Length Change Patterns in Asymptomatic Knees of Patients with Contralateral Patellar Instability

Objectives:Recreating the isometry of the medial patellofemoral ligament (MPFL) is critical during patellar stabilization surgery to restore patellar kinematics. The native MPFL is reported to remain constant in length from 0-70°knee flexion in normal knees. However, patients with patellar instability have morphologic abnormalities that may alter the isometric function of the ligament. Length change patterns of the intact MPFL in such patients have not been described.Methods:3D digital knee models were created from dynamic CT images of 10 patients with unilateral patellar instability who were confirmed to have no symptoms on the contralateral knee. At each flexion angle, MPFL length was calculated based on the distance between its known attachment points. Straight line representation of the MPFL was allowed to wrap around the femoral condyle to ensure accurate length measurement. Morphologic characteristics of each knee were recorded, including sulcus angle and lateral trochlear inclination (LTI) as measurements of trochlear dysplasia, trochlear alpha angle to measure trochlear length, tibial tuberosity to trochlear groove (TTTG) distance to measure malalignment, and Caton Deschamps Index (CDI) to measure patellar height. Changes in MPFL length were assessed relative to knee flexion angle in each patient and correlated with morphologic characteristics.Results:10 knees were included in this study, with a mean age of 20.4+/-4.7 yrs. Mean sulcus angle was 153.4+/-8.9°, LTI 14.1+/-4.0°, trochlear alpha angle 66.1+/-5.8°, TTTG distance 18.3+/-3.1mm, CDI 1.1+/-0.1. Mean MPFL length varied from 62.5+/-4.9mm at 50° knee flexion to 74.4+/-3.9mm at 0°, with a 20.1+/-8.8% change in length (p<0.001). No significant length changes were noted between 30° and 50° flexion. Moderate correlation was noted between increasing MPFL length change and measurements of trochlear length (R=-0.55, p=0.017).Conclusions:In the asymptomatic knees of patients with contralateral patellar instability, the calculated MPFL length based on known anatomic attachment points varied by 20.1%, or an average of 12.1mm, between 50° flexion and full extension. This suggests that the isometric function of the intact MPFL in these patients may not reflect previously described findings in anatomically normal patients. Further studies are needed to understand the pathoanatomy related to these changes, as well as the implications for graft placement and assessment of isometry in MPFL reconstruction techniques.

ISOLATED MPFL RECONSTRUCTION VS. TIBIAL TUBERCLE OSTEOTOMY AND MEDIAL RETINACULAR PLICATION FOR RECURRENT PATELLAR INSTABILITY: A MATCHED, COHORT ANALYSIS OF CLINICAL OUTCOMES COMPARING TWO TECHNIQUES

Background:Historically, the most commonly utilized technique to address recurrent patellofemoral instability (PFI) was a combined proximal and distal realignment, specifically the tibial tubercle osteotomy (TTO) with a proximal medial retinacular plication/reefing/tightening/repair (MRP). Rising interest in the medial patellofemoral ligament reconstruction (MPFLR) over the last decade, now frequently performed as a more powerful isolated proximal realignment procedure, has prompted debate over the optimal technique to treat this common condition.Hypothesis/Purpose:The study hypothesis was that no difference would be detected in recurrent PFI rates or revision surgery rates between patients who underwent TTO-MRP vs. MPFLR.Methods:With cohorts derived from a large, single-center PFI database of 523 patients who underwent a variety of stabilization procedures, 114 eligible MPFLR patients were matched to 109 TTO patients based on age, gender, BMI, and TT-TG distance. Propensity score matching was conducted using logistic regression models to produce 1:1 matching, and a caliper of 0.2 standard deviations of the estimated propensity score was used to for the nearest neighbor matching algorithm. Final matching procedure resulted in 84 MPFLR patients and 84 TTO patients. These were compared on demographics and post-operative clinical results.Results:Demographic and radiologic comparisons of the cohorts are shown in Table 1, with the only difference between groups being an expected higher rate of patients with open physes in the MPFLR cohort. Table 2 shows the TTO-MRP group had longer follow up times, but comparable rates of return to sports. The MPFLR group had a higher rate of recurrent instability, but not to a significant degree, and a significantly higher incidence of revision patellar stabilization surgery (p<0.001). The TTO group had a higher rate of additional knee surgery, the majority of which were implant removal for TTO screws.Conclusion:The TTO-MRP shows equivalent or superior results to the MPFLR for treatment of PFI. However, implant removal may be common with TTO, though this may be somewhat technique-dependent. In the current landscape of increasing interest and utilization of MPFLR as an all-encompassing PFI surgery, the influence of distal bony realignment to minimize recurrence should not be underappreciated.Tables/Figures:

SURGICAL MANAGEMENT OF PATELLAR INSTABILITY IN ADOLESCENTS WITH BODY MASS INDEX GREATER THAN 30

Background:Recurrent patellar instability is a common condition often requiring surgical stabilization in adolescents. Obesity, defined as body mass index (BMI) greater than 30 kg/m2 in adults, has been associated with poorer outcomes with many procedures including ACL reconstruction, spinal fusion, and joint arthroplasty. Data is limited regarding the results of surgery for patellar instability in adolescent patients with BMI > 30 kg/m2.Purpose:The purpose of this study was to report on rates of recurrent patellar instability following surgical management in adolescents with BMI >30 kg/m2 and to compare the rates of recurrent instability between different surgical procedures.MethodsA retrospective review of patients who underwent surgical management of patellar instability at our institution was performed. Inclusion criteria included patients aged 19 and younger, with BMI >30 kg/m2 who were followed for least 12 months post procedure. Patients with underlying collagen or systemic disorders, a history of prior ipsilateral knee surgery, or an osteochondral fragment greater than 10mm were excluded. Complications were defined as any recurrent subluxation or dislocation, or need for subsequent instability surgery. A subgroup analysis was performed to compare recurrent instability rates within our cohort between patients who underwent medial retinacular plication versus all other procedures. Categorical variables were compared using Fisher’s exact test. Statistical significance of p<0.05 was applied.Results:Fifty-five patients were identified. Mean age was 15.6±2.4 years. Mean BMI for this cohort was 34.9± 4.3 kg/m2. 72.7% of patients were female. All patients underwent either medial retincular plication, tibial tubercle osteotomy, MPFL reconstruction or combined procedures (Table 1). At a mean of 3.8 years, 16.4% of all patients had any recurrent subluxation or dislocation including 12.7% who had a recurrent dislocation, and 7.3% who required a revision patellar stabilization procedure. Subgroup analysis revealed that obese patients who underwent isolated medial retinacular plication had higher rates of recurrent subluxation or dislocation (24% vs 10%, p=0.272) including recurrent dislocation (20% vs 6.7%, 0.226), and had significantly higher rates of subsequent instability surgery (16% vs 0%, p=0.037) (Table 2).Conclusion:Adolescents with BMI > 30 who undergo patellar stabilization surgery have notable rates of recurrent subluxation or dislocation and subsequent instability surgery though comparable to results in non-obese patients. Obese patients who underwent medial retinacular plication had higher rates of postoperative instability and significantly higher rates of revision instability surgery compared to those who underwent MPFL reconstruction, tibial tubercle osteotomy or combined procedures.Tables/Figures:

Risk Factors for Opioid Use after Patellofemoral Stabilization Surgery: Analyses of 1,316 Cases

Orthopaedic surgeons are the third-highest group of opioid prescribers among all physicians in the United States, accounting for almost 8% of all opioid prescriptions. Given the recent opioid epidemic, identification of risk factors for prolonged opioid use after knee procedures may benefit patients and providers. Risk factors for increased postoperative opioid utilization following patellar stabilization surgery have yet to be fully delineated, especially in young, active patient populations at increased risk of abuse misuse. This study investigated risk factors for postoperative opioid use following patellofemoral stabilization surgery. Patients undergoing primary patellar stabilization surgery between 2007-2017 in the Humana Inc. administrative claims database were identified using Current Procedural Terminology (CPT) codes for patellofemoral stabilization procedures (CPT-27420, 27422, 27427, 27418). Patients were categorized into opioid naive (N-OU) and those who filled opioid prescriptions within 3 months prior to surgery (OU). Patients in the OU cohort were further categorized into those who filled prescriptions at 1-3 months before surgery (C-OU) and those who filled opioid prescriptions only in the month preceding surgery (A-OU). Descriptive statistics and multivariate analyses were performed to identify risk factors for postoperative opioid use at 3 and 12 months using the open-source R software (www.r-project.org) housed within Pearl Diver with statistical significance defined as p < 0.05. A total of 1,316 eligible patients were included. One year postoperatively, there was a greater risk of opioid consumption in the OU cohort (OU vs N-OU: 22.2% vs 4.1%; Relative Risk [RR]: 1.233; 95% CI: 1.172- 1.298; P < 0.0001). C-OU (OR: 5.74; 95% CI: 3.75- 8.9; P < 0.0001), obesity (OR: 1.76; 95% CI: 1.14- 2.69; P = 0.0099), and history of a psychiatric diagnosis (OR: 1.83; 95% CI: 1.01- 3.25; P = 0.0435) were independent risk factors for opioid use at 12 months postoperatively. Younger age (age < 30) was associated with a lower risk of opioid use at 3 months (OR: 0.3, 95% CI: 0.21- 0.44; P < 0.0001) and 12 months (OR: 0.29; 95% CI: 0.17- 0.46; P < 0.0001) postoperatively. Preoperative opioid utilization significantly increased opioid prescription filling following patellofemoral stabilization surgery. Given the relatively young age and high activity level of patients undergoing patellofemoral stabilization surgery, heightened awareness of patient-specific factors must be considered when selecting appropriate pain management regimens postoperatively.

Patellar stabilization surgeries in cases of recurrent patellar instability: a retrospective clinical and radiological audit.

Patellar instability is a disabling condition that limits the functional ability and physical aspirations of patients. There are multiple anatomical structures which stabilize the patella and surgical treatment is tailored to repair the underlying aetiology. To evaluate the clinical and radiological outcome of patellar stabilization procedures in patients with recurrent patellar instability. We analysed 34 patients (36 knees) (mean age, 26.6) with recurrent patellar instability who underwent patellar stabilization surgery from June 2009 to September 2014. Type of procedure was dependent on the concomitant aetiological factors; tibial tuberosity osteotomy (61.76%), medial patellofemoral ligament reconstruction (67.64%), lateral release (5.88%) and trochleoplasty (2.94%). Mean follow-up was 3years (range 9months-6years). At follow-up, 77% of patients were satisfied with the overall outcome of the procedure. The mean IKDC was 66.7, Lysholm 74.9. Mean patellar height decreased significantly (P < .05) to anatomical values. Pre-operatively, the mean tibial tuberosity-trochlear groove distance was 14.66mm (55.6% at borderline/abnormal level) and 81% showed evidence of trochlear dysplasia. Complications were found in 3 patients (8.33%), 2 of which had further episodes of instability. Patellar stabilization surgery is an effective method of treating patellar instability, resulting in stability of the knee in 94.4%. Despite this, patient dissatisfaction rates are quite high suggesting that this patient group, whilst mostly stable, remains significantly symptomatic from their knee. These positive results which are reflected in the recent literature represent a strong case for consideration of primary surgical stabilization in cases of patellar instability.

Development of a return to play checklist following patellar instability surgery: a Delphi-based consensus.

To date, there is no consensus for the appropriate timing or functional evaluation for safe return to play following patellar instability surgery. The purpose of this study is to develop a consensus-based return to play checklist following patellar stabilization surgery using the Delphi method. A 3-part survey series was conducted following the systematic guidelines of the Delphi technique for gathering consensus from experts in the management of patellofemoral instability. All surveys were completed between July and November of 2017. A literature search was performed in SCOPUS and PubMed to identify existing sources on return to play following patellar instability surgery and determining patellofemoral joint strength in athletes, which served as the basis for the surveys. 12 of the 19 selected participants (63%) completed the first-round survey, 11 of those 12 participants (92%) completed the second-round survey, and 10 of these 11 participants (91%) completed the final survey. Of the final ten participants, there was representation from seven different states in the USA. Nine of the ten (90%) respondents endorsed the final checklist. The final checklist included eight overarching domains with defined and reproducible objective criteria. The standardized list of objective and reproducible criteria for rehabilitation outlined below should help practitioners focus more on patient-centred factors and less on arbitrary timelines. No prior study has gathered consensus from experts on this topic; therefore, this study should serve as a benchmark to help guide patients back to sport safely. V.

Femoral trochlea does not remodel after patellar stabilization in children older than 10 years of age

Trochlear dysplasia is a major risk factor for patellar instability. It has been sparsely reported that the trochlea can remodel when patellar stabilization is performed in skeletally immature patients before the age of 10 years. It is not known whether trochlea can remodel significantly after the age of 10 years. The purpose of the study was to evaluate trochlear remodeling in skeletally immature patients after patellar stabilization surgery, with a focus on children older than 10 years of age. In a retrospective study, knee MRI of 21 patients who had undergone patellar stabilization surgery, were evaluated. Twenty of these 21 patients were older than 10 years of age at time of surgery. The measurements of cartilaginous and bony sulcus angles, trochlear depth, and cartilaginous trochlear bump were compared between preoperative and postoperative MRI, using paired t-tests. In 20 patients older than 10 years of age, the mean cartilaginous sulcus angle change between preoperative and postoperative axial MRI was not significant (2.2°±7.9°, P=0.6). The mean change in the bony sulcus angle value was not significant (3.6°±6.8°, P=0.07). Similarly, there was no significant change in trochlear depth (P=0.8), or size of the trochlear bump (P=0.1). For one patient under 10 years of age at the time of surgery, there was a 21° and a 15° improvement in cartilaginous and bony sulcus angle, respectively. There were no significant changes in the trochlear parameters and trochlear remodeling in patients older than 10 years of age. Patellar stabilization at a younger age (<10 years), may allow for trochlear remodeling. Level of Evidence: Level IV, case series.

Return-to-Sport Testing After Medial Patellofemoral Ligament Reconstruction in Adolescent Athletes.

Background:Return to sport (RTS) after patellar stabilization surgery involves the return of strength and dynamic knee stability, which can be assessed using isometric strength and functional performance testing.Purpose:To investigate the results of isometric strength and functional RTS testing between the surgical and uninvolved limbs in adolescent patients who underwent medial patellofemoral ligament (MPFL) reconstruction for patellar instability.Study Design:Case series; Level of evidence, 4.Methods:A retrospective review of adolescent patients who underwent MPFL reconstruction identified 28 patients (20 female, 8 male) who also underwent isometric and functional RTS testing. Data were compared with the uninvolved limb. The recovery of muscle strength was defined by a limb symmetry index (LSI) ≥90%. Differences in peak torque were compared using the Wilcoxon signed-rank test. Correlations were examined between dependent and independent variables using the Spearman correlation.Results:The mean age of the patients was 14.9 years (range, 12-16 years). Reconstruction was performed with a hamstring autograft in 17 (60.7%) patients. Concomitant tibial tubercle osteotomy was performed in 10 (35.7%) patients. Testing was performed at a mean 7.4 months (range, 5.5-11.9 months) postoperatively. The mean LSIs for quadriceps and hamstring strength were 85.3% and 95.1%, respectively. For knee extension, there was a statistically significant difference between isometric peak torque measured in the surgical and uninvolved limbs (P = .001). Only 32.0% of patients passed all 4 hop tests. Also, 63.0% of patients achieved an anterior reach asymmetry of <4 cm on the Lower Quarter Y-Balance Test (YBT-LQ). There were no statistically significant differences in isometric strength testing, hop tests, or the YBT-LQ based on graft type or concomitant procedures. There was no correlation between isometric strength and performance on the YBT-LQ or hop tests.Conclusion:Adolescent athletes undergoing MPFL reconstruction may need prolonged rehabilitation programs beyond 8 months to allow the adequate recovery of muscle strength for safe RTS. There is a significant deficit in isometric quadriceps strength in the surgical limb after surgery. Further investigation is needed to determine safe RTS criteria after MPFL reconstruction in the pediatric and adolescent population.

The Recurrent Instability of the Patella Score: A Statistically Based Model for Prediction of Long-Term Recurrence Risk After First-Time Dislocation

To describe the clinical history of a series of primary, lateral patellar dislocations and determine long-term predictors of recurrent instability while accounting for patients undergoing early operative management. Alarge geographic database of more than 500,000 patients was used to identify patients who sustained a first-time lateral patellar dislocation between 1990 and 2010. Charts were individually reviewed to document demographics, radiographic measures including tibial tubercle to trochlear groove distance (TT-TG) and patellar length (PL), recurrent episodes of instability, and patellar stabilization surgery. A risk score that accounted for early surgical management was calculated using Fine and Gray competing risk regression, and its ability to stratify patients was examined using cumulative incidence curves. Eighty-one patients (mean age 19.9 ± 9.4years, 38 male, 43 female) were identified and followed for a mean of 10.1years (range 4.1-20.2). Thirty-eight patients (46.9%) experienced an episode of recurrent instability and 30 (37.0%) underwent patellar stabilization surgery, including 7 who did so before recurrent dislocation. Amultivariate, statistically derived scoring system, the Recurrent Instability of the Patella Score (RIP Score), that employed age, skeletal maturity, trochlear dysplasia, and TT-TG/PL ratio to predict recurrent instability while accounting for patients managed surgically, was generated. The resulting RIP score stratified patients into low-, intermediate-, and high-risk categories, with 0.0%, 30.6%, and 79.2% 10-year recurrent instability rates, respectively (P= .000004), and an area under the curve of 0.875 (P= .00002). Patients who sustain a first-time, lateral patellar dislocation can be readily classified into low-, intermediate-, and high-risk categories employing the RIP score based on age, skeletal maturity, trochlear dysplasia, and TT-TG/PL ratio. This long-term risk stratification holds significant potential clinical utility for determination of patients who are at high risk for recurrent instability after primary patellar dislocation. LEVELOF EVIDENCE: Level III, retrospective comparative study.

Radiographic Landmarks for the Anterior Attachment of the Medial Patellofemoral Complex

Because fluoroscopy is often used in graft placement during patellar stabilization surgery, the purpose of this study was to describe the radiographic landmarks for the anterior attachment midpoint of the medial patellofemoral complex (MPFC). Seventeen fresh-frozen cadaveric knees were dissected, and the MPFC was exposed from the articular side after a lateral parapatellar approach. The midpoint of the anterior attachment of the MPFC was identified using a ruler and marked with a pin. Lateral fluoroscopic images of the patella were then obtained and analyzed using digital analysis software. The distance from the superior articular pole to the pin was divided by the length of the articular surface to describe the location of the pin as a percentage of patellar articular length. Of the 17 cadaveric knees, 2 were excluded because of lack of MPFC fibers. In the remaining 15 knees, the mean (±standard deviation) proximal-distal width of the attachment to the patella and/or vastus intermedius tendon was 41 ± 10mm, spanning from 15 ± 6mm proximal to the superior pole of the patella to 27 ± 8mm distal to it. When viewed on lateral fluoroscopic images, the MPFC midpoint was 19% ± 14% of the patellar articular length from the superior articular pole. In this study, the radiographic landmarks that correlate to the anatomic midpoint of the anterior MPFC attachment are 19% ± 14% of the articular surface from the superior pole of the patella. Recent reports on medial patellofemoral ligament anatomy now include fibers that extend to the quadriceps tendon, summarized as the MPFC. With the inclusion of these fibers, the midpoint of the anterior MPFC attachment is more proximal than that of the medial patellofemoral ligament alone. Because fluoroscopy is often used intraoperatively to guide graft placement, this study correlates radiographic landmarks with anatomic findings of the MPFC midpoint on its attachment to the extensor mechanism.